referrals: add "use expiry" option

adds an option when enabling referrals to use the duration of the source
invited (i.e., months, days, hours) for the referral invite. If enabled,
the user won't be able to make a new referral link after it expires. For
referrals enabled for new users via a profile, the clock starts ticking
as soon as the account is created.

ts/user.ts

@@ -116,6 +116,7 @@ interface MyReferral {
     remaining_uses: number;
     no_limit: boolean;
     expiry: number;
+    use_expiry: boolean;
 }
 
 interface ContactDTO {
@@ -252,6 +253,7 @@ class ReferralCard {
     private _url: string;
     private _expiry: Date;
     private _expiryUnix: number;
+    private _useExpiry: boolean;
     private _remainingUses: number;
     private _noLimit: boolean;
 
@@ -259,6 +261,7 @@ class ReferralCard {
     private _infoArea: HTMLDivElement;
     private _remainingUsesEl: HTMLSpanElement;
     private _expiryEl: HTMLSpanElement;
+    private _descriptionEl: HTMLSpanElement;
 
     get code(): string { return this._code; }
     set code(c: string) {
@@ -294,11 +297,22 @@ class ReferralCard {
         this._expiry = new Date(expiryUnix * 1000);
         this._expiryEl.textContent = toDateString(this._expiry);
     }
+
+    get use_expiry(): boolean { return this._useExpiry; }
+    set use_expiry(v: boolean) {
+        this._useExpiry = v;
+        if (v) {
+            this._descriptionEl.textContent = window.lang.strings("referralsWithExpiryDescription");
+        } else {
+            this._descriptionEl.textContent = window.lang.strings("referralsDescription");
+        }
+    }
     
     constructor(card: HTMLElement) {
         this._card = card;
         this._button = this._card.querySelector(".user-referrals-button") as HTMLButtonElement;
         this._infoArea = this._card.querySelector(".user-referrals-info") as HTMLDivElement;
+        this._descriptionEl = this._card.querySelector(".user-referrals-description") as HTMLSpanElement;
 
         this._infoArea.innerHTML = `
         <div class="row my-3">
@@ -344,6 +358,7 @@ class ReferralCard {
         this.no_limit = referral.no_limit;
         this.expiry = referral.expiry;
         this._card.classList.remove("unfocused");
+        this.use_expiry = referral.use_expiry;
     };
 }