package models

import (
	"context"
	"log"
	"time"

	"gorm.io/gorm"
)

// ReapExpiredTasks is the periodic cleanup function described in
// docs/plans/worker-notifier-mvp.md section 8.5:
//
//   - tasks in state='leased' whose lease_expires_at is past are returned to
//     state='queued' and have their lease_owner cleared, so the next selector
//     poll can pick them up.
//   - tasks in state='failed_retry' whose not_before is past AND
//     attempts >= max_attempts are moved to state='dead' so they show up on
//     the admin dead-letter page and stop consuming selector bandwidth.
//
// It returns the number of rows it touched so the caller can log a metric.
// Cheap enough to run from the web process every 30s.
func ReapExpiredTasks() (reaped int, deaded int, err error) {
	now := time.Now()
	err = DB().Transaction(func(tx *gorm.DB) error {
		if err := expireQueuedNotificationTasksTx(tx, now); err != nil {
			return err
		}
		var expired []Task
		if err := tx.Where("state = ? AND lease_expires_at IS NOT NULL AND lease_expires_at < ?", TaskStateLeased, now).Find(&expired).Error; err != nil {
			return err
		}
		for i := range expired {
			if expired[i].Attempts >= expired[i].MaxAttempts {
				result := tx.Model(&Task{}).Where("id = ? AND state = ?", expired[i].ID, TaskStateLeased).Updates(map[string]interface{}{"state": TaskStateDead, "lease_owner": "", "lease_token": "", "lease_expires_at": nil, "last_error": "lease expired after max attempts", "updated_at": now})
				if result.Error != nil {
					return result.Error
				}
				if result.RowsAffected == 1 {
					deaded++
					if err := FinalizeNotificationTaskTx(tx, &expired[i], "dead", "lease expired after max attempts"); err != nil {
						return err
					}
				}
				continue
			}
			result := tx.Model(&Task{}).Where("id = ? AND state = ?", expired[i].ID, TaskStateLeased).Updates(map[string]interface{}{"state": TaskStateQueued, "lease_owner": "", "lease_token": "", "lease_expires_at": nil, "updated_at": now})
			if result.Error != nil {
				return result.Error
			}
			reaped += int(result.RowsAffected)
		}
		var exhausted []Task
		if err := tx.Where("state = ? AND not_before <= ? AND attempts >= max_attempts", TaskStateFailedRetry, now).Find(&exhausted).Error; err != nil {
			return err
		}
		for i := range exhausted {
			result := tx.Model(&Task{}).Where("id = ? AND state = ?", exhausted[i].ID, TaskStateFailedRetry).Updates(map[string]interface{}{"state": TaskStateDead, "updated_at": now})
			if result.Error != nil {
				return result.Error
			}
			if result.RowsAffected == 1 {
				deaded++
				if err := FinalizeNotificationTaskTx(tx, &exhausted[i], "dead", exhausted[i].LastError); err != nil {
					return err
				}
			}
		}
		return nil
	})
	return reaped, deaded, err
}

// FinalizeNotificationTaskTx makes a terminal notification task customer-visible
// and auditable. The caller owns the task state transition in this transaction.
func FinalizeNotificationTaskTx(tx *gorm.DB, task *Task, status, reason string) error {
	if task == nil || task.Kind != TaskKindNotification || task.MessageID == nil {
		return nil
	}
	if err := tx.Model(&Message{}).Where("id = ? AND state NOT IN ?", *task.MessageID, []string{"sent", "error"}).Updates(map[string]interface{}{"state": "error", "error": reason}).Error; err != nil {
		return err
	}
	return tx.Create(&NotificationDelivery{MessageID: *task.MessageID, TaskID: task.ID, Status: status, Error: reason}).Error
}

func expireQueuedNotificationTasksTx(tx *gorm.DB, now time.Time) error {
	var tasks []Task
	if err := tx.Where("state = ? AND kind = ? AND deadline IS NOT NULL AND deadline <= ?", TaskStateQueued, TaskKindNotification, now).Find(&tasks).Error; err != nil {
		return err
	}
	for i := range tasks {
		result := tx.Model(&Task{}).Where("id = ? AND state = ?", tasks[i].ID, TaskStateQueued).Updates(map[string]interface{}{
			"state": TaskStateDead, "last_error": "notification deadline expired", "updated_at": now,
		})
		if result.Error != nil || result.RowsAffected == 0 {
			if result.Error != nil {
				return result.Error
			}
			continue
		}
		if err := FinalizeNotificationTaskTx(tx, &tasks[i], "expired", "notification deadline expired"); err != nil {
			return err
		}
	}
	return nil
}

// StartTaskReaper launches a goroutine that runs ReapExpiredTasks on the given
// interval. It honors ctx.Done() so the caller can wind it down without
// leaking. The function is safe to call once per process; the control plane
// runs the reaper from main.init() so only one ticker ever exists in a single
// web process.
func StartTaskReaper(ctx context.Context, interval time.Duration) {
	if interval <= 0 {
		interval = 30 * time.Second
	}
	go func() {
		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:
				reaped, deaded, err := ReapExpiredTasks()
				if err != nil {
					log.Printf("task_reaper: error: %v", err)
					continue
				}
				if reaped > 0 || deaded > 0 {
					log.Printf("task_reaper: reaped=%d dead=%d", reaped, deaded)
				}
			}
		}
	}()
}