package redisstate

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

	"galaxy/mail/internal/domain/attempt"
	deliverydomain "galaxy/mail/internal/domain/delivery"
	"galaxy/mail/internal/domain/idempotency"
	"galaxy/mail/internal/service/acceptgenericdelivery"

	"github.com/redis/go-redis/v9"
)

// AtomicWriter performs the minimal multi-key Redis mutations that later Mail
// Service acceptance flows will need.
type AtomicWriter struct {
	client   *redis.Client
	keyspace Keyspace
}

// CreateAcceptanceInput describes the frozen write set required to durably
// accept one delivery into Redis-backed state.
type CreateAcceptanceInput struct {
	// Delivery stores the accepted delivery record.
	Delivery deliverydomain.Delivery

	// FirstAttempt stores the optional first scheduled attempt record.
	FirstAttempt *attempt.Attempt

	// DeliveryPayload stores the optional raw attachment payload bundle.
	DeliveryPayload *acceptgenericdelivery.DeliveryPayload

	// Idempotency stores the optional idempotency reservation to create
	// together with the delivery. Resend clone creation can omit it.
	Idempotency *idempotency.Record
}

// MarkRenderedInput describes the durable mutation applied after successful
// template materialization.
type MarkRenderedInput struct {
	// Delivery stores the rendered delivery record.
	Delivery deliverydomain.Delivery
}

// Validate reports whether input contains one rendered template delivery.
func (input MarkRenderedInput) Validate() error {
	if err := input.Delivery.Validate(); err != nil {
		return fmt.Errorf("delivery: %w", err)
	}
	if input.Delivery.PayloadMode != deliverydomain.PayloadModeTemplate {
		return fmt.Errorf("delivery payload mode must be %q", deliverydomain.PayloadModeTemplate)
	}
	if input.Delivery.Status != deliverydomain.StatusRendered {
		return fmt.Errorf("delivery status must be %q", deliverydomain.StatusRendered)
	}

	return nil
}

// MarkRenderFailedInput describes the durable mutation applied after one
// classified render failure.
type MarkRenderFailedInput struct {
	// Delivery stores the failed delivery record.
	Delivery deliverydomain.Delivery

	// Attempt stores the terminal render-failed attempt.
	Attempt attempt.Attempt
}

// Validate reports whether input contains one failed delivery and its
// terminal render-failed attempt.
func (input MarkRenderFailedInput) Validate() error {
	if err := input.Delivery.Validate(); err != nil {
		return fmt.Errorf("delivery: %w", err)
	}
	if err := input.Attempt.Validate(); err != nil {
		return fmt.Errorf("attempt: %w", err)
	}
	if input.Delivery.PayloadMode != deliverydomain.PayloadModeTemplate {
		return fmt.Errorf("delivery payload mode must be %q", deliverydomain.PayloadModeTemplate)
	}
	if input.Delivery.Status != deliverydomain.StatusFailed {
		return fmt.Errorf("delivery status must be %q", deliverydomain.StatusFailed)
	}
	if input.Attempt.Status != attempt.StatusRenderFailed {
		return fmt.Errorf("attempt status must be %q", attempt.StatusRenderFailed)
	}
	if input.Attempt.DeliveryID != input.Delivery.DeliveryID {
		return errors.New("attempt delivery id must match delivery id")
	}
	if input.Delivery.LastAttemptStatus != attempt.StatusRenderFailed {
		return fmt.Errorf("delivery last attempt status must be %q", attempt.StatusRenderFailed)
	}

	return nil
}

// Validate reports whether CreateAcceptanceInput is internally consistent.
func (input CreateAcceptanceInput) Validate() error {
	if err := input.Delivery.Validate(); err != nil {
		return fmt.Errorf("delivery: %w", err)
	}

	switch {
	case input.FirstAttempt == nil:
		if input.Delivery.Status != deliverydomain.StatusSuppressed {
			return errors.New("first attempt must not be nil unless delivery status is suppressed")
		}
	case input.Delivery.Status == deliverydomain.StatusSuppressed:
		return errors.New("suppressed delivery must not create first attempt")
	default:
		if err := input.FirstAttempt.Validate(); err != nil {
			return fmt.Errorf("first attempt: %w", err)
		}
		if input.FirstAttempt.DeliveryID != input.Delivery.DeliveryID {
			return errors.New("first attempt delivery id must match delivery id")
		}
		if input.FirstAttempt.Status != attempt.StatusScheduled {
			return fmt.Errorf("first attempt status must be %q", attempt.StatusScheduled)
		}
	}

	if input.DeliveryPayload != nil {
		if err := input.DeliveryPayload.Validate(); err != nil {
			return fmt.Errorf("delivery payload: %w", err)
		}
		if input.DeliveryPayload.DeliveryID != input.Delivery.DeliveryID {
			return errors.New("delivery payload delivery id must match delivery id")
		}
	}

	if input.Idempotency == nil {
		return nil
	}

	if err := input.Idempotency.Validate(); err != nil {
		return fmt.Errorf("idempotency: %w", err)
	}
	if input.Idempotency.DeliveryID != input.Delivery.DeliveryID {
		return errors.New("idempotency delivery id must match delivery id")
	}
	if input.Idempotency.Source != input.Delivery.Source {
		return errors.New("idempotency source must match delivery source")
	}
	if input.Idempotency.IdempotencyKey != input.Delivery.IdempotencyKey {
		return errors.New("idempotency key must match delivery idempotency key")
	}
	if input.Idempotency.ExpiresAt.Sub(input.Idempotency.CreatedAt) != IdempotencyTTL {
		return fmt.Errorf("idempotency retention must equal %s", IdempotencyTTL)
	}

	return nil
}

// NewAtomicWriter constructs a low-level Redis mutation helper.
func NewAtomicWriter(client *redis.Client) (*AtomicWriter, error) {
	if client == nil {
		return nil, errors.New("new redis atomic writer: nil client")
	}

	return &AtomicWriter{
		client:   client,
		keyspace: Keyspace{},
	}, nil
}

// CreateAcceptance stores one delivery, the optional first scheduled attempt,
// the optional first schedule entry, the delivery-level secondary indexes, and
// an optional idempotency record in one optimistic Redis transaction.
func (writer *AtomicWriter) CreateAcceptance(ctx context.Context, input CreateAcceptanceInput) error {
	if writer == nil || writer.client == nil {
		return errors.New("create acceptance in redis: nil writer")
	}
	if ctx == nil {
		return errors.New("create acceptance in redis: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("create acceptance in redis: %w", err)
	}

	deliveryPayload, err := MarshalDelivery(input.Delivery)
	if err != nil {
		return fmt.Errorf("create acceptance in redis: %w", err)
	}
	var (
		attemptKey           string
		attemptPayload       []byte
		deliveryPayloadKey   string
		deliveryPayloadBytes []byte
		scheduleScore        float64
		idempotencyKey       string
		idempotencyPayload   []byte
		idempotencyTTL       time.Duration
	)
	if input.FirstAttempt != nil {
		attemptPayload, err = MarshalAttempt(*input.FirstAttempt)
		if err != nil {
			return fmt.Errorf("create acceptance in redis: %w", err)
		}
		attemptKey = writer.keyspace.Attempt(input.FirstAttempt.DeliveryID, input.FirstAttempt.AttemptNo)
		scheduleScore = ScheduledForScore(input.FirstAttempt.ScheduledFor)
	}
	if input.DeliveryPayload != nil {
		deliveryPayloadBytes, err = MarshalDeliveryPayload(*input.DeliveryPayload)
		if err != nil {
			return fmt.Errorf("create acceptance in redis: %w", err)
		}
		deliveryPayloadKey = writer.keyspace.DeliveryPayload(input.DeliveryPayload.DeliveryID)
	}
	if input.Idempotency != nil {
		idempotencyPayload, err = MarshalIdempotency(*input.Idempotency)
		if err != nil {
			return fmt.Errorf("create acceptance in redis: %w", err)
		}
		idempotencyTTL, err = ttlUntil(input.Idempotency.ExpiresAt)
		if err != nil {
			return fmt.Errorf("create acceptance in redis: %w", err)
		}
		idempotencyKey = writer.keyspace.Idempotency(input.Idempotency.Source, input.Idempotency.IdempotencyKey)
	}

	deliveryKey := writer.keyspace.Delivery(input.Delivery.DeliveryID)
	watchKeys := []string{deliveryKey}
	if attemptKey != "" {
		watchKeys = append(watchKeys, attemptKey)
	}
	if deliveryPayloadKey != "" {
		watchKeys = append(watchKeys, deliveryPayloadKey)
	}
	if idempotencyKey != "" {
		watchKeys = append(watchKeys, idempotencyKey)
	}

	indexKeys := writer.keyspace.DeliveryIndexKeys(input.Delivery)
	createdAtScore := CreatedAtScore(input.Delivery.CreatedAt)
	deliveryMember := input.Delivery.DeliveryID.String()

	watchErr := writer.client.Watch(ctx, func(tx *redis.Tx) error {
		for _, key := range watchKeys {
			if err := ensureKeyAbsent(ctx, tx, key); err != nil {
				return fmt.Errorf("create acceptance in redis: %w", err)
			}
		}

		_, err := tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, deliveryKey, deliveryPayload, DeliveryTTL)
			if attemptKey != "" {
				pipe.Set(ctx, attemptKey, attemptPayload, AttemptTTL)
			}
			if deliveryPayloadKey != "" {
				pipe.Set(ctx, deliveryPayloadKey, deliveryPayloadBytes, DeliveryTTL)
			}
			if idempotencyKey != "" {
				pipe.Set(ctx, idempotencyKey, idempotencyPayload, idempotencyTTL)
			}
			if attemptKey != "" {
				pipe.ZAdd(ctx, writer.keyspace.AttemptSchedule(), redis.Z{
					Score:  scheduleScore,
					Member: deliveryMember,
				})
			}
			for _, indexKey := range indexKeys {
				pipe.ZAdd(ctx, indexKey, redis.Z{
					Score:  createdAtScore,
					Member: deliveryMember,
				})
			}

			return nil
		})
		if err != nil {
			return fmt.Errorf("create acceptance in redis: %w", err)
		}

		return nil
	}, watchKeys...)

	switch {
	case errors.Is(watchErr, redis.TxFailedErr):
		return fmt.Errorf("create acceptance in redis: %w", ErrConflict)
	case watchErr != nil:
		return watchErr
	default:
		return nil
	}
}

// MarkRendered stores the successful materialization result for one queued
// template delivery and updates the delivery-status secondary index
// atomically.
func (writer *AtomicWriter) MarkRendered(ctx context.Context, input MarkRenderedInput) error {
	if writer == nil || writer.client == nil {
		return errors.New("mark rendered in redis: nil writer")
	}
	if ctx == nil {
		return errors.New("mark rendered in redis: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("mark rendered in redis: %w", err)
	}

	deliveryKey := writer.keyspace.Delivery(input.Delivery.DeliveryID)
	deliveryPayload, err := MarshalDelivery(input.Delivery)
	if err != nil {
		return fmt.Errorf("mark rendered in redis: %w", err)
	}

	watchErr := writer.client.Watch(ctx, func(tx *redis.Tx) error {
		currentDelivery, err := loadDeliveryFromTx(ctx, tx, deliveryKey)
		if err != nil {
			return fmt.Errorf("mark rendered in redis: %w", err)
		}
		if currentDelivery.Status != deliverydomain.StatusQueued {
			return fmt.Errorf("mark rendered in redis: %w", ErrConflict)
		}

		deliveryTTL, err := ttlForExistingKey(ctx, tx, deliveryKey, DeliveryTTL)
		if err != nil {
			return fmt.Errorf("mark rendered in redis: %w", err)
		}

		createdAtScore := CreatedAtScore(currentDelivery.CreatedAt)
		deliveryMember := input.Delivery.DeliveryID.String()

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, deliveryKey, deliveryPayload, deliveryTTL)
			pipe.ZRem(ctx, writer.keyspace.StatusIndex(currentDelivery.Status), deliveryMember)
			pipe.ZAdd(ctx, writer.keyspace.StatusIndex(input.Delivery.Status), redis.Z{
				Score:  createdAtScore,
				Member: deliveryMember,
			})
			return nil
		})
		if err != nil {
			return fmt.Errorf("mark rendered in redis: %w", err)
		}

		return nil
	}, deliveryKey)

	switch {
	case errors.Is(watchErr, redis.TxFailedErr):
		return fmt.Errorf("mark rendered in redis: %w", ErrConflict)
	case watchErr != nil:
		return watchErr
	default:
		return nil
	}
}

// MarkRenderFailed stores one terminal render-failed attempt together with
// the owning failed delivery and updates the delivery-status secondary index
// atomically.
func (writer *AtomicWriter) MarkRenderFailed(ctx context.Context, input MarkRenderFailedInput) error {
	if writer == nil || writer.client == nil {
		return errors.New("mark render failed in redis: nil writer")
	}
	if ctx == nil {
		return errors.New("mark render failed in redis: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("mark render failed in redis: %w", err)
	}

	deliveryKey := writer.keyspace.Delivery(input.Delivery.DeliveryID)
	attemptKey := writer.keyspace.Attempt(input.Attempt.DeliveryID, input.Attempt.AttemptNo)

	deliveryPayload, err := MarshalDelivery(input.Delivery)
	if err != nil {
		return fmt.Errorf("mark render failed in redis: %w", err)
	}
	attemptPayload, err := MarshalAttempt(input.Attempt)
	if err != nil {
		return fmt.Errorf("mark render failed in redis: %w", err)
	}

	watchErr := writer.client.Watch(ctx, func(tx *redis.Tx) error {
		currentDelivery, err := loadDeliveryFromTx(ctx, tx, deliveryKey)
		if err != nil {
			return fmt.Errorf("mark render failed in redis: %w", err)
		}
		currentAttempt, err := loadAttemptFromTx(ctx, tx, attemptKey)
		if err != nil {
			return fmt.Errorf("mark render failed in redis: %w", err)
		}
		if currentDelivery.Status != deliverydomain.StatusQueued {
			return fmt.Errorf("mark render failed in redis: %w", ErrConflict)
		}
		if currentAttempt.Status != attempt.StatusScheduled {
			return fmt.Errorf("mark render failed in redis: %w", ErrConflict)
		}

		deliveryTTL, err := ttlForExistingKey(ctx, tx, deliveryKey, DeliveryTTL)
		if err != nil {
			return fmt.Errorf("mark render failed in redis: %w", err)
		}
		attemptTTL, err := ttlForExistingKey(ctx, tx, attemptKey, AttemptTTL)
		if err != nil {
			return fmt.Errorf("mark render failed in redis: %w", err)
		}

		createdAtScore := CreatedAtScore(currentDelivery.CreatedAt)
		deliveryMember := input.Delivery.DeliveryID.String()

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, deliveryKey, deliveryPayload, deliveryTTL)
			pipe.Set(ctx, attemptKey, attemptPayload, attemptTTL)
			pipe.ZRem(ctx, writer.keyspace.StatusIndex(currentDelivery.Status), deliveryMember)
			pipe.ZAdd(ctx, writer.keyspace.StatusIndex(input.Delivery.Status), redis.Z{
				Score:  createdAtScore,
				Member: deliveryMember,
			})
			pipe.ZRem(ctx, writer.keyspace.AttemptSchedule(), deliveryMember)
			return nil
		})
		if err != nil {
			return fmt.Errorf("mark render failed in redis: %w", err)
		}

		return nil
	}, deliveryKey, attemptKey)

	switch {
	case errors.Is(watchErr, redis.TxFailedErr):
		return fmt.Errorf("mark render failed in redis: %w", ErrConflict)
	case watchErr != nil:
		return watchErr
	default:
		return nil
	}
}

func ensureKeyAbsent(ctx context.Context, tx *redis.Tx, key string) error {
	exists, err := tx.Exists(ctx, key).Result()
	if err != nil {
		return err
	}
	if exists > 0 {
		return ErrConflict
	}

	return nil
}

func loadDeliveryFromTx(ctx context.Context, tx *redis.Tx, key string) (deliverydomain.Delivery, error) {
	payload, err := tx.Get(ctx, key).Bytes()
	switch {
	case errors.Is(err, redis.Nil):
		return deliverydomain.Delivery{}, ErrConflict
	case err != nil:
		return deliverydomain.Delivery{}, err
	}

	record, err := UnmarshalDelivery(payload)
	if err != nil {
		return deliverydomain.Delivery{}, err
	}

	return record, nil
}

func loadAttemptFromTx(ctx context.Context, tx *redis.Tx, key string) (attempt.Attempt, error) {
	payload, err := tx.Get(ctx, key).Bytes()
	switch {
	case errors.Is(err, redis.Nil):
		return attempt.Attempt{}, ErrConflict
	case err != nil:
		return attempt.Attempt{}, err
	}

	record, err := UnmarshalAttempt(payload)
	if err != nil {
		return attempt.Attempt{}, err
	}

	return record, nil
}

func ttlForExistingKey(ctx context.Context, tx *redis.Tx, key string, fallback time.Duration) (time.Duration, error) {
	ttl, err := tx.PTTL(ctx, key).Result()
	if err != nil {
		return 0, err
	}
	if ttl <= 0 {
		return fallback, nil
	}

	return ttl, nil
}

func ttlUntil(expiresAt time.Time) (time.Duration, error) {
	ttl := time.Until(expiresAt)
	if ttl <= 0 {
		return 0, errors.New("idempotency expires at must be in the future")
	}

	return ttl, nil
}