// Package removemember implements the `lobby.membership.remove` message
// type. Before the game has reached the running engine slot the
// membership record is dropped from the store and the race name
// reservation is released; after the engine slot exists the membership
// transitions to `removed` and the reservation is preserved so the
// capability evaluator at game finish can resolve it.
package removemember

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

	"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"
)

// preStartStatuses enumerates the game statuses in which a membership
// may exist but the engine container slot does not. Removing in these
// statuses drops the membership outright and releases the reservation.
var preStartStatuses = map[game.Status]struct{}{
	game.StatusEnrollmentOpen: {},
	game.StatusReadyToStart:   {},
	game.StatusStarting:       {},
	game.StatusStartFailed:    {},
}

// postStartStatuses enumerates the game statuses in which the engine
// container slot is alive. Removing in these statuses transitions the
// membership to `removed` and keeps the reservation until the
// capability evaluator runs at `game_finished`.
var postStartStatuses = map[game.Status]struct{}{
	game.StatusRunning: {},
	game.StatusPaused:  {},
}

// Service executes the remove-member use case.
type Service struct {
	games       ports.GameStore
	memberships ports.MembershipStore
	directory   ports.RaceNameDirectory
	clock       func() time.Time
	logger      *slog.Logger
	telemetry   *telemetry.Runtime
}

// Dependencies groups the collaborators used by Service.
type Dependencies struct {
	// Games loads the game record so the service can branch on
	// game.Status and authorize the actor against the owner.
	Games ports.GameStore

	// Memberships persists the post-start status transition and the
	// pre-start drop.
	Memberships ports.MembershipStore

	// Directory releases the race name reservation in the pre-start
	// branch. The post-start branch never invokes Directory.
	Directory ports.RaceNameDirectory

	// Clock supplies the wall-clock used for the RemovedAt stamp.
	// 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.membership.changes` counter on each
	// successful removal. 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 remove member service: nil game store")
	case deps.Memberships == nil:
		return nil, errors.New("new remove member service: nil membership store")
	case deps.Directory == nil:
		return nil, errors.New("new remove member service: nil race name directory")
	}

	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,
		directory:   deps.Directory,
		clock:       clock,
		logger:      logger.With("service", "lobby.removemember"),
		telemetry:   deps.Telemetry,
	}, nil
}

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

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

	// MembershipID identifies the target membership.
	MembershipID common.MembershipID
}

// Handle authorizes the actor, asserts the membership belongs to the
// game, branches on the game status to either drop or transition the
// membership, and returns the post-removal record. The pre-start
// branch returns a synthesized record with status=removed because the
// underlying primary record has been deleted from the store.
func (service *Service) Handle(ctx context.Context, input Input) (membership.Membership, error) {
	if service == nil {
		return membership.Membership{}, errors.New("remove member: nil service")
	}
	if ctx == nil {
		return membership.Membership{}, errors.New("remove member: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: actor: %w", err)
	}
	if err := input.GameID.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: %w", err)
	}
	if err := input.MembershipID.Validate(); err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: %w", err)
	}

	member, err := service.memberships.Get(ctx, input.MembershipID)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: %w", err)
	}
	if member.GameID != input.GameID {
		return membership.Membership{}, fmt.Errorf(
			"remove member: membership %q does not belong to game %q: %w",
			member.MembershipID, input.GameID, membership.ErrNotFound,
		)
	}

	gameRecord, err := service.games.Get(ctx, member.GameID)
	if err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: %w", err)
	}
	if err := authorize(input.Actor, gameRecord); err != nil {
		return membership.Membership{}, err
	}

	if member.Status != membership.StatusActive {
		return membership.Membership{}, fmt.Errorf(
			"remove member: status %q is not %q: %w",
			member.Status, membership.StatusActive, membership.ErrConflict,
		)
	}

	_, preStart := preStartStatuses[gameRecord.Status]
	_, postStart := postStartStatuses[gameRecord.Status]
	if !preStart && !postStart {
		return membership.Membership{}, fmt.Errorf(
			"remove member: game status %q does not allow remove: %w",
			gameRecord.Status, game.ErrConflict,
		)
	}

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

	if postStart {
		if err := service.memberships.UpdateStatus(ctx, ports.UpdateMembershipStatusInput{
			MembershipID: member.MembershipID,
			ExpectedFrom: membership.StatusActive,
			To:           membership.StatusRemoved,
			At:           now,
		}); err != nil {
			return membership.Membership{}, fmt.Errorf("remove member: %w", err)
		}
		service.telemetry.RecordMembershipChange(ctx, "removed")
		updated, err := service.memberships.Get(ctx, member.MembershipID)
		if err != nil {
			return membership.Membership{}, fmt.Errorf("remove member: %w", err)
		}
		logArgs := []any{
			"game_id", gameRecord.GameID.String(),
			"game_status", string(gameRecord.Status),
			"membership_id", member.MembershipID.String(),
			"user_id", member.UserID,
			"trigger", "post_start",
			"actor_kind", string(input.Actor.Kind),
		}
		logArgs = append(logArgs, logging.ContextAttrs(ctx)...)
		service.logger.InfoContext(ctx, "member removed (post-start)", logArgs...)
		return updated, nil
	}

	if err := service.memberships.Delete(ctx, member.MembershipID); err != nil {
		return membership.Membership{}, fmt.Errorf("remove member: %w", err)
	}
	if err := service.directory.ReleaseReservation(
		ctx,
		gameRecord.GameID.String(),
		member.UserID,
		member.RaceName,
	); err != nil {
		// The directory contract states ReleaseReservation is a no-op
		// for missing / mismatched / invalid records, so a non-nil
		// error here is unexpected. Log and proceed — the membership
		// record is already gone.
		service.logger.WarnContext(ctx, "release reservation on pre-start remove",
			"membership_id", member.MembershipID.String(),
			"err", err.Error(),
		)
	}

	service.telemetry.RecordMembershipChange(ctx, "removed")

	logArgs := []any{
		"game_id", gameRecord.GameID.String(),
		"game_status", string(gameRecord.Status),
		"membership_id", member.MembershipID.String(),
		"user_id", member.UserID,
		"trigger", "pre_start",
		"actor_kind", string(input.Actor.Kind),
	}
	logArgs = append(logArgs, logging.ContextAttrs(ctx)...)
	service.logger.InfoContext(ctx, "member removed (pre-start drop)", logArgs...)

	removedAt := now
	synthesized := member
	synthesized.Status = membership.StatusRemoved
	synthesized.RemovedAt = &removedAt
	return synthesized, 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 remove members from game %q",
		shared.ErrForbidden, record.GameID.String())
}