package gtq

import (
	"runtime"
	"sync"
	"time"
)

// TaskQueue manages multiple Queues with different priorities.
// Task clients request tasks to run from this, and it decides which Task
// to give the client, based on a roughly even time division based on the
// priority numbers. Items from priority 2 will be given twice as much
// processing time as items from priorty 1, for instance.
type TaskQueue struct {
	queues sync.Map
	// task runners read off this channel, scheduler pushes onto it.
	nextTask chan func()
	// we need locking when cleaning up unused priorities.
	mutex   sync.Mutex
	running bool
	numJobs uint
}

// NewTaskQueue returns an initialized TaskQueue.
// numJobs specifies how many task workers you want running simultaneously, if
// 0, defaults to runtime.GOMAXPROCS(0).
func NewTaskQueue(numJobs uint) (tq *TaskQueue) {
	if numJobs == 0 {
		numJobs = uint(runtime.GOMAXPROCS(0))
	}
	tq = &TaskQueue{
		// make sure we can buffer up at least one extra job per worker.
		nextTask: make(chan func(), numJobs*2),
		numJobs:  numJobs,
	}
	return tq
}

// Add a task to the TaskQueue with a given priority.
func (tq *TaskQueue) Add(task func(), priority uint) {
	q, _ := tq.queues.LoadOrStore(priority, NewQueue())
	q.(*Queue).Add(task)
}

// Length returns the number of tasks at all priorities.
func (tq *TaskQueue) Length() (length uint) {
	tq.mutex.Lock()
	defer tq.mutex.Unlock()
	tq.queues.Range(func(_, q interface{}) bool {
		length += uint(q.(*Queue).Length())
		return true
	})
	return length
}

// PriorityCounts returns a map where the key is an active priority level,
// and the value is the number of tasks left at that priority.
func (tq *TaskQueue) PriorityCounts() (pc map[uint]int) {
	pc = make(map[uint]int)
	tq.mutex.Lock()
	defer tq.mutex.Unlock()
	tq.queues.Range(func(prio, q interface{}) bool {
		pc[prio.(uint)] = q.(*Queue).Length()
		return true
	})
	return pc
}

// Start begins processing tasks.
func (tq *TaskQueue) Start(scheduler Scheduler) {
	tq.mutex.Lock()
	tq.running = true
	tq.mutex.Unlock()
	// start workers!
	var j uint
	for j = 0; j < tq.numJobs; j++ {
		go func() {
			for job := range tq.nextTask {
				job()
			}
		}()
	}
	if scheduler == nil {
		scheduler = SimpleScheduler
	}
	go func() {
		for tq.running {
			workQueued := scheduler(tq)
			if !workQueued {
				time.Sleep(1 * time.Millisecond)
			}
		}
	}()
}

// Stop pauses processing of tasks. TaskQueue state is retained.
func (tq *TaskQueue) Stop() {
	tq.mutex.Lock()
	defer tq.mutex.Unlock()
	tq.running = false
}