package handlers

import "context"
import "crypto/rand"
import "crypto/sha1"
import "crypto/tls"
import "database/sql"
import "encoding/base64"
import "encoding/hex"
import "encoding/json"
import "errors"
import "fmt"
import "io"
import "net/http"
import "net/url"
import "strings"
import "time"

import "codit/internal/config"
import "codit/internal/models"
import "codit/internal/util"

type oidcTokenResponse struct {
	AccessToken string `json:"access_token"`
	IDToken     string `json:"id_token"`
}

type oidcUserClaims struct {
	Sub               string `json:"sub"`
	PreferredUsername string `json:"preferred_username"`
	Name              string `json:"name"`
	Email             string `json:"email"`
}

type oidcErrorResponse struct {
	Error            string `json:"error"`
	ErrorDescription string `json:"error_description"`
}

func (api *API) OIDCEnabled(w http.ResponseWriter, _ *http.Request, _ map[string]string) {
	var settings models.AuthSettings
	var err error
	var configured bool
	settings, err = api.getMergedAuthSettings()
	if err != nil {
		WriteJSON(w, http.StatusOK, map[string]any{"enabled": false, "configured": false, "auth_mode": "db"})
		return
	}
	configured = api.oidcConfiguredFromSettings(settings)
	WriteJSON(w, http.StatusOK, map[string]any{
		"enabled":    settings.OIDCEnabled,
		"configured": configured,
		"auth_mode":  strings.ToLower(strings.TrimSpace(settings.AuthMode)),
	})
}

func (api *API) OIDCLogin(w http.ResponseWriter, r *http.Request, _ map[string]string) {
	var settings models.AuthSettings
	var cfg config.Config
	var state string
	var err error
	var authURL string
	settings, err = api.getMergedAuthSettings()
	if err != nil {
		WriteJSON(w, http.StatusInternalServerError, map[string]string{"error": "failed to load auth settings"})
		return
	}
	cfg, err = api.effectiveAuthConfig()
	if err != nil {
		WriteJSON(w, http.StatusInternalServerError, map[string]string{"error": "failed to load auth settings"})
		return
	}
	if !settings.OIDCEnabled {
		WriteJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "oidc login is disabled"})
		return
	}
	if !api.oidcConfiguredFromSettings(settings) {
		WriteJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "oidc is not configured"})
		return
	}
	state, err = newOIDCState()
	if err != nil {
		WriteJSON(w, http.StatusInternalServerError, map[string]string{"error": "failed to create state"})
		return
	}
	http.SetCookie(w, &http.Cookie{
		Name:     "codit_oidc_state",
		Value:    state,
		HttpOnly: true,
		Path:     "/api/auth/oidc",
		Expires:  time.Now().UTC().Add(10 * time.Minute),
		SameSite: http.SameSiteLaxMode,
	})
	authURL = api.buildOIDCAuthorizeURL(cfg, state)
	if api.Logger != nil {
		api.Logger.Write("auth", util.LOG_INFO, "oidc login redirect authorize_url=%s", cfg.OIDCAuthorizeURL)
	}
	http.Redirect(w, r, authURL, http.StatusFound)
}

func (api *API) OIDCCallback(w http.ResponseWriter, r *http.Request, _ map[string]string) {
	var settings models.AuthSettings
	var cfg config.Config
	var state string
	var code string
	var cookie *http.Cookie
	var err error
	var token oidcTokenResponse
	var claims oidcUserClaims
	var user models.User
	settings, err = api.getMergedAuthSettings()
	if err != nil {
		WriteJSON(w, http.StatusInternalServerError, map[string]string{"error": "failed to load auth settings"})
		return
	}
	cfg, err = api.effectiveAuthConfig()
	if err != nil {
		WriteJSON(w, http.StatusInternalServerError, map[string]string{"error": "failed to load auth settings"})
		return
	}
	if !settings.OIDCEnabled {
		WriteJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "oidc login is disabled"})
		return
	}
	if !api.oidcConfiguredFromSettings(settings) {
		WriteJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "oidc is not configured"})
		return
	}
	state = strings.TrimSpace(r.URL.Query().Get("state"))
	code = strings.TrimSpace(r.URL.Query().Get("code"))
	cookie, err = r.Cookie("codit_oidc_state")
	clearOIDCStateCookie(w)
	if err != nil || cookie.Value == "" || state == "" || state != cookie.Value {
		WriteJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid oidc state"})
		return
	}
	if code == "" {
		WriteJSON(w, http.StatusBadRequest, map[string]string{"error": "missing authorization code"})
		return
	}
	token, err = api.oidcExchangeCode(r.Context(), cfg, code)
	if err != nil {
		if api.Logger != nil {
			api.Logger.Write("auth", util.LOG_WARN, "oidc token exchange failed err=%v", err)
		}
		WriteJSON(w, http.StatusUnauthorized, map[string]string{"error": err.Error()})
		return
	}
	claims, err = api.oidcResolveClaims(r.Context(), cfg, token)
	if err != nil {
		if api.Logger != nil {
			api.Logger.Write("auth", util.LOG_WARN, "oidc claims fetch failed err=%v", err)
		}
		WriteJSON(w, http.StatusUnauthorized, map[string]string{"error": "oidc claims fetch failed"})
		return
	}
	user, err = api.oidcGetOrCreateUser(claims)
	if err != nil {
		if api.Logger != nil {
			api.Logger.Write("auth", util.LOG_WARN, "oidc user mapping failed err=%v", err)
		}
		WriteJSON(w, http.StatusUnauthorized, map[string]string{"error": "oidc user mapping failed"})
		return
	}
	api.issueSession(w, user)
	if api.Logger != nil {
		api.Logger.Write("auth", util.LOG_INFO, "oidc login success username=%s", user.Username)
	}
	http.Redirect(w, r, "/", http.StatusFound)
}

func (api *API) oidcConfiguredFromSettings(settings models.AuthSettings) bool {
	if strings.TrimSpace(settings.OIDCClientID) == "" {
		return false
	}
	if strings.TrimSpace(settings.OIDCClientSecret) == "" {
		return false
	}
	if strings.TrimSpace(settings.OIDCAuthorizeURL) == "" {
		return false
	}
	if strings.TrimSpace(settings.OIDCTokenURL) == "" {
		return false
	}
	if strings.TrimSpace(settings.OIDCRedirectURL) == "" {
		return false
	}
	return true
}

func (api *API) buildOIDCAuthorizeURL(cfg config.Config, state string) string {
	var values url.Values
	var scopes string
	var endpoint string
	values = url.Values{}
	values.Set("response_type", "code")
	values.Set("client_id", cfg.OIDCClientID)
	values.Set("redirect_uri", cfg.OIDCRedirectURL)
	scopes = strings.TrimSpace(cfg.OIDCScopes)
	if scopes == "" {
		scopes = "openid profile email"
	}
	values.Set("scope", scopes)
	values.Set("state", state)
	endpoint = cfg.OIDCAuthorizeURL
	if strings.Contains(endpoint, "?") {
		return endpoint + "&" + values.Encode()
	}
	return endpoint + "?" + values.Encode()
}

func (api *API) oidcHTTPClient(cfg config.Config) *http.Client {
	var transport *http.Transport
	transport = &http.Transport{
		TLSClientConfig: &tls.Config{InsecureSkipVerify: cfg.OIDCTLSInsecureSkipVerify},
	}
	return &http.Client{Transport: transport, Timeout: 15 * time.Second}
}

func (api *API) oidcExchangeCode(ctx context.Context, cfg config.Config, code string) (oidcTokenResponse, error) {
	var client *http.Client
	var form url.Values
	var req *http.Request
	var res *http.Response
	var body []byte
	var token oidcTokenResponse
	var err error
	client = api.oidcHTTPClient(cfg)
	form = url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("code", code)
	form.Set("redirect_uri", cfg.OIDCRedirectURL)
	form.Set("client_id", cfg.OIDCClientID)
	form.Set("client_secret", cfg.OIDCClientSecret)
	req, err = http.NewRequestWithContext(ctx, http.MethodPost, cfg.OIDCTokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return token, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")
	res, err = client.Do(req)
	if err != nil {
		return token, err
	}
	defer res.Body.Close()
	body, err = io.ReadAll(io.LimitReader(res.Body, 1024*1024))
	if err != nil {
		return token, err
	}
	if res.StatusCode < 200 || res.StatusCode >= 300 {
		return token, fmt.Errorf("oidc token exchange failed: status=%d detail=%s", res.StatusCode, oidcErrorDetail(body))
	}
	err = json.Unmarshal(body, &token)
	if err != nil {
		return token, err
	}
	if strings.TrimSpace(token.AccessToken) == "" && strings.TrimSpace(token.IDToken) == "" {
		return token, errors.New("missing oidc token")
	}
	return token, nil
}

func oidcErrorDetail(body []byte) string {
	var payload oidcErrorResponse
	var err error
	var text string
	err = json.Unmarshal(body, &payload)
	if err == nil {
		if strings.TrimSpace(payload.ErrorDescription) != "" {
			return payload.ErrorDescription
		}
		if strings.TrimSpace(payload.Error) != "" {
			return payload.Error
		}
	}
	text = strings.TrimSpace(string(body))
	if len(text) > 240 {
		text = text[:240]
	}
	if text == "" {
		text = "empty response body"
	}
	return text
}

func (api *API) oidcResolveClaims(ctx context.Context, cfg config.Config, token oidcTokenResponse) (oidcUserClaims, error) {
	var claims oidcUserClaims
	var err error
	if strings.TrimSpace(cfg.OIDCUserInfoURL) != "" && strings.TrimSpace(token.AccessToken) != "" {
		claims, err = api.oidcUserInfo(ctx, cfg, token.AccessToken)
		if err == nil {
			return claims, nil
		}
	}
	if strings.TrimSpace(token.IDToken) == "" {
		return claims, errors.New("missing id token and userinfo unavailable")
	}
	claims, err = oidcClaimsFromIDToken(token.IDToken)
	if err != nil {
		return claims, err
	}
	return claims, nil
}

func (api *API) oidcUserInfo(ctx context.Context, cfg config.Config, accessToken string) (oidcUserClaims, error) {
	var client *http.Client
	var req *http.Request
	var res *http.Response
	var body []byte
	var claims oidcUserClaims
	var err error
	client = api.oidcHTTPClient(cfg)
	req, err = http.NewRequestWithContext(ctx, http.MethodGet, cfg.OIDCUserInfoURL, nil)
	if err != nil {
		return claims, err
	}
	req.Header.Set("Authorization", "Bearer "+accessToken)
	req.Header.Set("Accept", "application/json")
	res, err = client.Do(req)
	if err != nil {
		return claims, err
	}
	defer res.Body.Close()
	body, err = io.ReadAll(io.LimitReader(res.Body, 1024*1024))
	if err != nil {
		return claims, err
	}
	if res.StatusCode < 200 || res.StatusCode >= 300 {
		return claims, fmt.Errorf("userinfo status %d", res.StatusCode)
	}
	err = json.Unmarshal(body, &claims)
	if err != nil {
		return claims, err
	}
	if strings.TrimSpace(claims.Sub) == "" {
		return claims, errors.New("userinfo missing sub")
	}
	return claims, nil
}

func (api *API) oidcGetOrCreateUser(claims oidcUserClaims) (models.User, error) {
	var username string
	var displayName string
	var email string
	var user models.User
	var hash string
	var err error
	var created models.User
	username = oidcUsernameFromSub(claims.Sub)
	user, hash, err = api.Store.GetUserByUsername(username)
	_ = hash
	if err == nil {
		if user.Disabled {
			return user, errors.New("user disabled")
		}
		return user, nil
	}
	if !errors.Is(err, sql.ErrNoRows) {
		return user, err
	}
	displayName = strings.TrimSpace(claims.Name)
	if displayName == "" {
		displayName = strings.TrimSpace(claims.PreferredUsername)
	}
	if displayName == "" {
		displayName = username
	}
	email = strings.TrimSpace(claims.Email)
	if email == "" {
		email = username + "@oidc.local"
	}
	user = models.User{
		Username:    username,
		DisplayName: displayName,
		Email:       email,
		AuthSource:  "oidc",
	}
	created, err = api.Store.CreateUser(user, "")
	if err != nil {
		return created, err
	}
	return created, nil
}

func oidcClaimsFromIDToken(idToken string) (oidcUserClaims, error) {
	var claims oidcUserClaims
	var parts []string
	var payload []byte
	var err error
	parts = strings.Split(idToken, ".")
	if len(parts) < 2 {
		return claims, errors.New("invalid id token")
	}
	payload, err = base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return claims, err
	}
	err = json.Unmarshal(payload, &claims)
	if err != nil {
		return claims, err
	}
	if strings.TrimSpace(claims.Sub) == "" {
		return claims, errors.New("id token missing sub")
	}
	return claims, nil
}

func oidcUsernameFromSub(sub string) string {
	var sum [20]byte
	sum = sha1.Sum([]byte(strings.TrimSpace(sub)))
	return "oidc-" + hex.EncodeToString(sum[:6])
}

func newOIDCState() (string, error) {
	var buf []byte
	var err error
	buf = make([]byte, 24)
	_, err = rand.Read(buf)
	if err != nil {
		return "", err
	}
	return hex.EncodeToString(buf), nil
}

func clearOIDCStateCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     "codit_oidc_state",
		Value:    "",
		Path:     "/api/auth/oidc",
		Expires:  time.Unix(0, 0),
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
	})
}