Diffusion - move DiffusionExistsQuery to work over conduit

Summary: le title. However, this also "is the first" conversion so sets the precedence for how this will all work. See comments in the code. I think this helps us keep the new code we're writing to a minimum. Wondering if the conduit end point could be more generic, and rather than have a switch statement on VCS type, one can just implement the "handleSubversion" version and have that called?  Ref T2784

Test Plan: slapped an "or true" in the conditional protecting this code path. verified it worked on all 3 vcs systems, including typing in garbage and getting a 404

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2784

Differential Revision: https://secure.phabricator.com/D5803

src/applications/diffusion/conduit/ConduitAPI_diffusion_abstractquery_Method.php

@@ -0,0 +1,101 @@
+<?php
+
+/**
+ * @group conduit
+ */
+abstract class ConduitAPI_diffusion_abstractquery_Method
+  extends ConduitAPI_diffusion_Method {
+
+  private $diffusionRequest;
+  protected function setDiffusionRequest(DiffusionRequest $request) {
+    $this->diffusionRequest = $request;
+    return $this;
+  }
+  protected function getDiffusionRequest() {
+    return $this->diffusionRequest;
+  }
+
+  final public function defineErrorTypes() {
+    return $this->defineCustomErrorTypes() +
+      array(
+        'ERR-UNKNOWN-REPOSITORY-VCS' =>
+          pht('Unknown repository VCS type.'),
+        'ERR-UNSUPPORTED-VCS' =>
+          pht('VCS is not supported for this method.'));
+  }
+  /**
+   * Subclasses should override this to specify custom error types.
+   */
+  protected function defineCustomErrorTypes() {
+    return array();
+  }
+
+  final public function defineParamTypes() {
+    return $this->defineCustomParamTypes() +
+      array(
+      'callsign' => 'required string');
+  }
+  /**
+   * Subclasses should override this to specify custom param types.
+   */
+  protected function defineCustomParamTypes() {
+    return array();
+  }
+
+  /**
+   * Subclasses should override these methods with the proper result for the
+   * pertinent version control system, e.g. getGitResult for Git.
+   *
+   * If the result is not supported for that VCS, do not implement it. e.g.
+   * Subversion (SVN) does not support branches.
+   */
+  protected function getGitResult(ConduitAPIRequest $request) {
+    throw new ConduitException('ERR-UNSUPPORTED-VCS');
+  }
+  protected function getSVNResult(ConduitAPIRequest $request) {
+    throw new ConduitException('ERR-UNSUPPORTED-VCS');
+  }
+  protected function getMercurialResult(ConduitAPIRequest $request) {
+    throw new ConduitException('ERR-UNSUPPORTED-VCS');
+  }
+
+  /**
+   * This method is final because each query will need to construct a
+   * @{class:DiffusionRequest} and use it. Consolidating this codepath and
+   * enforcing @{method:getDiffusionRequest} works when we need it is good.
+   *
+   * @{method:getResult} should be overridden by subclasses as necessary, e.g.
+   * there is a common operation across all version control systems that
+   * should occur after @{method:getResult}, like formatting a timestamp.
+   */
+  final protected function execute(ConduitAPIRequest $request) {
+    $drequest = DiffusionRequest::newFromDictionary(
+      array(
+        'callsign'  => $request->getValue('callsign'),
+      ));
+    $this->setDiffusionRequest($drequest);
+
+    return $this->getResult($request);
+  }
+
+  protected function getResult(ConduitAPIRequest $request) {
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+    $result = null;
+    switch ($repository->getVersionControlSystem()) {
+      case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
+        $result = $this->getGitResult($request);
+        break;
+      case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
+        $result = $this->getMercurialResult($request);
+        break;
+      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
+        $result = $this->getSVNResult($request);
+        break;
+      default:
+        throw new ConduitException('ERR-UNKNOWN-REPOSITORY-VCS');
+        break;
+    }
+    return $result;
+  }
+}