package notify

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

// Webhook delivers notifications as a JSON POST of the Event to a
// project-configured URL. Config is {"url": "..."}. secret is currently
// unused (reserved for future request signing) and is never logged.
//
// The destination URL is project-controlled (any project owner can set it),
// so it is treated as untrusted input: isAllowedURL blocks requests to
// loopback/private/link-local/unspecified addresses to prevent SSRF against
// internal services and cloud metadata endpoints (e.g. 169.254.169.254).
// Redirects are not followed, since a redirect response could otherwise be
// used to bypass the destination check.
type Webhook struct {
	HTTP *http.Client

	// allowPrivate disables the SSRF guard. It exists only so tests can
	// exercise Send happy-paths against httptest servers, which listen on
	// loopback. Production Dispatchers (NewDispatcher) must never set this.
	allowPrivate bool
}

// isAllowedURL rejects any URL that is not a plain http/https request to a
// public, resolvable address. It resolves hostnames and checks every
// returned address — a hostname that resolves to even one
// private/loopback/link-local/unspecified address is rejected, since DNS
// answers are attacker-influenceable (rebinding) and partial trust is not
// safe.
func isAllowedURL(rawurl string) error {
	u, err := url.Parse(rawurl)
	if err != nil {
		return fmt.Errorf("webhook: invalid url: %w", err)
	}
	if u.Scheme != "http" && u.Scheme != "https" {
		return errors.New("webhook: destination not allowed")
	}
	host := u.Hostname()
	if host == "" {
		return errors.New("webhook: destination not allowed")
	}

	var ips []net.IP
	if ip := net.ParseIP(host); ip != nil {
		ips = []net.IP{ip}
	} else {
		resolved, err := net.LookupIP(host)
		if err != nil {
			return errors.New("webhook: destination not allowed")
		}
		ips = resolved
	}

	for _, ip := range ips {
		if isDisallowedIP(ip) {
			return errors.New("webhook: destination not allowed")
		}
	}
	return nil
}

func isDisallowedIP(ip net.IP) bool {
	return ip.IsLoopback() ||
		ip.IsPrivate() ||
		ip.IsLinkLocalUnicast() ||
		ip.IsLinkLocalMulticast() ||
		ip.IsUnspecified() ||
		ip.IsMulticast()
}

func (w *Webhook) Send(ctx context.Context, cfg json.RawMessage, secret string, ev Event) error {
	var c struct {
		URL string `json:"url"`
	}
	if err := json.Unmarshal(cfg, &c); err != nil {
		return err
	}
	if !w.allowPrivate {
		if err := isAllowedURL(c.URL); err != nil {
			return err
		}
	}
	body, err := json.Marshal(ev)
	if err != nil {
		return err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.URL, bytes.NewReader(body))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")

	client := w.HTTP
	if client.CheckRedirect == nil {
		clientCopy := *client
		clientCopy.CheckRedirect = func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		}
		client = &clientCopy
	}

	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("webhook: status %d", resp.StatusCode)
	}
	return nil
}