Settings = require "settings-sharelatex"
async = require "async"
_ = require "underscore"
logger = require "logger-sharelatex"
Metrics = require "metrics-sharelatex"

class Client
	constructor: (@clients) ->
		@SECONDARY_TIMEOUT = 200
		@HEARTBEAT_TIMEOUT = 2000
		
	multi: () ->
		return new MultiClient(
			@clients.map (client) -> {
				rclient: client.rclient.multi()
				key_schema: client.key_schema
				primary: client.primary
				driver: client.driver
			}
		)

	healthCheck: (callback) ->
		jobs = @clients.map (client) =>
			(cb) => @_healthCheckClient(client, cb)
		async.parallel jobs, callback
	
	_healthCheckClient: (client, callback) ->
		if client.driver == "ioredis"
			@_healthCheckClusterClient(client, callback)
		else
			@_healthCheckNodeRedisClient(client, callback)
	
	_healthCheckNodeRedisClient: (client, callback) ->
		client.healthCheck ?= require("redis-sharelatex").activeHealthCheckRedis(Settings.redis.web)
		if client.healthCheck.isAlive()
			return callback()
		else
			return callback(new Error("node-redis client failed health check"))
	
	_healthCheckClusterClient: (client, callback) ->
		jobs = client.rclient.nodes("all").map (n) =>
			(cb) => @_checkNode(n, cb)
		async.parallel jobs, callback
	
	_checkNode: (node, _callback) ->
		callback = (args...) ->
			_callback(args...)
			_callback = () ->
		timer = setTimeout () ->
			error = new Error("ioredis node ping check timed out")
			logger.error {err: error, key: node.options.key}, "node timed out"
			callback(error)
		, @HEARTBEAT_TIMEOUT
		node.ping (err) ->
			clearTimeout timer
			callback(err)

class MultiClient
	constructor: (@clients) ->
		@SECONDARY_TIMEOUT = 200
	
	exec: (callback) ->
		primaryError = null
		primaryResult = null
		jobs = @clients.map (client) =>
			(cb) =>
				cb = _.once(cb)
				timer = new Metrics.Timer("redis.#{client.driver}.exec")
				
				timeout = null
				if !client.primary
					timeout = setTimeout () ->
						logger.error {err: new Error("#{client.driver} backend timed out")}, "backend timed out"
						cb()
					, @SECONDARY_TIMEOUT

				client.rclient.exec (error, result) =>
					timer.done()
					if client.driver == "ioredis"
						# ioredis returns an results like:
						# [ [null, 42], [null, "foo"] ]
						# where the first entries in each 2-tuple are
						# presumably errors for each individual command,
						# and the second entry is the result. We need to transform
						# this into the same result as the old redis driver:
						# [ 42, "foo" ]
						filtered_result = []
						for entry in result or []
							if entry[0]?
								return cb(entry[0])
							else
								filtered_result.push entry[1]
						result = filtered_result
						
					if client.primary
						primaryError = error
						primaryResult = result
					if timeout?
						clearTimeout(timeout)
					cb(error, result)
		async.parallel jobs, (error, results) ->
			if error?
				logger.error {err: error}, "error in redis backend"
			else
				compareResults(results, "exec")
			callback(primaryError, primaryResult)

COMMANDS = {
	"get": 0,
	"smembers": 0,
	"set": 0,
	"srem": 0,
	"sadd": 0,
	"del": 0,
	"lrange": 0,
	"llen": 0,
	"rpush": 0,
	"expire": 0,
	"ltrim": 0,
	"incr": 0,
	"eval": 2
}
for command, key_pos of COMMANDS
	do (command, key_pos) ->
		Client.prototype[command] = (args..., callback) ->
			primaryError = null
			primaryResult = []
			jobs = @clients.map (client) =>
				(cb) =>
					cb = _.once(cb)
					key_builder = args[key_pos]
					key = key_builder(client.key_schema)
					args_with_key = args.slice(0)
					args_with_key[key_pos] = key
					timer = new Metrics.Timer("redis.#{client.driver}.#{command}")
					
					timeout = null
					if !client.primary
						timeout = setTimeout () ->
							logger.error {err: new Error("#{client.driver} backend timed out")}, "backend timed out"
							cb()
						, @SECONDARY_TIMEOUT
					
					client.rclient[command] args_with_key..., (error, result...) =>
						timer.done()
						if client.primary
							primaryError = error
							primaryResult = result
						if timeout?
							clearTimeout(timeout)
						cb(error, result...)
			async.parallel jobs, (error, results) ->
				if error?
					logger.error {err: error}, "error in redis backend"
				else
					compareResults(results, command)
				callback(primaryError, primaryResult...)

		MultiClient.prototype[command] = (args...) ->
			for client in @clients
				key_builder = args[key_pos]
				key = key_builder(client.key_schema)
				args_with_key = args.slice(0)
				args_with_key[key_pos] = key
				client.rclient[command] args_with_key...

compareResults = (results, command) ->
	return if results.length < 2
	first = results[0]
	if command == "smembers" and first?
		first = first.slice().sort()
	for result in results.slice(1)
		if command == "smembers" and result?
			result = result.slice().sort()
		if not _.isEqual(first, result)
			logger.error results: results, "redis backend conflict"
			Metrics.inc "backend-conflict"
		else
			Metrics.inc "backend-match"

module.exports =
	createClient: () ->
		client_configs = Settings.redis.documentupdater
		unless client_configs instanceof Array
			client_configs.primary = true
			client_configs = [client_configs]
		clients = client_configs.map (config) ->
			if config.cluster?
				Redis = require("ioredis")
				rclient = new Redis.Cluster(config.cluster)
				driver = "ioredis"
			else
				redis_config = {}
				for key in ["host", "port", "password", "endpoints", "masterName"]
					if config[key]?
						redis_config[key] = config[key]
				rclient = require("redis-sharelatex").createClient(redis_config)
				driver = "noderedis"
			return {
				rclient: rclient
				key_schema: config.key_schema
				primary: config.primary
				driver: driver
			}
		return new Client(clients)