Add ability to track visits thru the magic variable $visits_{node}

Author: weaversam8

examples/visits.csv

@@ -0,0 +1,3 @@
+id,text,file,node,lineNumber
+visits-loop-0,This is the loop node.,visits,loop,8
+visits-end-1,This is the end.,visits,end,19

examples/visits.yarn

@@ -0,0 +1,20 @@
+title: Start
+---
+[[loop]]
+===
+title: loop
+---
+
+This is the loop node.
+
+<<if $visits_loop > 3>>
+[[end]]
+<<endif>>
+
+[[loop]]
+===
+title: end
+---
+
+This is the end.
+===

examples/visits.yarnc

@@ -0,0 +1,26 @@
+import os
+from .context import YarnRunner
+
+compiled_yarn_f = open(os.path.join(os.path.dirname(
+    __file__), '../examples/visits.yarnc'), 'rb')
+names_csv_f = open(os.path.join(os.path.dirname(
+    __file__), '../examples/visits.csv'), 'r')
+
+runner = YarnRunner(compiled_yarn_f, names_csv_f)
+
+
+def test_visits():
+    assert "This is the loop node." == runner.get_line()
+    assert runner.has_line()
+    assert "This is the loop node." == runner.get_line()
+    assert runner.has_line()
+    assert "This is the loop node." == runner.get_line()
+    assert runner.has_line()
+    assert "This is the loop node." == runner.get_line()
+    assert runner.has_line()
+    assert "This is the end." == runner.get_line()
+    assert not runner.has_line()
+    assert runner.finished
+    assert runner.visits['loop'] == 4
+    assert runner.visits['Start'] == 1
+    assert runner.visits['end'] == 1

tests/test_visits.py

@@ -1,4 +1,5 @@
 import csv
+import re
 from warnings import warn
 from .yarn_spinner_pb2 import Program as YarnProgram, Instruction
 from .vm_std_lib import functions as std_lib_functions
@@ -210,8 +211,23 @@ def __call_func(self, instruction):
         self._vm_data_stack.insert(0, ret)
 
     def __push_variable(self, instruction):
+        variable_name = instruction.operands[0].string_value
+
+        match = re.search(r"\$visits_([a-zA-Z\_0-9]+)", variable_name)
+        if match:
+            node_name = match.group(1)
+            if node_name not in self.visits:
+                visits = 0
+            else:
+                visits = self.visits[node_name]
+            self._vm_data_stack.insert(0, visits)
+            return
+
+        if variable_name not in self.variables:
+            raise Exception(f"Variable {variable_name} has not been set.")
+
         self._vm_data_stack.insert(
-            0, self.variables[instruction.operands[0].string_value])
+            0, self.variables[variable_name])
 
     def __store_variable(self, instruction):
         self.variables[instruction.operands[0].string_value] = self._vm_data_stack[0]