package redisstate

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

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

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

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

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

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

// Save persists a new active membership record. Save is create-only; a
// second save against the same membership id returns
// membership.ErrConflict.
func (store *MembershipStore) Save(ctx context.Context, record membership.Membership) error {
	if store == nil || store.client == nil {
		return errors.New("save membership: nil store")
	}
	if ctx == nil {
		return errors.New("save membership: nil context")
	}
	if err := record.Validate(); err != nil {
		return fmt.Errorf("save membership: %w", err)
	}
	if record.Status != membership.StatusActive {
		return fmt.Errorf(
			"save membership: status must be %q, got %q",
			membership.StatusActive, record.Status,
		)
	}

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

	primaryKey := store.keys.Membership(record.MembershipID)
	gameIndexKey := store.keys.MembershipsByGame(record.GameID)
	userIndexKey := store.keys.MembershipsByUser(record.UserID)
	member := record.MembershipID.String()

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

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

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

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

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

	record, err := UnmarshalMembership(payload)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("get membership: %w", err)
	}
	return record, nil
}

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

	return store.loadMembershipsBySet(ctx,
		"get memberships by game",
		store.keys.MembershipsByGame(gameID),
	)
}

// GetByUser returns every membership held by userID.
func (store *MembershipStore) GetByUser(ctx context.Context, userID string) ([]membership.Membership, error) {
	if store == nil || store.client == nil {
		return nil, errors.New("get memberships by user: nil store")
	}
	if ctx == nil {
		return nil, errors.New("get memberships by user: nil context")
	}
	trimmed := strings.TrimSpace(userID)
	if trimmed == "" {
		return nil, fmt.Errorf("get memberships by user: user id must not be empty")
	}

	return store.loadMembershipsBySet(ctx,
		"get memberships by user",
		store.keys.MembershipsByUser(trimmed),
	)
}

// loadMembershipsBySet materializes memberships whose ids are stored in
// setKey. Stale set members are dropped silently.
func (store *MembershipStore) loadMembershipsBySet(ctx context.Context, operation, setKey string) ([]membership.Membership, 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.Membership(common.MembershipID(member))
	}

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

	records := make([]membership.Membership, 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 := UnmarshalMembership([]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 *MembershipStore) UpdateStatus(ctx context.Context, input ports.UpdateMembershipStatusInput) error {
	if store == nil || store.client == nil {
		return errors.New("update membership status: nil store")
	}
	if ctx == nil {
		return errors.New("update membership status: nil context")
	}
	if err := input.Validate(); err != nil {
		return fmt.Errorf("update membership status: %w", err)
	}

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

	primaryKey := store.keys.Membership(input.MembershipID)
	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 membership.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("update membership status: %w", getErr)
		}

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

		existing.Status = input.To
		removedAt := at
		existing.RemovedAt = &removedAt

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

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

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

// Delete removes the membership record identified by membershipID from
// the primary store and from the per-game and per-user index sets in
// one transaction. It returns membership.ErrNotFound when no record
// exists for the id and membership.ErrConflict when a concurrent
// mutation invalidates the watched key.
func (store *MembershipStore) Delete(ctx context.Context, membershipID common.MembershipID) error {
	if store == nil || store.client == nil {
		return errors.New("delete membership: nil store")
	}
	if ctx == nil {
		return errors.New("delete membership: nil context")
	}
	if err := membershipID.Validate(); err != nil {
		return fmt.Errorf("delete membership: %w", err)
	}

	primaryKey := store.keys.Membership(membershipID)
	member := membershipID.String()

	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 membership.ErrNotFound
		case getErr != nil:
			return fmt.Errorf("delete membership: %w", getErr)
		}

		existing, err := UnmarshalMembership(payload)
		if err != nil {
			return fmt.Errorf("delete membership: %w", err)
		}

		gameIndexKey := store.keys.MembershipsByGame(existing.GameID)
		userIndexKey := store.keys.MembershipsByUser(existing.UserID)

		_, err = tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
			pipe.Del(ctx, primaryKey)
			pipe.SRem(ctx, gameIndexKey, member)
			pipe.SRem(ctx, userIndexKey, member)
			return nil
		})
		return err
	}, primaryKey)

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

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