cache.ts

import { pathUtils } from './deps.ts'
import { readBytes, readDir, writeBytes } from './fs.ts'
import { Md5 } from './mod.ts'

export class FsCache {
	#dir: string
	#encoder = new TextEncoder()
	#decoder = new TextDecoder()

	constructor(scope?: string) {
		const subDir = scope ?? getFallbackScope()
		this.#dir = pathUtils.join(getCacheDirectory(), subDir)
	}

	#refineKey(key: string) {
		return btoa(key)
	}

	#unRefineKey(key: string) {
		return atob(key)
	}

	/** Set a cache entry at `key`. Entry can be either a string or plain bytes */
	async set(key: string, content: string | Uint8Array): Promise<void> {
		const bytes = typeof content === 'string' ? this.#encoder.encode(content) : content
		await writeBytes(pathUtils.join(this.#dir, this.#refineKey(key)), bytes)
	}

	/** Get cache entry `key` as a string */
	async getString(key: string): Promise<string | null> {
		const bytes = await this.getBytes(key)
		if (!bytes) return null

		return this.#decoder.decode(bytes)
	}

	/** Get a cache entry `key` as bytes */
	async getBytes(key: string): Promise<Uint8Array | null> {
		return await readBytes(pathUtils.join(this.#dir, this.#refineKey(key)))
	}

	/** List all the keys in this particular cache */
	async list(): Promise<string[]> {
		return await readDir(this.#dir).then((keys) => keys.map((key) => this.#unRefineKey(key)))
	}

	/** Removes all entries under `scope` in cache dir */
	async clear(): Promise<void> {
		try {
			const stat = await Deno.stat(this.#dir)
			if (!stat.isDirectory) return

			for await (const file of Deno.readDir(this.#dir)) {
				if (!file.isFile) continue

				await Deno.remove(pathUtils.join(this.#dir, file.name))
			}
		} catch (_) {
			return
		}
	}
}

function getFallbackScope() {
	return Md5.hash(Deno.mainModule)
}

function getCacheDirectory() {
	const home = Deno.env.get('HOME')
	if (!home) throw new Error('Could not detect users HOME directory')

	return pathUtils.join(home, '.cache', 'fs_cache')
}