// Package rtmclient provides the trusted-internal Runtime Manager
// REST client Game Master uses for synchronous lifecycle operations
// against an already-running container. Two routes are mounted:
//
//   - POST /api/v1/internal/runtimes/{game_id}/stop
//   - POST /api/v1/internal/runtimes/{game_id}/patch
//
// `Restart` is reserved per `gamemaster/PLAN.md` Stage 10 and is not
// part of the v1 surface.
package rtmclient

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

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

	"galaxy/gamemaster/internal/ports"
)

const (
	stopPathTemplate  = "/api/v1/internal/runtimes/%s/stop"
	patchPathTemplate = "/api/v1/internal/runtimes/%s/patch"
)

// Config configures one HTTP-backed Runtime Manager internal client.
type Config struct {
	// BaseURL stores the absolute base URL of the Runtime Manager
	// internal HTTP listener (e.g. `http://rtmanager:8096`).
	BaseURL string

	// RequestTimeout bounds one outbound stop/patch request.
	RequestTimeout time.Duration
}

// Client speaks REST/JSON to the Runtime Manager internal API.
type Client struct {
	baseURL              string
	requestTimeout       time.Duration
	httpClient           *http.Client
	closeIdleConnections func()
}

type stopRequestEnvelope struct {
	Reason string `json:"reason"`
}

type patchRequestEnvelope struct {
	ImageRef string `json:"image_ref"`
}

type errorEnvelope struct {
	Error *errorBody `json:"error"`
}

type errorBody struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

// NewClient constructs an RTM internal client with otelhttp-wrapped
// transport cloned from `http.DefaultTransport`. Call `Close` to
// release idle connections at shutdown.
func NewClient(cfg Config) (*Client, error) {
	transport, ok := http.DefaultTransport.(*http.Transport)
	if !ok {
		return nil, errors.New("new rtm client: default transport is not *http.Transport")
	}
	cloned := transport.Clone()
	return newClient(cfg, &http.Client{Transport: otelhttp.NewTransport(cloned)}, cloned.CloseIdleConnections)
}

func newClient(cfg Config, httpClient *http.Client, closeIdleConnections func()) (*Client, error) {
	switch {
	case strings.TrimSpace(cfg.BaseURL) == "":
		return nil, errors.New("new rtm client: base url must not be empty")
	case cfg.RequestTimeout <= 0:
		return nil, errors.New("new rtm client: request timeout must be positive")
	case httpClient == nil:
		return nil, errors.New("new rtm client: http client must not be nil")
	}
	parsed, err := url.Parse(strings.TrimRight(strings.TrimSpace(cfg.BaseURL), "/"))
	if err != nil {
		return nil, fmt.Errorf("new rtm client: parse base url: %w", err)
	}
	if parsed.Scheme == "" || parsed.Host == "" {
		return nil, errors.New("new rtm client: base url must be absolute")
	}
	return &Client{
		baseURL:              parsed.String(),
		requestTimeout:       cfg.RequestTimeout,
		httpClient:           httpClient,
		closeIdleConnections: closeIdleConnections,
	}, nil
}

// Close releases idle HTTP connections owned by the underlying
// transport. Safe to call multiple times.
func (client *Client) Close() error {
	if client == nil || client.closeIdleConnections == nil {
		return nil
	}
	client.closeIdleConnections()
	return nil
}

// Stop calls POST /api/v1/internal/runtimes/{game_id}/stop with body
// `{reason}`. Any non-success outcome is wrapped with
// `ports.ErrRTMUnavailable`.
func (client *Client) Stop(ctx context.Context, gameID, reason string) error {
	if err := client.validate(ctx, gameID); err != nil {
		return err
	}
	if strings.TrimSpace(reason) == "" {
		return errors.New("rtm stop: reason must not be empty")
	}
	body, err := json.Marshal(stopRequestEnvelope{Reason: reason})
	if err != nil {
		return fmt.Errorf("rtm stop: encode request: %w", err)
	}
	return client.callMutation(ctx, fmt.Sprintf(stopPathTemplate, url.PathEscape(gameID)), body, "rtm stop")
}

// Patch calls POST /api/v1/internal/runtimes/{game_id}/patch with body
// `{image_ref}`. A `409 conflict` from RTM (semver violation) is also
// wrapped with `ports.ErrRTMUnavailable`; the underlying `error_code`
// is preserved in the wrapped error message so callers can branch on
// the substring if needed.
func (client *Client) Patch(ctx context.Context, gameID, imageRef string) error {
	if err := client.validate(ctx, gameID); err != nil {
		return err
	}
	if strings.TrimSpace(imageRef) == "" {
		return errors.New("rtm patch: image ref must not be empty")
	}
	body, err := json.Marshal(patchRequestEnvelope{ImageRef: imageRef})
	if err != nil {
		return fmt.Errorf("rtm patch: encode request: %w", err)
	}
	return client.callMutation(ctx, fmt.Sprintf(patchPathTemplate, url.PathEscape(gameID)), body, "rtm patch")
}

func (client *Client) validate(ctx context.Context, gameID string) error {
	if client == nil || client.httpClient == nil {
		return errors.New("rtm client: nil client")
	}
	if ctx == nil {
		return errors.New("rtm client: nil context")
	}
	if err := ctx.Err(); err != nil {
		return err
	}
	if strings.TrimSpace(gameID) == "" {
		return errors.New("rtm client: game id must not be empty")
	}
	return nil
}

func (client *Client) callMutation(ctx context.Context, requestPath string, body []byte, opLabel string) error {
	payload, statusCode, err := client.doRequest(ctx, http.MethodPost, requestPath, body)
	if err != nil {
		return fmt.Errorf("%w: %s: %w", ports.ErrRTMUnavailable, opLabel, err)
	}
	if statusCode >= 200 && statusCode < 300 {
		return nil
	}
	errorCode := decodeErrorCode(payload)
	if errorCode != "" {
		return fmt.Errorf("%w: %s: unexpected status %d (error_code=%s)", ports.ErrRTMUnavailable, opLabel, statusCode, errorCode)
	}
	return fmt.Errorf("%w: %s: unexpected status %d", ports.ErrRTMUnavailable, opLabel, statusCode)
}

func (client *Client) doRequest(ctx context.Context, method, requestPath string, body []byte) ([]byte, int, error) {
	attemptCtx, cancel := context.WithTimeout(ctx, client.requestTimeout)
	defer cancel()

	var reader io.Reader
	if len(body) > 0 {
		reader = bytes.NewReader(body)
	}
	req, err := http.NewRequestWithContext(attemptCtx, method, client.baseURL+requestPath, reader)
	if err != nil {
		return nil, 0, fmt.Errorf("build request: %w", err)
	}
	req.Header.Set("Accept", "application/json")
	if len(body) > 0 {
		req.Header.Set("Content-Type", "application/json")
	}
	resp, err := client.httpClient.Do(req)
	if err != nil {
		return nil, 0, err
	}
	defer resp.Body.Close()
	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, resp.StatusCode, fmt.Errorf("read response body: %w", err)
	}
	return respBody, resp.StatusCode, nil
}

func decodeErrorCode(payload []byte) string {
	if len(payload) == 0 {
		return ""
	}
	var envelope errorEnvelope
	if err := json.Unmarshal(payload, &envelope); err != nil {
		return ""
	}
	if envelope.Error == nil {
		return ""
	}
	return envelope.Error.Code
}

// Compile-time assertion: Client implements ports.RTMClient.
var _ ports.RTMClient = (*Client)(nil)