From 40f8b237267e559b79400d9c5064e50734ad0ef2 Mon Sep 17 00:00:00 2001
From: Peter Savchenko <specc.dev@gmail.com>
Date: Wed, 10 Mar 2021 12:42:01 +0300
Subject: [PATCH] feature: indentations by tab

---
 package.json        |  2 +-
 src/index.js        | 75 ++++++++++++++++++++++++++++++++++++++++++---
 src/utils/string.js | 35 +++++++++++++++++++++
 webpack.config.js   | 15 ++++-----
 4 files changed, 115 insertions(+), 12 deletions(-)
 create mode 100644 src/utils/string.js

diff --git a/package.json b/package.json
index 3fb5f1f..98fff55 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@editorjs/code",
-  "version": "2.6.0",
+  "version": "2.7.0",
   "keywords": [
     "codex editor",
     "code",
diff --git a/src/index.js b/src/index.js
index 0f0dd71..d7506d9 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,7 +1,8 @@
 /**
  * Build styles
  */
-require('./index.css').toString();
+import { getLineStartPosition } from './utils/string';
+import './index.css';
 
 /**
  * CodeTool for Editor.js
@@ -17,7 +18,7 @@ require('./index.css').toString();
 /**
  * Code Tool for the Editor.js allows to include code examples in your articles.
  */
-class CodeTool {
+export default class CodeTool {
 
   /**
    * Notify core that read-only mode is supported
@@ -99,6 +100,17 @@ class CodeTool {
 
     wrapper.appendChild(textarea);
 
+    /**
+     * Enable keydown handlers
+     */
+    textarea.addEventListener('keydown', (event) => {
+      switch (event.code) {
+        case 'Tab':
+          this.tabHandler(event);
+          break;
+      }
+    });
+
     this.nodes.textarea = textarea;
 
     return wrapper;
@@ -209,6 +221,61 @@ class CodeTool {
       code: true, // Allow HTML tags
     };
   }
-}
 
-module.exports = CodeTool;
+  /**
+   * Handles Tab key pressing (adds/removes indentations)
+   *
+   * @private
+   * @param {KeyboardEvent} event - keydown
+   * @returns {void}
+   */
+  tabHandler(event) {
+    /**
+     * Prevent editor.js tab handler
+     */
+    event.stopPropagation();
+
+    /**
+     * Prevent native tab behaviour
+     */
+    event.preventDefault();
+
+    const textarea = event.target;
+    const isShiftPressed = event.shiftKey;
+    const caretPosition = textarea.selectionStart;
+    const value = textarea.value;
+    const indentation = '  ';
+
+    let newCaretPosition;
+
+    /**
+     * For Tab pressing, just add an indentation to the caret position
+     */
+    if (!isShiftPressed) {
+      newCaretPosition = caretPosition + indentation.length;
+
+      textarea.value = value.substring(0, caretPosition) + indentation + value.substring(caretPosition);
+    } else {
+      /**
+       * For Shift+Tab pressing, remove an indentation from the start of line
+       */
+      const currentLineStart = getLineStartPosition(value, caretPosition);
+      const firstLineChars = value.substr(currentLineStart, indentation.length);
+
+      if (firstLineChars !== indentation) {
+        return;
+      }
+
+      /**
+       * Trim the first two chars from the start of line
+       */
+      textarea.value = value.substring(0, currentLineStart) + value.substring(currentLineStart + indentation.length);
+      newCaretPosition = caretPosition - indentation.length;
+    }
+
+    /**
+     * Restore the caret
+     */
+    textarea.setSelectionRange(newCaretPosition, newCaretPosition);
+  }
+}
diff --git a/src/utils/string.js b/src/utils/string.js
new file mode 100644
index 0000000..06d220f
--- /dev/null
+++ b/src/utils/string.js
@@ -0,0 +1,35 @@
+/**
+ * Return the position of line starting from passed point
+ *
+ * ┌───────────────┐
+ * │1234\n         │
+ * │2eda | dadd\n  │ <-- returns 5
+ * └───────────────┘
+ *
+ * @param {string} string - string to process
+ * @param {number} position - search starting position
+ * @returns {number}
+ */
+export function getLineStartPosition(string, position) {
+  const charLength = 1;
+  let char = '';
+
+  /**
+   * Iterate through all the chars before the position till the
+   * - end of line (\n)
+   * - or start of string (position === 0)
+   */
+  while (char !== '\n' && position > 0) {
+    position = position - charLength;
+    char = string.substr(position, charLength);
+  }
+
+  /**
+   * Do not count the linebreak symbol because it is related to the previous line
+   */
+  if (char === '\n') {
+    position += 1;
+  }
+
+  return position;
+}
diff --git a/webpack.config.js b/webpack.config.js
index 829fd5b..9e90446 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -12,22 +12,23 @@ module.exports = {
               presets: [ '@babel/preset-env' ],
             },
           },
-        ]
+        ],
       },
       {
         test: /\.css$/,
         use: [
           'style-loader',
-          'css-loader'
-        ]
-      }
-    ]
+          'css-loader',
+        ],
+      },
+    ],
   },
   output: {
     path: __dirname + '/dist',
     publicPath: '/',
     filename: 'bundle.js',
     library: 'CodeTool',
-    libraryTarget: 'umd'
-  }
+    libraryTarget: 'umd',
+    libraryExport: 'default',
+  },
 };