package connect

import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"math"
	"net/http"

	"amadan.net/oficina/home/handoff"
)

const homeReturnCookie = "__Host-oficina-home-return"
const homeReturnLimit = 4096

type homeReturnIntent struct {
	Path    string `json:"path"`
	Issued  int64  `json:"issued"`
	Expires int64  `json:"expires"`
}

// Resource navigation is separate from the fixed-action local reauth marker.
// Neither cookie authorizes linking or access to the requested document.
func (n *localLinkNavigation) rememberReturn(w http.ResponseWriter, path string) bool {
	if !handoff.SafePath(path) {
		path = "/"
	}
	now := n.now().Unix()
	if now <= 0 || now > math.MaxInt64-localLinkNavigationLifetime {
		return false
	}
	raw, err := json.Marshal(homeReturnIntent{path, now, now + localLinkNavigationLifetime})
	if err != nil {
		return false
	}
	sealed, err := n.sealer.Seal(n.namespace+".home-return.v1:"+n.origin, raw)
	if err != nil {
		return false
	}
	value := base64.RawURLEncoding.EncodeToString(sealed)
	if len(value) > homeReturnLimit {
		return false
	}
	localNavigationCookie(w, homeReturnCookie, value, int(localLinkNavigationLifetime))
	return true
}

func (n *localLinkNavigation) returnPath(r *http.Request) string {
	value := ""
	if cookieCount(r, homeReturnCookie) != 1 {
		return "/"
	}
	cookie, err := r.Cookie(homeReturnCookie)
	if err != nil {
		return "/"
	}
	value = cookie.Value
	if value == "" || len(value) > homeReturnLimit {
		return "/"
	}
	sealed, err := base64.RawURLEncoding.Strict().DecodeString(value)
	if err != nil || base64.RawURLEncoding.EncodeToString(sealed) != value {
		return "/"
	}
	raw, err := n.sealer.Open(n.namespace+".home-return.v1:"+n.origin, sealed)
	if err != nil || len(raw) > homeReturnLimit {
		return "/"
	}
	var intent homeReturnIntent
	if json.Unmarshal(raw, &intent) != nil {
		return "/"
	}
	canonical, _ := json.Marshal(intent)
	now := n.now().Unix()
	if !bytes.Equal(raw, canonical) || intent.Issued <= 0 || intent.Issued > now || intent.Expires <= now || intent.Expires <= intent.Issued || intent.Expires-intent.Issued > localLinkNavigationLifetime || !handoff.SafePath(intent.Path) {
		return "/"
	}
	return intent.Path
}