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,
    Dot,
}

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 (" \t\r\n".Contains(current())) {
            while (!done() && " \t\r\n".Contains(current()))
                step();
            return next();
        } else if ("123456789".Contains(current())) {
            return intToken();
        } else if ("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_".Contains(current())) {
            return idToken();
        } else {
            return staticToken();
        }
    }

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

    private Token idToken() {
        var start = position();
        step();
        while (!done() && "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_".Contains(current()))
            step();
        this.text.Substring(start.index, this.i - start.index).switch {
            "false" => token(TokenType.False, start),
            "true" => token(TokenType.True, start),
            _ => token(TokenType.Id, start),
        };
    }

    private Token staticToken() {
        var start = position();
        switch (current()) {
            case '0':
                break;
            case '.':
                break;
            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 zeroToken() {
        var start = position();
        step();
        if (!done() && (current() == 'x' || current() == 'X')) {
            while (!done() && "1234567890abcdefABCDEF".Contains(current())) 
                step();
            return token(TokenType.Hex, start);
        } else {
            while (!done() && "1234567890".Contains(current())) 
                step();
            return token(TokenType.Int, start);
        }
    }
    
    private Token dotToken() {
        var start = position();
        step();
        if (!done() && "1234567890".Contains(current())) {
            while (!done() && "1234567890".Contains(current())) 
                step();
            return token(TokenType.Decimal, start);
        } else {
            return token(TokenType.Dot, 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 {
    string astString(int depth);
}

public ErrorExpr : Expr {
    public Position position;
    public string message;

    public override astString(int depth) =>
        $"ErrorExpr {{ {this.position.line}:{this.position.col} \"{this.message}\" }}";
}

public IdExpr : Expr {
    public string value;

    public override astString(int depth) =>
        $"IdExpr {{ \"{this.value}\" }}";
}

public IntExpr : Expr {
    public int value;

    public override astString(int depth) =>
        $"IntExpr {{ {this.value} }}";
}

public FloatExpr : Expr {
    public double value;

    public override astString(int depth) =>
        $"FloatExpr {{ {this.value} }}";
}

public StringExpr : Expr {
    public string value;

    public override astString(int depth) =>
        $"FloatExpr {{ \"{this.value}\" }}";
}

public BoolExpr : Expr {
    public bool value;

    public override astString(int depth) =>
        $"BoolExpr {{ {this.value} }}";
}

public enum UnaryType {
    Not,
    Negate,
}

public UnaryExpr : Expr {
    public UnaryType type;
    public Expr value;

    public override astString(int depth) =>
        $"UnaryExpr {{\n{new String(' ', depth) + 1}type: "
        + $"{this.type.ToString()},\n{new String(' ', depth + 1)}value: "
        + $"{this.value.astString(depth + 1)}\n{new String(' ', depth)}}}";
}

public enum BinaryType {
    Add,
    Subtract,
    Multiply,
    Divide,
    Modulus,
}

public BinaryExpr : Expr {
    public BinaryType type;
    public Expr left, right;

    public override astString(int depth) =>
        $"UnaryExpr {{\n{new String(' ', depth) + 1}type: "
        + $"{this.type.ToString()},\n{new String(' ', depth + 1)}left: "
        + $"{this.left.astString(depth + 1)},\n{new String(' ', depth + 1)}right: "
        + $"{this.right.astString(depth + 1)}\n{new String(' ', depth)}}}";
}

public class Parser {
    private int i = 0;
    private string text;
    private List<Token> tokens;

    public Parser(string text, List<Token> tokens) {
        this.text = text;
        this.tokens = tokens;
    }

    public Expr parseExpr() {
        return parsePrec11();
    }

    public Expr parsePrec11() {
        var left = parsePrec12();
        if (!done() && current().type == TokenType.Plus) {
            step();
            var right = parsePrec11();
            return new BinaryExpr() {
                type = BinaryType.Add,
                left = left,
                right = right,
            };
        } else if (!done() && current().type == TokenType.Minus) {
            step();
            var right = parsePrec11();
            return new BinaryExpr() {
                type = BinaryType.Subtraction,
                left = left,
                right = right,
            };
        } else {
            return left;
        }
    }

    public Expr parsePrec12() {
        var left = parsePrec13();
        if (!done() && current().type == TokenType.Asterisk) {
            step();
            var right = parePrec12();
            return new BinaryExpr() {
                type = BinaryType.Multiply,
                left = left,
                right = right,
            };
        } else if (!done() && current().type == TokenType.Slash) {
            step();
            var right = parePrec12();
            return new BinaryExpr() {
                type = BinaryType.Divide,
                left = left,
                right = right,
            };
        } else if (!done() && current().type == TokenType.Percent) {
            step();
            var right = parePrec12();
            return new BinaryExpr() {
                type = BinaryType.Modulus,
                left = left,
                right = right,
            };
        } else {
            return left;
        }
    }

    public Expr parsePrec13() {
        return parsePrec18();
    }

    public Expr parsePrec18() {
        if (!done() && current().type == TokenType.LParen) {
            step();
            var expr = parseExpr();
            if (done() || current().type TokenType.RParen) {
                var pos = position();
                step();
                return new ErrorExpr() {
                    position = pos,
                    message = "expected ')'"
                };
            }
            step();
            return expr;
        } else {
            return parseOperand();
        }
    }

    public parseOperand() {
        var start = position();
        if (done()) {
            step();
            return new ErrorExpr() {
                position = start,
                message = "expected value, got eof",
            };
        } else if (current().type == TokenType.Int) {
            var intToken = current();
            step();
            if (!done() && current().type == TokenType.Decimal) {
                var decimalToken = current();
                step();
                return new FloatExpr() {
                    value = double.Parse(this.text.Substring(start.index, intToken.length + decimalToken.length)),
                };
            } else {
                return new IntExpr() {
                    value = int.Parse(this.text.Substring(start.index, intToken.length));
                };
            }
        } else if (current().type == TokenType.String) {
            var stringToken = current();
            step();
            return new StringExpr() {
                value = this.text.Substring(start.index, stringToken.length),
            };
        } else if (current().type == TokenType.False) {
            step();
            return new BoolExpr() {
                value = false,
            };
        } else if (current().type == TokenType.True) {
            step();
            return new BoolExpr() {
                value = true,
            };
        } else {
            step();
            return new ErrorExpr() {
                position = start,
                message = "expected value",
            };
        }
    }

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

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

public interface Operation {}

public class PushInt {
    public int value;
} 

public class PushFloat {
    public double value;
}

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();
    }
}