[polari] thumbnailer: Add helper script

[Florian Müllner <fmuellner src gnome org>]

commit df44fb0d332a26721b86ad0305379bb3c6dc1ff3
Author: daronion <stefanosdimos 98 gmail com>
Date:   Mon Aug 26 17:44:41 2019 +0300

    thumbnailer: Add helper script
    
    We want to handle all types of URL content which means we will
    actually have to load the web page and take a snapshot of it.
    
    Embedding a web browser inside Polari isn't great for either
    performance or security, so implement the functionality in a
    separate script that can run from the main process.
    
    https://gitlab.gnome.org/GNOME/polari/issues/58

 src/meson.build    |   2 +
 src/thumbnailer.js | 117 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)
---
diff --git a/src/meson.build b/src/meson.build
index 1a30e3e..0d63989 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -110,3 +110,5 @@ gnome.generate_gir(libpolari,
 )
 
 subdir('tests')
+
+install_data('thumbnailer.js', install_dir: pkgdatadir)
diff --git a/src/thumbnailer.js b/src/thumbnailer.js
new file mode 100644
index 0000000..3640280
--- /dev/null
+++ b/src/thumbnailer.js
@@ -0,0 +1,117 @@
+imports.gi.versions.Gtk = '3.0';
+
+const { GLib, GObject, Gtk, WebKit2 } = imports.gi;
+const Cairo = imports.cairo;
+
+const PREVIEW_WIDTH = 120;
+const PREVIEW_HEIGHT = 90;
+
+let PreviewWindow = GObject.registerClass({
+    Properties: {
+        'uri': GObject.ParamSpec.string(
+            'uri', 'uri', 'uri',
+            GObject.ParamFlags.READWRITE | GObject.ParamFlags.CONSTRUCT_ONLY,
+            null),
+    },
+    Signals: {
+        'snapshot-ready': {},
+    },
+}, class PreviewWindow extends Gtk.Window {
+    _init(params) {
+        this._snapshot = null;
+
+        super._init(params);
+
+        this._view = new WebKit2.WebView({
+            is_ephemeral: true,
+            visible: true,
+        });
+        this.add(this._view);
+
+        this._view.connect('notify::is-loading',
+            this._onLoadingChanged.bind(this));
+        this._view.load_uri(this.uri);
+    }
+
+    _onLoadingChanged() {
+        if (this._view.is_loading)
+            return;
+
+        /* Hopefully wait long enough for a meaningful snapshot,
+           see https://bugs.webkit.org/show_bug.cgi?id=164180 */
+        GLib.timeout_add(GLib.PRIORITY_DEFAULT, 1000, () => {
+            this._createSnapshot();
+            return GLib.SOURCE_REMOVE;
+        });
+    }
+
+    _createSnapshot() {
+        this._view.get_snapshot(
+            WebKit2.SnapshotRegion.VISIBLE,
+            WebKit2.SnapshotOptions.TRANSPARENT_BACKGROUND,
+            null,
+            (o, res) => {
+                try {
+                    this._snapshot = this._view.get_snapshot_finish(res);
+                } catch (e) {
+                    log(`Creating snapshot failed: ${e}`);
+                }
+                this.emit('snapshot-ready');
+            });
+    }
+
+    getSnapshot() {
+        return this._snapshot;
+    }
+});
+
+class App {
+    constructor(url, filename) {
+        this._uri = url;
+        this._filename = filename;
+    }
+
+    run() {
+        Gtk.init(null);
+
+        let window = new PreviewWindow({
+            uri: this._uri,
+            default_width: 10 * PREVIEW_WIDTH,
+            default_height: 10 * PREVIEW_HEIGHT,
+        });
+
+        window.realize();
+        window.connect('snapshot-ready', this._onSnapshotReady.bind(this));
+        window.connect('destroy', () => Gtk.main_quit());
+
+        Gtk.main();
+    }
+
+    _onSnapshotReady(window) {
+        let surface = window.getSnapshot();
+        window.destroy();
+
+        if (!surface)
+            return;
+
+        let sourceWidth = surface.getWidth();
+        let sourceHeight = surface.getHeight();
+
+        let target = new Cairo.ImageSurface(Cairo.Format.ARGB32,
+            PREVIEW_WIDTH,
+            PREVIEW_HEIGHT);
+
+        let cr = new Cairo.Context(target);
+        cr.scale(
+            PREVIEW_WIDTH / sourceWidth,
+            PREVIEW_HEIGHT / sourceHeight);
+        cr.setSourceSurface(surface, 0, 0);
+        cr.paint();
+
+        target.writeToPNG(this._filename);
+    }
+}
+
+let [url, filename] = ARGV;
+let app = new App(url, filename);
+app.run();