import { RangeJSON, Range as SlateRange, Editor as CoreEditor } from 'slate';
import { Plugin } from '@grafana/slate-react';
import { isKeyHotkey } from 'is-hotkey';

const isIndentLeftHotkey = isKeyHotkey('mod+[');
const isShiftTabHotkey = isKeyHotkey('shift+tab');
const isIndentRightHotkey = isKeyHotkey('mod+]');

const SLATE_TAB = '  ';

const handleTabKey = (event: KeyboardEvent, editor: CoreEditor, next: Function): void => {
  const {
    startBlock,
    endBlock,
    selection: {
      start: { offset: startOffset, key: startKey },
      end: { offset: endOffset, key: endKey },
    },
  } = editor.value;

  const first = startBlock.getFirstText();

  const startBlockIsSelected =
    startOffset === 0 && startKey === first.key && endOffset === first.text.length && endKey === first.key;

  if (startBlockIsSelected || !startBlock.equals(endBlock)) {
    handleIndent(editor, 'right');
  } else {
    editor.insertText(SLATE_TAB);
  }
};

const handleIndent = (editor: CoreEditor, indentDirection: 'left' | 'right') => {
  const curSelection = editor.value.selection;
  const selectedBlocks = editor.value.document.getLeafBlocksAtRange(curSelection).toArray();

  if (indentDirection === 'left') {
    for (const block of selectedBlocks) {
      const blockWhitespace = block.text.length - block.text.trimLeft().length;

      const textKey = block.getFirstText().key;

      const rangeProperties: RangeJSON = {
        anchor: {
          key: textKey,
          offset: blockWhitespace,
          path: [],
        },
        focus: {
          key: textKey,
          offset: blockWhitespace,
          path: [],
        },
      };

      editor.deleteBackwardAtRange(SlateRange.create(rangeProperties), Math.min(SLATE_TAB.length, blockWhitespace));
    }
  } else {
    const { startText } = editor.value;
    const textBeforeCaret = startText.text.slice(0, curSelection.start.offset);
    const isWhiteSpace = /^\s*$/.test(textBeforeCaret);

    for (const block of selectedBlocks) {
      editor.insertTextByKey(block.getFirstText().key, 0, SLATE_TAB);
    }

    if (isWhiteSpace) {
      editor.moveStartBackward(SLATE_TAB.length);
    }
  }
};

// Clears the rest of the line after the caret
export default function IndentationPlugin(): Plugin {
  return {
    onKeyDown(event: KeyboardEvent, editor: CoreEditor, next: Function) {
      if (isIndentLeftHotkey(event) || isShiftTabHotkey(event)) {
        event.preventDefault();
        handleIndent(editor, 'left');
      } else if (isIndentRightHotkey(event)) {
        event.preventDefault();
        handleIndent(editor, 'right');
      } else if (event.key === 'Tab') {
        event.preventDefault();
        handleTabKey(event, editor, next);
      } else {
        return next();
      }

      return true;
    },
  };
}