feat: remove an address from an HD wallet, behind a confirmation (closes #162)

Address rows on Home gain an [x] control, on wallets that derive addresses from
an extended key and hold more than one, opening a DeleteAddress confirmation
screen.

Removal cannot destroy anything: the key material stays. Derivation indices are
not renumbered, so the next "+" derives the next unused index rather than
resurrecting the removed one. The confirmation states the real route back --
delete the whole wallet in Settings, which asks for the password and destroys
the stored recovery phrase, then import it again -- and notes that the scan
which follows only finds addresses with on-chain activity. The copy varies by
wallet type, since an xprv wallet has no recovery phrase.

Removing an address that holds a balance is allowed, with a warning naming no
figure; the funds are at the address on-chain and stay there either way.
Selection and active address move only when the removed address was the one
selected, and site permissions are dropped for it alone.

The state transition shares its address comparison, permission cleanup and
active-changed broadcast with the wallet-level removal.

src/popup/views/deleteAddress.js

@@ -0,0 +1,176 @@
+// Confirmation screen for removing one address from a wallet that derives
+// its addresses from an extended key.
+//
+// No password is asked for, unlike delete-wallet. A password gates the
+// disclosure or destruction of a secret, and this does neither: the address
+// is derived from key material the wallet still holds, so removing it only
+// stops the wallet tracking it. An explicit confirmation screen is the
+// proportionate treatment.
+
+const {
+    $,
+    showView,
+    showFlash,
+    goBack,
+    renderAddressHtml,
+    attachCopyHandlers,
+    addressHoldsFunds,
+    balanceLinesForAddress,
+} = require("./helpers");
+const { formatUsd, getAddressValueUsd } = require("../../shared/prices");
+const { walletHasRecoveryPhrase } = require("../../shared/wallet");
+const { state, saveState } = require("../../shared/state");
+const {
+    canRemoveAddress,
+    removeAddressFromState,
+    broadcastActiveChanged,
+} = require("../../shared/walletDelete");
+
+// The wallet and address indices this screen is confirming, or null when it
+// is not confirming anything.
+let target = null;
+let ctx = null;
+
+function setFlash(msg) {
+    const el = $("delete-address-flash");
+    el.textContent = msg;
+    el.style.visibility = msg ? "visible" : "hidden";
+}
+
+// What it actually takes to get the address back, which is not what the
+// screen used to claim.
+//
+// Neither obvious route works: "+" derives the next unused index, because
+// wallet.nextIndex is a high-water mark and is deliberately not rewound; and
+// re-importing this wallet's key material is refused as a duplicate by
+// findWalletByXpub() for as long as the wallet is here. What remains is to
+// delete the whole wallet in Settings — which asks for the password and
+// destroys the stored secret — and import again, after which
+// scanForAddresses() rediscovers the address only if it has on-chain
+// activity. An address that was never used is not found by that scan, and
+// the copy must not imply otherwise.
+//
+// The noun follows the wallet: an xprv wallet holds no recovery phrase, and
+// this screen is offered on xprv wallets too.
+function recoveryPathText(wallet) {
+    const secret = walletHasRecoveryPhrase(wallet)
+        ? "recovery phrase"
+        : "extended private key";
+    return (
+        "Getting the address back into this list is not easy, so be sure. " +
+        "Adding an address derives the next unused one, not this one, and " +
+        "importing this " +
+        secret +
+        " again is refused while this wallet is still here. The way back is " +
+        "to delete the whole wallet in Settings, which asks for your " +
+        "password and destroys the stored " +
+        secret +
+        ", and then import that " +
+        secret +
+        " again. The scan that follows only finds addresses that have " +
+        "on-chain activity, so an address that has never been used is not " +
+        "found by it."
+    );
+}
+
+// The balance warning, or a blank line when the address holds nothing.
+//
+// A balance is a reason to be careful, not a reason to refuse: the funds are
+// at the address, not in this list, and stay there either way.
+//
+// "Holds" means ETH or any ERC-20 the wallet knows about — an address with no
+// ETH and a five-figure stablecoin position must not get the blank line on
+// the one screen whose job is to warn. The sentence names no figure of its
+// own: the rendered lines round to four decimals, so a sentence built from a
+// rounded number would report "0.0000 ETH" for an address holding real money.
+// The lines below it carry the amounts, in the same format as Home and
+// AddressDetail, followed by the USD total when prices are known (null on
+// testnet and before the first price fetch, where the line is left off rather
+// than printed as $0.00).
+function balanceWarningHtml(addr) {
+    if (!addressHoldsFunds(addr)) return " ";
+    const usd = getAddressValueUsd(addr);
+    const total =
+        usd === null
+            ? ""
+            : `<div class="text-xs text-muted mt-1">Total: ${formatUsd(usd)}</div>`;
+    return (
+        `<p class="mb-1">This address holds a balance. Removing it does not ` +
+        `move or spend anything; the balance stays at the address.</p>` +
+        balanceLinesForAddress(addr, state.trackedTokens, false) +
+        total
+    );
+}
+
+function show(walletIdx, addrIdx) {
+    const wallet = state.wallets[walletIdx];
+    const addr = wallet && wallet.addresses[addrIdx];
+    if (!addr) return;
+    target = { walletIdx, addrIdx };
+
+    $("delete-address-label").textContent = "Address " + (addrIdx + 1);
+    $("delete-address-wallet-name").textContent =
+        wallet.name || "Wallet " + (walletIdx + 1);
+
+    const value = $("delete-address-value");
+    value.innerHTML = renderAddressHtml(addr.address, {
+        ensName: addr.ensName,
+    });
+    attachCopyHandlers(value);
+
+    $("delete-address-recovery").textContent = recoveryPathText(wallet);
+    $("delete-address-balance").innerHTML = balanceWarningHtml(addr);
+
+    setFlash("");
+    showView("delete-address-confirm");
+}
+
+function init(_ctx) {
+    ctx = _ctx;
+
+    $("btn-delete-address-back").addEventListener("click", () => {
+        target = null;
+        goBack();
+    });
+
+    $("btn-delete-address-confirm").addEventListener("click", async () => {
+        if (target === null) {
+            setFlash("No address is selected for removal.");
+            return;
+        }
+
+        const { walletIdx, addrIdx } = target;
+        if (!canRemoveAddress(state.wallets[walletIdx])) {
+            setFlash(
+                "This address cannot be removed, because a wallet always " +
+                    "keeps at least one address.",
+            );
+            return;
+        }
+
+        const { removed, activeAddressChanged } = removeAddressFromState(
+            state,
+            walletIdx,
+            addrIdx,
+        );
+        if (!removed) {
+            setFlash("This address could not be removed.");
+            return;
+        }
+
+        target = null;
+        // Save before broadcasting: the background reads the active address
+        // back out of storage to build accountsChanged.
+        await saveState();
+        if (activeAddressChanged) broadcastActiveChanged();
+
+        ctx.renderWalletList();
+        goBack();
+        showFlash("Address removed.");
+    });
+}
+
+// recoveryPathText and balanceWarningHtml are exported so the two pieces of
+// copy that carry the screen's substance can be tested without a DOM; show()
+// is a one-line assignment for each.
+module.exports = { init, show, recoveryPathText, balanceWarningHtml };