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/*
* Copyright (c) 2016-2023 Martin Donath <martin.donath@squidfunk.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
/* ----------------------------------------------------------------------------
* Functions
* ------------------------------------------------------------------------- */
/**
* Segment a search query using the inverted index
*
* This function implements a clever approach to text segmentation for Asian
* languages, as it used the information already available in the search index.
* The idea is to greedily segment the search query based on the tokens that are
* already part of the index, as described in the linked issue.
*
* @see https://bit.ly/3lwjrk7 - GitHub issue
*
* @param query - Query value
* @param index - Inverted index
*
* @returns Segmented query value
*/
export function segment(
query: string, index: object
): Iterable<string> {
const segments = new Set<string>()
/* Segment search query */
const wordcuts = new Uint16Array(query.length)
for (let i = 0; i < query.length; i++)
for (let j = i + 1; j < query.length; j++) {
const value = query.slice(i, j)
if (value in index)
wordcuts[i] = j - i
}
/* Compute longest matches with minimum overlap */
const stack = [0]
for (let s = stack.length; s > 0;) {
const p = stack[--s]
for (let q = 1; q < wordcuts[p]; q++)
if (wordcuts[p + q] > wordcuts[p] - q) {
segments.add(query.slice(p, p + q))
stack[s++] = p + q
}
/* Continue at end of query string */
const q = p + wordcuts[p]
if (wordcuts[q] && q < query.length - 1)
stack[s++] = q
/* Add current segment */
segments.add(query.slice(p, q))
}
// @todo fix this case in the code block above, this is a hotfix
if (segments.has(""))
return new Set([query])
/* Return segmented query value */
return segments
}
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