// Package approveapplication implements the `lobby.application.approve`
// message type. It reserves the applicant's race name, transitions the
// application from submitted to approved, creates the matching active
// membership, opens the gap window when the new approved count equals
// max_players, and publishes the lobby.membership.approved intent.
package approveapplication

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

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

// Service executes the public-game application approval use case.
type Service struct {
	games        ports.GameStore
	memberships  ports.MembershipStore
	applications ports.ApplicationStore
	directory    ports.RaceNameDirectory
	gapStore     ports.GapActivationStore
	intents      ports.IntentPublisher
	ids          ports.IDGenerator
	clock        func() time.Time
	logger       *slog.Logger
	telemetry    *telemetry.Runtime
}

// Dependencies groups the collaborators used by Service.
type Dependencies struct {
	// Games loads the target game record for status verification.
	Games ports.GameStore

	// Memberships persists the new active membership and supplies the
	// approved-count for the gap-window decision.
	Memberships ports.MembershipStore

	// Applications loads the target application and applies the
	// submitted → approved transition.
	Applications ports.ApplicationStore

	// Directory canonicalizes the race name and reserves it for the
	// applicant.
	Directory ports.RaceNameDirectory

	// GapStore records the gap-window activation timestamp when the
	// new approved count equals max_players.
	GapStore ports.GapActivationStore

	// Intents publishes the lobby.membership.approved intent.
	Intents ports.IntentPublisher

	// IDs mints the new opaque membership identifier.
	IDs ports.IDGenerator

	// Clock supplies the wall-clock used for DecidedAt, JoinedAt,
	// gap-activation time, and the notification's OccurredAt.
	Clock func() time.Time

	// Logger records structured service-level events.
	Logger *slog.Logger

	// Telemetry records the `lobby.application.outcomes` and
	// `lobby.membership.changes` counters. 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 approve application service: nil game store")
	case deps.Memberships == nil:
		return nil, errors.New("new approve application service: nil membership store")
	case deps.Applications == nil:
		return nil, errors.New("new approve application service: nil application store")
	case deps.Directory == nil:
		return nil, errors.New("new approve application service: nil race name directory")
	case deps.GapStore == nil:
		return nil, errors.New("new approve application service: nil gap activation store")
	case deps.Intents == nil:
		return nil, errors.New("new approve application service: nil intent publisher")
	case deps.IDs == nil:
		return nil, errors.New("new approve application 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,
		memberships:  deps.Memberships,
		applications: deps.Applications,
		directory:    deps.Directory,
		gapStore:     deps.GapStore,
		intents:      deps.Intents,
		ids:          deps.IDs,
		clock:        clock,
		logger:       logger.With("service", "lobby.approveapplication"),
		telemetry:    deps.Telemetry,
	}, nil
}

// Input stores the arguments required to approve one application.
type Input struct {
	// Actor identifies the caller. Must be ActorKindAdmin per the
	// README message catalog.
	Actor shared.Actor

	// GameID identifies the game referenced by the request path; it
	// must match the loaded application's GameID.
	GameID common.GameID

	// ApplicationID identifies the target application.
	ApplicationID common.ApplicationID
}

// Handle authorizes the actor, validates the application + game state,
// reserves the race name, transitions the application, persists the
// membership, opens the gap window if appropriate, and publishes the
// lobby.membership.approved intent on success.
func (service *Service) Handle(ctx context.Context, input Input) (membership.Membership, error) {
	if service == nil {
		return membership.Membership{}, errors.New("approve application: nil service")
	}
	if ctx == nil {
		return membership.Membership{}, errors.New("approve application: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: actor: %w", err)
	}
	if !input.Actor.IsAdmin() {
		return membership.Membership{}, fmt.Errorf(
			"%w: only admin callers may approve applications",
			shared.ErrForbidden,
		)
	}
	if err := input.GameID.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	if err := input.ApplicationID.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}

	app, err := service.applications.Get(ctx, input.ApplicationID)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	if app.GameID != input.GameID {
		// Defensive: opaque ids must not leak across games.
		return membership.Membership{}, fmt.Errorf(
			"approve application: application %q does not belong to game %q: %w",
			app.ApplicationID, input.GameID, application.ErrNotFound,
		)
	}
	if app.Status != application.StatusSubmitted {
		return membership.Membership{}, fmt.Errorf(
			"approve application: status %q is not %q: %w",
			app.Status, application.StatusSubmitted, application.ErrConflict,
		)
	}

	gameRecord, err := service.games.Get(ctx, input.GameID)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	if gameRecord.GameType != game.GameTypePublic {
		return membership.Membership{}, fmt.Errorf(
			"approve application: game %q is not public: %w",
			gameRecord.GameID, game.ErrConflict,
		)
	}
	if gameRecord.Status != game.StatusEnrollmentOpen {
		return membership.Membership{}, fmt.Errorf(
			"approve application: game %q is not in enrollment_open: %w",
			gameRecord.GameID, game.ErrConflict,
		)
	}

	cap := gameRecord.MaxPlayers + gameRecord.StartGapPlayers
	currentActive, err := shared.CountActiveMemberships(ctx, service.memberships, gameRecord.GameID)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	if currentActive >= cap {
		return membership.Membership{}, fmt.Errorf(
			"approve application: roster full (%d active >= %d cap): %w",
			currentActive, cap, game.ErrConflict,
		)
	}

	canonical, err := service.directory.Canonicalize(app.RaceName)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}

	if err := service.directory.Reserve(ctx, gameRecord.GameID.String(), app.ApplicantUserID, app.RaceName); err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}

	now := service.clock().UTC()
	updateErr := service.applications.UpdateStatus(ctx, ports.UpdateApplicationStatusInput{
		ApplicationID: app.ApplicationID,
		ExpectedFrom:  application.StatusSubmitted,
		To:            application.StatusApproved,
		At:            now,
	})
	if updateErr != nil {
		// Concurrent mutation lost the CAS race. Release the
		// reservation we just made so it does not orphan; the user
		// may retry submission later under the same canonical key.
		if releaseErr := service.directory.ReleaseReservation(ctx, gameRecord.GameID.String(), app.ApplicantUserID, app.RaceName); releaseErr != nil {
			service.logger.WarnContext(ctx, "release reservation after approve cas failure",
				"application_id", app.ApplicationID.String(),
				"err", releaseErr.Error(),
			)
		}
		return membership.Membership{}, fmt.Errorf("approve application: %w", updateErr)
	}

	membershipID, err := service.ids.NewMembershipID()
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	memberRecord, err := membership.New(membership.NewMembershipInput{
		MembershipID: membershipID,
		GameID:       gameRecord.GameID,
		UserID:       app.ApplicantUserID,
		RaceName:     app.RaceName,
		CanonicalKey: canonical,
		Now:          now,
	})
	if err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}
	if err := service.memberships.Save(ctx, memberRecord); err != nil {
		return membership.Membership{}, fmt.Errorf("approve application: %w", err)
	}

	// Gap-window trigger: count after Save now includes the new
	// membership, so if it equals max_players we just crossed the
	// threshold. The worker reads gap_activated_at to time
	// out the gap; auto-transition to ready_to_start is its job.
	if currentActive+1 == gameRecord.MaxPlayers {
		if err := service.gapStore.MarkActivated(ctx, gameRecord.GameID, now); err != nil {
			service.logger.WarnContext(ctx, "mark gap activation",
				"game_id", gameRecord.GameID.String(),
				"err", err.Error(),
			)
		}
	}

	intent, err := notificationintent.NewLobbyMembershipApprovedIntent(
		notificationintent.Metadata{
			IdempotencyKey: "lobby.membership.approved:" + memberRecord.MembershipID.String(),
			OccurredAt:     now,
		},
		memberRecord.UserID,
		notificationintent.LobbyMembershipApprovedPayload{
			GameID:   gameRecord.GameID.String(),
			GameName: gameRecord.GameName,
		},
	)
	if err != nil {
		service.logger.ErrorContext(ctx, "build membership approved intent",
			"membership_id", memberRecord.MembershipID.String(),
			"err", err.Error(),
		)
	} else if _, publishErr := service.intents.Publish(ctx, intent); publishErr != nil {
		service.logger.WarnContext(ctx, "publish membership approved intent",
			"membership_id", memberRecord.MembershipID.String(),
			"err", publishErr.Error(),
		)
	}

	service.telemetry.RecordApplicationOutcome(ctx, "approved")
	service.telemetry.RecordMembershipChange(ctx, "activated")

	logArgs := []any{
		"game_id", gameRecord.GameID.String(),
		"game_status", string(gameRecord.Status),
		"application_id", app.ApplicationID.String(),
		"membership_id", memberRecord.MembershipID.String(),
		"user_id", memberRecord.UserID,
		"race_name", memberRecord.RaceName,
		"canonical_key", string(canonical),
	}
	logArgs = append(logArgs, logging.ContextAttrs(ctx)...)
	service.logger.InfoContext(ctx, "application approved", logArgs...)
	return memberRecord, nil
}