src/components/Editor/EditorCore.tsx

import { useEffect, useState, useCallback, useRef } from 'react';
import { useFileStore } from '../../stores/fileStore';
import { LexicalComposer } from '@lexical/react/LexicalComposer';
import { RichTextPlugin } from '@lexical/react/LexicalRichTextPlugin';
import { ContentEditable } from '@lexical/react/LexicalContentEditable';
import { HistoryPlugin } from '@lexical/react/LexicalHistoryPlugin';
import { OnChangePlugin } from '@lexical/react/LexicalOnChangePlugin';
import LexicalErrorBoundary from '@lexical/react/LexicalErrorBoundary';

import LineNumbers from './LineNumberPlugin';
import HoverToolbar from './HoverToolbar';
import AutoHighlighterPlugin from '../../plugins/AutoHighlighterPlugin';
import { CloudSavingDone01Icon, Tick02Icon } from 'hugeicons-react';
import { useLexicalComposerContext } from '@lexical/react/LexicalComposerContext';
import { INSERT_LINE_BREAK_COMMAND, COMMAND_PRIORITY_EDITOR, $createLineBreakNode, $getSelection, $isRangeSelection } from 'lexical';

// Premium Theme mapping for Lexical
const theme = {
  paragraph: 'editor-paragraph',
  text: {
    bold: 'editor-text-bold',
    italic: 'editor-text-italic',
    strikethrough: 'editor-text-strikethrough',
    underline: 'editor-text-underline',
  },
};

export default function EditorCore() {
  const { files, activeFileId, updateFileContent } = useFileStore();
  const [editorKey, setEditorKey] = useState(0);
  const [isSaving, setIsSaving] = useState(false);
  const debounceRef = useRef<any>(null);

  const ShiftEnterPlugin = () => {
    const [editor] = useLexicalComposerContext();
    useEffect(() => {
      return editor.registerCommand(
        INSERT_LINE_BREAK_COMMAND,
        () => {
          editor.update(() => {
            const selection = $getSelection();
            if ($isRangeSelection(selection)) {
              selection.insertNodes([$createLineBreakNode()]);
            }
          });
          return true;
        },
        COMMAND_PRIORITY_EDITOR
      );
    }, [editor]);
    return null;
  };

  const activeFile = files.find(f => f.id === activeFileId && f.type === 'file');

  // Ensure editor re-initializes exactly on file change
  useEffect(() => {
    setEditorKey(k => k + 1);
  }, [activeFileId]);

  // Clipboard Transformation (Emdash Prefix)
  useEffect(() => {
    const handleCopy = (e: ClipboardEvent) => {
      const selection = window.getSelection();
      if (!selection || selection.rangeCount === 0) return;
      
      let text = selection.toString();
      if (!text) return;

      // SPEC: Emdash as very beginning of number line with content
      // Logic: Prefix lines with content with "— " (emdash + space)
      const lines = text.split('\n');
      const transformed = lines.map(line => {
        if (line.trim().length > 0) {
          return `— ${line}`;
        }
        return line;
      }).join('\n');

      e.clipboardData?.setData('text/plain', transformed);
      e.preventDefault();
    };

    document.addEventListener('copy', handleCopy);
    return () => document.removeEventListener('copy', handleCopy);
  }, []);

  const handleOnChange = useCallback((editorState: any) => {
    setIsSaving(true);
    if (debounceRef.current) clearTimeout(debounceRef.current);
    
    debounceRef.current = setTimeout(() => {
      editorState.read(() => {
         const jsonString = JSON.stringify(editorState.toJSON());
         if (activeFileId) {
            updateFileContent(activeFileId, jsonString).then(() => {
               setIsSaving(false);
            });
         } else {
            setIsSaving(false);
         }
      });
    }, 300); // 300ms debounce for near-instant premium persistence
  }, [activeFileId, updateFileContent]);

  if (!activeFile) {
    return (
      <div className="editor-placeholder" style={{ 
        display: 'flex', flexDirection: 'column', gap: '8px', opacity: 0.4, 
        fontFamily: 'var(--font-ibm-plex)' 
      }}>
        <div style={{ fontSize: '14px', fontWeight: 500 }}>No active document</div>
        <div style={{ fontSize: '11px' }}>Select a file from the sidebar to begin editing.</div>
      </div>
    );
  }

  const initialConfig = {
    namespace: 'HybridDocEditor',
    theme,
    nodes: [],
    onError(error: Error) {
      console.error('Lexical Error:', error);
    },
    editorState: activeFile.content ? (
       activeFile.content.includes('"root":{') ? activeFile.content : undefined
    ) : undefined,
  };

  return (
    <div key={`editor-${editorKey}`} className="editor-shell" style={{ display: 'flex', flexDirection: 'column', height: '100%', flex: 1 }}>
       <LexicalComposer initialConfig={initialConfig}>
        <div className="editor-scroller" style={{ flex: 1, overflowY: 'auto', display: 'flex', position: 'relative' }}>
          <LineNumbers />
          <div className="editor-input-container" style={{ flex: 1, padding: '24px 32px', position: 'relative' }}>
              <RichTextPlugin
                contentEditable={
                  <ContentEditable 
                    className="ContentEditable" 
                    spellCheck={true}
                    data-gramm="true"
                    data-gramm_editor="true"
                    data-enable-grammarly="true"
                    style={{ 
                      minHeight: '100%', 
                      outline: 'none', 
                      lineHeight: '1.5',
                      fontSize: '15px'
                    }} 
                  />
                }
                placeholder={
                  <div className="editor-placeholder" style={{ 
                    position: 'absolute', top: 24, left: 32, pointerEvents: 'none', opacity: 0.3, fontSize: '15px' 
                  }}>
                    Start your thinking here...
                  </div>
                }
                ErrorBoundary={LexicalErrorBoundary}
              />
              <HistoryPlugin />
              <OnChangePlugin onChange={handleOnChange} ignoreSelectionChange />
              <ShiftEnterPlugin />
              <HoverToolbar />
              <AutoHighlighterPlugin />
              
              {/* Save Status Indicator */}
              <div style={{
                position: 'fixed',
                bottom: '24px',
                right: '24px',
                display: 'flex',
                alignItems: 'center',
                gap: '8px',
                padding: '6px 12px',
                background: 'var(--bg-panel)',
                border: '1px solid var(--border-color)',
                borderRadius: '20px',
                fontSize: '11px',
                fontWeight: 600,
                color: 'var(--text-secondary)',
                opacity: isSaving ? 1 : 0.4,
                transition: 'opacity 0.3s ease',
                pointerEvents: 'none',
                boxShadow: '0 4px 12px rgba(0,0,0,0.05)',
                zIndex: 10
              }}>
                {isSaving ? <CloudSavingDone01Icon size={14} className="spin" /> : <Tick02Icon size={14} />}
                {isSaving ? 'Syncing...' : 'Saved'}
              </div>
          </div>
        </div>
       </LexicalComposer>
    </div>
  );
}