textAreaEditContextState.ts

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

import { commonPrefixLength, commonSuffixLength } from '../../../../../base/common/strings.js';
import { Position } from '../../../../common/core/position.js';
import { Range } from '../../../../common/core/range.js';
import { ISimpleScreenReaderContentState } from '../screenReaderUtils.js';

export const _debugComposition = false;

export interface ITextAreaWrapper {
	getValue(): string;
	setValue(reason: string, value: string): void;

	getSelectionStart(): number;
	getSelectionEnd(): number;
	setSelectionRange(reason: string, selectionStart: number, selectionEnd: number): void;
}

export interface ITypeData {
	text: string;
	replacePrevCharCnt: number;
	replaceNextCharCnt: number;
	positionDelta: number;
}

export class TextAreaState {

	public static readonly EMPTY = new TextAreaState('', 0, 0, null, undefined);

	constructor(
		public readonly value: string,
		/** the offset where selection starts inside `value` */
		public readonly selectionStart: number,
		/** the offset where selection ends inside `value` */
		public readonly selectionEnd: number,
		/** the editor range in the view coordinate system that matches the selection inside `value` */
		public readonly selection: Range | null,
		/** the visible line count (wrapped, not necessarily matching \n characters) for the text in `value` before `selectionStart` */
		public readonly newlineCountBeforeSelection: number | undefined,
	) { }

	public toString(): string {
		return `[ <${this.value}>, selectionStart: ${this.selectionStart}, selectionEnd: ${this.selectionEnd}]`;
	}

	public static readFromTextArea(textArea: ITextAreaWrapper, previousState: TextAreaState | null): TextAreaState {
		const value = textArea.getValue();
		const selectionStart = textArea.getSelectionStart();
		const selectionEnd = textArea.getSelectionEnd();
		let newlineCountBeforeSelection: number | undefined = undefined;
		if (previousState) {
			const valueBeforeSelectionStart = value.substring(0, selectionStart);
			const previousValueBeforeSelectionStart = previousState.value.substring(0, previousState.selectionStart);
			if (valueBeforeSelectionStart === previousValueBeforeSelectionStart) {
				newlineCountBeforeSelection = previousState.newlineCountBeforeSelection;
			}
		}
		return new TextAreaState(value, selectionStart, selectionEnd, null, newlineCountBeforeSelection);
	}

	public collapseSelection(): TextAreaState {
		if (this.selectionStart === this.value.length) {
			return this;
		}
		return new TextAreaState(this.value, this.value.length, this.value.length, null, undefined);
	}

	public isWrittenToTextArea(textArea: ITextAreaWrapper, select: boolean): boolean {
		const valuesEqual = this.value === textArea.getValue();
		if (!select) {
			return valuesEqual;
		}
		const selectionsEqual = this.selectionStart === textArea.getSelectionStart() && this.selectionEnd === textArea.getSelectionEnd();
		return selectionsEqual && valuesEqual;
	}

	public writeToTextArea(reason: string, textArea: ITextAreaWrapper, select: boolean): void {
		if (_debugComposition) {
			console.log(`writeToTextArea ${reason}: ${this.toString()}`);
		}
		textArea.setValue(reason, this.value);
		if (select) {
			textArea.setSelectionRange(reason, this.selectionStart, this.selectionEnd);
		}
	}

	public deduceEditorPosition(offset: number): [Position | null, number, number] {
		if (offset <= this.selectionStart) {
			const str = this.value.substring(offset, this.selectionStart);
			return this._finishDeduceEditorPosition(this.selection?.getStartPosition() ?? null, str, -1);
		}
		if (offset >= this.selectionEnd) {
			const str = this.value.substring(this.selectionEnd, offset);
			return this._finishDeduceEditorPosition(this.selection?.getEndPosition() ?? null, str, 1);
		}
		const str1 = this.value.substring(this.selectionStart, offset);
		if (str1.indexOf(String.fromCharCode(8230)) === -1) {
			return this._finishDeduceEditorPosition(this.selection?.getStartPosition() ?? null, str1, 1);
		}
		const str2 = this.value.substring(offset, this.selectionEnd);
		return this._finishDeduceEditorPosition(this.selection?.getEndPosition() ?? null, str2, -1);
	}

	private _finishDeduceEditorPosition(anchor: Position | null, deltaText: string, signum: number): [Position | null, number, number] {
		let lineFeedCnt = 0;
		let lastLineFeedIndex = -1;
		while ((lastLineFeedIndex = deltaText.indexOf('\n', lastLineFeedIndex + 1)) !== -1) {
			lineFeedCnt++;
		}
		return [anchor, signum * deltaText.length, lineFeedCnt];
	}

	public static deduceInput(previousState: TextAreaState, currentState: TextAreaState, couldBeEmojiInput: boolean): ITypeData {
		if (!previousState) {
			// This is the EMPTY state
			return {
				text: '',
				replacePrevCharCnt: 0,
				replaceNextCharCnt: 0,
				positionDelta: 0
			};
		}

		if (_debugComposition) {
			console.log('------------------------deduceInput');
			console.log(`PREVIOUS STATE: ${previousState.toString()}`);
			console.log(`CURRENT STATE: ${currentState.toString()}`);
		}

		const prefixLength = Math.min(
			commonPrefixLength(previousState.value, currentState.value),
			previousState.selectionStart,
			currentState.selectionStart
		);
		const suffixLength = Math.min(
			commonSuffixLength(previousState.value, currentState.value),
			previousState.value.length - previousState.selectionEnd,
			currentState.value.length - currentState.selectionEnd
		);
		const previousValue = previousState.value.substring(prefixLength, previousState.value.length - suffixLength);
		const currentValue = currentState.value.substring(prefixLength, currentState.value.length - suffixLength);
		const previousSelectionStart = previousState.selectionStart - prefixLength;
		const previousSelectionEnd = previousState.selectionEnd - prefixLength;
		const currentSelectionStart = currentState.selectionStart - prefixLength;
		const currentSelectionEnd = currentState.selectionEnd - prefixLength;

		if (_debugComposition) {
			console.log(`AFTER DIFFING PREVIOUS STATE: <${previousValue}>, selectionStart: ${previousSelectionStart}, selectionEnd: ${previousSelectionEnd}`);
			console.log(`AFTER DIFFING CURRENT STATE: <${currentValue}>, selectionStart: ${currentSelectionStart}, selectionEnd: ${currentSelectionEnd}`);
		}

		if (currentSelectionStart === currentSelectionEnd) {
			// no current selection
			const replacePreviousCharacters = (previousState.selectionStart - prefixLength);
			if (_debugComposition) {
				console.log(`REMOVE PREVIOUS: ${replacePreviousCharacters} chars`);
			}

			return {
				text: currentValue,
				replacePrevCharCnt: replacePreviousCharacters,
				replaceNextCharCnt: 0,
				positionDelta: 0
			};
		}

		// there is a current selection => composition case
		const replacePreviousCharacters = previousSelectionEnd - previousSelectionStart;
		return {
			text: currentValue,
			replacePrevCharCnt: replacePreviousCharacters,
			replaceNextCharCnt: 0,
			positionDelta: 0
		};
	}

	public static deduceAndroidCompositionInput(previousState: TextAreaState, currentState: TextAreaState): ITypeData {
		if (!previousState) {
			// This is the EMPTY state
			return {
				text: '',
				replacePrevCharCnt: 0,
				replaceNextCharCnt: 0,
				positionDelta: 0
			};
		}

		if (_debugComposition) {
			console.log('------------------------deduceAndroidCompositionInput');
			console.log(`PREVIOUS STATE: ${previousState.toString()}`);
			console.log(`CURRENT STATE: ${currentState.toString()}`);
		}

		if (previousState.value === currentState.value) {
			return {
				text: '',
				replacePrevCharCnt: 0,
				replaceNextCharCnt: 0,
				positionDelta: currentState.selectionEnd - previousState.selectionEnd
			};
		}

		const prefixLength = Math.min(commonPrefixLength(previousState.value, currentState.value), previousState.selectionEnd);
		const suffixLength = Math.min(commonSuffixLength(previousState.value, currentState.value), previousState.value.length - previousState.selectionEnd);
		const previousValue = previousState.value.substring(prefixLength, previousState.value.length - suffixLength);
		const currentValue = currentState.value.substring(prefixLength, currentState.value.length - suffixLength);
		const previousSelectionStart = previousState.selectionStart - prefixLength;
		const previousSelectionEnd = previousState.selectionEnd - prefixLength;
		const currentSelectionStart = currentState.selectionStart - prefixLength;
		const currentSelectionEnd = currentState.selectionEnd - prefixLength;

		if (_debugComposition) {
			console.log(`AFTER DIFFING PREVIOUS STATE: <${previousValue}>, selectionStart: ${previousSelectionStart}, selectionEnd: ${previousSelectionEnd}`);
			console.log(`AFTER DIFFING CURRENT STATE: <${currentValue}>, selectionStart: ${currentSelectionStart}, selectionEnd: ${currentSelectionEnd}`);
		}

		return {
			text: currentValue,
			replacePrevCharCnt: previousSelectionEnd,
			replaceNextCharCnt: previousValue.length - previousSelectionEnd,
			positionDelta: currentSelectionEnd - currentValue.length
		};
	}

	public static fromScreenReaderContentState(screenReaderContentState: ISimpleScreenReaderContentState) {
		return new TextAreaState(
			screenReaderContentState.value,
			screenReaderContentState.selectionStart,
			screenReaderContentState.selectionEnd,
			screenReaderContentState.selection,
			screenReaderContentState.newlineCountBeforeSelection
		);
	}
}