74 lines
2.1 KiB
TypeScript
74 lines
2.1 KiB
TypeScript
import { createHash } from 'crypto';
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import { existsSync, mkdirSync, statSync, createReadStream, writeFileSync } from 'fs';
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import { join } from 'path';
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import type { Readable } from 'stream';
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const MAX_AGE_MS = 24 * 60 * 60 * 1000; // 24 hours
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export class ScreenshotCache {
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private dir: string;
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constructor(dir: string) {
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this.dir = dir;
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if (!existsSync(dir)) {
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mkdirSync(dir, { recursive: true });
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}
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}
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/**
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* Build a cache key by quantizing view params and hashing.
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* lat/lon are rounded to 2 decimals and zoom to an integer so nearby views
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* share a cache entry; all other params are sorted for order-independence.
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*/
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buildKey(params: URLSearchParams): string {
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const normalized: Record<string, string> = {};
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const lat = params.get('lat');
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const lon = params.get('lon');
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const zoom = params.get('zoom');
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if (lat && lon && zoom) {
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normalized.lat = parseFloat(lat).toFixed(2);
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normalized.lon = parseFloat(lon).toFixed(2);
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normalized.zoom = Math.round(parseFloat(zoom)).toString();
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}
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const quantized = new Set(['lat', 'lon', 'zoom']);
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const keys = [...new Set(params.keys())].filter((k) => !quantized.has(k)).sort();
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for (const key of keys) {
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normalized[key] = params.getAll(key).sort().join(',');
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}
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const input = JSON.stringify(normalized);
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const hash = createHash('sha256').update(input).digest('hex').substring(0, 16);
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return hash;
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}
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getPath(key: string): string {
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return join(this.dir, `${key}.jpg`);
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}
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/**
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* Returns a readable stream if a fresh cached file exists, null otherwise.
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*/
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get(key: string): Readable | null {
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const path = this.getPath(key);
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if (!existsSync(path)) return null;
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try {
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const stat = statSync(path);
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const age = Date.now() - stat.mtimeMs;
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if (age > MAX_AGE_MS) return null;
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return createReadStream(path);
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} catch {
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return null;
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}
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}
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/**
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* Write screenshot bytes to cache.
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*/
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set(key: string, data: Buffer): void {
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const path = this.getPath(key);
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writeFileSync(path, data);
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}
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}
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