package notification

import (
	"context"
	"errors"
	"fmt"
	"time"

	"galaxy/backend/internal/user"

	"github.com/google/uuid"
	"go.uber.org/zap"
)

// Submit accepts a producer intent, validates it against the catalog,
// resolves recipients, materialises route rows, persists everything in
// one transaction, and best-effort dispatches the routes synchronously.
//
// The contract: producers never block on Submit, and Submit never
// surfaces a validation failure as an error — malformed intents go to
// `notification_malformed_intents` and the call returns nil. Real
// errors (encoder failure, Postgres trouble) are wrapped and returned.
//
// On idempotent re-submit (same kind + idempotency_key) the existing
// notification id is honoured and route materialisation is skipped.
func (s *Service) Submit(ctx context.Context, intent Intent) (uuid.UUID, error) {
	entry, ok := LookupCatalog(intent.Kind)
	if !ok {
		s.recordMalformed(ctx, intent, ErrUnknownKind.Error())
		return uuid.Nil, nil
	}
	if trimSpace(intent.IdempotencyKey) == "" {
		s.recordMalformed(ctx, intent, ErrEmptyIdempotencyKey.Error())
		return uuid.Nil, nil
	}
	if !entry.Admin && len(intent.Recipients) == 0 {
		s.recordMalformed(ctx, intent, ErrNoRecipients.Error())
		return uuid.Nil, nil
	}

	now := s.nowUTC()
	notificationID := uuid.New()
	var primaryUserID *uuid.UUID
	if !entry.Admin && len(intent.Recipients) == 1 {
		uid := intent.Recipients[0]
		primaryUserID = &uid
	}

	routes, err := s.materialiseRoutes(ctx, notificationID, entry, intent, now)
	if err != nil {
		return uuid.Nil, err
	}

	storedID, inserted, err := s.deps.Store.InsertNotification(ctx, InsertNotificationArgs{
		NotificationID: notificationID,
		Kind:           intent.Kind,
		IdempotencyKey: intent.IdempotencyKey,
		UserID:         primaryUserID,
		Payload:        intent.Payload,
		Routes:         routes,
	})
	if err != nil {
		return uuid.Nil, fmt.Errorf("notification submit: %w", err)
	}
	if !inserted {
		s.deps.Logger.Debug("idempotent submit, returning existing notification",
			zap.String("kind", intent.Kind),
			zap.String("idempotency_key", intent.IdempotencyKey),
			zap.String("notification_id", storedID.String()),
		)
		return storedID, nil
	}

	// Best-effort synchronous dispatch: any pending route gets a single
	// attempt right now. Failures stay on the row for the worker to
	// retry; they are not surfaced to producers.
	for i := range routes {
		if routes[i].Status != RouteStatusPending {
			continue
		}
		s.bestEffortDispatch(ctx, Notification{
			NotificationID: notificationID,
			Kind:           intent.Kind,
			IdempotencyKey: intent.IdempotencyKey,
			UserID:         primaryUserID,
			Payload:        intent.Payload,
			CreatedAt:      now,
		}, routeFromSeed(notificationID, routes[i], now))
	}

	return notificationID, nil
}

// materialiseRoutes builds the per-(recipient, channel) seeds that
// land in `notification_routes`. The function performs recipient
// resolution and the catalog-aware channel fan-out. Each seed already
// carries its terminal status (`pending` for live routes, `skipped`
// for cases where the destination cannot be resolved).
func (s *Service) materialiseRoutes(ctx context.Context, notificationID uuid.UUID, entry CatalogEntry, intent Intent, now time.Time) ([]RouteSeed, error) {
	_ = notificationID
	maxAttempts := int32(s.deps.Config.MaxAttempts)
	if maxAttempts <= 0 {
		maxAttempts = 1
	}
	pendingNext := timePtr(now.UTC())

	if entry.Admin {
		// Admin-channel kinds: one row per channel, no per-user fan-out.
		seeds := make([]RouteSeed, 0, len(entry.Channels))
		for _, ch := range entry.Channels {
			seed := RouteSeed{
				RouteID:     uuid.New(),
				Channel:     ch,
				Status:      RouteStatusPending,
				MaxAttempts: maxAttempts,
				NextAttemptAt: pendingNext,
			}
			if ch == ChannelEmail {
				seed.ResolvedEmail = s.adminEmail()
				if seed.ResolvedEmail == "" {
					seed.Status = RouteStatusSkipped
					seed.NextAttemptAt = nil
					seed.SkippedAt = timePtr(now.UTC())
					seed.LastError = "BACKEND_NOTIFICATION_ADMIN_EMAIL not configured"
					s.deps.Logger.Warn("admin notification skipped: admin email not configured",
						zap.String("kind", intent.Kind),
						zap.String("idempotency_key", intent.IdempotencyKey),
					)
				}
			}
			seeds = append(seeds, seed)
		}
		return seeds, nil
	}

	// Per-user kinds: fan out across (recipient × channel).
	seeds := make([]RouteSeed, 0, len(intent.Recipients)*len(entry.Channels))
	for _, userID := range intent.Recipients {
		uid := userID
		account, err := s.resolveAccount(ctx, userID)
		for _, ch := range entry.Channels {
			seed := RouteSeed{
				RouteID:         uuid.New(),
				Channel:         ch,
				Status:          RouteStatusPending,
				MaxAttempts:     maxAttempts,
				NextAttemptAt:   pendingNext,
				UserID:          &uid,
				DeviceSessionID: intent.DeviceSessionID,
			}
			switch ch {
			case ChannelEmail:
				if err != nil {
					seed.Status = RouteStatusSkipped
					seed.NextAttemptAt = nil
					seed.SkippedAt = timePtr(now.UTC())
					seed.LastError = err.Error()
				} else {
					seed.ResolvedEmail = account.Email
					seed.ResolvedLocale = account.PreferredLanguage
					if trimSpace(seed.ResolvedEmail) == "" {
						seed.Status = RouteStatusSkipped
						seed.NextAttemptAt = nil
						seed.SkippedAt = timePtr(now.UTC())
						seed.LastError = "recipient has no email on file"
					}
				}
			case ChannelPush:
				if err != nil {
					seed.Status = RouteStatusSkipped
					seed.NextAttemptAt = nil
					seed.SkippedAt = timePtr(now.UTC())
					seed.LastError = err.Error()
				} else if account.PreferredLanguage != "" {
					seed.ResolvedLocale = account.PreferredLanguage
				}
			}
			seeds = append(seeds, seed)
		}
	}
	return seeds, nil
}

// resolveAccount fetches the recipient profile through the configured
// AccountResolver. user.ErrAccountNotFound is mapped to a sentinel-free
// error string so the route is skipped without a stack-trace log.
func (s *Service) resolveAccount(ctx context.Context, userID uuid.UUID) (user.Account, error) {
	account, err := s.deps.Accounts.GetAccount(ctx, userID)
	if err != nil {
		if errors.Is(err, user.ErrAccountNotFound) {
			return user.Account{}, errors.New("recipient account not found")
		}
		return user.Account{}, fmt.Errorf("resolve recipient %s: %w", userID, err)
	}
	if account.DeletedAt != nil {
		return user.Account{}, errors.New("recipient account soft-deleted")
	}
	return account, nil
}

// recordMalformed best-effort persists an invalid intent. Logger is
// informational; a Postgres failure here is logged but never bubbles
// up to the producer, matching the README §10 contract.
func (s *Service) recordMalformed(ctx context.Context, intent Intent, reason string) {
	payload := map[string]any{
		"kind":            intent.Kind,
		"idempotency_key": intent.IdempotencyKey,
	}
	if len(intent.Payload) > 0 {
		payload["payload"] = intent.Payload
	}
	if len(intent.Recipients) > 0 {
		recipients := make([]string, 0, len(intent.Recipients))
		for _, r := range intent.Recipients {
			recipients = append(recipients, r.String())
		}
		payload["recipients"] = recipients
	}
	if intent.DeviceSessionID != nil {
		payload["device_session_id"] = intent.DeviceSessionID.String()
	}
	if err := s.deps.Store.InsertMalformed(ctx, payload, reason); err != nil {
		s.deps.Logger.Warn("failed to persist malformed notification intent",
			zap.String("kind", intent.Kind),
			zap.String("reason", reason),
			zap.Error(err),
		)
		return
	}
	s.deps.Logger.Info("notification intent dropped as malformed",
		zap.String("kind", intent.Kind),
		zap.String("reason", reason),
	)
}

// routeFromSeed converts a RouteSeed (the pre-insert snapshot the
// dispatcher needs) to a Route value the worker / dispatcher exchange
// after the row is durably persisted.
func routeFromSeed(notificationID uuid.UUID, seed RouteSeed, now time.Time) Route {
	r := Route{
		RouteID:         seed.RouteID,
		NotificationID:  notificationID,
		Channel:         seed.Channel,
		Status:          seed.Status,
		Attempts:        0,
		MaxAttempts:     seed.MaxAttempts,
		NextAttemptAt:   seed.NextAttemptAt,
		ResolvedEmail:   seed.ResolvedEmail,
		ResolvedLocale:  seed.ResolvedLocale,
		UserID:          seed.UserID,
		DeviceSessionID: seed.DeviceSessionID,
		CreatedAt:       now.UTC(),
		UpdatedAt:       now.UTC(),
		SkippedAt:       seed.SkippedAt,
		LastError:       seed.LastError,
	}
	return r
}