Add chart functions "x()" and "constant(3)"

Summary:
Depends on D20442. Ref T13279. Add basic support for drawing chart functions that are not based on Facts first-party ETL datasets. Some general goals:

  - This might be useful to draw a line like "goal" or "profitability".
  - This might be useful to pull data from an external source.
  - For composable functions like "add" or "subtract", which are useful in manipulating ETL datasets, these value functions will make testing easier.

Test Plan:
Added a `constant(256)` function:

{F6382408}

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20443

src/__phutil_library_map__.php

@@ -2802,6 +2802,7 @@ phutil_register_library_map(array(
     'PhabricatorConpherenceWidgetVisibleSetting' => 'applications/settings/setting/PhabricatorConpherenceWidgetVisibleSetting.php',
     'PhabricatorConsoleApplication' => 'applications/console/application/PhabricatorConsoleApplication.php',
     'PhabricatorConsoleContentSource' => 'infrastructure/contentsource/PhabricatorConsoleContentSource.php',
+    'PhabricatorConstantChartFunction' => 'applications/fact/chart/PhabricatorConstantChartFunction.php',
     'PhabricatorContactNumbersSettingsPanel' => 'applications/settings/panel/PhabricatorContactNumbersSettingsPanel.php',
     'PhabricatorContentSource' => 'infrastructure/contentsource/PhabricatorContentSource.php',
     'PhabricatorContentSourceModule' => 'infrastructure/contentsource/PhabricatorContentSourceModule.php',
@@ -4935,6 +4936,7 @@ phutil_register_library_map(array(
     'PhabricatorWorkingCopyDiscoveryTestCase' => 'applications/repository/engine/__tests__/PhabricatorWorkingCopyDiscoveryTestCase.php',
     'PhabricatorWorkingCopyPullTestCase' => 'applications/repository/engine/__tests__/PhabricatorWorkingCopyPullTestCase.php',
     'PhabricatorWorkingCopyTestCase' => 'applications/repository/engine/__tests__/PhabricatorWorkingCopyTestCase.php',
+    'PhabricatorXChartFunction' => 'applications/fact/chart/PhabricatorXChartFunction.php',
     'PhabricatorXHPASTDAO' => 'applications/phpast/storage/PhabricatorXHPASTDAO.php',
     'PhabricatorXHPASTParseTree' => 'applications/phpast/storage/PhabricatorXHPASTParseTree.php',
     'PhabricatorXHPASTViewController' => 'applications/phpast/controller/PhabricatorXHPASTViewController.php',
@@ -8790,6 +8792,7 @@ phutil_register_library_map(array(
     'PhabricatorConpherenceWidgetVisibleSetting' => 'PhabricatorInternalSetting',
     'PhabricatorConsoleApplication' => 'PhabricatorApplication',
     'PhabricatorConsoleContentSource' => 'PhabricatorContentSource',
+    'PhabricatorConstantChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorContactNumbersSettingsPanel' => 'PhabricatorSettingsPanel',
     'PhabricatorContentSource' => 'Phobject',
     'PhabricatorContentSourceModule' => 'PhabricatorConfigModule',
@@ -11288,6 +11291,7 @@ phutil_register_library_map(array(
     'PhabricatorWorkingCopyDiscoveryTestCase' => 'PhabricatorWorkingCopyTestCase',
     'PhabricatorWorkingCopyPullTestCase' => 'PhabricatorWorkingCopyTestCase',
     'PhabricatorWorkingCopyTestCase' => 'PhabricatorTestCase',
+    'PhabricatorXChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorXHPASTDAO' => 'PhabricatorLiskDAO',
     'PhabricatorXHPASTParseTree' => 'PhabricatorXHPASTDAO',
     'PhabricatorXHPASTViewController' => 'PhabricatorController',

src/applications/fact/chart/PhabricatorChartFunction.php

@@ -25,6 +25,10 @@ abstract class PhabricatorChartFunction
 
   abstract protected function newArguments(array $arguments);
 
+  public function loadData() {
+    return;
+  }
+
   final public function setXAxis(PhabricatorChartAxis $x_axis) {
     $this->xAxis = $x_axis;
     return $this;
@@ -43,4 +47,53 @@ abstract class PhabricatorChartFunction
     return $this->yAxis;
   }
 
+  protected function newLinearSteps($src, $dst, $count) {
+    $count = (int)$count;
+    $src = (int)$src;
+    $dst = (int)$dst;
+
+    if ($count === 0) {
+      throw new Exception(
+        pht('Can not generate zero linear steps between two values!'));
+    }
+
+    if ($src === $dst) {
+      return array($src);
+    }
+
+    if ($count === 1) {
+      return array($src);
+    }
+
+    $is_reversed = ($src > $dst);
+    if ($is_reversed) {
+      $min = (double)$dst;
+      $max = (double)$src;
+    } else {
+      $min = (double)$src;
+      $max = (double)$dst;
+    }
+
+    $step = (double)($max - $min) / (double)($count - 1);
+
+    $steps = array();
+    for ($cursor = $min; $cursor <= $max; $cursor += $step) {
+      $x = (int)round($cursor);
+
+      if (isset($steps[$x])) {
+        continue;
+      }
+
+      $steps[$x] = $x;
+    }
+
+    $steps = array_values($steps);
+
+    if ($is_reversed) {
+      $steps = array_reverse($steps);
+    }
+
+    return $steps;
+  }
+
 }

src/applications/fact/chart/PhabricatorConstantChartFunction.php

@@ -0,0 +1,51 @@
+<?php
+
+final class PhabricatorConstantChartFunction
+  extends PhabricatorChartFunction {
+
+  const FUNCTIONKEY = 'constant';
+
+  private $value;
+
+  protected function newArguments(array $arguments) {
+    if (count($arguments) !== 1) {
+      throw new Exception(
+        pht(
+          'Chart function "constant(...)" expects one argument, got %s. '.
+          'Pass a constant.',
+          count($arguments)));
+    }
+
+    if (!is_int($arguments[0])) {
+      throw new Exception(
+        pht(
+          'First argument for "fact(...)" is invalid: expected int, '.
+          'got %s.',
+          phutil_describe_type($arguments[0])));
+    }
+
+    $this->value = $arguments[0];
+  }
+
+  public function getDatapoints($limit) {
+    $axis = $this->getXAxis();
+    $x_min = $axis->getMinimumValue();
+    $x_max = $axis->getMaximumValue();
+
+    $points = array();
+    $steps = $this->newLinearSteps($x_min, $x_max, 2);
+    foreach ($steps as $step) {
+      $points[] = array(
+        'x' => $step,
+        'y' => $this->value,
+      );
+    }
+
+    return $points;
+  }
+
+  public function hasDomain() {
+    return false;
+  }
+
+}

src/applications/fact/chart/PhabricatorXChartFunction.php

@@ -0,0 +1,38 @@
+<?php
+
+final class PhabricatorXChartFunction
+  extends PhabricatorChartFunction {
+
+  const FUNCTIONKEY = 'x';
+
+  protected function newArguments(array $arguments) {
+    if (count($arguments) !== 0) {
+      throw new Exception(
+        pht(
+          'Chart function "x()" expects zero arguments, got %s.',
+          count($arguments)));
+    }
+  }
+
+  public function getDatapoints($limit) {
+    $axis = $this->getXAxis();
+    $x_min = $axis->getMinimumValue();
+    $x_max = $axis->getMaximumValue();
+
+    $points = array();
+    $steps = $this->newLinearSteps($x_min, $x_max, $limit);
+    foreach ($steps as $step) {
+      $points[] = array(
+        'x' => $step,
+        'y' => $step,
+      );
+    }
+
+    return $points;
+  }
+
+  public function hasDomain() {
+    return false;
+  }
+
+}

src/applications/fact/controller/PhabricatorFactChartController.php

@@ -20,9 +20,11 @@ final class PhabricatorFactChartController extends PhabricatorFactController {
     $functions[] = id(new PhabricatorFactChartFunction())
       ->setArguments(array('tasks.open-count.create'));
 
-    if ($is_chart_mode) {
-      return $this->newChartResponse();
-    }
+    $functions[] = id(new PhabricatorConstantChartFunction())
+      ->setArguments(array(256));
+
+    $functions[] = id(new PhabricatorXChartFunction())
+      ->setArguments(array());
 
     list($domain_min, $domain_max) = $this->getDomain($functions);
 
@@ -73,6 +75,10 @@ final class PhabricatorFactChartController extends PhabricatorFactController {
       'yMax' => $y_max,
     );
 
+    if ($is_chart_mode) {
+      return $this->newChartResponse();
+    }
+
     return id(new AphrontAjaxResponse())->setContent($chart_data);
   }