import { useState, useMemo, useRef } from 'react';
import { X, Trash2, GripVertical } from 'lucide-react';

// ─────────────────────────────────────────────────────────────────
// Categorías morfológicas — cada una con su identidad visual
// ─────────────────────────────────────────────────────────────────
const CATEGORIES = {
  gen: {
    label: 'Generadores',
    subtitle: 'Anamorfismos',
    signature: 'seed → [a]',
    color: '#7dd3fc',
  },
  map: {
    label: 'Transformaciones',
    subtitle: 'Functor · map',
    signature: '(a→b) → [a]→[b]',
    color: '#c4b5fd',
  },
  filter: {
    label: 'Filtros',
    subtitle: 'Refinamientos',
    signature: '[a] → [a]',
    color: '#fcd34d',
  },
  scan: {
    label: 'Scans',
    subtitle: 'Folds acumulativos',
    signature: '[a] → [a]',
    color: '#86efac',
  },
  fold: {
    label: 'Plegados',
    subtitle: 'Catamorfismos',
    signature: '[a] → b',
    color: '#fda4af',
  },
};

// PRNG determinista para que `random` sea reproducible
function mulberry32(seed) {
  let a = seed;
  return function() {
    a = (a + 0x6D2B79F5) | 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

// ─────────────────────────────────────────────────────────────────
// Catálogo de funciones disponibles
// ─────────────────────────────────────────────────────────────────
const FUNCTIONS = {
  // — GENERADORES (anamorfismos: producen estructura desde un seed) —
  range:    { cat: 'gen', symbol: 'range',    sig: 'n → [1..n]',     params: [{k:'n',d:20,min:1,max:120}],                             run: (_,p) => Array.from({length:p.n}, (_,i)=>i+1) },
  linspace: { cat: 'gen', symbol: 'linspace', sig: 'n → [0..2π]',    params: [{k:'n',d:60,min:2,max:200}],                             run: (_,p) => Array.from({length:p.n}, (_,i)=>(i/(p.n-1))*2*Math.PI) },
  sine:     { cat: 'gen', symbol: 'sine',     sig: 'n → sin(4π·t)',  params: [{k:'n',d:80,min:4,max:200}],                             run: (_,p) => Array.from({length:p.n}, (_,i)=>Math.sin((i/(p.n-1))*4*Math.PI)) },
  noise:    { cat: 'gen', symbol: 'noise',    sig: 'seed → U(-1,1)', params: [{k:'n',d:50,min:2,max:200},{k:'seed',d:7,min:1,max:9999}], run: (_,p) => { const r=mulberry32(p.seed); return Array.from({length:p.n}, ()=>r()*2-1); } },
  fib:      { cat: 'gen', symbol: 'fib',      sig: 'n → Fibₙ',       params: [{k:'n',d:12,min:2,max:25}],                              run: (_,p) => { const r=[1,1]; while(r.length<p.n) r.push(r[r.length-1]+r[r.length-2]); return r.slice(0,p.n); } },

  // — MAPS (functor f: a→b aplicado punto-a-punto) —
  double:   { cat: 'map', symbol: '·2',   sig: 'x ↦ 2x',         run: (a) => a.map(x=>x*2) },
  square:   { cat: 'map', symbol: 'x²',   sig: 'x ↦ x²',         run: (a) => a.map(x=>x*x) },
  negate:   { cat: 'map', symbol: '-x',   sig: 'x ↦ -x',         run: (a) => a.map(x=>-x) },
  abs:      { cat: 'map', symbol: '|x|',  sig: 'x ↦ |x|',        run: (a) => a.map(x=>Math.abs(x)) },
  sqrt:     { cat: 'map', symbol: '√',    sig: 'x ↦ √|x|',       run: (a) => a.map(x=>Math.sqrt(Math.abs(x))) },
  sin:      { cat: 'map', symbol: 'sin',  sig: 'x ↦ sin x',      run: (a) => a.map(x=>Math.sin(x)) },
  log:      { cat: 'map', symbol: 'ln',   sig: 'x ↦ ln(1+|x|)',  run: (a) => a.map(x=>Math.log(1+Math.abs(x))) },

  // — FILTROS (refinamiento) —
  positive: { cat: 'filter', symbol: '>0',  sig: 'x > 0',   run: (a) => a.filter(x=>x>0) },
  even:     { cat: 'filter', symbol: 'par', sig: 'x even',  run: (a) => a.filter(x=>Math.round(x)%2===0) },
  gt:       { cat: 'filter', symbol: '>t',  sig: 'x > t',   params: [{k:'t',d:0,min:-50,max:50,step:0.5}], run: (a,p) => a.filter(x=>x>p.t) },

  // — SCANS (folds acumulativos: dejan rastro) —
  cumsum:   { cat: 'scan', symbol: 'Σ*',     sig: 'Σ prefix',      run: (a) => { let s=0; return a.map(x=>s+=x); } },
  cummax:   { cat: 'scan', symbol: 'max*',   sig: 'max prefix',    run: (a) => { let m=-Infinity; return a.map(x=>{m=Math.max(m,x); return m;}); } },
  diff:     { cat: 'scan', symbol: 'Δ',      sig: 'xₙ - xₙ₋₁',     run: (a) => a.map((x,i)=>i===0?0:x-a[i-1]) },
  mavg:     { cat: 'scan', symbol: 'μ_k',    sig: 'media móvil k', params: [{k:'k',d:3,min:1,max:15}], run: (a,p) => a.map((_,i)=>{ const s=Math.max(0,i-p.k+1); const sl=a.slice(s,i+1); return sl.reduce((t,v)=>t+v,0)/sl.length; }) },

  // — FOLDS (catamorfismos: colapsan a escalar · terminales) —
  sum:     { cat: 'fold', symbol: 'Σ',   sig: '[a] → Σa',  run: (a) => a.reduce((s,x)=>s+x, 0) },
  product: { cat: 'fold', symbol: '∏',   sig: '[a] → ∏a',  run: (a) => a.reduce((s,x)=>s*x, 1) },
  max:     { cat: 'fold', symbol: 'max', sig: '[a] → max', run: (a) => a.length ? Math.max(...a) : 0 },
  min:     { cat: 'fold', symbol: 'min', sig: '[a] → min', run: (a) => a.length ? Math.min(...a) : 0 },
  mean:    { cat: 'fold', symbol: 'μ',   sig: '[a] → μ',   run: (a) => a.length ? a.reduce((s,x)=>s+x,0)/a.length : 0 },
  count:   { cat: 'fold', symbol: '#',   sig: '[a] → ℕ',   run: (a) => a.length },
};

const BY_CATEGORY = Object.entries(CATEGORIES).map(([catKey, catMeta]) => ({
  ...catMeta,
  key: catKey,
  items: Object.entries(FUNCTIONS).filter(([, f]) => f.cat === catKey).map(([name, f]) => ({ name, ...f })),
}));

// ─────────────────────────────────────────────────────────────────
// Ejecutor: aplica el pipeline y conserva salidas intermedias
// ─────────────────────────────────────────────────────────────────
function executePipeline(pipeline) {
  const steps = [];
  let current = Array.from({length: 10}, (_, i) => i + 1); // semilla si no hay generador
  let terminated = false;

  for (const item of pipeline) {
    const def = FUNCTIONS[item.name];
    if (!def) continue;
    if (terminated) { steps.push({ ...item, def, unreachable: true }); continue; }
    try {
      const value = def.run(current, item.params || {});
      steps.push({ ...item, def, value });
      if (def.cat === 'fold') terminated = true;
      else current = value;
    } catch (e) {
      steps.push({ ...item, def, error: e.message });
      terminated = true;
    }
  }
  return { steps, terminated };
}

// ─────────────────────────────────────────────────────────────────
// Helpers de id y parámetros
// ─────────────────────────────────────────────────────────────────
let _uid = 0;
const uid = () => `n${++_uid}_${Date.now().toString(36)}`;

function defaultParams(name) {
  const def = FUNCTIONS[name];
  if (!def.params) return {};
  return Object.fromEntries(def.params.map(p => [p.k, p.d]));
}

// ─────────────────────────────────────────────────────────────────
// Sparkline compacto (SVG manual)
// ─────────────────────────────────────────────────────────────────
function Sparkline({ data, color = '#888', w = 180, h = 34 }) {
  if (!Array.isArray(data) || data.length === 0) {
    return <div style={{width:w, height:h}} className="flex items-center justify-center text-[10px] text-neutral-600">∅</div>;
  }
  const min = Math.min(...data);
  const max = Math.max(...data);
  const span = max - min || 1;
  const n = data.length;
  const xStep = n > 1 ? (w - 6) / (n - 1) : 0;
  const pts = data.map((v, i) => [3 + i * xStep, h - 3 - ((v - min) / span) * (h - 6)]);
  const path = pts.map((p, i) => (i === 0 ? `M${p[0].toFixed(1)},${p[1].toFixed(1)}` : `L${p[0].toFixed(1)},${p[1].toFixed(1)}`)).join(' ');
  const zeroY = h - 3 - ((0 - min) / span) * (h - 6);
  const showZero = min < 0 && max > 0;
  return (
    <svg width={w} height={h} className="block">
      {showZero && <line x1={0} x2={w} y1={zeroY} y2={zeroY} stroke={color} strokeOpacity={0.15} strokeDasharray="2 3" />}
      <path d={path} fill="none" stroke={color} strokeWidth={1.3} strokeLinecap="round" strokeLinejoin="round" />
      {n <= 40 && pts.map((p, i) => (
        <circle key={i} cx={p[0]} cy={p[1]} r={1.4} fill={color} fillOpacity={0.85} />
      ))}
    </svg>
  );
}

// ─────────────────────────────────────────────────────────────────
// Ficha en la paleta (draggable)
// ─────────────────────────────────────────────────────────────────
function PaletteItem({ fnName, fn, color, onDragStart, onClick }) {
  return (
    <div
      draggable
      onDragStart={(e) => { e.dataTransfer.setData('text/fn-name', fnName); e.dataTransfer.effectAllowed = 'copy'; onDragStart?.(); }}
      onClick={onClick}
      className="group flex items-center gap-2 px-2.5 py-1.5 rounded-md cursor-grab active:cursor-grabbing select-none transition-colors hover:bg-neutral-800/60"
      style={{ borderLeft: `2px solid ${color}` }}
      title={`${fnName} :: ${fn.sig}`}
    >
      <span className="font-mono text-[11px] font-semibold tracking-tight" style={{ color }}>{fn.symbol}</span>
      <span className="font-mono text-[11px] text-neutral-400 flex-1 truncate">{fnName}</span>
      <span className="font-mono text-[9px] text-neutral-600 opacity-0 group-hover:opacity-100 transition-opacity">drag</span>
    </div>
  );
}

// ─────────────────────────────────────────────────────────────────
// Nodo del pipeline
// ─────────────────────────────────────────────────────────────────
function PipelineNode({ step, index, isLast, onRemove, onParamChange, onDragStart, onDragOver, onDrop, isDragging }) {
  const { def, value, unreachable, error } = step;
  const cat = CATEGORIES[def.cat];
  const color = cat.color;
  const isScalar = def.cat === 'fold';

  return (
    <div
      draggable
      onDragStart={(e) => { e.dataTransfer.setData('text/reorder-index', String(index)); e.dataTransfer.effectAllowed = 'move'; onDragStart?.(index); }}
      onDragOver={(e) => { e.preventDefault(); onDragOver?.(index); }}
      onDrop={(e) => onDrop?.(e, index)}
      className="relative group"
      style={{ opacity: isDragging ? 0.4 : 1 }}
    >
      <div
        className="flex flex-col rounded-lg backdrop-blur-sm transition-all"
        style={{
          background: `linear-gradient(180deg, ${color}14 0%, ${color}06 100%)`,
          border: `1px solid ${color}40`,
          boxShadow: `0 0 0 1px ${color}10, 0 8px 24px -12px ${color}30`,
          minWidth: 200,
        }}
      >
        {/* cabecera */}
        <div className="flex items-center gap-1.5 px-2.5 py-1.5 border-b" style={{ borderColor: `${color}25` }}>
          <GripVertical size={12} className="text-neutral-600 cursor-grab" />
          <span className="font-mono text-[11px] font-bold" style={{ color }}>{def.symbol}</span>
          <span className="font-mono text-[10px] text-neutral-500 flex-1">{step.name}</span>
          <button
            onClick={() => onRemove(index)}
            className="opacity-0 group-hover:opacity-100 transition-opacity text-neutral-500 hover:text-neutral-200 p-0.5 rounded"
            aria-label="Eliminar"
          >
            <X size={11} />
          </button>
        </div>

        {/* params */}
        {def.params && (
          <div className="flex items-center gap-1.5 px-2.5 py-1.5 border-b flex-wrap" style={{ borderColor: `${color}18` }}>
            {def.params.map(p => (
              <label key={p.k} className="flex items-center gap-1 font-mono text-[10px] text-neutral-500">
                <span>{p.k}=</span>
                <input
                  type="number"
                  value={step.params?.[p.k] ?? p.d}
                  min={p.min} max={p.max} step={p.step ?? 1}
                  onChange={(e) => onParamChange(index, p.k, Number(e.target.value))}
                  className="w-12 bg-neutral-900/60 border border-neutral-700/50 rounded px-1 py-0.5 text-neutral-200 font-mono text-[10px] focus:outline-none focus:border-neutral-500"
                />
              </label>
            ))}
          </div>
        )}

        {/* preview */}
        <div className="px-2.5 py-1.5">
          {unreachable ? (
            <div className="font-mono text-[10px] text-neutral-600 italic">inalcanzable · fold anterior terminó el pipeline</div>
          ) : error ? (
            <div className="font-mono text-[10px] text-rose-400">error: {error}</div>
          ) : isScalar ? (
            <div className="flex items-baseline gap-2">
              <span className="font-mono text-[10px] text-neutral-500">resultado</span>
              <span className="font-display text-2xl font-light" style={{ color }}>{formatScalar(value)}</span>
            </div>
          ) : (
            <div>
              <Sparkline data={value} color={color} w={180} h={32} />
              <div className="font-mono text-[9px] text-neutral-600 mt-1">
                n={value?.length ?? 0} · range [{formatScalar(Math.min(...(value?.length?value:[0])))}, {formatScalar(Math.max(...(value?.length?value:[0])))}]
              </div>
            </div>
          )}
        </div>
      </div>

      {/* flecha de composición */}
      {!isLast && (
        <div className="absolute top-1/2 -right-5 -translate-y-1/2 font-mono text-neutral-600 text-sm pointer-events-none">→</div>
      )}
    </div>
  );
}

function formatScalar(v) {
  if (v === undefined || v === null || !isFinite(v)) return '—';
  if (Number.isInteger(v)) return String(v);
  const abs = Math.abs(v);
  if (abs >= 1000 || (abs > 0 && abs < 0.01)) return v.toExponential(2);
  return v.toFixed(3);
}

// ─────────────────────────────────────────────────────────────────
// Visualización grande del output final
// ─────────────────────────────────────────────────────────────────
function FinalView({ lastStep }) {
  if (!lastStep) {
    return (
      <div className="flex-1 flex items-center justify-center text-neutral-600 font-mono text-xs">
        arrastra una función para empezar
      </div>
    );
  }
  const { def, value, error, unreachable } = lastStep;
  if (error || unreachable) return null;
  const color = CATEGORIES[def.cat].color;

  if (def.cat === 'fold') {
    return (
      <div className="flex flex-col items-center justify-center py-6 w-full">
        <span className="font-mono text-[10px] uppercase tracking-[0.2em] text-neutral-500 mb-2">resultado · escalar</span>
        <span className="font-display text-5xl font-light break-all text-center" style={{ color }}>{formatScalar(value)}</span>
      </div>
    );
  }

  // plot grande
  if (!Array.isArray(value) || value.length === 0) {
    return <div className="font-mono text-xs text-neutral-600 p-4">∅  (lista vacía)</div>;
  }
  const W = 720, H = 180, pad = 20;
  const min = Math.min(...value), max = Math.max(...value);
  const span = max - min || 1;
  const n = value.length;
  const xStep = n > 1 ? (W - 2 * pad) / (n - 1) : 0;
  const pts = value.map((v, i) => [pad + i * xStep, H - pad - ((v - min) / span) * (H - 2 * pad)]);
  const path = pts.map((p, i) => (i === 0 ? `M${p[0].toFixed(1)},${p[1].toFixed(1)}` : `L${p[0].toFixed(1)},${p[1].toFixed(1)}`)).join(' ');
  const areaPath = `${path} L${pts[pts.length-1][0]},${H-pad} L${pts[0][0]},${H-pad} Z`;
  const zeroY = H - pad - ((0 - min) / span) * (H - 2 * pad);
  const showZero = min < 0 && max > 0;

  return (
    <div className="flex flex-col">
      <div className="flex items-baseline justify-between mb-2">
        <span className="font-mono text-[10px] uppercase tracking-[0.2em] text-neutral-500">resultado · señal</span>
        <span className="font-mono text-[10px] text-neutral-500">n={n} · [{formatScalar(min)}, {formatScalar(max)}]</span>
      </div>
      <svg viewBox={`0 0 ${W} ${H}`} className="w-full h-auto" preserveAspectRatio="none">
        <defs>
          <linearGradient id="areaGrad" x1="0" y1="0" x2="0" y2="1">
            <stop offset="0%" stopColor={color} stopOpacity="0.3" />
            <stop offset="100%" stopColor={color} stopOpacity="0" />
          </linearGradient>
        </defs>
        {/* grid */}
        {[0.25, 0.5, 0.75].map(f => (
          <line key={f} x1={pad} x2={W-pad} y1={pad + f*(H-2*pad)} y2={pad + f*(H-2*pad)} stroke="#fff" strokeOpacity={0.04} />
        ))}
        {showZero && <line x1={pad} x2={W-pad} y1={zeroY} y2={zeroY} stroke={color} strokeOpacity={0.25} strokeDasharray="3 4" />}
        <path d={areaPath} fill="url(#areaGrad)" />
        <path d={path} fill="none" stroke={color} strokeWidth={1.8} strokeLinecap="round" strokeLinejoin="round" />
        {n <= 80 && pts.map((p, i) => (
          <circle key={i} cx={p[0]} cy={p[1]} r={2} fill={color} />
        ))}
        {/* eje */}
        <line x1={pad} x2={W-pad} y1={H-pad} y2={H-pad} stroke="#fff" strokeOpacity={0.1} />
        <line x1={pad} x2={pad} y1={pad} y2={H-pad} stroke="#fff" strokeOpacity={0.1} />
      </svg>
    </div>
  );
}

// ─────────────────────────────────────────────────────────────────
// APP principal
// ─────────────────────────────────────────────────────────────────
export default function App() {
  const [pipeline, setPipeline] = useState([
    { id: uid(), name: 'range',  params: defaultParams('range') },
    { id: uid(), name: 'square', params: defaultParams('square') },
    { id: uid(), name: 'cumsum', params: defaultParams('cumsum') },
  ]);
  const [dragIndex, setDragIndex] = useState(null);
  const [hoverIndex, setHoverIndex] = useState(null);
  const dropZoneRef = useRef(null);

  const { steps } = useMemo(() => executePipeline(pipeline), [pipeline]);
  const lastStep = steps[steps.length - 1];

  // expresión simbólica: fold_sum ∘ map_square ∘ gen_range(20)
  const expression = useMemo(() => {
    if (pipeline.length === 0) return '∅';
    const parts = pipeline.map(s => {
      const def = FUNCTIONS[s.name];
      const paramStr = def.params ? '(' + def.params.map(p => `${p.k}=${s.params?.[p.k] ?? p.d}`).join(',') + ')' : '';
      return `${s.name}${paramStr}`;
    }).reverse();
    return parts.join('  ∘  ');
  }, [pipeline]);

  const addFunction = (name) => {
    setPipeline(p => [...p, { id: uid(), name, params: defaultParams(name) }]);
  };

  const removeFunction = (index) => {
    setPipeline(p => p.filter((_, i) => i !== index));
  };

  const changeParam = (index, key, value) => {
    setPipeline(p => p.map((s, i) => i === index ? { ...s, params: { ...s.params, [key]: value } } : s));
  };

  const handleDropOnZone = (e) => {
    e.preventDefault();
    const fnName = e.dataTransfer.getData('text/fn-name');
    const reorderIdx = e.dataTransfer.getData('text/reorder-index');
    if (fnName && FUNCTIONS[fnName]) {
      addFunction(fnName);
    } else if (reorderIdx !== '') {
      // soltar al final si vino de un nodo
      const from = Number(reorderIdx);
      setPipeline(p => {
        const copy = [...p];
        const [moved] = copy.splice(from, 1);
        copy.push(moved);
        return copy;
      });
    }
    setDragIndex(null);
    setHoverIndex(null);
  };

  const handleDropOnNode = (e, targetIdx) => {
    e.preventDefault();
    e.stopPropagation();
    const fnName = e.dataTransfer.getData('text/fn-name');
    const reorderIdx = e.dataTransfer.getData('text/reorder-index');
    if (fnName && FUNCTIONS[fnName]) {
      setPipeline(p => {
        const copy = [...p];
        copy.splice(targetIdx, 0, { id: uid(), name: fnName, params: defaultParams(fnName) });
        return copy;
      });
    } else if (reorderIdx !== '') {
      const from = Number(reorderIdx);
      if (from === targetIdx) return;
      setPipeline(p => {
        const copy = [...p];
        const [moved] = copy.splice(from, 1);
        const adjusted = from < targetIdx ? targetIdx - 1 : targetIdx;
        copy.splice(adjusted, 0, moved);
        return copy;
      });
    }
    setDragIndex(null);
    setHoverIndex(null);
  };

  return (
    <div className="w-full min-h-screen text-neutral-200" style={{
      background: 'radial-gradient(ellipse at top, #0f1419 0%, #06080a 60%, #030506 100%)',
      fontFamily: "'JetBrains Mono', ui-monospace, monospace",
    }}>
      <style>{`
        @import url('https://fonts.googleapis.com/css2?family=Fraunces:ital,opsz,wght@0,9..144,300..900;1,9..144,300..900&family=JetBrains+Mono:wght@400;500;600;700&display=swap');
        .font-display { font-family: 'Fraunces', serif; font-optical-sizing: auto; }
        .font-mono { font-family: 'JetBrains Mono', ui-monospace, monospace; }
        .grid-bg {
          background-image:
            linear-gradient(rgba(255,255,255,0.02) 1px, transparent 1px),
            linear-gradient(90deg, rgba(255,255,255,0.02) 1px, transparent 1px);
          background-size: 24px 24px;
        }
        /* scrollbar */
        ::-webkit-scrollbar { width: 8px; height: 8px; }
        ::-webkit-scrollbar-track { background: transparent; }
        ::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.08); border-radius: 4px; }
        ::-webkit-scrollbar-thumb:hover { background: rgba(255,255,255,0.16); }
      `}</style>

      <div className="grid-bg min-h-screen">
        {/* HEADER */}
        <header className="px-6 pt-6 pb-5 border-b border-white/5">
          <div className="flex items-end justify-between flex-wrap gap-4">
            <div>
              <div className="flex items-baseline gap-3">
                <span className="font-mono text-[10px] uppercase tracking-[0.3em] text-neutral-500">lab · 001</span>
                <span className="font-mono text-[10px] text-neutral-700">/</span>
                <span className="font-mono text-[10px] text-neutral-500">composición funcional</span>
              </div>
              <h1 className="font-display text-3xl font-light tracking-tight mt-1.5">
                laboratorio de <em className="italic" style={{color:'#c4b5fd'}}>morfismos</em>
              </h1>
              <p className="font-mono text-[11px] text-neutral-500 mt-1.5 max-w-2xl">
                arrastra funciones al pipeline y componlas de izquierda a derecha. cada tipo corresponde a un esquema de recursión distinto.
              </p>
            </div>
            <button
              onClick={() => setPipeline([])}
              className="flex items-center gap-2 font-mono text-[10px] uppercase tracking-wider text-neutral-500 hover:text-neutral-200 border border-white/10 hover:border-white/30 px-3 py-1.5 rounded transition-colors"
            >
              <Trash2 size={11} /> vaciar
            </button>
          </div>
        </header>

        {/* MAIN GRID · 2 columnas: paleta | (expresión + pipeline + visualizador apilados) */}
        <main
          style={{
            display: 'grid',
            gridTemplateColumns: '200px minmax(280px, 1fr)',
            minHeight: 'calc(100vh - 140px)',
            overflowX: 'auto',
          }}
        >
          {/* ─── IZQUIERDA · PALETA ─── */}
          <aside className="border-r border-white/5 p-5 overflow-y-auto" style={{maxHeight: 'calc(100vh - 140px)'}}>
            <div className="font-mono text-[10px] uppercase tracking-[0.25em] text-neutral-500 mb-4">primitivas</div>
            <div className="flex flex-col gap-5">
              {BY_CATEGORY.map(cat => (
                <section key={cat.key}>
                  <div className="flex items-center gap-2 mb-2 px-1">
                    <span className="w-1.5 h-1.5 rounded-full" style={{background: cat.color, boxShadow: `0 0 8px ${cat.color}`}} />
                    <span className="font-display text-sm italic" style={{color: cat.color}}>{cat.label}</span>
                  </div>
                  <div className="font-mono text-[9px] text-neutral-600 mb-2 px-1 leading-snug">
                    {cat.subtitle} · <span className="text-neutral-500">{cat.signature}</span>
                  </div>
                  <div className="flex flex-col gap-0.5">
                    {cat.items.map(item => (
                      <PaletteItem
                        key={item.name}
                        fnName={item.name}
                        fn={item}
                        color={cat.color}
                        onClick={() => addFunction(item.name)}
                      />
                    ))}
                  </div>
                </section>
              ))}
            </div>
            <div className="mt-6 pt-4 border-t border-white/5 font-mono text-[9px] text-neutral-600 leading-relaxed">
              tip · click o drag para añadir al pipeline. reordena arrastrando nodos existentes.
            </div>
          </aside>

          {/* ─── DERECHA · EXPRESIÓN + PIPELINE + VISUALIZADOR ─── */}
          <section className="p-4 md:p-6 overflow-y-auto flex flex-col gap-5" style={{maxHeight: 'calc(100vh - 140px)'}}>
            {/* Expresión simbólica */}
            <div>
              <div className="flex items-baseline gap-3 mb-2">
                <span className="font-mono text-[10px] uppercase tracking-[0.25em] text-neutral-500">expresión</span>
                <span className="font-mono text-[9px] text-neutral-600">se aplica de derecha a izquierda</span>
              </div>
              <div className="rounded-lg bg-white/[0.03] border border-white/10 p-3">
                <code className="font-mono text-xs text-neutral-200 break-all leading-relaxed">
                  {expression}
                </code>
              </div>
            </div>

            {/* Pipeline */}
            <div>
              <div className="flex items-baseline gap-3 mb-2">
                <span className="font-mono text-[10px] uppercase tracking-[0.25em] text-neutral-500">pipeline</span>
                <span className="font-mono text-[10px] text-neutral-600">{pipeline.length} {pipeline.length === 1 ? 'nodo' : 'nodos'}</span>
              </div>
              <div
                ref={dropZoneRef}
                onDragOver={(e) => { e.preventDefault(); e.dataTransfer.dropEffect = 'copy'; }}
                onDrop={handleDropOnZone}
                className="rounded-xl border border-dashed border-white/10 p-5 transition-colors hover:border-white/20"
                style={{background: 'rgba(255,255,255,0.015)', minHeight: '180px'}}
              >
                {pipeline.length === 0 ? (
                  <div className="h-full flex flex-col items-center justify-center py-12 text-center">
                    <div className="font-display text-xl italic text-neutral-500 mb-2">zona de composición</div>
                    <div className="font-mono text-[10px] text-neutral-600 max-w-xs">arrastra una primitiva desde la izquierda. los nodos se encadenan de izquierda a derecha.</div>
                  </div>
                ) : (
                  <div className="flex flex-wrap gap-x-8 gap-y-4 items-start">
                    {steps.map((step, i) => (
                      <PipelineNode
                        key={step.id}
                        step={step}
                        index={i}
                        isLast={i === steps.length - 1}
                        onRemove={removeFunction}
                        onParamChange={changeParam}
                        onDragStart={setDragIndex}
                        onDragOver={setHoverIndex}
                        onDrop={handleDropOnNode}
                        isDragging={dragIndex === i}
                      />
                    ))}
                  </div>
                )}
              </div>
            </div>

            {/* Visualizador */}
            <div>
              <div className="font-mono text-[10px] uppercase tracking-[0.25em] text-neutral-500 mb-2">visualizador</div>
              <div className="rounded-lg border border-white/5 bg-white/[0.015] p-4" style={{minHeight: '220px'}}>
                <div className="h-full flex items-center justify-center">
                  <FinalView lastStep={lastStep} />
                </div>
              </div>
            </div>

            {/* Nota didáctica */}
            <div className="font-mono text-[10px] text-neutral-600 leading-relaxed border-l-2 border-neutral-800 pl-3">
              <span style={{color:'#7dd3fc'}}>anamorfismo</span> genera estructura · <span style={{color:'#c4b5fd'}}>functor map</span> transforma punto a punto ·{' '}
              <span style={{color:'#fcd34d'}}>filtro</span> refina · <span style={{color:'#86efac'}}>scan</span> acumula dejando rastro ·{' '}
              <span style={{color:'#fda4af'}}>catamorfismo</span> colapsa (es terminal)
            </div>
          </section>
        </main>
      </div>
    </div>
  );
}