using System;
using System.Collections.Generic;

namespace Amogulator.Suslang;

public enum TokenType {
    Eof,
    Invalid,
    Id,
    Int,
    Hex,
    Decimal,
    String,
    True,
    False,
    LParen,
    RParen,
    Plus,
    Minus,
    Asterisk,
    Slash,
    Percent,
}

public struct Position {
    public int index;
    public int line, col;
}

public struct Token {
    public TokenType type;
    public Position position;
    public int length;
}

public class Lexer {
    private int i = 0;
    private string text;
    private int line = 1;
    private int col = 1;

    public Lexer(string text) {
        this.text = text;
    }

    public Token next() {
        if (done()) {
            return token(TokenType.Eof, position());
        } else if ("123456789".Contains(current())) {
            return intToken();
        } else if ("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_".Contains(current())) {
            return idToken();
        } else {
            return staticToken();
        }
    }

    private Token intToken() {
        var start = position();
        var value = "";
        value += current();
        step();
        while (!done() && "1234567890".Contains(current())) {
            value += current();
            step();
        }
        return token(TokenType.Int, start);
    }

    private Token idToken() {
        var start = position();
        var value = "";
        value += current();
        step();
        while (!done() && "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_".Contains(current())) {
            value += current();
            step();
        }
        return token(TokenType.Id, start);
    }

    private Token staticToken() {
        var start = position();
        switch (current()) {
            case '(':
                step();
                return token(TokenType.LParen, start);
            case ')':
                step();
                return token(TokenType.RParen, start);
            case '+':
                step();
                return token(TokenType.Plus, start);
            case '-':
                step();
                return token(TokenType.Minus, start);
            case '*':
                step();
                return token(TokenType.Asterisk, start);
            case '/':
                step();
                return token(TokenType.Slash, start);
            case '%':
                step();
                return token(TokenType.Percent, start);
            default:
                step();
                return token(TokenType.Invalid, start);
        }
    }

    private Token token(TokenType type, Position start) => new Token() {
        type = type,
        position = start,
        length = this.i - start.index,
    };

    private Position position() => new Position() {
        index = this.i,
        line = this.line,
        col = this.col,
    };

    private char current() => this.text[this.i];
    private bool done() => this.i >= this.text.Length;

    private void step() {
        this.i += 1;
    }
}

public interface Expr {

}

public class Parser {
    public Expr parseExpr() {
        throw new NotImplementedException();
    }
}

public interface Operation {
}

public class Compiler {
    public List<Operation> compileExpr(Expr expr) {
        throw new NotImplementedException();
    }
}

public interface Value { }

public class VM {
    public Value evaluate(List<Operation> program) {
        throw new NotImplementedException();
    }
}