import {assertEquals} from "https://deno.land/std@0.224.0/assert/assert_equals.ts";
import {AST, FunctionToken, printAST, readAST} from "./reader-printer.ts";

type MalEnv = Map<string, FunctionToken>;

function functionToken(fn: (...args: any[]) => any): FunctionToken {
    return { type: "function", value: fn };
}

function isBoolean(v: unknown): v is boolean {
    return v === true || v === false;
}

function isNumber(v: unknown): v is number {
    return typeof v === "number" && isFinite(v);
}

function isString(v: unknown): v is string {
    return typeof v === "string" || v instanceof String;
}

class REPL {
    private readonly env: MalEnv;

    constructor(env: MalEnv) {
        this.env = env;
    }

    static mathRepl(): REPL {
        const mathFunctions = new Map<string, FunctionToken>();
        mathFunctions.set("+", functionToken((a, b) => a + b));
        mathFunctions.set("-", functionToken((a, b) => a - b));
        mathFunctions.set("*", functionToken((a, b) => a * b));
        mathFunctions.set("/", functionToken((a, b) => a / b));

        return new REPL(mathFunctions);
    }

    read(source: string): AST {
        return readAST(source);
    }

    cast(value: unknown): AST {
        if (value === true || value === false) {
            return { type: "boolean", value: value };
        }
        if (isBoolean(value)) {
            return { type: "boolean", value: value };
        }
        if (isString(value)) {
            return { type: "string", value: value };
        }
        if (isNumber(value)) {
            return { type: "number", value: value };
        }
        throw new Error(`Unknown return type from functon: ${value}`);
    }

    eval_(ast: AST): AST {
        if (ast.type === "list") {
            const fn = this.eval_(ast.value[0]) as FunctionToken;
            const ret = fn.value(
                ...ast.value.slice(1).map((n) => this.eval_(n).value),
            );
            return this.cast(ret);
        }
        if (ast.type === "sym") {
            const ret = this.env.get(ast.value);
            if (ret === undefined) {
                throw new Error(`Unknown reference ${ast.value}`);
            }
            return ret;
        }
        return ast;
    }

    print(form: AST): string {
        return printAST(form);
    }

    rep(source: string): string {
        return this.print(this.eval_(this.read(source)));
    }
}

Deno.test("basic", function (): void {
    const repl = REPL.mathRepl();
    assertEquals(repl.rep("(+ 1 1)"), "2");
    assertEquals(repl.rep("(+ 2 (* 3 4))"), "14");
});