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47 lines
1.5 KiB
47 lines
1.5 KiB
import { DocState } from 'app/common/UserAPI';
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/**
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*
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* Helper class to support a small subset of git-style references for state hashes:
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* HEAD = the most recent state
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* [HASH]^1 = the parent of [HASH]
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* [HASH]~1 = the parent of [HASH]
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* [HASH]~2 = the grandparent of [HASH]
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* [HASH]^1^1 = the grandparent of [HASH]
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* [HASH]~3 = the great grandparent of [HASH]
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* For git, where commits have multiple parents, "~" refers to the first parent,
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* and "^1" also refers to the first parent. For grist, there are only first parents
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* (unless/until we start tracking history across merges).
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*
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*/
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export class HashUtil {
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/**
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* To construct, provide a list of states, most recent first.
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*/
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constructor(private _state: DocState[]) {}
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/**
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* Find the named hash in the list of states, allowing for aliases.
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* Returns an index into the list of states provided in constructor.
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*/
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public hashToOffset(hash: string): number {
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const parts = hash.split(/([~^][0-9]*)/);
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hash = parts.shift() || '';
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let offset = hash === 'HEAD' ? 0 : this._state.findIndex(state => state.h === hash);
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if (offset < 0) { throw new Error('Cannot read hash'); }
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for (const part of parts) {
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if (part === '^' || part === '^1') {
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offset++;
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} else if (part.startsWith('~')) {
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offset += parseInt(part.slice(1) || '1', 10);
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} else if (part === '') {
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// pass
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} else {
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throw new Error('cannot parse hash');
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}
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}
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return offset;
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}
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}
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