import { dynvar } from "@thi.ng/dynvar";
import { appendFileSync } from "fs";

interface Logger {
    log(...args: any[]): void;
}

// create dynamically scoped variable
// set default/root binding
const logger = dynvar<Logger>(console);

// dummy function using `logger`
const foo = () => {
    // deref() returns var's current value
    logger.deref().log("begin foo...");
    for (let i = 0; i < 5; i++) {
        logger.deref().log(i);
    }
    logger.deref().log("foo done.");
};

foo();
// (output in console)
// begin foo...
// 0
// 1
// 2
// 3
// 4
// foo done.

// Alternative Logger impl
class FileLogger implements Logger {
    constructor(protected path: string) {}

    log(...args: any[]) {
        appendFileSync(this.path, args.join(", ") + "\n");
    }
}

// re-execute `foo` with temporary dynamic scope in which
// logger is bound to given new value (i.e. here file logger)
logger.withBinding(new FileLogger("./foo.txt"), foo);

// old scope again (back to using console)
logger.deref().log("good bye");
// "good bye"