var async = require('async')
  , assert = require('assert')
  , UError = require('./error').UserError
  , Local = require('./local-storage')
  , Proxy = require('./up-storage')
  , mystreams = require('./streams')
  , utils = require('./utils')
  , Logger = require('./logger')

//
// Implements Storage interface
// (same for storage.js, local-storage.js, up-storage.js)
//
function Storage(config) {
	if (!(this instanceof Storage)) return new Storage(config)

	this.config = config

	// we support a number of uplinks, but only one local storage
	// Proxy and Local classes should have similar API interfaces
	this.uplinks = {}
	for (var p in config.uplinks) {
		this.uplinks[p] = new Proxy(config.uplinks[p], config)
		this.uplinks[p].upname = p
	}
	this.local = new Local(config)
	this.logger = Logger.logger.child()

	return this
}

//
// Add a {name} package to a system
//
// Function checks if package with the same name is available from uplinks.
// If it isn't, we create package locally
//
// Used storages: local (write) && uplinks
//
Storage.prototype.add_package = function(name, metadata, callback) {
	var self = this

	// NOTE:
	// - when we checking package for existance, we ask ALL uplinks
	// - when we publishing package, we only publish it to some of them
	// so all requests are necessary

	check_package_local(function(err) {
		if (err) return callback(err)

		check_package_remote(function(err) {
			if (err) return callback(err)

			publish_package(function(err) {
				if (err) return callback(err)
				callback()
			})
		})
	})

	function check_package_local(cb) {
		self.local.get_package(name, {}, function(err, results) {
			if (err && err.status !== 404) return cb(err)

			if (results) {
				return cb(new UError({
					status: 409,
					msg: 'this package is already present'
				}))
			}

			cb()
		})
	}

	function check_package_remote(cb) {
		self._sync_package_with_uplinks(name, null, {}, function(err, results, err_results) {
			// something weird
			if (err && err.status !== 404) return cb(err)

			// checking package
			if (results) {
				return cb(new UError({
					status: 409,
					msg: 'this package is already present'
				}))
			}

			for (var i=0; i<err_results.length; i++) {
				// checking error
				// if uplink fails with a status other than 404, we report failure
				if (err_results[i][0] != null) {
					if (err_results[i][0].status !== 404) {
						return cb(new UError({
							status: 503,
							msg: 'one of the uplinks is down, refuse to publish'
						}))
					}
				}
			}

			return cb()
		})
	}

	function publish_package(cb) {
		self.local.add_package(name, metadata, callback)
	}
}

//
// Add a new version of package {name} to a system
//
// Used storages: local (write)
//
Storage.prototype.add_version = function(name, version, metadata, tag, callback) {
	return this.local.add_version(name, version, metadata, tag, callback)
}

//
// Tags a package version with a provided tag
//
// Used storages: local (write)
//
Storage.prototype.add_tag = function(name, version, tag, callback) {
	return this.local.add_tag(name, version, tag, callback)
}

//
// Change an existing package (i.e. unpublish one version)
//
// Function changes a package info from local storage and all uplinks with
// write access.
//
// Used storages: local (write)
//
Storage.prototype.change_package = function(name, metadata, revision, callback) {
	return this.local.change_package(name, metadata, revision, callback)
}

//
// Remove a package from a system
//
// Function removes a package from local storage
//
// Used storages: local (write)
//
Storage.prototype.remove_package = function(name, callback) {
	return this.local.remove_package(name, callback)
}

//
// Remove a tarball from a system
//
// Function removes a tarball from local storage.
// Tarball in question should not be linked to in any existing
// versions, i.e. package version should be unpublished first.
//
// Used storages: local (write)
//
Storage.prototype.remove_tarball = function(name, filename, revision, callback) {
	return this.local.remove_tarball(name, filename, revision, callback)
}

//
// Upload a tarball for {name} package
//
// Function is syncronous and returns a WritableStream
//
// Used storages: local (write)
//
Storage.prototype.add_tarball = function(name, filename) {
	return this.local.add_tarball(name, filename)
}

//
// Get a tarball from a storage for {name} package
//
// Function is syncronous and returns a ReadableStream
//
// Function tries to read tarball locally, if it fails then it reads package
// information in order to figure out where we can get this tarball from
//
// Used storages: local || uplink (just one)
//
Storage.prototype.get_tarball = function(name, filename) {
	var stream = new mystreams.ReadTarballStream()
	stream.abort = function() {}

	var self = this

	// if someone requesting tarball, it means that we should already have some
	// information about it, so fetching package info is unnecessary

	// trying local first
	var rstream = self.local.get_tarball(name, filename)
	var is_open = false
	rstream.on('error', function(err) {
		if (is_open || err.status !== 404) {
			return stream.emit('error', err)
		}

		// local reported 404
		var err404 = err
		var uplink = null
		rstream.abort()
		rstream = null // gc

		self.local.get_package(name, function(err, info) {
			if (!err && info._distfiles && info._distfiles[filename] != null) {
				// information about this file exists locally
				serve_file(info._distfiles[filename])

			} else {
				// we know nothing about this file, trying to get information elsewhere

				self._sync_package_with_uplinks(name, info, {}, function(err, info) {
					if (err) return stream.emit('error', err)

					if (!info._distfiles || info._distfiles[filename] == null) {
						return stream.emit('error', err404)
					}

					serve_file(info._distfiles[filename])
				})
			}
		})
	})
	rstream.on('open', function() {
		is_open = true
		rstream.pipe(stream)
	})
	return stream

	function serve_file(file) {
		var uplink = null
		for (var p in self.uplinks) {
			if (self.uplinks[p].can_fetch_url(file.url)) {
				uplink = self.uplinks[p]
			}
		}
		if (uplink == null) {
			uplink = new Proxy({
				url: file.url,
				_autogenerated: true,
			}, self.config)
		}

		var savestream = self.local.add_tarball(name, filename)
		savestream.on('error', function(err) {
			savestream.abort()
			stream.emit('error', err)
		})
		savestream.on('open', function() {
			var rstream2 = uplink.get_url(file.url)
			rstream2.on('error', function(err) {
				savestream.abort()
				stream.emit('error', err)
			})
			rstream2.on('end', function() {
				savestream.done()
			})

			// XXX: check, what would happen if client disconnects?
			rstream2.pipe(stream)
			rstream2.pipe(savestream)
		})
	}
}

//
// Retrieve a package metadata for {name} package
//
// Function invokes local.get_package and uplink.get_package for every
// uplink with proxy_access rights against {name} and combines results
// into one json object
//
// Used storages: local && uplink (proxy_access)
//
Storage.prototype.get_package = function(name, options, callback) {
	if (typeof(options) === 'function') callback = options, options = {}

	var self = this

	self.local.get_package(name, options, function(err, data) {
		if (err && (!err.status || err.status >= 500)) {
			// report internal errors right away
			return callback(err)
		}

		self._sync_package_with_uplinks(name, data, options, function(err, result, uplink_errors) {
			if (err) return callback(err)
			var whitelist = ['_rev', 'name', 'versions', 'dist-tags']
			for (var i in result) {
				if (whitelist.indexOf(i) === -1) delete result[i]
			}

			result['dist-tags'].latest = utils.semver_sort(Object.keys(result.versions))
			for (var i in result['dist-tags']) {
				if (Array.isArray(result['dist-tags'][i])) {
					result['dist-tags'][i] = result['dist-tags'][i][result['dist-tags'][i].length-1]
					if (result['dist-tags'][i] == null) delete result['dist-tags'][i]
				}
			}

			// npm can throw if this field doesn't exist
			result._attachments = {}

			callback(null, result, uplink_errors)
		})
	})
}

// function fetches package information from uplinks and synchronizes it with local data
// if package is available locally, it MUST be provided in pkginfo
// returns callback(err, result, uplink_errors)
Storage.prototype._sync_package_with_uplinks = function(name, pkginfo, options, callback) {
	var self = this

	if (!pkginfo) {
		var exists = false

		pkginfo = {
			name: name,
			versions: {},
			'dist-tags': {},
			_uplinks: {},
		}
	} else {
		var exists = true
	}

	var uplinks = []
	for (var i in self.uplinks) {
		if (self.config.proxy_access(name, i)) {
			uplinks.push(self.uplinks[i])
		}
	}

	async.map(uplinks, function(up, cb) {
		var _options = Object.create(options)
		if (utils.is_object(pkginfo._uplinks[up.upname]))
			_options.etag = pkginfo._uplinks[up.upname].etag

		up.get_package(name, _options, function(err, up_res, etag) {
			if (err || !up_res) return cb(null, [err || new Error('no data')])

			try {
				utils.validate_metadata(up_res, name)
			} catch(err) {
				self.logger.error({
					sub: 'out',
					err: err,
				}, 'package.json validating error @{!err.message}\n@{err.stack}')
				return cb(null, [err])
			}

			pkginfo._uplinks[up.upname] = {
				etag: etag
			}

			try {
				Storage._merge_versions(pkginfo, up_res)
			} catch(err) {
				self.logger.error({
					sub: 'out',
					err: err,
				}, 'package.json parsing error @{!err.message}\n@{err.stack}')
				return cb(null, [err])
			}

			// if we got to this point, assume that the correct package exists
			// on the uplink
			exists = true
			cb()
		})
	}, function(err, uplink_errors) {
		assert(!err && Array.isArray(uplink_errors))

		if (!exists) {
			return callback(new UError({
				status: 404,
				msg: 'no such package available'
			}), null, uplink_errors)
		}

		self.local.update_versions(name, pkginfo, function(err, pkginfo) {
			if (err) return callback(err)
			return callback(null, pkginfo, uplink_errors)
		})
	})
}

// function gets a local info and an info from uplinks and tries to merge it
// exported for unit tests only
Storage._merge_versions = function(local, up) {
	// copy new versions to a cache
	// NOTE: if a certain version was updated, we can't refresh it reliably
	for (var i in up.versions) {
		if (local.versions[i] == null) {
			local.versions[i] = up.versions[i]
		}
	}

	// refresh dist-tags
	for (var i in up['dist-tags']) {
		utils.tag_version(local, up['dist-tags'][i], i)
	}
}

module.exports = Storage