1 files changed, 59 insertions, 0 deletions
diff --git a/ofborg/ofborg-viewer/src/state.js b/ofborg/ofborg-viewer/src/state.js
new file mode 100644
index 0000000000..936d07653a
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+++ b/ofborg/ofborg-viewer/src/state.js
@@ -0,0 +1,59 @@
+import queryString from "query-string";
+import isEqual from "lodash/isEqual";
+
+/**
+ * Maps the state of the application to the history API.
+ * This is used to make the current view linkable.
+ * In the URL, the hash part is **reserved for line numbers**.
+ * (line number links are not implemented yet.)
+ */
+class State {
+
+	/**
+	 * Loads the state from URL.
+	 *
+	 * Prepares event listeners.
+	 */
+	constructor() {
+		const params = queryString.parse(location.search);
+		const {history} = window;
+		// Loads from params in URL, then history in order of importance.
+		this.params = Object.assign({}, params, history.state);
+
+		window.onpopstate = (e) => this.handle_popstate(e);
+	}
+
+	handle_popstate(e) {
+		console.log(e);
+		const {state} = e;
+		if (state) {
+			this.set_state(state, {push: false});
+			if (this.on_state_change) {
+				this.on_state_change(state);
+			}
+		}
+	}
+
+	set_state(new_state, {push} = {push: true}) {
+		const {history} = window;
+		const params = Object.assign({}, this.params, new_state);
+		Object.keys(params).forEach((k) => {
+			if (!params[k]) {
+				Reflect.deleteProperty(params, k);
+			}
+		});
+
+		if (isEqual(params, this.params)) {
+			// set_state won't fire on "identity" change.
+			return;
+		}
+
+		this.params = params;
+
+		if (push) {
+			history.pushState(this.params, "", `?${queryString.stringify(params)}`);
+		}
+	}
+}
+
+export default State;