42 lines
1.1 KiB
Plaintext
42 lines
1.1 KiB
Plaintext
'use strict';
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const {Transform} = require('stream');
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const defaultInitial = 0;
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const defaultReducer = (acc, value) => value;
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class Scan extends Transform {
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constructor(options) {
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super(Object.assign({}, options, {writableObjectMode: true, readableObjectMode: true}));
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this._accumulator = defaultInitial;
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this._reducer = defaultReducer;
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if (options) {
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'initial' in options && (this._accumulator = options.initial);
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'reducer' in options && (this._reducer = options.reducer);
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}
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}
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_transform(chunk, encoding, callback) {
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const result = this._reducer.call(this, this._accumulator, chunk);
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if (result && typeof result.then == 'function') {
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result.then(
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value => {
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this._accumulator = value;
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this.push(this._accumulator);
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callback(null);
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},
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error => callback(error)
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);
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} else {
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this._accumulator = result;
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this.push(this._accumulator);
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callback(null);
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}
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}
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static make(reducer, initial) {
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return new Scan(typeof reducer == 'object' ? reducer : {reducer, initial});
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}
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}
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Scan.make.Constructor = Scan;
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module.exports = Scan.make;
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