package redisstate

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"galaxy/lobby/internal/domain/application"
	"galaxy/lobby/internal/domain/common"
	"galaxy/lobby/internal/ports"

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

// ApplicationStore provides Redis-backed durable storage for application
// records.
type ApplicationStore struct {
	client *redis.Client
	keys   Keyspace
}

// NewApplicationStore constructs one Redis-backed application store. It
// returns an error when client is nil.
func NewApplicationStore(client *redis.Client) (*ApplicationStore, error) {
	if client == nil {
		return nil, errors.New("new application store: nil redis client")
	}

	return &ApplicationStore{
		client: client,
		keys:   Keyspace{},
	}, nil
}

// Save persists a new submitted application record and enforces the
// single-active (non-rejected) constraint per (applicant, game) pair.
func (store *ApplicationStore) Save(ctx context.Context, record application.Application) error {
	if store == nil || store.client == nil {
		return errors.New("save application: nil store")
	}
	if ctx == nil {
		return errors.New("save application: nil context")
	}
	if err := record.Validate(); err != nil {
		return fmt.Errorf("save application: %w", err)
	}
	if record.Status != application.StatusSubmitted {
		return fmt.Errorf(
			"save application: status must be %q, got %q",
			application.StatusSubmitted, record.Status,
		)
	}

	payload, err := MarshalApplication(record)
	if err != nil {
		return fmt.Errorf("save application: %w", err)
	}

	primaryKey := store.keys.Application(record.ApplicationID)
	activeLookupKey := store.keys.UserGameApplication(record.ApplicantUserID, record.GameID)
	gameIndexKey := store.keys.ApplicationsByGame(record.GameID)
	userIndexKey := store.keys.ApplicationsByUser(record.ApplicantUserID)
	member := record.ApplicationID.String()

	watchErr := store.client.Watch(ctx, func(tx *redis.Tx) error {
		existingPrimary, getErr := tx.Exists(ctx, primaryKey).Result()
		if getErr != nil {
			return fmt.Errorf("save application: %w", getErr)
		}
		if existingPrimary != 0 {
			return fmt.Errorf("save application: %w", application.ErrConflict)
		}

		existingActive, getErr := tx.Exists(ctx, activeLookupKey).Result()
		if getErr != nil {
			return fmt.Errorf("save application: %w", getErr)
		}
		if existingActive != 0 {
			return fmt.Errorf("save application: %w", application.ErrConflict)
		}

		_, err := tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, payload, ApplicationRecordTTL)
			pipe.Set(ctx, activeLookupKey, member, ApplicationRecordTTL)
			pipe.SAdd(ctx, gameIndexKey, member)
			pipe.SAdd(ctx, userIndexKey, member)
			return nil
		})
		return err
	}, primaryKey, activeLookupKey)

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

// Get returns the record identified by applicationID.
func (store *ApplicationStore) Get(ctx context.Context, applicationID common.ApplicationID) (application.Application, error) {
	if store == nil || store.client == nil {
		return application.Application{}, errors.New("get application: nil store")
	}
	if ctx == nil {
		return application.Application{}, errors.New("get application: nil context")
	}
	if err := applicationID.Validate(); err != nil {
		return application.Application{}, fmt.Errorf("get application: %w", err)
	}

	payload, err := store.client.Get(ctx, store.keys.Application(applicationID)).Bytes()
	switch {
	case errors.Is(err, redis.Nil):
		return application.Application{}, application.ErrNotFound
	case err != nil:
		return application.Application{}, fmt.Errorf("get application: %w", err)
	}

	record, err := UnmarshalApplication(payload)
	if err != nil {
		return application.Application{}, fmt.Errorf("get application: %w", err)
	}
	return record, nil
}

// GetByGame returns every application attached to gameID.
func (store *ApplicationStore) GetByGame(ctx context.Context, gameID common.GameID) ([]application.Application, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("get applications by game: nil store")
	}
	if ctx == nil {
		return nil, errors.New("get applications by game: nil context")
	}
	if err := gameID.Validate(); err != nil {
		return nil, fmt.Errorf("get applications by game: %w", err)
	}

	return store.loadApplicationsBySet(ctx,
		"get applications by game",
		store.keys.ApplicationsByGame(gameID),
	)
}

// GetByUser returns every application submitted by applicantUserID.
func (store *ApplicationStore) GetByUser(ctx context.Context, applicantUserID string) ([]application.Application, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("get applications by user: nil store")
	}
	if ctx == nil {
		return nil, errors.New("get applications by user: nil context")
	}
	trimmed := strings.TrimSpace(applicantUserID)
	if trimmed == "" {
		return nil, fmt.Errorf("get applications by user: applicant user id must not be empty")
	}

	return store.loadApplicationsBySet(ctx,
		"get applications by user",
		store.keys.ApplicationsByUser(trimmed),
	)
}

// loadApplicationsBySet materializes applications whose ids are stored in
// setKey. Stale set members (primary key removed out-of-band) are dropped
// silently, mirroring gamestore.GetByStatus.
func (store *ApplicationStore) loadApplicationsBySet(ctx context.Context, operation, setKey string) ([]application.Application, error) {
	members, err := store.client.SMembers(ctx, setKey).Result()
	if err != nil {
		return nil, fmt.Errorf("%s: %w", operation, err)
	}
	if len(members) == 0 {
		return nil, nil
	}

	primaryKeys := make([]string, len(members))
	for index, member := range members {
		primaryKeys[index] = store.keys.Application(common.ApplicationID(member))
	}

	payloads, err := store.client.MGet(ctx, primaryKeys...).Result()
	if err != nil {
		return nil, fmt.Errorf("%s: %w", operation, err)
	}

	records := make([]application.Application, 0, len(payloads))
	for _, entry := range payloads {
		if entry == nil {
			continue
		}
		raw, ok := entry.(string)
		if !ok {
			return nil, fmt.Errorf("%s: unexpected payload type %T", operation, entry)
		}
		record, err := UnmarshalApplication([]byte(raw))
		if err != nil {
			return nil, fmt.Errorf("%s: %w", operation, err)
		}
		records = append(records, record)
	}

	return records, nil
}

// UpdateStatus applies one status transition in a compare-and-swap fashion.
func (store *ApplicationStore) UpdateStatus(ctx context.Context, input ports.UpdateApplicationStatusInput) error {
	if store == nil || store.client == nil {
		return errors.New("update application status: nil store")
	}
	if ctx == nil {
		return errors.New("update application status: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("update application status: %w", err)
	}

	if err := application.Transition(input.ExpectedFrom, input.To); err != nil {
		return err
	}

	primaryKey := store.keys.Application(input.ApplicationID)
	at := input.At.UTC()

	watchErr := store.client.Watch(ctx, func(tx *redis.Tx) error {
		payload, getErr := tx.Get(ctx, primaryKey).Bytes()
		switch {
		case errors.Is(getErr, redis.Nil):
			return application.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("update application status: %w", getErr)
		}

		existing, err := UnmarshalApplication(payload)
		if err != nil {
			return fmt.Errorf("update application status: %w", err)
		}
		if existing.Status != input.ExpectedFrom {
			return fmt.Errorf("update application status: %w", application.ErrConflict)
		}

		existing.Status = input.To
		decidedAt := at
		existing.DecidedAt = &decidedAt

		encoded, err := MarshalApplication(existing)
		if err != nil {
			return fmt.Errorf("update application status: %w", err)
		}

		activeLookupKey := store.keys.UserGameApplication(existing.ApplicantUserID, existing.GameID)

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, encoded, ApplicationRecordTTL)
			if input.To == application.StatusRejected {
				pipe.Del(ctx, activeLookupKey)
			}
			return nil
		})
		return err
	}, primaryKey)

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

// Ensure ApplicationStore satisfies the ports.ApplicationStore interface
// at compile time.
var _ ports.ApplicationStore = (*ApplicationStore)(nil)