contextkey.ts

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import { CharCode } from '../../../base/common/charCode.js';
import { Event } from '../../../base/common/event.js';
import { isChrome, isEdge, isFirefox, isLinux, isMacintosh, isSafari, isWeb, isWindows } from '../../../base/common/platform.js';
import { isFalsyOrWhitespace } from '../../../base/common/strings.js';
import { Scanner, LexingError, Token, TokenType } from './scanner.js';
import { createDecorator } from '../../instantiation/common/instantiation.js';
import { localize } from '../../../nls.js';
import { IDisposable } from '../../../base/common/lifecycle.js';
import { illegalArgument } from '../../../base/common/errors.js';

const CONSTANT_VALUES = new Map<string, boolean>();
CONSTANT_VALUES.set('false', false);
CONSTANT_VALUES.set('true', true);
CONSTANT_VALUES.set('isMac', isMacintosh);
CONSTANT_VALUES.set('isLinux', isLinux);
CONSTANT_VALUES.set('isWindows', isWindows);
CONSTANT_VALUES.set('isWeb', isWeb);
CONSTANT_VALUES.set('isMacNative', isMacintosh && !isWeb);
CONSTANT_VALUES.set('isEdge', isEdge);
CONSTANT_VALUES.set('isFirefox', isFirefox);
CONSTANT_VALUES.set('isChrome', isChrome);
CONSTANT_VALUES.set('isSafari', isSafari);

/** allow register constant context keys that are known only after startup; requires running `substituteConstants` on the context key - https://github.com/microsoft/vscode/issues/174218#issuecomment-1437972127 */
export function setConstant(key: string, value: boolean) {
	if (CONSTANT_VALUES.get(key) !== undefined) { throw illegalArgument('contextkey.setConstant(k, v) invoked with already set constant `k`'); }

	CONSTANT_VALUES.set(key, value);
}

const hasOwnProperty = Object.prototype.hasOwnProperty;

export const enum ContextKeyExprType {
	False = 0,
	True = 1,
	Defined = 2,
	Not = 3,
	Equals = 4,
	NotEquals = 5,
	And = 6,
	Regex = 7,
	NotRegex = 8,
	Or = 9,
	In = 10,
	NotIn = 11,
	Greater = 12,
	GreaterEquals = 13,
	Smaller = 14,
	SmallerEquals = 15,
}

export interface IContextKeyExprMapper {
	mapDefined(key: string): ContextKeyExpression;
	mapNot(key: string): ContextKeyExpression;
	mapEquals(key: string, value: any): ContextKeyExpression;
	mapNotEquals(key: string, value: any): ContextKeyExpression;
	mapGreater(key: string, value: any): ContextKeyExpression;
	mapGreaterEquals(key: string, value: any): ContextKeyExpression;
	mapSmaller(key: string, value: any): ContextKeyExpression;
	mapSmallerEquals(key: string, value: any): ContextKeyExpression;
	mapRegex(key: string, regexp: RegExp | null): ContextKeyRegexExpr;
	mapIn(key: string, valueKey: string): ContextKeyInExpr;
	mapNotIn(key: string, valueKey: string): ContextKeyNotInExpr;
}

export interface IContextKeyExpression {
	cmp(other: ContextKeyExpression): number;
	equals(other: ContextKeyExpression): boolean;
	substituteConstants(): ContextKeyExpression | undefined;
	evaluate(context: IContext): boolean;
	serialize(): string;
	keys(): string[];
	map(mapFnc: IContextKeyExprMapper): ContextKeyExpression;
	negate(): ContextKeyExpression;

}

export type ContextKeyExpression = (
	ContextKeyFalseExpr | ContextKeyTrueExpr | ContextKeyDefinedExpr | ContextKeyNotExpr
	| ContextKeyEqualsExpr | ContextKeyNotEqualsExpr | ContextKeyRegexExpr
	| ContextKeyNotRegexExpr | ContextKeyAndExpr | ContextKeyOrExpr | ContextKeyInExpr
	| ContextKeyNotInExpr | ContextKeyGreaterExpr | ContextKeyGreaterEqualsExpr
	| ContextKeySmallerExpr | ContextKeySmallerEqualsExpr
);


/*

Syntax grammar:

```ebnf

expression ::= or

or ::= and { '||' and }*

and ::= term { '&&' term }*

term ::=
	| '!' (KEY | true | false | parenthesized)
	| primary

primary ::=
	| 'true'
	| 'false'
	| parenthesized
	| KEY '=~' REGEX
	| KEY [ ('==' | '!=' | '<' | '<=' | '>' | '>=' | 'not' 'in' | 'in') value ]

parenthesized ::=
	| '(' expression ')'

value ::=
	| 'true'
	| 'false'
	| 'in'      	// we support `in` as a value because there's an extension that uses it, ie "when": "languageId == in"
	| VALUE 		// matched by the same regex as KEY; consider putting the value in single quotes if it's a string (e.g., with spaces)
	| SINGLE_QUOTED_STR
	| EMPTY_STR  	// this allows "when": "foo == " which's used by existing extensions

```
*/

export type ParserConfig = {
	/**
	 * with this option enabled, the parser can recover from regex parsing errors, e.g., unescaped slashes: `/src//` is accepted as `/src\//` would be
	 */
	regexParsingWithErrorRecovery: boolean;
};

const defaultConfig: ParserConfig = {
	regexParsingWithErrorRecovery: true
};

export type ParsingError = {
	message: string;
	offset: number;
	lexeme: string;
	additionalInfo?: string;
};

const errorEmptyString = localize('contextkey.parser.error.emptyString', "Empty context key expression");
const hintEmptyString = localize('contextkey.parser.error.emptyString.hint', "Did you forget to write an expression? You can also put 'false' or 'true' to always evaluate to false or true, respectively.");
const errorNoInAfterNot = localize('contextkey.parser.error.noInAfterNot', "'in' after 'not'.");
const errorClosingParenthesis = localize('contextkey.parser.error.closingParenthesis', "closing parenthesis ')'");
const errorUnexpectedToken = localize('contextkey.parser.error.unexpectedToken', "Unexpected token");
const hintUnexpectedToken = localize('contextkey.parser.error.unexpectedToken.hint', "Did you forget to put && or || before the token?");
const errorUnexpectedEOF = localize('contextkey.parser.error.unexpectedEOF', "Unexpected end of expression");
const hintUnexpectedEOF = localize('contextkey.parser.error.unexpectedEOF.hint', "Did you forget to put a context key?");

/**
 * A parser for context key expressions.
 *
 * Example:
 * ```ts
 * const parser = new Parser();
 * const expr = parser.parse('foo == "bar" && baz == true');
 *
 * if (expr === undefined) {
 * 	// there were lexing or parsing errors
 * 	// process lexing errors with `parser.lexingErrors`
 *  // process parsing errors with `parser.parsingErrors`
 * } else {
 * 	// expr is a valid expression
 * }
 * ```
 */
export class Parser {
	// Note: this doesn't produce an exact syntax tree but a normalized one
	// ContextKeyExpression's that we use as AST nodes do not expose constructors that do not normalize

	private static _parseError = new Error();

	// lifetime note: `_scanner` lives as long as the parser does, i.e., is not reset between calls to `parse`
	private readonly _scanner = new Scanner();

	// lifetime note: `_tokens`, `_current`, and `_parsingErrors` must be reset between calls to `parse`
	private _tokens: Token[] = [];
	private _current = 0; 					// invariant: 0 <= this._current < this._tokens.length ; any incrementation of this value must first call `_isAtEnd`
	private _parsingErrors: ParsingError[] = [];

	get lexingErrors(): Readonly<LexingError[]> {
		return this._scanner.errors;
	}

	get parsingErrors(): Readonly<ParsingError[]> {
		return this._parsingErrors;
	}

	constructor(private readonly _config: ParserConfig = defaultConfig) {
	}

	/**
	 * Parse a context key expression.
	 *
	 * @param input the expression to parse
	 * @returns the parsed expression or `undefined` if there's an error - call `lexingErrors` and `parsingErrors` to see the errors
	 */
	parse(input: string): ContextKeyExpression | undefined {

		if (input === '') {
			this._parsingErrors.push({ message: errorEmptyString, offset: 0, lexeme: '', additionalInfo: hintEmptyString });
			return undefined;
		}

		this._tokens = this._scanner.reset(input).scan();
		// @ulugbekna: we do not stop parsing if there are lexing errors to be able to reconstruct regexes with unescaped slashes; TODO@ulugbekna: make this respect config option for recovery

		this._current = 0;
		this._parsingErrors = [];

		try {
			const expr = this._expr();
			if (!this._isAtEnd()) {
				const peek = this._peek();
				const additionalInfo = peek.type === TokenType.Str ? hintUnexpectedToken : undefined;
				this._parsingErrors.push({ message: errorUnexpectedToken, offset: peek.offset, lexeme: Scanner.getLexeme(peek), additionalInfo });
				throw Parser._parseError;
			}
			return expr;
		} catch (e) {
			if (!(e === Parser._parseError)) {
				throw e;
			}
			return undefined;
		}
	}

	private _expr(): ContextKeyExpression | undefined {
		return this._or();
	}

	private _or(): ContextKeyExpression | undefined {
		const expr = [this._and()];

		while (this._matchOne(TokenType.Or)) {
			const right = this._and();
			expr.push(right);
		}

		return expr.length === 1 ? expr[0] : ContextKeyExpr.or(...expr);
	}

	private _and(): ContextKeyExpression | undefined {
		const expr = [this._term()];

		while (this._matchOne(TokenType.And)) {
			const right = this._term();
			expr.push(right);
		}

		return expr.length === 1 ? expr[0] : ContextKeyExpr.and(...expr);
	}

	private _term(): ContextKeyExpression | undefined {
		if (this._matchOne(TokenType.Neg)) {
			const peek = this._peek();
			switch (peek.type) {
				case TokenType.True:
					this._advance();
					return ContextKeyFalseExpr.INSTANCE;
				case TokenType.False:
					this._advance();
					return ContextKeyTrueExpr.INSTANCE;
				case TokenType.LParen: {
					this._advance();
					const expr = this._expr();
					this._consume(TokenType.RParen, errorClosingParenthesis);
					return expr?.negate();
				}
				case TokenType.Str:
					this._advance();
					return ContextKeyNotExpr.create(peek.lexeme);
				default:
					throw this._errExpectedButGot(`KEY | true | false | '(' expression ')'`, peek);
			}
		}
		return this._primary();
	}

	private _primary(): ContextKeyExpression | undefined {

		const peek = this._peek();
		switch (peek.type) {
			case TokenType.True:
				this._advance();
				return ContextKeyExpr.true();

			case TokenType.False:
				this._advance();
				return ContextKeyExpr.false();

			case TokenType.LParen: {
				this._advance();
				const expr = this._expr();
				this._consume(TokenType.RParen, errorClosingParenthesis);
				return expr;
			}

			case TokenType.Str: {
				// KEY
				const key = peek.lexeme;
				this._advance();

				// =~ regex
				if (this._matchOne(TokenType.RegexOp)) {

					// @ulugbekna: we need to reconstruct the regex from the tokens because some extensions use unescaped slashes in regexes
					const expr = this._peek();

					if (!this._config.regexParsingWithErrorRecovery) {
						this._advance();
						if (expr.type !== TokenType.RegexStr) {
							throw this._errExpectedButGot(`REGEX`, expr);
						}
						const regexLexeme = expr.lexeme;
						const closingSlashIndex = regexLexeme.lastIndexOf('/');
						const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : this._removeFlagsGY(regexLexeme.substring(closingSlashIndex + 1));
						let regexp: RegExp | null;
						try {
							regexp = new RegExp(regexLexeme.substring(1, closingSlashIndex), flags);
						} catch (e) {
							throw this._errExpectedButGot(`REGEX`, expr);
						}
						return ContextKeyRegexExpr.create(key, regexp);
					}

					switch (expr.type) {
						case TokenType.RegexStr:
						case TokenType.Error: { // also handle an ErrorToken in case of smth such as /(/file)/
							const lexemeReconstruction = [expr.lexeme]; // /REGEX/ or /REGEX/FLAGS
							this._advance();

							let followingToken = this._peek();
							let parenBalance = 0;
							for (let i = 0; i < expr.lexeme.length; i++) {
								if (expr.lexeme.charCodeAt(i) === CharCode.OpenParen) {
									parenBalance++;
								} else if (expr.lexeme.charCodeAt(i) === CharCode.CloseParen) {
									parenBalance--;
								}
							}

							while (!this._isAtEnd() && followingToken.type !== TokenType.And && followingToken.type !== TokenType.Or) {
								switch (followingToken.type) {
									case TokenType.LParen:
										parenBalance++;
										break;
									case TokenType.RParen:
										parenBalance--;
										break;
									case TokenType.RegexStr:
									case TokenType.QuotedStr:
										for (let i = 0; i < followingToken.lexeme.length; i++) {
											if (followingToken.lexeme.charCodeAt(i) === CharCode.OpenParen) {
												parenBalance++;
											} else if (expr.lexeme.charCodeAt(i) === CharCode.CloseParen) {
												parenBalance--;
											}
										}
								}
								if (parenBalance < 0) {
									break;
								}
								lexemeReconstruction.push(Scanner.getLexeme(followingToken));
								this._advance();
								followingToken = this._peek();
							}

							const regexLexeme = lexemeReconstruction.join('');
							const closingSlashIndex = regexLexeme.lastIndexOf('/');
							const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : this._removeFlagsGY(regexLexeme.substring(closingSlashIndex + 1));
							let regexp: RegExp | null;
							try {
								regexp = new RegExp(regexLexeme.substring(1, closingSlashIndex), flags);
							} catch (e) {
								throw this._errExpectedButGot(`REGEX`, expr);
							}
							return ContextKeyExpr.regex(key, regexp);
						}

						case TokenType.QuotedStr: {
							const serializedValue = expr.lexeme;
							this._advance();
							// replicate old regex parsing behavior

							let regex: RegExp | null = null;

							if (!isFalsyOrWhitespace(serializedValue)) {
								const start = serializedValue.indexOf('/');
								const end = serializedValue.lastIndexOf('/');
								if (start !== end && start >= 0) {

									const value = serializedValue.slice(start + 1, end);
									const caseIgnoreFlag = serializedValue[end + 1] === 'i' ? 'i' : '';
									try {
										regex = new RegExp(value, caseIgnoreFlag);
									} catch (_e) {
										throw this._errExpectedButGot(`REGEX`, expr);
									}
								}
							}

							if (regex === null) {
								throw this._errExpectedButGot('REGEX', expr);
							}

							return ContextKeyRegexExpr.create(key, regex);
						}

						default:
							throw this._errExpectedButGot('REGEX', this._peek());
					}
				}

				// [ 'not' 'in' value ]
				if (this._matchOne(TokenType.Not)) {
					this._consume(TokenType.In, errorNoInAfterNot);
					const right = this._value();
					return ContextKeyExpr.notIn(key, right);
				}

				// [ ('==' | '!=' | '<' | '<=' | '>' | '>=' | 'in') value ]
				const maybeOp = this._peek().type;
				switch (maybeOp) {
					case TokenType.Eq: {
						this._advance();

						const right = this._value();
						if (this._previous().type === TokenType.QuotedStr) { // to preserve old parser behavior: "foo == 'true'" is preserved as "foo == 'true'", but "foo == true" is optimized as "foo"
							return ContextKeyExpr.equals(key, right);
						}
						switch (right) {
							case 'true':
								return ContextKeyExpr.has(key);
							case 'false':
								return ContextKeyExpr.not(key);
							default:
								return ContextKeyExpr.equals(key, right);
						}
					}

					case TokenType.NotEq: {
						this._advance();

						const right = this._value();
						if (this._previous().type === TokenType.QuotedStr) { // same as above with "foo != 'true'"
							return ContextKeyExpr.notEquals(key, right);
						}
						switch (right) {
							case 'true':
								return ContextKeyExpr.not(key);
							case 'false':
								return ContextKeyExpr.has(key);
							default:
								return ContextKeyExpr.notEquals(key, right);
						}
					}
					// TODO: ContextKeyExpr.smaller(key, right) accepts only `number` as `right` AND during eval of this node, we just eval to `false` if `right` is not a number
					// consequently, package.json linter should _warn_ the user if they're passing undesired things to ops
					case TokenType.Lt:
						this._advance();
						return ContextKeySmallerExpr.create(key, this._value());

					case TokenType.LtEq:
						this._advance();
						return ContextKeySmallerEqualsExpr.create(key, this._value());

					case TokenType.Gt:
						this._advance();
						return ContextKeyGreaterExpr.create(key, this._value());

					case TokenType.GtEq:
						this._advance();
						return ContextKeyGreaterEqualsExpr.create(key, this._value());

					case TokenType.In:
						this._advance();
						return ContextKeyExpr.in(key, this._value());

					default:
						return ContextKeyExpr.has(key);
				}
			}

			case TokenType.EOF:
				this._parsingErrors.push({ message: errorUnexpectedEOF, offset: peek.offset, lexeme: '', additionalInfo: hintUnexpectedEOF });
				throw Parser._parseError;

			default:
				throw this._errExpectedButGot(`true | false | KEY \n\t| KEY '=~' REGEX \n\t| KEY ('==' | '!=' | '<' | '<=' | '>' | '>=' | 'in' | 'not' 'in') value`, this._peek());

		}
	}

	private _value(): string {
		const token = this._peek();
		switch (token.type) {
			case TokenType.Str:
			case TokenType.QuotedStr:
				this._advance();
				return token.lexeme;
			case TokenType.True:
				this._advance();
				return 'true';
			case TokenType.False:
				this._advance();
				return 'false';
			case TokenType.In: // we support `in` as a value, e.g., "when": "languageId == in" - exists in existing extensions
				this._advance();
				return 'in';
			default:
				// this allows "when": "foo == " which's used by existing extensions
				// we do not call `_advance` on purpose - we don't want to eat unintended tokens
				return '';
		}
	}

	private _flagsGYRe = /g|y/g;
	private _removeFlagsGY(flags: string): string {
		return flags.replaceAll(this._flagsGYRe, '');
	}

	// careful: this can throw if current token is the initial one (ie index = 0)
	private _previous() {
		return this._tokens[this._current - 1];
	}

	private _matchOne(token: TokenType) {
		if (this._check(token)) {
			this._advance();
			return true;
		}

		return false;
	}

	private _advance() {
		if (!this._isAtEnd()) {
			this._current++;
		}
		return this._previous();
	}

	private _consume(type: TokenType, message: string) {
		if (this._check(type)) {
			return this._advance();
		}

		throw this._errExpectedButGot(message, this._peek());
	}

	private _errExpectedButGot(expected: string, got: Token, additionalInfo?: string) {
		const message = localize('contextkey.parser.error.expectedButGot', "Expected: {0}\nReceived: '{1}'.", expected, Scanner.getLexeme(got));
		const offset = got.offset;
		const lexeme = Scanner.getLexeme(got);
		this._parsingErrors.push({ message, offset, lexeme, additionalInfo });
		return Parser._parseError;
	}

	private _check(type: TokenType) {
		return this._peek().type === type;
	}

	private _peek() {
		return this._tokens[this._current];
	}

	private _isAtEnd() {
		return this._peek().type === TokenType.EOF;
	}
}

export abstract class ContextKeyExpr {

	public static false(): ContextKeyExpression {
		return ContextKeyFalseExpr.INSTANCE;
	}
	public static true(): ContextKeyExpression {
		return ContextKeyTrueExpr.INSTANCE;
	}
	public static has(key: string): ContextKeyExpression {
		return ContextKeyDefinedExpr.create(key);
	}
	public static equals(key: string, value: any): ContextKeyExpression {
		return ContextKeyEqualsExpr.create(key, value);
	}
	public static notEquals(key: string, value: any): ContextKeyExpression {
		return ContextKeyNotEqualsExpr.create(key, value);
	}
	public static regex(key: string, value: RegExp): ContextKeyExpression {
		return ContextKeyRegexExpr.create(key, value);
	}
	public static in(key: string, value: string): ContextKeyExpression {
		return ContextKeyInExpr.create(key, value);
	}
	public static notIn(key: string, value: string): ContextKeyExpression {
		return ContextKeyNotInExpr.create(key, value);
	}
	public static not(key: string): ContextKeyExpression {
		return ContextKeyNotExpr.create(key);
	}
	public static and(...expr: Array<ContextKeyExpression | undefined | null>): ContextKeyExpression | undefined {
		return ContextKeyAndExpr.create(expr, null, true);
	}
	public static or(...expr: Array<ContextKeyExpression | undefined | null>): ContextKeyExpression | undefined {
		return ContextKeyOrExpr.create(expr, null, true);
	}
	public static greater(key: string, value: number): ContextKeyExpression {
		return ContextKeyGreaterExpr.create(key, value);
	}
	public static greaterEquals(key: string, value: number): ContextKeyExpression {
		return ContextKeyGreaterEqualsExpr.create(key, value);
	}
	public static smaller(key: string, value: number): ContextKeyExpression {
		return ContextKeySmallerExpr.create(key, value);
	}
	public static smallerEquals(key: string, value: number): ContextKeyExpression {
		return ContextKeySmallerEqualsExpr.create(key, value);
	}

	private static _parser = new Parser({ regexParsingWithErrorRecovery: false });
	public static deserialize(serialized: string | null | undefined): ContextKeyExpression | undefined {
		if (serialized === undefined || serialized === null) { // an empty string needs to be handled by the parser to get a corresponding parsing error reported
			return undefined;
		}

		const expr = this._parser.parse(serialized);
		return expr;
	}

}


export function validateWhenClauses(whenClauses: string[]): any {

	const parser = new Parser({ regexParsingWithErrorRecovery: false }); // we run with no recovery to guide users to use correct regexes

	return whenClauses.map(whenClause => {
		parser.parse(whenClause);

		if (parser.lexingErrors.length > 0) {
			return parser.lexingErrors.map((se: LexingError) => ({
				errorMessage: se.additionalInfo ?
					localize('contextkey.scanner.errorForLinterWithHint', "Unexpected token. Hint: {0}", se.additionalInfo) :
					localize('contextkey.scanner.errorForLinter', "Unexpected token."),
				offset: se.offset,
				length: se.lexeme.length,
			}));
		} else if (parser.parsingErrors.length > 0) {
			return parser.parsingErrors.map((pe: ParsingError) => ({
				errorMessage: pe.additionalInfo ? `${pe.message}. ${pe.additionalInfo}` : pe.message,
				offset: pe.offset,
				length: pe.lexeme.length,
			}));
		} else {
			return [];
		}
	});
}

export function expressionsAreEqualWithConstantSubstitution(a: ContextKeyExpression | null | undefined, b: ContextKeyExpression | null | undefined): boolean {
	const aExpr = a ? a.substituteConstants() : undefined;
	const bExpr = b ? b.substituteConstants() : undefined;
	if (!aExpr && !bExpr) {
		return true;
	}
	if (!aExpr || !bExpr) {
		return false;
	}
	return aExpr.equals(bExpr);
}

function cmp(a: ContextKeyExpression, b: ContextKeyExpression): number {
	return a.cmp(b);
}

export class ContextKeyFalseExpr implements IContextKeyExpression {
	public static INSTANCE = new ContextKeyFalseExpr();

	public readonly type = ContextKeyExprType.False;

	protected constructor() {
	}

	public cmp(other: ContextKeyExpression): number {
		return this.type - other.type;
	}

	public equals(other: ContextKeyExpression): boolean {
		return (other.type === this.type);
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		return false;
	}

	public serialize(): string {
		return 'false';
	}

	public keys(): string[] {
		return [];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return this;
	}

	public negate(): ContextKeyExpression {
		return ContextKeyTrueExpr.INSTANCE;
	}
}

export class ContextKeyTrueExpr implements IContextKeyExpression {
	public static INSTANCE = new ContextKeyTrueExpr();

	public readonly type = ContextKeyExprType.True;

	protected constructor() {
	}

	public cmp(other: ContextKeyExpression): number {
		return this.type - other.type;
	}

	public equals(other: ContextKeyExpression): boolean {
		return (other.type === this.type);
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		return true;
	}

	public serialize(): string {
		return 'true';
	}

	public keys(): string[] {
		return [];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return this;
	}

	public negate(): ContextKeyExpression {
		return ContextKeyFalseExpr.INSTANCE;
	}
}

export class ContextKeyDefinedExpr implements IContextKeyExpression {
	public static create(key: string, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		const constantValue = CONSTANT_VALUES.get(key);
		if (typeof constantValue === 'boolean') {
			return constantValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE;
		}
		return new ContextKeyDefinedExpr(key, negated);
	}

	public readonly type = ContextKeyExprType.Defined;

	protected constructor(
		readonly key: string,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp1(this.key, other.key);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const constantValue = CONSTANT_VALUES.get(this.key);
		if (typeof constantValue === 'boolean') {
			return constantValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE;
		}
		return this;
	}

	public evaluate(context: IContext): boolean {
		return (!!context.getValue(this.key));
	}

	public serialize(): string {
		return this.key;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapDefined(this.key);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyNotExpr.create(this.key, this);
		}
		return this.negated;
	}
}

export class ContextKeyEqualsExpr implements IContextKeyExpression {

	public static create(key: string, value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		if (typeof value === 'boolean') {
			return (value ? ContextKeyDefinedExpr.create(key, negated) : ContextKeyNotExpr.create(key, negated));
		}
		const constantValue = CONSTANT_VALUES.get(key);
		if (typeof constantValue === 'boolean') {
			const trueValue = constantValue ? 'true' : 'false';
			return (value === trueValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE);
		}
		return new ContextKeyEqualsExpr(key, value, negated);
	}

	public readonly type = ContextKeyExprType.Equals;

	private constructor(
		private readonly key: string,
		private readonly value: any,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const constantValue = CONSTANT_VALUES.get(this.key);
		if (typeof constantValue === 'boolean') {
			const trueValue = constantValue ? 'true' : 'false';
			return (this.value === trueValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE);
		}
		return this;
	}

	public evaluate(context: IContext): boolean {
		// Intentional ==
		// eslint-disable-next-line eqeqeq
		return (context.getValue(this.key) == this.value);
	}

	public serialize(): string {
		return `${this.key} == '${this.value}'`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapEquals(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyNotEqualsExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeyInExpr implements IContextKeyExpression {

	public static create(key: string, valueKey: string): ContextKeyInExpr {
		return new ContextKeyInExpr(key, valueKey);
	}

	public readonly type = ContextKeyExprType.In;
	private negated: ContextKeyExpression | null = null;

	private constructor(
		private readonly key: string,
		private readonly valueKey: string,
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.valueKey, other.key, other.valueKey);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.valueKey === other.valueKey);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		const source = context.getValue(this.valueKey);

		const item = context.getValue(this.key);

		if (Array.isArray(source)) {
			return source.includes(item as any);
		}

		if (typeof item === 'string' && typeof source === 'object' && source !== null) {
			return hasOwnProperty.call(source, item);
		}
		return false;
	}

	public serialize(): string {
		return `${this.key} in '${this.valueKey}'`;
	}

	public keys(): string[] {
		return [this.key, this.valueKey];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyInExpr {
		return mapFnc.mapIn(this.key, this.valueKey);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyNotInExpr.create(this.key, this.valueKey);
		}
		return this.negated;
	}
}

export class ContextKeyNotInExpr implements IContextKeyExpression {

	public static create(key: string, valueKey: string): ContextKeyNotInExpr {
		return new ContextKeyNotInExpr(key, valueKey);
	}

	public readonly type = ContextKeyExprType.NotIn;

	private readonly _negated: ContextKeyInExpr;

	private constructor(
		private readonly key: string,
		private readonly valueKey: string,
	) {
		this._negated = ContextKeyInExpr.create(key, valueKey);
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return this._negated.cmp(other._negated);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return this._negated.equals(other._negated);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		return !this._negated.evaluate(context);
	}

	public serialize(): string {
		return `${this.key} not in '${this.valueKey}'`;
	}

	public keys(): string[] {
		return this._negated.keys();
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapNotIn(this.key, this.valueKey);
	}

	public negate(): ContextKeyExpression {
		return this._negated;
	}
}

export class ContextKeyNotEqualsExpr implements IContextKeyExpression {

	public static create(key: string, value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		if (typeof value === 'boolean') {
			if (value) {
				return ContextKeyNotExpr.create(key, negated);
			}
			return ContextKeyDefinedExpr.create(key, negated);
		}
		const constantValue = CONSTANT_VALUES.get(key);
		if (typeof constantValue === 'boolean') {
			const falseValue = constantValue ? 'true' : 'false';
			return (value === falseValue ? ContextKeyFalseExpr.INSTANCE : ContextKeyTrueExpr.INSTANCE);
		}
		return new ContextKeyNotEqualsExpr(key, value, negated);
	}

	public readonly type = ContextKeyExprType.NotEquals;

	private constructor(
		private readonly key: string,
		private readonly value: any,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const constantValue = CONSTANT_VALUES.get(this.key);
		if (typeof constantValue === 'boolean') {
			const falseValue = constantValue ? 'true' : 'false';
			return (this.value === falseValue ? ContextKeyFalseExpr.INSTANCE : ContextKeyTrueExpr.INSTANCE);
		}
		return this;
	}

	public evaluate(context: IContext): boolean {
		// Intentional !=
		// eslint-disable-next-line eqeqeq
		return (context.getValue(this.key) != this.value);
	}

	public serialize(): string {
		return `${this.key} != '${this.value}'`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapNotEquals(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyEqualsExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeyNotExpr implements IContextKeyExpression {

	public static create(key: string, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		const constantValue = CONSTANT_VALUES.get(key);
		if (typeof constantValue === 'boolean') {
			return (constantValue ? ContextKeyFalseExpr.INSTANCE : ContextKeyTrueExpr.INSTANCE);
		}
		return new ContextKeyNotExpr(key, negated);
	}

	public readonly type = ContextKeyExprType.Not;

	private constructor(
		private readonly key: string,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp1(this.key, other.key);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const constantValue = CONSTANT_VALUES.get(this.key);
		if (typeof constantValue === 'boolean') {
			return (constantValue ? ContextKeyFalseExpr.INSTANCE : ContextKeyTrueExpr.INSTANCE);
		}
		return this;
	}

	public evaluate(context: IContext): boolean {
		return (!context.getValue(this.key));
	}

	public serialize(): string {
		return `!${this.key}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapNot(this.key);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyDefinedExpr.create(this.key, this);
		}
		return this.negated;
	}
}

function withFloatOrStr<T extends ContextKeyExpression>(value: any, callback: (value: number | string) => T): T | ContextKeyFalseExpr {
	if (typeof value === 'string') {
		const n = parseFloat(value);
		if (!isNaN(n)) {
			value = n;
		}
	}
	if (typeof value === 'string' || typeof value === 'number') {
		return callback(value);
	}
	return ContextKeyFalseExpr.INSTANCE;
}

export class ContextKeyGreaterExpr implements IContextKeyExpression {

	public static create(key: string, _value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		return withFloatOrStr(_value, (value) => new ContextKeyGreaterExpr(key, value, negated));
	}

	public readonly type = ContextKeyExprType.Greater;

	private constructor(
		private readonly key: string,
		private readonly value: number | string,
		private negated: ContextKeyExpression | null
	) { }

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		if (typeof this.value === 'string') {
			return false;
		}
		return (parseFloat(<any>context.getValue(this.key)) > this.value);
	}

	public serialize(): string {
		return `${this.key} > ${this.value}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapGreater(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeySmallerEqualsExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeyGreaterEqualsExpr implements IContextKeyExpression {

	public static create(key: string, _value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		return withFloatOrStr(_value, (value) => new ContextKeyGreaterEqualsExpr(key, value, negated));
	}

	public readonly type = ContextKeyExprType.GreaterEquals;

	private constructor(
		private readonly key: string,
		private readonly value: number | string,
		private negated: ContextKeyExpression | null
	) { }

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		if (typeof this.value === 'string') {
			return false;
		}
		return (parseFloat(<any>context.getValue(this.key)) >= this.value);
	}

	public serialize(): string {
		return `${this.key} >= ${this.value}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapGreaterEquals(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeySmallerExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeySmallerExpr implements IContextKeyExpression {

	public static create(key: string, _value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		return withFloatOrStr(_value, (value) => new ContextKeySmallerExpr(key, value, negated));
	}

	public readonly type = ContextKeyExprType.Smaller;

	private constructor(
		private readonly key: string,
		private readonly value: number | string,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		if (typeof this.value === 'string') {
			return false;
		}
		return (parseFloat(<any>context.getValue(this.key)) < this.value);
	}

	public serialize(): string {
		return `${this.key} < ${this.value}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapSmaller(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyGreaterEqualsExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeySmallerEqualsExpr implements IContextKeyExpression {

	public static create(key: string, _value: any, negated: ContextKeyExpression | null = null): ContextKeyExpression {
		return withFloatOrStr(_value, (value) => new ContextKeySmallerEqualsExpr(key, value, negated));
	}

	public readonly type = ContextKeyExprType.SmallerEquals;

	private constructor(
		private readonly key: string,
		private readonly value: number | string,
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return cmp2(this.key, this.value, other.key, other.value);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return (this.key === other.key && this.value === other.value);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		if (typeof this.value === 'string') {
			return false;
		}
		return (parseFloat(<any>context.getValue(this.key)) <= this.value);
	}

	public serialize(): string {
		return `${this.key} <= ${this.value}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return mapFnc.mapSmallerEquals(this.key, this.value);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyGreaterExpr.create(this.key, this.value, this);
		}
		return this.negated;
	}
}

export class ContextKeyRegexExpr implements IContextKeyExpression {

	public static create(key: string, regexp: RegExp | null): ContextKeyRegexExpr {
		return new ContextKeyRegexExpr(key, regexp);
	}

	public readonly type = ContextKeyExprType.Regex;
	private negated: ContextKeyExpression | null = null;

	private constructor(
		private readonly key: string,
		private readonly regexp: RegExp | null
	) {
		//
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		if (this.key < other.key) {
			return -1;
		}
		if (this.key > other.key) {
			return 1;
		}
		const thisSource = this.regexp ? this.regexp.source : '';
		const otherSource = other.regexp ? other.regexp.source : '';
		if (thisSource < otherSource) {
			return -1;
		}
		if (thisSource > otherSource) {
			return 1;
		}
		return 0;
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			const thisSource = this.regexp ? this.regexp.source : '';
			const otherSource = other.regexp ? other.regexp.source : '';
			return (this.key === other.key && thisSource === otherSource);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		const value = context.getValue<any>(this.key);
		return this.regexp ? this.regexp.test(value) : false;
	}

	public serialize(): string {
		const value = this.regexp
			? `/${this.regexp.source}/${this.regexp.flags}`
			: '/invalid/';
		return `${this.key} =~ ${value}`;
	}

	public keys(): string[] {
		return [this.key];
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyRegexExpr {
		return mapFnc.mapRegex(this.key, this.regexp);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			this.negated = ContextKeyNotRegexExpr.create(this);
		}
		return this.negated;
	}
}

export class ContextKeyNotRegexExpr implements IContextKeyExpression {

	public static create(actual: ContextKeyRegexExpr): ContextKeyExpression {
		return new ContextKeyNotRegexExpr(actual);
	}

	public readonly type = ContextKeyExprType.NotRegex;

	private constructor(private readonly _actual: ContextKeyRegexExpr) {
		//
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		return this._actual.cmp(other._actual);
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			return this._actual.equals(other._actual);
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		return this;
	}

	public evaluate(context: IContext): boolean {
		return !this._actual.evaluate(context);
	}

	public serialize(): string {
		return `!(${this._actual.serialize()})`;
	}

	public keys(): string[] {
		return this._actual.keys();
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return new ContextKeyNotRegexExpr(this._actual.map(mapFnc));
	}

	public negate(): ContextKeyExpression {
		return this._actual;
	}
}

/**
 * @returns the same instance if nothing changed.
 */
function eliminateConstantsInArray(arr: ContextKeyExpression[]): (ContextKeyExpression | undefined)[] {
	// Allocate array only if there is a difference
	let newArr: (ContextKeyExpression | undefined)[] | null = null;
	for (let i = 0, len = arr.length; i < len; i++) {
		const newExpr = arr[i].substituteConstants();

		if (arr[i] !== newExpr) {
			// something has changed!

			// allocate array on first difference
			if (newArr === null) {
				newArr = [];
				for (let j = 0; j < i; j++) {
					newArr[j] = arr[j];
				}
			}
		}

		if (newArr !== null) {
			newArr[i] = newExpr;
		}
	}

	if (newArr === null) {
		return arr;
	}
	return newArr;
}

export class ContextKeyAndExpr implements IContextKeyExpression {

	public static create(_expr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
		return ContextKeyAndExpr._normalizeArr(_expr, negated, extraRedundantCheck);
	}

	public readonly type = ContextKeyExprType.And;

	private constructor(
		public readonly expr: ContextKeyExpression[],
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		if (this.expr.length < other.expr.length) {
			return -1;
		}
		if (this.expr.length > other.expr.length) {
			return 1;
		}
		for (let i = 0, len = this.expr.length; i < len; i++) {
			const r = cmp(this.expr[i], other.expr[i]);
			if (r !== 0) {
				return r;
			}
		}
		return 0;
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			if (this.expr.length !== other.expr.length) {
				return false;
			}
			for (let i = 0, len = this.expr.length; i < len; i++) {
				if (!this.expr[i].equals(other.expr[i])) {
					return false;
				}
			}
			return true;
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const exprArr = eliminateConstantsInArray(this.expr);
		if (exprArr === this.expr) {
			// no change
			return this;
		}
		return ContextKeyAndExpr.create(exprArr, this.negated, false);
	}

	public evaluate(context: IContext): boolean {
		for (let i = 0, len = this.expr.length; i < len; i++) {
			if (!this.expr[i].evaluate(context)) {
				return false;
			}
		}
		return true;
	}

	private static _normalizeArr(arr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
		const expr: ContextKeyExpression[] = [];
		let hasTrue = false;

		for (const e of arr) {
			if (!e) {
				continue;
			}

			if (e.type === ContextKeyExprType.True) {
				// anything && true ==> anything
				hasTrue = true;
				continue;
			}

			if (e.type === ContextKeyExprType.False) {
				// anything && false ==> false
				return ContextKeyFalseExpr.INSTANCE;
			}

			if (e.type === ContextKeyExprType.And) {
				expr.push(...e.expr);
				continue;
			}

			expr.push(e);
		}

		if (expr.length === 0 && hasTrue) {
			return ContextKeyTrueExpr.INSTANCE;
		}

		if (expr.length === 0) {
			return undefined;
		}

		if (expr.length === 1) {
			return expr[0];
		}

		expr.sort(cmp);

		// eliminate duplicate terms
		for (let i = 1; i < expr.length; i++) {
			if (expr[i - 1].equals(expr[i])) {
				expr.splice(i, 1);
				i--;
			}
		}

		if (expr.length === 1) {
			return expr[0];
		}

		// We must distribute any OR expression because we don't support parens
		// OR extensions will be at the end (due to sorting rules)
		while (expr.length > 1) {
			const lastElement = expr[expr.length - 1];
			if (lastElement.type !== ContextKeyExprType.Or) {
				break;
			}
			// pop the last element
			expr.pop();

			// pop the second to last element
			const secondToLastElement = expr.pop()!;

			const isFinished = (expr.length === 0);

			// distribute `lastElement` over `secondToLastElement`
			const resultElement = ContextKeyOrExpr.create(
				lastElement.expr.map(el => ContextKeyAndExpr.create([el, secondToLastElement], null, extraRedundantCheck)),
				null,
				isFinished
			);

			if (resultElement) {
				expr.push(resultElement);
				expr.sort(cmp);
			}
		}

		if (expr.length === 1) {
			return expr[0];
		}

		// resolve false AND expressions
		if (extraRedundantCheck) {
			for (let i = 0; i < expr.length; i++) {
				for (let j = i + 1; j < expr.length; j++) {
					if (expr[i].negate().equals(expr[j])) {
						// A && !A case
						return ContextKeyFalseExpr.INSTANCE;
					}
				}
			}

			if (expr.length === 1) {
				return expr[0];
			}
		}

		return new ContextKeyAndExpr(expr, negated);
	}

	public serialize(): string {
		return this.expr.map(e => e.serialize()).join(' && ');
	}

	public keys(): string[] {
		const result: string[] = [];
		for (const expr of this.expr) {
			result.push(...expr.keys());
		}
		return result;
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return new ContextKeyAndExpr(this.expr.map(expr => expr.map(mapFnc)), null);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			const result: ContextKeyExpression[] = [];
			for (const expr of this.expr) {
				result.push(expr.negate());
			}
			this.negated = ContextKeyOrExpr.create(result, this, true)!;
		}
		return this.negated;
	}
}

export class ContextKeyOrExpr implements IContextKeyExpression {

	public static create(_expr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
		return ContextKeyOrExpr._normalizeArr(_expr, negated, extraRedundantCheck);
	}

	public readonly type = ContextKeyExprType.Or;

	private constructor(
		public readonly expr: ContextKeyExpression[],
		private negated: ContextKeyExpression | null
	) {
	}

	public cmp(other: ContextKeyExpression): number {
		if (other.type !== this.type) {
			return this.type - other.type;
		}
		if (this.expr.length < other.expr.length) {
			return -1;
		}
		if (this.expr.length > other.expr.length) {
			return 1;
		}
		for (let i = 0, len = this.expr.length; i < len; i++) {
			const r = cmp(this.expr[i], other.expr[i]);
			if (r !== 0) {
				return r;
			}
		}
		return 0;
	}

	public equals(other: ContextKeyExpression): boolean {
		if (other.type === this.type) {
			if (this.expr.length !== other.expr.length) {
				return false;
			}
			for (let i = 0, len = this.expr.length; i < len; i++) {
				if (!this.expr[i].equals(other.expr[i])) {
					return false;
				}
			}
			return true;
		}
		return false;
	}

	public substituteConstants(): ContextKeyExpression | undefined {
		const exprArr = eliminateConstantsInArray(this.expr);
		if (exprArr === this.expr) {
			// no change
			return this;
		}
		return ContextKeyOrExpr.create(exprArr, this.negated, false);
	}

	public evaluate(context: IContext): boolean {
		for (let i = 0, len = this.expr.length; i < len; i++) {
			if (this.expr[i].evaluate(context)) {
				return true;
			}
		}
		return false;
	}

	private static _normalizeArr(arr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
		let expr: ContextKeyExpression[] = [];
		let hasFalse = false;

		if (arr) {
			for (let i = 0, len = arr.length; i < len; i++) {
				const e = arr[i];
				if (!e) {
					continue;
				}

				if (e.type === ContextKeyExprType.False) {
					// anything || false ==> anything
					hasFalse = true;
					continue;
				}

				if (e.type === ContextKeyExprType.True) {
					// anything || true ==> true
					return ContextKeyTrueExpr.INSTANCE;
				}

				if (e.type === ContextKeyExprType.Or) {
					expr = expr.concat(e.expr);
					continue;
				}

				expr.push(e);
			}

			if (expr.length === 0 && hasFalse) {
				return ContextKeyFalseExpr.INSTANCE;
			}

			expr.sort(cmp);
		}

		if (expr.length === 0) {
			return undefined;
		}

		if (expr.length === 1) {
			return expr[0];
		}

		// eliminate duplicate terms
		for (let i = 1; i < expr.length; i++) {
			if (expr[i - 1].equals(expr[i])) {
				expr.splice(i, 1);
				i--;
			}
		}

		if (expr.length === 1) {
			return expr[0];
		}

		// resolve true OR expressions
		if (extraRedundantCheck) {
			for (let i = 0; i < expr.length; i++) {
				for (let j = i + 1; j < expr.length; j++) {
					if (expr[i].negate().equals(expr[j])) {
						// A || !A case
						return ContextKeyTrueExpr.INSTANCE;
					}
				}
			}

			if (expr.length === 1) {
				return expr[0];
			}
		}

		return new ContextKeyOrExpr(expr, negated);
	}

	public serialize(): string {
		return this.expr.map(e => e.serialize()).join(' || ');
	}

	public keys(): string[] {
		const result: string[] = [];
		for (const expr of this.expr) {
			result.push(...expr.keys());
		}
		return result;
	}

	public map(mapFnc: IContextKeyExprMapper): ContextKeyExpression {
		return new ContextKeyOrExpr(this.expr.map(expr => expr.map(mapFnc)), null);
	}

	public negate(): ContextKeyExpression {
		if (!this.negated) {
			const result: ContextKeyExpression[] = [];
			for (const expr of this.expr) {
				result.push(expr.negate());
			}

			// We don't support parens, so here we distribute the AND over the OR terminals
			// We always take the first 2 AND pairs and distribute them
			while (result.length > 1) {
				const LEFT = result.shift()!;
				const RIGHT = result.shift()!;

				const all: ContextKeyExpression[] = [];
				for (const left of getTerminals(LEFT)) {
					for (const right of getTerminals(RIGHT)) {
						all.push(ContextKeyAndExpr.create([left, right], null, false)!);
					}
				}

				result.unshift(ContextKeyOrExpr.create(all, null, false)!);
			}

			this.negated = ContextKeyOrExpr.create(result, this, true)!;
		}
		return this.negated;
	}
}

export interface ContextKeyInfo {
	readonly key: string;
	readonly type?: string;
	readonly description?: string;
}

export class RawContextKey<T extends ContextKeyValue> extends ContextKeyDefinedExpr {

	private static _info: ContextKeyInfo[] = [];

	static all(): IterableIterator<ContextKeyInfo> {
		return RawContextKey._info.values();
	}

	private readonly _defaultValue: T | undefined;

	constructor(key: string, defaultValue: T | undefined, metaOrHide?: string | true | { type: string; description: string }) {
		super(key, null);
		this._defaultValue = defaultValue;

		// collect all context keys into a central place
		if (typeof metaOrHide === 'object') {
			RawContextKey._info.push({ ...metaOrHide, key });
		} else if (metaOrHide !== true) {
			RawContextKey._info.push({ key, description: metaOrHide, type: defaultValue !== null && defaultValue !== undefined ? typeof defaultValue : undefined });
		}
	}

	public bindTo(target: IContextKeyService): IContextKey<T> {
		return target.createKey(this.key, this._defaultValue);
	}

	public getValue(target: IContextKeyService): T | undefined {
		return target.getContextKeyValue<T>(this.key);
	}

	public toNegated(): ContextKeyExpression {
		return this.negate();
	}

	public isEqualTo(value: any): ContextKeyExpression {
		return ContextKeyEqualsExpr.create(this.key, value);
	}

	public notEqualsTo(value: any): ContextKeyExpression {
		return ContextKeyNotEqualsExpr.create(this.key, value);
	}

	public greater(value: any): ContextKeyExpression {
		return ContextKeyGreaterExpr.create(this.key, value);
	}
}

export type ContextKeyValue = null | undefined | boolean | number | string
	| Array<null | undefined | boolean | number | string>
	| Record<string, null | undefined | boolean | number | string>;

export interface IContext {
	getValue<T extends ContextKeyValue = ContextKeyValue>(key: string): T | undefined;
}

export interface IContextKey<T extends ContextKeyValue = ContextKeyValue> {
	set(value: T): void;
	reset(): void;
	get(): T | undefined;
}

export interface IContextKeyServiceTarget {
	parentElement: IContextKeyServiceTarget | null;
	setAttribute(attr: string, value: string): void;
	removeAttribute(attr: string): void;
	hasAttribute(attr: string): boolean;
	getAttribute(attr: string): string | null;
}

export const IContextKeyService = createDecorator<IContextKeyService>('contextKeyService');

export interface IReadableSet<T> {
	has(value: T): boolean;
}

export interface IContextKeyChangeEvent {
	affectsSome(keys: IReadableSet<string>): boolean;
	allKeysContainedIn(keys: IReadableSet<string>): boolean;
}

export type IScopedContextKeyService = IContextKeyService & IDisposable;

export interface IContextKeyService {
	readonly _serviceBrand: undefined;

	onDidChangeContext: Event<IContextKeyChangeEvent>;
	bufferChangeEvents(callback: Function): void;

	createKey<T extends ContextKeyValue>(key: string, defaultValue: T | undefined): IContextKey<T>;
	contextMatchesRules(rules: ContextKeyExpression | undefined): boolean;
	getContextKeyValue<T>(key: string): T | undefined;

	createScoped(target: IContextKeyServiceTarget): IScopedContextKeyService;
	createOverlay(overlay: Iterable<[string, any]>): IContextKeyService;
	getContext(target: IContextKeyServiceTarget | null): IContext;

	updateParent(parentContextKeyService: IContextKeyService): void;
}

function cmp1(key1: string, key2: string): number {
	if (key1 < key2) {
		return -1;
	}
	if (key1 > key2) {
		return 1;
	}
	return 0;
}

function cmp2(key1: string, value1: any, key2: string, value2: any): number {
	if (key1 < key2) {
		return -1;
	}
	if (key1 > key2) {
		return 1;
	}
	if (value1 < value2) {
		return -1;
	}
	if (value1 > value2) {
		return 1;
	}
	return 0;
}

/**
 * Returns true if it is provable `p` implies `q`.
 */
export function implies(p: ContextKeyExpression, q: ContextKeyExpression): boolean {

	if (p.type === ContextKeyExprType.False || q.type === ContextKeyExprType.True) {
		// false implies anything
		// anything implies true
		return true;
	}

	if (p.type === ContextKeyExprType.Or) {
		if (q.type === ContextKeyExprType.Or) {
			// `a || b || c` can only imply something like `a || b || c || d`
			return allElementsIncluded(p.expr, q.expr);
		}
		return false;
	}

	if (q.type === ContextKeyExprType.Or) {
		for (const element of q.expr) {
			if (implies(p, element)) {
				return true;
			}
		}
		return false;
	}

	if (p.type === ContextKeyExprType.And) {
		if (q.type === ContextKeyExprType.And) {
			// `a && b && c` implies `a && c`
			return allElementsIncluded(q.expr, p.expr);
		}
		for (const element of p.expr) {
			if (implies(element, q)) {
				return true;
			}
		}
		return false;
	}

	return p.equals(q);
}

/**
 * Returns true if all elements in `p` are also present in `q`.
 * The two arrays are assumed to be sorted
 */
function allElementsIncluded(p: ContextKeyExpression[], q: ContextKeyExpression[]): boolean {
	let pIndex = 0;
	let qIndex = 0;
	while (pIndex < p.length && qIndex < q.length) {
		const cmp = p[pIndex].cmp(q[qIndex]);

		if (cmp < 0) {
			// an element from `p` is missing from `q`
			return false;
		} else if (cmp === 0) {
			pIndex++;
			qIndex++;
		} else {
			qIndex++;
		}
	}
	return (pIndex === p.length);
}

function getTerminals(node: ContextKeyExpression) {
	if (node.type === ContextKeyExprType.Or) {
		return node.expr;
	}
	return [node];
}