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366 lines (327 loc) · 13.1 KB
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import type {ChangeObject, AllDiffOptions, AbortableDiffOptions, DiffCallbackNonabortable, CallbackOptionAbortable, CallbackOptionNonabortable, DiffCallbackAbortable, TimeoutOption, MaxEditLengthOption} from '../types.js';
/**
* Like a ChangeObject, but with no value and an extra `previousComponent` property.
* A linked list of these (linked via `.previousComponent`) is used internally in the code below to
* keep track of the state of the diffing algorithm, but gets converted to an array of
* ChangeObjects before being returned to the caller.
*/
interface DraftChangeObject {
added: boolean;
removed: boolean;
count: number;
previousComponent?: DraftChangeObject;
// Only added in buildValues:
value?: any;
}
interface Path {
oldPos: number;
lastComponent: DraftChangeObject | undefined
}
export default class Diff<
TokenT,
ValueT extends Iterable<TokenT> = Iterable<TokenT>,
InputValueT = ValueT
> {
diff(
oldStr: InputValueT,
newStr: InputValueT,
options: DiffCallbackNonabortable<ValueT>
): undefined;
diff(
oldStr: InputValueT,
newStr: InputValueT,
options: AllDiffOptions & AbortableDiffOptions & CallbackOptionAbortable<ValueT>
): undefined
diff(
oldStr: InputValueT,
newStr: InputValueT,
options: AllDiffOptions & CallbackOptionNonabortable<ValueT>
): undefined
diff(
oldStr: InputValueT,
newStr: InputValueT,
options: AllDiffOptions & AbortableDiffOptions
): ChangeObject<ValueT>[] | undefined
diff(
oldStr: InputValueT,
newStr: InputValueT,
options?: AllDiffOptions
): ChangeObject<ValueT>[]
diff(
oldStr: InputValueT,
newStr: InputValueT,
// Type below is not accurate/complete - see above for full possibilities - but it compiles
options: DiffCallbackNonabortable<ValueT> | AllDiffOptions & Partial<CallbackOptionNonabortable<ValueT>> = {}
): ChangeObject<ValueT>[] | undefined {
let callback: DiffCallbackAbortable<ValueT> | DiffCallbackNonabortable<ValueT> | undefined;
if (typeof options === 'function') {
callback = options;
options = {};
} else if ('callback' in options) {
callback = options.callback;
}
// Allow subclasses to massage the input prior to running
const oldString = this.castInput(oldStr, options);
const newString = this.castInput(newStr, options);
const oldTokens = this.removeEmpty(this.tokenize(oldString, options));
const newTokens = this.removeEmpty(this.tokenize(newString, options));
return this.diffWithOptionsObj(oldTokens, newTokens, options, callback);
}
private diffWithOptionsObj(
oldTokens: TokenT[],
newTokens: TokenT[],
options: AllDiffOptions & Partial<TimeoutOption> & Partial<MaxEditLengthOption>,
callback: DiffCallbackAbortable<ValueT> | DiffCallbackNonabortable<ValueT> | undefined
): ChangeObject<ValueT>[] | undefined {
const done = (value: ChangeObject<ValueT>[]) => {
value = this.postProcess(value, options);
if (callback) {
setTimeout(function() { callback(value); }, 0);
return undefined;
} else {
return value;
}
};
const newLen = newTokens.length, oldLen = oldTokens.length;
let editLength = 1;
let maxEditLength = newLen + oldLen;
if(options.maxEditLength != null) {
maxEditLength = Math.min(maxEditLength, options.maxEditLength);
}
const maxExecutionTime = options.timeout ?? Infinity;
const abortAfterTimestamp = Date.now() + maxExecutionTime;
const bestPath: Path[] = [{ oldPos: -1, lastComponent: undefined }];
// Seed editLength = 0, i.e. the content starts with the same values
let newPos = this.extractCommon(bestPath[0], newTokens, oldTokens, 0, options);
if (bestPath[0].oldPos + 1 >= oldLen && newPos + 1 >= newLen) {
// Identity per the equality and tokenizer
return done(this.buildValues(bestPath[0].lastComponent, newTokens, oldTokens));
}
// Once we hit the right edge of the edit graph on some diagonal k, we can
// definitely reach the end of the edit graph in no more than k edits, so
// there's no point in considering any moves to diagonal k+1 any more (from
// which we're guaranteed to need at least k+1 more edits).
// Similarly, once we've reached the bottom of the edit graph, there's no
// point considering moves to lower diagonals.
// We record this fact by setting minDiagonalToConsider and
// maxDiagonalToConsider to some finite value once we've hit the edge of
// the edit graph.
// This optimization is not faithful to the original algorithm presented in
// Myers's paper, which instead pointlessly extends D-paths off the end of
// the edit graph - see page 7 of Myers's paper which notes this point
// explicitly and illustrates it with a diagram. This has major performance
// implications for some common scenarios. For instance, to compute a diff
// where the new text simply appends d characters on the end of the
// original text of length n, the true Myers algorithm will take O(n+d^2)
// time while this optimization needs only O(n+d) time.
let minDiagonalToConsider = -Infinity, maxDiagonalToConsider = Infinity;
// Main worker method. checks all permutations of a given edit length for acceptance.
const execEditLength = () => {
for (
let diagonalPath = Math.max(minDiagonalToConsider, -editLength);
diagonalPath <= Math.min(maxDiagonalToConsider, editLength);
diagonalPath += 2
) {
let basePath;
const removePath = bestPath[diagonalPath - 1],
addPath = bestPath[diagonalPath + 1];
if (removePath) {
// No one else is going to attempt to use this value, clear it
// @ts-expect-error - perf optimisation. This type-violating value will never be read.
bestPath[diagonalPath - 1] = undefined;
}
let canAdd = false;
if (addPath) {
// what newPos will be after we do an insertion:
const addPathNewPos = addPath.oldPos - diagonalPath;
canAdd = addPath && 0 <= addPathNewPos && addPathNewPos < newLen;
}
const canRemove = removePath && removePath.oldPos + 1 < oldLen;
if (!canAdd && !canRemove) {
// If this path is a terminal then prune
// @ts-expect-error - perf optimisation. This type-violating value will never be read.
bestPath[diagonalPath] = undefined;
continue;
}
// Select the diagonal that we want to branch from. We select the prior
// path whose position in the old string is the farthest from the origin
// and does not pass the bounds of the diff graph
if (!canRemove || (canAdd && removePath.oldPos < addPath.oldPos)) {
basePath = this.addToPath(addPath, true, false, 0, options);
} else {
basePath = this.addToPath(removePath, false, true, 1, options);
}
newPos = this.extractCommon(basePath, newTokens, oldTokens, diagonalPath, options);
if (basePath.oldPos + 1 >= oldLen && newPos + 1 >= newLen) {
// If we have hit the end of both strings, then we are done
return done(this.buildValues(basePath.lastComponent, newTokens, oldTokens)) || true;
} else {
bestPath[diagonalPath] = basePath;
if (basePath.oldPos + 1 >= oldLen) {
maxDiagonalToConsider = Math.min(maxDiagonalToConsider, diagonalPath - 1);
}
if (newPos + 1 >= newLen) {
minDiagonalToConsider = Math.max(minDiagonalToConsider, diagonalPath + 1);
}
}
}
editLength++;
};
// Performs the length of edit iteration. Is a bit fugly as this has to support the
// sync and async mode which is never fun. Loops over execEditLength until a value
// is produced, or until the edit length exceeds options.maxEditLength (if given),
// in which case it will return undefined.
if (callback) {
(function exec() {
setTimeout(function() {
if (editLength > maxEditLength || Date.now() > abortAfterTimestamp) {
return (callback as DiffCallbackAbortable<ValueT>)(undefined);
}
if (!execEditLength()) {
exec();
}
}, 0);
}());
} else {
while (editLength <= maxEditLength && Date.now() <= abortAfterTimestamp) {
const ret = execEditLength();
if (ret) {
return ret as ChangeObject<ValueT>[];
}
}
}
}
private addToPath(
path: Path,
added: boolean,
removed: boolean,
oldPosInc: number,
options: AllDiffOptions
): Path {
const last = path.lastComponent;
if (last && !options.oneChangePerToken && last.added === added && last.removed === removed) {
return {
oldPos: path.oldPos + oldPosInc,
lastComponent: {count: last.count + 1, added: added, removed: removed, previousComponent: last.previousComponent }
};
} else {
return {
oldPos: path.oldPos + oldPosInc,
lastComponent: {count: 1, added: added, removed: removed, previousComponent: last }
};
}
}
private extractCommon(
basePath: Path,
newTokens: TokenT[],
oldTokens: TokenT[],
diagonalPath: number,
options: AllDiffOptions
): number {
const newLen = newTokens.length,
oldLen = oldTokens.length;
let oldPos = basePath.oldPos,
newPos = oldPos - diagonalPath,
commonCount = 0;
while (newPos + 1 < newLen && oldPos + 1 < oldLen && this.equals(oldTokens[oldPos + 1], newTokens[newPos + 1], options)) {
newPos++;
oldPos++;
commonCount++;
if (options.oneChangePerToken) {
basePath.lastComponent = {count: 1, previousComponent: basePath.lastComponent, added: false, removed: false};
}
}
if (commonCount && !options.oneChangePerToken) {
basePath.lastComponent = {count: commonCount, previousComponent: basePath.lastComponent, added: false, removed: false};
}
basePath.oldPos = oldPos;
return newPos;
}
equals(left: TokenT, right: TokenT, options: AllDiffOptions): boolean {
if (options.comparator) {
return options.comparator(left, right);
} else {
return left === right
|| (!!options.ignoreCase && (left as string).toLowerCase() === (right as string).toLowerCase());
}
}
removeEmpty(array: TokenT[]): TokenT[] {
const ret: TokenT[] = [];
for (let i = 0; i < array.length; i++) {
if (array[i]) {
ret.push(array[i]);
}
}
return ret;
}
// eslint-disable-next-line @typescript-eslint/no-unused-vars
castInput(value: InputValueT, options: AllDiffOptions): ValueT {
return value as unknown as ValueT;
}
// eslint-disable-next-line @typescript-eslint/no-unused-vars
tokenize(value: ValueT, options: AllDiffOptions): TokenT[] {
return Array.from(value);
}
join(chars: TokenT[]): ValueT {
// Assumes ValueT is string, which is the case for most subclasses.
// When it's false, e.g. in diffArrays, this method needs to be overridden (e.g. with a no-op)
// Yes, the casts are verbose and ugly, because this pattern - of having the base class SORT OF
// assume tokens and values are strings, but not completely - is weird and janky.
return (chars as string[]).join('') as unknown as ValueT;
}
postProcess(
changeObjects: ChangeObject<ValueT>[],
// eslint-disable-next-line @typescript-eslint/no-unused-vars
options: AllDiffOptions
): ChangeObject<ValueT>[] {
return changeObjects;
}
get useLongestToken(): boolean {
return false;
}
private buildValues(
lastComponent: DraftChangeObject | undefined,
newTokens: TokenT[],
oldTokens: TokenT[]
): ChangeObject<ValueT>[] {
// First we convert our linked list of components in reverse order to an
// array in the right order:
const components: DraftChangeObject[] = [];
let nextComponent;
while (lastComponent) {
components.push(lastComponent);
nextComponent = lastComponent.previousComponent;
delete lastComponent.previousComponent;
lastComponent = nextComponent;
}
components.reverse();
const componentLen = components.length;
let componentPos = 0,
newPos = 0,
oldPos = 0;
for (; componentPos < componentLen; componentPos++) {
const component = components[componentPos];
if (!component.removed) {
if (!component.added && this.useLongestToken) {
let value = newTokens.slice(newPos, newPos + component.count);
value = value.map(function(value, i) {
const oldValue = oldTokens[oldPos + i];
return (oldValue as string).length > (value as string).length ? oldValue : value;
});
component.value = this.join(value);
} else {
component.value = this.join(newTokens.slice(newPos, newPos + component.count));
}
newPos += component.count;
// Common case
if (!component.added) {
oldPos += component.count;
}
} else {
component.value = this.join(oldTokens.slice(oldPos, oldPos + component.count));
oldPos += component.count;
}
}
return components as ChangeObject<ValueT>[];
}
}