package boomer

import (
	"fmt"
	"math/rand"
	"os"
	"runtime/debug"
	"sync"
	"sync/atomic"
	"time"

	"github.com/rs/zerolog/log"
)

const (
	stateInit     = "ready"
	stateSpawning = "spawning"
	stateRunning  = "running"
	stateStopped  = "stopped"
	stateQuitting = "quitting"
)

const (
	reportStatsInterval = 3 * time.Second
)

type runner struct {
	state string

	tasks           []*Task
	totalTaskWeight int

	rateLimiter      RateLimiter
	rateLimitEnabled bool
	stats            *requestStats

	numClients int32
	spawnRate  float64

	// all running workers(goroutines) will select on this channel.
	// close this channel will stop all running workers.
	stopChan chan bool

	// close this channel will stop all goroutines used in runner.
	closeChan chan bool

	outputs []Output
}

// safeRun runs fn and recovers from unexpected panics.
// it prevents panics from Task.Fn crashing boomer.
func (r *runner) safeRun(fn func()) {
	defer func() {
		// don't panic
		err := recover()
		if err != nil {
			stackTrace := debug.Stack()
			errMsg := fmt.Sprintf("%v", err)
			os.Stderr.Write([]byte(errMsg))
			os.Stderr.Write([]byte("\n"))
			os.Stderr.Write(stackTrace)
		}
	}()
	fn()
}

func (r *runner) addOutput(o Output) {
	r.outputs = append(r.outputs, o)
}

func (r *runner) outputOnStart() {
	size := len(r.outputs)
	if size == 0 {
		return
	}
	wg := sync.WaitGroup{}
	wg.Add(size)
	for _, output := range r.outputs {
		go func(o Output) {
			o.OnStart()
			wg.Done()
		}(output)
	}
	wg.Wait()
}

func (r *runner) outputOnEevent(data map[string]interface{}) {
	size := len(r.outputs)
	if size == 0 {
		return
	}
	wg := sync.WaitGroup{}
	wg.Add(size)
	for _, output := range r.outputs {
		go func(o Output) {
			o.OnEvent(data)
			wg.Done()
		}(output)
	}
	wg.Wait()
}

func (r *runner) outputOnStop() {
	size := len(r.outputs)
	if size == 0 {
		return
	}
	wg := sync.WaitGroup{}
	wg.Add(size)
	for _, output := range r.outputs {
		go func(o Output) {
			o.OnStop()
			wg.Done()
		}(output)
	}
	wg.Wait()
}

func (r *runner) spawnWorkers(spawnCount int, quit chan bool, spawnCompleteFunc func()) {
	log.Info().Int("spawnCount", spawnCount).Msg("Spawning clients immediately")

	for i := 1; i <= spawnCount; i++ {
		select {
		case <-quit:
			// quit spawning goroutine
			return
		default:
			atomic.AddInt32(&r.numClients, 1)
			go func() {
				for {
					select {
					case <-quit:
						return
					default:
						if r.rateLimitEnabled {
							blocked := r.rateLimiter.Acquire()
							if !blocked {
								task := r.getTask()
								r.safeRun(task.Fn)
							}
						} else {
							task := r.getTask()
							r.safeRun(task.Fn)
						}
					}
				}
			}()
		}
	}

	if spawnCompleteFunc != nil {
		spawnCompleteFunc()
	}
}

// setTasks will set the runner's task list AND the total task weight
// which is used to get a random task later
func (r *runner) setTasks(t []*Task) {
	r.tasks = t

	weightSum := 0
	for _, task := range r.tasks {
		weightSum += task.Weight
	}
	r.totalTaskWeight = weightSum
}

func (r *runner) getTask() *Task {
	tasksCount := len(r.tasks)
	if tasksCount == 1 {
		// Fast path
		return r.tasks[0]
	}

	rs := rand.New(rand.NewSource(time.Now().UnixNano()))

	totalWeight := r.totalTaskWeight
	if totalWeight <= 0 {
		// If all the tasks have not weights defined, they have the same chance to run
		randNum := rs.Intn(tasksCount)
		return r.tasks[randNum]
	}

	randNum := rs.Intn(totalWeight)
	runningSum := 0
	for _, task := range r.tasks {
		runningSum += task.Weight
		if runningSum > randNum {
			return task
		}
	}

	return nil
}

func (r *runner) startSpawning(spawnCount int, spawnRate float64, spawnCompleteFunc func()) {
	r.stats.clearStatsChan <- true
	r.stopChan = make(chan bool)

	r.numClients = 0

	go r.spawnWorkers(spawnCount, r.stopChan, spawnCompleteFunc)
}

func (r *runner) stop() {
	// stop previous goroutines without blocking
	// those goroutines will exit when r.safeRun returns
	close(r.stopChan)
	if r.rateLimitEnabled {
		r.rateLimiter.Stop()
	}
}

type localRunner struct {
	runner

	spawnCount int
}

func newLocalRunner(tasks []*Task, rateLimiter RateLimiter, spawnCount int, spawnRate float64) (r *localRunner) {
	r = &localRunner{}
	r.setTasks(tasks)
	r.spawnRate = spawnRate
	r.spawnCount = spawnCount
	r.closeChan = make(chan bool)

	if rateLimiter != nil {
		r.rateLimitEnabled = true
		r.rateLimiter = rateLimiter
	}

	r.stats = newRequestStats()
	return r
}

func (r *localRunner) run() {
	r.state = stateInit
	r.stats.start()
	r.outputOnStart()

	wg := sync.WaitGroup{}
	wg.Add(1)
	go func() {
		for {
			select {
			case data := <-r.stats.messageToRunnerChan:
				data["user_count"] = r.numClients
				r.outputOnEevent(data)
			case <-r.closeChan:
				r.stop()
				wg.Done()
				r.outputOnStop()
				return
			}
		}
	}()

	if r.rateLimitEnabled {
		r.rateLimiter.Start()
	}
	r.startSpawning(r.spawnCount, r.spawnRate, nil)

	wg.Wait()
}

func (r *localRunner) close() {
	if r.stats != nil {
		r.stats.close()
	}
	close(r.closeChan)
}