package dispenser

import (
	"context"
	"sync"
	"time"

	log "github.com/sirupsen/logrus"
)

const maintenanceInterval = time.Minute
const maintenanceTimeout = 5 * time.Second

// activityGuard arbitrates admission, not the duration of serial transactions.
// The serial worker remains the sole owner of the port and deliveryPending.
type activityGuard struct {
	sync.Mutex
	foreground int
	generation uint64
	enabled    bool
	closed     bool
	next       time.Time
	cancel     context.CancelFunc
	finished   chan struct{}
}

func (c *Client) wakeWorker() {
	select {
	case c.activityWake <- struct{}{}:
	default:
	}
}

// BeginForeground suppresses idle work until the returned release function runs.
func (c *Client) BeginForeground() func() {
	c.activity.Lock()
	c.activity.foreground++
	c.activity.generation++
	c.activity.next = time.Time{}
	c.activity.Unlock()
	c.wakeWorker()
	var once sync.Once
	return func() {
		once.Do(func() {
			c.activity.Lock()
			c.activity.foreground--
			if c.activity.foreground == 0 && c.activity.enabled && !c.activity.closed {
				c.activity.next = c.now().Add(maintenanceInterval)
			}
			c.activity.Unlock()
			c.wakeWorker()
		})
	}
}

// StartMaintenance enables the worker timer once, with an initial one-minute delay.
func (c *Client) StartMaintenance() {
	c.activity.Lock()
	if !c.activity.enabled && !c.activity.closed {
		c.activity.enabled = true
		c.activity.generation++
		if c.activity.foreground == 0 {
			c.activity.next = c.now().Add(maintenanceInterval)
		}
	}
	c.activity.Unlock()
	c.wakeWorker()
}

// StopMaintenance prevents new admissions and waits for an admitted attempt to exit.
// An underlying serial read can finish only according to its existing read timeout.
func (c *Client) StopMaintenance() {
	c.activity.Lock()
	c.activity.enabled = false
	c.activity.generation++
	c.activity.next = time.Time{}
	if c.activity.cancel != nil {
		c.activity.cancel()
	}
	finished := c.activity.finished
	c.activity.Unlock()
	c.wakeWorker()
	if finished != nil {
		<-finished
	}
}

func (c *Client) maintenanceDelay() (time.Duration, bool) {
	c.activity.Lock()
	defer c.activity.Unlock()
	if !c.activity.enabled || c.activity.closed || c.activity.foreground != 0 || c.activity.next.IsZero() {
		return 0, false
	}
	remaining := c.activity.next.Sub(c.now())
	if remaining < 0 {
		remaining = 0
	}
	return remaining, true
}

func (c *Client) passiveGeneration() (uint64, bool) {
	c.activity.Lock()
	defer c.activity.Unlock()
	return c.activity.generation, c.activity.foreground == 0 && !c.activity.closed
}

func (c *Client) admitPassive(ctx context.Context, generation uint64) bool {
	c.activity.Lock()
	defer c.activity.Unlock()
	return ctx.Err() == nil && !c.activity.closed && c.activity.foreground == 0 && c.activity.generation == generation
}

func (c *Client) admitMaintenance(ctx context.Context, generation uint64) bool {
	c.activity.Lock()
	defer c.activity.Unlock()
	return ctx.Err() == nil && c.activity.enabled && !c.activity.closed && c.activity.foreground == 0 && c.activity.generation == generation
}

// maintainIdleCard is called only by the serial worker, never through its queue.
func (c *Client) maintainIdleCard() {
	c.activity.Lock()
	if !c.activity.enabled || c.activity.closed || c.activity.foreground != 0 || c.activity.next.IsZero() || c.now().Before(c.activity.next) {
		c.activity.Unlock()
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), maintenanceTimeout)
	generation := c.activity.generation
	finished := make(chan struct{})
	c.activity.cancel, c.activity.finished = cancel, finished
	c.activity.Unlock()
	defer func() {
		cancel()
		c.activity.Lock()
		c.activity.cancel, c.activity.finished = nil, nil
		if c.activity.enabled && !c.activity.closed && c.activity.foreground == 0 && c.activity.generation == generation {
			c.activity.next = c.now().Add(maintenanceInterval)
		}
		close(finished)
		c.activity.Unlock()
	}()
	if !c.admitMaintenance(ctx, generation) {
		return
	}
	// Quiet observation: do not publish stock callbacks or manufacture cached status.
	st, err := checkDispenserStatus(ctx, c.port)
	if err != nil {
		log.Debugf("idle dispenser maintenance AP: %v", err)
		return
	}
	class, err := classifyPreparationStatus(st)
	if err != nil {
		log.Debugf("idle dispenser maintenance unusable AP: %v", err)
		return
	}
	log.Debugf("idle dispenser maintenance AP; class=%s raw status: % X", class, st)
	if class == encoderConfirmed || class == positionWellEmpty {
		return
	}
	clear, err := deliveryClearance(st)
	if err != nil || !clear {
		return
	}
	if c.deliveryPending && c.now().Sub(c.deliveryStarted) < deliveryMinimumWait {
		return
	}
	// This is the admission boundary shared with foreground registration and stop.
	if !c.admitMaintenance(ctx, generation) {
		return
	}
	if c.deliveryPending {
		c.deliveryPending = false
	}
	err = cardToEncoderPosition(ctx, c.port)
	c.invalidateStatusCache()
	if err != nil {
		log.Warnf("idle dispenser maintenance FC7 dispatch: %v", err)
		return
	}
	log.Info("idle dispenser maintenance FC7 dispatched")
}