package yggdrasil

import (
	"errors"
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/yggdrasil-network/yggdrasil-go/src/crypto"
	"github.com/yggdrasil-network/yggdrasil-go/src/util"
)

// ConnError implements the net.Error interface
type ConnError struct {
	error
	timeout   bool
	temporary bool
	maxsize   int
}

// Timeout returns true if the error relates to a timeout condition on the
// connection.
func (e *ConnError) Timeout() bool {
	return e.timeout
}

// Temporary return true if the error is temporary or false if it is a permanent
// error condition.
func (e *ConnError) Temporary() bool {
	return e.temporary
}

// PacketTooBig returns in response to sending a packet that is too large, and
// if so, the maximum supported packet size that should be used for the
// connection.
func (e *ConnError) PacketTooBig() (bool, int) {
	return e.maxsize > 0, e.maxsize
}

type Conn struct {
	core          *Core
	nodeID        *crypto.NodeID
	nodeMask      *crypto.NodeID
	mutex         sync.RWMutex
	closed        bool
	session       *sessionInfo
	readDeadline  atomic.Value  // time.Time // TODO timer
	writeDeadline atomic.Value  // time.Time // TODO timer
	searching     atomic.Value  // bool
	searchwait    chan struct{} // Never reset this, it's only used for the initial search
	writebuf      [][]byte      // Packets to be sent if/when the search finishes
}

// TODO func NewConn() that initializes additional fields as needed
func newConn(core *Core, nodeID *crypto.NodeID, nodeMask *crypto.NodeID, session *sessionInfo) *Conn {
	conn := Conn{
		core:       core,
		nodeID:     nodeID,
		nodeMask:   nodeMask,
		session:    session,
		searchwait: make(chan struct{}),
	}
	conn.searching.Store(false)
	return &conn
}

func (c *Conn) String() string {
	return fmt.Sprintf("conn=%p", c)
}

// This method should only be called from the router goroutine
func (c *Conn) startSearch() {
	// The searchCompleted callback is given to the search
	searchCompleted := func(sinfo *sessionInfo, err error) {
		defer c.searching.Store(false)
		// If the search failed for some reason, e.g. it hit a dead end or timed
		// out, then do nothing
		if err != nil {
			c.core.log.Debugln(c.String(), "DHT search failed:", err)
			return
		}
		// Take the connection mutex
		c.mutex.Lock()
		defer c.mutex.Unlock()
		// Were we successfully given a sessionInfo pointer?
		if sinfo != nil {
			// Store it, and update the nodeID and nodeMask (which may have been
			// wildcarded before now) with their complete counterparts
			c.core.log.Debugln(c.String(), "DHT search completed")
			c.session = sinfo
			c.nodeID = crypto.GetNodeID(&sinfo.theirPermPub)
			for i := range c.nodeMask {
				c.nodeMask[i] = 0xFF
			}
			// Make sure that any blocks on read/write operations are lifted
			defer func() { recover() }() // So duplicate searches don't panic
			close(c.searchwait)
		} else {
			// No session was returned - this shouldn't really happen because we
			// should always return an error reason if we don't return a session
			panic("DHT search didn't return an error or a sessionInfo")
		}
		if c.closed {
			// Things were closed before the search returned
			// Go ahead and close it again to make sure the session is cleaned up
			go c.Close()
		} else {
			// Send any messages we may have buffered
			var msgs [][]byte
			msgs, c.writebuf = c.writebuf, nil
			go func() {
				for _, msg := range msgs {
					c.Write(msg)
					util.PutBytes(msg)
				}
			}()
		}
	}
	// doSearch will be called below in response to one or more conditions
	doSearch := func() {
		c.searching.Store(true)
		// Check to see if there is a search already matching the destination
		sinfo, isIn := c.core.searches.searches[*c.nodeID]
		if !isIn {
			// Nothing was found, so create a new search
			sinfo = c.core.searches.newIterSearch(c.nodeID, c.nodeMask, searchCompleted)
			c.core.log.Debugf("%s DHT search started: %p", c.String(), sinfo)
		}
		// Continue the search
		c.core.searches.continueSearch(sinfo)
	}
	// Take a copy of the session object, in case it changes later
	c.mutex.RLock()
	sinfo := c.session
	c.mutex.RUnlock()
	if c.session == nil {
		// No session object is present so previous searches, if we ran any, have
		// not yielded a useful result (dead end, remote host not found)
		doSearch()
	} else {
		sinfo.worker <- func() {
			switch {
			case !sinfo.init:
				doSearch()
			case time.Since(sinfo.time) > 6*time.Second:
				if sinfo.time.Before(sinfo.pingTime) && time.Since(sinfo.pingTime) > 6*time.Second {
					// TODO double check that the above condition is correct
					doSearch()
				} else {
					c.core.sessions.ping(sinfo)
				}
			default: // Don't do anything, to keep traffic throttled
			}
		}
	}
}

func getDeadlineTimer(value *atomic.Value) *time.Timer {
	timer := time.NewTimer(24 * 365 * time.Hour) // FIXME for some reason setting this to 0 doesn't always let it stop and drain the channel correctly
	util.TimerStop(timer)
	if deadline, ok := value.Load().(time.Time); ok {
		timer.Reset(time.Until(deadline))
	}
	return timer
}

func (c *Conn) Read(b []byte) (int, error) {
	// Take a copy of the session object
	c.mutex.RLock()
	sinfo := c.session
	c.mutex.RUnlock()
	timer := getDeadlineTimer(&c.readDeadline)
	defer util.TimerStop(timer)
	// If there is a search in progress then wait for the result
	if sinfo == nil {
		// Wait for the search to complete
		select {
		case <-c.searchwait:
		case <-timer.C:
			return 0, ConnError{errors.New("timeout"), true, false, 0}
		}
		// Retrieve our session info again
		c.mutex.RLock()
		sinfo = c.session
		c.mutex.RUnlock()
		// If sinfo is still nil at this point then the search failed and the
		// searchwait channel has been recreated, so might as well give up and
		// return an error code
		if sinfo == nil {
			return 0, errors.New("search failed")
		}
	}
	for {
		// Wait for some traffic to come through from the session
		select {
		case <-timer.C:
			return 0, ConnError{errors.New("timeout"), true, false, 0}
		case p, ok := <-sinfo.recv:
			// If the session is closed then do nothing
			if !ok {
				return 0, errors.New("session is closed")
			}
			defer util.PutBytes(p.Payload)
			var err error
			done := make(chan struct{})
			workerFunc := func() {
				defer close(done)
				// If the nonce is bad then drop the packet and return an error
				if !sinfo.nonceIsOK(&p.Nonce) {
					err = ConnError{errors.New("packet dropped due to invalid nonce"), false, true, 0}
					return
				}
				// Decrypt the packet
				bs, isOK := crypto.BoxOpen(&sinfo.sharedSesKey, p.Payload, &p.Nonce)
				defer util.PutBytes(bs) // FIXME commenting this out leads to illegal buffer reuse, this implies there's a memory error somewhere and that this is just flooding things out of the finite pool of old slices that get reused
				// Check if we were unable to decrypt the packet for some reason and
				// return an error if we couldn't
				if !isOK {
					err = ConnError{errors.New("packet dropped due to decryption failure"), false, true, 0}
					return
				}
				// Return the newly decrypted buffer back to the slice we were given
				copy(b, bs)
				// Trim the slice down to size based on the data we received
				if len(bs) < len(b) {
					b = b[:len(bs)]
				}
				// Update the session
				sinfo.updateNonce(&p.Nonce)
				sinfo.time = time.Now()
				sinfo.bytesRecvd += uint64(len(b))
			}
			// Hand over to the session worker
			select { // Send to worker
			case sinfo.worker <- workerFunc:
			case <-timer.C:
				return 0, ConnError{errors.New("timeout"), true, false, 0}
			}
			<-done // Wait for the worker to finish, failing this can cause memory errors (util.[Get||Put]Bytes stuff)
			// Something went wrong in the session worker so abort
			if err != nil {
				if ce, ok := err.(*ConnError); ok && ce.Temporary() {
					continue
				}
				return 0, err
			}
			// If we've reached this point then everything went to plan, return the
			// number of bytes we populated back into the given slice
			return len(b), nil
		}
	}
}

func (c *Conn) Write(b []byte) (bytesWritten int, err error) {
	c.mutex.RLock()
	sinfo := c.session
	c.mutex.RUnlock()
	// If the session doesn't exist, or isn't initialised (which probably means
	// that the search didn't complete successfully) then we may need to wait for
	// the search to complete or start the search again
	if sinfo == nil || !sinfo.init {
		// Is a search already taking place?
		if searching, sok := c.searching.Load().(bool); !sok || (sok && !searching) {
			// No search was already taking place so start a new one
			c.core.router.doAdmin(c.startSearch)
		}
		// Buffer the packet to be sent if/when the search is finished
		c.mutex.Lock()
		defer c.mutex.Unlock()
		c.writebuf = append(c.writebuf, append(util.GetBytes(), b...))
		for len(c.writebuf) > 32 {
			util.PutBytes(c.writebuf[0])
			c.writebuf = c.writebuf[1:]
		}
		return len(b), nil
	} else {
		// This triggers some session keepalive traffic
		// FIXME this desparately needs to be refactored, since the ping case needlessly goes through the router goroutine just to have it pass a function to the session worker when it determines that a session already exists.
		c.core.router.doAdmin(c.startSearch)
	}
	var packet []byte
	done := make(chan struct{})
	written := len(b)
	workerFunc := func() {
		defer close(done)
		// Does the packet exceed the permitted size for the session?
		if uint16(len(b)) > sinfo.getMTU() {
			written, err = 0, ConnError{errors.New("packet too big"), true, false, int(sinfo.getMTU())}
			return
		}
		// Encrypt the packet
		payload, nonce := crypto.BoxSeal(&sinfo.sharedSesKey, b, &sinfo.myNonce)
		defer util.PutBytes(payload)
		// Construct the wire packet to send to the router
		p := wire_trafficPacket{
			Coords:  sinfo.coords,
			Handle:  sinfo.theirHandle,
			Nonce:   *nonce,
			Payload: payload,
		}
		packet = p.encode()
		sinfo.bytesSent += uint64(len(b))
	}
	// Set up a timer so this doesn't block forever
	timer := getDeadlineTimer(&c.writeDeadline)
	defer util.TimerStop(timer)
	// Hand over to the session worker
	select { // Send to worker
	case sinfo.worker <- workerFunc:
	case <-timer.C:
		return 0, ConnError{errors.New("timeout"), true, false, 0}
	}
	// Wait for the worker to finish, otherwise there are memory errors ([Get||Put]Bytes stuff)
	<-done
	// Give the packet to the router
	if written > 0 {
		sinfo.core.router.out(packet)
	}
	// Finally return the number of bytes we wrote
	return written, err
}

func (c *Conn) Close() error {
	c.mutex.Lock()
	defer c.mutex.Unlock()
	if c.session != nil {
		// Close the session, if it hasn't been closed already
		c.session.close()
		c.session = nil
	}
	// This can't fail yet - TODO?
	c.closed = true
	return nil
}

func (c *Conn) LocalAddr() crypto.NodeID {
	return *crypto.GetNodeID(&c.session.core.boxPub)
}

func (c *Conn) RemoteAddr() crypto.NodeID {
	c.mutex.RLock()
	defer c.mutex.RUnlock()
	return *c.nodeID
}

func (c *Conn) SetDeadline(t time.Time) error {
	c.SetReadDeadline(t)
	c.SetWriteDeadline(t)
	return nil
}

func (c *Conn) SetReadDeadline(t time.Time) error {
	c.readDeadline.Store(t)
	return nil
}

func (c *Conn) SetWriteDeadline(t time.Time) error {
	c.writeDeadline.Store(t)
	return nil
}