// internal/auth/handler/auth_handler.go
package handler

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"time"
	"log"

	"server/internal/auth/models"
	"server/internal/auth/repository"
	"server/internal/auth/service"
	"server/internal/shared/crypto"
	"server/internal/shared/utils"
	"go.mongodb.org/mongo-driver/mongo"

)

type LoggingResponseWriter struct {
    http.ResponseWriter
    StatusCode int
}

func (rw *LoggingResponseWriter) WriteHeader(statusCode int) {
    rw.StatusCode = statusCode
    rw.ResponseWriter.WriteHeader(statusCode)
}

func Login(w http.ResponseWriter, r *http.Request) {
    log.Println("Login handler triggered")
    
    // Generate secure random values
    state, _ := utils.SecureRandom(32)
    codeVerifier, _ := utils.SecureRandom(64)
    codeChallenge := crypto.SHA256Base64URL(codeVerifier)

    // Set cookies
    http.SetCookie(w, &http.Cookie{
        Name:     "oauth_state",
        Value:    state,
        HttpOnly: true,
        Secure:   true,
        SameSite: http.SameSiteNoneMode,
        Path:     "/",
        MaxAge:   300,
    })
    log.Println("Cookies set 1")
    
    http.SetCookie(w, &http.Cookie{
        Name:     "pkce_verifier",
        Value:    codeVerifier,
        HttpOnly: true,
        Secure:   true,
        SameSite: http.SameSiteNoneMode,
        Path:     "/",
        MaxAge:   300,
    })
    log.Println("Cookies set 2")

    // Construct the authorization URL for Keycloak
    authURL := fmt.Sprintf("%s/realms/%s/protocol/openid-connect/auth?client_id=%s&response_type=code&scope=openid profile email&redirect_uri=%s&state=%s&code_challenge=%s&code_challenge_method=S256",
        os.Getenv("KEYCLOAK_URL"),
        os.Getenv("KEYCLOAK_REALM"),
        os.Getenv("KEYCLOAK_CLIENT_ID"),
        url.QueryEscape(os.Getenv("KEYCLOAK_REDIRECT_URL")),
        state,
        codeChallenge,
    )

    // Log the URL being redirected to
    log.Printf("Redirecting to URL: %s", authURL)

    // Perform the actual redirect
    http.Redirect(w, r, authURL, http.StatusTemporaryRedirect)
}

func Callback(w http.ResponseWriter, r *http.Request) {
    log.Println("Callback handler triggered")
	ctx, cancel := context.WithTimeout(r.Context(), 15*time.Second)
	defer cancel()

	code := r.URL.Query().Get("code")
	state := r.URL.Query().Get("state")

	stateCookie, err := r.Cookie("oauth_state")
	if err != nil || state != stateCookie.Value {
		http.Error(w, "Invalid state", http.StatusBadRequest)
		return
	}

	pkceCookie, err := r.Cookie("pkce_verifier")
	if err != nil {
		http.Error(w, "Missing PKCE verifier", http.StatusBadRequest)
		return
	}

	tokenResp, err := exchangeCodeForToken(code, pkceCookie.Value)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	claims, err := verifyIDToken(tokenResp.IDToken)
	if err != nil {
		http.Error(w, fmt.Sprintf("Invalid ID token: %v", err), http.StatusUnauthorized)
		return
	}

	userID := claims["sub"].(string)
	email := claims["email"].(string)
	username := claims["preferred_username"].(string)
	sid, _ := claims["sid"].(string)

	sessionID, _ := utils.SecureRandom(32)
	csrfToken, _ := utils.SecureRandom(32)

	encAccess, _ := crypto.Encrypt(tokenResp.AccessToken)
	encRefresh, _ := crypto.Encrypt(tokenResp.RefreshToken)

	expiresAt := time.Now().Add(time.Hour * 24)
	accessExpires := time.Now().Add(time.Second * time.Duration(tokenResp.ExpiresIn))

	session := models.Session{
		SessionID:        sessionID,
		UserID:           userID,
		Email:            email,
		Username:         username,
		KeycloakSID:      sid,  
		EncryptedAccess:  encAccess,
		EncryptedRefresh: encRefresh,
		AccessExpiresAt:  accessExpires,
		ExpiresAt:        expiresAt,
	}

	if err := repository.Save(ctx, session); err != nil {
		http.Error(w, fmt.Sprintf("Failed to save session: %v", err), http.StatusInternalServerError)
		return
	}

	http.SetCookie(w, &http.Cookie{
		Name:     "session_id",
		Value:    sessionID,
		Path:     "/",
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteLaxMode,
        Domain: os.Getenv("COOKIE_DOMAIN"),
	})

	http.SetCookie(w, &http.Cookie{
		Name:     "XSRF-TOKEN",
		Value:    csrfToken,
		Path:     "/",
		HttpOnly: false,
		Secure:   true,
		SameSite: http.SameSiteLaxMode,
        Domain: os.Getenv("COOKIE_DOMAIN"),
	})

	clearCookie(w, "oauth_state")
	clearCookie(w, "pkce_verifier")

	http.Redirect(w, r, os.Getenv("FRONTEND_ORIGIN"), http.StatusFound)
}

func Me(w http.ResponseWriter, r *http.Request) {
	user, err := service.GetCurrentUser(r.Context())
	if err != nil {
		http.Error(w, "Unauthorized", http.StatusUnauthorized)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(user)
}


func Logout(w http.ResponseWriter, r *http.Request) {
	// 1. Delete local session
	cookie, err := r.Cookie("session_id")
	if err == nil {
		_ = repository.DeleteSession(r.Context(), cookie.Value)
	}

	clearCookie := func(name string, httpOnly bool) {
		http.SetCookie(w, &http.Cookie{
			Name:     name,
			Value:    "",
			Path:     "/",
			HttpOnly: httpOnly,
			Secure:   true, // only HTTPS
			MaxAge:   -1,
			SameSite: http.SameSiteLaxMode,
            Domain: os.Getenv("COOKIE_DOMAIN"),
        })
	}
	clearCookie("session_id", true)
	clearCookie("XSRF-TOKEN", false)

	logoutURL := fmt.Sprintf("%s/realms/%s/protocol/openid-connect/logout?redirect_uri=%s",
		os.Getenv("KEYCLOAK_URL"),
		os.Getenv("KEYCLOAK_REALM"),
		url.QueryEscape(os.Getenv("FRONTEND_ORIGIN")),
	)
	http.Redirect(w, r, logoutURL, http.StatusFound)
}


func clearCookie(w http.ResponseWriter, name string) {
	http.SetCookie(w, &http.Cookie{
		Name:     name,
		Value:    "",
		MaxAge:   -1,
		Path:     "/",
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteNoneMode,
        Domain: os.Getenv("COOKIE_DOMAIN"),
	})
}

type tokenResponse struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	ExpiresIn    int    `json:"expires_in"`
	IDToken      string `json:"id_token"`
}

func exchangeCodeForToken(code, verifier string) (*tokenResponse, error) {
	tokenURL := fmt.Sprintf("%s/realms/%s/protocol/openid-connect/token",
		os.Getenv("KEYCLOAK_URL"),
		os.Getenv("KEYCLOAK_REALM"),
	)

	data := url.Values{}
	data.Set("grant_type", "authorization_code")
	data.Set("client_id", os.Getenv("KEYCLOAK_CLIENT_ID"))
	data.Set("client_secret", os.Getenv("KEYCLOAK_CLIENT_SECRET"))
	data.Set("code", code)
	data.Set("redirect_uri", os.Getenv("KEYCLOAK_REDIRECT_URL"))
	data.Set("code_verifier", verifier)

	resp, err := http.PostForm(tokenURL, data)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	body, _ := io.ReadAll(resp.Body)
	if resp.StatusCode != http.StatusOK {
		return nil, errors.New("token exchange failed: " + string(body))
	}

	var tr tokenResponse
	if err := json.Unmarshal(body, &tr); err != nil {
		return nil, err
	}
	return &tr, nil
}

func verifyIDToken(idToken string) (map[string]interface{}, error) {
	claims, err := service.VerifyIDTokenJWKS(idToken)
	if err != nil {
		return nil, err
	}
	return claims, nil
}

func BackchannelLogout(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()

    if err := r.ParseForm(); err != nil {
        http.Error(w, "Invalid form", http.StatusBadRequest)
        return
    }

    logoutToken := r.FormValue("logout_token")
    if logoutToken == "" {
        http.Error(w, "Missing logout_token", http.StatusBadRequest)
        return
    }

    claims, err := service.VerifyIDTokenJWKS(logoutToken)
    if err != nil {
        log.Println("Invalid logout token:", err)
        http.Error(w, "Invalid token", http.StatusUnauthorized)
        return
    }

    expectedIssuer := fmt.Sprintf("%s/realms/%s",
        os.Getenv("KEYCLOAK_URL"),
        os.Getenv("KEYCLOAK_REALM"),
    )
    if claims["iss"] != expectedIssuer {
        http.Error(w, "Invalid issuer", http.StatusUnauthorized)
        return
    }

    if claims["aud"] != os.Getenv("KEYCLOAK_CLIENT_ID") {
        http.Error(w, "Invalid audience", http.StatusUnauthorized)
        return
    }

    events, ok := claims["events"].(map[string]interface{})
    if !ok {
        http.Error(w, "Invalid logout token structure", http.StatusUnauthorized)
        return
    }

    if _, ok := events["http://schemas.openid.net/event/backchannel-logout"]; !ok {
        http.Error(w, "Not a backchannel logout event", http.StatusUnauthorized)
        return
    }

    sid, ok := claims["sid"].(string)
    if !ok || sid == "" {
        http.Error(w, "Missing sid", http.StatusBadRequest)
        return
    }

    if err := repository.DeleteByKeycloakSID(ctx, sid); err != nil {
        if !errors.Is(err, mongo.ErrNoDocuments) {
            log.Println("DB delete error:", err)
            http.Error(w, "Internal error", http.StatusInternalServerError)
            return
        }
    }

    w.WriteHeader(http.StatusOK)
}