40 lines
1.4 KiB
JavaScript
40 lines
1.4 KiB
JavaScript
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/**
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* Tracks newlines during parsing in order to provide an efficient API for
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* determining the one-indexed `{ line, col }` position for any offset
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* within the input.
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*/
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class LineCounter {
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constructor() {
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this.lineStarts = [];
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/**
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* Should be called in ascending order. Otherwise, call
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* `lineCounter.lineStarts.sort()` before calling `linePos()`.
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*/
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this.addNewLine = (offset) => this.lineStarts.push(offset);
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/**
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* Performs a binary search and returns the 1-indexed { line, col }
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* position of `offset`. If `line === 0`, `addNewLine` has never been
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* called or `offset` is before the first known newline.
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*/
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this.linePos = (offset) => {
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let low = 0;
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let high = this.lineStarts.length;
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while (low < high) {
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const mid = (low + high) >> 1; // Math.floor((low + high) / 2)
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if (this.lineStarts[mid] < offset)
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low = mid + 1;
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else
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high = mid;
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}
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if (this.lineStarts[low] === offset)
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return { line: low + 1, col: 1 };
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if (low === 0)
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return { line: 0, col: offset };
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const start = this.lineStarts[low - 1];
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return { line: low, col: offset - start + 1 };
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};
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}
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}
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export { LineCounter };
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