import fs from 'fs'
import fsPromise from 'fs/promises'
import path from 'path'
import events from 'events'
import hasNativeRecursive from './has-native-recursive.mjs'
import * as is from './is.mjs'

const EVENT_UPDATE = 'update';
const EVENT_REMOVE = 'remove';
const TYPE_FILE = 'file'
const TYPE_DIRECTORY = 'directory'

function unique(arr) {
  return arr.filter(function(v, i, self) {
    return self.indexOf(v) === i;
  });
}

export default class Watcher extends events.EventEmitter {
  constructor(path, options = null, fn = null, { fs: fsoverwrite } = {}) {
    super()

    this.ac = new AbortController()
    events.setMaxListeners(2000, this.ac.signal)
    this._fs = fsoverwrite || fs
    this._cache = []
    this._cacheTimeout = null
    this.listeners = []
    this.closed = false
    let paths = path
    if (is.buffer(paths)) {
      paths = paths.toString()
    }

    if (!is.array(paths)) {
      paths = [paths]
    }

    paths = unique(paths)
    this.options = options || {}
    this.fn = fn || null

    if (is.func(this.options)) {
      this.fn = this.options
      this.options = {}
    }

    this._verifyOptions(paths)
  }

  isClosed() {
    return this.closed
  }

  close() {
    this.closed = true
    this.ac.abort()
    this._cache = this.listeners = []
    
    this.emitAsync('close')
  }

  emitAsync(name, ...args) {
    process.nextTick(() => this.emit(name, ...args))
  }

  _verifyOptions(paths) {
    for (let path of paths) {
      if (!is.exists(path)) {
        this.emitAsync('error', new Error(path + ' does not exist.'))
      }
    }

    if (this.options.encoding) {
      if (this.options.encoding && this.options.encoding !== 'buffer' && !Buffer.isEncoding(this.options.encoding)) {
        throw new Error('Unknown encoding: ' + this.options.encoding);
      }
    } else {
      this.options.encoding = 'utf8'
    }

    if (this.options.delay !== 0 && !this.options.delay) {
      this.options.delay = 200
    }

    if (is.func(this.fn)) {
      this.on('change', this.fn)
    }
    
    if (this.options.manualRecursive !== true) {
      hasNativeRecursive(nativeRecursive => {
        this.supportsNativeRecursive = nativeRecursive
        this.options.manualRecursive = !nativeRecursive
        this._startListeners(paths)
      })
    } else {
      this._startListeners(paths)
    }
  }

  _startListeners(paths) {
    Promise.all(paths.map(path => this.safeAdd(path)))
    .then(
      () => this.emit('ready'),
      err => this.emit('error', err),
    )
  }

  getWatcherOrNull(name) {
    for (let check of this.listeners) {
      if (check.path === name) {
        return check
      }
    }
    return null
  }

  shouldInclude(name) {
    return this.options.filter
      ? 
        (is.func(this.options.filter) && this.options.filter.call(this, name) === true)
        || (is.regExp(this.options.filter) && this.options.filter.test(name))
      : true
  }

  closeWatch(orgItem) {
    let item = orgItem
    if (typeof item === 'string') {
      item = getWatcherOrNull(item)
    }
    if (!item) {
      this.emit('error', new Error(`attempted to close watcher for ${item} but such a watcher could not be found`))
      return
    }

    if (item.watcher) {
      item.watcher.close()
    }

    this._emitEvent(item, EVENT_REMOVE, item.path)
    let index = this.listeners.indexOf(item)
    if (index < 0) return
    this.listeners.splice(index, 1)
  }

  _emitEvent(item, evt, name) {
    if (item.type === TYPE_FILE && !is.samePath(name, item.filename)) return
    if (item.type === TYPE_DIRECTORY && !this.shouldInclude(name)) return

    if (item.flag) {
      item.flag = ''
      return
    }

    let outputName = name

    if (this.options.encoding !== 'utf8') {
      outputName = Buffer.from(outputName)

      if (this.options.encoding !== 'buffer') {
        outputName = outputName.toString(this.options.encoding)
      }
    }

    if (!this.options.delay) {
      this.emit('change', evt, outputName)
      return
    }

    this._cache.push([evt, name, outputName])

    if (this._cacheTimeout) return

    this._cacheTimeout = setTimeout(() => {
      let cache = this._filterCache(this._cache)
      this._cache = []
      this._cacheTimeout = null

      for (let event of cache) {
        try {
          this.emit('change', event[0], event[2])
        } catch (err) {
          this.emit('error', err)
        }
      }
    }, this.options.delay)
  }

  _filterCache(cache) {
    let setFound = new Set()

    let out = cache.reverse().filter(([evt, name]) => {
      if (setFound.has(name)) return false
      setFound.add(name)
      return true
    }).reverse()
    return out
  }

  _watcherSink(item, rawEvt, rawName) {
    if (this.closed) return

    let name = path.join(item.path, rawName || '')
    let evt = is.exists(name) ? EVENT_UPDATE : EVENT_REMOVE

    if (this.options.recursive && this.options.manualRecursive && item.type === TYPE_DIRECTORY) {
      if (evt === EVENT_REMOVE) {
        this.closeWatch(name)
        return
      } else {
        if (is.directory(name)
            && this.getWatcherOrNull(name) === null
            && this.shouldInclude(name) === false) {
          this.safeAdd(subItem, TYPE_DIRECTORY)
        }
      }
    }

    this._emitEvent(item, evt, name)
  }

  _pathToItem(name, type) {
    if (type === TYPE_FILE) {
      let parent = path.join(name, '../')
      return {
        path: parent,
        type: TYPE_FILE,
        filename: name,
        watcher: null,
        flag: '',
      }
    } else {
      return {
        path: name,
        type: TYPE_DIRECTORY,
        watcher: null,
        flag: '',
      }
    }
  }

  _watcherError(item, err) {
    if (this.closed) return
    
    if (is.windows() && err.code === 'EPERM') {
      this.closeWatch(item)
      item.flag = 'windows-error'
    } else {
      self.emit('error', err)
    }
  }

  safeAdd(name, orgType) {
    let type = orgType
    if (!type) {
      type = is.file(name) ? TYPE_FILE : TYPE_DIRECTORY
    }

    let item = this._pathToItem(name, type)
    let options = {
      encoding: 'utf8',
      signal: this.ac.signal,
    }
    if (!this.options.manualRecursive && item.type !== TYPE_FILE && this.options.recursive) {
      options.recursive = true
    }

    try {
      item.watcher = this._fs.watch(item.path, options)
    } catch (err) {
      this.emitAsync('error', err)
    }

    if (!item.watcher) return
    
    this.listeners.push(item)

    item.watcher.on('error', this._watcherError.bind(this, item))
    item.watcher.on('change', this._watcherSink.bind(this, item))

    if (options.recursive || item.type === TYPE_FILE) return

    return fsPromise.readdir(item.path, { withFileTypes: true })
      .then(directories => directories.filter(dir => dir.isDirectory()))
      .then(directories => {
        return Promise.all(directories.map(dir => this.safeAdd(path.join(item.path, dir.name), TYPE_DIRECTORY)))
      })
  }
}