// Package startgame implements the `lobby.game.start` message type. It
// validates the actor authorization, transitions the game from
// `ready_to_start` to `starting` via a CAS update, and publishes the
// start job to Runtime Manager. The remainder of the start sequence
// (Runtime Manager result + Game Master registration) lives in the
// runtimejobresult worker.
package startgame

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

	"galaxy/lobby/internal/domain/common"
	"galaxy/lobby/internal/domain/engineimage"
	"galaxy/lobby/internal/domain/game"
	"galaxy/lobby/internal/logging"
	"galaxy/lobby/internal/ports"
	"galaxy/lobby/internal/service/shared"
	"galaxy/lobby/internal/telemetry"
)

// Service executes the start-game use case.
type Service struct {
	games           ports.GameStore
	runtimeManager  ports.RuntimeManager
	imageResolver   *engineimage.Resolver
	clock           func() time.Time
	logger          *slog.Logger
	telemetry       *telemetry.Runtime
}

// Dependencies groups the collaborators used by Service.
type Dependencies struct {
	// Games mediates the CAS status transition and the result read.
	Games ports.GameStore

	// RuntimeManager publishes the start job after the CAS succeeds.
	RuntimeManager ports.RuntimeManager

	// ImageResolver substitutes a game's TargetEngineVersion into the
	// configured engine-image template to produce the `image_ref`
	// published on `runtime:start_jobs`.
	ImageResolver *engineimage.Resolver

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

	// Logger records structured service-level events. Defaults to
	// slog.Default when nil.
	Logger *slog.Logger

	// Telemetry records the `lobby.game.transitions` counter on each
	// successful start. Optional; nil disables metric emission.
	Telemetry *telemetry.Runtime
}

// NewService constructs one Service with deps.
func NewService(deps Dependencies) (*Service, error) {
	switch {
	case deps.Games == nil:
		return nil, errors.New("new start game service: nil game store")
	case deps.RuntimeManager == nil:
		return nil, errors.New("new start game service: nil runtime manager")
	case deps.ImageResolver == nil:
		return nil, errors.New("new start game service: nil image resolver")
	}

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

	return &Service{
		games:          deps.Games,
		runtimeManager: deps.RuntimeManager,
		imageResolver:  deps.ImageResolver,
		clock:          clock,
		logger:         logger.With("service", "lobby.startgame"),
		telemetry:      deps.Telemetry,
	}, nil
}

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

	// GameID identifies the target game record.
	GameID common.GameID
}

// Handle authorizes the actor, asserts the game is in `ready_to_start`,
// transitions it to `starting`, and publishes the start job to Runtime
// Manager. The CAS guarantees that two concurrent start commands cannot
// both succeed.
//
// On Runtime Manager publish failure the game record stays in
// `starting`; the caller is informed through the returned error. The
// next start attempt will be rejected with game.ErrConflict because the
// status is no longer `ready_to_start`. The runtimejobresult worker
// resolves the situation when (or if) a job result later arrives;
// otherwise an admin must intervene through tooling. This
// trade-off is documented in the decision record.
func (service *Service) Handle(ctx context.Context, input Input) (game.Game, error) {
	if service == nil {
		return game.Game{}, errors.New("start game: nil service")
	}
	if ctx == nil {
		return game.Game{}, errors.New("start game: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("start game: actor: %w", err)
	}
	if err := input.GameID.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("start game: %w", err)
	}

	record, err := service.games.Get(ctx, input.GameID)
	if err != nil {
		return game.Game{}, fmt.Errorf("start game: %w", err)
	}
	if err := authorize(input.Actor, record); err != nil {
		return game.Game{}, err
	}
	if record.Status != game.StatusReadyToStart {
		return game.Game{}, fmt.Errorf(
			"start game: status %q is not %q: %w",
			record.Status, game.StatusReadyToStart, game.ErrConflict,
		)
	}

	imageRef, err := service.imageResolver.Resolve(record.TargetEngineVersion)
	if err != nil {
		return game.Game{}, fmt.Errorf("start game: resolve image ref: %w", err)
	}

	at := service.clock().UTC()
	if err := service.games.UpdateStatus(ctx, ports.UpdateStatusInput{
		GameID:       input.GameID,
		ExpectedFrom: game.StatusReadyToStart,
		To:           game.StatusStarting,
		Trigger:      game.TriggerCommand,
		At:           at,
	}); err != nil {
		return game.Game{}, fmt.Errorf("start game: %w", err)
	}

	service.telemetry.RecordGameTransition(ctx,
		string(game.StatusReadyToStart),
		string(game.StatusStarting),
		string(game.TriggerCommand),
	)

	if err := service.runtimeManager.PublishStartJob(ctx, input.GameID.String(), imageRef); err != nil {
		// Status is already `starting` and the domain forbids a direct
		// rollback to `ready_to_start`. We surface the publish error to
		// the caller; the game stays in `starting` until either a
		// runtime job result arrives (worker handles the outcome) or an
		// admin intervenes manually.
		service.logger.ErrorContext(ctx, "publish runtime start job",
			"game_id", input.GameID.String(),
			"err", err.Error(),
		)
		return game.Game{}, fmt.Errorf("start game: %w", errors.Join(shared.ErrServiceUnavailable, err))
	}

	updated, err := service.games.Get(ctx, input.GameID)
	if err != nil {
		return game.Game{}, fmt.Errorf("start game: %w", err)
	}

	logArgs := []any{
		"game_id", updated.GameID.String(),
		"from_status", string(game.StatusReadyToStart),
		"to_status", string(updated.Status),
		"trigger", string(game.TriggerCommand),
		"actor_kind", string(input.Actor.Kind),
	}
	logArgs = append(logArgs, logging.ContextAttrs(ctx)...)
	service.logger.InfoContext(ctx, "game start job published", logArgs...)
	return updated, nil
}

// authorize enforces admin OR private-owner access to the record.
func authorize(actor shared.Actor, record game.Game) error {
	if actor.IsAdmin() {
		return nil
	}
	if record.GameType == game.GameTypePrivate && actor.UserID == record.OwnerUserID {
		return nil
	}
	return fmt.Errorf("%w: actor is not authorized to start game %q",
		shared.ErrForbidden, record.GameID.String())
}