package redisstate

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

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

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

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

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

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

// Save upserts record and rewrites the status secondary index when the
// status changes.
func (store *GameStore) Save(ctx context.Context, record game.Game) error {
	if store == nil || store.client == nil {
		return errors.New("save game: nil store")
	}
	if ctx == nil {
		return errors.New("save game: nil context")
	}
	if err := record.Validate(); err != nil {
		return fmt.Errorf("save game: %w", err)
	}

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

	primaryKey := store.keys.Game(record.GameID)
	newIndexKey := store.keys.GamesByStatus(record.Status)
	member := record.GameID.String()
	createdAtScore := CreatedAtScore(record.CreatedAt)

	watchErr := store.client.Watch(ctx, func(tx *redis.Tx) error {
		var previousStatus game.Status
		existingPayload, getErr := tx.Get(ctx, primaryKey).Bytes()
		switch {
		case errors.Is(getErr, redis.Nil):
			previousStatus = ""
		case getErr != nil:
			return fmt.Errorf("save game: %w", getErr)
		default:
			existing, err := UnmarshalGame(existingPayload)
			if err != nil {
				return fmt.Errorf("save game: %w", err)
			}
			previousStatus = existing.Status
		}

		_, err := tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, payload, GameRecordTTL)
			if previousStatus != "" && previousStatus != record.Status {
				pipe.ZRem(ctx, store.keys.GamesByStatus(previousStatus), member)
			}
			pipe.ZAdd(ctx, newIndexKey, redis.Z{
				Score:  createdAtScore,
				Member: member,
			})
			if owner := strings.TrimSpace(record.OwnerUserID); owner != "" {
				pipe.SAdd(ctx, store.keys.GamesByOwner(owner), member)
			}
			return nil
		})
		return err
	}, primaryKey)

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

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

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

	record, err := UnmarshalGame(payload)
	if err != nil {
		return game.Game{}, fmt.Errorf("get game: %w", err)
	}

	return record, nil
}

// GetByStatus returns every record indexed under status. Stale index
// entries (primary key removed out-of-band) are dropped silently.
func (store *GameStore) GetByStatus(ctx context.Context, status game.Status) ([]game.Game, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("get games by status: nil store")
	}
	if ctx == nil {
		return nil, errors.New("get games by status: nil context")
	}
	if !status.IsKnown() {
		return nil, fmt.Errorf("get games by status: status %q is unsupported", status)
	}

	members, err := store.client.ZRange(ctx, store.keys.GamesByStatus(status), 0, -1).Result()
	if err != nil {
		return nil, fmt.Errorf("get games by status: %w", err)
	}
	if len(members) == 0 {
		return nil, nil
	}

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

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

	records := make([]game.Game, 0, len(payloads))
	for _, entry := range payloads {
		if entry == nil {
			continue
		}
		raw, ok := entry.(string)
		if !ok {
			return nil, fmt.Errorf("get games by status: unexpected payload type %T", entry)
		}
		record, err := UnmarshalGame([]byte(raw))
		if err != nil {
			return nil, fmt.Errorf("get games by status: %w", err)
		}
		records = append(records, record)
	}

	return records, nil
}

// CountByStatus returns the number of game identifiers indexed under each
// known status. The map carries one entry per game.AllStatuses, with zero
// counts for empty buckets. The implementation issues one ZCARD per status
// in a single Redis pipeline so the cost stays O(number of statuses).
func (store *GameStore) CountByStatus(ctx context.Context) (map[game.Status]int, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("count games by status: nil store")
	}
	if ctx == nil {
		return nil, errors.New("count games by status: nil context")
	}

	statuses := game.AllStatuses()
	pipeline := store.client.Pipeline()
	results := make([]*redis.IntCmd, len(statuses))
	for index, status := range statuses {
		results[index] = pipeline.ZCard(ctx, store.keys.GamesByStatus(status))
	}
	if _, err := pipeline.Exec(ctx); err != nil {
		return nil, fmt.Errorf("count games by status: %w", err)
	}

	counts := make(map[game.Status]int, len(statuses))
	for index, status := range statuses {
		count, err := results[index].Result()
		if err != nil {
			return nil, fmt.Errorf("count games by status: %s: %w", status, err)
		}
		counts[status] = int(count)
	}
	return counts, nil
}

// GetByOwner returns every record whose OwnerUserID equals userID.
// Stale index entries (primary key removed out-of-band) are dropped
// silently. The slice order is adapter-defined.
func (store *GameStore) GetByOwner(ctx context.Context, userID string) ([]game.Game, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("get games by owner: nil store")
	}
	if ctx == nil {
		return nil, errors.New("get games by owner: nil context")
	}
	trimmed := strings.TrimSpace(userID)
	if trimmed == "" {
		return nil, fmt.Errorf("get games by owner: user id must not be empty")
	}

	members, err := store.client.SMembers(ctx, store.keys.GamesByOwner(trimmed)).Result()
	if err != nil {
		return nil, fmt.Errorf("get games by owner: %w", err)
	}
	if len(members) == 0 {
		return nil, nil
	}

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

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

	records := make([]game.Game, 0, len(payloads))
	for _, entry := range payloads {
		if entry == nil {
			continue
		}
		raw, ok := entry.(string)
		if !ok {
			return nil, fmt.Errorf("get games by owner: unexpected payload type %T", entry)
		}
		record, err := UnmarshalGame([]byte(raw))
		if err != nil {
			return nil, fmt.Errorf("get games by owner: %w", err)
		}
		records = append(records, record)
	}

	return records, nil
}

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

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

	primaryKey := store.keys.Game(input.GameID)
	member := input.GameID.String()
	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 game.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("update game status: %w", getErr)
		}

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

		existing.Status = input.To
		existing.UpdatedAt = at
		if input.To == game.StatusRunning && existing.StartedAt == nil {
			startedAt := at
			existing.StartedAt = &startedAt
		}
		if input.To == game.StatusFinished && existing.FinishedAt == nil {
			finishedAt := at
			existing.FinishedAt = &finishedAt
		}

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

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, encoded, GameRecordTTL)
			pipe.ZRem(ctx, store.keys.GamesByStatus(input.ExpectedFrom), member)
			pipe.ZAdd(ctx, store.keys.GamesByStatus(input.To), redis.Z{
				Score:  CreatedAtScore(existing.CreatedAt),
				Member: member,
			})
			return nil
		})
		return err
	}, primaryKey)

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

// UpdateRuntimeSnapshot overwrites the denormalized runtime snapshot
// fields on the record identified by input.GameID.
func (store *GameStore) UpdateRuntimeSnapshot(ctx context.Context, input ports.UpdateRuntimeSnapshotInput) error {
	if store == nil || store.client == nil {
		return errors.New("update runtime snapshot: nil store")
	}
	if ctx == nil {
		return errors.New("update runtime snapshot: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("update runtime snapshot: %w", err)
	}

	primaryKey := store.keys.Game(input.GameID)
	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 game.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("update runtime snapshot: %w", getErr)
		}

		existing, err := UnmarshalGame(payload)
		if err != nil {
			return fmt.Errorf("update runtime snapshot: %w", err)
		}

		existing.RuntimeSnapshot = input.Snapshot
		existing.UpdatedAt = at

		encoded, err := MarshalGame(existing)
		if err != nil {
			return fmt.Errorf("update runtime snapshot: %w", err)
		}

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, encoded, GameRecordTTL)
			return nil
		})
		return err
	}, primaryKey)

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

// UpdateRuntimeBinding overwrites the runtime binding metadata on the
// record identified by input.GameID. calls this method from
// the runtimejobresult worker after a successful container start.
func (store *GameStore) UpdateRuntimeBinding(ctx context.Context, input ports.UpdateRuntimeBindingInput) error {
	if store == nil || store.client == nil {
		return errors.New("update runtime binding: nil store")
	}
	if ctx == nil {
		return errors.New("update runtime binding: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("update runtime binding: %w", err)
	}

	primaryKey := store.keys.Game(input.GameID)
	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 game.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("update runtime binding: %w", getErr)
		}

		existing, err := UnmarshalGame(payload)
		if err != nil {
			return fmt.Errorf("update runtime binding: %w", err)
		}

		binding := input.Binding
		existing.RuntimeBinding = &binding
		existing.UpdatedAt = at

		encoded, err := MarshalGame(existing)
		if err != nil {
			return fmt.Errorf("update runtime binding: %w", err)
		}

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Set(ctx, primaryKey, encoded, GameRecordTTL)
			return nil
		})
		return err
	}, primaryKey)

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

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