package ipfetcher

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"strings"
	"time"
)

var defaultProviders = []string{
	"https://api.ipify.org",
	"https://ifconfig.me/ip",
	"https://icanhazip.com",
}

var httpClient = &http.Client{Timeout: 5 * time.Second}

// Result holds the outcome of a successful public IP fetch.
type Result struct {
	IP     string // The detected public IP.
	Source string // The URL that returned the IP (e.g. https://api.ipify.org).
}

// FetchPublicIPFrom fetches the public IP by trying each URL in order.
// If urls is nil or empty, the built-in default providers are used.
func FetchPublicIPFrom(ctx context.Context, urls []string) (*Result, error) {
	slog.Debug("fetching public IP...")
	if len(urls) == 0 {
		urls = defaultProviders
	}
	var lastErr error
	for _, url := range urls {
		ip, err := fetchFrom(ctx, url)
		if err != nil {
			lastErr = err
			continue
		}
		slog.Default().Debug("public IP fetched", "ip", ip, "source", url)
		return &Result{IP: ip, Source: url}, nil
	}
	return nil, fmt.Errorf("all IP providers failed, last error: %w", lastErr)
}

func fetchFrom(ctx context.Context, url string) (string, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return "", err
	}

	resp, err := httpClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("%s returned status %d", url, resp.StatusCode)
	}

	body, err := io.ReadAll(io.LimitReader(resp.Body, 256))
	if err != nil {
		return "", err
	}

	ip := strings.TrimSpace(string(body))
	if net.ParseIP(ip) == nil {
		return "", fmt.Errorf("%s returned invalid IP: %q", url, ip)
	}

	return ip, nil
}