//
//  rhimportd
//
//  The Radio Helsinki Rivendell Import Daemon
//
//
//  Copyright (C) 2015-2016 Christian Pointner <equinox@helsinki.at>
//
//  This file is part of rhimportd.
//
//  rhimportd is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  any later version.
//
//  rhimportd is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with rhimportd. If not, see <http://www.gnu.org/licenses/>.
//

package rhimport

import (
	"fmt"
	"net/http"
	"time"
)

const (
	_SESSION_NEW = iota
	_SESSION_RUNNING
	_SESSION_CANCELED
	_SESSION_DONE
	_SESSION_TIMEOUT
)

type sessionProgressCB struct {
	cb       ProgressCB
	userdata interface{}
}

type sessionDoneCB struct {
	cb       DoneCB
	userdata interface{}
}

type sessionAddProgressHandlerResponse struct {
	err error
}

type sessionAddProgressHandlerRequest struct {
	userdata interface{}
	callback ProgressCB
	response chan<- sessionAddProgressHandlerResponse
}

type sessionAddDoneHandlerResponse struct {
	err error
}

type sessionAddDoneHandlerRequest struct {
	userdata interface{}
	callback DoneCB
	response chan<- sessionAddDoneHandlerResponse
}

type attachUploaderResponse struct {
	cancel     <-chan bool
	attachment chan<- AttachmentChunk
}

type attachUploaderRequest struct {
	response chan<- attachUploaderResponse
}

type session struct {
	ctx                Context
	state              int
	removeFunc         func()
	done               chan bool
	quit               chan bool
	timer              *time.Timer
	cancelIntChan      chan bool
	progressRateLimit  time.Duration
	progressIntChan    chan ProgressData
	doneIntChan        chan Result
	runChan            chan time.Duration
	cancelChan         chan bool
	addProgressChan    chan sessionAddProgressHandlerRequest
	addDoneChan        chan sessionAddDoneHandlerRequest
	attachUploaderChan chan attachUploaderRequest
	progressCBs        []*sessionProgressCB
	doneCBs            []*sessionDoneCB
	cancelUploader     chan bool
}

func sessionProgressCallback(step int, stepName string, current, total float64, title string, cart, cut uint, userdata interface{}) bool {
	out := userdata.(chan<- ProgressData)
	out <- ProgressData{step, stepName, current, total, title, cart, cut}
	return true
}

func sessionRun(ctx Context, done chan<- Result) {
	err := ctx.SanityCheck()
	if err != nil {
		done <- Result{ResponseCode: http.StatusBadRequest, ErrorString: err.Error()}
		return
	}

	var res *Result
	res, err = FetchFile(&ctx)
	if err != nil {
		done <- Result{ResponseCode: http.StatusInternalServerError, ErrorString: err.Error()}
		return
	}
	if res.ResponseCode != http.StatusOK {
		done <- *res
		return
	}

	if res, err = NormalizeFile(&ctx); err != nil {
		done <- Result{ResponseCode: http.StatusInternalServerError, ErrorString: err.Error()}
		return
	}
	if res.ResponseCode != http.StatusOK {
		done <- *res
		return
	}

	if res, err = ImportFile(&ctx); err != nil {
		res.ResponseCode = http.StatusInternalServerError
		res.ErrorString = err.Error()
	}
	done <- *res
}

func (s *session) run(timeout time.Duration) {
	s.ctx.ProgressCallBack = sessionProgressCallback
	s.ctx.ProgressCallBackData = (chan<- ProgressData)(s.progressIntChan)
	s.ctx.Cancel = s.cancelIntChan
	go sessionRun(s.ctx, s.doneIntChan)
	s.state = _SESSION_RUNNING
	if timeout > 3*time.Hour {
		s.ctx.stdlog.Printf("requested session timeout (%v) is to high - lowering to 3h", timeout)
		timeout = 3 * time.Hour
	}
	s.timer.Reset(timeout)
	return
}

func (s *session) cancel() {
	s.ctx.dbglog.Println("Session: canceling running import")
	select {
	case s.cancelIntChan <- true:
	default: // session got canceled already??
	}
	s.state = _SESSION_CANCELED
}

func (s *session) addProgressHandler(userdata interface{}, cb ProgressCB) (resp sessionAddProgressHandlerResponse) {
	if s.state != _SESSION_NEW && s.state != _SESSION_RUNNING {
		resp.err = fmt.Errorf("session is already done/canceled")
	}
	s.progressCBs = append(s.progressCBs, &sessionProgressCB{cb, userdata})
	return
}

func (s *session) addDoneHandler(userdata interface{}, cb DoneCB) (resp sessionAddDoneHandlerResponse) {
	if s.state != _SESSION_NEW && s.state != _SESSION_RUNNING {
		resp.err = fmt.Errorf("session is already done/canceled")
	}
	s.doneCBs = append(s.doneCBs, &sessionDoneCB{cb, userdata})
	return
}

func (s *session) callProgressHandler(p *ProgressData) {
	for _, cb := range s.progressCBs {
		if cb.cb != nil {
			if keep := cb.cb(p.Step, p.StepName, p.Current, p.Total, p.Title, p.Cart, p.Cut, cb.userdata); !keep {
				cb.cb = nil
			}
		}
	}
}

func (s *session) callDoneHandler(r *Result) {
	for _, cb := range s.doneCBs {
		if cb.cb != nil {
			if keep := cb.cb(*r, cb.userdata); !keep {
				cb.cb = nil
			}
		}
	}
}

func (s *session) attachUploader() (resp attachUploaderResponse) {
	if s.cancelUploader != nil {
		return
	}
	s.cancelUploader = make(chan bool, 1)
	resp.cancel = s.cancelUploader
	resp.attachment = s.ctx.AttachmentChan
	return
}

func (s *session) dispatchRequests() {
	defer func() {
		if s.cancelUploader != nil {
			close(s.cancelUploader)
		}
		s.done <- true
	}()

	var lastProgress *ProgressData
	progressPending := 0
	pt := time.NewTimer(s.progressRateLimit)
	pt.Stop()

	for {
		select {
		case <-s.quit:
			if s.state == _SESSION_RUNNING {
				s.cancel()
			}
			return
		case <-s.timer.C:
			if s.state == _SESSION_RUNNING {
				s.cancel()
			}
			s.state = _SESSION_TIMEOUT
			r := &Result{ResponseCode: http.StatusInternalServerError, ErrorString: "session timed out"}
			s.callDoneHandler(r)
			if s.removeFunc != nil {
				s.removeFunc()
			}
		case t := <-s.runChan:
			if s.state == _SESSION_NEW {
				s.run(t)
			}
		case <-s.cancelChan:
			if s.state == _SESSION_RUNNING {
				s.cancel()
			}
		case req := <-s.addProgressChan:
			req.response <- s.addProgressHandler(req.userdata, req.callback)
		case req := <-s.addDoneChan:
			req.response <- s.addDoneHandler(req.userdata, req.callback)
		case <-pt.C:
			if progressPending > 1 && lastProgress != nil {
				s.callProgressHandler(lastProgress)
			}
			progressPending = 0
			lastProgress = nil
		case p := <-s.progressIntChan:
			if s.state == _SESSION_RUNNING {
				if lastProgress == nil {
					s.callProgressHandler(&p)
					pt.Reset(s.progressRateLimit)
				} else if lastProgress.Step != p.Step {
					s.callProgressHandler(lastProgress)
					s.callProgressHandler(&p)
					pt.Reset(s.progressRateLimit)
				}
				lastProgress = &p
				progressPending++
			}
		case r := <-s.doneIntChan:
			if s.state != _SESSION_TIMEOUT {
				s.timer.Stop()
				s.state = _SESSION_DONE
				s.callDoneHandler(&r)
				if s.removeFunc != nil {
					s.removeFunc()
				}
			}
		case req := <-s.attachUploaderChan:
			req.response <- s.attachUploader()
		}
	}
}

// *********************************************************
// Public Interface

type Session struct {
	runChan            chan<- time.Duration
	cancelChan         chan<- bool
	addProgressChan    chan<- sessionAddProgressHandlerRequest
	addDoneChan        chan<- sessionAddDoneHandlerRequest
	attachUploaderChan chan<- attachUploaderRequest
}

func (s *Session) Run(timeout time.Duration) {
	select {
	case s.runChan <- timeout:
	default: // command is already pending or session is about to be closed/removed
	}
}

func (s *Session) Cancel() {
	select {
	case s.cancelChan <- true:
	default: // cancel is already pending or session is about to be closed/removed
	}
}

func (s *Session) AddProgressHandler(userdata interface{}, cb ProgressCB) error {
	resCh := make(chan sessionAddProgressHandlerResponse)
	req := sessionAddProgressHandlerRequest{}
	req.userdata = userdata
	req.callback = cb
	req.response = resCh
	select {
	case s.addProgressChan <- req:
	default:
		return fmt.Errorf("session is about to be closed/removed")
	}

	res := <-resCh
	return res.err
}

func (s *Session) AddDoneHandler(userdata interface{}, cb DoneCB) error {
	resCh := make(chan sessionAddDoneHandlerResponse)
	req := sessionAddDoneHandlerRequest{}
	req.userdata = userdata
	req.callback = cb
	req.response = resCh
	select {
	case s.addDoneChan <- req:
	default:
		return fmt.Errorf("session is about to be closed/removed")
	}

	res := <-resCh
	return res.err
}

func (s *Session) AttachUploader() (<-chan bool, chan<- AttachmentChunk) {
	resCh := make(chan attachUploaderResponse)
	req := attachUploaderRequest{}
	req.response = resCh
	select {
	case s.attachUploaderChan <- req:
	default:
		// session is about to be closed/removed
		return nil, nil
	}

	res := <-resCh
	return res.cancel, res.attachment
}

// *********************************************************
// Semi-Public Interface (only used by sessionStore)

func (s *session) getInterface() *Session {
	ch := &Session{}
	ch.runChan = s.runChan
	ch.cancelChan = s.cancelChan
	ch.addProgressChan = s.addProgressChan
	ch.addDoneChan = s.addDoneChan
	ch.attachUploaderChan = s.attachUploaderChan
	return ch
}

func (s *session) cleanup() {
	s.quit <- true
	s.ctx.dbglog.Printf("Session: waiting for session to close")
	<-s.done
	close(s.quit)
	close(s.done)
	s.timer.Stop()
	//   don't close the channels we give out because this might lead to a panic if
	//   somebody wites to an already removed session
	// close(s.cancelIntChan)
	// close(s.progressIntChan)
	// close(s.doneIntChan)
	// close(s.runChan)
	// close(s.cancelChan)
	// close(s.addProgressChan)
	// close(s.addDoneChan)
	// close(s.attachUploader)
	s.ctx.dbglog.Printf("Session: cleanup is now done")
}

func newSession(ctx *Context, removeFunc func()) (s *session) {
	s = &session{}
	s.state = _SESSION_NEW
	s.removeFunc = removeFunc
	s.ctx = *ctx
	s.quit = make(chan bool, 1)
	s.done = make(chan bool)
	s.timer = time.NewTimer(10 * time.Second)
	s.cancelIntChan = make(chan bool, 1)
	s.progressRateLimit = 100 * time.Millisecond // TODO: hardcoded value
	s.progressIntChan = make(chan ProgressData, 10)
	s.doneIntChan = make(chan Result, 1)
	s.runChan = make(chan time.Duration, 1)
	s.cancelChan = make(chan bool, 1)
	s.addProgressChan = make(chan sessionAddProgressHandlerRequest, 10)
	s.addDoneChan = make(chan sessionAddDoneHandlerRequest, 10)
	s.attachUploaderChan = make(chan attachUploaderRequest, 1)
	go s.dispatchRequests()
	return
}