qt swap dialog: attempt at clearer logic (at the cost of more lines)

fixes #6853

electrum/gui/qt/swap_dialog.py

@@ -104,6 +104,7 @@ class SwapDialog(WindowModalDialog):
         self.is_reverse = not self.is_reverse
         self.send_amount_e.setAmount(None)
         self.recv_amount_e.setAmount(None)
+        self.max_button.setChecked(False)
         self.update()
 
     def spend_max(self):
@@ -115,19 +116,20 @@ class SwapDialog(WindowModalDialog):
         else:
             self.send_amount_e.setAmount(None)
         self.update_fee()
+        self.update_ok_button()
 
     def uncheck_max(self):
         self.max_button.setChecked(False)
         self.update()
 
     def _spend_max_forward_swap(self):
-        self.update_tx('!')
+        self._update_tx('!')
         if self.tx:
             amount = self.tx.output_value_for_address(ln_dummy_address())
             max_amt = self.swap_manager.get_max_amount()
             if amount > max_amt:
                 amount = max_amt
-                self.update_tx(amount)
+                self._update_tx(amount)
             if self.tx:
                 amount = self.tx.output_value_for_address(ln_dummy_address())
                 assert amount <= max_amt
@@ -155,8 +157,9 @@ class SwapDialog(WindowModalDialog):
         self.recv_amount_e.setStyleSheet(ColorScheme.BLUE.as_stylesheet())
         self.recv_amount_e.follows = False
         self.send_follows = False
-        self.ok_button.setEnabled((recv_amount is not None)
+        self._update_tx(send_amount)
-                                  and (self.tx is not None or self.is_reverse))
+        self.update_fee()
+        self.update_ok_button()
 
     def on_recv_edited(self):
         if self.recv_amount_e.follows:
@@ -171,8 +174,9 @@ class SwapDialog(WindowModalDialog):
         self.send_amount_e.setStyleSheet(ColorScheme.BLUE.as_stylesheet())
         self.send_amount_e.follows = False
         self.send_follows = True
-        self.ok_button.setEnabled((send_amount is not None)
+        self._update_tx(send_amount)
-                                  and (self.tx is not None or self.is_reverse))
+        self.update_fee()
+        self.update_ok_button()
 
     def update(self):
         sm = self.swap_manager
@@ -186,25 +190,17 @@ class SwapDialog(WindowModalDialog):
         server_fee_str = '%.2f'%sm.percentage + '%  +  '  + self.window.format_amount(server_mining_fee) + ' ' + self.window.base_unit()
         self.server_fee_label.setText(server_fee_str)
         self.server_fee_label.repaint()  # macOS hack for #6269
+        self.update_tx()
         self.update_fee()
+        self.update_ok_button()
 
     def update_fee(self):
-        self.tx = None
+        """Updates self.fee_label. No other side-effects."""
-        is_max = self.max_button.isChecked()
         if self.is_reverse:
-            if is_max:
-                self._spend_max_reverse_swap()
             sm = self.swap_manager
             fee = sm.get_claim_fee()
         else:
-            if is_max:
-                self._spend_max_forward_swap()
-            else:
-                onchain_amount = self.send_amount_e.get_amount()
-                self.update_tx(onchain_amount)
             fee = self.tx.get_fee() if self.tx else None
-            if self.tx is None:
-                self.ok_button.setEnabled(False)
         fee_text = self.window.format_amount(fee) + ' ' + self.window.base_unit() if fee else ''
         self.fee_label.setText(fee_text)
         self.fee_label.repaint()  # macOS hack for #6269
@@ -233,10 +229,22 @@ class SwapDialog(WindowModalDialog):
                     return
             self.window.protect(self.do_normal_swap, (lightning_amount, onchain_amount))
 
-    def update_tx(self, onchain_amount):
+    def update_tx(self):
+        if self.is_reverse:
+            return
+        is_max = self.max_button.isChecked()
+        if is_max:
+            self._spend_max_forward_swap()
+        else:
+            onchain_amount = self.send_amount_e.get_amount()
+            self._update_tx(onchain_amount)
+
+    def _update_tx(self, onchain_amount):
+        """Updates self.tx. No other side-effects."""
+        if self.is_reverse:
+            return
         if onchain_amount is None:
             self.tx = None
-            self.ok_button.setEnabled(False)
             return
         outputs = [PartialTxOutput.from_address_and_value(ln_dummy_address(), onchain_amount)]
         coins = self.window.get_coins()
@@ -246,7 +254,16 @@ class SwapDialog(WindowModalDialog):
                 outputs=outputs)
         except (NotEnoughFunds, NoDynamicFeeEstimates) as e:
             self.tx = None
-            self.ok_button.setEnabled(False)
+
+    def update_ok_button(self):
+        """Updates self.ok_button. No other side-effects."""
+        send_amount = self.send_amount_e.get_amount()
+        recv_amount = self.recv_amount_e.get_amount()
+        self.ok_button.setEnabled(
+            (send_amount is not None)
+            and (recv_amount is not None)
+            and (self.tx is not None or self.is_reverse)
+        )
 
     def do_normal_swap(self, lightning_amount, onchain_amount, password):
         tx = self.tx