// Package raft implements raft.
package raft

import (
	"code.google.com/p/go.net/context"
	pb "github.com/coreos/etcd/raft/raftpb"
)

type Ready struct {
	// The current state of a Node
	pb.State

	// Entries specifies entries to be saved to stable storage BEFORE
	// Messages are sent.
	Entries []pb.Entry

	// CommittedEntries specifies entries to be committed to a
	// store/state-machine. These have previously been committed to stable
	// store.
	CommittedEntries []pb.Entry

	// Messages specifies outbound messages to be sent AFTER Entries are
	// committed to stable storage.
	Messages []pb.Message
}

func isStateEqual(a, b pb.State) bool {
	return a.Term == b.Term && a.Vote == b.Vote && a.LastIndex == b.LastIndex
}

func (rd Ready) containsUpdates(prev Ready) bool {
	return !isStateEqual(prev.State, rd.State) || len(rd.Entries) > 0 || len(rd.CommittedEntries) > 0 || len(rd.Messages) > 0
}

type Node struct {
	ctx          context.Context
	propc        chan pb.Message
	recvc        chan pb.Message
	readyc       chan Ready
	tickc        chan struct{}
	alwaysreadyc chan Ready
}

func Start(ctx context.Context, id int64, peers []int64) Node {
	n := Node{
		ctx:          ctx,
		propc:        make(chan pb.Message),
		recvc:        make(chan pb.Message),
		readyc:       make(chan Ready),
		tickc:        make(chan struct{}),
		alwaysreadyc: make(chan Ready),
	}
	r := newRaft(id, peers)
	go n.run(r)
	return n
}

func (n *Node) run(r *raft) {
	propc := n.propc
	readyc := n.readyc

	var prev Ready
	for {
		if r.hasLeader() {
			propc = n.propc
		} else {
			// We cannot accept proposals because we don't know who
			// to send them to, so we'll apply back-pressure and
			// block senders.
			propc = nil
		}

		rd := Ready{
			r.State,
			r.raftLog.unstableEnts(),
			r.raftLog.nextEnts(),
			r.msgs,
		}

		if rd.containsUpdates(prev) {
			readyc = n.readyc
			prev = rd
		} else {
			readyc = nil
		}

		select {
		case m := <-propc:
			m.From = r.id
			r.Step(m)
		case m := <-n.recvc:
			r.Step(m) // raft never returns an error
		case <-n.tickc:
			// r.tick()
		case readyc <- rd:
			r.raftLog.resetNextEnts()
			r.raftLog.resetUnstable()
			r.msgs = nil
		case n.alwaysreadyc <- rd:
			// this is for testing only
		case <-n.ctx.Done():
			return
		}
	}
}

func (n *Node) Tick() error {
	select {
	case n.tickc <- struct{}{}:
		return nil
	case <-n.ctx.Done():
		return n.ctx.Err()
	}
}

func (n *Node) Campaign(ctx context.Context) error {
	return n.Step(ctx, pb.Message{Type: msgHup})
}

// Propose proposes data be appended to the log.
func (n *Node) Propose(ctx context.Context, data []byte) error {
	return n.Step(ctx, pb.Message{Type: msgProp, Entries: []pb.Entry{{Data: data}}})
}

// Step advances the state machine using msgs. The ctx.Err() will be returned,
// if any.
func (n *Node) Step(ctx context.Context, m pb.Message) error {
	ch := n.recvc
	if m.Type == msgProp {
		ch = n.propc
	}

	select {
	case ch <- m:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	case <-n.ctx.Done():
		return n.ctx.Err()
	}
}

// ReadState returns the current point-in-time state.
func (n *Node) Ready() <-chan Ready {
	return n.readyc
}

// RecvReadyNow returns the state of n without blocking. It is primarly for
// testing purposes only.
func RecvReadyNow(n Node) Ready {
	return <-n.alwaysreadyc
}