"use client";

import { useMemo, useState } from "react";
import ToolShell from "@/components/toolkit/ToolShell";
import { Card, CardHeader, CardTitle, CardContent } from "@/components/ui/card";
import { Input } from "@/components/ui/input";

function num(v: string) {
  const n = parseFloat(v);
  return Number.isFinite(n) ? n : 0;
}

// Focused Gaussian 1/e² diameter: d = 4 M² λ f / (π D).
export default function Page() {
  const [lambdaNm, setLambdaNm] = useState("1064"); // nm (default fiber)
  const [focalMm, setFocalMm] = useState("160");   // mm
  const [beamDm, setBeamDm] = useState("6");       // mm (input beam diameter at lens)
  const [m2, setM2] = useState("1.3");

  const dUm = useMemo(() => {
    const lamUm = num(lambdaNm) / 1000; // convert nm -> µm
    const f = num(focalMm);
    const D = num(beamDm);
    const M2 = num(m2);
    if (lamUm <= 0 || f <= 0 || D <= 0 || M2 < 1) return 0;
    return (4 / Math.PI) * M2 * lamUm * (f / D);
  }, [lambdaNm, focalMm, beamDm, m2]);

  const dMm = dUm / 1000;

  return (
    <ToolShell title="Beam Spot Size">
      <Card>
        <CardHeader>
          <CardTitle className="text-base">Inputs</CardTitle>
        </CardHeader>
        <CardContent className="grid gap-3 sm:grid-cols-4">
          <label className="text-[11px] sm:text-xs">
            <div className="mb-1 text-muted-foreground">Wavelength (nm)</div>
            <Input value={lambdaNm} onChange={(e) => setLambdaNm(e.target.value)} />
            <div className="mt-1 text-[11px] text-muted-foreground space-x-2">
              <button type="button" className="underline" onClick={() => setLambdaNm("1064")}>
                Fiber (1064 nm)
              </button>
              <button type="button" className="underline" onClick={() => setLambdaNm("10600")}>
                CO₂ (10600 nm)
              </button>
            </div>
          </label>

          <label className="text-[11px] sm:text-xs">
            <div className="mb-1 text-muted-foreground">Focal length (mm)</div>
            <Input value={focalMm} onChange={(e) => setFocalMm(e.target.value)} />
          </label>

          <label className="text-[11px] sm:text-xs">
            <div className="mb-1 text-muted-foreground">Beam Ø @ lens (mm)</div>
            <Input value={beamDm} onChange={(e) => setBeamDm(e.target.value)} />
          </label>

          <label className="text-[11px] sm:text-xs">
            <div className="mb-1 text-muted-foreground">M²</div>
            <Input value={m2} onChange={(e) => setM2(e.target.value)} />
          </label>
        </CardContent>
      </Card>

      <Card className="mt-4">
        <CardHeader>
          <CardTitle className="text-base">Result</CardTitle>
        </CardHeader>
        <CardContent className="grid gap-3 sm:grid-cols-2">
          <div>
            <div className="text-sm text-muted-foreground">1/e² spot diameter</div>
            <div className="text-lg">{dMm.toFixed(4)} mm</div>
            <div className="text-xs text-muted-foreground">{dUm.toFixed(2)} µm</div>
          </div>
          <div>
            <div className="text-sm text-muted-foreground">Spot radius</div>
            <div className="text-lg">{(dMm / 2).toFixed(4)} mm</div>
            <div className="text-xs text-muted-foreground">{(dUm / 2).toFixed(2)} µm</div>
          </div>
        </CardContent>
      </Card>
      <p className="mt-4 text-xs leading-relaxed text-muted-foreground">
        Gaussian-beam estimate: d = 4 M²λf/(πD), where D is the 1/e² beam diameter at the
        lens. Real spots may be larger because of lens aberration, clipping, beam expansion, and focus error.
      </p>
    </ToolShell>
  );
}