gis-tools-ts/dist/dataStore/externalSort/sortChunk.js

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import { compareIDs } from '../..';
import { open } from 'fs/promises';
/**
 * @param chunk - chunk information needed to start sorting
 * @returns - output file that it created
 */
export async function sortChunk(chunk) {
    const { name, input, outDir, start, end, valueOffset } = chunk;
    const outFile = `${outDir}/es_${name}_${start}_${end}.tmp`;
    await _sortChunk(input, outFile, start, end, valueOffset);
    return outFile;
}
/**
 * @param input - input file
 * @param output - output file
 * @param start - start index
 * @param end - end index
 * @param valueOffset - actual value offset if merging values of multiple files
 */
async function _sortChunk(input, output, start, end, valueOffset) {
    // prepare the input and output files
    const inputHandle = await open(input, 'r').catch((err) => {
        throw new Error(err);
    });
    const outputHandle = await open(output, 'a').catch((err) => {
        throw new Error(err);
    });
    // read in the chunk
    const inputBuffer = Buffer.alloc(end - start);
    await inputHandle.read(inputBuffer, 0, inputBuffer.length, start);
    // sort the chunk
    const keys = bufferToKeys(inputBuffer);
    keys.sort(keySort);
    // update keys to correct offset
    for (const key of keys)
        key.offset += valueOffset;
    // write out the sorted chunk
    const sortedBuffer = keysToBuffer(keys);
    await outputHandle.appendFile(sortedBuffer);
    // close the files
    await inputHandle.close();
    await outputHandle.close();
}
/**
 * @param buffer - buffer containing an encoded list of keys
 * @returns - decoded list of keys
 */
export function bufferToKeys(buffer) {
    // for each 16 bytes in the buffer, create a key
    const keys = [];
    for (let i = 0; i < buffer.length; i += 16) {
        keys.push({
            id: buffer.readBigUInt64LE(i),
            offset: buffer.readUInt32LE(i + 8),
            length: buffer.readUInt32LE(i + 12),
        });
    }
    return keys;
}
/**
 * @param keys - list of keys
 * @returns - buffer containing an encoded list of keys
 */
export function keysToBuffer(keys) {
    const buffer = Buffer.alloc(keys.length * 16);
    for (let i = 0; i < keys.length; i++) {
        const key = keys[i];
        buffer.writeBigUInt64LE(key.id, i * 16);
        buffer.writeUInt32LE(key.offset, i * 16 + 8);
        buffer.writeUInt32LE(key.length, i * 16 + 12);
    }
    return buffer;
}
/**
 * @param a - key A
 * @param b - key B
 * @returns - ordered answer between A and B
 */
export function keySort(a, b) {
    return compareIDs(a.id, b.id);
}
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