"use client";
/* Variance over time — the pattern, not the number. A line short at every count is a different
   problem from one short once, so the chart is the point and the latest gap is the caption. */
import { useMemo } from "react";
import { useSnap } from "@/lib/client";
import { itemMap, monthLabel, variantName } from "@/lib/compute";
import { INK, MBody, MEmpty, MNav, MRule, MTop } from "@/components/m";

const MAX_BAR = 56;

export default function MVarianceOverTime() {
  const { s } = useSnap();

  const { rows, counts } = useMemo(() => {
    const byId = itemMap(s);
    // Oldest-first, shelf counts only, last six.
    const takes = s.stocktakes.filter((t) => t.mode !== "preloved").slice(0, 6).reverse();
    const seen: Record<string, { name: string; gaps: (number | null)[] }> = {};
    takes.forEach((t, col) => {
      for (const l of t.lines) {
        const k = `${l.itemId}:${l.si}`;
        const it = byId[l.itemId];
        if (!it) continue;
        (seen[k] ||= { name: variantName(it, it.sizes[l.si] ?? l.si), gaps: takes.map(() => null) });
        seen[k].gaps[col] = l.counted - l.sys;
      }
    });
    const out = Object.entries(seen).map(([k, v]) => {
      const known = v.gaps.filter((g): g is number => g !== null);
      const latest = [...v.gaps].reverse().find((g) => g !== null) ?? 0;
      const shortEvery = known.length >= 2 && known.every((g) => g < 0);
      const worsening = known.length >= 3 && known[known.length - 1] < known[0] && known[known.length - 1] < 0;
      const verdict = known.every((g) => g === 0) ? "Steady"
        : shortEvery ? `Short at every count since ${monthLabel(takes[v.gaps.findIndex((g) => g !== null)]?.date.slice(0, 7) || "", { month: "long" })}`
        : worsening ? "Drifting short"
        : latest === 0 ? "Back in line" : "Occasional gap";
      const persistent = shortEvery || worsening;
      return { key: k, name: v.name, gaps: v.gaps, latest, verdict, persistent };
    });
    // Worst pattern first: persistent problems, then biggest gap.
    out.sort((a, b) => Number(b.persistent) - Number(a.persistent) || a.latest - b.latest || a.name.localeCompare(b.name));
    return { rows: out, counts: takes };
  }, [s]);

  const peak = Math.max(1, ...rows.flatMap((r) => r.gaps.map((g) => Math.abs(g ?? 0))));

  return (
    <>
      <MTop title="Variance" back right={`${counts.length} count${counts.length === 1 ? "" : "s"}`} />
      <MRule />
      <MBody>
        <div style={{ padding: "20px 16px 22px", borderBottom: "2px solid " + INK }}>
          <h2 style={{ fontFamily: "var(--font-heading)", fontWeight: 800, fontSize: 30, letterSpacing: "-0.03em", lineHeight: 1.05 }}>What keeps going missing</h2>
          <p style={{ fontSize: 14, color: "var(--color-neutral-700)", marginTop: 8 }}>
            {counts.length ? `Gap against expected at each count since ${monthLabel(counts[0].date.slice(0, 7), { month: "long" })}.` : "Nothing counted yet."}
          </p>
        </div>

        {rows.length === 0 ? (
          <MEmpty title="No counts to compare yet" sub="File two stocktakes and the pattern starts showing here." />
        ) : rows.slice(0, 40).map((r) => (
          <div key={r.key} style={{ padding: "18px 16px 14px", background: r.persistent ? "#fff" : "var(--color-bg)", borderBottom: "1px solid var(--color-divider)" }}>
            <div style={{ display: "flex", alignItems: "flex-start", gap: 12 }}>
              <div style={{ flex: 1, minWidth: 0 }}>
                <div style={{ fontSize: 17, fontWeight: 700, letterSpacing: "-0.01em" }}>{r.name}</div>
                <div style={{ fontSize: 13.5, color: "var(--color-neutral-600)", marginTop: 3 }}>{r.verdict}</div>
              </div>
              <div style={{ fontFamily: "var(--font-heading)", fontWeight: 800, fontSize: r.latest === 0 ? 21 : 24, letterSpacing: "-0.02em", color: r.latest === 0 ? INK : "var(--color-accent-700)", fontVariantNumeric: "tabular-nums" }}>
                {r.latest === 0 ? "Match" : r.latest > 0 ? `+${r.latest}` : `−${-r.latest}`}
              </div>
            </div>

            <div className="tcx-chart" style={{ marginTop: 18 }} role="img"
              aria-label={`Gap at each count: ${r.gaps.map((g, i) => `${counts[i] ? monthLabel(counts[i].date.slice(0, 7), { month: "short" }) : ""} ${g === null ? "not counted" : g}`).join(", ")}`}>
              {r.gaps.map((g, i) => {
                const mag = Math.abs(g ?? 0);
                const h = g === null ? 4 : Math.max(4, Math.round((mag / peak) * MAX_BAR));
                const col = g === null ? "var(--color-neutral-300)" : mag === 0 ? "var(--color-divider)" : mag >= 3 ? "var(--color-accent)" : INK;
                return <i key={i} style={{ height: h, background: col }} />;
              })}
            </div>
            <div style={{ display: "flex", gap: 5, marginTop: 6 }}>
              {counts.map((t, i) => (
                <span key={i} style={{ flex: 1, textAlign: "center", fontSize: 10.5, fontWeight: 600, letterSpacing: "0.08em", textTransform: "uppercase", color: "var(--color-neutral-600)" }}>
                  {monthLabel(t.date.slice(0, 7), { month: "short" })}
                </span>
              ))}
            </div>
          </div>
        ))}
      </MBody>
      <MNav />
    </>
  );
}