commit 5c48b3088d26f317a44cbc6f7a52c0c494e4c344
Author: Jason Park <parkjs814@gmail.com>
Date:   Fri Jun 7 15:43:44 2019 +0900

    Separate backend from algorithm-visualizer repo

diff --git a/.DS_Store b/.DS_Store
new file mode 100644
index 0000000..5eaa47a
Binary files /dev/null and b/.DS_Store differ
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..689bc6a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+/.idea
+/node_modules
+/npm-debug.log
+/public
+/pm2.config.js
+.DS_Store
diff --git a/.idea/encodings.xml b/.idea/encodings.xml
new file mode 100644
index 0000000..15a15b2
--- /dev/null
+++ b/.idea/encodings.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding" addBOMForNewFiles="with NO BOM" />
+</project>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 0000000..28a804d
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="JavaScriptSettings">
+    <option name="languageLevel" value="ES6" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
new file mode 100644
index 0000000..fbd90b4
--- /dev/null
+++ b/.idea/modules.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/server.iml" filepath="$PROJECT_DIR$/.idea/server.iml" />
+    </modules>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/server.iml b/.idea/server.iml
new file mode 100644
index 0000000..24643cc
--- /dev/null
+++ b/.idea/server.iml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$">
+      <excludeFolder url="file://$MODULE_DIR$/.tmp" />
+      <excludeFolder url="file://$MODULE_DIR$/temp" />
+      <excludeFolder url="file://$MODULE_DIR$/tmp" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..d6eacee
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+    <mapping directory="$PROJECT_DIR$/public/algorithms" vcs="Git" />
+    <mapping directory="$PROJECT_DIR$/src/public/algorithms" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/webResources.xml b/.idea/webResources.xml
new file mode 100644
index 0000000..edf30b3
--- /dev/null
+++ b/.idea/webResources.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="WebResourcesPaths">
+    <contentEntries>
+      <entry url="file://$PROJECT_DIR$">
+        <entryData>
+          <resourceRoots>
+            <path value="file://$PROJECT_DIR$/src" />
+          </resourceRoots>
+        </entryData>
+      </entry>
+    </contentEntries>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
new file mode 100644
index 0000000..3b2c9de
--- /dev/null
+++ b/.idea/workspace.xml
@@ -0,0 +1,266 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ChangeListManager">
+    <list default="true" id="33967b4c-80ab-44ef-aea7-fe45cd91b9b7" name="Default Changelist" comment="">
+      <change afterPath="$PROJECT_DIR$/.gitignore" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/encodings.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/misc.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/modules.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/server.iml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/vcs.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/webResources.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/app/backend.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/app/frontend.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/app/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/bin/pull" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/bin/www" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/package.json" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/pm2.config.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/public/algorithm-visualizer.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main.cpp" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/apis/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/common/config.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/common/error.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/common/hierarchy.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/common/util.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/common/webhook.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/controllers/algorithms.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/controllers/auth.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/controllers/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/controllers/tracers.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/controllers/visualizations.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/models/Algorithm.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/models/Category.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/models/File.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/models/Hierarchy.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/models/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/ImageBuilder.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/WorkerBuilder.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/cpp/Dockerfile" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/index.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/java/Dockerfile" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/src/tracers/js/worker.js" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/webpack.backend.config.js" afterDir="false" />
+    </list>
+    <ignored path="$PROJECT_DIR$/.tmp/" />
+    <ignored path="$PROJECT_DIR$/temp/" />
+    <ignored path="$PROJECT_DIR$/tmp/" />
+    <option name="EXCLUDED_CONVERTED_TO_IGNORED" value="true" />
+    <option name="SHOW_DIALOG" value="false" />
+    <option name="HIGHLIGHT_CONFLICTS" value="true" />
+    <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
+    <option name="LAST_RESOLUTION" value="IGNORE" />
+  </component>
+  <component name="FileEditorManager">
+    <leaf>
+      <file pinned="false" current-in-tab="true">
+        <entry file="file://$PROJECT_DIR$/bin/pull">
+          <provider selected="true" editor-type-id="text-editor">
+            <state relative-caret-position="105">
+              <caret line="7" lean-forward="true" selection-start-line="7" selection-end-line="7" />
+            </state>
+          </provider>
+        </entry>
+      </file>
+    </leaf>
+  </component>
+  <component name="FindInProjectRecents">
+    <findStrings>
+      <find>robot</find>
+    </findStrings>
+    <dirStrings>
+      <dir>$PROJECT_DIR$</dir>
+    </dirStrings>
+  </component>
+  <component name="Git.Settings">
+    <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
+  </component>
+  <component name="IdeDocumentHistory">
+    <option name="CHANGED_PATHS">
+      <list>
+        <option value="$PROJECT_DIR$/package.json" />
+        <option value="$PROJECT_DIR$/.gitignore" />
+        <option value="$PROJECT_DIR$/bin/pull" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectFrameBounds" extendedState="6" fullScreen="true">
+    <option name="width" value="1680" />
+    <option name="height" value="1050" />
+  </component>
+  <component name="ProjectLevelVcsManager" settingsEditedManually="true" />
+  <component name="ProjectView">
+    <navigator proportions="" version="1">
+      <foldersAlwaysOnTop value="true" />
+    </navigator>
+    <panes>
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+            <path>
+              <item name="server" type="b2602c69:ProjectViewProjectNode" />
+              <item name="server" type="462c0819:PsiDirectoryNode" />
+            </path>
+            <path>
+              <item name="server" type="b2602c69:ProjectViewProjectNode" />
+              <item name="server" type="462c0819:PsiDirectoryNode" />
+              <item name="app" type="462c0819:PsiDirectoryNode" />
+            </path>
+            <path>
+              <item name="server" type="b2602c69:ProjectViewProjectNode" />
+              <item name="server" type="462c0819:PsiDirectoryNode" />
+              <item name="bin" type="462c0819:PsiDirectoryNode" />
+            </path>
+            <path>
+              <item name="server" type="b2602c69:ProjectViewProjectNode" />
+              <item name="server" type="462c0819:PsiDirectoryNode" />
+              <item name="src" type="462c0819:PsiDirectoryNode" />
+            </path>
+            <path>
+              <item name="server" type="b2602c69:ProjectViewProjectNode" />
+              <item name="server" type="462c0819:PsiDirectoryNode" />
+              <item name="src" type="462c0819:PsiDirectoryNode" />
+              <item name="controllers" type="462c0819:PsiDirectoryNode" />
+            </path>
+          </expand>
+          <select />
+        </subPane>
+      </pane>
+      <pane id="Scope" />
+    </panes>
+  </component>
+  <component name="PropertiesComponent">
+    <property name="WebServerToolWindowFactoryState" value="false" />
+    <property name="last_opened_file_path" value="$PROJECT_DIR$" />
+    <property name="nodejs_interpreter_path.stuck_in_default_project" value="undefined stuck path" />
+    <property name="nodejs_npm_path_reset_for_default_project" value="true" />
+    <property name="nodejs_package_manager_path" value="npm" />
+  </component>
+  <component name="RecentsManager">
+    <key name="MoveFile.RECENT_KEYS">
+      <recent name="$PROJECT_DIR$" />
+    </key>
+    <key name="CopyFile.RECENT_KEYS">
+      <recent name="$PROJECT_DIR$" />
+    </key>
+  </component>
+  <component name="RunDashboard">
+    <option name="ruleStates">
+      <list>
+        <RuleState>
+          <option name="name" value="ConfigurationTypeDashboardGroupingRule" />
+        </RuleState>
+        <RuleState>
+          <option name="name" value="StatusDashboardGroupingRule" />
+        </RuleState>
+      </list>
+    </option>
+  </component>
+  <component name="SvnConfiguration">
+    <configuration />
+  </component>
+  <component name="TaskManager">
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+      <changelist id="33967b4c-80ab-44ef-aea7-fe45cd91b9b7" name="Default Changelist" comment="" />
+      <created>1559885518055</created>
+      <option name="number" value="Default" />
+      <option name="presentableId" value="Default" />
+      <updated>1559885518055</updated>
+      <workItem from="1559885519397" duration="1598000" />
+    </task>
+    <servers />
+  </component>
+  <component name="TimeTrackingManager">
+    <option name="totallyTimeSpent" value="1598000" />
+  </component>
+  <component name="ToolWindowManager">
+    <frame x="0" y="0" width="1680" height="1050" extended-state="6" />
+    <editor active="true" />
+    <layout>
+      <window_info id="Favorites" side_tool="true" />
+      <window_info active="true" content_ui="combo" id="Project" order="0" visible="true" weight="0.24954791" />
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+      <window_info anchor="bottom" id="Terminal" visible="true" weight="0.32959184" />
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+      <window_info anchor="bottom" id="Run" order="2" />
+      <window_info anchor="bottom" id="Debug" order="3" weight="0.4" />
+      <window_info anchor="bottom" id="Cvs" order="4" weight="0.25" />
+      <window_info anchor="bottom" id="Inspection" order="5" weight="0.4" />
+      <window_info anchor="bottom" id="TODO" order="6" />
+      <window_info anchor="right" id="Commander" internal_type="SLIDING" order="0" type="SLIDING" weight="0.4" />
+      <window_info anchor="right" id="Ant Build" order="1" weight="0.25" />
+      <window_info anchor="right" content_ui="combo" id="Hierarchy" order="2" weight="0.25" />
+    </layout>
+  </component>
+  <component name="TypeScriptGeneratedFilesManager">
+    <option name="version" value="1" />
+  </component>
+  <component name="editorHistoryManager">
+    <entry file="file://$PROJECT_DIR$/package.json">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="75">
+          <caret line="5" column="56" selection-start-line="5" selection-start-column="56" selection-end-line="5" selection-end-column="56" />
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+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/src/apis/index.js">
+      <provider selected="true" editor-type-id="text-editor">
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+          <caret line="2" column="20" lean-forward="true" selection-start-line="2" selection-start-column="20" selection-end-line="2" selection-end-column="20" />
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/pm2.config.js">
+      <provider selected="true" editor-type-id="text-editor" />
+    </entry>
+    <entry file="file://$PROJECT_DIR$/webpack.backend.config.js">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="-47" />
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/app/backend.js">
+      <provider selected="true" editor-type-id="text-editor" />
+    </entry>
+    <entry file="file://$PROJECT_DIR$/app/index.js">
+      <provider selected="true" editor-type-id="text-editor" />
+    </entry>
+    <entry file="file://$PROJECT_DIR$/src/controllers/index.js">
+      <provider selected="true" editor-type-id="text-editor">
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+      <provider selected="true" editor-type-id="text-editor">
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+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/src/index.js">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="285">
+          <caret line="19" column="13" selection-start-line="19" selection-start-column="13" selection-end-line="19" selection-end-column="13" />
+          <folding>
+            <element signature="e#0#30#0" expanded="true" />
+          </folding>
+        </state>
+      </provider>
+    </entry>
+    <entry file="file://$PROJECT_DIR$/bin/pull">
+      <provider selected="true" editor-type-id="text-editor">
+        <state relative-caret-position="105">
+          <caret line="7" lean-forward="true" selection-start-line="7" selection-end-line="7" />
+        </state>
+      </provider>
+    </entry>
+  </component>
+</project>
\ No newline at end of file
diff --git a/app/backend.js b/app/backend.js
new file mode 100644
index 0000000..ebec15a
--- /dev/null
+++ b/app/backend.js
@@ -0,0 +1,42 @@
+const {
+  __DEV__,
+  backendBuildPath,
+} = require('../environment');
+
+if (__DEV__) {
+  const webpack = require('webpack');
+  const webpackConfig = require('../webpack.backend.config.js');
+  const compiler = webpack(webpackConfig);
+
+  let backend = null;
+  let lastHash = null;
+  compiler.watch({
+    watchOptions: {
+      ignored: /public/,
+    },
+  }, (err, stats) => {
+    if (err) {
+      lastHash = null;
+      compiler.purgeInputFileSystem();
+      console.error(err);
+    } else if (stats.hash !== lastHash) {
+      lastHash = stats.hash;
+      console.info(stats.toString({
+        cached: false,
+        colors: true,
+      }));
+
+      delete require.cache[require.resolve(backendBuildPath)];
+      backend = require(backendBuildPath).default;
+    }
+  });
+
+  const backendWrapper = (req, res, next) => backend(req, res, next);
+  backendWrapper.getHierarchy = () => backend.hierarchy;
+  module.exports = backendWrapper;
+} else {
+  const backend = require(backendBuildPath).default;
+  const backendWrapper = (req, res, next) => backend(req, res, next);
+  backendWrapper.getHierarchy = () => backend.hierarchy;
+  module.exports = backendWrapper;
+}
diff --git a/app/frontend.js b/app/frontend.js
new file mode 100644
index 0000000..d54c3fb
--- /dev/null
+++ b/app/frontend.js
@@ -0,0 +1,78 @@
+const express = require('express');
+const path = require('path');
+const fs = require('fs');
+const url = require('url');
+const packageJson = require('../package');
+
+const {
+  __DEV__,
+  frontendSrcPath,
+  frontendBuildPath,
+} = require('../environment');
+
+const app = express();
+
+if (__DEV__) {
+  const webpack = require('webpack');
+  const webpackDev = require('webpack-dev-middleware');
+  const webpackHot = require('webpack-hot-middleware');
+  const webpackConfig = require('../webpack.frontend.config.js');
+  const compiler = webpack(webpackConfig);
+  app.use(express.static(path.resolve(frontendSrcPath, 'static')));
+  app.use(webpackDev(compiler, {
+    stats: {
+      cached: false,
+      colors: true,
+    },
+    serverSideRender: true,
+    index: false,
+  }));
+  app.use(webpackHot(compiler));
+  app.use((req, res, next) => {
+    const { fs } = res.locals;
+    const outputPath = res.locals.webpackStats.toJson().outputPath;
+    const filePath = path.resolve(outputPath, 'index.html');
+    fs.readFile(filePath, 'utf8', (err, data) => {
+      if (err) return next(err);
+      res.indexFile = data;
+      next();
+    });
+  });
+} else {
+  app.use(express.static(frontendBuildPath, { index: false }));
+  app.use((req, res, next) => {
+    const filePath = path.resolve(frontendBuildPath, 'index.html');
+    fs.readFile(filePath, 'utf8', (err, data) => {
+      if (err) return next(err);
+      res.indexFile = data;
+      next();
+    });
+  });
+}
+
+app.use((req, res) => {
+  const backend = require('./backend');
+  const hierarchy = backend.getHierarchy();
+
+  const [, categoryKey, algorithmKey] = url.parse(req.originalUrl).pathname.split('/');
+  let { title, description } = packageJson;
+  let algorithm = undefined;
+  if (categoryKey && categoryKey !== 'scratch-paper') {
+    algorithm = hierarchy.find(categoryKey, algorithmKey) || null;
+    if (algorithm) {
+      title = [algorithm.categoryName, algorithm.algorithmName].join(' - ');
+      description = algorithm.description;
+    } else {
+      res.status(404);
+    }
+  }
+
+  const indexFile = res.indexFile
+    .replace(/\$TITLE/g, title)
+    .replace(/\$DESCRIPTION/g, description)
+    .replace(/\$ALGORITHM/g, algorithm === undefined ? 'undefined' :
+      JSON.stringify(algorithm).replace(/</g, '\\u003c'));
+  res.send(indexFile);
+});
+
+module.exports = app;
diff --git a/app/index.js b/app/index.js
new file mode 100644
index 0000000..2cd4d10
--- /dev/null
+++ b/app/index.js
@@ -0,0 +1,30 @@
+const path = require('path');
+const express = require('express');
+const compression = require('compression');
+const app = express();
+
+const frontend = require('./frontend');
+const backend = require('./backend');
+
+const {
+  apiEndpoint,
+  credentials,
+} = require('../environment');
+
+app.use(compression());
+app.use((req, res, next) => {
+  if (req.hostname === 'algo-visualizer.jasonpark.me') {
+    res.redirect(301, 'https://algorithm-visualizer.org/');
+  } else if (credentials && !req.secure) {
+    res.redirect(301, `https://${req.hostname}${req.url}`);
+  } else {
+    next();
+  }
+});
+app.get('/robots.txt', (req, res) => {
+  res.sendFile(path.resolve(__dirname, '..', 'robots.txt'));
+});
+app.use(apiEndpoint, backend);
+app.use(frontend);
+
+module.exports = app;
diff --git a/bin/pull b/bin/pull
new file mode 100755
index 0000000..e0acb4d
--- /dev/null
+++ b/bin/pull
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+git fetch &&
+! git diff-index --quiet origin/master -- ':!package-lock.json' &&
+git reset --hard origin/master &&
+npm install &&
+npm run build
diff --git a/bin/www b/bin/www
new file mode 100755
index 0000000..19bd763
--- /dev/null
+++ b/bin/www
@@ -0,0 +1,21 @@
+#!/usr/bin/env node
+
+const http = require('http');
+const https = require('https');
+
+const app = require('../app');
+const {
+  httpPort,
+  httpsPort,
+  credentials,
+} = require('../environment');
+
+const httpServer = http.createServer(app);
+httpServer.listen(httpPort);
+console.info(`http: listening on port ${httpPort}`);
+
+if (credentials) {
+  const httpsServer = https.createServer(credentials, app);
+  httpsServer.listen(httpsPort);
+  console.info(`https: listening on port ${httpsPort}`);
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..c212fb9
--- /dev/null
+++ b/package.json
@@ -0,0 +1,13 @@
+{
+  "name": "@algorithm-visualizer/server",
+  "version": "2.0.0",
+  "description": "Server for Algorithm Visualizer",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/algorithm-visualizer/server.git"
+  },
+  "license": "MIT"
+}
diff --git a/pm2.config.js b/pm2.config.js
new file mode 100644
index 0000000..92786cc
--- /dev/null
+++ b/pm2.config.js
@@ -0,0 +1,23 @@
+const env = {
+  NODE_ENV: 'production',
+  HTTP_PORT: '80',
+  HTTPS_PORT: '443',
+  GITHUB_CLIENT_ID: '4ca41e5d1e4ae21b6f75',
+  GITHUB_CLIENT_SECRET: '72fb530eb676b89a1a77e5371f8e21c5965f56ea',
+  GITHUB_WEBHOOK_SECRET: 'flapdoodle_blandiloquence',
+  CREDENTIALS_ENABLED: '1',
+  CREDENTIALS_PATH: '/etc/letsencrypt/live/algorithm-visualizer.org',
+  CREDENTIALS_CA: 'chain.pem',
+  CREDENTIALS_KEY: 'privkey.pem',
+  CREDENTIALS_CERT: 'cert.pem',
+};
+
+module.exports = {
+  apps: [
+    {
+      name: 'algorithm-visualizer',
+      script: 'npm run pm2',
+      env,
+    },
+  ],
+};
diff --git a/public/algorithm-visualizer.js b/public/algorithm-visualizer.js
new file mode 100644
index 0000000..ff8035b
--- /dev/null
+++ b/public/algorithm-visualizer.js
@@ -0,0 +1 @@
+!function webpackUniversalModuleDefinition(t,r){"object"==typeof exports&&"object"==typeof module?module.exports=r():"function"==typeof define&&define.amd?define([],r):"object"==typeof exports?exports.AlgorithmVisualizer=r():t.AlgorithmVisualizer=r()}("undefined"!=typeof self?self:this,function(){return function(t){var r={};function __webpack_require__(e){if(r[e])return r[e].exports;var o=r[e]={i:e,l:!1,exports:{}};return t[e].call(o.exports,o,o.exports,__webpack_require__),o.l=!0,o.exports}return __webpack_require__.m=t,__webpack_require__.c=r,__webpack_require__.d=function(t,r,e){__webpack_require__.o(t,r)||Object.defineProperty(t,r,{enumerable:!0,get:e})},__webpack_require__.r=function(t){"undefined"!=typeof Symbol&&Symbol.toStringTag&&Object.defineProperty(t,Symbol.toStringTag,{value:"Module"}),Object.defineProperty(t,"__esModule",{value:!0})},__webpack_require__.t=function(t,r){if(1&r&&(t=__webpack_require__(t)),8&r)return t;if(4&r&&"object"==typeof t&&t&&t.__esModule)return 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Commander(t){Commander.objectCount++;var r=this.constructor.name;this.key=Commander.keyRandomizer.create(),this.command(r,t)}return Commander.command=function(t,r,e){var o=Array.from(e);if(this.commands.push({key:t,method:r,args:JSON.parse(JSON.stringify(o))}),this.commands.length>1e6)throw new Error("Too Many Commands");if(this.objectCount>100)throw new Error("Too Many Objects")},Commander.prototype.destroy=function(){Commander.objectCount--,this.command("destroy",arguments)},Commander.prototype.command=function(t,r){Commander.command(this.key,t,r)},Commander.prototype.toJSON=function(){return this.key},Commander.keyRandomizer=new o.Randomize.String(8,"abcdefghijklmnopqrstuvwxyz0123456789"),Commander.objectCount=0,Commander.commands=[],Commander}();if(!process.env.ALGORITHM_VISUALIZER){var a=e(3),i=e(4);process.on("beforeExit",function(){a.post("https://algorithm-visualizer.org/api/visualizations",{content:JSON.stringify(n.commands)}).then(function(t){return 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\ No newline at end of file
diff --git a/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main b/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main
new file mode 100755
index 0000000..6bb425a
Binary files /dev/null and b/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main differ
diff --git a/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main.cpp b/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main.cpp
new file mode 100644
index 0000000..3719b86
--- /dev/null
+++ b/public/codes/3fe76da7-b5cb-4925-8b32-9ff05204e78d/Main.cpp
@@ -0,0 +1,22 @@
+#include <string>
+#include <iostream>
+#include "algorithm-visualizer/GraphTracer.h"
+#include "algorithm-visualizer/Randomize.h"
+
+#define N 5
+
+using namespace std;
+
+int main() {
+    int array[N][N];
+    Randomize::Graph<int>(N, 1, *(new Randomize::Integer(1, 9))).weighted().directed(false).fill(&array[0][0]);
+    GraphTracer graphTracer;
+    graphTracer.set(array);
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++) {
+            cout << array[i][j] << " ";
+        }
+        cout << endl;
+    }
+    return 0;
+}
diff --git a/src/apis/index.js b/src/apis/index.js
new file mode 100644
index 0000000..5aedb72
--- /dev/null
+++ b/src/apis/index.js
@@ -0,0 +1,82 @@
+import Promise from 'bluebird';
+import axios from 'axios';
+import fs from 'fs';
+import { githubClientId, githubClientSecret } from '/environment';
+
+const instance = axios.create();
+
+instance.interceptors.request.use(request => {
+  request.params = { client_id: githubClientId, client_secret: githubClientSecret, ...request.params };
+  return request;
+});
+
+instance.interceptors.response.use(response => {
+  return response.data;
+}, error => {
+  return Promise.reject(error.response.data);
+});
+
+const request = (url, process) => {
+  const tokens = url.split('/');
+  const baseURL = /^https?:\/\//i.test(url) ? '' : 'https://api.github.com';
+  return (...args) => {
+    return new Promise((resolve, reject) => {
+      const mappedURL = baseURL + tokens.map((token, i) => token.startsWith(':') ? args.shift() : token).join('/');
+      return resolve(process(mappedURL, args));
+    });
+  };
+};
+
+const GET = URL => {
+  return request(URL, (mappedURL, args) => {
+    const [params] = args;
+    return instance.get(mappedURL, { params });
+  });
+};
+
+const DELETE = URL => {
+  return request(URL, (mappedURL, args) => {
+    const [params] = args;
+    return instance.delete(mappedURL, { params });
+  });
+};
+
+const POST = URL => {
+  return request(URL, (mappedURL, args) => {
+    const [body, params] = args;
+    return instance.post(mappedURL, body, { params });
+  });
+};
+
+const PUT = URL => {
+  return request(URL, (mappedURL, args) => {
+    const [body, params] = args;
+    return instance.put(mappedURL, body, { params });
+  });
+};
+
+const PATCH = URL => {
+  return request(URL, (mappedURL, args) => {
+    const [body, params] = args;
+    return instance.patch(mappedURL, body, { params });
+  });
+};
+
+const GitHubApi = {
+  listCommits: GET('/repos/:owner/:repo/commits'),
+  getAccessToken: code => instance.post('https://github.com/login/oauth/access_token', { code }, { headers: { Accept: 'application/json' } }),
+  getLatestRelease: GET('/repos/:owner/:repo/releases/latest'),
+  download: (url, path) => instance({
+    method: 'get',
+    url,
+    responseType: 'stream',
+  }).then(data => new Promise((resolve, reject) => {
+    data.pipe(fs.createWriteStream(path));
+    data.on('end', resolve);
+    data.on('error', reject);
+  })),
+};
+
+export {
+  GitHubApi,
+};
\ No newline at end of file
diff --git a/src/common/config.js b/src/common/config.js
new file mode 100644
index 0000000..6e06a99
--- /dev/null
+++ b/src/common/config.js
@@ -0,0 +1,7 @@
+const memoryLimit = 256; // in megabytes
+const timeLimit = 5000; // in milliseconds
+
+export {
+  memoryLimit,
+  timeLimit,
+};
diff --git a/src/common/error.js b/src/common/error.js
new file mode 100644
index 0000000..c089470
--- /dev/null
+++ b/src/common/error.js
@@ -0,0 +1,18 @@
+class ClientError extends Error {
+}
+
+class NotFoundError extends ClientError {
+}
+
+class ForbiddenError extends ClientError {
+}
+
+class UnauthorizedError extends ClientError {
+}
+
+export {
+  ClientError,
+  NotFoundError,
+  ForbiddenError,
+  UnauthorizedError,
+};
diff --git a/src/common/hierarchy.js b/src/common/hierarchy.js
new file mode 100644
index 0000000..61635f1
--- /dev/null
+++ b/src/common/hierarchy.js
@@ -0,0 +1,7 @@
+import { Hierarchy } from '/models';
+import path from 'path';
+
+const repoPath = path.resolve(__dirname, '..', 'public', 'algorithms');
+const hierarchy = new Hierarchy(repoPath);
+
+export default hierarchy;
diff --git a/src/common/util.js b/src/common/util.js
new file mode 100644
index 0000000..8c9ddfa
--- /dev/null
+++ b/src/common/util.js
@@ -0,0 +1,52 @@
+import Promise from 'bluebird';
+import axios from 'axios';
+import child_process from 'child_process';
+import path from 'path';
+import fs from 'fs-extra';
+import removeMarkdown from 'remove-markdown';
+
+const execute = (command, { stdout = process.stdout, stderr = process.stderr, ...options } = {}) => new Promise((resolve, reject) => {
+  const child = child_process.exec(command, options, (error, stdout, stderr) => {
+    if (error) return reject(error.code ? new Error(stderr) : error);
+    resolve(stdout);
+  });
+  if (stdout) child.stdout.pipe(stdout);
+  if (stderr) child.stderr.pipe(stderr);
+});
+
+const createKey = name => name.toLowerCase().trim().replace(/[^\w \-]/g, '').replace(/ /g, '-');
+
+const isDirectory = dirPath => fs.lstatSync(dirPath).isDirectory();
+
+const listFiles = dirPath => fs.readdirSync(dirPath).filter(fileName => !fileName.startsWith('.'));
+
+const listDirectories = dirPath => listFiles(dirPath).filter(fileName => isDirectory(path.resolve(dirPath, fileName)));
+
+const getDescription = files => {
+  const readmeFile = files.find(file => file.name === 'README.md');
+  if (!readmeFile) return '';
+  const lines = readmeFile.content.split('\n');
+  lines.shift();
+  while (lines.length && !lines[0].trim()) lines.shift();
+  let descriptionLines = [];
+  while (lines.length && lines[0].trim()) descriptionLines.push(lines.shift());
+  return removeMarkdown(descriptionLines.join(' '));
+};
+
+const download = (url, localPath) => axios({ url, method: 'GET', responseType: 'stream' })
+  .then(response => new Promise((resolve, reject) => {
+    const writer = fs.createWriteStream(localPath);
+    writer.on('finish', resolve);
+    writer.on('error', reject);
+    response.data.pipe(writer);
+  }));
+
+export {
+  execute,
+  createKey,
+  isDirectory,
+  listFiles,
+  listDirectories,
+  getDescription,
+  download,
+};
diff --git a/src/common/webhook.js b/src/common/webhook.js
new file mode 100644
index 0000000..5f7599a
--- /dev/null
+++ b/src/common/webhook.js
@@ -0,0 +1,6 @@
+import GithubWebHook from 'express-github-webhook';
+import { githubWebhookSecret } from '/environment';
+
+const webhook = GithubWebHook({ path: '/', secret: githubWebhookSecret });
+
+export default webhook;
diff --git a/src/controllers/algorithms.js b/src/controllers/algorithms.js
new file mode 100644
index 0000000..6bac374
--- /dev/null
+++ b/src/controllers/algorithms.js
@@ -0,0 +1,49 @@
+import express from 'express';
+import fs from 'fs-extra';
+import { execute } from '/common/util';
+import webhook from '/common/webhook';
+import hierarchy from '/common/hierarchy';
+import { NotFoundError } from '/common/error';
+
+const router = express.Router();
+
+const downloadCategories = () => (
+  fs.pathExistsSync(hierarchy.path) ?
+    execute(`git fetch && git reset --hard origin/master`, { cwd: hierarchy.path }) :
+    execute(`git clone https://github.com/algorithm-visualizer/algorithms.git ${hierarchy.path}`)
+).then(() => hierarchy.refresh());
+
+downloadCategories().catch(console.error);
+
+webhook.on('algorithms', event => {
+  switch (event) {
+    case 'push':
+      downloadCategories().catch(console.error);
+      break;
+  }
+});
+
+router.route('/')
+  .get((req, res, next) => {
+    res.json(hierarchy);
+  });
+
+router.route('/:categoryKey/:algorithmKey')
+  .get((req, res, next) => {
+    const { categoryKey, algorithmKey } = req.params;
+    const algorithm = hierarchy.find(categoryKey, algorithmKey);
+    if (!algorithm) return next(new NotFoundError());
+    res.json({ algorithm });
+  });
+
+router.route('/sitemap.txt')
+  .get((req, res, next) => {
+    const urls = [];
+    hierarchy.iterate((category, algorithm) => {
+      urls.push(`https://algorithm-visualizer.org/${category.key}/${algorithm.key}`);
+    });
+    res.set('Content-Type', 'text/plain');
+    res.send(urls.join('\n'));
+  });
+
+export default router;
diff --git a/src/controllers/auth.js b/src/controllers/auth.js
new file mode 100644
index 0000000..45e156e
--- /dev/null
+++ b/src/controllers/auth.js
@@ -0,0 +1,32 @@
+import express from 'express';
+import { githubClientId } from '/environment';
+import { GitHubApi } from '/apis';
+
+const router = express.Router();
+
+const request = (req, res, next) => {
+  res.redirect(`https://github.com/login/oauth/authorize?client_id=${githubClientId}&scope=user,gist`);
+};
+
+const response = (req, res, next) => {
+  const { code } = req.query;
+
+  GitHubApi.getAccessToken(code).then(({ access_token }) => {
+    res.send(`<script>window.opener.signIn('${access_token}');window.close();</script>`);
+  }).catch(next);
+};
+
+const destroy = (req, res, next) => {
+  res.send(`<script>window.opener.signOut();window.close();</script>`);
+};
+
+router.route('/request')
+  .get(request);
+
+router.route('/response')
+  .get(response);
+
+router.route('/destroy')
+  .get(destroy);
+
+export default router;
diff --git a/src/controllers/index.js b/src/controllers/index.js
new file mode 100644
index 0000000..a971818
--- /dev/null
+++ b/src/controllers/index.js
@@ -0,0 +1,4 @@
+export { default as auth } from './auth';
+export { default as algorithms } from './algorithms';
+export { default as tracers } from './tracers';
+export { default as visualizations } from './visualizations';
diff --git a/src/controllers/tracers.js b/src/controllers/tracers.js
new file mode 100644
index 0000000..04806e4
--- /dev/null
+++ b/src/controllers/tracers.js
@@ -0,0 +1,81 @@
+import express from 'express';
+import fs from 'fs-extra';
+import Promise from 'bluebird';
+import uuid from 'uuid';
+import path from 'path';
+import { GitHubApi } from '/apis';
+import { execute } from '/common/util';
+import webhook from '/common/webhook';
+import { ImageBuilder, WorkerBuilder } from '/tracers';
+import { memoryLimit, timeLimit } from '/common/config';
+
+const router = express.Router();
+
+const trace = lang => (req, res, next) => {
+  const { code } = req.body;
+  const tempPath = path.resolve(__dirname, '..', 'public', 'codes', uuid.v4());
+  fs.outputFile(path.resolve(tempPath, `Main.${lang}`), code)
+    .then(() => {
+      const builder = builderMap[lang];
+      const containerName = uuid.v4();
+      let killed = false;
+      const timer = setTimeout(() => {
+        execute(`docker kill ${containerName}`).then(() => {
+          killed = true;
+        });
+      }, timeLimit);
+      return execute([
+        'docker run --rm',
+        `--name=${containerName}`,
+        '-w=/usr/visualization',
+        `-v=${tempPath}:/usr/visualization:rw`,
+        `-m=${memoryLimit}m`,
+        '-e ALGORITHM_VISUALIZER=1',
+        builder.imageName,
+      ].join(' '), { stdout: null, stderr: null }).catch(error => {
+        if (killed) throw new Error('Time Limit Exceeded');
+        throw error;
+      }).finally(() => clearTimeout(timer));
+    })
+    .then(() => new Promise((resolve, reject) => {
+      const visualizationPath = path.resolve(tempPath, 'visualization.json');
+      res.sendFile(visualizationPath, err => {
+        if (err) return reject(new Error('Visualization Not Found'));
+        resolve();
+      });
+    }))
+    .catch(next)
+    .finally(() => fs.remove(tempPath));
+};
+
+const builderMap = {
+  js: new WorkerBuilder(),
+  cpp: new ImageBuilder('cpp'),
+  java: new ImageBuilder('java'),
+};
+
+Promise.map(Object.keys(builderMap), lang => {
+  const builder = builderMap[lang];
+  return GitHubApi.getLatestRelease('algorithm-visualizer', `tracers.${lang}`).then(builder.build);
+}).catch(console.error);
+
+webhook.on('release', (repo, data) => {
+  const result = /^tracers\.(\w+)$/.exec(repo);
+  if (result) {
+    const [, lang] = result;
+    const builder = builderMap[lang];
+    builder.build(data.release).catch(console.error);
+  }
+});
+
+Object.keys(builderMap).forEach(lang => {
+  const builder = builderMap[lang];
+  if (builder instanceof ImageBuilder) {
+    router.post(`/${lang}`, trace(lang));
+  } else if (builder instanceof WorkerBuilder) {
+    router.get(`/${lang}`, (req, res) => res.sendFile(builder.tracerPath));
+    router.get(`/${lang}/worker`, (req, res) => res.sendFile(builder.workerPath));
+  }
+});
+
+export default router;
diff --git a/src/controllers/visualizations.js b/src/controllers/visualizations.js
new file mode 100644
index 0000000..968f78a
--- /dev/null
+++ b/src/controllers/visualizations.js
@@ -0,0 +1,42 @@
+import express from 'express';
+import path from 'path';
+import uuid from 'uuid';
+import fs from 'fs-extra';
+import Promise from 'bluebird';
+
+const router = express.Router();
+
+const uploadPath = path.resolve(__dirname, '..', 'public', 'visualizations');
+const getVisualizationPath = visualizationId => path.resolve(uploadPath, `${visualizationId}.json`);
+
+fs.remove(uploadPath).catch(console.error);
+
+const uploadVisualization = (req, res, next) => {
+  const { content } = req.body;
+  const visualizationId = uuid.v4();
+  const tracesPath = getVisualizationPath(visualizationId);
+  const url = `https://algorithm-visualizer.org/scratch-paper/new?visualizationId=${visualizationId}`;
+  fs.outputFile(tracesPath, content)
+    .then(() => res.send(url))
+    .catch(next);
+};
+
+const getVisualization = (req, res, next) => {
+  const { visualizationId } = req.params;
+  const visualizationPath = getVisualizationPath(visualizationId);
+  new Promise((resolve, reject) => {
+    res.sendFile(visualizationPath, err => {
+      if (err) return reject(new Error('Visualization Expired'));
+      resolve();
+    });
+  }).catch(next)
+    .finally(() => fs.remove(visualizationPath));
+};
+
+router.route('/')
+  .post(uploadVisualization);
+
+router.route('/:visualizationId')
+  .get(getVisualization);
+
+export default router;
diff --git a/src/index.js b/src/index.js
new file mode 100644
index 0000000..3f9df62
--- /dev/null
+++ b/src/index.js
@@ -0,0 +1,41 @@
+import express from 'express';
+import morgan from 'morgan';
+import cookieParser from 'cookie-parser';
+import bodyParser from 'body-parser';
+import * as controllers from '/controllers';
+import { ClientError, ForbiddenError, NotFoundError, UnauthorizedError } from '/common/error';
+import webhook from '/common/webhook';
+import hierarchy from '/common/hierarchy';
+
+const app = express();
+app.use(morgan('tiny'));
+app.use(cookieParser());
+app.use(bodyParser.json());
+app.use(bodyParser.urlencoded({ extended: true }));
+Object.keys(controllers).forEach(key => app.use(`/${key}`, controllers[key]));
+app.use('/webhook', webhook);
+app.use((req, res, next) => next(new NotFoundError()));
+app.use((err, req, res, next) => {
+  const statusMap = [
+    [UnauthorizedError, 401],
+    [ForbiddenError, 403],
+    [NotFoundError, 404],
+    [ClientError, 400],
+    [Error, 500],
+  ];
+  const [, status] = statusMap.find(([Error]) => err instanceof Error);
+  res.status(status);
+  res.send(err.message);
+  console.error(err);
+});
+app.hierarchy = hierarchy;
+
+webhook.on('algorithm-visualizer', event => {
+  switch (event) {
+    case 'push':
+      process.exit(0);
+      break;
+  }
+});
+
+export default app;
diff --git a/src/models/Algorithm.js b/src/models/Algorithm.js
new file mode 100644
index 0000000..45dfde2
--- /dev/null
+++ b/src/models/Algorithm.js
@@ -0,0 +1,25 @@
+import path from 'path';
+import { createKey, getDescription, listFiles } from '/common/util';
+import { File } from '/models';
+
+class Algorithm {
+  constructor(path, name) {
+    this.path = path;
+    this.key = createKey(name);
+    this.name = name;
+    this.refresh();
+  }
+
+  refresh() {
+    this.files = listFiles(this.path)
+      .map(fileName => new File(path.resolve(this.path, fileName), fileName));
+    this.description = getDescription(this.files);
+  }
+
+  toJSON() {
+    const { key, name } = this;
+    return { key, name };
+  }
+}
+
+export default Algorithm;
diff --git a/src/models/Category.js b/src/models/Category.js
new file mode 100644
index 0000000..03ea980
--- /dev/null
+++ b/src/models/Category.js
@@ -0,0 +1,24 @@
+import path from 'path';
+import { createKey, listDirectories } from '/common/util';
+import { Algorithm } from '/models';
+
+class Category {
+  constructor(path, name) {
+    this.path = path;
+    this.key = createKey(name);
+    this.name = name;
+    this.refresh();
+  }
+
+  refresh() {
+    this.algorithms = listDirectories(this.path)
+      .map(algorithmName => new Algorithm(path.resolve(this.path, algorithmName), algorithmName));
+  }
+
+  toJSON() {
+    const { key, name, algorithms } = this;
+    return { key, name, algorithms };
+  }
+}
+
+export default Category;
diff --git a/src/models/File.js b/src/models/File.js
new file mode 100644
index 0000000..3bb69da
--- /dev/null
+++ b/src/models/File.js
@@ -0,0 +1,21 @@
+import fs from 'fs-extra';
+
+class File {
+  constructor(path, name) {
+    this.path = path;
+    this.name = name;
+    this.refresh();
+  }
+
+  refresh() {
+    this.content = fs.readFileSync(this.path, 'utf-8');
+    this.contributors = [];
+  }
+
+  toJSON() {
+    const { name, content, contributors } = this;
+    return { name, content, contributors };
+  }
+}
+
+export default File;
diff --git a/src/models/Hierarchy.js b/src/models/Hierarchy.js
new file mode 100644
index 0000000..589910e
--- /dev/null
+++ b/src/models/Hierarchy.js
@@ -0,0 +1,84 @@
+import Promise from 'bluebird';
+import path from 'path';
+import { execute, listDirectories } from '/common/util';
+import { GitHubApi } from '/apis';
+import { Category } from '/models';
+
+class Hierarchy {
+  constructor(path) {
+    this.path = path;
+    this.refresh();
+  }
+
+  refresh() {
+    this.categories = listDirectories(this.path)
+      .map(categoryName => new Category(path.resolve(this.path, categoryName), categoryName));
+
+    const files = [];
+    this.categories.forEach(category => category.algorithms.forEach(algorithm => files.push(...algorithm.files)));
+    this.cacheCommitAuthors().then(commitAuthors => this.cacheContributors(files, commitAuthors));
+  }
+
+  cacheCommitAuthors(page = 1, commitAuthors = {}) {
+    const per_page = 100;
+    return GitHubApi.listCommits('algorithm-visualizer', 'algorithms', {
+      per_page,
+      page,
+    }).then(commits => {
+      commits.forEach(({ sha, commit, author }) => {
+        if (!author) return;
+        const { login, avatar_url } = author;
+        commitAuthors[sha] = { login, avatar_url };
+      });
+      if (commits.length < per_page) {
+        return commitAuthors;
+      } else {
+        return this.cacheCommitAuthors(page + 1, commitAuthors);
+      }
+    });
+  }
+
+  cacheContributors(files, commitAuthors) {
+    return Promise.each(files, file => {
+      return execute(`git --no-pager log --follow --no-merges --format="%H" "${file.path}"`, {
+        cwd: this.path, stdout: null,
+      }).then(stdout => {
+        const output = stdout.toString().replace(/\n$/, '');
+        const shas = output.split('\n').reverse();
+        const contributors = [];
+        for (const sha of shas) {
+          const author = commitAuthors[sha];
+          if (author && !contributors.find(contributor => contributor.login === author.login)) {
+            contributors.push(author);
+          }
+        }
+        file.contributors = contributors;
+      });
+    });
+  }
+
+  find(categoryKey, algorithmKey) {
+    const category = this.categories.find(category => category.key === categoryKey);
+    if (!category) return;
+    const algorithm = category.algorithms.find(algorithm => algorithm.key === algorithmKey);
+    if (!algorithm) return;
+
+    const categoryName = category.name;
+    const algorithmName = algorithm.name;
+    const files = algorithm.files;
+    const description = algorithm.description;
+
+    return { categoryKey, categoryName, algorithmKey, algorithmName, files, description };
+  }
+
+  iterate(callback) {
+    this.categories.forEach(category => category.algorithms.forEach(algorithm => callback(category, algorithm)));
+  }
+
+  toJSON() {
+    const { categories } = this;
+    return { categories };
+  }
+}
+
+export default Hierarchy;
diff --git a/src/models/index.js b/src/models/index.js
new file mode 100644
index 0000000..64dea13
--- /dev/null
+++ b/src/models/index.js
@@ -0,0 +1,4 @@
+export { default as Algorithm } from './Algorithm';
+export { default as Category } from './Category';
+export { default as File } from './File';
+export { default as Hierarchy } from './Hierarchy';
diff --git a/src/tracers/ImageBuilder.js b/src/tracers/ImageBuilder.js
new file mode 100644
index 0000000..e25d7c1
--- /dev/null
+++ b/src/tracers/ImageBuilder.js
@@ -0,0 +1,19 @@
+import path from 'path';
+import { execute } from '/common/util';
+
+class ImageBuilder {
+  constructor(lang) {
+    this.lang = lang;
+    this.directory = path.resolve(__dirname, lang);
+    this.imageName = `tracer-${this.lang}`;
+
+    this.build = this.build.bind(this);
+  }
+
+  build(release) {
+    const { tag_name } = release;
+    return execute(`docker build -t ${this.imageName} . --build-arg tag_name=${tag_name}`, { cwd: this.directory });
+  }
+}
+
+export default ImageBuilder;
diff --git a/src/tracers/WorkerBuilder.js b/src/tracers/WorkerBuilder.js
new file mode 100644
index 0000000..07369cd
--- /dev/null
+++ b/src/tracers/WorkerBuilder.js
@@ -0,0 +1,18 @@
+import path from 'path';
+import { download } from '/common/util';
+
+class WorkerBuilder {
+  constructor() {
+    this.tracerPath = path.resolve(__dirname, '..', 'public', 'algorithm-visualizer.js');
+    this.workerPath = path.resolve(__dirname, 'js', 'worker.js');
+
+    this.build = this.build.bind(this);
+  }
+
+  build(release) {
+    const { tag_name } = release;
+    return download(`https://github.com/algorithm-visualizer/tracers.js/releases/download/${tag_name}/algorithm-visualizer.js`, this.tracerPath);
+  }
+}
+
+export default WorkerBuilder;
diff --git a/src/tracers/cpp/Dockerfile b/src/tracers/cpp/Dockerfile
new file mode 100644
index 0000000..03b3d94
--- /dev/null
+++ b/src/tracers/cpp/Dockerfile
@@ -0,0 +1,17 @@
+FROM rikorose/gcc-cmake
+
+ARG tag_name
+
+RUN curl --create-dirs -o /usr/local/include/nlohmann/json.hpp -L "https://github.com/nlohmann/json/releases/download/v3.1.2/json.hpp" \
+ && curl --create-dirs -o /usr/tmp/algorithm-visualizer.tar.gz -L "https://github.com/algorithm-visualizer/tracers.cpp/archive/${tag_name}.tar.gz" \
+ && cd /usr/tmp \
+ && mkdir algorithm-visualizer \
+ && tar xvzf algorithm-visualizer.tar.gz -C algorithm-visualizer --strip-components=1 \
+ && cd /usr/tmp/algorithm-visualizer \
+ && mkdir build \
+ && cd build \
+ && cmake .. \
+ && make install
+
+CMD g++ Main.cpp -o Main -O2 -std=c++11 -lcurl \
+ && ./Main
diff --git a/src/tracers/index.js b/src/tracers/index.js
new file mode 100644
index 0000000..d41b049
--- /dev/null
+++ b/src/tracers/index.js
@@ -0,0 +1,2 @@
+export { default as ImageBuilder } from './ImageBuilder';
+export { default as WorkerBuilder } from './WorkerBuilder';
diff --git a/src/tracers/java/Dockerfile b/src/tracers/java/Dockerfile
new file mode 100644
index 0000000..8aabc07
--- /dev/null
+++ b/src/tracers/java/Dockerfile
@@ -0,0 +1,8 @@
+FROM openjdk:8
+
+ARG tag_name
+
+RUN curl --create-dirs -o /usr/local/lib/algorithm-visualizer.jar -L "https://github.com/algorithm-visualizer/tracers.java/releases/download/${tag_name}/algorithm-visualizer.jar"
+
+CMD javac -cp /usr/local/lib/algorithm-visualizer.jar Main.java \
+ && java -cp /usr/local/lib/algorithm-visualizer.jar:. Main
diff --git a/src/tracers/js/worker.js b/src/tracers/js/worker.js
new file mode 100644
index 0000000..7d5ac5b
--- /dev/null
+++ b/src/tracers/js/worker.js
@@ -0,0 +1,14 @@
+const process = { env: { ALGORITHM_VISUALIZER: '1' } };
+importScripts('/api/tracers/js');
+
+const sandbox = code => {
+  const require = name => ({ 'algorithm-visualizer': AlgorithmVisualizer }[name]); // fake require
+  eval(code);
+};
+
+onmessage = e => {
+  const lines = e.data.split('\n').map((line, i) => line.replace(/(\.\s*delay\s*)\(\s*\)/g, `$1(${i})`));
+  const code = lines.join('\n');
+  sandbox(code);
+  postMessage(AlgorithmVisualizer.Commander.commands);
+};
diff --git a/webpack.backend.config.js b/webpack.backend.config.js
new file mode 100644
index 0000000..5185c70
--- /dev/null
+++ b/webpack.backend.config.js
@@ -0,0 +1,45 @@
+const CleanWebpackPlugin = require('clean-webpack-plugin');
+const nodeExternals = require('webpack-node-externals');
+const path = require('path');
+const fs = require('fs');
+
+const {
+  __DEV__,
+  backendBuildPath: buildPath,
+  backendSrcPath: srcPath,
+} = require('./environment');
+
+const alias = {
+  '/environment': path.resolve(__dirname, 'environment.js'),
+};
+fs.readdirSync(srcPath).forEach(name => {
+  alias['/' + name] = path.resolve(srcPath, name);
+});
+
+module.exports = {
+  target: 'node',
+  node: {
+    __dirname: true,
+  },
+  entry: srcPath,
+  externals: [nodeExternals()],
+  resolve: {
+    modules: [srcPath],
+    extensions: ['.js'],
+    alias,
+  },
+  output: {
+    path: buildPath,
+    filename: 'index.js',
+    libraryTarget: 'umd',
+  },
+  module: {
+    rules: [
+      { test: /\.js$/, use: 'babel-loader', include: srcPath },
+    ],
+  },
+  plugins: [
+    new CleanWebpackPlugin([buildPath]),
+  ],
+  mode: __DEV__ ? 'development' : 'production',
+};
\ No newline at end of file