import { useCallback, useEffect, useReducer, useRef, useState } from 'react';
import { Eye, Pencil, Redo2, Save, Search, Undo2, X } from 'lucide-react';

const BYTES_PER_ROW = 16;
const ROW_HEIGHT    = 20; // px — matches leading-5 at Tailwind's 16px base
const CHUNK_ROWS    = 256; // virtual-scroll overscan: render prev+curr+next windows

// ── History ───────────────────────────────────────────────────────────────────

type HistState = { stack: Uint8Array[]; idx: number };
type HistAction =
  | { type: 'push';  data: Uint8Array }
  | { type: 'undo' }
  | { type: 'redo' }
  | { type: 'reset'; data: Uint8Array };

function histReducer(s: HistState, a: HistAction): HistState {
  switch (a.type) {
    case 'push': {
      const prev   = s.stack.slice(0, s.idx + 1);
      const capped = prev.length > 100 ? prev.slice(prev.length - 100) : prev;
      const next   = [...capped, a.data];
      return { stack: next, idx: next.length - 1 };
    }
    case 'undo':  return s.idx > 0                  ? { ...s, idx: s.idx - 1 } : s;
    case 'redo':  return s.idx < s.stack.length - 1 ? { ...s, idx: s.idx + 1 } : s;
    case 'reset': return { stack: [a.data], idx: 0 };
  }
}

// ── Search ────────────────────────────────────────────────────────────────────

function matchAll(data: Uint8Array, needle: Uint8Array): number[] {
  if (needle.length === 0) return [];
  const results: number[] = [];
  outer: for (let i = 0; i <= data.length - needle.length; i++) {
    for (let j = 0; j < needle.length; j++) {
      if (data[i + j] !== needle[j]) continue outer;
    }
    results.push(i);
  }
  return results;
}

function parseHex(s: string): Uint8Array | null {
  const clean = s.replace(/\s+/g, '');
  if (!clean || clean.length % 2 !== 0 || !/^[0-9a-fA-F]+$/.test(clean)) return null;
  return new Uint8Array(
    Array.from({ length: clean.length / 2 }, (_, i) =>
      parseInt(clean.slice(i * 2, i * 2 + 2), 16),
    ),
  );
}

// ── Component ─────────────────────────────────────────────────────────────────

interface HexEditorProps {
  data: Uint8Array;
  readOnly?: boolean;
  onSave?: (data: Uint8Array) => Promise<void>;
}

export default function HexEditor({ data, readOnly = false, onSave }: HexEditorProps) {
  const [hist, dispatch] = useReducer(histReducer, { stack: [data.slice()], idx: 0 });
  const current = hist.stack[hist.idx];

  const [editMode, setEditMode] = useState(false);
  const [saving, setSaving]     = useState(false);
  const [cursor, setCursor]     = useState(-1);
  const [nibble, setNibble]     = useState<0 | 1>(0);
  const [pane, setPane]         = useState<'hex' | 'ascii'>('hex');

  const [searchOpen, setSearchOpen] = useState(false);
  const [query, setQuery]           = useState('');
  const [searchType, setSearchType] = useState<'text' | 'hex'>('text');
  const [matchIdx, setMatchIdx]     = useState(-1);

  // Virtual scroll
  const scrollRef  = useRef<HTMLDivElement>(null);
  const searchRef  = useRef<HTMLInputElement>(null);
  const [scrollTop, setScrollTop] = useState(0);

  const totalRows       = Math.ceil(current.length / BYTES_PER_ROW);
  const firstRenderRow  = Math.max(0, Math.floor(scrollTop / ROW_HEIGHT) - CHUNK_ROWS);
  const lastRenderRow   = Math.min(totalRows, firstRenderRow + CHUNK_ROWS * 3);
  const paddingTop      = firstRenderRow * ROW_HEIGHT;
  const paddingBottom   = (totalRows - lastRenderRow) * ROW_HEIGHT;

  const needle    = query.trim() ? (searchType === 'text' ? new TextEncoder().encode(query) : parseHex(query)) : null;
  const matches   = needle ? matchAll(current, needle) : [];
  const needleLen = needle?.length ?? 0;
  const dirty     = hist.idx > 0;
  const canUndo   = hist.idx > 0;
  const canRedo   = hist.idx < hist.stack.length - 1;

  // Reset history when the data prop changes (e.g. after a save that updates the prop)
  useEffect(() => {
    dispatch({ type: 'reset', data: data.slice() });
  }, [data]);

  // Jump to first result when query / search type changes
  useEffect(() => {
    if (matches.length > 0) { setMatchIdx(0); setCursor(matches[0]); }
    else setMatchIdx(-1);
  // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [query, searchType]);

  // Scroll cursor row into view (programmatic, works with virtual scroll)
  useEffect(() => {
    if (cursor < 0) return;
    const row    = Math.floor(cursor / BYTES_PER_ROW);
    const rowTop = row * ROW_HEIGHT + 12; // 12 = top padding equivalent
    const el = scrollRef.current;
    if (!el) return;
    if (rowTop < el.scrollTop) {
      el.scrollTop = rowTop;
    } else if (rowTop + ROW_HEIGHT > el.scrollTop + el.clientHeight) {
      el.scrollTop = rowTop + ROW_HEIGHT - el.clientHeight;
    }
  }, [cursor]);

  const pushByte = useCallback((offset: number, value: number) => {
    const next = current.slice();
    next[offset] = value;
    dispatch({ type: 'push', data: next });
  }, [current]);

  const handleSave = async () => {
    if (!onSave || !dirty) return;
    setSaving(true);
    try {
      await onSave(current);
      dispatch({ type: 'reset', data: current.slice() });
    } finally {
      setSaving(false);
    }
  };

  const goToMatch = (idx: number) => {
    if (!matches.length) return;
    const i = ((idx % matches.length) + matches.length) % matches.length;
    setMatchIdx(i);
    setCursor(matches[i]);
    scrollRef.current?.focus();
  };

  const openSearch = () => {
    setSearchOpen(true);
    setTimeout(() => searchRef.current?.focus(), 50);
  };
  const closeSearch = () => {
    setSearchOpen(false);
    setQuery('');
    scrollRef.current?.focus();
  };

  const onKeyDown = (e: React.KeyboardEvent) => {
    const ctrl = e.ctrlKey || e.metaKey;

    if (ctrl && e.key === 'f') { e.preventDefault(); openSearch(); return; }
    if (ctrl && e.key === 'z') { e.preventDefault(); dispatch({ type: 'undo' }); return; }
    if (ctrl && (e.key === 'y' || (e.shiftKey && e.key === 'Z'))) { e.preventDefault(); dispatch({ type: 'redo' }); return; }
    if (ctrl && e.key === 's' && editMode) { e.preventDefault(); void handleSave(); return; }
    if (e.key === 'Escape') { if (editMode) setEditMode(false); return; }

    const len = current.length;
    if (e.key === 'ArrowRight') { e.preventDefault(); setNibble(0); setCursor(c => Math.min(c < 0 ? 0 : c + 1, len - 1)); return; }
    if (e.key === 'ArrowLeft')  { e.preventDefault(); setNibble(0); setCursor(c => c <= 0 ? 0 : c - 1); return; }
    if (e.key === 'ArrowDown')  { e.preventDefault(); setCursor(c => Math.min(c < 0 ? 0 : c + BYTES_PER_ROW, len - 1)); return; }
    if (e.key === 'ArrowUp')    { e.preventDefault(); setCursor(c => c < 0 ? 0 : Math.max(c - BYTES_PER_ROW, 0)); return; }
    if (e.key === 'Home')       { e.preventDefault(); setCursor(c => Math.floor(Math.max(c, 0) / BYTES_PER_ROW) * BYTES_PER_ROW); return; }
    if (e.key === 'End')        { e.preventDefault(); setCursor(c => Math.min(Math.ceil((Math.max(c, 0) + 1) / BYTES_PER_ROW) * BYTES_PER_ROW - 1, len - 1)); return; }

    if (!editMode || cursor < 0) return;

    if (pane === 'hex') {
      const hex = e.key.toLowerCase();
      if (/^[0-9a-f]$/.test(hex) && !ctrl) {
        e.preventDefault();
        const v = parseInt(hex, 16);
        const cur = current[cursor] ?? 0;
        if (nibble === 0) {
          pushByte(cursor, (v << 4) | (cur & 0x0f));
          setNibble(1);
        } else {
          pushByte(cursor, (cur & 0xf0) | v);
          setNibble(0);
          setCursor(c => Math.min(c + 1, current.length - 1));
        }
      }
    } else {
      if (e.key.length === 1 && !ctrl) {
        e.preventDefault();
        pushByte(cursor, e.key.charCodeAt(0) & 0xff);
        setCursor(c => Math.min(c + 1, current.length - 1));
      }
    }
  };

  // Highlight sets
  const allMatchSet = new Set<number>();
  for (const pos of matches) { for (let i = 0; i < needleLen; i++) allMatchSet.add(pos + i); }
  const curStart = matchIdx >= 0 && matches[matchIdx] !== undefined ? matches[matchIdx] : -1;
  const curMatchSet = new Set<number>();
  if (curStart >= 0) { for (let i = 0; i < needleLen; i++) curMatchSet.add(curStart + i); }

  return (
    <div className="flex flex-col h-full bg-neutral-950">

      {/* ── Toolbar ── */}
      <div className="flex items-center gap-2 px-3 py-1.5 bg-neutral-900 border-b border-neutral-700 flex-shrink-0 text-xs">
        {!readOnly && (
          <button
            onClick={() => { setEditMode(v => !v); scrollRef.current?.focus(); }}
            className={`px-2 py-1 rounded inline-flex items-center gap-1 ${editMode ? 'bg-amber-600 text-white' : 'bg-neutral-700 text-neutral-300 hover:bg-neutral-600'}`}
          >
            {editMode ? <><Eye className="w-3.5 h-3.5" /> View</> : <><Pencil className="w-3.5 h-3.5" /> Edit</>}
          </button>
        )}
        {editMode && (
          <>
            <button onClick={() => dispatch({ type: 'undo' })} disabled={!canUndo}
              className="p-1 rounded text-neutral-400 hover:text-white disabled:opacity-30" title="Undo (Ctrl+Z)">
              <Undo2 className="w-3.5 h-3.5" />
            </button>
            <button onClick={() => dispatch({ type: 'redo' })} disabled={!canRedo}
              className="p-1 rounded text-neutral-400 hover:text-white disabled:opacity-30" title="Redo (Ctrl+Y)">
              <Redo2 className="w-3.5 h-3.5" />
            </button>
            {dirty && onSave && (
              <button onClick={() => void handleSave()} disabled={saving}
                className="px-2 py-1 rounded bg-blue-600 text-white hover:bg-blue-700 disabled:opacity-50 inline-flex items-center gap-1">
                <Save className="w-3.5 h-3.5" /> {saving ? 'Saving…' : 'Save'}
              </button>
            )}
          </>
        )}
        <div className="flex-1" />
        <span className="text-neutral-500 mr-1">{current.length.toLocaleString()} bytes</span>
        <button
          onClick={openSearch}
          className={`p-1 rounded ${searchOpen ? 'bg-neutral-700 text-white' : 'text-neutral-400 hover:text-white'}`}
          title="Search (Ctrl+F)"
        >
          <Search className="w-3.5 h-3.5" />
        </button>
      </div>

      {/* ── Search bar ── */}
      {searchOpen && (
        <div className="flex items-center gap-2 px-3 py-1.5 bg-neutral-800 border-b border-neutral-700 flex-shrink-0 text-xs">
          <Search className="w-3 h-3 text-neutral-500 flex-shrink-0" />
          <input
            ref={searchRef}
            value={query}
            onChange={e => setQuery(e.target.value)}
            onKeyDown={e => {
              if (e.key === 'Enter') { e.preventDefault(); goToMatch(matchIdx + (e.shiftKey ? -1 : 1)); }
              if (e.key === 'Escape') closeSearch();
            }}
            placeholder={searchType === 'text' ? 'Search text…' : 'Search hex (e.g. 48 65 6c)…'}
            className="flex-1 bg-transparent text-neutral-200 focus:outline-none placeholder:text-neutral-600"
          />
          <button
            onClick={() => setSearchType(t => t === 'text' ? 'hex' : 'text')}
            className="px-2 py-0.5 rounded bg-neutral-700 text-neutral-300 hover:bg-neutral-600 font-mono"
            title="Toggle text / hex search"
          >
            {searchType === 'text' ? 'Txt' : 'Hex'}
          </button>
          {query.trim() && (
            <span className={matches.length > 0 ? 'text-neutral-400' : 'text-red-400'}>
              {matches.length > 0 ? `${matchIdx + 1}/${matches.length}` : 'Not found'}
            </span>
          )}
          {matches.length > 1 && (
            <>
              <button onClick={() => goToMatch(matchIdx - 1)} className="text-neutral-400 hover:text-white px-0.5" title="Previous (Shift+Enter)">‹</button>
              <button onClick={() => goToMatch(matchIdx + 1)} className="text-neutral-400 hover:text-white px-0.5" title="Next (Enter)">›</button>
            </>
          )}
          <button onClick={closeSearch} className="text-neutral-500 hover:text-neutral-300">
            <X className="w-3.5 h-3.5" />
          </button>
        </div>
      )}

      {/* ── Hex grid (virtual scroll) ── */}
      <div
        ref={scrollRef}
        tabIndex={0}
        onKeyDown={onKeyDown}
        onScroll={e => setScrollTop(e.currentTarget.scrollTop)}
        className="flex-1 overflow-auto focus:outline-none select-none"
        onClick={() => scrollRef.current?.focus()}
      >
        {/* top spacer — 12px mimics former p-3 top padding */}
        <div style={{ height: paddingTop + 12 }} />

        {/* {cursor < 0 && firstRenderRow === 0 && (
          <div className="px-3 text-neutral-600 text-xs mb-2 font-mono">
            Click a cell to position cursor{editMode ? ' · type hex digits or ASCII to edit' : ''}
          </div>
        )} */}

        <div className="px-3 font-mono text-xs leading-5 whitespace-nowrap">
          {Array.from({ length: lastRenderRow - firstRenderRow }, (_, i) => {
            const row  = firstRenderRow + i;
            const base = row * BYTES_PER_ROW;
            return (
              <div key={row} className="flex items-center">

                {/* Address */}
                <span className="text-neutral-600 w-20 flex-shrink-0 select-none">
                  {base.toString(16).padStart(8, '0').toUpperCase()}
                </span>

                {/* Hex pane */}
                <div className="flex mr-2">
                  {Array.from({ length: BYTES_PER_ROW }, (_, col) => {
                    const idx = base + col;
                    if (idx >= current.length) {
                      return <span key={col} className={`inline-block w-6 text-center${col === 8 ? ' ml-2' : ''}`} />;
                    }
                    const byte       = current[idx];
                    const isCursor   = idx === cursor;
                    const isCurMatch = curMatchSet.has(idx);
                    const isAllMatch = allMatchSet.has(idx) && !isCurMatch;
                    const color = isCurMatch  ? 'bg-orange-500 text-white'
                                : isAllMatch  ? 'bg-yellow-800 text-yellow-200'
                                : byte === 0  ? 'text-neutral-700'
                                :               'text-green-400';
                    const ring  = isCursor && pane === 'hex' ? ' ring-1 ring-inset ring-blue-400' : '';
                    const gap   = col === 8 ? ' ml-2' : '';
                    return (
                      <span
                        key={col}
                        className={`inline-block w-6 text-center cursor-pointer${gap} ${color}${ring}`}
                        onClick={() => { setCursor(idx); setNibble(0); setPane('hex'); scrollRef.current?.focus(); }}
                      >
                        {byte.toString(16).padStart(2, '0').toUpperCase()}
                      </span>
                    );
                  })}
                </div>

                {/* Separator */}
                <span className="text-neutral-700 mr-2 select-none">│</span>

                {/* ASCII pane */}
                <div className="flex">
                  {Array.from({ length: BYTES_PER_ROW }, (_, col) => {
                    const idx = base + col;
                    if (idx >= current.length) return <span key={col} className="inline-block w-[9px]" />;
                    const byte       = current[idx];
                    const printable  = byte >= 32 && byte < 127;
                    const char       = printable ? String.fromCharCode(byte) : '·';
                    const isCursor   = idx === cursor;
                    const isCurMatch = curMatchSet.has(idx);
                    const isAllMatch = allMatchSet.has(idx) && !isCurMatch;
                    const color = isCurMatch ? 'bg-orange-500 text-white'
                                : isAllMatch ? 'bg-yellow-800 text-yellow-200'
                                : printable  ? 'text-blue-300'
                                :              'text-neutral-700';
                    const ring  = isCursor && pane === 'ascii' ? ' ring-1 ring-inset ring-blue-400' : '';
                    return (
                      <span
                        key={col}
                        className={`inline-block w-[9px] text-center cursor-pointer ${color}${ring}`}
                        onClick={() => { setCursor(idx); setPane('ascii'); scrollRef.current?.focus(); }}
                      >
                        {char}
                      </span>
                    );
                  })}
                </div>

              </div>
            );
          })}
        </div>

        {/* bottom spacer */}
        <div style={{ height: paddingBottom + 12 }} />
      </div>
    </div>
  );
}