// Package cancelgame implements the `lobby.game.cancel` message type. It
// transitions a game record to `cancelled` from one of the allowed source
// statuses (`draft`, `enrollment_open`, `ready_to_start`, `start_failed`)
// after enforcing admin-or-owner authorization. Any other source status is
// rejected with game.ErrConflict.
package cancelgame

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

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

// cancellableStatuses enumerates the source statuses from which a game may
// transition directly to `cancelled`. The set mirrors the allowed
// transitions defined in `internal/domain/game/status.go` and the
// PLAN.md exit criteria.
var cancellableStatuses = map[game.Status]struct{}{
	game.StatusDraft:          {},
	game.StatusEnrollmentOpen: {},
	game.StatusReadyToStart:   {},
	game.StatusStartFailed:    {},
}

// Service executes the cancel-game use case.
type Service struct {
	games     ports.GameStore
	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

	// 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 cancellation. Optional; nil disables metric emission.
	Telemetry *telemetry.Runtime
}

// NewService constructs one Service with deps.
func NewService(deps Dependencies) (*Service, error) {
	if deps.Games == nil {
		return nil, errors.New("new cancel game service: nil game store")
	}

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

	return &Service{
		games:     deps.Games,
		clock:     clock,
		logger:    logger.With("service", "lobby.cancelgame"),
		telemetry: deps.Telemetry,
	}, nil
}

// Input stores the arguments required to cancel 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, checks the source status, transitions the
// record to `cancelled`, and returns the post-transition snapshot.
func (service *Service) Handle(ctx context.Context, input Input) (game.Game, error) {
	if service == nil {
		return game.Game{}, errors.New("cancel game: nil service")
	}
	if ctx == nil {
		return game.Game{}, errors.New("cancel game: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("cancel game: actor: %w", err)
	}
	if err := input.GameID.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("cancel game: %w", err)
	}

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

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

	if _, ok := cancellableStatuses[record.Status]; !ok {
		return game.Game{}, fmt.Errorf(
			"cancel game: status %q cannot be cancelled: %w",
			record.Status, game.ErrConflict,
		)
	}

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

	service.telemetry.RecordGameTransition(ctx,
		string(record.Status),
		string(game.StatusCancelled),
		string(game.TriggerCommand),
	)

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

	logArgs := []any{
		"game_id", updated.GameID.String(),
		"from_status", string(record.Status),
		"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 cancelled", 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 cancel game %q",
		shared.ErrForbidden, record.GameID.String())
}