package main

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"net/http"
	"net/url"
	"strings"
)

func (app *App) getSSOConfig() (ssoURL, ssoSecret string) {
	app.db.QueryRow(`SELECT value FROM config WHERE key = 'discourse_sso_url'`).Scan(&ssoURL)
	app.db.QueryRow(`SELECT value FROM config WHERE key = 'discourse_sso_secret'`).Scan(&ssoSecret)
	return
}

func (app *App) handleSSOEnabled(w http.ResponseWriter, r *http.Request) {
	ssoURL, ssoSecret := app.getSSOConfig()
	writeJSON(w, map[string]bool{"enabled": ssoURL != "" && ssoSecret != ""})
}

func (app *App) getBaseURL() string {
	if app.baseURL != "" {
		return app.baseURL
	}
	var u string
	app.db.QueryRow(`SELECT value FROM config WHERE key = 'base_url'`).Scan(&u)
	return u
}

func (app *App) handleSSOInit(w http.ResponseWriter, r *http.Request) {
	ssoURL, ssoSecret := app.getSSOConfig()
	if ssoURL == "" || ssoSecret == "" {
		writeError(w, "SSO not configured", http.StatusNotFound)
		return
	}

	baseURL := app.getBaseURL()
	if baseURL == "" {
		writeError(w, "base_url must be configured for SSO", http.StatusBadRequest)
		return
	}

	b := make([]byte, 32)
	rand.Read(b)
	nonce := hex.EncodeToString(b)

	app.cleanExpiredNonces()
	if err := app.createSSONonce(nonce); err != nil {
		writeError(w, "internal error", http.StatusInternalServerError)
		return
	}

	returnURL := strings.TrimRight(baseURL, "/") + "/api/sso/callback"

	payload := fmt.Sprintf("nonce=%s&return_sso_url=%s", url.QueryEscape(nonce), url.QueryEscape(returnURL))
	encoded := base64.StdEncoding.EncodeToString([]byte(payload))

	mac := hmac.New(sha256.New, []byte(ssoSecret))
	mac.Write([]byte(encoded))
	sig := hex.EncodeToString(mac.Sum(nil))

	redirect := fmt.Sprintf("%s/session/sso_provider?sso=%s&sig=%s",
		strings.TrimRight(ssoURL, "/"), url.QueryEscape(encoded), url.QueryEscape(sig))

	writeJSON(w, map[string]string{"redirect_url": redirect})
}

func (app *App) handleSSOCallback(w http.ResponseWriter, r *http.Request) {
	baseURL := app.getBaseURL()

	ssoRedirectError := func(msg string) {
		if baseURL != "" {
			http.Redirect(w, r, strings.TrimRight(baseURL, "/")+"/#sso_error="+url.QueryEscape(msg), http.StatusFound)
		} else {
			writeError(w, msg, http.StatusBadRequest)
		}
	}

	_, ssoSecret := app.getSSOConfig()
	if ssoSecret == "" {
		ssoRedirectError("SSO not configured")
		return
	}

	ssoParam := r.URL.Query().Get("sso")
	sigParam := r.URL.Query().Get("sig")
	if ssoParam == "" || sigParam == "" {
		ssoRedirectError("Invalid SSO response")
		return
	}

	mac := hmac.New(sha256.New, []byte(ssoSecret))
	mac.Write([]byte(ssoParam))
	expectedSig := hex.EncodeToString(mac.Sum(nil))
	if !hmac.Equal([]byte(expectedSig), []byte(sigParam)) {
		ssoRedirectError("Invalid SSO signature")
		return
	}

	decoded, err := base64.StdEncoding.DecodeString(ssoParam)
	if err != nil {
		ssoRedirectError("Invalid SSO payload")
		return
	}

	vals, err := url.ParseQuery(string(decoded))
	if err != nil {
		ssoRedirectError("Invalid SSO payload")
		return
	}

	nonce := vals.Get("nonce")
	valid, err := app.consumeSSONonce(nonce)
	if err != nil || !valid {
		ssoRedirectError("SSO session expired. Please try again.")
		return
	}

	email := strings.ToLower(vals.Get("email"))
	if email == "" {
		ssoRedirectError("No email in SSO response")
		return
	}

	name := vals.Get("name")
	if name == "" {
		name = vals.Get("username")
	}

	user, _, err := app.getLoginParticipant(email)
	if err != nil {
		ssoRedirectError("Login failed. Please try again.")
		return
	}

	if user == nil {
		p, err := app.getParticipantByEmail(email)
		if err != nil {
			ssoRedirectError("Login failed. Please try again.")
			return
		}
		if p != nil {
			if _, err := app.db.Exec(
				`UPDATE participants SET login_enabled = 1, updated_at = ? WHERE id = ?`,
				now(), p.ID,
			); err != nil {
				ssoRedirectError("Login failed. Please try again.")
				return
			}
			user, err = app.getUser(p.ID)
			if err != nil {
				ssoRedirectError("Login failed. Please try again.")
				return
			}
		}
	}

	if user == nil {
		if name == "" {
			name = strings.Split(email, "@")[0]
		}
		res, err := app.db.Exec(
			`INSERT INTO participants (email, preferred_name, login_enabled, updated_at) VALUES (?, ?, 1, ?)`,
			email, name, now(),
		)
		if err != nil {
			ssoRedirectError("Login failed. Please try again.")
			return
		}
		id, _ := res.LastInsertId()
		user, err = app.getUser(int(id))
		if err != nil || user == nil {
			ssoRedirectError("Login failed. Please try again.")
			return
		}
	}

	token, err := app.signToken(user)
	if err != nil {
		ssoRedirectError("Login failed. Please try again.")
		return
	}

	http.Redirect(w, r, strings.TrimRight(baseURL, "/")+"/#sso_token="+url.QueryEscape(token), http.StatusFound)
}