package client

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

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

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

type Client interface {
	Connect() error
	Close()

	Send(method string, args ...interface{}) (err error)
	Call(result interface{}, method string, args ...interface{}) error
	CallTimeout(timeout time.Duration, result interface{}, method string, args ...interface{}) (err error)
}

type client struct {
	ctx        ClientContext
	ch         ClientHandler
	rwcHandler ClientReadWriteCloseHandler

	conn interface{}

	pendingRequestsCount uint32
	pendingRequests      map[uint64]*RequestState
	pendingRequestsLock  sync.Mutex

	requestQueueChan chan *RequestState

	stopChan chan struct{}
	stopWg   sync.WaitGroup

	requestMtx  sync.Mutex
	responseMtx sync.Mutex
}

func (c *client) Connect() error {
	var err error

	if nil == c.ch {
		return fmt.Errorf("RPC Client: Client handler must be specified")
	}
	c.ch.Validate()

	if nil == c.rwcHandler {
		return fmt.Errorf("RPC Client: Client RWC handler must be specified")
	}
	c.rwcHandler.Validate()

	if c.stopChan != nil {
		return fmt.Errorf("RPC Client: the given client is already started. Call Client.Stop() before calling Client.Start() again")
	}
	c.ctx = c.ch.ClientContext(nil)

	if err := c.ch.Init(c.ctx); nil != err {
		return fmt.Errorf("RPC Client: Initialization of client has been failed %v", err)
	}

	if c.conn, err = c.rwcHandler.Connect(c.ctx); nil != err {
		return err
	}

	c.stopChan = make(chan struct{})
	c.requestQueueChan = make(chan *RequestState, c.ch.GetPendingRequests())
	c.pendingRequests = make(map[uint64]*RequestState)

	go c.handleRPC()

	return nil
}

func (c *client) Close() {
	if c.stopChan == nil {
		logging.Logger().Warnf("RPC Client: the client must be started before stopping it")
		return
	}

	c.ch.Destroy(c.ctx)

	close(c.stopChan)
	c.stopWg.Wait()
	c.stopChan = nil

	logging.Logger().Infof("RPC Client: stopped")
}

func (c *client) Send(method string, args ...interface{}) (err error) {
	var rs *RequestState
	if rs, err = c.send(true, false, nil, method, args...); nil != err {
		return
	}

	select {
	case <-rs.DoneChan:
		err = rs.Error
		releaseCallState(rs)
	}

	return
}

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

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

	t := retainTimer(timeout)

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

	releaseTimer(t)

	return
}

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

	if usePool {
		rs = retainRequestState()
	} else {
		rs = &RequestState{}
	}

	rs.hasResponse = hasResponse
	rs.Method = method
	rs.Args = args
	rs.DoneChan = make(chan *RequestState, 1)

	if hasResponse {
		rs.ID = c.ch.GetRequestID()
		rs.Result = result
	}

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

func (c *client) handleRPC() {
	subStopChan := make(chan struct{})

	writerDone := make(chan error, 1)
	go c.rpcWriter(subStopChan, writerDone)

	readerDone := make(chan error, 1)
	go c.rpcReader(readerDone)

	var err error

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

	if nil != c.conn {
		c.rwcHandler.Disconnect(c.ctx, c.conn)
	}

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

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

}

func (c *client) rpcWriter(stopChan <-chan struct{}, writerDone chan<- error) {
	var err error
	defer func() {
		writerDone <- err
	}()

	for {
		var rs *RequestState

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

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

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

		if rs.hasResponse {
			c.pendingRequestsLock.Lock()
			n := len(c.pendingRequests)
			c.pendingRequests[rs.ID] = rs
			c.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)
				logging.Logger().Error(err.Error())
				continue
			}
		}

		var requestID interface{}
		if 0 < rs.ID {
			requestID = rs.ID
		}

		if nil == c.conn {
			err = io.EOF
			return
		}

		c.requestMtx.Lock()
		err = c.rwcHandler.WriteRequest(c.ctx, c.ch.GetCodec(), c.conn, rs.Method, rs.Args, requestID)
		c.requestMtx.Unlock()
		if !rs.hasResponse {
			rs.Error = err
			rs.Done()
		}
		if nil != err {
			if err == io.ErrUnexpectedEOF || err == io.EOF {
				logging.Logger().Infof("Client: disconnected from server")
				return
			}

			err = fmt.Errorf("Client: Cannot send request to wire: [%s]", err)
			logging.Logger().Error(err)
			continue
		}
	}
}

func (c *client) rpcReader(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 {
		if nil == c.conn {
			err = io.EOF
			return
		}
		c.responseMtx.Lock()
		resCodec, err := c.rwcHandler.ReadResponse(c.ctx, c.ch.GetCodec(), c.conn)
		c.responseMtx.Unlock()
		if nil != err {
			if err == io.ErrUnexpectedEOF || err == io.EOF {
				logging.Logger().Infof("Client: disconnected from server")
				return
			}
			logging.Logger().Errorf("Client: Cannot decode response or notify: [%s]", err)
			continue
		}

		if nil != resCodec.ID() {
			err = c.handleResponse(resCodec)
		} else {
			err = c.handleNotification(resCodec)
		}

		if nil != err {
			logging.Logger().Error(err.Error())
			continue
		}
	}

}

func (c *client) handleResponse(resCodec protocol.ClientResponseCodec) error {
	c.pendingRequestsLock.Lock()
	id := reflect.ValueOf(resCodec.ID()).Convert(uint64Type).Uint()

	rs, ok := c.pendingRequests[id]
	if ok {
		delete(c.pendingRequests, id)
	}
	c.pendingRequestsLock.Unlock()

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

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

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

	rs.Done()

	return nil
}

func (c *client) handleNotification(resCodec protocol.ClientResponseCodec) error {
	notiCodec, err := resCodec.Notification()
	if nil != err {
		return err
	}

	if nil == c.ch.GetRPCInvoker() {
		params, err := notiCodec.Params()
		if nil != err {
			return err
		}
		return fmt.Errorf("Client: Get Notification[method: %s, params: %v]. But RPC registry is not specified", notiCodec.Method(), params)
	}

	_, err = c.ch.GetRPCInvoker().Invoke(notiCodec)

	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,
	}
}