/* kineticslab.jsx — KineticsTutor: the reaction-kinetics bench. Built on window.BenchKit
   (harness) + window.BenchFields (shared field math), so this file is just the FIGURE.
   computeFields = window.BenchFields.kinetics — the SAME function server/benches/kinetics.js
   calls, so client and server fields are identical by construction. A single reactant decays
   under rate = k[A]ⁿ: sliders → BenchFields.fn(state) → report + meters. */
(function () {
  const { useState, useMemo, useEffect } = React;
  const K = window.BenchKit, C = K.C, SVG_BG = K.SVG_BG, fmt = K.fmt;
  const TaskStrip = K.TaskStrip, StatMeter = K.StatMeter;
  const compute = (s) => window.BenchFields.kinetics(s);

  function Slider({ label, value, set, min, max, step, unit, color, onUp }) {
    return (
      <div style={{ display: "flex", alignItems: "center", gap: 10, marginTop: 9 }}>
        <span style={{ fontSize: 12, color: C.mute, width: 116 }}>{label}</span>
        <input type="range" min={min} max={max} step={step} value={value} onChange={(e) => set(parseFloat(e.target.value))} onPointerUp={onUp} style={{ flex: 1 }} />
        <span style={{ color: color || C.amber, width: 64, textAlign: "right" }}>{value}{unit ? ` ${unit}` : ""}</span>
      </div>
    );
  }

  function KineticsFig({ task, setTask, tasks, report, event, done }) {
    const [concA, setConcA] = useState(1);
    const [rateConstant, setRateConstant] = useState(0.5);
    const [order, setOrder] = useState(1);
    const fld = useMemo(() => compute({ concA, rateConstant, order }), [concA, rateConstant, order]);
    useEffect(() => { report(fld); }, [concA, rateConstant, order]); // eslint-disable-line

    // concentration-vs-time decay curve, shaped qualitatively by the order; steepness ∝ rate.
    const X0 = 70, X1 = 540, AY0 = 50, AY1 = 250;
    const span = 12; // arbitrary "time" window
    // [A](t) for the chosen order, qualitatively (avoid blow-ups; just for the shape).
    const conc = (t) => {
      if (order === 0) return Math.max(0, concA - rateConstant * t);
      if (order === 2) return concA / (1 + rateConstant * concA * t);
      return concA * Math.exp(-rateConstant * t); // first order
    };
    const N = 60;
    const pts = [];
    for (let i = 0; i <= N; i++) {
      const t = (i / N) * span;
      const cx = X0 + (i / N) * (X1 - X0);
      const cy = AY1 - (conc(t) / 5) * (AY1 - AY0); // [A] axis 0..5 M
      pts.push(`${cx.toFixed(1)},${Math.max(AY0, Math.min(AY1, cy)).toFixed(1)}`);
    }
    // half-life marker: find t where [A] = [A]/2 within the window.
    const half = concA / 2;
    let tHalf = null;
    for (let i = 0; i <= N; i++) { const t = (i / N) * span; if (conc(t) <= half) { tHalf = t; break; } }
    const hlX = tHalf != null ? X0 + (tHalf / span) * (X1 - X0) : null;
    const hlY = AY1 - (half / 5) * (AY1 - AY0);

    const t = tasks.find((x) => x.id === task) || tasks[0];
    const rate = fld.rate, fast = fld.isFast;

    return (
      <>
        <TaskStrip tasks={tasks} cur={task} setCur={setTask} done={done} goal={t && t.goal} />
        <svg viewBox="0 0 600 300" style={{ width: "100%", background: SVG_BG, border: `1px solid ${C.line}`, borderRadius: 8 }}>
          {/* axes */}
          <line x1={X0} y1={AY0} x2={X0} y2={AY1} stroke={C.faint} strokeWidth="1.5" />
          <line x1={X0} y1={AY1} x2={X1} y2={AY1} stroke={C.faint} strokeWidth="1.5" />
          <text x={X0 - 8} y={AY0 + 4} textAnchor="end" fill={C.mute} fontSize="10" fontFamily="monospace">[A]</text>
          <text x={X1} y={AY1 + 16} textAnchor="end" fill={C.mute} fontSize="10" fontFamily="monospace">time →</text>
          {/* decay curve */}
          <polyline points={pts.join(" ")} fill="none" stroke={fast ? C.crimson : C.teal} strokeWidth="2.5" />
          {/* half-life marker */}
          {hlX != null && <>
            <line x1={hlX} y1={hlY} x2={hlX} y2={AY1} stroke={C.gold} strokeWidth="1.5" strokeDasharray="4 3" />
            <line x1={X0} y1={hlY} x2={hlX} y2={hlY} stroke={C.gold} strokeWidth="1.5" strokeDasharray="4 3" />
            <circle cx={hlX} cy={hlY} r={4} fill={C.gold} />
            <text x={hlX + 6} y={hlY - 6} fill={C.gold} fontSize="10" fontFamily="monospace">t½ = {fmt(fld.halfLifeRxn)}</text>
          </>}
          <text x={X0 + 6} y={AY0 - 6} fill={C.mute} fontSize="11" fontFamily="monospace">[A] = {fmt(concA)} M · k = {fmt(rateConstant)} · n = {order}</text>
          <text x={(X0 + X1) / 2} y={AY0 + 18} textAnchor="middle" fill={C.ink} fontSize="13" fontFamily="monospace">rate = k[A]ⁿ = {fmt(rate)}</text>
        </svg>
        <div style={{ marginTop: 10, padding: "8px 12px", borderRadius: 6, background: C.panel, border: `1px solid ${fast ? C.crimson : C.line}`, color: fast ? C.crimson : C.mute, fontSize: 12.5 }}>
          rate = k[A]ⁿ = {fmt(rate)}. {fast ? "⚡ fast reaction." : "Raise k, [A] or the order n to speed it up."}
        </div>
        <Slider label="concentration [A]" value={concA} set={setConcA} min={0.1} max={5} step={0.1} unit="M" color={C.blue} onUp={() => event("adjusted", `Set [A] = ${fmt(concA)} M`, { response: `rate ${fmt(fld.rate)}` }, C.blue)} />
        <Slider label="rate constant k" value={rateConstant} set={setRateConstant} min={0.01} max={2} step={0.01} unit="" color={C.amber} onUp={() => event("adjusted", `Set k = ${fmt(rateConstant)}`, { response: `rate ${fmt(fld.rate)}` }, C.amber)} />
        <Slider label="reaction order n" value={order} set={setOrder} min={0} max={2} step={1} unit="" color={C.crimson} onUp={() => event("adjusted", `Set n = ${order}`, { response: `rate ${fmt(fld.rate)}` }, C.crimson)} />
        <div style={{ display: "grid", gridTemplateColumns: "repeat(4,1fr)", gap: 8, marginTop: 12 }}>
          <StatMeter label="rate" v={fld.rate} d={2} color={fast ? C.crimson : C.teal} />
          <StatMeter label="rate constant k" v={fld.rateConstant} d={2} color={C.amber} />
          <StatMeter label="order n" v={fld.order} d={0} color={C.crimson} />
          <StatMeter label="half-life t½" v={fld.halfLifeRxn} d={2} color={C.gold} />
        </div>
      </>
    );
  }

  window.KineticsTutor = K.makeTutor(KineticsFig, { moduleLabel: "Reaction kinetics bench", benchId: "kinetics" });
})();