// Copyright 2022 @qoobing.com. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
// Unique id creator tools, It can be used to create 'userid' or
// 'transaction id' or something else need global unique id in a
// service cluster.
package uid

import (
	"errors"
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/gammazero/deque"
	"qoobing.com/gomod/log"
)

// IdCreator
type IdCreator interface {
	GetId(parts ...interface{}) string
}

// IdCreatorHelper
type IdCreatorHelper interface {
	// CreatePrefix create id prefix
	CreatePrefix(parts ...interface{}) string
	// CreateRange create id range from database table t_id.
	CreateRange(prefix string) (start int64, length int, err error)
	// CreateMixedId create finnal transaction id
	CreateMixedId(prefix string, id int64, parts ...interface{}) string
}

// Range Range define the range [start, end] of ids.
type Range struct {
	Next   int64  // next id
	Status int    // 0:invlid; 1:ok; 2:useout
	Prefix string // prefix
	Start  int64  // begin id of this range(include)
	End    int64  // end id of this range(include)
	Length int    // lenght of this range
}
type rangeQueue struct {
	deque.Deque[*Range]
}

const (
	RANGE_STATUS_OK     = 1
	RANGE_STATUS_USEOUT = 2
)

// idCreator
type idCreator struct {
	lock        sync.Mutex
	Type        string
	Ranges      map[string]*rangeQueue
	RangesLocks map[string]*sync.Mutex
	Helper      IdCreatorHelper
}

// NewIdCreator to new a id creator by helper.
func NewIdCreator(typ string, helper IdCreatorHelper) IdCreator {
	// Step 1. basic value
	var idg = &idCreator{
		lock:        sync.Mutex{},
		Type:        typ,
		Ranges:      map[string]*rangeQueue{},
		RangesLocks: map[string]*sync.Mutex{},
		Helper:      helper,
	}

	// Step 2. generate the first range.
	if prefix, err := idg.createDefaultPrefix(); err == nil {
		idg.createNewRangeWithErrorPanic(prefix)
	}

	// Step 3. backgroud task for generate range
	go func() {
		for {
			for prefix, queue := range idg.Ranges {
				var qlen = queue.Len()
				var timeoutMs = 1 * time.Millisecond

				if qlen <= 0 {
					timeoutMs = 1 * time.Millisecond
				} else if qlen <= 2 {
					timeoutMs = 50 * time.Millisecond
				} else {
					timeoutMs = -1000 * time.Millisecond
				}

				if int(timeoutMs) > 0 {
					idg.createNewRangeWithErrorPanic(prefix)
					time.Sleep(timeoutMs * time.Millisecond)
				} else if int(timeoutMs) < 0 {
					time.Sleep((-timeoutMs) * time.Millisecond)
				}
			}
			time.Sleep(1000 * time.Millisecond)
		}
	}()

	return idg
}

func (idg *idCreator) GetId(idparts ...interface{}) string {
	var prefix = idg.Helper.CreatePrefix(idparts...)
	for {
		var id int64 = 0
		var currange = idg.getCurrentRange(prefix)
		log.Infof("success get current range:(%s, %d-%d)",
			prefix, currange.Start, currange.End)
		// Step 1. Optimistic[no lock] to add id in current range.
		for {
			id = atomic.LoadInt64(&currange.Next)
			if id > currange.End {
				//next range
				break
			}
			if atomic.CompareAndSwapInt64(&currange.Next, id, id+1) {
				//success
				break
			}
		}

		// Step 2. No lock add failed, try add id in next range.
		if id > currange.End {
			//next range
			log.Infof("failed get id from current range, try next")
			idg.turnToNextRange(currange)
			continue
		}

		// Step 3. Success, return mixed id.
		log.Infof("success get id(not miexed):(%s, %d)", prefix, id)
		return idg.Helper.CreateMixedId(prefix, id, idparts...)
	}
}

func (idg *idCreator) createDefaultPrefix() (prefix string, err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("default prefix not surport by user")
		}
	}()
	if prefix = idg.Helper.CreatePrefix(); len(prefix) == 0 {
		err = fmt.Errorf("default prefix not surport by user")
	}
	return prefix, err
}

func (idg *idCreator) createNewRangeWithErrorPanic(prefix string) {
	if err := idg.createNewRange(prefix); err != nil {
		panic("create new range error:" + err.Error())
	}
}

func (idg *idCreator) removeOldRangeWithErrorPanic(prefix string) {
	if err := idg.removeOldRange(prefix); err != nil {
		panic("remove old range error:" + err.Error())
	}
}

func (idg *idCreator) createNewRange(prefix string) error {
	// Step 1. create range from db or something else.
	start, length, err := idg.Helper.CreateRange(prefix)
	if err != nil {
		str := fmt.Sprintf(
			"idCreator '%s' generate range err:'%s'",
			idg.Type, err.Error())
		log.Errorf("%s", str)
		return errors.New(str)
	}

	// Step 2. lock generator.
	idg.lock.Lock()
	defer idg.lock.Unlock()
	if _, ok := idg.RangesLocks[prefix]; !ok {
		idg.Ranges[prefix] = &rangeQueue{Deque: *deque.New[*Range]()}
		idg.RangesLocks[prefix] = &sync.Mutex{}
	}
	var queue = idg.Ranges[prefix]
	var lock = idg.RangesLocks[prefix]
	lock.Lock()
	defer lock.Unlock()

	// Step 3. push to ranges queue.
	var r = &Range{
		Next:   start,
		Status: RANGE_STATUS_OK,
		Prefix: prefix,
		Start:  start,
		End:    start + int64(length) - 1,
		Length: length,
	}
	queue.PushBack(r)
	log.Infof("success createNewRange (%s, %d-%d)", prefix, start, r.End)
	return nil
}

func (idg *idCreator) removeOldRange(prefix string) error {
	if lock, ok := idg.RangesLocks[prefix]; ok {
		lock.Lock()
		defer lock.Unlock()

		queue := idg.Ranges[prefix]
		for queue.Len() > 0 {
			r := queue.Front()
			if r.Status == RANGE_STATUS_OK {
				break
			} else if r.Status == RANGE_STATUS_USEOUT {
				queue.PopFront()
				log.Infof("success remove old range:(%s,%d-%d)",
					prefix, r.Start, r.End)
			} else {
				panic("invalid status, maybe somethong bug")
			}
		}
	} else {
		log.Infof("rare case: rangequeue:(%s) have remove by others", prefix)
	}
	return nil
}

func (idg *idCreator) getCurrentRange(prefix string) (r *Range) {
	var (
		ok                = false
		lock  *sync.Mutex = nil
		queue *rangeQueue = nil
	)

	// Step 0. get ranges queue by prefix.
	for trycount := 0; !ok && trycount < 3; trycount++ {
		if queue, ok = idg.Ranges[prefix]; ok {
			lock = idg.RangesLocks[prefix]
			break
		}
		// try create new range
		idg.createNewRange(prefix)
	}
	if !ok {
		panic("maybe something bug or too many pressures," +
			"cannot found range queue after createNewRange retry 3 times")
	}

	// Step 1. try read from queue directly.
	lock.Lock()
	if queue.Len() >= 1 {
		r = queue.Front()
		lock.Unlock()
		return r
	}
	lock.Unlock()

	// Step 2. retry create a new range & try again.
	idg.createNewRange(prefix)
	lock.Lock()
	defer lock.Unlock()
	if queue.Len() >= 1 {
		r = queue.Front()
		return r
	}
	panic("get current range failed, too many pressure???")
}

func (idg *idCreator) turnToNextRange(r *Range) {
	// We donot lock the range, because there is no too much
	// side effect even if 'createNewRange' execute twice.
	switch r.Status {
	case RANGE_STATUS_OK:
		r.Status = RANGE_STATUS_USEOUT
		idg.createNewRangeWithErrorPanic(r.Prefix)
		idg.removeOldRangeWithErrorPanic(r.Prefix)
	case RANGE_STATUS_USEOUT:
		// have turn by others, we do nothing.
		log.Debugf("have turn by others, we do nothing.")
	default:
		panic("invalid status, maybe somethong bug")
	}
}