import type { Font, Measure } from "./types.js";

export const fontString = (font: Font) =>
  `${font.italic ? "italic " : ""}${font.weight === "bold" ? "bold " : ""}${font.size}px ${font.family}`;

// A bounded per-surface cache replaces the original global memoizee cache.
// Font loading creates a new measure/layout so fallback metrics cannot persist.
export function canvasMeasure(context: CanvasRenderingContext2D, maximum = 12000): Measure {
  const cache = new Map<string, ReturnType<Measure>>();
  return (text, font) => {
    const key = `${fontString(font)}/${text}`;
    const cached = cache.get(key);
    if (cached) return cached;
    context.font = fontString(font);
    const metrics = context.measureText(text);
    const value = {
      width: Math.max(0, metrics.width),
      ascent: Math.max(metrics.actualBoundingBoxAscent || 0, font.size * 0.85),
      descent: Math.max(metrics.actualBoundingBoxDescent || 0, font.size * 0.22),
    };
    if (cache.size >= maximum) cache.clear();
    cache.set(key, value);
    return value;
  };
}