// Package creategame implements the `lobby.game.create` message type. It
// validates the request, enforces the actor-to-game-type pairing rule
// (admin creates public games; user creates private games), generates a new
// game identifier, and persists the record in `draft` status via the
// GameStore port.
package creategame

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"time"

	"galaxy/lobby/internal/domain/game"
	"galaxy/lobby/internal/ports"
	"galaxy/lobby/internal/service/shared"
)

// Service executes the create-game use case on the frozen surface.
type Service struct {
	games  ports.GameStore
	ids    ports.IDGenerator
	clock  func() time.Time
	logger *slog.Logger
}

// Dependencies groups the collaborators used by Service. Logger is optional;
// nil falls back to slog.Default. Clock is optional; nil falls back to
// time.Now.
type Dependencies struct {
	// Games persists the created record.
	Games ports.GameStore

	// IDs generates the opaque game identifier.
	IDs ports.IDGenerator

	// Clock supplies the wall-clock used for CreatedAt and UpdatedAt. It
	// defaults to time.Now when nil.
	Clock func() time.Time

	// Logger records structured service-level events. It defaults to
	// slog.Default when nil.
	Logger *slog.Logger
}

// NewService constructs one Service with deps. It returns an error when
// mandatory collaborators are missing.
func NewService(deps Dependencies) (*Service, error) {
	if deps.Games == nil {
		return nil, errors.New("new create game service: nil game store")
	}
	if deps.IDs == nil {
		return nil, errors.New("new create game service: nil id generator")
	}

	clock := deps.Clock
	if clock == nil {
		clock = time.Now
	}
	logger := deps.Logger
	if logger == nil {
		logger = slog.Default()
	}

	return &Service{
		games:  deps.Games,
		ids:    deps.IDs,
		clock:  clock,
		logger: logger.With("service", "lobby.creategame"),
	}, nil
}

// Input stores the arguments required to create one draft game record.
type Input struct {
	// Actor identifies the caller.
	Actor shared.Actor

	// GameName stores the human-readable game name. Must be non-empty after
	// trim.
	GameName string

	// Description stores the optional human-readable game description.
	Description string

	// GameType stores the admission model. Must pair with Actor.Kind:
	// admin ⇒ public, user ⇒ private.
	GameType game.GameType

	// MinPlayers stores the minimum approved participants required before
	// the game may start.
	MinPlayers int

	// MaxPlayers stores the target roster size that activates the gap
	// window.
	MaxPlayers int

	// StartGapHours stores the gap window length in hours.
	StartGapHours int

	// StartGapPlayers stores the number of additional participants
	// admitted during the gap window.
	StartGapPlayers int

	// EnrollmentEndsAt stores the enrollment deadline.
	EnrollmentEndsAt time.Time

	// TurnSchedule stores the five-field cron expression.
	TurnSchedule string

	// TargetEngineVersion stores the semver of the engine to launch.
	TargetEngineVersion string
}

// Handle validates input, authorizes the actor, and persists the new draft
// record. On success it returns the persisted game. The following error
// classes are surfaced and relied on by transport mapping:
//
//   - shared.ErrForbidden — actor-to-game-type pairing mismatch.
//   - game input validation errors from game.New — translated to
//     invalid_request at the transport layer.
func (service *Service) Handle(ctx context.Context, input Input) (game.Game, error) {
	if service == nil {
		return game.Game{}, errors.New("create game: nil service")
	}
	if ctx == nil {
		return game.Game{}, errors.New("create game: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("create game: actor: %w", err)
	}

	ownerUserID, err := authorize(input.Actor, input.GameType)
	if err != nil {
		return game.Game{}, err
	}

	gameID, err := service.ids.NewGameID()
	if err != nil {
		return game.Game{}, fmt.Errorf("create game: %w", err)
	}

	now := service.clock().UTC()

	record, err := game.New(game.NewGameInput{
		GameID:              gameID,
		GameName:            input.GameName,
		Description:         input.Description,
		GameType:            input.GameType,
		OwnerUserID:         ownerUserID,
		MinPlayers:          input.MinPlayers,
		MaxPlayers:          input.MaxPlayers,
		StartGapHours:       input.StartGapHours,
		StartGapPlayers:     input.StartGapPlayers,
		EnrollmentEndsAt:    input.EnrollmentEndsAt,
		TurnSchedule:        input.TurnSchedule,
		TargetEngineVersion: input.TargetEngineVersion,
		Now:                 now,
	})
	if err != nil {
		return game.Game{}, fmt.Errorf("create game: %w", err)
	}

	if err := service.games.Save(ctx, record); err != nil {
		return game.Game{}, fmt.Errorf("create game: %w", err)
	}

	service.logger.InfoContext(ctx, "game created",
		"game_id", record.GameID.String(),
		"game_type", string(record.GameType),
		"actor_kind", string(input.Actor.Kind),
	)

	return record, nil
}

// authorize enforces the actor-to-game-type pairing rule and returns the
// owner_user_id value appropriate for the requested game type.
func authorize(actor shared.Actor, gameType game.GameType) (string, error) {
	switch actor.Kind {
	case shared.ActorKindAdmin:
		if gameType != game.GameTypePublic {
			return "", fmt.Errorf(
				"%w: admin caller may only create public games, got %q",
				shared.ErrForbidden, gameType,
			)
		}
		return "", nil
	case shared.ActorKindUser:
		if gameType != game.GameTypePrivate {
			return "", fmt.Errorf(
				"%w: user caller may only create private games, got %q",
				shared.ErrForbidden, gameType,
			)
		}
		return actor.UserID, nil
	default:
		return "", fmt.Errorf("%w: actor kind %q is unsupported", shared.ErrForbidden, actor.Kind)
	}
}