1 files changed, 123 insertions, 0 deletions
diff --git a/src/content/follow.js b/src/content/follow.js
new file mode 100644
index 0000000..ffa16b9
--- /dev/null
+++ b/src/content/follow.js
@@ -0,0 +1,123 @@
+import Hint from './hint';
+import HintKeyProducer from './hint-key-producer';
+
+const DEFAULT_HINT_CHARSET = 'abcdefghijklmnopqrstuvwxyz'
+
+export default class Follow {
+  constructor(doc) {
+    this.doc = doc;
+    this.hintElements = {};
+    this.keys = [];
+
+    // TODO activate input elements and push button elements
+    let links = Follow.getTargetElements(doc);
+
+    this.addHints(links);
+
+    this.boundKeydown = this.handleKeydown.bind(this);
+    doc.addEventListener('keydown', this.boundKeydown);
+  }
+
+  addHints(elements) {
+    let producer = new HintKeyProducer(DEFAULT_HINT_CHARSET);
+    Array.prototype.forEach.call(elements, (ele) => {
+      let keys = producer.produce();
+      let hint = new Hint(ele, keys)
+
+      this.hintElements[keys] = hint;
+    });
+  }
+
+  handleKeydown(e) {
+    let keyCode = e.keyCode;
+    if (keyCode === KeyboardEvent.DOM_VK_ESCAPE) {
+      this.remove();
+      return;
+    } else if (keyCode === KeyboardEvent.DOM_VK_ENTER ||
+               keyCode === KeyboardEvent.DOM_VK_RETURN) {
+      let chars = Follow.codeChars(this.keys);
+      this.hintElements[chars].activate();
+      return;
+    } else if (Follow.availableKey(keyCode)) {
+      this.keys.push(keyCode);
+    } else if (keyCode === KeyboardEvent.DOM_VK_BACK_SPACE ||
+               keyCode === KeyboardEvent.DOM_VK_DELETE) {
+      this.keys.pop();
+    }
+
+    this.refreshKeys();
+  }
+
+  refreshKeys() {
+    let chars = Follow.codeChars(this.keys);
+    let shown = Object.keys(this.hintElements).filter((key) => {
+      return key.startsWith(chars);
+    });
+    let hidden = Object.keys(this.hintElements).filter((key) => {
+      return !key.startsWith(chars);
+    });
+    if (shown.length == 0) {
+      this.remove();
+      return;
+    } else if (shown.length == 1) {
+      this.remove();
+      this.hintElements[chars].activate();
+    }
+
+    shown.forEach((key) => {
+      this.hintElements[key].show();
+    });
+    hidden.forEach((key) => {
+      this.hintElements[key].hide();
+    });
+  }
+
+
+  remove() {
+    this.doc.removeEventListener("keydown", this.boundKeydown);
+    Object.keys(this.hintElements).forEach((key) => {
+      this.hintElements[key].remove();
+    });
+  }
+
+  static availableKey(keyCode) {
+    return (
+      KeyboardEvent.DOM_VK_0 <= keyCode && keyCode <= KeyboardEvent.DOM_VK_9 ||
+      KeyboardEvent.DOM_VK_A <= keyCode && keyCode <= KeyboardEvent.DOM_VK_Z
+    );
+  }
+
+  static codeChars(codes) {
+    const CHARCODE_ZERO = '0'.charCodeAt(0);
+    const CHARCODE_A = 'a'.charCodeAt(0);
+
+    let chars = '';
+
+    for (let code of codes) {
+      if (KeyboardEvent.DOM_VK_0 <= code && code <= KeyboardEvent.DOM_VK_9) {
+        chars += String.fromCharCode(code - KeyboardEvent.DOM_VK_0 + CHARCODE_ZERO);
+      } else if (KeyboardEvent.DOM_VK_A <= code && code <= KeyboardEvent.DOM_VK_Z) {
+        chars += String.fromCharCode(code - KeyboardEvent.DOM_VK_A + CHARCODE_A);
+      }
+    }
+    return chars;
+  }
+
+  static getTargetElements(doc) {
+    let all = doc.querySelectorAll('a');
+    let filtered = Array.prototype.filter.call(all, (e) => {
+      return Follow.isVisibleElement(e);
+    });
+    return filtered;
+  }
+
+  static isVisibleElement(element) {
+    var style = window.getComputedStyle(element);
+    if (style.display === 'none') {
+      return false;
+    } else if (style.visibility === 'hidden') {
+      return false;
+    }
+    return true;
+  }
+}