"use strict";

import * as fs from "node:fs";
import process from "node:process";

function main() {
    const text = fs.readFileSync(process.argv[2]).toString();

    const ast = new Parser(text).parse();

    let lastValue = null;

    const evaluator = new Evaluator();
    for (const expr of ast) {
        const result = evaluator.eval(expr);
        if (result.type !== "value") {
            break;
        }
        lastValue = result.value;
    }
    if (lastValue !== null) {
        console.log(valueToJs(lastValue));
    }
}

class Evaluator {
    constructor() {
        this.syms = { parent: undefined, map: new Map(builtins) };
    }

    /**
     * @param {Expr} expr
     */
    eval(expr) {
        if (expr.type === "list") {
            return this.evalList(expr, expr.line);
        } else if (expr.type === "int") {
            return { type: "value", value: { type: "int", value: expr.value } };
        } else if (expr.type === "string") {
            return {
                type: "value",
                value: { type: "string", value: expr.value },
            };
        } else if (expr.type === "ident") {
            const sym = this.findSym(expr.value);
            if (!sym) {
                throw new Error(
                    `could not find symbol '${expr.value}' on line ${expr.line}`,
                );
            }
            return { type: "value", value: sym };
        } else {
            throw new Error(
                `unknown expr type '${expr.type}' on line ${expr.line}`,
            );
        }
    }

    evalToValue(expr) {
        const result = this.eval(expr);
        if (result.type !== "value") {
            throw new Error(`expected value on line ${expr.line}`);
        }
        return result.value;
    }

    evalList(expr) {
        const s = expr.values;
        const id = s[0]?.type === "ident" ? s[0].value : undefined;
        if (id === "fn") {
            const name = s[1].value;
            this.syms.map.set(name, {
                type: "fn",
                name,
                params: s[2].values.map((ident) => ident.value),
                body: s[3],
                syms: this.syms,
            });
            return { type: "value", value: { type: "null" } };
        } else if (id === "return") {
            return {
                type: "return",
                value: s[1] ? this.evalToValue(s[1]) : { type: "null" },
            };
        } else if (id === "let") {
            const value = this.evalToValue(s[2]);
            this.syms.map.set(s[1].value, value);
            return { type: "value", value: { type: "null" } };
        } else if (id === "if") {
            const cond = this.evalToValue(s[1]);
            if (cond.type !== "bool") {
                throw new Error(
                    `expected bool on line ${expr.line}`,
                );
            }
            if (cond.value) {
                return this.eval(s[2]);
            } else if (s[3]) {
                return this.eval(s[3]);
            } else {
                return { type: "value", value: "null" };
            }
        } else if (id === "loop") {
            while (true) {
                const result = this.eval(s[1]);
                if (result.type === "break") {
                    return { type: "value", value: result.value };
                } else if (result.type !== "value") {
                    return result;
                }
            }
        } else if (id === "break") {
            return {
                type: "break",
                value: s[1] ? this.evalToValue(s[1]) : { type: "null" },
            };
        } else if (id === "do") {
            let lastValue = { type: "null" };

            for (const expr of s.slice(1)) {
                const result = this.eval(expr);
                if (result.type !== "value") {
                    return result;
                }
                lastValue = result.value;
            }
            return { type: "value", value: lastValue };
        } else if (id === "call") {
            const args = s.slice(2).map((arg) => this.evalToValue(arg));
            const fnValue = this.evalToValue(s[1]);

            if (fnValue.type === "builtin") {
                return { type: "value", value: fnValue.fn(...args) };
            } else if (fnValue.type !== "fn") {
                throw new Error("cannot call non-function");
            }
            const callerSyms = this.syms;
            this.syms = {
                parent: fnValue.syms,
                map: new Map(),
            };
            if (fnValue.params.length !== args.length) {
                throw new Error(
                    `incorrect amount of arguments on line ${line}`,
                );
            }
            for (let i = 0; i < fnValue.params.length; ++i) {
                this.syms.map.set(fnValue.params[i], args[i]);
            }

            let returnValue = { type: "null" };
            const result = this.eval(fnValue.body);

            if (result.type === "value" || result.type === "return") {
                returnValue = result.value;
            } else {
                throw new Error(`illegal ${result.type} across boundry`);
            }

            this.syms = callerSyms;
            return { type: "value", value: returnValue };
        } else if (id === "not") {
            const value = this.evalToValue(s[1]);
            return {
                type: "value",
                value: { type: "bool", value: !value.value },
            };
        } else if (id === "or") {
            const left = this.evalToValue(s[1]);
            if (left.value) {
                return { type: "value", value: left };
            } else {
                const right = this.evalToValue(s[2]);
                return { type: "value", value: right };
            }
        } else if (id === "and") {
            const left = this.evalToValue(s[1]);
            if (left.value) {
                const right = this.evalToValue(s[2]);
                return { type: "value", value: right };
            } else {
                return { type: "value", value: left };
            }
        } else if (id in artithmeticOps) {
            const left = this.evalToValue(s[1]);
            const right = this.evalToValue(s[2]);
            return {
                type: "value",
                value: {
                    type: "int",
                    value: artithmeticOps[id](left.value, right.value),
                },
            };
        } else if (id in comparisonOps) {
            const left = this.evalToValue(s[1]);
            const right = this.evalToValue(s[2]);
            return {
                type: "value",
                value: {
                    type: "bool",
                    value: comparisonOps[id](left.value, right.value),
                },
            };
        } else if (id in assignOps) {
            if (s[1].type === "ident") {
                const sym = this.findSym(s[1].value);
                if (!sym) {
                    throw new Error(
                        `could not find symbol '${expr.value}' on line ${expr.line}`,
                    );
                }
                const right = this.evalToValue(s[2]);
                const newValue = assignOps[id](sym, right);
                sym.type = newValue.type;
                sym.value = newValue.value;
            } else {
                throw new Error(
                    `cannot assign to expression on line ${expr.line}`,
                );
            }
            return { type: "value", value: { type: "null" } };
        } else {
            return {
                type: "value",
                value: {
                    type: "list",
                    values: s.map((expr) => this.evalToValue(expr)),
                },
            };
        }
    }

    findSym(ident, syms = this.syms) {
        if (syms.map.has(ident)) {
            return syms.map.get(ident);
        } else if (syms.parent) {
            return this.findSym(ident, syms.parent);
        } else {
            return undefined;
        }
    }
}

const artithmeticOps = {
    "+": (left, right) => right + left,
    "-": (left, right) => right - left,
};
const comparisonOps = {
    "==": (left, right) => left === right,
    "!=": (left, right) => left !== right,
    "<": (left, right) => left < right,
    ">": (left, right) => left > right,
    "<=": (left, right) => left <= right,
    ">=": (left, right) => left >= right,
};
const assignOps = {
    "=": (_, right) => right,
    "+=": (left, right) => ({ type: "int", value: left.value + right.value }),
    "-=": (left, right) => ({ type: "int", value: left.value - right.value }),
};

const builtinFns = {
    println(msg, ...args) {
        let text = valueToPrint(msg);

        for (const arg of args) {
            text = text.replace("%", valueToPrint(arg));
        }

        console.log(text);
        return { type: "null" };
    },
    read_text_file(path) {
        const text = fs.readFileSync(path.value).toString();
        return { type: "string", value: text };
    },
    push(list, value) {
        if (list.type === "string") {
            list.value += value.value;
            return list;
        }
        list.values.push(value);
        return list;
    },
    at(value, index) {
        if (value.type === "string") {
            return { type: "string", value: value.value[index.value] };
        }
        return value.values[index.value];
    },
    len(value) {
        if (value.type === "string") {
            return { type: "int", value: value.value.length };
        }
        return { type: "int", value: value.values.length };
    },
};

const consts = {
    "null": { type: "null" },
    "false": { type: "bool", value: false },
    "true": { type: "bool", value: true },
};

const builtins = [
    ...Object.entries(builtinFns)
        .map(([key, fn]) => [key, { type: "builtin", fn }]),
    ...Object.entries(consts),
];

function valueToPrint(value) {
    if (value.type === "null") {
        return "null";
    } else if (value.type === "bool") {
        return `${value.value}`;
    } else if (value.type === "int") {
        return `${value.value}`;
    } else if (value.type === "string") {
        return `${value.value}`;
    } else if (value.type === "list") {
        return `(${value.values.map((v) => valueToString(v)).join(" ")})`;
    } else {
        throw new Error(`unknown value type ${value.type}`);
    }
}

function valueToString(value) {
    if (value.type === "null") {
        return "null";
    } else if (value.type === "bool") {
        return `${value.value}`;
    } else if (value.type === "int") {
        return `${value.value}`;
    } else if (value.type === "string") {
        return `"${value.value}"`;
    } else if (value.type === "list") {
        return `(${value.values.map((v) => valueToString(v)).join(" ")})`;
    } else {
        throw new Error(`unknown value type ${value.type}`);
    }
}

function valueToJs(value) {
    if (value.type === "null") {
        return null;
    } else if (value.type === "bool") {
        return value.value;
    } else if (value.type === "int") {
        return value.value;
    } else if (value.type === "string") {
        return value.value;
    } else if (value.type === "list") {
        return value.values.map((v) => valueToJs(v));
    } else {
        throw new Error(`unknown value type ${value.type}`);
    }
}

/**
 * @param {Expr} expr
 * @returns {string}
 */
function exprToString(expr) {
    if (expr.type === "ident") {
        return expr.value;
    } else if (expr.type === "int") {
        return `${expr.value}`;
    } else if (expr.type === "string") {
        return `"${expr.value}"`;
    } else if (expr.type === "list") {
        return `(${expr.values.map((v) => exprToString(v)).join(" ")})`;
    } else {
        throw new Error(`unknown value type ${expr.type}`);
    }
}

/**
 * @typedef {{ type: string, line: number, value: any, values?: Expr } } Expr
 */

class Parser {
    constructor(text) {
        const stringExtractor = new StringExtractor(text);
        stringExtractor.extract();
        this.strings = stringExtractor.getStrings();
        this.text = stringExtractor.getOutputText();
        this.tokens = this.text
            .replace(/\/\/.*?$/mg, "")
            .replace(/([\(\)\n])/g, " $1 ")
            .split(/[ \t\r]/)
            .filter((tok) => tok !== "");
        this.idx = 0;
        this.line = 1;
    }

    /**
     * @returns {Expr[]}
     */
    parse() {
        if (this.curr === "\n") {
            this.step();
        }

        const exprs = [];
        while (!this.done) {
            exprs.push(this.parseExpr());
        }
        return exprs;
    }

    parseExpr() {
        const line = this.line;
        if (this.eat("(")) {
            const values = [];
            while (!this.test(")")) {
                values.push(this.parseExpr());
            }
            if (!this.test(")")) {
                throw new Error(`expected ')'`);
            }
            this.step();
            return { type: "list", line, values };
        } else if (this.test(/STRING_\d+/)) {
            const id = Number(this.curr.match(/STRING_(\d+)/)[1]);
            this.step();
            return { type: "string", line, value: this.strings[id] };
        } else if (this.test(/0|(:?[1-9][0-9]*)/)) {
            const value = Number(this.curr);
            this.step();
            return { type: "int", line, value };
        } else if (this.test(/[a-zA-Z0-9\+\-\*/%&\|=\?\!<>'_]+/)) {
            const value = this.curr;
            this.step();
            return { type: "ident", line, value };
        } else {
            throw new Error(
                `expected expression, got ${this.curr} on line ${this.line}`,
            );
        }
    }

    eat(tok) {
        if (!this.test(tok)) {
            return false;
        }
        this.step();
        return true;
    }
    test(tok) {
        if (this.done) {
            return false;
        }
        if (typeof tok === "string") {
            return this.curr === tok;
        } else if (tok instanceof RegExp) {
            return new RegExp(`^${tok.source}$`)
                .test(this.curr);
        } else {
            throw new Error();
        }
    }
    step() {
        do {
            if (!this.done && this.curr === "\n") {
                this.line += 1;
            }
            this.idx += 1;
        } while (!this.done && this.curr === "\n");
    }

    get done() {
        return this.idx >= this.tokens.length;
    }
    get curr() {
        return this.tokens[this.idx];
    }
}

class StringExtractor {
    constructor(text) {
        this.text = text;
        this.idx = 0;
        this.outputText = "";
        this.strings = [];
    }

    extract() {
        while (this.idx < this.text.length) {
            if (this.text[this.idx] == '"') {
                this.extractString();
            } else {
                this.outputText += this.text[this.idx];
                this.idx += 1;
            }
        }
    }

    extractString() {
        this.idx += 1;
        let value = "";
        while (this.idx < this.text.length && this.text[this.idx] != '"') {
            if (this.text[this.idx] == "\\") {
                this.idx += 1;
                if (this.idx > this.text.length) {
                    break;
                }
                const ch = this.text[this.idx];
                value += {
                    "0": "\0",
                    "t": "\t",
                    "r": "\r",
                    "n": "\n",
                }[ch] ?? ch;
            } else {
                value += this.text[this.idx];
            }
            this.idx += 1;
        }
        if (this.idx >= this.text.length || this.text[this.idx] != '"') {
            throw new Error("expected '\"'");
        }
        this.idx += 1;
        const id = this.strings.length;
        this.strings.push(value);
        this.outputText += `STRING_${id}`;
    }

    getStrings() {
        return this.strings;
    }
    getOutputText() {
        return this.outputText;
    }
}

main();