previous-map.js

'use strict'

let { SourceMapConsumer, SourceMapGenerator } = require('source-map-js')
let { existsSync, readFileSync } = require('fs')
let { dirname, join } = require('path')

function fromBase64(str) {
  if (Buffer) {
    return Buffer.from(str, 'base64').toString()
  } else {
    // istanbul ignore next
    return window.atob(str)
  }
}

class PreviousMap {
  constructor(css, opts) {
    if (opts.map === false) return
    this.loadAnnotation(css)
    this.inline = this.startWith(this.annotation, 'data:')

    let prev = opts.map ? opts.map.prev : undefined
    let text = this.loadMap(opts.from, prev)
    if (!this.mapFile && opts.from) {
      this.mapFile = opts.from
    }
    if (this.mapFile) this.root = dirname(this.mapFile)
    if (text) this.text = text
  }

  consumer() {
    if (!this.consumerCache) {
      this.consumerCache = new SourceMapConsumer(this.text)
    }
    return this.consumerCache
  }

  withContent() {
    return !!(
      this.consumer().sourcesContent &&
      this.consumer().sourcesContent.length > 0
    )
  }

  startWith(string, start) {
    if (!string) return false
    return string.substr(0, start.length) === start
  }

  getAnnotationURL(sourceMapString) {
    return sourceMapString
      .match(/\/\*\s*# sourceMappingURL=((?:(?!sourceMappingURL=).)*)\*\//)[1]
      .trim()
  }

  loadAnnotation(css) {
    let annotations = css.match(
      /\/\*\s*# sourceMappingURL=(?:(?!sourceMappingURL=).)*\*\//gm
    )

    if (annotations && annotations.length > 0) {
      // Locate the last sourceMappingURL to avoid picking up
      // sourceMappingURLs from comments, strings, etc.
      let lastAnnotation = annotations[annotations.length - 1]
      if (lastAnnotation) {
        this.annotation = this.getAnnotationURL(lastAnnotation)
      }
    }
  }

  decodeInline(text) {
    let baseCharsetUri = /^data:application\/json;charset=utf-?8;base64,/
    let baseUri = /^data:application\/json;base64,/
    let charsetUri = /^data:application\/json;charset=utf-?8,/
    let uri = /^data:application\/json,/

    if (charsetUri.test(text) || uri.test(text)) {
      return decodeURIComponent(text.substr(RegExp.lastMatch.length))
    }

    if (baseCharsetUri.test(text) || baseUri.test(text)) {
      return fromBase64(text.substr(RegExp.lastMatch.length))
    }

    let encoding = text.match(/data:application\/json;([^,]+),/)[1]
    throw new Error('Unsupported source map encoding ' + encoding)
  }

  loadFile(path) {
    this.root = dirname(path)
    if (existsSync(path)) {
      this.mapFile = path
      return readFileSync(path, 'utf-8').toString().trim()
    }
  }

  loadMap(file, prev) {
    if (prev === false) return false

    if (prev) {
      if (typeof prev === 'string') {
        return prev
      } else if (typeof prev === 'function') {
        let prevPath = prev(file)
        if (prevPath) {
          let map = this.loadFile(prevPath)
          if (!map) {
            throw new Error(
              'Unable to load previous source map: ' + prevPath.toString()
            )
          }
          return map
        }
      } else if (prev instanceof SourceMapConsumer) {
        return SourceMapGenerator.fromSourceMap(prev).toString()
      } else if (prev instanceof SourceMapGenerator) {
        return prev.toString()
      } else if (this.isMap(prev)) {
        return JSON.stringify(prev)
      } else {
        throw new Error(
          'Unsupported previous source map format: ' + prev.toString()
        )
      }
    } else if (this.inline) {
      return this.decodeInline(this.annotation)
    } else if (this.annotation) {
      let map = this.annotation
      if (file) map = join(dirname(file), map)
      return this.loadFile(map)
    }
  }

  isMap(map) {
    if (typeof map !== 'object') return false
    return (
      typeof map.mappings === 'string' ||
      typeof map._mappings === 'string' ||
      Array.isArray(map.sections)
    )
  }
}

module.exports = PreviousMap
PreviousMap.default = PreviousMap