1 | /**
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2 | * @module create-prefix-transform-stream
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3 | * @author Toru Nagashima
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4 | * @copyright 2016 Toru Nagashima. All rights reserved.
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5 | * See LICENSE file in root directory for full license.
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6 | */
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7 |
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8 |
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9 | //------------------------------------------------------------------------------
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10 | // Requirements
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11 | //------------------------------------------------------------------------------
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12 |
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13 | const stream = require("stream")
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14 |
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15 | //------------------------------------------------------------------------------
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16 | // Helpers
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17 | //------------------------------------------------------------------------------
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18 |
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19 | const ALL_BR = /\n/g
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20 |
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21 | /**
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22 | * The transform stream to insert a specific prefix.
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23 | *
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24 | * Several streams can exist for the same output stream.
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25 | * This stream will insert the prefix if the last output came from other instance.
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26 | * To do that, this stream is using a shared state object.
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27 | *
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28 | * @private
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29 | */
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30 | class PrefixTransform extends stream.Transform {
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31 | /**
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32 | * @param {string} prefix - A prefix text to be inserted.
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33 | * @param {object} state - A state object.
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34 | * @param {string} state.lastPrefix - The last prefix which is printed.
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35 | * @param {boolean} state.lastIsLinebreak -The flag to check whether the last output is a line break or not.
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36 | */
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37 | constructor(prefix, state) {
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38 | super()
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39 |
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40 | this.prefix = prefix
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41 | this.state = state
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42 | }
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43 |
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44 | /**
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45 | * Transforms the output chunk.
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46 | *
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47 | * @param {string|Buffer} chunk - A chunk to be transformed.
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48 | * @param {string} _encoding - The encoding of the chunk.
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49 | * @param {function} callback - A callback function that is called when done.
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50 | * @returns {void}
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51 | */
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52 | _transform(chunk, _encoding, callback) {
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53 | const prefix = this.prefix
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54 | const nPrefix = `\n${prefix}`
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55 | const state = this.state
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56 | const firstPrefix =
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57 | state.lastIsLinebreak ? prefix :
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58 | (state.lastPrefix !== prefix) ? "\n" :
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59 | /* otherwise */ ""
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60 | const prefixed = `${firstPrefix}${chunk}`.replace(ALL_BR, nPrefix)
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61 | const index = prefixed.indexOf(prefix, Math.max(0, prefixed.length - prefix.length))
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62 |
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63 | state.lastPrefix = prefix
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64 | state.lastIsLinebreak = (index !== -1)
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65 |
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66 | callback(null, (index !== -1) ? prefixed.slice(0, index) : prefixed)
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67 | }
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68 | }
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69 |
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70 | //------------------------------------------------------------------------------
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71 | // Public API
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72 | //------------------------------------------------------------------------------
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73 |
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74 | /**
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75 | * Create a transform stream to insert the specific prefix.
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76 | *
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77 | * Several streams can exist for the same output stream.
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78 | * This stream will insert the prefix if the last output came from other instance.
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79 | * To do that, this stream is using a shared state object.
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80 | *
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81 | * @param {string} prefix - A prefix text to be inserted.
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82 | * @param {object} state - A state object.
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83 | * @param {string} state.lastPrefix - The last prefix which is printed.
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84 | * @param {boolean} state.lastIsLinebreak -The flag to check whether the last output is a line break or not.
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85 | * @returns {stream.Transform} The created transform stream.
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86 | */
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87 | module.exports = function createPrefixTransform(prefix, state) {
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88 | return new PrefixTransform(prefix, state)
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89 | }
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