// Copyright (c) 2017 Shivaram Lingamneni <slingamn@cs.stanford.edu>
// released under the MIT license

package irc

import (
	"fmt"
	"sync"
	"time"

	"github.com/oragono/oragono/irc/caps"
)

const (
	// RegisterTimeout is how long clients have to register before we disconnect them
	RegisterTimeout = time.Minute
	// IdleTimeout is how long without traffic before a registered client is considered idle.
	IdleTimeout = time.Minute + time.Second*30
	// IdleTimeoutWithResumeCap is how long without traffic before a registered client is considered idle, when they have the resume capability.
	IdleTimeoutWithResumeCap = time.Minute*2 + time.Second*30
	// QuitTimeout is how long without traffic before an idle client is disconnected
	QuitTimeout = time.Minute
)

// client idleness state machine

type TimerState uint

const (
	TimerUnregistered TimerState = iota // client is unregistered
	TimerActive                         // client is actively sending commands
	TimerIdle                           // client is idle, we sent PING and are waiting for PONG
	TimerDead                           // client was terminated
)

type IdleTimer struct {
	sync.Mutex // tier 1

	// immutable after construction
	registerTimeout       time.Duration
	idleTimeout           time.Duration
	idleTimeoutWithResume time.Duration
	quitTimeout           time.Duration
	client                *Client

	// mutable
	state TimerState
	timer *time.Timer
}

// NewIdleTimer sets up a new IdleTimer using constant timeouts.
func NewIdleTimer(client *Client) *IdleTimer {
	it := IdleTimer{
		registerTimeout:       RegisterTimeout,
		idleTimeout:           IdleTimeout,
		idleTimeoutWithResume: IdleTimeoutWithResumeCap,
		quitTimeout:           QuitTimeout,
		client:                client,
	}
	return &it
}

// Start starts counting idle time; if there is no activity from the client,
// it will eventually be stopped.
func (it *IdleTimer) Start() {
	it.Lock()
	defer it.Unlock()
	it.state = TimerUnregistered
	it.resetTimeout()
}

func (it *IdleTimer) Touch() {
	// ignore touches from unregistered clients
	if !it.client.Registered() {
		return
	}

	it.Lock()
	defer it.Unlock()
	// a touch transitions TimerUnregistered or TimerIdle into TimerActive
	if it.state != TimerDead {
		it.state = TimerActive
		it.resetTimeout()
	}
}

func (it *IdleTimer) processTimeout() {
	var previousState TimerState
	func() {
		it.Lock()
		defer it.Unlock()
		previousState = it.state
		// TimerActive transitions to TimerIdle, all others to TimerDead
		if it.state == TimerActive {
			// send them a ping, give them time to respond
			it.state = TimerIdle
			it.resetTimeout()
		} else {
			it.state = TimerDead
		}
	}()

	if previousState == TimerActive {
		it.client.Ping()
	} else {
		it.client.Quit(it.quitMessage(previousState))
		it.client.destroy()
	}
}

// Stop stops counting idle time.
func (it *IdleTimer) Stop() {
	it.Lock()
	defer it.Unlock()
	it.state = TimerDead
	it.resetTimeout()
}

func (it *IdleTimer) resetTimeout() {
	if it.timer != nil {
		it.timer.Stop()
	}
	var nextTimeout time.Duration
	switch it.state {
	case TimerUnregistered:
		nextTimeout = it.registerTimeout
	case TimerActive:
		// if they have the resume cap, wait longer before pinging them out
		// to give them a chance to resume their connection
		if it.client.capabilities.Has(caps.Resume) {
			nextTimeout = it.idleTimeoutWithResume
		} else {
			nextTimeout = it.idleTimeout
		}
	case TimerIdle:
		nextTimeout = it.quitTimeout
	case TimerDead:
		return
	}
	it.timer = time.AfterFunc(nextTimeout, it.processTimeout)
}

func (it *IdleTimer) quitMessage(state TimerState) string {
	switch state {
	case TimerUnregistered:
		return fmt.Sprintf("Registration timeout: %v", it.registerTimeout)
	case TimerIdle:
		// how many seconds before registered clients are timed out (IdleTimeout plus QuitTimeout).
		return fmt.Sprintf("Ping timeout: %v", (it.idleTimeout + it.quitTimeout))
	default:
		// shouldn't happen
		return ""
	}
}