package service

import (
	"context"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"github.com/ez-api/ez-api/internal/model"
	"github.com/ez-api/foundation/jsoncodec"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

const (
	outboxStatusPending = "pending"
	outboxStatusFailed  = "failed"
)

// SyncOutboxConfig controls retry behavior for CP -> Redis sync failures.
type SyncOutboxConfig struct {
	Enabled    bool
	Interval   time.Duration
	BatchSize  int
	MaxRetries int
}

// SyncOutboxEntry captures a sync operation for retry.
type SyncOutboxEntry struct {
	ResourceType string
	Action       string
	ResourceID   *uint
	Payload      any
}

// SyncOutboxService retries failed sync operations stored in the database.
type SyncOutboxService struct {
	db      *gorm.DB
	sync    *SyncService
	cfg     SyncOutboxConfig
	logger  *slog.Logger
	started bool
}

func NewSyncOutboxService(db *gorm.DB, sync *SyncService, cfg SyncOutboxConfig, logger *slog.Logger) *SyncOutboxService {
	if logger == nil {
		logger = slog.Default()
	}
	if cfg.Interval <= 0 {
		cfg.Interval = 5 * time.Second
	}
	if cfg.BatchSize <= 0 {
		cfg.BatchSize = 200
	}
	if cfg.MaxRetries <= 0 {
		cfg.MaxRetries = 10
	}
	return &SyncOutboxService{db: db, sync: sync, cfg: cfg, logger: logger}
}

func (s *SyncOutboxService) Enabled() bool {
	return s != nil && s.cfg.Enabled
}

// Enqueue persists a failed sync operation for retry.
func (s *SyncOutboxService) Enqueue(entry SyncOutboxEntry) error {
	if s == nil || !s.cfg.Enabled {
		return fmt.Errorf("sync outbox disabled")
	}
	if s.db == nil {
		return fmt.Errorf("sync outbox db missing")
	}
	entry.ResourceType = strings.TrimSpace(entry.ResourceType)
	entry.Action = strings.TrimSpace(entry.Action)
	if entry.ResourceType == "" || entry.Action == "" {
		return fmt.Errorf("resource_type and action required")
	}

	payload := ""
	if entry.Payload != nil {
		if raw, err := jsoncodec.Marshal(entry.Payload); err == nil {
			payload = string(raw)
		}
	}

	next := time.Now().UTC()
	outbox := model.SyncOutbox{
		ResourceType: entry.ResourceType,
		Action:       entry.Action,
		ResourceID:   entry.ResourceID,
		Payload:      payload,
		RetryCount:   0,
		LastError:    "",
		NextRetryAt:  &next,
		Status:       outboxStatusPending,
	}
	if err := s.db.Create(&outbox).Error; err != nil {
		return err
	}
	return nil
}

// Start begins the background retry loop.
func (s *SyncOutboxService) Start(ctx context.Context) {
	if s == nil || !s.cfg.Enabled || s.started {
		return
	}
	s.started = true

	ticker := time.NewTicker(s.cfg.Interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			s.processBatch(ctx)
		}
	}
}

func (s *SyncOutboxService) processBatch(ctx context.Context) {
	if s == nil || !s.cfg.Enabled || s.db == nil || s.sync == nil {
		return
	}
	if ctx == nil {
		ctx = context.Background()
	}

	now := time.Now().UTC()
	var items []model.SyncOutbox
	q := s.db.WithContext(ctx).
		Where("status = ?", outboxStatusPending).
		Where("next_retry_at <= ?", now).
		Order("id asc").
		Limit(s.cfg.BatchSize)
	if err := q.Clauses(clause.Locking{Strength: "UPDATE", Options: "SKIP LOCKED"}).Find(&items).Error; err != nil {
		s.logger.Warn("sync outbox load failed", "err", err)
		return
	}
	for i := range items {
		item := items[i]
		if err := s.processItem(ctx, &item); err != nil {
			s.logger.Warn("sync outbox retry failed", "id", item.ID, "err", err)
		}
	}
}

func (s *SyncOutboxService) processItem(ctx context.Context, item *model.SyncOutbox) error {
	if item == nil {
		return nil
	}
	if err := s.applyItem(ctx, item); err != nil {
		return s.recordFailure(ctx, item, err)
	}
	return s.db.WithContext(ctx).Delete(&model.SyncOutbox{}, item.ID).Error
}

func (s *SyncOutboxService) recordFailure(ctx context.Context, item *model.SyncOutbox, err error) error {
	item.RetryCount++
	item.LastError = err.Error()
	if item.RetryCount >= s.cfg.MaxRetries {
		item.Status = outboxStatusFailed
		item.NextRetryAt = nil
		s.logger.Error("sync outbox max retries reached", "id", item.ID, "resource_type", item.ResourceType, "action", item.Action, "err", err)
	} else {
		next := time.Now().UTC().Add(s.cfg.Interval)
		item.NextRetryAt = &next
	}
	return s.db.WithContext(ctx).Save(item).Error
}

func (s *SyncOutboxService) applyItem(ctx context.Context, item *model.SyncOutbox) error {
	resource := strings.TrimSpace(item.ResourceType)
	action := strings.TrimSpace(item.Action)
	if resource == "" || action == "" {
		return fmt.Errorf("resource_type/action missing")
	}

	switch resource {
	case "master":
		return s.applyMaster(ctx, item)
	case "key":
		return s.applyKey(ctx, item)
	case "model":
		return s.applyModel(ctx, item)
	case "provider_group", "api_key":
		switch action {
		case "sync_bindings":
			return s.sync.SyncBindingsNow(ctx, s.db)
		case "sync_providers":
			return s.sync.SyncProvidersNow(ctx, s.db)
		default:
			return fmt.Errorf("unsupported %s action: %s", resource, action)
		}
	case "binding":
		return s.sync.SyncBindingsNow(ctx, s.db)
	case "snapshot":
		switch action {
		case "sync_all":
			return s.sync.SyncAllNow(ctx, s.db)
		case "sync_bindings":
			return s.sync.SyncBindingsNow(ctx, s.db)
		case "sync_providers":
			return s.sync.SyncProvidersNow(ctx, s.db)
		default:
			return fmt.Errorf("unsupported snapshot action: %s", action)
		}
	default:
		return fmt.Errorf("unsupported resource_type: %s", resource)
	}
}

func (s *SyncOutboxService) applyMaster(ctx context.Context, item *model.SyncOutbox) error {
	if item.ResourceID == nil {
		return fmt.Errorf("master id missing")
	}
	var m model.Master
	if err := s.db.WithContext(ctx).First(&m, *item.ResourceID).Error; err != nil {
		return err
	}
	return s.sync.SyncMasterNow(ctx, &m)
}

func (s *SyncOutboxService) applyKey(ctx context.Context, item *model.SyncOutbox) error {
	if item.ResourceID == nil {
		return fmt.Errorf("key id missing")
	}
	var k model.Key
	if err := s.db.WithContext(ctx).First(&k, *item.ResourceID).Error; err != nil {
		return err
	}
	return s.sync.SyncKeyNow(ctx, &k)
}

func (s *SyncOutboxService) applyModel(ctx context.Context, item *model.SyncOutbox) error {
	action := strings.TrimSpace(item.Action)
	switch action {
	case "delete":
		var payload struct {
			Name string `json:"name"`
		}
		if item.Payload != "" {
			if err := jsoncodec.Unmarshal([]byte(item.Payload), &payload); err != nil {
				return err
			}
		}
		if strings.TrimSpace(payload.Name) == "" {
			return fmt.Errorf("model name missing")
		}
		m := model.Model{Name: strings.TrimSpace(payload.Name)}
		return s.sync.SyncModelDeleteNow(ctx, &m)
	default:
		if item.ResourceID == nil {
			return fmt.Errorf("model id missing")
		}
		var m model.Model
		if err := s.db.WithContext(ctx).First(&m, *item.ResourceID).Error; err != nil {
			return err
		}
		return s.sync.SyncModelNow(ctx, &m)
	}
}