package jobs

import (
	"context"
	"slices"
	"sync"
	"time"
)

const slotWaitInterval = 500 * time.Millisecond

const (
	queueFirst = "first"
	queueUp    = "up"
	queueDown  = "down"
)

type slotLimiter struct {
	mutex   sync.Mutex
	active  int
	waiting []string
}

func (limiter *slotLimiter) enqueue(id string) {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	if !slices.Contains(limiter.waiting, id) {
		limiter.waiting = append(limiter.waiting, id)
	}
}

func (limiter *slotLimiter) acquire(ctx context.Context, id string, limit func() int) bool {
	limiter.enqueue(id)
	ticker := time.NewTicker(slotWaitInterval)
	defer ticker.Stop()
	for {
		if limiter.tryAcquire(id, limit()) {
			return true
		}
		select {
		case <-ctx.Done():
			limiter.remove(id)
			return false
		case <-ticker.C:
		}
	}
}

func (limiter *slotLimiter) tryAcquire(id string, limit int) bool {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	if limiter.active >= limit || len(limiter.waiting) == 0 || limiter.waiting[0] != id {
		return false
	}
	limiter.waiting = limiter.waiting[1:]
	limiter.active++
	return true
}

func (limiter *slotLimiter) release() {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	limiter.active--
}

func (limiter *slotLimiter) remove(id string) {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	limiter.waiting = slices.DeleteFunc(limiter.waiting, func(waitingID string) bool {
		return waitingID == id
	})
}

func (limiter *slotLimiter) position(id string) int {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	return slices.Index(limiter.waiting, id) + 1
}

func (limiter *slotLimiter) reorder(id, direction string) bool {
	limiter.mutex.Lock()
	defer limiter.mutex.Unlock()
	index := slices.Index(limiter.waiting, id)
	if index < 0 {
		return false
	}

	target := index
	switch direction {
	case queueFirst:
		target = 0
	case queueUp:
		target = max(index-1, 0)
	case queueDown:
		target = min(index+1, len(limiter.waiting)-1)
	}
	limiter.waiting = slices.Delete(limiter.waiting, index, index+1)
	limiter.waiting = slices.Insert(limiter.waiting, target, id)
	return true
}