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package tanja

import (
	"blicky.net/asyncwr"
	"bufio"
	"errors"
	"io"
	"strings"
)

type Link struct {
	Sync    bool
	Ready   bool
	ReadyCh <-chan bool
	readyWr chan<- bool
	Closed  bool
	node    *Node
	io      io.ReadWriteCloser
	wr      *asyncwr.Writer
	err     chan<- error
	regs    map[int32]*Registration
	paths   map[int32]*ReturnPath
	lastId  int32
	lastTup *Tuple
}

func (n *Node) Link(io io.ReadWriteCloser) (l *Link) {
	l = &Link{}
	l.Sync = true
	ready := make(chan bool, 1)
	l.ReadyCh = ready
	l.readyWr = ready
	l.io = io
	l.wr = asyncwr.New(io, 1024*1024) // TODO: make configurable
	l.node = n
	l.regs = make(map[int32]*Registration)
	l.paths = make(map[int32]*ReturnPath)
	l.lastId = 1
	return l
}

func (l *Link) handleHandshake(buf []byte) (err error) {
	strl := strings.Split(string(buf), " ")
	hasver := false
	hasseri := false
	hassero := false
	for _, arg := range strl {
		if strings.HasPrefix(arg, "ver,") && strings.Contains(arg, ",1.") {
			hasver = true
		}
		// TODO: These checks aren't too good, would also match "json-whatever"
		if strings.HasPrefix(arg, "seri,") && strings.Contains(arg, ",json") {
			hasseri = true
		}
		if strings.HasPrefix(arg, "sero,") && strings.Contains(arg, ",json") {
			hassero = true
		}
	}

	if !hasver || !hasseri || !hassero {
		err = errors.New("Invalid handshake message.")
	} else {
		if l.Sync {
			linkMsgWrite(l.wr, linkMsgPatternsync(true))
		} else {
			l.node.lock.Lock()
			r := &Registration{pat: Tup(), active: true, willReply: true, recv: l}
			l.node.reg(r)
			l.regs[0] = r
			l.node.lock.Unlock()
			l.Ready = true
			l.readyWr <- true
			close(l.readyWr)
		}
	}
	return
}

// Called while the node lock is held
func (l *Link) nodeUnreg(id int32) {
	if !l.Closed {
		linkMsgWrite(l.wr, linkMsgUnregister(id))
	}
}

// Called while the node lock is held.
func (l *Link) nodeReg(r *Registration) {
	if !l.Closed && r.recv != l {
		linkMsgWrite(l.wr, &linkMsgRegister{r.id, r.pat})
	}
}

// Called while the node lock is held.
func (l *Link) nodeSend(t *Tuple, p *ReturnPath) {
	if !l.Closed && l.lastTup != t {
		m := &linkMsgTuple{0, *t}

		if p != nil {
			old := l.lastId
			for old == l.lastId || l.paths[l.lastId] != nil {
				l.lastId++
				if l.lastId < 0 {
					l.lastId = 1
				}
			}
			m.tid = l.lastId
			l.paths[m.tid] = p
		}

		linkMsgWrite(l.wr, m)
		l.lastTup = t
	} else {
		p.unref()
	}
}

// Node lock may or may not be held when this function is called
func (l *Link) pathReply(r *ReturnPath, t Tuple) {
	if !l.Closed {
		linkMsgWrite(l.wr, &linkMsgReply{r.id, t})
	}
}

// Node lock is held when this is called.
func (l *Link) pathClose(r *ReturnPath) {
	if !l.Closed {
		linkMsgWrite(l.wr, linkMsgClose(r.id))
	}
}

func (l *Link) handleMessage(msg interface{}) error {
	switch m := msg.(type) {
	case linkMsgPatternsync:
		l.node.lock.Lock()
		if bool(m) && !l.Closed {
			l.node.links[l] = true
			for k, v := range l.node.regs {
				linkMsgWrite(l.wr, &linkMsgRegister{k, v.pat})
			}
			linkMsgWrite(l.wr, linkMsgRegdone{})
		} else {
			delete(l.node.links, l)
		}
		l.node.lock.Unlock()

	case *linkMsgRegister:
		l.node.lock.Lock()
		if l.Sync && !l.Closed {
			if r := l.regs[m.pid]; r != nil {
				l.node.unregOne(r)
			}
			r := &Registration{pat: m.pat, active: true, willReply: true, recv: l}
			l.node.reg(r)
			l.regs[m.pid] = r
		}
		l.node.lock.Unlock()

	case linkMsgRegdone:
		if !l.Ready {
			l.Ready = true
			l.readyWr <- true
			close(l.readyWr)
		}

	case linkMsgUnregister:
		l.node.lock.Lock()
		if l.Sync && !l.Closed {
			if r := l.regs[int32(m)]; r != nil {
				l.node.unregOne(r)
				delete(l.regs, int32(m))
			}
		}
		l.node.lock.Unlock()

	case *linkMsgTuple:
		l.node.lock.Lock()
		var r *ReturnPath
		if m.tid != 0 {
			r = &ReturnPath{obj: l, id: m.tid}
		}
		l.node.send(m.tup, r, l)
		l.node.lock.Unlock()

	case *linkMsgReply:
		// l.paths is protected by the node lock. (This lock does protect a lot...)
		l.node.lock.Lock()
		if r := l.paths[m.tid]; r != nil {
			r.reply(m.tup)
		}
		l.node.lock.Unlock()

	case linkMsgClose:
		l.node.lock.Lock()
		if r := l.paths[int32(m)]; r != nil {
			r.unref()
		}
		l.node.lock.Unlock()
	}
	return nil
}

// TODO: There should be a timeout on the handshake (+ remote pattern syncing)
func (l *Link) reader() {
	// Make sure we've got a buffered reader with a large enough buffer to fit
	// any message. This isn't the most elegant approach, but should do the
	// trick.
	rd := bufio.NewReaderSize(l.io, 1*1024*1024)

	// Handshake
	line, prefix, err := rd.ReadLine()
	if prefix && err == nil {
		err = errors.New("Read buffer overflow.")
	} else if err == nil {
		err = l.handleHandshake(line)
	}

	// Message loop
	for err == nil {
		var m interface{}
		if m, err = linkMsgRead(rd); err == nil {
			err = l.handleMessage(m)
		}
	}

	if err != nil {
		l.err <- err
		return
	}
}

// The returned channel will get exactly a single message when the link is
// closed. Either nil after a normal Close() or an error otherwise.
func (l *Link) Start() <-chan error {
	err := make(chan error, 5) // Must be buffered to allow some extra errors (which will be ignored)
	uerr := make(chan error)
	l.err = err

	go l.reader()

	// A control goroutine to shut things down. This allows multiple writes to
	// l.err, but only the first is handled.
	go func() {
		var e error
		select {
		case e = <-err:
		case e = <-l.wr.ErrorCh():
		}

		l.node.lock.Lock()
		delete(l.node.links, l)
		for _, r := range l.regs {
			l.node.unregOne(r)
		}
		for _, r := range l.paths {
			r.unref()
		}
		l.Closed = true
		l.node.lock.Unlock()

		l.io.Close() // should wake up the reader (with an error)
		uerr <- e
	}()

	// Send handshake
	l.wr.Write([]byte("ver,1.0 seri,json sero,json\n"))

	return uerr
}

func (l *Link) Close() {
	l.err <- nil
}