/**
 * The last six months of attempts — LeetCode's calendar heatmap, halved to
 * share its row with the submissions chart: one cell per day, weeks as
 * columns, each month its own block, and the window's attempt count, active
 * days and longest streak above it. The figures are counted from exactly the
 * cells drawn, so they cannot disagree with the grid. 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 its column instead of scrolling.
 */
import { StatsPending, TipRow, useHoverTip } from "../components/progress/shared";
import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "../components/ui/card";
import { type Day, useStats, utcDate } from "../lib/stats";

export const client = "load";

const MONTHS = 6;
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 Cell {
  x: number;
  y: number;
  date: Date;
  attempts: number;
  passes: number;
}

interface Block {
  label: string;
  x: number;
  width: number;
  cells: Cell[];
}

/**
 * Month blocks laid left to right over the last MONTHS calendar months. Within
 * a block a day sits at row = weekday (Mon = 0) and column = its week counted
 * from the 1st, so a month starting on a Thursday opens with a short column.
 */
function layout(year: Day[]): { blocks: Block[]; width: number } {
  const last = utcDate(year.at(-1)?.date ?? "1970-01-01");
  const from = Date.UTC(last.getUTCFullYear(), last.getUTCMonth() - (MONTHS - 1), 1);
  const blocks: Block[] = [];
  let x = 0;
  for (const day of year) {
    const date = utcDate(day.date);
    if (date.getTime() < from) continue;
    let block = blocks.at(-1);
    if (date.getUTCDate() === 1 || !block) {
      if (block) x += block.width + MONTH_GAP;
      block = { label: MONTH.format(date), x, width: 0, cells: [] };
      blocks.push(block);
    }
    const first = new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), 1));
    const index = (first.getUTCDay() + 6) % 7 + date.getUTCDate() - 1;
    const col = Math.floor(index / 7);
    block.cells.push({
      x: x + col * STEP,
      y: (index % 7) * STEP,
      date,
      attempts: day.attempts.easy + day.attempts.medium + day.attempts.hard,
      passes: day.passes,
    });
    block.width = col * STEP + CELL;
  }
  const end = blocks.at(-1);
  return { blocks, width: end ? end.x + end.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-40 w-full" />
        </CardContent>
      </Card>
    );
  }

  const { blocks, width } = layout(load.stats.year);
  const cells = blocks.flatMap((b) => b.cells);
  let run = 0;
  let streak = 0;
  for (const c of cells) {
    run = c.attempts > 0 ? run + 1 : 0;
    streak = Math.max(streak, run);
  }
  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">{cells.reduce((n, c) => n + c.attempts, 0)}</span>
          <span className="font-normal text-muted-foreground text-sm">attempts in the past {MONTHS} months</span>
        </CardTitle>
        <CardDescription className="flex gap-4">
          <span>
            Active days:{" "}
            <span className="text-foreground tabular-nums">{cells.filter((c) => c.attempts > 0).length}</span>
          </span>
          <span>
            Max streak: <span className="text-foreground tabular-nums">{streak}</span>
          </span>
        </CardDescription>
      </CardHeader>
      <CardContent className="flex flex-1 items-center">
        <div ref={hover.ref} className="relative w-full" onPointerLeave={hover.hide}>
          <svg
            viewBox={`0 0 ${width} ${height}`}
            className="h-auto w-full"
            role="img"
            aria-label={`Attempts per day over the past ${MONTHS} months`}
          >
            {blocks.map((block) => (
              <g key={`${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} />
                        </>,
                      )
                    }
                  />
                ))}
                <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>
  );
}