package client

import (
	"fmt"
	"io"
	"runtime"
	"sync"
	"sync/atomic"
	"time"

	"git.loafle.net/commons_go/rpc/protocol"
)

func New(ch ClientHandler) Client {
	c := &client{
		ch: ch,
	}
	return c
}

type Client interface {
	Start(rwc io.ReadWriteCloser)
	Stop()
	Notify(method string, args interface{}) error
	Call(method string, args interface{}, result interface{}) error
	CallTimeout(method string, args interface{}, result interface{}, timeout time.Duration) error
}

type client struct {
	ch ClientHandler

	rwc io.ReadWriteCloser

	pendingRequestsCount uint32

	requestQueueChan chan *CallState

	stopChan chan struct{}
	stopWg   sync.WaitGroup
}

func (c *client) Start(rwc io.ReadWriteCloser) {
	c.ch.Validate()

	if nil == rwc {
		panic("RWC(io.ReadWriteCloser) must be specified.")
	}

	if c.stopChan != nil {
		panic("Client: the given client is already started. Call Client.Stop() before calling Client.Start() again!")
	}

	c.rwc = rwc
	c.stopChan = make(chan struct{})
	c.requestQueueChan = make(chan *CallState, c.ch.GetPendingRequests())

	c.ch.OnStart()

	c.stopWg.Add(1)
	go handleRPC(c)
}

func (c *client) Stop() {
	if c.stopChan == nil {
		panic("Client: the client must be started before stopping it")
	}
	close(c.stopChan)
	c.stopWg.Wait()
	c.stopChan = nil
}

func (c *client) Notify(method string, args interface{}) error {
	_, err := c.send(method, args, nil, false, true)
	return err
}

func (c *client) Call(method string, args interface{}, result interface{}) error {
	return c.CallTimeout(method, args, result, c.ch.GetRequestTimeout())
}

func (c *client) CallTimeout(method string, args interface{}, result interface{}, timeout time.Duration) (err error) {
	var cs *CallState
	if cs, err = c.send(method, args, result, true, true); nil != err {
		return
	}

	t := retainTimer(timeout)

	select {
	case <-cs.DoneChan:
		result, err = cs.Result, cs.Error
		releaseCallState(cs)
	case <-t.C:
		cs.Cancel()
		err = getClientTimeoutError(c, timeout)
	}

	releaseTimer(t)

	return nil
}

func (c *client) send(method string, args interface{}, result interface{}, hasResponse bool, usePool bool) (cs *CallState, err error) {
	if !hasResponse {
		usePool = true
	}

	if usePool {
		cs = retainCallState()
	} else {
		cs = &CallState{}
	}

	cs.Method = method
	cs.Args = args

	if hasResponse {
		cs.ID = c.ch.GetRequestID()
		cs.Result = result
		cs.DoneChan = make(chan *CallState, 1)
	}

	select {
	case c.requestQueueChan <- cs:
		return cs, nil
	default:
		// Try substituting the oldest async request by the new one
		// on requests' queue overflow.
		// This increases the chances for new request to succeed
		// without timeout.
		if !hasResponse {
			// Immediately notify the caller not interested
			// in the response on requests' queue overflow, since
			// there are no other ways to notify it later.
			releaseCallState(cs)
			return nil, getClientOverflowError(c)
		}

		select {
		case rcs := <-c.requestQueueChan:
			if rcs.DoneChan != nil {
				rcs.Error = getClientOverflowError(c)
				//close(rcs.DoneChan)
				rcs.done()
			} else {
				releaseCallState(rcs)
			}
		default:
		}

		select {
		case c.requestQueueChan <- cs:
			return cs, nil
		default:
			// Release m even if usePool = true, since m wasn't exposed
			// to the caller yet.
			releaseCallState(cs)
			return nil, getClientOverflowError(c)
		}
	}
}

func handleRPC(c *client) {
	defer c.stopWg.Done()

	stopChan := make(chan struct{})

	pendingRequests := make(map[interface{}]*CallState)
	var pendingRequestsLock sync.Mutex

	writerDone := make(chan error, 1)
	go rpcWriter(c, pendingRequests, &pendingRequestsLock, stopChan, writerDone)

	readerDone := make(chan error, 1)
	go rpcReader(c, pendingRequests, &pendingRequestsLock, readerDone)

	var err error

	select {
	case err = <-writerDone:
		close(stopChan)
		c.rwc.Close()
		<-readerDone
	case err = <-readerDone:
		close(stopChan)
		c.rwc.Close()
		<-writerDone
	case <-c.stopChan:
		close(stopChan)
		c.rwc.Close()
		<-readerDone
		<-writerDone
	}

	if err != nil {
		//c.LogError("%s", err)
		err = &ClientError{
			Connection: true,
			err:        err,
		}
	}

	for _, cs := range pendingRequests {
		atomic.AddUint32(&c.pendingRequestsCount, ^uint32(0))
		cs.Error = err
		if cs.DoneChan != nil {
			cs.done()
		}
	}

}

func rpcWriter(c *client, pendingRequests map[interface{}]*CallState, pendingRequestsLock *sync.Mutex, stopChan <-chan struct{}, writerDone chan<- error) {
	var err error
	defer func() {
		writerDone <- err
	}()

	for {
		var cs *CallState

		select {
		case cs = <-c.requestQueueChan:
		default:
			// Give the last chance for ready goroutines filling c.requestsChan :)
			runtime.Gosched()

			select {
			case <-stopChan:
				return
			case cs = <-c.requestQueueChan:
			}
		}

		if cs.IsCanceled() {
			if nil != cs.DoneChan {
				// cs.Error = ErrCanceled
				// close(m.done)
				cs.done()
			} else {
				releaseCallState(cs)
			}
			continue
		}

		if nil != cs.DoneChan {
			pendingRequestsLock.Lock()
			n := len(pendingRequests)
			pendingRequests[cs.ID] = cs
			pendingRequestsLock.Unlock()
			atomic.AddUint32(&c.pendingRequestsCount, 1)

			if n > 10*c.ch.GetPendingRequests() {
				err = fmt.Errorf("Client: The server didn't return %d responses yet. Closing server connection in order to prevent client resource leaks", n)
				return
			}
		}

		if nil == cs.DoneChan {
			releaseCallState(cs)
		}

		if err = c.ch.GetCodec().Write(c.rwc, cs.Method, cs.Args, cs.ID); nil != err {
			err = fmt.Errorf("Client: Cannot send request to wire: [%s]", err)
			return
		}
	}
}

func rpcReader(c *client, pendingRequests map[interface{}]*CallState, pendingRequestsLock *sync.Mutex, readerDone chan<- error) {
	var err error
	defer func() {
		if r := recover(); r != nil {
			if err == nil {
				err = fmt.Errorf("Client: Panic when reading data from server: %v", r)
			}
		}
		readerDone <- err
	}()

	for {
		crn, err := c.ch.GetCodec().NewResponseOrNotify(c.rwc)
		if nil != err {
			err = fmt.Errorf("Client: Cannot decode response or notify: [%s]", err)
			return
		}

		if crn.IsResponse() {
			err = responseHandle(c, crn.GetResponse(), pendingRequests, pendingRequestsLock)
		} else {
			err = notifyHandle(c, crn.GetNotify())
		}
		if nil != err {
			return
		}
	}

}

func responseHandle(c *client, codecResponse protocol.ClientCodecResponse, pendingRequests map[interface{}]*CallState, pendingRequestsLock *sync.Mutex) error {
	pendingRequestsLock.Lock()
	cs, ok := pendingRequests[codecResponse.ID()]
	if ok {
		delete(pendingRequests, codecResponse.ID())
	}
	pendingRequestsLock.Unlock()

	if !ok {
		return fmt.Errorf("Client: Unexpected ID=[%v] obtained from server", codecResponse.ID())
	}

	atomic.AddUint32(&c.pendingRequestsCount, ^uint32(0))

	cs.Result = codecResponse.Result()
	if err := codecResponse.Error(); nil != err {
		// cs.Error = &ClientError{
		// 	Server: true,
		// 	err:    fmt.Errorf("gorpc.Client: [%s]. Server error: [%s]", c.Addr, wr.Error),
		// }
	}

	cs.done()

	return nil
}

func notifyHandle(c *client, codecNotify protocol.ClientCodecNotify) error {
	_, err := c.ch.GetRPCRegistry().Invoke(codecNotify)

	return err
}

func getClientTimeoutError(c *client, timeout time.Duration) error {
	err := fmt.Errorf("Client: Cannot obtain response during timeout=%s", timeout)
	//c.LogError("%s", err)
	return &ClientError{
		Timeout: true,
		err:     err,
	}
}

func getClientOverflowError(c *client) error {
	err := fmt.Errorf("Client: Requests' queue with size=%d is overflown. Try increasing Client.PendingRequests value", cap(c.requestQueueChan))
	//c.LogError("%s", err)
	return &ClientError{
		Overflow: true,
		err:      err,
	}
}