Factor scenario step and implementation connector into yarnlib

Rather than passing allow-missing-steps in, `missing_step_cb` can be
passed to the ScenarioStepConnector, which if it returns true, will
exclude that scenario, rather than raising an exception.

This was chosen, as it also works as a status update callback.

3 files changed, 125 insertions, 47 deletions

diff --git a/yarn b/yarn
index d01b2af..12e01dd 100755
--- a/yarn
+++ b/yarn
@@ -178,44 +178,18 @@ class YarnRunner(cliapp.Application):
         return block_parser.scenarios, block_parser.implementations
 
     def connect_implementations(self, scenarios, implementations):
-        new_list = []
-        for scenario in scenarios:
-            missing_step = False
-            for step in scenario.steps:
-                self.connect_implementation(
-                    scenario, step, implementations)
-                if step.implementation is None:
-                    missing_step = True
-            if not missing_step:
-                new_list.append(scenario)
-        return new_list
-
-    def connect_implementation(self, scenario, step, implementations):
-        matching = [i for i in implementations
-                    if step.what == i.what and
-                       self.implements_matches_step(i, step)]
-
-        if len(matching) == 0:
-            if self.settings['allow-missing-steps']:
+        if self.settings['allow-missing-steps']:
+            def warn_missing(scenario, step):
                 self.warning(
                     'Scenario %s has missing step %s %s' %
                     (scenario.name, step.what, step.text))
-                return
-            raise cliapp.AppException(
-                'Scenario "%s", step "%s %s" has no matching '
-                'implementation' %
-                (scenario.name, step.what, step.text))
-        if len(matching) > 1:
-            s = '\n'.join(
-                'IMPLEMENTS %s %s' % (i.what, i.regexp)
-                for i in matching)
-            raise cliapp.AppException(
-                'Scenario "%s", step "%s %s" has more than one '
-                'matching implementations:\n%s' %
-                (scenario.name, step.what, step.text, s))
+                return True
+            step_connector = yarnlib.ScenarioStepConnector(
+                implementations, missing_step_cb=warn_missing)
+        else:
+            step_connector = yarnlib.ScenarioStepConnector(implementations)
 
-        assert step.implementation is None
-        step.implementation = matching[0]
+        return step_connector.connect_implementations(scenarios)
 
     def load_shell_libraries(self):
         if not self.settings['shell-library']:
@@ -366,7 +340,7 @@ class YarnRunner(cliapp.Application):
         self.ts['step_name'] = '%s %s' % (step.what, step.text)
         self.steps_run += 1
 
-        m = self.implements_matches_step(step.implementation, step)
+        m = yarnlib.implements_matches_step(step.implementation, step)
         assert m is not None
         env = self.clean_env()
         env['DATADIR'] = datadir
@@ -435,18 +409,6 @@ class YarnRunner(cliapp.Application):
         nice = ''.join(nice)
         return nice
 
-    def implements_matches_step(self, implements, step):
-        '''Return re.Match if implements matches the step.
-
-        Otherwise, return None.
-
-        '''
-
-        m = re.match(implements.regexp, step.text, re.I)
-        if m and m.end() != len(step.text):
-            return None
-        return m
-
     def indent(self, s):
         return ''.join('    %s\n' % line for line in s.splitlines())
 
diff --git a/yarnlib/__init__.py b/yarnlib/__init__.py
index 33cdc46..0d36668 100644
--- a/yarnlib/__init__.py
+++ b/yarnlib/__init__.py
@@ -21,5 +21,10 @@ from elements import Scenario, ScenarioStep, Implementation
 from block_parser import BlockParser, BlockError
 from scenario_validator import (NoScenariosError, DuplicateScenariosError,
                                 NoThensError, ScenarioValidator)
+from scenario_step_connector import (implements_matches_step,
+                                     ScenarioStepConnector,
+                                     StepNotImplementedError,
+                                     StepMultipleImplementationsError)
+
 
 import shell_libraries
diff --git a/yarnlib/scenario_step_connector.py b/yarnlib/scenario_step_connector.py
new file mode 100644
index 0000000..e0a29f0
--- /dev/null
+++ b/yarnlib/scenario_step_connector.py
@@ -0,0 +1,111 @@
+# Copyright 2014  Codethink Limited
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# =*= License: GPL-3+ =*=
+
+
+import cliapp
+import re
+
+
+def implements_matches_step(implements, step):
+    '''Return re.Match if implements matches the step.
+
+    Otherwise, return None.
+
+    '''
+
+    m = re.match(implements.regexp, step.text, re.I)
+    if m and m.end() != len(step.text):
+        return None
+    return m
+
+
+class StepNotImplementedError(cliapp.AppException):
+
+    def __init__(self, scenario, step):
+        cliapp.AppException.__init__(
+            self, 'Scenario "%s", step "%s %s" has no matching '
+                  'implementation' %
+                  (scenario.name, step.what, step.text))
+
+
+class StepMultipleImplementationsError(cliapp.AppException):
+
+    def __init__(self, scenario, step, matching):
+        s = '\n'.join(
+            'IMPLEMENTS %s %s' % (i.what, i.regexp)
+            for i in matching)
+        cliapp.AppException.__init__(
+            self, 'Scenario "%s", step "%s %s" has more than one '
+                  'matching implementations:\n%s' %
+                  (scenario.name, step.what, step.text, s))
+
+
+class ScenarioStepConnector(object):
+    '''Connect scenario steps to their implementations.'''
+
+    def __init__(self, implementations, missing_step_cb=lambda sc, st: None):
+        self.implementations = implementations
+        self.missing_step_cb = missing_step_cb
+
+    def connect_implementations(self, scenarios):
+        '''Connect scenario steps, returning implemented scenarios.
+
+        For each scenario given, connect known implementations to
+        the steps.
+
+        This returns only scenarios that were fully implemented.
+        Unless ``missing_step_cb`` is provided and returns true for all
+        missing steps, an exception is raised instead.
+
+        '''
+        implemented_scenarios = []
+        for scenario in scenarios:
+            missing_step = False
+            for step in scenario.steps:
+                self.connect_implementation(scenario, step)
+                if step.implementation is None:
+                    missing_step = True
+            if not missing_step:
+                implemented_scenarios.append(scenario)
+        return implemented_scenarios
+
+    def connect_implementation(self, scenario, step):
+        '''Connect the step of a scenario to its implementation.
+
+        Always raises an exception if there are multiple matching
+        implementations.
+
+        Raises an exception if there are no matching implementations
+        unless ``missing_step_cb`` returns true.
+
+        '''
+        matching = [i for i in self.implementations
+                    if step.what == i.what and
+                       implements_matches_step(i, step)]
+
+        if len(matching) == 0:
+            if self.missing_step_cb(scenario, step):
+                return
+            raise StepNotImplementedError(scenario, step)
+        if len(matching) > 1:
+            raise StepMultipleImplementationsError(scenario, step, matching)
+
+        assert step.implementation is None
+        step.implementation = matching[0]
+
+
+# vim: set ts=4 sw=4 et: