/**
 * The past year of attempts — LeetCode's calendar heatmap: one cell per day,
 * weeks as columns, each month its own block with a gap between, and the
 * year's attempt count, active days and longest streak above it. The colour
 * ramp is the README/email heatmap's (theme.css `--heat-0..4`, level =
 * attempts capped at 4) and rows start on Monday like it, so the three
 * heatmaps read the same. Drawn as SVG in a viewBox, so it scales to the
 * column instead of scrolling.
 */
import { StatsPending, TipRow, useHoverTip } from "../components/progress/shared";
import { Card, CardAction, CardContent, CardDescription, CardHeader, CardTitle } from "../components/ui/card";
import { type Stats, useStats, utcDate } from "../lib/stats";

export const client = "load";

const CELL = 10;
const STEP = 13; // cell + gap
const MONTH_GAP = 8;
const LABEL_H = 16;
const HEAT = ["var(--heat-0)", "var(--heat-1)", "var(--heat-2)", "var(--heat-3)", "var(--heat-4)"];

const MONTH = new Intl.DateTimeFormat("en-US", { month: "short", timeZone: "UTC" });
const DAY = new Intl.DateTimeFormat("en-US", { month: "short", day: "numeric", year: "numeric", timeZone: "UTC" });

interface Block {
  label: string;
  x: number;
  width: number;
  cells: { x: number; y: number; date: Date; attempts: number; passes: number }[];
}

/**
 * Month blocks laid left to right. Within a block a day sits at row =
 * weekday (Mon = 0) and column = its week counted from the block's first day,
 * so a month starting on a Thursday opens with a short first column.
 */
function layout(days: Stats["year"]["days"]): { blocks: Block[]; width: number } {
  const blocks: Block[] = [];
  let x = 0;
  let month = -1;
  let block: Block | undefined;
  let lead = 0;
  let index = 0;
  for (const day of days) {
    const date = utcDate(day.date);
    if (date.getUTCMonth() !== month) {
      if (block) x += block.width + MONTH_GAP;
      month = date.getUTCMonth();
      lead = (date.getUTCDay() + 6) % 7;
      index = 0;
      block = { label: MONTH.format(date), x, width: 0, cells: [] };
      blocks.push(block);
    }
    const row = (lead + index) % 7;
    const col = Math.floor((lead + index) / 7);
    block!.cells.push({ x: x + col * STEP, y: row * STEP, date, attempts: day.attempts, passes: day.passes });
    block!.width = (col + 1) * STEP - (STEP - CELL);
    index++;
  }
  return { blocks, width: block ? x + block.width : 0 };
}

export default function SubmissionHeatmap() {
  const load = useStats();
  const hover = useHoverTip<HTMLDivElement>();

  if (load.phase !== "ready") {
    return (
      <Card>
        <CardContent>
          <StatsPending load={load} className="h-32 w-full" />
        </CardContent>
      </Card>
    );
  }

  const { year } = load.stats;
  const { blocks, width } = layout(year.days);
  const height = 7 * STEP - (STEP - CELL) + LABEL_H;

  return (
    <Card>
      <CardHeader>
        <CardTitle className="flex items-baseline gap-2">
          <span className="font-semibold text-2xl tabular-nums">{year.attempts}</span>
          <span className="font-normal text-muted-foreground">attempts in the past one year</span>
        </CardTitle>
        <CardDescription>
          Total active days: <span className="text-foreground tabular-nums">{year.active_days}</span>
        </CardDescription>
        <CardAction className="text-muted-foreground text-sm">
          Max streak: <span className="text-foreground tabular-nums">{year.max_streak}</span>
        </CardAction>
      </CardHeader>
      <CardContent>
        <div ref={hover.ref} className="relative" onPointerLeave={hover.hide}>
          <svg viewBox={`0 0 ${width} ${height}`} className="h-auto w-full" role="img" aria-label="Attempts per day over the past year">
            {blocks.map((block) => (
              <g key={`${block.label}-${block.x}`}>
                {block.cells.map((cell) => (
                  <rect
                    key={cell.x * 1000 + cell.y}
                    x={cell.x}
                    y={cell.y}
                    width={CELL}
                    height={CELL}
                    rx={2}
                    fill={HEAT[Math.min(cell.attempts, 4)]}
                    onPointerMove={(event) =>
                      hover.show(
                        event,
                        <>
                          <div className="font-medium">{DAY.format(cell.date)}</div>
                          <TipRow color={HEAT[Math.min(cell.attempts, 4)]!} label="Attempts" value={cell.attempts} />
                          <TipRow color="var(--chart-4)" label="Passed" value={cell.passes} />
                        </>,
                      )
                    }
                  />
                ))}
                {block.width >= 2 * STEP && (
                  <text
                    x={block.x + block.width / 2}
                    y={height - 3}
                    textAnchor="middle"
                    className="fill-muted-foreground text-[9px]"
                  >
                    {block.label}
                  </text>
                )}
              </g>
            ))}
          </svg>
          {hover.node}
        </div>
      </CardContent>
    </Card>
  );
}