// ------------------------------------------------------------------------
//   Project atila
//   Active Thing (activething.com) git.activething.com/go
//
//   File name  rkey.go
//   Created by DEV
//   Modified   05/02/2024
//
//   Copyright 2024 activething.com
// ------------------------------------------------------------------------
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ------------------------------------------------------------------------

package times

import (
	"activething.com/go/gogo/core/opts"
	"container/heap"
	"context"
	"sync/atomic"
	"time"


)

const (
	timerQueueLen  = 4096
	timerQueueTime = time.Hour * 86400
)

type (


	TimerQueue 		struct {
		heap  		TimerTaskHeap
		state 		uint32

		pushCh      chan *TimerTask
		ctx         context.Context
		ctxCancelFn context.CancelFunc

		nextTask 	*time.Time
		timer    	*time.Timer
	}


)


func NewTimerQueue(options ... opts.OptionFnc[TimerQueue]) *TimerQueue {
	tq := &TimerQueue{
		heap : TimerTaskHeap{},
		state: uint32(TimerStateCreated),
	}
	heap.Init(&tq.heap)
	opts.Apply(tq, options ...)
	if tq.pushCh == nil {
		tq.pushCh = make(chan *TimerTask, timerQueueLen)
	}
	return tq
}


func (q *TimerQueue) State() TimerState {
	return TimerState(atomic.LoadUint32(&q.state)) }


func (q *TimerQueue) Start(ctx context.Context) error {
	if !atomic.CompareAndSwapUint32(&q.state,uint32(TimerStateCreated),uint32(TimerStateStarted)) {
		// error already started
		return G.ErrAlreadyStarted
	}
	if q.timer == nil {
		q.timer = time.NewTimer(timerQueueTime)
	} else {
		q.timer.Reset(timerQueueTime)
	}

	q.ctx, q.ctxCancelFn = context.WithCancel(ctx)
	go func(qu *TimerQueue, cx context.Context) {
		ts := make([]*TimerTask, 0, 10)
	EXIT:
		for {
			select {
			//--
			case <-cx.Done():
				atomic.CompareAndSwapUint32(&qu.state,uint32(TimerStateStarted),uint32(TimerStateCanceled))
				break EXIT
			//--
			case nw := <-qu.timer.C:
				ts = ts[:0]
				for ix, ln := 0, qu.heap.Len(); ix < ln; ix++ {
					pk := qu.heap[0]
					if pk.RunAt.Before(nw) {
						pp := heap.Pop(&qu.heap).(*TimerTask)
						ts = append(ts, pp)
						continue
					}
					break
				}

				if len(ts) > 0 {
					go func(tm time.Time, tk []*TimerTask) {
						for _, tt := range tk {
							tt.TaskFn(tm, ctx)
						}
					}(nw, ts)
				}

				if qu.heap.Len() > 0 {
					nr := qu.heap[0].RunAt
					qu.nextTask = &nr
					qu.timer.Reset(nr.Sub(time.Now()))
				} else {
					qu.timer.Stop()
					qu.nextTask = nil
				}
			//--
			case tt := <-q.pushCh:
				heap.Push(&q.heap, tt)
				if qu.nextTask == nil || qu.nextTask.After(tt.RunAt) {
					if qu.nextTask != nil && !qu.timer.Stop() {
						<-qu.timer.C
					}
					qu.timer.Reset(tt.RunAt.Sub(time.Now()))
					qu.nextTask = &tt.RunAt
				}
			}
		}

		if !q.timer.Stop() {
			<-qu.timer.C
		}
		qu.heap.Reset()

	}(q, q.ctx)

	return nil
}


func (q *TimerQueue) Stop() error {
	if atomic.CompareAndSwapUint32(&q.state,uint32(TimerStateStarted),uint32(TimerStateCanceled)) {
		q.ctxCancelFn()
		return nil
	}
	return G.ErrNotStarted
}


func (q *TimerQueue) Push(runAt time.Time, task TimeTaskFnc) error {
	switch {
	case runAt.Before(time.Now()):
		return G.ErrExpired
	case task == nil:
		return G.ErrTimerTaskInvalid
	case TimerState(atomic.LoadUint32(&q.state)) != TimerStateStarted:
		return G.ErrNotStarted
	default:
		select {
		case q.pushCh <- NewTimerTask(runAt, task):
			return nil
		case <-q.ctx.Done():
			return context.Canceled
		}
	}
}

/*
   ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

   I HAVE NO DESIRE TO WALK ON WATER," SAID SIDDHARTA.
   "LET THE OLD SHRAMANAS SATISFY THEMSELVES WITH SUCH SKILLS.

   SIDDHARTA
   - HERMANN HESSE -

   :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

*/