package clientapi

import (
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"net/http"
	"time"

	"github.com/dariuszjaniak/warp/server/internal/httputil"
	"github.com/dariuszjaniak/warp/server/internal/storage"
	"github.com/dariuszjaniak/warp/server/internal/userapi"
)

// openIDTokenLifetime is how long an OpenID token is good for. The LiveKit
// JWT service checks it once, when a call is joined, so an hour is plenty.
const openIDTokenLifetime = time.Hour

// openIDTokenPrefix marks OpenID tokens the way the userapi marks access
// tokens, so one handed to the wrong endpoint is recognisable.
const openIDTokenPrefix = "warp_oi_"

// openIDUserInfoPath is where a third party exchanges an OpenID token for
// the user's ID. It is a federation endpoint by name, but needs neither
// federation nor a signing key: Synapse serves it as a resource of its own
// for the same reason. It is registered here so that a server with
// federation off can still let its users into a group call.
const openIDUserInfoPath = "/_matrix/federation/v1/openid/userinfo"

// registerOpenIDRoutes adds the OpenID endpoints, if there is a store for
// the tokens.
func (c *ClientAPI) registerOpenIDRoutes(r *httputil.Router) {
	if c.openID == nil {
		return
	}
	c.authed(r, "POST "+v3+"/user/{userID}/openid/request_token", c.limitDefault, c.handleRequestOpenIDToken)
	c.public(r, "GET "+openIDUserInfoPath, c.limitDefault, c.handleOpenIDUserInfo)
}

type openIDTokenResponse struct {
	AccessToken      string `json:"access_token"`
	TokenType        string `json:"token_type"`
	MatrixServerName string `json:"matrix_server_name"`
	ExpiresIn        int64  `json:"expires_in"`
}

// handleRequestOpenIDToken implements
// POST /_matrix/client/v3/user/{userID}/openid/request_token.
//
// The token proves who the user is to whoever they hand it to, and nothing
// else: it is not an access token and opens no other endpoint.
func (c *ClientAPI) handleRequestOpenIDToken(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	if r.PathValue("userID") != auth.UserID {
		return httputil.Forbidden("You cannot request an OpenID token for another user")
	}
	// The body is an empty object; anything in it is ignored.
	var ignored map[string]any
	if _, err := httputil.DecodeOptionalJSON(w, r, &ignored); err != nil {
		return err
	}

	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return fmt.Errorf("generate OpenID token: %w", err)
	}
	token := openIDTokenPrefix + base64.RawURLEncoding.EncodeToString(raw)
	now := c.now()
	// Expired tokens go as new ones are made; nothing else reads them.
	if err := c.openID.PurgeOpenIDTokens(r.Context(), now.UnixMilli()); err != nil {
		c.log.Warn("could not purge expired OpenID tokens", "error", err)
	}
	if err := c.openID.InsertOpenIDToken(r.Context(), userapi.HashToken(token), auth.UserID,
		now.Add(openIDTokenLifetime).UnixMilli()); err != nil {
		return err
	}
	httputil.WriteJSON(w, http.StatusOK, openIDTokenResponse{
		AccessToken:      token,
		TokenType:        "Bearer",
		MatrixServerName: c.serverName,
		ExpiresIn:        int64(openIDTokenLifetime.Seconds()),
	})
	return nil
}

type openIDUserInfoResponse struct {
	Sub string `json:"sub"`
}

// handleOpenIDUserInfo implements
// GET /_matrix/federation/v1/openid/userinfo.
func (c *ClientAPI) handleOpenIDUserInfo(w http.ResponseWriter, r *http.Request) error {
	token := r.URL.Query().Get("access_token")
	if token == "" {
		return httputil.MissingToken()
	}
	userID, err := c.openID.OpenIDTokenUser(r.Context(), userapi.HashToken(token), c.now().UnixMilli())
	if errors.Is(err, storage.ErrNoSuchOpenIDToken) {
		return httputil.UnknownToken(false)
	}
	if err != nil {
		return err
	}
	httputil.WriteJSON(w, http.StatusOK, openIDUserInfoResponse{Sub: userID})
	return nil
}