package turnstile

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/caddyserver/caddy/v2"
	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
	"go.uber.org/zap"
)

const (
	sessionPassCookieVersion = "4"
	forgejoSettingsPath      = "/user/settings"
	forgejoUserPath          = "/api/v1/user"
)

func normalizeUpstream(raw string) (string, error) {
	if raw == "" {
		return "", fmt.Errorf("turnstile: upstream is required")
	}
	if !strings.Contains(raw, "://") {
		raw = "http://" + raw
	}
	u, err := url.Parse(raw)
	if err != nil {
		return "", fmt.Errorf("turnstile: invalid upstream: %w", err)
	}
	if u.Host == "" {
		return "", fmt.Errorf("turnstile: invalid upstream: missing host")
	}
	if u.Path != "" && u.Path != "/" {
		return "", fmt.Errorf("turnstile: upstream must not include a path")
	}
	return u.Scheme + "://" + u.Host, nil
}

type sessionPassSigner struct {
	secret []byte
	name   string
	ttl    time.Duration
}

func newSessionPassSigner(secret, name string, ttl time.Duration) (*sessionPassSigner, error) {
	if secret == "" {
		return nil, fmt.Errorf("cookie_secret is required")
	}
	if name == "" {
		name = "__turnstile_session_pass"
	}
	if ttl < time.Minute {
		ttl = time.Hour
	}
	return &sessionPassSigner{
		secret: []byte(secret),
		name:   name,
		ttl:    ttl,
	}, nil
}

func credentialBinding(secret []byte, token string) string {
	if token == "" {
		return ""
	}
	mac := hmac.New(sha256.New, secret)
	mac.Write([]byte(token))
	return hex.EncodeToString(mac.Sum(nil))
}

func bindingMatches(secret []byte, token, binding string) bool {
	if token == "" || binding == "" {
		return false
	}
	expected := credentialBinding(secret, token)
	return hmac.Equal([]byte(expected), []byte(binding))
}

func (s *sessionPassSigner) set(w http.ResponseWriter, r *http.Request, sessionToken, rememberToken, username string) error {
	if sessionToken == "" && rememberToken == "" {
		return fmt.Errorf("session pass requires a session or remember-me token")
	}
	if username == "" {
		return fmt.Errorf("session pass requires a username")
	}
	nonce := make([]byte, 16)
	if _, err := rand.Read(nonce); err != nil {
		return err
	}
	exp := time.Now().Add(s.ttl).Unix()
	sessionBinding := credentialBinding(s.secret, sessionToken)
	rememberBinding := credentialBinding(s.secret, rememberToken)
	payload := fmt.Sprintf("%s|%d|%s|%s|%s|%s", sessionPassCookieVersion, exp, hex.EncodeToString(nonce), sessionBinding, rememberBinding, username)
	mac := hmac.New(sha256.New, s.secret)
	mac.Write([]byte(payload))
	sig := hex.EncodeToString(mac.Sum(nil))
	value := base64.RawURLEncoding.EncodeToString([]byte(payload + "|" + sig))

	http.SetCookie(w, &http.Cookie{
		Name:     s.name,
		Value:    value,
		Path:     "/",
		HttpOnly: true,
		Secure:   r.TLS != nil || strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https"),
		SameSite: http.SameSiteLaxMode,
		Expires:  time.Unix(exp, 0),
		MaxAge:   int(s.ttl.Seconds()),
	})
	return nil
}

func (s *sessionPassSigner) valid(r *http.Request, sessionToken, rememberToken string) (string, bool) {
	if sessionToken == "" && rememberToken == "" {
		return "", false
	}
	cookie, err := r.Cookie(s.name)
	if err != nil || cookie.Value == "" {
		return "", false
	}
	raw, err := base64.RawURLEncoding.DecodeString(cookie.Value)
	if err != nil {
		return "", false
	}
	parts := strings.Split(string(raw), "|")
	if len(parts) != 7 {
		return "", false
	}
	ver, expStr, nonce, sessionBinding, rememberBinding, username, sig := parts[0], parts[1], parts[2], parts[3], parts[4], parts[5], parts[6]
	if ver != sessionPassCookieVersion || nonce == "" || sig == "" || username == "" {
		return "", false
	}
	if sessionBinding == "" && rememberBinding == "" {
		return "", false
	}
	exp, err := strconv.ParseInt(expStr, 10, 64)
	if err != nil || time.Now().Unix() > exp {
		return "", false
	}
	matched := false
	if sessionToken != "" {
		// Session cookie present: only it may validate. A changed SID must
		// not fall through to remember-me; caller re-verifies the new session.
		matched = bindingMatches(s.secret, sessionToken, sessionBinding)
	} else {
		matched = bindingMatches(s.secret, rememberToken, rememberBinding)
	}
	if !matched {
		return "", false
	}
	payload := fmt.Sprintf("%s|%s|%s|%s|%s|%s", ver, expStr, nonce, sessionBinding, rememberBinding, username)
	mac := hmac.New(sha256.New, s.secret)
	mac.Write([]byte(payload))
	expected := hex.EncodeToString(mac.Sum(nil))
	if !hmac.Equal([]byte(expected), []byte(sig)) {
		return "", false
	}
	return username, true
}

func (m *Middleware) cookieValue(r *http.Request, name string) string {
	if name == "" {
		return ""
	}
	cookie, err := r.Cookie(name)
	if err != nil || cookie.Value == "" {
		return ""
	}
	return cookie.Value
}

func (m *Middleware) sessionToken(r *http.Request) string {
	return m.cookieValue(r, m.ForgejoCookieName)
}

func (m *Middleware) rememberToken(r *http.Request) string {
	return m.cookieValue(r, m.ForgejoRememberCookieName)
}

func setSessionUserID(r *http.Request, username string) {
	if username == "" {
		return
	}
	caddyhttp.SetVar(r.Context(), "user_id", username)
	if repl, ok := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer); ok {
		repl.Set("http.auth.user.id", username)
	}
}

func forgejoAuthorizationHeaderToken(r *http.Request) (string, bool) {
	auth := strings.TrimSpace(r.Header.Get("Authorization"))
	if auth == "" {
		return "", false
	}
	lower := strings.ToLower(auth)
	if !strings.HasPrefix(lower, "token ") && !strings.HasPrefix(lower, "bearer ") {
		return "", false
	}
	parts := strings.SplitN(auth, " ", 2)
	if len(parts) != 2 || parts[1] == "" {
		return "", false
	}
	return auth, true
}

func (m *Middleware) ensureSessionUserID(w http.ResponseWriter, r *http.Request) bool {
	if m.ForgejoCookieName == "" || m.sessionPasses == nil {
		return false
	}

	if authHeader, ok := forgejoAuthorizationHeaderToken(r); ok {
		if username, ok := m.sessionPasses.valid(r, authHeader, ""); ok {
			setSessionUserID(r, username)
			return true
		}
		username, ok, err := m.verifyForgejoAuthorizationToken(r, authHeader)
		if err != nil {
			m.logger.Warn("forgejo authorization verify error", zap.Error(err))
			return false
		}
		if !ok {
			return false
		}
		if err := m.sessionPasses.set(w, r, authHeader, "", username); err != nil {
			m.logger.Warn("session pass cookie error", zap.Error(err))
		}
		setSessionUserID(r, username)
		return true
	}

	sessionToken := m.sessionToken(r)
	rememberToken := m.rememberToken(r)
	if username, ok := m.sessionPasses.valid(r, sessionToken, rememberToken); ok {
		setSessionUserID(r, username)
		return true
	}
	if sessionToken == "" {
		return false
	}
	username, ok, err := m.verifyForgejoSession(r, sessionToken)
	if err != nil {
		m.logger.Warn("session verify error", zap.Error(err))
		return false
	}
	if !ok {
		return false
	}
	if err := m.sessionPasses.set(w, r, sessionToken, rememberToken, username); err != nil {
		m.logger.Warn("session pass cookie error", zap.Error(err))
	}
	setSessionUserID(r, username)
	return true
}

func parseForgejoAPIUser(body []byte) (string, bool) {
	var user struct {
		Username string `json:"username"`
	}
	if err := json.Unmarshal(body, &user); err != nil || user.Username == "" {
		return "", false
	}
	return user.Username, true
}

func (m *Middleware) verifyForgejoAuthorizationToken(r *http.Request, authHeader string) (string, bool, error) {
	req, err := http.NewRequestWithContext(r.Context(), http.MethodGet, m.Upstream+forgejoUserPath, nil)
	if err != nil {
		return "", false, err
	}
	if host := r.Host; host != "" {
		req.Host = host
	}
	req.Header.Set("Authorization", authHeader)

	resp, err := forgejoVerifyClient.Do(req)
	if err != nil {
		return "", false, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", false, nil
	}
	body, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return "", false, err
	}
	username, ok := parseForgejoAPIUser(body)
	if !ok {
		return "", false, nil
	}
	return username, true, nil
}

func parseForgejoSettingsUser(body []byte) (string, bool) {
	html := string(body)
	if !strings.Contains(html, `class="page-content user settings profile"`) {
		return "", false
	}
	if !strings.Contains(html, `action="/user/settings"`) {
		return "", false
	}
	const prefix = `name="name" value="`
	i := strings.Index(html, prefix)
	if i < 0 {
		return "", false
	}
	rest := html[i+len(prefix):]
	j := strings.IndexByte(rest, '"')
	if j <= 0 {
		return "", false
	}
	return rest[:j], true
}

func (m *Middleware) verifyForgejoSession(r *http.Request, sessionToken string) (string, bool, error) {
	req, err := http.NewRequestWithContext(r.Context(), http.MethodGet, m.Upstream+forgejoSettingsPath, nil)
	if err != nil {
		return "", false, err
	}
	if host := r.Host; host != "" {
		req.Host = host
	}
	req.AddCookie(&http.Cookie{Name: m.ForgejoCookieName, Value: sessionToken})

	resp, err := forgejoVerifyClient.Do(req)
	if err != nil {
		return "", false, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", false, nil
	}
	body, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return "", false, err
	}
	username, ok := parseForgejoSettingsUser(body)
	if !ok {
		return "", false, nil
	}
	return username, true, nil
}

var forgejoVerifyClient = &http.Client{
	Timeout: 10 * time.Second,
	CheckRedirect: func(*http.Request, []*http.Request) error {
		return http.ErrUseLastResponse
	},
}