1 files changed, 176 insertions, 0 deletions
diff --git a/config/helpers/incremental_webpack_compiler/history.js b/config/helpers/incremental_webpack_compiler/history.js
new file mode 100644
index 00000000000..24599900011
--- /dev/null
+++ b/config/helpers/incremental_webpack_compiler/history.js
@@ -0,0 +1,176 @@
+/* eslint-disable max-classes-per-file, no-underscore-dangle */
+
+const fs = require('fs');
+const log = require('./log');
+
+const ESSENTIAL_ENTRY_POINTS = [
+  // Login page
+  'pages.sessions.new',
+  // Explore page
+  'pages.root',
+];
+
+// TODO: Find a way to keep this list up-to-date/relevant.
+const COMMON_ENTRY_POINTS = [
+  ...ESSENTIAL_ENTRY_POINTS,
+  'pages.admin',
+  'pages.admin.dashboard',
+  'pages.dashboard.groups.index',
+  'pages.dashboard.projects.index',
+  'pages.groups.new',
+  'pages.groups.show',
+  'pages.profiles.preferences.show',
+  'pages.projects.commit.show',
+  'pages.projects.edit',
+  'pages.projects.issues.index',
+  'pages.projects.issues.new',
+  'pages.projects.issues.show',
+  'pages.projects.jobs.show',
+  'pages.projects.merge_requests.index',
+  'pages.projects.merge_requests.show',
+  'pages.projects.milestones.index',
+  'pages.projects.new',
+  'pages.projects.pipelines.index',
+  'pages.projects.pipelines.show',
+  'pages.projects.settings.ci_cd.show',
+  'pages.projects.settings.repository.show',
+  'pages.projects.show',
+  'pages.users',
+];
+
+/**
+ * The History class is responsible for tracking which entry points have been
+ * requested, and persisting/loading the history to/from disk.
+ */
+class History {
+  constructor(historyFilePath) {
+    this._historyFilePath = historyFilePath;
+    this._history = {};
+
+    this._loadHistoryFile();
+  }
+
+  onRequestEntryPoint(entryPoint) {
+    const wasVisitedRecently = this.isRecentlyVisited(entryPoint);
+
+    this._addEntryPoint(entryPoint);
+
+    this._writeHistoryFile();
+
+    return wasVisitedRecently;
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  isRecentlyVisited() {
+    return true;
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  get size() {
+    return 0;
+  }
+
+  // Private methods
+
+  _addEntryPoint(entryPoint) {
+    if (!this._history[entryPoint]) {
+      this._history[entryPoint] = { lastVisit: null, count: 0 };
+    }
+
+    this._history[entryPoint].lastVisit = Date.now();
+    this._history[entryPoint].count += 1;
+  }
+
+  _writeHistoryFile() {
+    try {
+      fs.writeFileSync(this._historyFilePath, JSON.stringify(this._history), 'utf8');
+    } catch (error) {
+      log('Warning – Could not write to history', error.message);
+    }
+  }
+
+  _loadHistoryFile() {
+    try {
+      fs.accessSync(this._historyFilePath);
+    } catch (e) {
+      // History file doesn't exist; attempt to seed it, and return early
+      this._seedHistory();
+      return;
+    }
+
+    // History file already exists; attempt to load its contents into memory
+    try {
+      this._history = JSON.parse(fs.readFileSync(this._historyFilePath, 'utf8'));
+      const historySize = Object.keys(this._history).length;
+      log(`Successfully loaded history containing ${historySize} entry points`);
+    } catch (error) {
+      log('Could not load history', error.message);
+    }
+  }
+
+  /**
+   * Seeds a reasonable set of approximately the most common entry points to
+   * seed the history. This helps to avoid fresh GDK installs showing the
+   * compiling overlay too often.
+   */
+  _seedHistory() {
+    log('Seeding history...');
+    COMMON_ENTRY_POINTS.forEach((entryPoint) => this._addEntryPoint(entryPoint));
+    this._writeHistoryFile();
+  }
+}
+
+const MS_PER_DAY = 1000 * 60 * 60 * 24;
+
+/**
+ * The HistoryWithTTL class adds LRU-like behaviour onto the base History
+ * behaviour. Entry points visited within the last `ttl` days are considered
+ * "recent", and therefore should be eagerly compiled.
+ */
+class HistoryWithTTL extends History {
+  constructor(historyFilePath, ttl) {
+    super(historyFilePath);
+    this._ttl = ttl;
+    this._calculateRecentEntryPoints();
+  }
+
+  onRequestEntryPoint(entryPoint) {
+    const wasVisitedRecently = super.onRequestEntryPoint(entryPoint);
+
+    this._calculateRecentEntryPoints();
+
+    return wasVisitedRecently;
+  }
+
+  isRecentlyVisited(entryPoint) {
+    return this._recentEntryPoints.has(entryPoint);
+  }
+
+  get size() {
+    return this._recentEntryPoints.size;
+  }
+
+  // Private methods
+
+  _calculateRecentEntryPoints() {
+    const oldestVisitAllowed = Date.now() - MS_PER_DAY * this._ttl;
+
+    const recentEntryPoints = Object.entries(this._history).reduce(
+      (acc, [entryPoint, { lastVisit }]) => {
+        if (lastVisit > oldestVisitAllowed) {
+          acc.push(entryPoint);
+        }
+
+        return acc;
+      },
+      [],
+    );
+
+    this._recentEntryPoints = new Set([...ESSENTIAL_ENTRY_POINTS, ...recentEntryPoints]);
+  }
+}
+
+module.exports = {
+  History,
+  HistoryWithTTL,
+};