package common

import (
	"context"
	"fmt"
	"io"
	"net/http"
)

// maxResponseBodyBytes is a hard safety limit on HTTP response bodies.
// API responses should be small, so this protects us from accidental
// or malicious large responses.
const maxResponseBodyBytes = 2 << 21 // 4 MiB

func FetchBody(ctx context.Context, client *http.Client, url, userAgent, accept string) ([]byte, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}

	if userAgent != "" {
		req.Header.Set("User-Agent", userAgent)
	}
	if accept != "" {
		req.Header.Set("Accept", accept)
	}

	res, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()

	if res.StatusCode < 200 || res.StatusCode >= 300 {
		return nil, fmt.Errorf("HTTP %s", res.Status)
	}

	// Read at most maxResponseBodyBytes + 1 so we can detect overflow.
	limited := io.LimitReader(res.Body, maxResponseBodyBytes+1)

	b, err := io.ReadAll(limited)
	if err != nil {
		return nil, err
	}

	if len(b) == 0 {
		return nil, fmt.Errorf("empty response body")
	}

	if len(b) > maxResponseBodyBytes {
		return nil, fmt.Errorf("response body too large (>%d bytes)", maxResponseBodyBytes)
	}

	return b, nil
}