lazy-result.es6

import MapGenerator from './map-generator'
import stringify from './stringify'
import warnOnce from './warn-once'
import Result from './result'
import parse from './parse'

function isPromise (obj) {
  return typeof obj === 'object' && typeof obj.then === 'function'
}

/**
 * A Promise proxy for the result of PostCSS transformations.
 *
 * A `LazyResult` instance is returned by {@link Processor#process}.
 *
 * @example
 * const lazy = postcss([autoprefixer]).process(css)
 */
class LazyResult {
  constructor (processor, css, opts) {
    this.stringified = false
    this.processed = false

    let root
    if (typeof css === 'object' && css !== null && css.type === 'root') {
      root = css
    } else if (css instanceof LazyResult || css instanceof Result) {
      root = css.root
      if (css.map) {
        if (typeof opts.map === 'undefined') opts.map = { }
        if (!opts.map.inline) opts.map.inline = false
        opts.map.prev = css.map
      }
    } else {
      let parser = parse
      if (opts.syntax) parser = opts.syntax.parse
      if (opts.parser) parser = opts.parser
      if (parser.parse) parser = parser.parse

      try {
        root = parser(css, opts)
      } catch (error) {
        this.error = error
      }
    }

    this.result = new Result(processor, root, opts)
  }

  /**
   * Returns a {@link Processor} instance, which will be used
   * for CSS transformations.
   *
   * @type {Processor}
   */
  get processor () {
    return this.result.processor
  }

  /**
   * Options from the {@link Processor#process} call.
   *
   * @type {processOptions}
   */
  get opts () {
    return this.result.opts
  }

  /**
   * Processes input CSS through synchronous plugins, converts `Root`
   * to a CSS string and returns {@link Result#css}.
   *
   * This property will only work with synchronous plugins.
   * If the processor contains any asynchronous plugins
   * it will throw an error. This is why this method is only
   * for debug purpose, you should always use {@link LazyResult#then}.
   *
   * @type {string}
   * @see Result#css
   */
  get css () {
    return this.stringify().css
  }

  /**
   * An alias for the `css` property. Use it with syntaxes
   * that generate non-CSS output.
   *
   * This property will only work with synchronous plugins.
   * If the processor contains any asynchronous plugins
   * it will throw an error. This is why this method is only
   * for debug purpose, you should always use {@link LazyResult#then}.
   *
   * @type {string}
   * @see Result#content
   */
  get content () {
    return this.stringify().content
  }

  /**
   * Processes input CSS through synchronous plugins
   * and returns {@link Result#map}.
   *
   * This property will only work with synchronous plugins.
   * If the processor contains any asynchronous plugins
   * it will throw an error. This is why this method is only
   * for debug purpose, you should always use {@link LazyResult#then}.
   *
   * @type {SourceMapGenerator}
   * @see Result#map
   */
  get map () {
    return this.stringify().map
  }

  /**
   * Processes input CSS through synchronous plugins
   * and returns {@link Result#root}.
   *
   * This property will only work with synchronous plugins. If the processor
   * contains any asynchronous plugins it will throw an error.
   *
   * This is why this method is only for debug purpose,
   * you should always use {@link LazyResult#then}.
   *
   * @type {Root}
   * @see Result#root
   */
  get root () {
    return this.sync().root
  }

  /**
   * Processes input CSS through synchronous plugins
   * and returns {@link Result#messages}.
   *
   * This property will only work with synchronous plugins. If the processor
   * contains any asynchronous plugins it will throw an error.
   *
   * This is why this method is only for debug purpose,
   * you should always use {@link LazyResult#then}.
   *
   * @type {Message[]}
   * @see Result#messages
   */
  get messages () {
    return this.sync().messages
  }

  /**
   * Processes input CSS through synchronous plugins
   * and calls {@link Result#warnings()}.
   *
   * @return {Warning[]} Warnings from plugins.
   */
  warnings () {
    return this.sync().warnings()
  }

  /**
   * Alias for the {@link LazyResult#css} property.
   *
   * @example
   * lazy + '' === lazy.css
   *
   * @return {string} Output CSS.
   */
  toString () {
    return this.css
  }

  /**
   * Processes input CSS through synchronous and asynchronous plugins
   * and calls `onFulfilled` with a Result instance. If a plugin throws
   * an error, the `onRejected` callback will be executed.
   *
   * It implements standard Promise API.
   *
   * @param {onFulfilled} onFulfilled Callback will be executed
   *                                  when all plugins will finish work.
   * @param {onRejected}  onRejected  Callback will be executed on any error.
   *
   * @return {Promise} Promise API to make queue.
   *
   * @example
   * postcss([autoprefixer]).process(css, { from: cssPath }).then(result => {
   *   console.log(result.css)
   * })
   */
  then (onFulfilled, onRejected) {
    if (process.env.NODE_ENV !== 'production') {
      if (!('from' in this.opts)) {
        warnOnce(
          'Without `from` option PostCSS could generate wrong source map ' +
          'and will not find Browserslist config. Set it to CSS file path ' +
          'or to `undefined` to prevent this warning.'
        )
      }
    }
    return this.async().then(onFulfilled, onRejected)
  }

  /**
   * Processes input CSS through synchronous and asynchronous plugins
   * and calls onRejected for each error thrown in any plugin.
   *
   * It implements standard Promise API.
   *
   * @param {onRejected} onRejected Callback will be executed on any error.
   *
   * @return {Promise} Promise API to make queue.
   *
   * @example
   * postcss([autoprefixer]).process(css).then(result => {
   *   console.log(result.css)
   * }).catch(error => {
   *   console.error(error)
   * })
   */
  catch (onRejected) {
    return this.async().catch(onRejected)
  }
  /**
   * Processes input CSS through synchronous and asynchronous plugins
   * and calls onFinally on any error or when all plugins will finish work.
   *
   * It implements standard Promise API.
   *
   * @param {onFinally} onFinally Callback will be executed on any error or
   *                              when all plugins will finish work.
   *
   * @return {Promise} Promise API to make queue.
   *
   * @example
   * postcss([autoprefixer]).process(css).finally(() => {
   *   console.log('processing ended')
   * })
   */
  finally (onFinally) {
    return this.async().then(onFinally, onFinally)
  }

  handleError (error, plugin) {
    try {
      this.error = error
      if (error.name === 'CssSyntaxError' && !error.plugin) {
        error.plugin = plugin.postcssPlugin
        error.setMessage()
      } else if (plugin.postcssVersion) {
        if (process.env.NODE_ENV !== 'production') {
          let pluginName = plugin.postcssPlugin
          let pluginVer = plugin.postcssVersion
          let runtimeVer = this.result.processor.version
          let a = pluginVer.split('.')
          let b = runtimeVer.split('.')

          if (a[0] !== b[0] || parseInt(a[1]) > parseInt(b[1])) {
            console.error(
              'Unknown error from PostCSS plugin. Your current PostCSS ' +
              'version is ' + runtimeVer + ', but ' + pluginName + ' uses ' +
              pluginVer + '. Perhaps this is the source of the error below.'
            )
          }
        }
      }
    } catch (err) {
      if (console && console.error) console.error(err)
    }
  }

  asyncTick (resolve, reject) {
    if (this.plugin >= this.processor.plugins.length) {
      this.processed = true
      return resolve()
    }

    try {
      let plugin = this.processor.plugins[this.plugin]
      let promise = this.run(plugin)
      this.plugin += 1

      if (isPromise(promise)) {
        promise.then(() => {
          this.asyncTick(resolve, reject)
        }).catch(error => {
          this.handleError(error, plugin)
          this.processed = true
          reject(error)
        })
      } else {
        this.asyncTick(resolve, reject)
      }
    } catch (error) {
      this.processed = true
      reject(error)
    }
  }

  async () {
    if (this.processed) {
      return new Promise((resolve, reject) => {
        if (this.error) {
          reject(this.error)
        } else {
          resolve(this.stringify())
        }
      })
    }
    if (this.processing) {
      return this.processing
    }

    this.processing = new Promise((resolve, reject) => {
      if (this.error) return reject(this.error)
      this.plugin = 0
      this.asyncTick(resolve, reject)
    }).then(() => {
      this.processed = true
      return this.stringify()
    })

    return this.processing
  }

  sync () {
    if (this.processed) return this.result
    this.processed = true

    if (this.processing) {
      throw new Error(
        'Use process(css).then(cb) to work with async plugins')
    }

    if (this.error) throw this.error

    for (let plugin of this.result.processor.plugins) {
      let promise = this.run(plugin)
      if (isPromise(promise)) {
        throw new Error(
          'Use process(css).then(cb) to work with async plugins')
      }
    }

    return this.result
  }

  run (plugin) {
    this.result.lastPlugin = plugin

    try {
      return plugin(this.result.root, this.result)
    } catch (error) {
      this.handleError(error, plugin)
      throw error
    }
  }

  stringify () {
    if (this.stringified) return this.result
    this.stringified = true

    this.sync()

    let opts = this.result.opts
    let str = stringify
    if (opts.syntax) str = opts.syntax.stringify
    if (opts.stringifier) str = opts.stringifier
    if (str.stringify) str = str.stringify

    let map = new MapGenerator(str, this.result.root, this.result.opts)
    let data = map.generate()
    this.result.css = data[0]
    this.result.map = data[1]

    return this.result
  }
}

export default LazyResult

/**
 * @callback onFulfilled
 * @param {Result} result
 */

/**
 * @callback onRejected
 * @param {Error} error
 */