heuristicSequenceOptimizations.ts

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

import { forEachWithNeighbors } from '../../../../base/common/arrays.js';
import { OffsetRange } from '../../core/ranges/offsetRange.js';
import { ISequence, OffsetPair, SequenceDiff } from './algorithms/diffAlgorithm.js';
import { LineSequence } from './lineSequence.js';
import { LinesSliceCharSequence } from './linesSliceCharSequence.js';

export function optimizeSequenceDiffs(sequence1: ISequence, sequence2: ISequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	let result = sequenceDiffs;
	result = joinSequenceDiffsByShifting(sequence1, sequence2, result);
	// Sometimes, calling this function twice improves the result.
	// Uncomment the second invocation and run the tests to see the difference.
	result = joinSequenceDiffsByShifting(sequence1, sequence2, result);
	result = shiftSequenceDiffs(sequence1, sequence2, result);
	return result;
}

/**
 * This function fixes issues like this:
 * ```
 * import { Baz, Bar } from "foo";
 * ```
 * <->
 * ```
 * import { Baz, Bar, Foo } from "foo";
 * ```
 * Computed diff: [ {Add "," after Bar}, {Add "Foo " after space} }
 * Improved diff: [{Add ", Foo" after Bar}]
 */
function joinSequenceDiffsByShifting(sequence1: ISequence, sequence2: ISequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	if (sequenceDiffs.length === 0) {
		return sequenceDiffs;
	}

	const result: SequenceDiff[] = [];
	result.push(sequenceDiffs[0]);

	// First move them all to the left as much as possible and join them if possible
	for (let i = 1; i < sequenceDiffs.length; i++) {
		const prevResult = result[result.length - 1];
		let cur = sequenceDiffs[i];

		if (cur.seq1Range.isEmpty || cur.seq2Range.isEmpty) {
			const length = cur.seq1Range.start - prevResult.seq1Range.endExclusive;
			let d;
			for (d = 1; d <= length; d++) {
				if (
					sequence1.getElement(cur.seq1Range.start - d) !== sequence1.getElement(cur.seq1Range.endExclusive - d) ||
					sequence2.getElement(cur.seq2Range.start - d) !== sequence2.getElement(cur.seq2Range.endExclusive - d)) {
					break;
				}
			}
			d--;

			if (d === length) {
				// Merge previous and current diff
				result[result.length - 1] = new SequenceDiff(
					new OffsetRange(prevResult.seq1Range.start, cur.seq1Range.endExclusive - length),
					new OffsetRange(prevResult.seq2Range.start, cur.seq2Range.endExclusive - length),
				);
				continue;
			}

			cur = cur.delta(-d);
		}

		result.push(cur);
	}

	const result2: SequenceDiff[] = [];
	// Then move them all to the right and join them again if possible
	for (let i = 0; i < result.length - 1; i++) {
		const nextResult = result[i + 1];
		let cur = result[i];

		if (cur.seq1Range.isEmpty || cur.seq2Range.isEmpty) {
			const length = nextResult.seq1Range.start - cur.seq1Range.endExclusive;
			let d;
			for (d = 0; d < length; d++) {
				if (
					!sequence1.isStronglyEqual(cur.seq1Range.start + d, cur.seq1Range.endExclusive + d) ||
					!sequence2.isStronglyEqual(cur.seq2Range.start + d, cur.seq2Range.endExclusive + d)
				) {
					break;
				}
			}

			if (d === length) {
				// Merge previous and current diff, write to result!
				result[i + 1] = new SequenceDiff(
					new OffsetRange(cur.seq1Range.start + length, nextResult.seq1Range.endExclusive),
					new OffsetRange(cur.seq2Range.start + length, nextResult.seq2Range.endExclusive),
				);
				continue;
			}

			if (d > 0) {
				cur = cur.delta(d);
			}
		}

		result2.push(cur);
	}

	if (result.length > 0) {
		result2.push(result[result.length - 1]);
	}

	return result2;
}

// align character level diffs at whitespace characters
// import { IBar } from "foo";
// import { I[Arr, I]Bar } from "foo";
// ->
// import { [IArr, ]IBar } from "foo";

// import { ITransaction, observableValue, transaction } from 'vs/base/common/observable';
// import { ITransaction, observable[FromEvent, observable]Value, transaction } from 'vs/base/common/observable';
// ->
// import { ITransaction, [observableFromEvent, ]observableValue, transaction } from 'vs/base/common/observable';

// collectBrackets(level + 1, levelPerBracketType);
// collectBrackets(level + 1, levelPerBracket[ + 1, levelPerBracket]Type);
// ->
// collectBrackets(level + 1, [levelPerBracket + 1, ]levelPerBracketType);

function shiftSequenceDiffs(sequence1: ISequence, sequence2: ISequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	if (!sequence1.getBoundaryScore || !sequence2.getBoundaryScore) {
		return sequenceDiffs;
	}

	for (let i = 0; i < sequenceDiffs.length; i++) {
		const prevDiff = (i > 0 ? sequenceDiffs[i - 1] : undefined);
		const diff = sequenceDiffs[i];
		const nextDiff = (i + 1 < sequenceDiffs.length ? sequenceDiffs[i + 1] : undefined);

		const seq1ValidRange = new OffsetRange(prevDiff ? prevDiff.seq1Range.endExclusive + 1 : 0, nextDiff ? nextDiff.seq1Range.start - 1 : sequence1.length);
		const seq2ValidRange = new OffsetRange(prevDiff ? prevDiff.seq2Range.endExclusive + 1 : 0, nextDiff ? nextDiff.seq2Range.start - 1 : sequence2.length);

		if (diff.seq1Range.isEmpty) {
			sequenceDiffs[i] = shiftDiffToBetterPosition(diff, sequence1, sequence2, seq1ValidRange, seq2ValidRange);
		} else if (diff.seq2Range.isEmpty) {
			sequenceDiffs[i] = shiftDiffToBetterPosition(diff.swap(), sequence2, sequence1, seq2ValidRange, seq1ValidRange).swap();
		}
	}

	return sequenceDiffs;
}

function shiftDiffToBetterPosition(diff: SequenceDiff, sequence1: ISequence, sequence2: ISequence, seq1ValidRange: OffsetRange, seq2ValidRange: OffsetRange,) {
	const maxShiftLimit = 100; // To prevent performance issues

	// don't touch previous or next!
	let deltaBefore = 1;
	while (
		diff.seq1Range.start - deltaBefore >= seq1ValidRange.start &&
		diff.seq2Range.start - deltaBefore >= seq2ValidRange.start &&
		sequence2.isStronglyEqual(diff.seq2Range.start - deltaBefore, diff.seq2Range.endExclusive - deltaBefore) && deltaBefore < maxShiftLimit
	) {
		deltaBefore++;
	}
	deltaBefore--;

	let deltaAfter = 0;
	while (
		diff.seq1Range.start + deltaAfter < seq1ValidRange.endExclusive &&
		diff.seq2Range.endExclusive + deltaAfter < seq2ValidRange.endExclusive &&
		sequence2.isStronglyEqual(diff.seq2Range.start + deltaAfter, diff.seq2Range.endExclusive + deltaAfter) && deltaAfter < maxShiftLimit
	) {
		deltaAfter++;
	}

	if (deltaBefore === 0 && deltaAfter === 0) {
		return diff;
	}

	// Visualize `[sequence1.text, diff.seq1Range.start + deltaAfter]`
	// and `[sequence2.text, diff.seq2Range.start + deltaAfter, diff.seq2Range.endExclusive + deltaAfter]`

	let bestDelta = 0;
	let bestScore = -1;
	// find best scored delta
	for (let delta = -deltaBefore; delta <= deltaAfter; delta++) {
		const seq2OffsetStart = diff.seq2Range.start + delta;
		const seq2OffsetEndExclusive = diff.seq2Range.endExclusive + delta;
		const seq1Offset = diff.seq1Range.start + delta;

		const score = sequence1.getBoundaryScore!(seq1Offset) + sequence2.getBoundaryScore!(seq2OffsetStart) + sequence2.getBoundaryScore!(seq2OffsetEndExclusive);
		if (score > bestScore) {
			bestScore = score;
			bestDelta = delta;
		}
	}

	return diff.delta(bestDelta);
}

export function removeShortMatches(sequence1: ISequence, sequence2: ISequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	const result: SequenceDiff[] = [];
	for (const s of sequenceDiffs) {
		const last = result[result.length - 1];
		if (!last) {
			result.push(s);
			continue;
		}

		if (s.seq1Range.start - last.seq1Range.endExclusive <= 2 || s.seq2Range.start - last.seq2Range.endExclusive <= 2) {
			result[result.length - 1] = new SequenceDiff(last.seq1Range.join(s.seq1Range), last.seq2Range.join(s.seq2Range));
		} else {
			result.push(s);
		}
	}

	return result;
}

export function extendDiffsToEntireWordIfAppropriate(
	sequence1: LinesSliceCharSequence,
	sequence2: LinesSliceCharSequence,
	sequenceDiffs: SequenceDiff[],
	findParent: (seq: LinesSliceCharSequence, idx: number) => OffsetRange | undefined,
	force: boolean = false,
): SequenceDiff[] {
	const equalMappings = SequenceDiff.invert(sequenceDiffs, sequence1.length);

	const additional: SequenceDiff[] = [];

	let lastPoint = new OffsetPair(0, 0);

	function scanWord(pair: OffsetPair, equalMapping: SequenceDiff) {
		if (pair.offset1 < lastPoint.offset1 || pair.offset2 < lastPoint.offset2) {
			return;
		}

		const w1 = findParent(sequence1, pair.offset1);
		const w2 = findParent(sequence2, pair.offset2);
		if (!w1 || !w2) {
			return;
		}
		let w = new SequenceDiff(w1, w2);
		const equalPart = w.intersect(equalMapping)!;

		let equalChars1 = equalPart.seq1Range.length;
		let equalChars2 = equalPart.seq2Range.length;

		// The words do not touch previous equals mappings, as we would have processed them already.
		// But they might touch the next ones.

		while (equalMappings.length > 0) {
			const next = equalMappings[0];
			const intersects = next.seq1Range.intersects(w.seq1Range) || next.seq2Range.intersects(w.seq2Range);
			if (!intersects) {
				break;
			}

			const v1 = findParent(sequence1, next.seq1Range.start);
			const v2 = findParent(sequence2, next.seq2Range.start);
			// Because there is an intersection, we know that the words are not empty.
			const v = new SequenceDiff(v1!, v2!);
			const equalPart = v.intersect(next)!;

			equalChars1 += equalPart.seq1Range.length;
			equalChars2 += equalPart.seq2Range.length;

			w = w.join(v);

			if (w.seq1Range.endExclusive >= next.seq1Range.endExclusive) {
				// The word extends beyond the next equal mapping.
				equalMappings.shift();
			} else {
				break;
			}
		}

		if ((force && equalChars1 + equalChars2 < w.seq1Range.length + w.seq2Range.length) || equalChars1 + equalChars2 < (w.seq1Range.length + w.seq2Range.length) * 2 / 3) {
			additional.push(w);
		}

		lastPoint = w.getEndExclusives();
	}

	while (equalMappings.length > 0) {
		const next = equalMappings.shift()!;
		if (next.seq1Range.isEmpty) {
			continue;
		}
		scanWord(next.getStarts(), next);
		// The equal parts are not empty, so -1 gives us a character that is equal in both parts.
		scanWord(next.getEndExclusives().delta(-1), next);
	}

	const merged = mergeSequenceDiffs(sequenceDiffs, additional);
	return merged;
}

function mergeSequenceDiffs(sequenceDiffs1: SequenceDiff[], sequenceDiffs2: SequenceDiff[]): SequenceDiff[] {
	const result: SequenceDiff[] = [];

	while (sequenceDiffs1.length > 0 || sequenceDiffs2.length > 0) {
		const sd1 = sequenceDiffs1[0];
		const sd2 = sequenceDiffs2[0];

		let next: SequenceDiff;
		if (sd1 && (!sd2 || sd1.seq1Range.start < sd2.seq1Range.start)) {
			next = sequenceDiffs1.shift()!;
		} else {
			next = sequenceDiffs2.shift()!;
		}

		if (result.length > 0 && result[result.length - 1].seq1Range.endExclusive >= next.seq1Range.start) {
			result[result.length - 1] = result[result.length - 1].join(next);
		} else {
			result.push(next);
		}
	}

	return result;
}

export function removeVeryShortMatchingLinesBetweenDiffs(sequence1: LineSequence, _sequence2: LineSequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	let diffs = sequenceDiffs;
	if (diffs.length === 0) {
		return diffs;
	}

	let counter = 0;
	let shouldRepeat: boolean;
	do {
		shouldRepeat = false;

		const result: SequenceDiff[] = [
			diffs[0]
		];

		for (let i = 1; i < diffs.length; i++) {
			const cur = diffs[i];
			const lastResult = result[result.length - 1];

			function shouldJoinDiffs(before: SequenceDiff, after: SequenceDiff): boolean {
				const unchangedRange = new OffsetRange(lastResult.seq1Range.endExclusive, cur.seq1Range.start);

				const unchangedText = sequence1.getText(unchangedRange);
				const unchangedTextWithoutWs = unchangedText.replace(/\s/g, '');
				if (unchangedTextWithoutWs.length <= 4
					&& (before.seq1Range.length + before.seq2Range.length > 5 || after.seq1Range.length + after.seq2Range.length > 5)) {
					return true;
				}

				return false;
			}

			const shouldJoin = shouldJoinDiffs(lastResult, cur);
			if (shouldJoin) {
				shouldRepeat = true;
				result[result.length - 1] = result[result.length - 1].join(cur);
			} else {
				result.push(cur);
			}
		}

		diffs = result;
	} while (counter++ < 10 && shouldRepeat);

	return diffs;
}

export function removeVeryShortMatchingTextBetweenLongDiffs(sequence1: LinesSliceCharSequence, sequence2: LinesSliceCharSequence, sequenceDiffs: SequenceDiff[]): SequenceDiff[] {
	let diffs = sequenceDiffs;
	if (diffs.length === 0) {
		return diffs;
	}

	let counter = 0;
	let shouldRepeat: boolean;
	do {
		shouldRepeat = false;

		const result: SequenceDiff[] = [
			diffs[0]
		];

		for (let i = 1; i < diffs.length; i++) {
			const cur = diffs[i];
			const lastResult = result[result.length - 1];

			function shouldJoinDiffs(before: SequenceDiff, after: SequenceDiff): boolean {
				const unchangedRange = new OffsetRange(lastResult.seq1Range.endExclusive, cur.seq1Range.start);

				const unchangedLineCount = sequence1.countLinesIn(unchangedRange);
				if (unchangedLineCount > 5 || unchangedRange.length > 500) {
					return false;
				}

				const unchangedText = sequence1.getText(unchangedRange).trim();
				if (unchangedText.length > 20 || unchangedText.split(/\r\n|\r|\n/).length > 1) {
					return false;
				}

				const beforeLineCount1 = sequence1.countLinesIn(before.seq1Range);
				const beforeSeq1Length = before.seq1Range.length;
				const beforeLineCount2 = sequence2.countLinesIn(before.seq2Range);
				const beforeSeq2Length = before.seq2Range.length;

				const afterLineCount1 = sequence1.countLinesIn(after.seq1Range);
				const afterSeq1Length = after.seq1Range.length;
				const afterLineCount2 = sequence2.countLinesIn(after.seq2Range);
				const afterSeq2Length = after.seq2Range.length;

				// TODO: Maybe a neural net can be used to derive the result from these numbers

				const max = 2 * 40 + 50;
				function cap(v: number): number {
					return Math.min(v, max);
				}

				if (Math.pow(Math.pow(cap(beforeLineCount1 * 40 + beforeSeq1Length), 1.5) + Math.pow(cap(beforeLineCount2 * 40 + beforeSeq2Length), 1.5), 1.5)
					+ Math.pow(Math.pow(cap(afterLineCount1 * 40 + afterSeq1Length), 1.5) + Math.pow(cap(afterLineCount2 * 40 + afterSeq2Length), 1.5), 1.5) > ((max ** 1.5) ** 1.5) * 1.3) {
					return true;
				}
				return false;
			}

			const shouldJoin = shouldJoinDiffs(lastResult, cur);
			if (shouldJoin) {
				shouldRepeat = true;
				result[result.length - 1] = result[result.length - 1].join(cur);
			} else {
				result.push(cur);
			}
		}

		diffs = result;
	} while (counter++ < 10 && shouldRepeat);

	const newDiffs: SequenceDiff[] = [];

	// Remove short suffixes/prefixes
	forEachWithNeighbors(diffs, (prev, cur, next) => {
		let newDiff = cur;

		function shouldMarkAsChanged(text: string): boolean {
			return text.length > 0 && text.trim().length <= 3 && cur.seq1Range.length + cur.seq2Range.length > 100;
		}

		const fullRange1 = sequence1.extendToFullLines(cur.seq1Range);
		const prefix = sequence1.getText(new OffsetRange(fullRange1.start, cur.seq1Range.start));
		if (shouldMarkAsChanged(prefix)) {
			newDiff = newDiff.deltaStart(-prefix.length);
		}
		const suffix = sequence1.getText(new OffsetRange(cur.seq1Range.endExclusive, fullRange1.endExclusive));
		if (shouldMarkAsChanged(suffix)) {
			newDiff = newDiff.deltaEnd(suffix.length);
		}

		const availableSpace = SequenceDiff.fromOffsetPairs(
			prev ? prev.getEndExclusives() : OffsetPair.zero,
			next ? next.getStarts() : OffsetPair.max,
		);
		const result = newDiff.intersect(availableSpace)!;
		if (newDiffs.length > 0 && result.getStarts().equals(newDiffs[newDiffs.length - 1].getEndExclusives())) {
			newDiffs[newDiffs.length - 1] = newDiffs[newDiffs.length - 1].join(result);
		} else {
			newDiffs.push(result);
		}
	});

	return newDiffs;
}