enforce checklocktimeverify for nLockTime when adding input. tx.prevOut method.

lib/bcoin/tx.js

@@ -97,6 +97,20 @@ TX.prototype._input = function _input(i, index) {
     seq: i.seq === undefined ? 0xffffffff : i.seq
   };
 
+  if (input.out.tx) {
+    var prev = input.out.tx.outputs[input.out.index].script;
+    var lock = bcoin.script.lockTime(prev);
+    if (lock) {
+      this.lock = Math.max(lock.toNumber(), this.lock);
+      // if (this.lock === 0)
+      //   this.lock = lock.toNumber();
+      // if (!bcoin.script.spendable(this, this.lock))
+      //   throw new Error('Cannot spend ' + utils.revHex(input.out.hash));
+      if (input.seq === 0xffffffff)
+        input.seq = 0;
+    }
+  }
+
   // Try modifying existing input first
   var index = this._inputIndex(hash, index);
   if (index !== -1) {
@@ -125,6 +139,18 @@ TX.prototype._inputIndex = function _inputIndex(hash, index) {
   return -1;
 };
 
+TX.prototype.prevOut = function prevOut(i, def) {
+  if (typeof i === 'object')
+    i = this.inputs.indexOf(i);
+
+  var input = this.inputs[i];
+
+  if (!input || !input.out.tx || input.out.index == null)
+    return def;
+
+  return input.out.tx.outputs[input.out.index] || def;
+};
+
 TX.prototype.signatureHash = function signatureHash(i, type) {
   if (typeof i === 'object')
     i = this.inputs.indexOf(i);