package dataext

import (
	"context"
	"sync"
	"time"

	"git.blackforestbytes.com/BlackForestBytes/goext/langext"
	"git.blackforestbytes.com/BlackForestBytes/goext/syncext"
)

type DelayedCombiningInvoker struct {
	syncLock           sync.Mutex
	triggerChan        chan bool
	cancelChan         chan bool
	execNowChan        chan bool
	action             func()
	delay              time.Duration
	maxDelay           time.Duration
	executorRunning    *syncext.AtomicBool
	pendingRequests    *syncext.Atomic[int]
	lastRequestTime    time.Time
	initialRequestTime time.Time

	onExecutionStart []func(immediately bool)          // listener ( actual execution of action starts )
	onExecutionDone  []func()                          // listener ( actual execution of action finished )
	onRequest        []func(pending int, initial bool) // listener ( a request came in, waiting for execution )
}

func NewDelayedCombiningInvoker(action func(), delay time.Duration, maxDelay time.Duration) *DelayedCombiningInvoker {
	return &DelayedCombiningInvoker{
		action:             action,
		delay:              delay,
		maxDelay:           maxDelay,
		executorRunning:    syncext.NewAtomicBool(false),
		pendingRequests:    syncext.NewAtomic[int](0),
		triggerChan:        make(chan bool),
		cancelChan:         make(chan bool, 1),
		execNowChan:        make(chan bool, 1),
		lastRequestTime:    time.Now(),
		initialRequestTime: time.Now(),
		onExecutionStart:   make([]func(bool), 0),
		onExecutionDone:    make([]func(), 0),
		onRequest:          make([]func(int, bool), 0),
	}
}

func (d *DelayedCombiningInvoker) Request() {
	now := time.Now()

	d.syncLock.Lock()
	defer d.syncLock.Unlock()

	if d.executorRunning.Get() {
		d.lastRequestTime = now
		d.pendingRequests.Update(func(v int) int { return v + 1 })

		for _, fn := range d.onRequest {
			_ = langext.RunPanicSafe(func() { fn(d.pendingRequests.Get(), true) })
		}

		d.triggerChan <- true
	} else {
		d.initialRequestTime = now
		d.lastRequestTime = now

		d.executorRunning.Set(true)
		d.pendingRequests.Set(1)
		syncext.ReadNonBlocking(d.triggerChan) // clear the channel
		syncext.ReadNonBlocking(d.cancelChan)  // clear the channel
		syncext.ReadNonBlocking(d.execNowChan) // clear the channel

		for _, fn := range d.onRequest {
			_ = langext.RunPanicSafe(func() { fn(d.pendingRequests.Get(), false) })
		}

		go d.run()
	}
}

func (d *DelayedCombiningInvoker) run() {
	defer func() {
		d.syncLock.Lock()
		d.executorRunning.Set(false)
		d.syncLock.Unlock()
	}()

	for {
		d.syncLock.Lock()
		timeOut := min(d.maxDelay-time.Since(d.initialRequestTime), d.delay-time.Since(d.lastRequestTime))
		if timeOut < 0 {
			timeOut = 0
		}
		d.syncLock.Unlock()

		immediately := false

		select {
		case <-d.execNowChan:
			// run immediately
			immediately = true
			break
		case <-d.triggerChan:
			// external trigger - needs to re-evaluate
			break
		case <-d.cancelChan:
			// cancel
			return
		case <-time.After(timeOut):
			// time elapsed - check for execution
			break

		}

		d.syncLock.Lock()
		execute := immediately || time.Since(d.lastRequestTime) >= d.delay || time.Since(d.initialRequestTime) >= d.maxDelay
		if !execute {
			d.syncLock.Unlock()
			continue
		}

		d.pendingRequests.Set(0)

		for _, fn := range d.onExecutionStart {
			_ = langext.RunPanicSafe(func() { fn(immediately) })
		}

		// =================================================
		_ = langext.RunPanicSafe(d.action)
		// =================================================

		for _, fn := range d.onExecutionDone {
			_ = langext.RunPanicSafe(fn)
		}

		d.syncLock.Unlock()

		return
	}
}

func (d *DelayedCombiningInvoker) CancelPendingRequests() {
	d.syncLock.Lock()
	defer d.syncLock.Unlock()

	syncext.WriteNonBlocking(d.cancelChan, true)
}

func (d *DelayedCombiningInvoker) HasPendingRequests() bool {
	return d.executorRunning.Get()
}

func (d *DelayedCombiningInvoker) CountPendingRequests() int {
	return d.pendingRequests.Get()
}

func (d *DelayedCombiningInvoker) ExecuteNow() bool {
	d.syncLock.Lock()
	defer d.syncLock.Unlock()

	if d.executorRunning.Get() {
		syncext.WriteNonBlocking(d.execNowChan, true)
		return true
	} else {
		return false
	}
}

func (d *DelayedCombiningInvoker) WaitForCompletion(ctx context.Context) error {
	return d.executorRunning.WaitWithContext(ctx, false)
}

func (d *DelayedCombiningInvoker) RegisterOnExecutionStart(fn func(immediately bool)) {
	d.syncLock.Lock()
	defer d.syncLock.Unlock()
	d.onExecutionStart = append(d.onExecutionStart, fn)
}

func (d *DelayedCombiningInvoker) RegisterOnExecutionDone(fn func()) {
	d.syncLock.Lock()
	defer d.syncLock.Unlock()
	d.onExecutionDone = append(d.onExecutionDone, fn)
}

func (d *DelayedCombiningInvoker) RegisterOnRequest(fn func(pending int, initial bool)) {
	d.syncLock.Lock()
	defer d.syncLock.Unlock()
	d.onRequest = append(d.onRequest, fn)
}