"use client";
/* Size exchange — one movement, not a return followed by an issue. What comes back, what goes out,
   and the staff record updated so nobody hands them the wrong size again next month. */
import { useCallback, useMemo, useState } from "react";
import { useParams, useRouter } from "next/navigation";
import { useDerived, useSnap } from "@/lib/client";
import { isPantItem, isTopItem, key, label, onhand, staffName } from "@/lib/compute";
import MScan from "@/components/MScan";
import { GROUND, INK, MBar, MBody, MChips, MEmpty, MError, MRow, MRule, MSection, MTop } from "@/components/m";
import { useHeld, type Held } from "@/components/MPerson";

export default function MExchange() {
  const { s, mutate, busy } = useSnap();
  const { L, byId } = useDerived();
  const router = useRouter();
  const id = String(useParams().id || "");
  const st = s.staff.find((x) => x.id === id);
  const held = useHeld(s, id);

  const [pick, setPick] = useState<Held | null>(null);
  const [si, setSi] = useState(-1);
  const [scan, setScan] = useState(false);
  const [err, setErr] = useState("");

  const it = pick ? byId[pick.itemId] : undefined;
  const stock = useMemo(() => {
    if (!it) return [] as number[];
    return it.sizes.map((_, i) => onhand(s, L, key(it.id, i)));
  }, [it, s, L]);

  const onCode = useCallback((raw: string) => {
    const k = s.barcodes[raw.trim()];
    const hit = held.find((h) => h.key === k);
    if (!hit) { setErr(`${raw.trim()} isn’t something ${st?.first ?? "they"} is holding.`); return; }
    setPick(hit); setSi(-1); setErr("");
  }, [s.barcodes, held, st]);

  if (!st) return (<><MTop title="Exchange" back /><MRule /><MBody><MEmpty title="No such staff member" /></MBody></>);

  const commit = async () => {
    if (!pick || si < 0) return;
    const r = await mutate<{ size: string }>("issue.exchange", { id: pick.issues[0].id, si, qty: 1 });
    if (!r.ok) { setErr(r.error); return; }
    router.push(`/m/person/${st.id}`);
  };

  const willUpdate = it && (isTopItem(it) || isPantItem(it));

  return (
    <>
      <MTop title="Exchange" back right={staffName(st)} />
      <MRule />
      <MError msg={err} onDismiss={() => setErr("")} />
      <MBody>
        {!pick ? (
          <>
            <MSection label="What doesn’t fit?" right={`${held.reduce((t, h) => t + h.qty, 0)} out`} />
            {held.length === 0
              ? <MEmpty title="Nothing to exchange" sub={`${staffName(st)} has no garments out at the moment.`} />
              : held.map((h) => <MRow key={h.key} onClick={() => { setPick(h); setSi(-1); }} mark="ink" title={h.name} sub={`${h.qty} held`} />)}
            {/* Same rule as the return screen: the scan bar is off when nothing is out, so the line
                offering a scan goes with it. */}
            {held.length > 0 && <div style={{ padding: "18px 16px", fontSize: 14, color: "var(--color-neutral-700)" }}>Or scan the garment they’ve brought back.</div>}
          </>
        ) : (
          <>
            <section style={{ background: INK, color: GROUND, padding: 16 }}>
              <div style={{ fontSize: 11, fontWeight: 600, letterSpacing: "0.12em", textTransform: "uppercase", color: "var(--color-accent-300)" }}>Taking back</div>
              <div style={{ display: "flex", alignItems: "center", gap: 12, marginTop: 8 }}>
                <span aria-hidden="true" style={{ width: 4, height: 34, background: "#fff" }} />
                <span style={{ fontFamily: "var(--font-heading)", fontWeight: 800, fontSize: 20, letterSpacing: "-0.02em" }}>{pick.name}</span>
              </div>
              <button onClick={() => setPick(null)} style={{ marginTop: 12, background: "none", border: 0, padding: 0, color: "#fff", fontSize: 13, fontWeight: 700, textDecoration: "underline", textUnderlineOffset: 3, cursor: "pointer" }}>Choose a different garment</button>
            </section>

            <MSection label="Giving out" right={it ? label(it) : ""} />
            <div style={{ padding: 16 }}>
              <div style={{ display: "flex", alignItems: "center", gap: 12 }}>
                <span aria-hidden="true" style={{ width: 4, height: 34, background: "var(--color-accent)" }} />
                <span style={{ fontSize: 14, color: "var(--color-neutral-700)" }}>Pick the size that fits. Greyed sizes are the one coming back, or have none on the shelf.</span>
              </div>
              {it && <MChips sizes={it.sizes.map(String)} value={si} onPick={(i) => setSi(i)} disabled={(i) => i === pick.si || stock[i] <= 0} />}
              {si >= 0 && it && (
                <p style={{ fontSize: 13.5, color: "var(--color-neutral-700)", marginTop: 14, lineHeight: 1.6 }}>
                  {stock[si]} on the shelf in size {it.sizes[si]}. The old garment goes back to stock in the same movement
                  {willUpdate ? `, and ${st.first}’s recorded size becomes ${it.sizes[si]}.` : "."}
                </p>
              )}
            </div>
          </>
        )}
      </MBody>

      {pick
        ? <MBar label={busy ? "Recording…" : si >= 0 && it ? `Exchange for size ${it.sizes[si]}` : "Pick a size"} glyph="check" onClick={commit} disabled={busy || si < 0} />
        : <MBar label="Scan the garment" glyph="scan" onClick={() => setScan(true)} disabled={held.length === 0} />}

      {scan && <MScan title="Scan the garment" onHit={(r) => { onCode(r); setScan(false); }} onClose={() => setScan(false)} />}
    </>
  );
}