package calls

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"net/http"
	"strconv"
	"strings"
	"time"
)

const joinCookieName = "calls_join"

// joinCookie tells POST /signin which live link this browser followed.
// It carries the token's hash, not the token, so a cookie leak is not a
// link leak, and it is signed under the instance key so it cannot be
// forged. Its only job is that one hand-off (spec §3.2).
type joinCookie struct {
	TokenHash string
	Expires   time.Time
}

func (a *app) joinMAC(payload string) string {
	mac := hmac.New(sha256.New, []byte("calls/join\x00"+a.cfg.instanceKey))
	mac.Write([]byte(payload))
	return hex.EncodeToString(mac.Sum(nil))
}

func (a *app) setJoinCookie(w http.ResponseWriter, tokenHash string) {
	exp := a.store.now().Add(pendingLife)
	payload := tokenHash + "|" + strconv.FormatInt(exp.Unix(), 10)
	value := base64.RawURLEncoding.EncodeToString([]byte(payload)) + "." + a.joinMAC(payload)
	http.SetCookie(w, &http.Cookie{
		Name: joinCookieName, Value: value, Path: "/", HttpOnly: true,
		Secure: strings.HasPrefix(a.cfg.Origin, "https://"), SameSite: http.SameSiteLaxMode,
		MaxAge: int(pendingLife.Seconds()),
	})
}

func (a *app) clearJoinCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{Name: joinCookieName, Value: "", Path: "/", MaxAge: -1, HttpOnly: true})
}

func (a *app) readJoinCookie(r *http.Request) (joinCookie, bool) {
	ck, err := r.Cookie(joinCookieName)
	if err != nil {
		return joinCookie{}, false
	}
	parts := strings.SplitN(ck.Value, ".", 2)
	if len(parts) != 2 {
		return joinCookie{}, false
	}
	raw, err := base64.RawURLEncoding.DecodeString(parts[0])
	if err != nil {
		return joinCookie{}, false
	}
	payload := string(raw)
	if !hmac.Equal([]byte(a.joinMAC(payload)), []byte(parts[1])) {
		return joinCookie{}, false
	}
	hash, expStr, ok := strings.Cut(payload, "|")
	if !ok || len(hash) != 64 {
		return joinCookie{}, false
	}
	exp, err := strconv.ParseInt(expStr, 10, 64)
	if err != nil {
		return joinCookie{}, false
	}
	c := joinCookie{TokenHash: hash, Expires: time.Unix(exp, 0)}
	if !c.Expires.After(a.store.now()) {
		return joinCookie{}, false
	}
	return c, true
}