const DEFAULT_MAX_BYTES = 128 * 1024 * 1024;

const DEFAULT_MAX_ENTRIES = 128;

function bitmapBytes(canvas) {

return canvas.width * canvas.height * 4;

}

function zeroCanvas(canvas) {

canvas.width = 0;

canvas.height = 0;

}

export class BitmapCache {

#entries = new Map();

#bytes = 0;

#maxBytes;

#maxEntries;

constructor({ maxBytes = DEFAULT_MAX_BYTES, maxEntries = DEFAULT_MAX_ENTRIES } = {}) {

this.#maxBytes = maxBytes;

this.#maxEntries = maxEntries;

}

get(key) {

const entry = this.#entries.get(key);

if (!entry) return undefined;

this.#entries.delete(key);

this.#entries.set(key, entry);

return entry.canvas;

}

set(key, canvas) {

const bytes = bitmapBytes(canvas);

if (bytes > this.#maxBytes || this.#maxEntries <= 0) return false;

const existing = this.#entries.get(key);

if (existing) {

this.#entries.delete(key);

this.#bytes -= existing.bytes;

if (existing.canvas !== canvas) this.#release(existing.canvas);

}

while (this.#entries.size >= this.#maxEntries || this.#bytes + bytes > this.#maxBytes) {

const [oldestKey, oldest] = this.#entries.entries().next().value;

this.#entries.delete(oldestKey);

this.#bytes -= oldest.bytes;

this.#release(oldest.canvas, canvas);

}

this.#entries.set(key, { canvas, bytes });

this.#bytes += bytes;

return true;

}

delete(key) {

const entry = this.#entries.get(key);

if (!entry) return false;

this.#entries.delete(key);

this.#bytes -= entry.bytes;

this.#release(entry.canvas);

return true;

}

clear() {

const canvases = new Set();

for (const entry of this.#entries.values()) canvases.add(entry.canvas);

this.#entries.clear();

this.#bytes = 0;

for (const canvas of canvases) zeroCanvas(canvas);

}

stats() {

return {

bytes: this.#bytes,

entries: this.#entries.size,

maxBytes: this.#maxBytes,

maxEntries: this.#maxEntries,

};

}

#release(canvas, protectedCanvas) {

if (canvas === protectedCanvas) return;

for (const entry of this.#entries.values()) {

if (entry.canvas === canvas) return;

}

zeroCanvas(canvas);

}

}