// Package updategame implements the `lobby.game.update` message type. It
// applies partial edits to a game record under the following rules:
//
//   - in status `draft`: any field from the request schema is mutable;
//   - in status `enrollment_open`: only `description` is mutable;
//   - in every other status: no field is mutable and the call returns
//     game.ErrConflict.
//
// Authorization is admin OR (user + private game + matching OwnerUserID).
// Non-owners receive shared.ErrForbidden.
package updategame

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

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

// Service executes the update-game use case.
type Service struct {
	games  ports.GameStore
	clock  func() time.Time
	logger *slog.Logger
}

// Dependencies groups the collaborators used by Service.
type Dependencies struct {
	// Games persists the updated record.
	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
}

// NewService constructs one Service with deps.
func NewService(deps Dependencies) (*Service, error) {
	if deps.Games == nil {
		return nil, errors.New("new update 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.updategame"),
	}, nil
}

// Input stores the arguments required to update one game record. Every
// mutable field is represented by a pointer so callers can distinguish
// "absent" from the zero value.
type Input struct {
	// Actor identifies the caller.
	Actor shared.Actor

	// GameID identifies the record to update.
	GameID common.GameID

	// GameName updates the human-readable game name when non-nil.
	GameName *string

	// Description updates the human-readable description when non-nil.
	Description *string

	// MinPlayers updates the minimum approved participant count when
	// non-nil.
	MinPlayers *int

	// MaxPlayers updates the target roster size when non-nil.
	MaxPlayers *int

	// StartGapHours updates the gap window length in hours when non-nil.
	StartGapHours *int

	// StartGapPlayers updates the gap window additional participant count
	// when non-nil.
	StartGapPlayers *int

	// EnrollmentEndsAt updates the enrollment deadline when non-nil.
	EnrollmentEndsAt *time.Time

	// TurnSchedule updates the cron expression when non-nil.
	TurnSchedule *string

	// TargetEngineVersion updates the engine semver when non-nil.
	TargetEngineVersion *string
}

// HasNonDescriptionFields reports whether input carries any mutation other
// than Description.
func (input Input) HasNonDescriptionFields() bool {
	return input.GameName != nil ||
		input.MinPlayers != nil ||
		input.MaxPlayers != nil ||
		input.StartGapHours != nil ||
		input.StartGapPlayers != nil ||
		input.EnrollmentEndsAt != nil ||
		input.TurnSchedule != nil ||
		input.TargetEngineVersion != nil
}

// Handle validates, authorizes, and applies the partial update. It returns
// the persisted record on success.
func (service *Service) Handle(ctx context.Context, input Input) (game.Game, error) {
	if service == nil {
		return game.Game{}, errors.New("update game: nil service")
	}
	if ctx == nil {
		return game.Game{}, errors.New("update game: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("update game: actor: %w", err)
	}
	if err := input.GameID.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("update game: %w", err)
	}

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

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

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

	applyPatch(&record, input, service.clock().UTC())

	if err := record.Validate(); err != nil {
		return game.Game{}, fmt.Errorf("update game: %w", err)
	}

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

	service.logger.InfoContext(ctx, "game updated",
		"game_id", record.GameID.String(),
		"status", string(record.Status),
		"actor_kind", string(input.Actor.Kind),
	)

	return record, 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 update game %q",
		shared.ErrForbidden, record.GameID.String())
}

// enforceStatusGate returns game.ErrConflict when the request attempts a
// field mutation disallowed by the current status.
func enforceStatusGate(status game.Status, input Input) error {
	switch status {
	case game.StatusDraft:
		return nil
	case game.StatusEnrollmentOpen:
		if input.HasNonDescriptionFields() {
			return fmt.Errorf(
				"update game: only description is editable in status %q: %w",
				status, game.ErrConflict,
			)
		}
		return nil
	default:
		return fmt.Errorf(
			"update game: status %q does not accept field updates: %w",
			status, game.ErrConflict,
		)
	}
}

// applyPatch overwrites non-nil fields from input onto record. Callers must
// re-validate the result before persisting.
func applyPatch(record *game.Game, input Input, now time.Time) {
	if input.GameName != nil {
		record.GameName = *input.GameName
	}
	if input.Description != nil {
		record.Description = *input.Description
	}
	if input.MinPlayers != nil {
		record.MinPlayers = *input.MinPlayers
	}
	if input.MaxPlayers != nil {
		record.MaxPlayers = *input.MaxPlayers
	}
	if input.StartGapHours != nil {
		record.StartGapHours = *input.StartGapHours
	}
	if input.StartGapPlayers != nil {
		record.StartGapPlayers = *input.StartGapPlayers
	}
	if input.EnrollmentEndsAt != nil {
		record.EnrollmentEndsAt = input.EnrollmentEndsAt.UTC()
	}
	if input.TurnSchedule != nil {
		record.TurnSchedule = *input.TurnSchedule
	}
	if input.TargetEngineVersion != nil {
		record.TargetEngineVersion = *input.TargetEngineVersion
	}
	record.UpdatedAt = now
}