render in queue

ppfun-bridge/src/pixelplanet/constants.js

@@ -4,3 +4,4 @@ export const MAX_SCALE = 40; // 52 in log2
 export const TILE_SIZE = 256;
 export const TILE_ZOOM_LEVEL = 2;
 export const BACKGROUND_CLR_RGB = [ 196, 196, 196 ];
+export const QUEUE_LIMIT = 3;

ppfun-bridge/src/pixelplanet/index.js

@@ -2,6 +2,7 @@ import fetch from 'node-fetch';
 
 import canvases from './canvases.js';
 import renderCanvas from './renderCanvas.js';
+import { QUEUE_LIMIT }  from './constants.js';
 
 const linkRegExp = /(#[a-z]*,-?[0-9]*,-?[0-9]*(,-?[0-9]+)?)/gi;
 const linkRegExpFilter = (val, ind) => ((ind % 3) !== 2);
@@ -17,8 +18,50 @@ function compArray(arr1, arr2) {
   return true;
 }
 
-export async function parseCanvasLinks(text) {
+/*
+ * render canvas snapshots sequentially in a queue,
+ * don't repeat most recent render
+ */
+const queue = [];
+let rendering = false;
+let lastTitle = '';
 
+async function render() {
+  if (!queue.length) {
+    rendering = false;
+    return;
+  }
+  rendering = true;
+  const [args, resolve, reject] = queue.shift();
+  try {
+    const ret = await renderCanvas(...args);
+    resolve(ret);
+    setTimeout(render, 100);
+  } catch (err) {
+    reject(err)
+  }
+}
+
+function renderCanvasQueue(...args) {
+  if (queue.length >= QUEUE_LIMIT || args[0] === lastTitle) {
+    return null;
+  }
+  return new Promise((resolve, reject) => {
+    lastTitle = args[0];
+    queue.push([args, resolve, reject]);
+    if (!rendering) {
+      setImmediate(render);
+    }
+  });
+}
+
+/**
+ * check if canvas link is in message and return screenshot of the
+ * current canvas if so
+ * @param text message text
+ * @return object with image, name, type, w, h, size
+ */
+export async function parseCanvasLinks(text) {
   if (!text || !canvases) {
     return null;
   }
@@ -50,9 +93,10 @@ export async function parseCanvasLinks(text) {
   ) {
     return;
   }
-  console.log(`Fetch canvas ${canvas.title} on ${x}/${y} with zoom ${z}`);
-
-  const imageData = await renderCanvas(canvas, x, y, z);
+  
+  const title = `${canvas.title}_${x}_${y}_${z}`;
+  console.log(`Fetch canvas ${title}`);
+  const imageData = await renderCanvasQueue(title, canvas, x, y, z);
 
   return imageData;
 }