// Package gmclient provides the HTTP adapter for the ports.GMClient
// surface. It implements the registration path
// `POST /api/v1/internal/games/{game_id}/register-runtime` and the
// liveness probe `GET /api/v1/internal/healthz` used by the voluntary
// resume flow.
//
// Every transport-level failure (timeout, network error, non-2xx
// response) is wrapped with ports.ErrGMUnavailable so callers can
// detect the GM-unavailable case via errors.Is and follow the
// `lobby.runtime_paused_after_start` branch or the
// `service_unavailable` branch documented in the
// README Game Start Flow.
package gmclient

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

	"galaxy/lobby/internal/ports"

	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
)

// Client implements ports.GMClient against the trusted internal HTTP
// surface of Game Master.
type Client struct {
	baseURL    string
	httpClient *http.Client
}

// Config groups the construction parameters of Client.
type Config struct {
	// BaseURL is the absolute root URL of Game Master (no trailing
	// slash required).
	BaseURL string

	// Timeout bounds one round trip including TLS handshake. It must
	// be positive.
	Timeout time.Duration
}

// Validate reports whether cfg stores a usable Client configuration.
func (cfg Config) Validate() error {
	switch {
	case strings.TrimSpace(cfg.BaseURL) == "":
		return errors.New("gm client base url must not be empty")
	case cfg.Timeout <= 0:
		return errors.New("gm client timeout must be positive")
	default:
		return nil
	}
}

// NewClient constructs a Client from cfg. The transport is wrapped with
// otelhttp.NewTransport so traces propagate to Game Master.
func NewClient(cfg Config) (*Client, error) {
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("new gm client: %w", err)
	}
	httpClient := &http.Client{
		Timeout:   cfg.Timeout,
		Transport: otelhttp.NewTransport(http.DefaultTransport),
	}
	return &Client{
		baseURL:    strings.TrimRight(cfg.BaseURL, "/"),
		httpClient: httpClient,
	}, nil
}

// registerRuntimeBody mirrors the JSON body Lobby sends to Game Master.
// The shape is owned by Lobby for the Game Master is expected to
// accept it as-is when it implements the receiving handler.
type registerRuntimeBody struct {
	ContainerID         string `json:"container_id"`
	EngineEndpoint      string `json:"engine_endpoint"`
	TargetEngineVersion string `json:"target_engine_version"`
	TurnSchedule        string `json:"turn_schedule"`
}

// RegisterGame issues
// POST /api/v1/internal/games/{game_id}/register-runtime against Game
// Master. Any non-success outcome (validation error, transport error,
// timeout, non-2xx response) is wrapped with ports.ErrGMUnavailable so
// the caller can branch on errors.Is(err, ports.ErrGMUnavailable).
func (client *Client) RegisterGame(ctx context.Context, request ports.RegisterGameRequest) error {
	if client == nil || client.httpClient == nil {
		return errors.New("register game: nil client")
	}
	if ctx == nil {
		return errors.New("register game: nil context")
	}
	if err := request.Validate(); err != nil {
		return fmt.Errorf("register game: %w", err)
	}

	endpoint := client.baseURL + "/api/v1/internal/games/" + url.PathEscape(request.GameID.String()) + "/register-runtime"
	body := registerRuntimeBody{
		ContainerID:         request.ContainerID,
		EngineEndpoint:      request.EngineEndpoint,
		TargetEngineVersion: request.TargetEngineVersion,
		TurnSchedule:        request.TurnSchedule,
	}
	encoded, err := json.Marshal(body)
	if err != nil {
		return fmt.Errorf("register game: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(encoded))
	if err != nil {
		return fmt.Errorf("register game: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	resp, err := client.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("register game: %w", errors.Join(ports.ErrGMUnavailable, err))
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf(
			"register game: unexpected status %d: %w",
			resp.StatusCode, ports.ErrGMUnavailable,
		)
	}
	return nil
}

// Ping issues GET /api/v1/internal/healthz against Game Master. Any
// non-success outcome (validation error, transport error, timeout,
// non-2xx response) is wrapped with ports.ErrGMUnavailable so the
// caller can branch on errors.Is(err, ports.ErrGMUnavailable). Stage
// 16 voluntary resume uses this method as the liveness gate before
// transitioning a paused game back to running.
func (client *Client) Ping(ctx context.Context) error {
	if client == nil || client.httpClient == nil {
		return errors.New("ping: nil client")
	}
	if ctx == nil {
		return errors.New("ping: nil context")
	}

	endpoint := client.baseURL + "/api/v1/internal/healthz"
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return fmt.Errorf("ping: %w", err)
	}
	req.Header.Set("Accept", "application/json")

	resp, err := client.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("ping: %w", errors.Join(ports.ErrGMUnavailable, err))
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf(
			"ping: unexpected status %d: %w",
			resp.StatusCode, ports.ErrGMUnavailable,
		)
	}
	return nil
}

// Compile-time interface assertion.
var _ ports.GMClient = (*Client)(nil)