package boomer

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

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

const (
	stateInit     = iota + 1 // initializing
	stateSpawning            // spawning
	stateRunning             // running
	stateQuitting            // quitting
	stateStopped             // stopped
)

const (
	reportStatsInterval = 3 * time.Second
)

type runner struct {
	state int32

	tasks           []*Task
	totalTaskWeight int

	rateLimiter      RateLimiter
	rateLimitEnabled bool
	stats            *requestStats

	currentClientsNum int32 // current clients count
	spawnCount        int   // target clients to spawn
	spawnRate         float64

	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, spawnRate float64, quit chan bool, spawnCompleteFunc func()) {
	log.Info().
		Int("spawnCount", spawnCount).
		Float64("spawnRate", spawnRate).
		Msg("Spawning workers")

	atomic.StoreInt32(&r.state, stateSpawning)
	for i := 1; i <= spawnCount; i++ {
		// spawn workers with rate limit
		sleepTime := time.Duration(1000000/r.spawnRate) * time.Microsecond
		time.Sleep(sleepTime)

		select {
		case <-quit:
			// quit spawning goroutine
			log.Info().Msg("Quitting spawning workers")
			return
		default:
			atomic.AddInt32(&r.currentClientsNum, 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()
	}
	atomic.StoreInt32(&r.state, stateRunning)
}

// 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
}

type localRunner struct {
	runner

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

func newLocalRunner(spawnCount int, spawnRate float64) *localRunner {
	return &localRunner{
		runner: runner{
			state:      stateInit,
			spawnRate:  spawnRate,
			spawnCount: spawnCount,
			stats:      newRequestStats(),
			outputs:    make([]Output, 0),
		},
		stopChan: make(chan bool),
	}
}

func (r *localRunner) start() {
	// init state
	atomic.StoreInt32(&r.state, stateInit)
	atomic.StoreInt32(&r.currentClientsNum, 0)
	r.stats.clearAll()

	// start rate limiter
	if r.rateLimitEnabled {
		r.rateLimiter.Start()
	}

	// all running workers(goroutines) will select on this channel.
	// close this channel will stop all running workers.
	quitChan := make(chan bool)
	go r.spawnWorkers(r.spawnCount, r.spawnRate, quitChan, nil)

	// output setup
	r.outputOnStart()

	// start running
	var ticker = time.NewTicker(reportStatsInterval)
	for {
		select {
		// record stats
		case t := <-r.stats.transactionChan:
			r.stats.logTransaction(t.name, t.success, t.elapsedTime, t.contentSize)
		case m := <-r.stats.requestSuccessChan:
			r.stats.logRequest(m.requestType, m.name, m.responseTime, m.responseLength)
		case n := <-r.stats.requestFailureChan:
			r.stats.logRequest(n.requestType, n.name, n.responseTime, 0)
			r.stats.logError(n.requestType, n.name, n.errMsg)
		// report stats
		case <-ticker.C:
			data := r.stats.collectReportData()
			data["user_count"] = atomic.LoadInt32(&r.currentClientsNum)
			data["state"] = atomic.LoadInt32(&r.state)
			r.outputOnEevent(data)
		// stop
		case <-r.stopChan:
			atomic.StoreInt32(&r.state, stateQuitting)

			// stop previous goroutines without blocking
			// those goroutines will exit when r.safeRun returns
			close(quitChan)

			// stop rate limiter
			if r.rateLimitEnabled {
				r.rateLimiter.Stop()
			}

			// output teardown
			r.outputOnStop()

			atomic.StoreInt32(&r.state, stateStopped)
			return
		}
	}
}

func (r *localRunner) stop() {
	close(r.stopChan)
}