import { useMemo, type CSSProperties } from 'react';

export interface HeatmapCell {
  /** ISO date or any stable label. */
  date: string;
  /** Value — drives intensity. */
  value: number;
  /** Optional tooltip text. */
  label?: string;
}

export interface HeatmapProps {
  /** Cells laid out top-to-bottom then left-to-right (calendar style). */
  cells: HeatmapCell[];
  /** Rows. Default 7 (week). */
  rows?: number;
  /** Cell size in px (square). Default 12. */
  cell?: number;
  /** Gap between cells in px. Default 3. */
  gap?: number;
  /** Active color (interpolated by intensity). */
  color?: string;
  /** Empty cell color. */
  emptyColor?: string;
  ariaLabel?: string;
  className?: string;
  style?: CSSProperties;
}

/**
 * `<Heatmap>` — GitHub-style calendar heatmap. Pure CSS grid, no
 * tooltips library — uses native `title` attributes for the on-hover
 * label so the bundle stays tiny.
 */
export function Heatmap({
  cells,
  rows = 7,
  cell = 12,
  gap = 3,
  color = 'var(--bl-accent, #6366f1)',
  emptyColor = 'var(--bl-surface-muted, rgba(0,0,0,0.04))',
  ariaLabel,
  className,
  style,
}: HeatmapProps) {
  const max = useMemo(
    () => cells.reduce((m, c) => Math.max(m, c.value), 0) || 1,
    [cells],
  );
  return (
    <div
      data-testid="bl-heatmap"
      role="img"
      aria-label={ariaLabel ?? 'Activity heatmap'}
      className={className}
      style={{
        display: 'grid',
        gridTemplateRows: `repeat(${rows}, ${cell}px)`,
        gridAutoFlow: 'column',
        gap,
        ...style,
      }}
    >
      {cells.map((c, i) => {
        const intensity = c.value > 0 ? 0.15 + 0.85 * (c.value / max) : 0;
        return (
          <div
            key={`${c.date}-${i}`}
            data-testid={`bl-heatmap-cell-${i}`}
            data-value={c.value}
            data-intensity={intensity.toFixed(2)}
            title={c.label ?? `${c.date}: ${c.value}`}
            style={{
              width: cell,
              height: cell,
              borderRadius: 2,
              background:
                intensity === 0
                  ? emptyColor
                  : `color-mix(in srgb, ${color} ${Math.round(intensity * 100)}%, transparent)`,
              transition: 'transform 120ms ease',
            }}
          />
        );
      })}
    </div>
  );
}