/**
 * V2HistoryPanel – History-Anzeige für das V2-Dokument (Task A4.12).
 *
 * Liest die Undo/Redo-Stacks des aktiven Dokuments (documentService).
 * Klick auf einen aktiven Eintrag: macht alles DANACH rückgängig.
 * Redo-Einträge sind rein informativ (gezielter Sprung nicht nativ).
 *
 * Wird statt des Legacy HistoryPanel gerendert, wenn
 * VITE_TOOL_DISPATCHER=v2 gesetzt ist (App.tsx entscheidet).
 */
import React, { useEffect, useState } from 'react';
import { getActiveDocument, undoActive, redoActive } from '../kernel/document/documentService';
import type { CADDocument } from '../kernel/document/CADDocument';

type StackKind = 'undo' | 'redo';
interface StackItemInfo {
  kind: StackKind;
  index: number;   // Position im jeweiligen Stack (0 = ältester)
}

const V2HistoryPanel: React.FC<{ onClose: () => void }> = ({ onClose }) => {
  const [doc, setDoc] = useState<CADDocument | null>(getActiveDocument());
  const [, bump] = useState(0);

  // Auf Dokumentwechsel reagieren + bei Doc-Änderung neu rendern
  useEffect(() => {
    const unsubChange = doc?.onChanged(() => bump((b) => b + 1));
    const interval = setInterval(() => {
      const active = getActiveDocument();
      if (active !== doc) setDoc(active);
    }, 500); // einfacher Registry-Poll bis A5 einen Hook liefert
    return () => {
      unsubChange?.();
      clearInterval(interval);
    };
  }, [doc]);

  const um = doc?.getUndoManager();
  const undoCount = um ? um.undoStack.length : 0;
  const redoCount = um ? um.redoStack.length : 0;
  const items: Array<StackItemInfo & { isCurrent: boolean }> = [];
  // Neueste zuerst auflisten:
  for (let i = undoCount - 1; i >= 0; i--) {
    items.push({ kind: 'undo', index: i, isCurrent: i === undoCount - 1 });
  }
  for (let i = redoCount - 1; i >= 0; i--) {
    items.push({ kind: 'redo', index: i, isCurrent: false });
  }

  /** Macht alle Schritte nach slotIndex rückgängig (slot 0 = ältester). */
  const undoUntilSlot = (slotIndex: number): void => {
    if (!doc) return;
    const targetLen = slotIndex + 1;
    let guard = 0;
    while (
      doc.canUndo() &&
      doc.getUndoManager().undoStack.length > targetLen &&
      guard < 500
    ) {
      doc.undo();
      guard++;
    }
  };

  const shellStyle: React.CSSProperties = {
    position: 'fixed', top: '50%', right: '320px', transform: 'translateY(-50%)',
    background: 'var(--color-bg-primary, #1e1e2e)', borderRadius: '8px',
    padding: '16px', width: '280px', maxHeight: '60vh', overflow: 'auto',
    border: '1px solid var(--color-border, #333)', zIndex: 900,
    color: 'var(--color-text, #e0e0e0)',
  };

  if (!doc || items.length === 0) {
    return (
      <div style={shellStyle}>
        <Header onClose={onClose} count={items.length} />
        <p style={{ fontSize: '13px', color: '#888' }}>
          {doc ? 'Keine Historie vorhanden.' : 'Kein V2-Dokument aktiv (Flag aus?).'}
        </p>
        <UndoRedoButtons doc={doc} />
      </div>
    );
  }

  return (
    <div style={shellStyle}>
      <Header onClose={onClose} count={items.length} />
      <UndoRedoButtons doc={doc} />
      <div style={{ display: 'flex', flexDirection: 'column', gap: '2px' }}>
        {items.map((item) => (
          <button
            key={`${item.kind}-${item.index}`}
            onClick={() => item.kind === 'undo' && undoUntilSlot(item.index)}
            title={item.kind === 'undo'
              ? 'Klicken: alles danach rückgängig machen'
              : 'Redo-Eintrag (nur anzeigbar)'}
            style={{
              display: 'flex', alignItems: 'center', gap: '8px',
              padding: '6px 8px', borderRadius: '4px',
              cursor: item.kind === 'undo' ? 'pointer' : 'default',
              border: item.isCurrent && item.kind === 'undo'
                ? '1px solid rgba(80,250,123,0.4)' : 'none',
              textAlign: 'left', width: '100%',
              background: item.isCurrent && item.kind === 'undo'
                ? 'rgba(80, 250, 123, 0.12)' : item.kind === 'redo'
                ? 'rgba(255,255,255,0.03)' : 'transparent',
              color: item.kind === 'redo' ? '#888' : 'var(--color-text, #e0e0e0)',
              fontWeight: item.isCurrent && item.kind === 'undo' ? 600 : 400,
              fontSize: '13px', opacity: item.kind === 'redo' ? 0.6 : 1,
            }}
          >
            <span style={{ fontSize: '10px', minWidth: '44px', color: '#666' }}>
              {item.kind === 'undo' ? `Schritt ${item.index + 1}` : 'Redo'}
            </span>
            {item.isCurrent && item.kind === 'undo' && (
              <span style={{ fontSize: '10px', color: '#50fa7b' }}>● aktuell</span>
            )}
          </button>
        ))
      }
      </div>
    </div>
  );
};

function Header({ onClose, count }: { onClose: () => void; count: number }): JSX.Element {
  return (
    <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: '12px' }}>
      <h3 style={{ margin: 0, fontSize: '15px' }}>Historie V2{count > 0 ? ` (${count})` : ''}</h3>
      <button onClick={onClose} style={{ background: 'none', border: 'none', color: 'inherit', cursor: 'pointer', fontSize: '18px' }}>×</button>
    </div>
  );
}

function UndoRedoButtons({ doc }: { doc: CADDocument | null }): JSX.Element {
  return (
    <div style={{ display: 'flex', gap: '8px', marginBottom: doc && (doc.canUndo() || doc.canRedo()) ? '10px' : '4px' }}>
      <button
        onClick={() => undoActive()}
        disabled={!doc?.canUndo()}
        title="Strg+Z"
        style={btnStyle(doc?.canUndo() ?? false)}
      >↶ Undo</button>
      <button
        onClick={() => redoActive()}
        disabled={!doc?.canRedo()}
        title="Strg+Y"
        style={btnStyle(doc?.canRedo() ?? false)}
      >↷ Redo</button>
    </div>
  );
}

function btnStyle(enabled: boolean): React.CSSProperties {
  return {
    padding: '5px 12px', borderRadius: '4px', fontSize: '12px',
    cursor: enabled ? 'pointer' : 'not-allowed',
    border: '1px solid var(--color-border, #333)',
    background: 'var(--color-bg-secondary, #2a2a3a)',
    color: enabled ? 'inherit' : '#555',
  };
}

export default V2HistoryPanel;