import { fmtValue } from '@/lib/format';

export interface TrendSeries {
  key: string;
  name: string;
  href?: string;
  points: Array<{ x: number; y: number }>;
  dashed?: boolean; // estimated / projected values
}

/**
 * Eight-way colour set that stays distinguishable in print and for common colour-vision deficiencies;
 * shape (dash) and the legend label carry the meaning too — colour is never the only carrier.
 */
const TREND_COLORS = ['var(--color-series-1)', 'var(--color-series-2)', 'var(--color-series-5)', 'var(--color-series-4)', 'var(--color-series-3)', 'var(--color-series-7)', 'var(--color-series-6)', 'var(--color-series-8)'];

/**
 * Multi-series yearly line chart in pure SVG for country trend panels (up to 8 series). Zero-based y axis,
 * light grid, year ticks, end-of-line labels when space allows, plus a text legend with the last value.
 */
export function TrendChart({ series, unit, ariaLabel, height = 300, yLabel }: { series: TrendSeries[]; unit?: string | null; ariaLabel: string; height?: number; yLabel?: string }) {
  const shown = series.filter((s) => s.points.length > 0).slice(0, TREND_COLORS.length);
  const all = shown.flatMap((s) => s.points);
  if (all.length === 0) return null;
  const xs = all.map((p) => p.x);
  const xMin = Math.min(...xs);
  const xMax = Math.max(...xs);
  const yMax = Math.max(...all.map((p) => p.y), Number.EPSILON) * 1.08;
  const width = 760;
  const pad = { l: 58, r: 16, t: 12, b: 30 };
  const iw = width - pad.l - pad.r;
  const ih = height - pad.t - pad.b;
  const sx = (x: number) => pad.l + (xMax === xMin ? iw / 2 : ((x - xMin) / (xMax - xMin)) * iw);
  const sy = (y: number) => pad.t + ih - (y / yMax) * ih;
  const yTicks = 5;
  const span = xMax - xMin;
  const step = span <= 8 ? 1 : span <= 16 ? 2 : span <= 30 ? 5 : 10;
  const xTicks: number[] = [];
  for (let x = Math.ceil(xMin / step) * step; x <= xMax; x += step) xTicks.push(x);
  if (!xTicks.includes(xMin)) xTicks.unshift(xMin);
  if (!xTicks.includes(xMax)) xTicks.push(xMax);

  return (
    <figure className="w-full">
      <div className="overflow-x-auto">
        <svg viewBox={`0 0 ${width} ${height}`} width="100%" role="img" aria-label={ariaLabel} className="block min-w-[520px]">
          <title>{ariaLabel}</title>
          {Array.from({ length: yTicks + 1 }, (_, i) => {
            const v = (yMax / yTicks) * i;
            const y = sy(v);
            return (
              <g key={i}>
                <line x1={pad.l} x2={width - pad.r} y1={y} y2={y} stroke="var(--color-rule)" strokeWidth="1" />
                <text x={pad.l - 6} y={y + 4} textAnchor="end" fontSize="11" fill="var(--color-ink-3)" style={{ fontVariantNumeric: 'tabular-nums' }}>
                  {fmtValue(v, unit)}
                </text>
              </g>
            );
          })}
          {yLabel ? (
            <text x={pad.l} y={pad.t - 2} fontSize="10.5" fill="var(--color-ink-3)">
              {yLabel}
            </text>
          ) : null}
          {xTicks.map((x) => (
            <g key={x}>
              <line x1={sx(x)} x2={sx(x)} y1={pad.t + ih} y2={pad.t + ih + 4} stroke="var(--color-rule-strong)" />
              <text x={sx(x)} y={height - 9} textAnchor="middle" fontSize="11" fill="var(--color-ink-3)">
                {x}
              </text>
            </g>
          ))}
          {shown.map((s, si) => {
            const pts = [...s.points].sort((a, b) => a.x - b.x);
            const color = TREND_COLORS[si % TREND_COLORS.length];
            const d = pts.map((p, i) => `${i === 0 ? 'M' : 'L'}${sx(p.x).toFixed(1)},${sy(p.y).toFixed(1)}`).join(' ');
            return (
              <g key={s.key}>
                <path d={d} fill="none" stroke={color} strokeWidth="1.75" strokeDasharray={s.dashed ? '4 3' : undefined} strokeLinejoin="round" />
                {pts.map((p) => (
                  <circle key={p.x} cx={sx(p.x)} cy={sy(p.y)} r="2" fill={color}>
                    <title>{`${s.name} — ${p.x}: ${fmtValue(p.y, unit)}`}</title>
                  </circle>
                ))}
              </g>
            );
          })}
        </svg>
      </div>
      <figcaption className="mt-1.5 grid grid-cols-1 gap-x-4 gap-y-1 text-[12px] text-ink-2 sm:grid-cols-2 lg:grid-cols-4">
        {shown.map((s, si) => {
          const last = [...s.points].sort((a, b) => a.x - b.x).at(-1);
          return (
            <span key={s.key} className="inline-flex min-w-0 items-baseline gap-1.5">
              <span className="inline-block h-[3px] w-4 shrink-0 self-center" style={{ background: s.dashed ? 'transparent' : TREND_COLORS[si % TREND_COLORS.length], borderTop: s.dashed ? `2px dashed ${TREND_COLORS[si % TREND_COLORS.length]}` : undefined }} aria-hidden />
              {s.href ? (
                <a className="ci-link truncate" href={s.href}>
                  {s.name}
                </a>
              ) : (
                <span className="truncate">{s.name}</span>
              )}
              {last ? (
                <span className="ci-num shrink-0 text-ink-3">
                  {fmtValue(last.y, unit)} <span className="text-[10.5px]">({last.x})</span>
                </span>
              ) : null}
              {s.dashed ? <span className="text-[10.5px] italic text-warn">estimated</span> : null}
            </span>
          );
        })}
      </figcaption>
    </figure>
  );
}