import { useMemo } from 'react';
import { Button } from '@astryxdesign/core/Button';
import { Text } from '@astryxdesign/core/Text';
import { VStack } from '@astryxdesign/core/VStack';
import { Download } from 'lucide-react';
import { encodeQr, qrPath } from './qr';

/**
 * One branch's storefront QR — the code, and a print-quality copy of it.
 *
 * ── Why the code is derived and not stored ──────────────────────────────────
 *
 * It encodes the literal JSON `{"tenantid":N,"locationid":M}` and nothing else:
 * not a URL, not the shop's name, not a token. The customer app reads those two
 * numbers and opens THAT outlet's storefront, which is the whole mechanism —
 * until somebody scans it the shop is not listed for them and they cannot
 * order.
 *
 * Two numbers that already exist means the code is unique per branch by
 * construction, and it cannot drift from the branch it belongs to, be lost, or
 * need a migration to reissue. Nothing is written to Fiesta and nothing needs
 * to be: reprinting a lost poster is opening this panel again.
 *
 * ── Why it is a component and not a page ────────────────────────────────────
 *
 * The same code has to appear at every moment somebody needs it — when a store
 * is onboarded, when a branch is commissioned, and any day after that from
 * either login. One component, one payload, so the poster taped to a counter
 * cannot disagree with the one printed a month later.
 */
export interface StoreQrPanelProps {
  tenantid: number;
  locationid: number;
  /** The branch's name, printed above the code and used for the file name. */
  locationname?: string;
  /** Suburb, city — whatever is worth reading under the name. */
  where?: string;
  /** On-screen size in px. The download is always 1024. */
  size?: number;
}

export function StoreQrPanel({
  tenantid,
  locationid,
  locationname,
  where,
  size = 220,
}: StoreQrPanelProps) {
  const payload = useMemo(
    () => JSON.stringify({ tenantid, locationid }),
    [tenantid, locationid],
  );
  const matrix = useMemo(() => encodeQr(payload), [payload]);
  const path = useMemo(() => qrPath(matrix), [matrix]);

  const quiet = 4;
  const span = matrix.length + quiet * 2;
  const name = locationname ?? 'your store';

  /**
   * The print copy, drawn at 1024px into a canvas that never enters the page.
   *
   * The on-screen SVG would scale, but a poster printed from a 220px raster is
   * soft, and a shop prints this once and lives with it.
   */
  function download() {
    const px = 1024;
    const canvas = document.createElement('canvas');
    canvas.width = px;
    canvas.height = px;
    const context = canvas.getContext('2d');
    if (!context) return;
    const scale = px / span;
    context.fillStyle = '#ffffff';
    context.fillRect(0, 0, px, px);
    context.fillStyle = '#000000';
    for (let y = 0; y < matrix.length; y += 1) {
      const row = matrix[y] as boolean[];
      for (let x = 0; x < row.length; x += 1) {
        if (!row[x]) continue;
        // Ceil, not round: a fractional module edge left hairline gaps between
        // neighbouring dark squares, which a scanner reads as a broken pattern.
        context.fillRect(
          Math.floor((x + quiet) * scale),
          Math.floor((y + quiet) * scale),
          Math.ceil(scale),
          Math.ceil(scale),
        );
      }
    }
    const link = document.createElement('a');
    link.download = `${slug(locationname ?? 'store')}-qr.png`;
    link.href = canvas.toDataURL('image/png');
    link.click();
  }

  return (
    <VStack gap={2} style={{ alignItems: 'center' }}>
      <VStack gap={0} style={{ alignItems: 'center' }}>
        <Text type="label" size="lg" weight="semibold">
          {locationname ?? 'Your store'}
        </Text>
        {where ? (
          <Text type="body" size="sm" color="secondary">
            {where}
          </Text>
        ) : null}
      </VStack>

      <div
        style={{
          padding: 10,
          borderRadius: 'var(--card-radius)',
          background: 'var(--card-bg)',
          border: 'var(--card-border)',
          lineHeight: 0,
        }}
      >
        <svg
          width={size}
          height={size}
          viewBox={`0 0 ${span} ${span}`}
          role="img"
          aria-label={`Storefront QR code for ${name}`}
          shapeRendering="crispEdges"
        >
          <rect width={span} height={span} fill="#ffffff" />
          <g transform={`translate(${quiet} ${quiet})`}>
            <path d={path} fill="#000000" />
          </g>
        </svg>
      </div>

      <Text
        type="body"
        size="sm"
        color="secondary"
        style={{ textAlign: 'center', lineHeight: 1.6, maxWidth: 300 }}
      >
        This code is this branch&apos;s alone. A shopper scans it to add the store to their app —
        until they do, it is not listed for them and they cannot order from it.
      </Text>

      <Button
        label="Download for print"
        variant="secondary"
        size="sm"
        icon={<Download size={14} />}
        onClick={download}
      />
    </VStack>
  );
}

/** A file name that survives a shop called "R mart — RS Puram". */
function slug(value: string): string {
  return (
    value
      .toLowerCase()
      .replace(/[^a-z0-9]+/g, '-')
      .replace(/^-+|-+$/g, '') || 'store'
  );
}