Separate the check runner from file processor

This separates concerns so that the check runner can rely on the file
processor to store state and such. It introduces two logical
collaborators and will allow us to keep feature parity with flake8 2's
plugin design (where it could request any attribute from pep8.Checker).

flake8/checker.py

@@ -179,7 +179,73 @@ class FileChecker(object):
         self.filename = filename
         self.checks = checks
         self.results = []
-        self.lines = []
+        self.processor = FileProcessor(filename)
+
+    def report(self, error_code, line_number, column, text):
+        # type: (str, int, int, str) -> NoneType
+        """Report an error by storing it in the results list."""
+        error = (error_code, self.filename, line_number, column, text)
+        self.results.append(error)
+
+    def run_check(self, plugin):
+        """Run the check in a single plugin."""
+        arguments = {}
+        for parameter in plugin.parameters:
+            arguments[parameter] = self.attributes[parameter]
+        return plugin.execute(**arguments)
+
+    def run_checks(self):
+        """Run checks against the file."""
+        self.run_ast_checks()
+        self.run_physical_checks()
+        self.run_logical_checks()
+
+    def run_ast_checks(self):
+        """Run checks that require an abstract syntax tree."""
+        pass
+
+    def run_physical_checks(self):
+        """Run checks that require the physical line."""
+        pass
+
+    def run_logical_checks(self):
+        """Run checks that require the logical line from a file."""
+        pass
+
+
+class FileProcessor(object):
+    """Processes a file and holdes state.
+
+    This processes a file by generating tokens, logical and physical lines,
+    and AST trees. This also provides a way of passing state about the file
+    to checks expecting that state. Any public attribute on this object can
+    be requested by a plugin. The known public attributes are:
+
+    - multiline
+    - max_line_length
+    - tokens
+    - indent_level
+    - indect_char
+    - noqa
+    - verbose
+    - line_number
+    - total_lines
+    - previous_logical
+    - logical_line
+    - previous_indent_level
+    - blank_before
+    - blank_lines
+    """
+
+    def __init__(self, filename):
+        """Initialice our file processor.
+
+        :param str filename:
+            Name of the file to process
+        """
+        self.filename = filename
+        self.lines = self.read_lines()
+        self.strip_utf_bom()
 
     def read_lines(self):
         # type: () -> List[str]
@@ -235,17 +301,6 @@ class FileChecker(object):
         """Read the lines from standard in."""
         return utils.stdin_get_value().splitlines(True)
 
-    def report(self, error_code, line_number, column, text):
-        # type: (str, int, int, str) -> NoneType
-        """Report an error by storing it in the results list."""
-        error = (error_code, self.filename, line_number, column, text)
-        self.results.append(error)
-
-    def run_checks(self):
-        """Run checks against the file."""
-        self.lines = self.read_lines()
-        self.strip_utf_bom()
-
     def strip_utf_bom(self):
         # type: () -> NoneType
         """Strip the UTF bom from the lines of the file."""