package metadata

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

const defaultTimeout = 10 * time.Second

// newHTTPClient собирает http.Client с опциональным прокси и таймаутом.
func newHTTPClient(proxy string, timeout time.Duration) (*http.Client, error) {
	if timeout <= 0 {
		timeout = defaultTimeout
	}
	transport := http.DefaultTransport
	if proxy != "" {
		u, err := url.Parse(proxy)
		if err != nil {
			return nil, fmt.Errorf("metadata: parse proxy %q: %w", proxy, err)
		}
		transport = &http.Transport{Proxy: http.ProxyURL(u)}
	}
	return &http.Client{Timeout: timeout, Transport: transport}, nil
}

const maxBody = 4 << 20 // 4 MiB — потолок на тело ответа

// getJSON выполняет GET и декодирует JSON-ответ в out. headers — опц.
// дополнительные заголовки (напр. Authorization).
func getJSON(ctx context.Context, hc *http.Client, rawURL string, headers map[string]string, out any) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, rawURL, nil)
	if err != nil {
		return fmt.Errorf("metadata: build request: %w", err)
	}
	req.Header.Set("Accept", "application/json")
	for k, v := range headers {
		req.Header.Set(k, v)
	}
	return doJSON(hc, req, out)
}

// postJSON выполняет POST с JSON-телом и декодирует ответ.
func postJSON(ctx context.Context, hc *http.Client, rawURL string, body, out any) error {
	payload, err := json.Marshal(body)
	if err != nil {
		return fmt.Errorf("metadata: marshal body: %w", err)
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, rawURL, bytes.NewReader(payload))
	if err != nil {
		return fmt.Errorf("metadata: build request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")
	return doJSON(hc, req, out)
}

func doJSON(hc *http.Client, req *http.Request, out any) error {
	resp, err := hc.Do(req)
	if err != nil {
		return fmt.Errorf("metadata: request: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	raw, err := io.ReadAll(io.LimitReader(resp.Body, maxBody))
	if err != nil {
		return fmt.Errorf("metadata: read body: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("metadata: status %d: %s", resp.StatusCode, snippet(raw))
	}
	if err := json.Unmarshal(raw, out); err != nil {
		return fmt.Errorf("metadata: decode: %w (body: %s)", err, snippet(raw))
	}
	return nil
}

func snippet(b []byte) string {
	const max = 200
	if len(b) > max {
		return string(b[:max]) + "…"
	}
	return string(b)
}