// Package listmyinvites implements the `lobby.my_invites.list` message
// type. It returns invites addressed to the acting user with status
// `created`, joined with the host game's `game_name` and the inviter's
// display name as defined in `lobby/README.md` §«My open invitations»:
// the inviter's race name when the inviter holds an active membership
// in the host game, and the inviter's `user_id` otherwise.
//
// The service is exclusively self-service: admin actors are rejected
// with `shared.ErrForbidden`.
package listmyinvites

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

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

// Service executes the list-my-invites use case.
type Service struct {
	games       ports.GameStore
	invites     ports.InviteStore
	memberships ports.MembershipStore
	logger      *slog.Logger
}

// Dependencies groups the collaborators used by Service.
type Dependencies struct {
	// Games is loaded per invite to enrich the response with the host
	// game's name and to access its OwnerUserID.
	Games ports.GameStore

	// Invites supplies the per-invitee index.
	Invites ports.InviteStore

	// Memberships is consulted per invite's host game to derive the
	// inviter's race name. It may be replaced with a denormalized field
	// later without changing this contract.
	Memberships ports.MembershipStore

	// Logger records structured diagnostics. Defaults to slog.Default
	// when nil.
	Logger *slog.Logger
}

// NewService constructs one Service with deps.
func NewService(deps Dependencies) (*Service, error) {
	switch {
	case deps.Games == nil:
		return nil, errors.New("new list my invites service: nil game store")
	case deps.Invites == nil:
		return nil, errors.New("new list my invites service: nil invite store")
	case deps.Memberships == nil:
		return nil, errors.New("new list my invites service: nil membership store")
	}
	logger := deps.Logger
	if logger == nil {
		logger = slog.Default()
	}
	return &Service{
		games:       deps.Games,
		invites:     deps.Invites,
		memberships: deps.Memberships,
		logger:      logger.With("service", "lobby.listmyinvites"),
	}, nil
}

// Input stores the arguments required to compute the acting user's
// open-invites view.
type Input struct {
	// Actor identifies the caller. Must be ActorKindUser.
	Actor shared.Actor

	// Page stores the pagination request.
	Page shared.Page
}

// Item enriches one open invite with the host game's name and the
// derived inviter display name, mirroring the OpenAPI `MyInviteItem`
// schema.
type Item struct {
	Invite      invite.Invite
	GameName    string
	InviterName string
}

// Output stores the page returned by Handle.
type Output struct {
	// Items stores the enriched invite records included in the current
	// page.
	Items []Item

	// NextPageToken stores the opaque continuation token; empty when
	// the current page is the last one.
	NextPageToken string
}

// Handle authorizes the actor as a user, fetches their invites,
// filters to `created`, joins with the game store and the inviter's
// active membership, sorts, and returns the requested page.
func (service *Service) Handle(ctx context.Context, input Input) (Output, error) {
	if service == nil {
		return Output{}, errors.New("list my invites: nil service")
	}
	if ctx == nil {
		return Output{}, errors.New("list my invites: nil context")
	}
	if err := input.Actor.Validate(); err != nil {
		return Output{}, fmt.Errorf("list my invites: actor: %w", err)
	}
	if !input.Actor.IsUser() {
		return Output{}, fmt.Errorf(
			"%w: only authenticated user actors may list their invites",
			shared.ErrForbidden,
		)
	}

	records, err := service.invites.GetByUser(ctx, input.Actor.UserID)
	if err != nil {
		return Output{}, fmt.Errorf("list my invites: %w", err)
	}

	candidates := make([]Item, 0, len(records))
	for _, record := range records {
		if record.Status != invite.StatusCreated {
			continue
		}
		gameName, ok := service.lookupGameName(ctx, record.GameID, record.InviteID)
		if !ok {
			continue
		}
		inviterName, err := service.deriveInviterName(ctx, record)
		if err != nil {
			return Output{}, fmt.Errorf("list my invites: %w", err)
		}
		candidates = append(candidates, Item{
			Invite:      record,
			GameName:    gameName,
			InviterName: inviterName,
		})
	}

	sortItems(candidates)

	start, end, nextOffset, hasMore := shared.Window(len(candidates), input.Page)
	out := Output{Items: append([]Item(nil), candidates[start:end]...)}
	if hasMore {
		out.NextPageToken = shared.EncodeToken(nextOffset)
	}
	return out, nil
}

// lookupGameName returns the host game's name. A missing game record
// is logged at warn and the invite is dropped from the response — the
// invite cannot meaningfully render without the parent game.
func (service *Service) lookupGameName(
	ctx context.Context,
	gameID common.GameID,
	inviteID common.InviteID,
) (string, bool) {
	record, err := service.games.Get(ctx, gameID)
	if err == nil {
		return record.GameName, true
	}
	if errors.Is(err, game.ErrNotFound) {
		service.logger.WarnContext(ctx, "invite references missing game",
			"invite_id", inviteID.String(),
			"game_id", gameID.String(),
		)
		return "", false
	}
	service.logger.ErrorContext(ctx, "load invite game",
		"invite_id", inviteID.String(),
		"game_id", gameID.String(),
		"err", err.Error(),
	)
	return "", false
}

// deriveInviterName returns the inviter's race name when an active
// membership exists in the host game; otherwise it returns the
// inviter's user_id verbatim, matching README §«Invite Lifecycle».
func (service *Service) deriveInviterName(ctx context.Context, record invite.Invite) (string, error) {
	memberships, err := service.memberships.GetByGame(ctx, record.GameID)
	if err != nil {
		return "", err
	}
	for _, mb := range memberships {
		if mb.UserID == record.InviterUserID && mb.Status == membership.StatusActive {
			return mb.RaceName, nil
		}
	}
	return record.InviterUserID, nil
}

// sortItems orders invites by CreatedAt descending; InviteID breaks
// ties for stable output across adapters.
func sortItems(items []Item) {
	sort.Slice(items, func(i, j int) bool {
		ci, cj := items[i].Invite.CreatedAt, items[j].Invite.CreatedAt
		if !ci.Equal(cj) {
			return ci.After(cj)
		}
		return items[i].Invite.InviteID < items[j].Invite.InviteID
	})
}