import { GameRoot } from "../game/root";
import { clearBufferBacklog, freeCanvas, getBufferStats, makeOffscreenBuffer } from "./buffer_utils";
import { createLogger } from "./logging";
import { round1Digit } from "./utils";

/**
 * @typedef {{
 *  canvas: HTMLCanvasElement,
 *  context: CanvasRenderingContext2D,
 *  lastUse: number,
 * }} CacheEntry
 */

const logger = createLogger("buffers");

const bufferGcDurationSeconds = 10;

export class BufferMaintainer {
    /**
     * @param {GameRoot} root
     */
    constructor(root) {
        this.root = root;

        /** @type {Map<string, Map<string, CacheEntry>>} */
        this.cache = new Map();

        this.iterationIndex = 1;
        this.lastIteration = 0;
    }

    /**
     * Goes to the next buffer iteration, clearing all buffers which were not used
     * for a few iterations
     */
    garbargeCollect() {
        let totalKeys = 0;
        let deletedKeys = 0;
        const minIteration = this.iterationIndex;

        this.cache.forEach((subCache, key) => {
            let unusedSubKeys = [];

            // Filter sub cache
            subCache.forEach((cacheEntry, subKey) => {
                if (cacheEntry.lastUse < minIteration) {
                    unusedSubKeys.push(subKey);
                    freeCanvas(cacheEntry.canvas);
                    ++deletedKeys;
                } else {
                    ++totalKeys;
                }
            });

            // Delete unused sub keys
            for (let i = 0; i < unusedSubKeys.length; ++i) {
                subCache.delete(unusedSubKeys[i]);
            }
        });

        // Make sure our backlog never gets too big
        clearBufferBacklog();

        const bufferStats = getBufferStats();
        const mbUsed = round1Digit(bufferStats.vramUsage / (1024 * 1024));
        logger.log(
            "GC: Remove",
            (deletedKeys + "").padStart(4),
            ", Remain",
            (totalKeys + "").padStart(4),
            "(",
            (bufferStats.bufferCount + "").padStart(4),
            "total",
            ")",

            "(",
            (bufferStats.backlog + "").padStart(4),
            "backlog",
            ")",

            "VRAM:",
            mbUsed,
            "MB"
        );

        ++this.iterationIndex;
    }

    update() {
        const now = this.root.time.realtimeNow();
        if (now - this.lastIteration > bufferGcDurationSeconds) {
            this.lastIteration = now;
            this.garbargeCollect();
        }
    }

    /**
     *
     * @param {string} key
     * @param {string} subKey
     * @param {function(HTMLCanvasElement, CanvasRenderingContext2D, number, number, number, object?) : void} redrawMethod
     * @param {object=} additionalParams
     * @returns {HTMLCanvasElement}
     *
     */
    getForKey(key, subKey, w, h, dpi, redrawMethod, additionalParams) {
        // First, create parent key
        let parent = this.cache.get(key);
        if (!parent) {
            parent = new Map();
            this.cache.set(key, parent);
        }

        // Now search for sub key
        const cacheHit = parent.get(subKey);
        if (cacheHit) {
            cacheHit.lastUse = this.iterationIndex;
            return cacheHit.canvas;
        }

        // Need to generate new buffer
        const effectiveWidth = w * dpi;
        const effectiveHeight = h * dpi;

        const [canvas, context] = makeOffscreenBuffer(effectiveWidth, effectiveHeight, {
            reusable: true,
            label: "buffer-" + key + "/" + subKey,
            smooth: true,
        });

        redrawMethod(canvas, context, w, h, dpi, additionalParams);

        parent.set(subKey, {
            canvas,
            context,
            lastUse: this.iterationIndex,
        });
        return canvas;
    }
}