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import { writeFile, readFile } from "fs";
import { promisify } from "util";
import { DatabaseInterface } from "./database.model";
import { Context } from "./context.model";
import { NaiveError, NaiveErrorCode as e } from "./error.model";
import { last } from "./util";
const splitPath = (path: string): string[] => path.split("/").filter(k => k);
const write = promisify(writeFile);
const read = promisify(readFile);
export const DEFAULT_CTX = {
logger: console.log,
cachePath: `${__dirname}/db.json`,
maxDbSizeMB: 6
};
/**
* Implementation of NoSQL DB that uses paths and objects.
*
* See DatabaseInterface for docs on public API
*
* Uses a plain object as a buffer and reads/writes to a
* plain JSON file. A better implementation could be backed
* by somethig a little nicer and not hold the buffer
* in memory
*/
export class Database implements DatabaseInterface {
private buff: any = {};
constructor(private ctx: Context = DEFAULT_CTX) {}
async init(): Promise<void> {
try {
const buff = await read(this.ctx.cachePath);
this.buff = JSON.parse(buff.toString());
} catch (e) {
this.ctx.logger("Failed to init database, using empty object");
this.ctx.logger(e);
}
}
// this currently runs synchronously,
// but only because we hold the entire DB in memory
// (which obviously becomes a bad idea at some point)
async read(path: string): Promise<Object> {
// root node case
if (path === "/") return this.buff;
const pathParts = splitPath(path);
return this.resolve(pathParts);
}
async write(path: string, toWrite: any): Promise<void> {
if (path === "/") {
this.buff = toWrite;
} else {
const pathParts = splitPath(path);
const writeTo = this.resolve(pathParts, false, 1);
writeTo[last(pathParts)] = toWrite;
}
await this.serialize();
}
remove(path: string): Promise<void> {
return this.write(path, null);
}
async flush(): Promise<void> {
this.buff = {};
await this.serialize();
}
toString() {
return JSON.stringify(this.buff);
}
/**
* Resolve the object located at path.
*
* If isRead == true, no new nodes will
* be created, and the function will return
* null if a null node is encountered on the path.
* Else, we create each node on the path.
*
* Level is used to determine how deep
* to recurse on path. Callers interested in
* writing may wish to stop higher up the tree.
*/
private resolve(
pathParts: string[],
isRead: boolean = true,
level: number = 0
): any {
// start at the root of our buffer
let lastNode = this.buff;
let node;
for (let i = 0; i < pathParts.length - level; i++) {
const part: string = pathParts[i];
// handle null node
if (!lastNode[part]) {
// if we're reading from the object
// we want to stop as soon
// as we hit a null node
if (isRead) {
return null;
}
// but if we're writing and the node is missing,
// we should make it and continue
else {
lastNode[part] = {};
}
}
// traverse to the next node
node = lastNode[part];
lastNode = node;
}
return node;
}
/**
* Serialize the current buffer
* into a plain file.
*
* Change the path by injecting custom
* Context
*
* Throws OUT_OF_SPACE
*/
private serialize(): Promise<void> {
if (!this.hasSpace()) throw new NaiveError(e.OUT_OF_SPACE);
return write(this.ctx.cachePath, this.toString());
}
private hasSpace(): boolean {
// convert from MB to B
return this.toString().length <= this.ctx.maxDbSizeMB * 1024 ** 2;
}
}
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