package backendclient

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"

	"galaxy/gateway/internal/downstream"
	lobbymodel "galaxy/model/lobby"
	"galaxy/transcoder"
)

const (
	lobbyResultCodeOK            = "ok"
	defaultLobbyErrorCodeInvalid = "invalid_request"
	defaultLobbyErrorCodeNoSubj  = "subject_not_found"
	defaultLobbyErrorCodeForbid  = "forbidden"
	defaultLobbyErrorCodeConfl   = "conflict"
	defaultLobbyErrorCodeIntErr  = "internal_error"
)

var stableLobbyErrorMessages = map[string]string{
	defaultLobbyErrorCodeInvalid: "request is invalid",
	defaultLobbyErrorCodeNoSubj:  "subject not found",
	defaultLobbyErrorCodeForbid:  "operation is forbidden for the calling user",
	defaultLobbyErrorCodeConfl:   "request conflicts with current state",
	defaultLobbyErrorCodeIntErr:  "internal server error",
}

// ExecuteLobbyCommand routes one authenticated lobby command into
// backend's `/api/v1/user/lobby/*` endpoints.
func (c *RESTClient) ExecuteLobbyCommand(ctx context.Context, command downstream.AuthenticatedCommand) (downstream.UnaryResult, error) {
	if c == nil || c.httpClient == nil {
		return downstream.UnaryResult{}, errors.New("backendclient: execute lobby command: nil client")
	}
	if ctx == nil {
		return downstream.UnaryResult{}, errors.New("backendclient: execute lobby command: nil context")
	}
	if err := ctx.Err(); err != nil {
		return downstream.UnaryResult{}, err
	}
	if strings.TrimSpace(command.UserID) == "" {
		return downstream.UnaryResult{}, errors.New("backendclient: execute lobby command: user_id must not be empty")
	}

	switch command.MessageType {
	case lobbymodel.MessageTypeMyGamesList:
		if _, err := transcoder.PayloadToMyGamesListRequest(command.PayloadBytes); err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("backendclient: execute lobby command %q: %w", command.MessageType, err)
		}
		return c.executeLobbyMyGames(ctx, command.UserID)
	case lobbymodel.MessageTypeOpenEnrollment:
		req, err := transcoder.PayloadToOpenEnrollmentRequest(command.PayloadBytes)
		if err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("backendclient: execute lobby command %q: %w", command.MessageType, err)
		}
		return c.executeLobbyOpenEnrollment(ctx, command.UserID, req)
	default:
		return downstream.UnaryResult{}, fmt.Errorf("backendclient: execute lobby command: unsupported message type %q", command.MessageType)
	}
}

func (c *RESTClient) executeLobbyMyGames(ctx context.Context, userID string) (downstream.UnaryResult, error) {
	body, status, err := c.do(ctx, http.MethodGet, c.baseURL+"/api/v1/user/lobby/my/games", userID, nil)
	if err != nil {
		return downstream.UnaryResult{}, fmt.Errorf("execute lobby.my.games.list: %w", err)
	}
	if status == http.StatusOK {
		var response lobbymodel.MyGamesListResponse
		if err := decodeStrictJSON(body, &response); err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("decode success response: %w", err)
		}
		payloadBytes, err := transcoder.MyGamesListResponseToPayload(&response)
		if err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("encode success response payload: %w", err)
		}
		return downstream.UnaryResult{
			ResultCode:   lobbyResultCodeOK,
			PayloadBytes: payloadBytes,
		}, nil
	}
	return projectLobbyErrorResponse(status, body)
}

func (c *RESTClient) executeLobbyOpenEnrollment(ctx context.Context, userID string, req *lobbymodel.OpenEnrollmentRequest) (downstream.UnaryResult, error) {
	if req == nil || strings.TrimSpace(req.GameID) == "" {
		return downstream.UnaryResult{}, errors.New("execute lobby.game.open-enrollment: game_id must not be empty")
	}
	target := c.baseURL + "/api/v1/user/lobby/games/" + url.PathEscape(req.GameID) + "/open-enrollment"
	body, status, err := c.do(ctx, http.MethodPost, target, userID, struct{}{})
	if err != nil {
		return downstream.UnaryResult{}, fmt.Errorf("execute lobby.game.open-enrollment: %w", err)
	}
	if status == http.StatusOK {
		// Backend returns the full LobbyGameDetail; gateway projects the
		// minimal {game_id, status} pair onto the existing wire shape.
		var detail struct {
			GameID string `json:"game_id"`
			Status string `json:"status"`
		}
		if err := json.NewDecoder(bytes.NewReader(body)).Decode(&detail); err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("decode success response: %w", err)
		}
		payloadBytes, err := transcoder.OpenEnrollmentResponseToPayload(&lobbymodel.OpenEnrollmentResponse{
			GameID: detail.GameID,
			Status: detail.Status,
		})
		if err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("encode success response payload: %w", err)
		}
		return downstream.UnaryResult{
			ResultCode:   lobbyResultCodeOK,
			PayloadBytes: payloadBytes,
		}, nil
	}
	return projectLobbyErrorResponse(status, body)
}

func projectLobbyErrorResponse(statusCode int, payload []byte) (downstream.UnaryResult, error) {
	switch {
	case statusCode == http.StatusServiceUnavailable:
		return downstream.UnaryResult{}, downstream.ErrDownstreamUnavailable
	case statusCode >= 400 && statusCode <= 599:
		errResp, err := decodeLobbyError(statusCode, payload)
		if err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("decode error response: %w", err)
		}
		payloadBytes, err := transcoder.LobbyErrorResponseToPayload(errResp)
		if err != nil {
			return downstream.UnaryResult{}, fmt.Errorf("encode error response payload: %w", err)
		}
		return downstream.UnaryResult{
			ResultCode:   errResp.Error.Code,
			PayloadBytes: payloadBytes,
		}, nil
	default:
		return downstream.UnaryResult{}, fmt.Errorf("unexpected HTTP status %d", statusCode)
	}
}

func decodeLobbyError(statusCode int, payload []byte) (*lobbymodel.ErrorResponse, error) {
	var response lobbymodel.ErrorResponse
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&response); err != nil {
		return nil, err
	}
	if err := decoder.Decode(&struct{}{}); err != io.EOF {
		if err == nil {
			return nil, errors.New("unexpected trailing JSON input")
		}
		return nil, err
	}
	response.Error.Code = normalizeLobbyErrorCode(statusCode, response.Error.Code)
	response.Error.Message = normalizeLobbyErrorMessage(response.Error.Code, response.Error.Message)
	if strings.TrimSpace(response.Error.Code) == "" {
		return nil, errors.New("missing error code")
	}
	if strings.TrimSpace(response.Error.Message) == "" {
		return nil, errors.New("missing error message")
	}
	return &response, nil
}

func normalizeLobbyErrorCode(statusCode int, code string) string {
	if trimmed := strings.TrimSpace(code); trimmed != "" {
		return trimmed
	}
	switch statusCode {
	case http.StatusBadRequest:
		return defaultLobbyErrorCodeInvalid
	case http.StatusForbidden:
		return defaultLobbyErrorCodeForbid
	case http.StatusNotFound:
		return defaultLobbyErrorCodeNoSubj
	case http.StatusConflict:
		return defaultLobbyErrorCodeConfl
	default:
		return defaultLobbyErrorCodeIntErr
	}
}

func normalizeLobbyErrorMessage(code, message string) string {
	if trimmed := strings.TrimSpace(message); trimmed != "" {
		return trimmed
	}
	if stable, ok := stableLobbyErrorMessages[code]; ok {
		return stable
	}
	return stableLobbyErrorMessages[defaultLobbyErrorCodeIntErr]
}