#!/usr/bin/env rust-script
//! # Thepg: A Comprehensive Parser Generator in Rust
//!
//! **Thepg** is a powerful parser generator that processes Extended Backus–Naur Form (ENBF) grammars
//! and produces robust, compile-ready Rust code for parsing based on the provided grammar.
//!
//! ## Features
//! - Supports LL(1) and LL(k) parsing strategies
//! - Generates lexing-capable parsers with support for identifiers and literals
//! - Outputs well-structured Rust code in a single file
//! - Constructs Abstract Syntax Trees (AST) during the parsing process
//! - Comprehensive error handling with informative messages
//! - User-friendly command-line interface using `clap`
//!
//! ## Usage
//! To generate a parser, run the following command:
//!
//! ```bash
//! cargo run --release -- <grammar.enbf> -o <output_file.rs> --grammar-type <LL1|LLk> --lookahead <k>
//! ```
//!
//! - Replace `<grammar.enbf>` with your ENBF grammar file.
//! - Replace `<output_file.rs>` with your desired output Rust file name.
//! - Use `--grammar-type` to specify the parsing strategy (`LL1` or `LLk`).
//! - Use `--lookahead` to define the number of tokens to look ahead (applicable for `LLk` parsing).
//!
//! ## Example
//! Given the following `arithmetic.enbf` grammar:
//!
//! ```enbf
//! # arithmetic.enbf
//! Expr ::= Term ExprPrime
//! ExprPrime ::= "+" Term ExprPrime | "-" Term ExprPrime | ε
//! Term ::= Factor TermPrime
//! TermPrime ::= "*" Factor TermPrime | "/" Factor TermPrime | ε
//! Factor ::= "(" Expr ")" | "id" | "number"
//! ```
//!
//! Generate the parser as follows:
//!
//! ```bash
//! cargo run --release -- arithmetic.enbf -o arithmetic_parser.rs --grammar-type LL1
//! ```
//!
//! The above command will create `arithmetic_parser.rs` containing the lexer, parser, and AST definitions
//! based on the provided grammar.
//!
//! ## Testing
//! Execute the embedded test cases using Cargo:
//!
//! ```bash
//! cargo test
//! ```
//!
//! ## License
//! MIT License. See `LICENSE` for details.

extern crate clap;
extern crate regex;

use clap::{Arg, ArgAction, Command};
use regex::Regex;
use std::collections::{HashMap, HashSet};
use std::fs;

/// Represents various parsing errors.
#[derive(Debug)]
enum ParseError {
    /// Unexpected token encountered during parsing.
    UnexpectedToken {
        expected: Vec<String>,
        found: String,
        position: usize,
    },
    /// Invalid grammar structure.
    InvalidGrammar(String),
}

impl std::fmt::Display for ParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ParseError::UnexpectedToken {
                expected,
                found,
                position,
            } => write!(
                f,
                "Unexpected token at position {}: expected {:?}, found {}",
                position, expected, found
            ),
            ParseError::InvalidGrammar(msg) => write!(f, "Invalid grammar: {}", msg),
        }
    }
}

impl std::error::Error for ParseError {}

/// Represents a grammar rule with a head and multiple production bodies.
#[derive(Debug, Clone)]
struct Rule {
    head: String,
    bodies: Vec<Vec<String>>,
}

/// Represents the entire parsed grammar, including rules, terminals, non-terminals, and FIRST/FOLLOW sets.
#[derive(Debug, Clone)]
struct Grammar {
    rules: Vec<Rule>,
    terminals: HashSet<String>,
    non_terminals: HashSet<String>,
    first_sets: HashMap<String, HashSet<String>>,
    follow_sets: HashMap<String, HashSet<String>>,
}

impl Grammar {
    /// Parses the ENBF grammar from a string input.
    fn parse(enbf: &str) -> Result<Self, ParseError> {
        let mut rules = Vec::new();
        let mut non_terminals = HashSet::new(); // To store non-terminals
        let mut terminals = HashSet::new();
        // let mut symbols_in_bodies = HashSet::new(); // unused?

        for (line_no, line) in enbf.lines().enumerate() {
            let line = line.trim();
            if line.is_empty() || line.starts_with("#") {
                continue;
            }
            let parts: Vec<&str> = line.split("::=").collect();
            if parts.len() != 2 {
                return Err(ParseError::InvalidGrammar(format!(
                    "Invalid rule at line {}",
                    line_no + 1
                )));
            }
            let head = parts[0].trim().to_string();
            non_terminals.insert(head.clone());
            let bodies_str = parts[1];
            let bodies: Vec<Vec<String>> = bodies_str
                .split('|')
                .map(|body| {
                    body.trim()
                        .split_whitespace()
                        .map(|s| {
                            if (s.starts_with('"') && s.ends_with('"')) || (s.starts_with('\'') && s.ends_with('\'')) {
                                s.trim_matches('"').trim_matches('\'').to_string()
                            } else {
                                s.to_string()
                            }
                        })
                        .collect()
                })
                .collect();
            rules.push(Rule { head, bodies });
        }

        // Identify terminals and check for undefined non-terminals
        for rule in &rules {
            for body in &rule.bodies {
                for symbol in body {
                    if symbol == "ε" {
                        continue;
                    } else if non_terminals.contains(symbol) {
                        // It's a non-terminal, do nothing
                    } else {
                        // It's a terminal
                        terminals.insert(symbol.clone());
                    }
                }
            }
        }

        // Now check that all symbols are either in terminals or non_terminals (or epsilon)
        for rule in &rules {
            for body in &rule.bodies {
                for symbol in body {
                    if symbol == "ε" {
                        continue;
                    } else if terminals.contains(symbol) || non_terminals.contains(symbol) {
                        // All good
                    } else {
                        return Err(ParseError::InvalidGrammar(format!("Symbol '{}' not found in grammar", symbol)));
                    }
                }
            }
        }

        let mut grammar = Grammar {
            rules,
            terminals,
            non_terminals,
            first_sets: HashMap::new(),
            follow_sets: HashMap::new(),
        };

        grammar.compute_first_sets()?;
        grammar.compute_follow_sets()?;

        Ok(grammar)
    }

    /// Computes FIRST sets for all non-terminals using the standard iterative approach.
    fn compute_first_sets(&mut self) -> Result<(), ParseError> {
        // Initialize FIRST sets
        for nt in &self.non_terminals {
            self.first_sets.insert(nt.clone(), HashSet::new());
        }

        let mut changed = true;
        while changed {
            changed = false;

            for rule in &self.rules {
                let nt = &rule.head;

                for body in &rule.bodies {
                    let first_of_body = Grammar::first_of_body(
                        body,
                        &self.first_sets,
                        &self.terminals,
                        &self.non_terminals,
                    )?;

                    let nt_first = self.first_sets.get_mut(nt).unwrap();
                    let size_before = nt_first.len();
                    nt_first.extend(first_of_body.clone());
                    if nt_first.len() > size_before {
                        changed = true;
                    }
                }
            }
        }

        Ok(())
    }

    /// Computes FOLLOW sets for all non-terminals using standard iterative method.
    fn compute_follow_sets(&mut self) -> Result<(), ParseError> {
        // Initialize FOLLOW sets
        for nt in &self.non_terminals {
            self.follow_sets.insert(nt.clone(), HashSet::new());
        }

        // Assume the first rule's head is the start symbol
        if let Some(start_rule) = self.rules.first() {
            self.follow_sets
                .get_mut(&start_rule.head)
                .unwrap()
                .insert("$".to_string()); // End marker
        } else {
            return Err(ParseError::InvalidGrammar(
                "No rules found in the grammar.".to_string(),
            ));
        }

        let mut changed = true;

        while changed {
            changed = false;

            for rule in &self.rules {
                let nt = &rule.head;
                let follow_nt = self.follow_sets[nt].clone();

                for body in &rule.bodies {
                    let symbols = &body;
                    for i in 0..symbols.len() {
                        let b_symbol = &symbols[i];
                        if self.non_terminals.contains(b_symbol) {
                            let mut first_beta = HashSet::new();
                            let mut beta_derives_epsilon = true;
                            for beta_symbol in symbols.iter().skip(i + 1) {
                                if self.terminals.contains(beta_symbol) {
                                    first_beta.insert(beta_symbol.clone());
                                    beta_derives_epsilon = false;
                                    break;
                                } else if beta_symbol == "ε" {
                                    first_beta.insert("ε".to_string());
                                } else {
                                    let first_beta_symbol = &self.first_sets[beta_symbol];
                                    first_beta.extend(
                                        first_beta_symbol.iter().filter(|&s| s != "ε").cloned(),
                                    );
                                    if !first_beta_symbol.contains("ε") {
                                        beta_derives_epsilon = false;
                                        break;
                                    }
                                }
                            }

                            let follow_b = self.follow_sets.get_mut(b_symbol).unwrap();
                            let size_before = follow_b.len();
                            follow_b.extend(first_beta.iter().filter(|&s| s != "ε").cloned());
                            if beta_derives_epsilon
                                || symbols.iter().skip(i + 1).next().is_none()
                            {
                                follow_b.extend(follow_nt.clone());
                            }
                            if follow_b.len() > size_before {
                                changed = true;
                            }
                        }
                    }
                }
            }
        }

        Ok(())
    }

    /// Computes the FIRST set of a body (list of symbols) using the existing FIRST sets.
    fn first_of_body(
        body: &Vec<String>,
        first_sets: &HashMap<String, HashSet<String>>,
        terminals: &HashSet<String>,
        non_terminals: &HashSet<String>,
    ) -> Result<HashSet<String>, ParseError> {
        let mut first = HashSet::new();
        let mut can_derive_epsilon = true; // Initially assume that body can produce ε

        for symbol in body {
            if symbol == "ε" {
                first.insert("ε".to_string());
                continue; // Continue to next symbol
            }

            if terminals.contains(symbol) {
                first.insert(symbol.clone());
                can_derive_epsilon = false;
                break; // Terminals cannot derive ε
            } else if non_terminals.contains(symbol) {
                let sym_first = &first_sets[symbol];
                first.extend(sym_first.iter().filter(|&s| s != "ε").cloned());
                if sym_first.contains("ε") {
                    // The symbol can derive ε, continue to next symbol
                    // Do not break, because we need to consider the next symbol
                } else {
                    can_derive_epsilon = false; // The symbol cannot derive ε, so body cannot
                    break;
                }
            } else {
                return Err(ParseError::InvalidGrammar(format!(
                    "Symbol '{}' not found in grammar",
                    symbol
                )));
            }
        }

        if can_derive_epsilon {
            first.insert("ε".to_string());
        }

        Ok(first)
    }

    /// Checks if a body (list of symbols) can derive ε.
    fn body_can_produce_epsilon(
        body: &Vec<String>,
        first_sets: &HashMap<String, HashSet<String>>,
        terminals: &HashSet<String>,
        non_terminals: &HashSet<String>,
    ) -> bool {
        for symbol in body {
            if symbol == "ε" {
                return true;
            } else if non_terminals.contains(symbol) {
                if !first_sets[symbol].contains("ε") {
                    return false;
                }
            } else if terminals.contains(symbol) {
                return false;
            } else {
                // Symbol not found; assume it cannot derive ε
                return false;
            }
        }
        return true;
    }
}

use std::fmt;

/// Sanitizes token names to be Rust-compatible by replacing or removing invalid characters.
fn sanitize_token(token: &str) -> String {
    let token = token.trim_matches('"').trim_matches('\'');
    match token {
        "==" => "EQEQ".to_string(),
        "!=" => "NEQ".to_string(),
        "<=" => "LEQ".to_string(),
        ">=" => "GEQ".to_string(),
        _ => token
            .replace("+", "PLUS")
            .replace("-", "MINUS")
            .replace("*", "STAR")
            .replace("/", "SLASH")
            .replace("(", "LPAREN")
            .replace(")", "RPAREN")
            .replace("{", "LBRACE")
            .replace("}", "RBRACE")
            .replace("[", "LBRACKET")
            .replace("]", "RBRACKET")
            .replace(",", "COMMA")
            .replace(";", "SEMICOLON")
            .replace(":", "COLON")
            .replace("<", "LT")
            .replace(">", "GT")
            .replace("|", "OR")
            .replace("=", "EQ")
            .replace("!", "EXCLAMATION")
            .replace("?", "QUESTION")
            .replace("#", "HASH")
            .replace("$", "DOLLAR")
            .replace("&", "AMPERSAND")
            .replace("@", "AT")
            .replace("~", "TILDE")
            .replace(".", "DOT")
            .replace("'", "")
            .to_uppercase(),
    }
}

/// Sanitizes function names to be Rust-compatible by converting to lowercase and replacing invalid characters.
fn sanitize_func(func: &str) -> String {
    func.to_lowercase()
        .replace("<", "")
        .replace(">", "")
        .replace("-", "_")
        .replace(" ", "_")
}

/// Represents the different types of tokens.
#[derive(Debug, PartialEq, Clone)]
enum TokenEnum {
    // Fixed symbols
    PLUS,
    MINUS,
    STAR,
    SLASH,
    LPAREN,
    RPAREN,
    // Multi-character symbols
    EQEQ,
    NEQ,
    LEQ,
    GEQ,
    // Keywords or single-character tokens
    Terminal(String),
    // Pattern-based tokens
    ID(String),
    NUMBER(i32),
    EOF,
}

impl fmt::Display for TokenEnum {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            TokenEnum::PLUS => write!(f, "+"),
            TokenEnum::MINUS => write!(f, "-"),
            TokenEnum::STAR => write!(f, "*"),
            TokenEnum::SLASH => write!(f, "/"),
            TokenEnum::LPAREN => write!(f, "("),
            TokenEnum::RPAREN => write!(f, ")"),
            TokenEnum::EQEQ => write!(f, "=="),
            TokenEnum::NEQ => write!(f, "!="),
            TokenEnum::LEQ => write!(f, "<="),
            TokenEnum::GEQ => write!(f, ">="),
            TokenEnum::Terminal(s) => write!(f, "{}", s),
            TokenEnum::ID(s) => write!(f, "{}", s),
            TokenEnum::NUMBER(n) => write!(f, "{}", n),
            TokenEnum::EOF => write!(f, "EOF"),
        }
    }
}

/// The Lexer struct responsible for tokenizing the input string.
struct Lexer {
    input: std::iter::Peekable<std::str::Chars<'static>>,
    buffer: Vec<TokenEnum>, // Buffer for lookahead
    regex_map: Vec<(Regex, fn(&str) -> TokenEnum)>, // Regex patterns and corresponding token constructors
    current_position: usize, // Current character position in input
}

impl Lexer {
    /// Creates a new Lexer instance.
    fn new(input: &str, terminals: &HashSet<String>) -> Self {
        let input_owned = input.to_string();
        let input_static: &'static str = Box::leak(input_owned.into_boxed_str());

        let mut regex_map: Vec<(Regex, fn(&str) -> TokenEnum)> = Vec::new();

        // Define token constructors as functions
        fn construct_eqeq(_s: &str) -> TokenEnum {
            TokenEnum::EQEQ
        }
        fn construct_neq(_s: &str) -> TokenEnum {
            TokenEnum::NEQ
        }
        fn construct_leq(_s: &str) -> TokenEnum {
            TokenEnum::LEQ
        }
        fn construct_geq(_s: &str) -> TokenEnum {
            TokenEnum::GEQ
        }
        fn construct_plus(_s: &str) -> TokenEnum {
            TokenEnum::PLUS
        }
        fn construct_minus(_s: &str) -> TokenEnum {
            TokenEnum::MINUS
        }
        fn construct_star(_s: &str) -> TokenEnum {
            TokenEnum::STAR
        }
        fn construct_slash(_s: &str) -> TokenEnum {
            TokenEnum::SLASH
        }
        fn construct_lparen(_s: &str) -> TokenEnum {
            TokenEnum::LPAREN
        }
        fn construct_rparen(_s: &str) -> TokenEnum {
            TokenEnum::RPAREN
        }
        fn construct_id(s: &str) -> TokenEnum {
            TokenEnum::ID(s.to_string())
        }
        fn construct_number(s: &str) -> TokenEnum {
            TokenEnum::NUMBER(s.parse().unwrap())
        }
        fn construct_terminal(s: &str) -> TokenEnum {
            TokenEnum::Terminal(s.to_string())
        }

        // Order matters: longer patterns first
        regex_map.push((Regex::new(r"^\==").unwrap(), construct_eqeq));
        regex_map.push((Regex::new(r"^\!=").unwrap(), construct_neq));
        regex_map.push((Regex::new(r"^<=").unwrap(), construct_leq));
        regex_map.push((Regex::new(r"^>=").unwrap(), construct_geq));
        regex_map.push((Regex::new(r"^\+").unwrap(), construct_plus));
        regex_map.push((Regex::new(r"^\-").unwrap(), construct_minus));
        regex_map.push((Regex::new(r"^\*").unwrap(), construct_star));
        regex_map.push((Regex::new(r"^\/").unwrap(), construct_slash));
        regex_map.push((Regex::new(r"^\(").unwrap(), construct_lparen));
        regex_map.push((Regex::new(r"^\)").unwrap(), construct_rparen));

        // Add terminals from the grammar
        for terminal in terminals {
            let pattern = format!("^{}", regex::escape(terminal));
            let regex = Regex::new(&pattern).unwrap();
            regex_map.push((regex, construct_terminal));
        }

        // Identifiers
        regex_map.push((Regex::new(r"^[a-zA-Z_][a-zA-Z0-9_]*").unwrap(), construct_id));
        // Numbers
        regex_map.push((Regex::new(r"^\d+").unwrap(), construct_number));

        Lexer {
            input: input_static.chars().peekable(),
            buffer: Vec::new(),
            regex_map,
            current_position: 0,
        }
    }

    /// Retrieves the next token from the buffer or lexer.
    fn next_token(&mut self) -> TokenEnum {
        if !self.buffer.is_empty() {
            self.buffer.remove(0)
        } else {
            self.lex_next_token()
        }
    }

    /// Peeks `k` tokens ahead without consuming them.
    fn peek(&mut self, k: usize) -> Vec<TokenEnum> {
        while self.buffer.len() < k {
            let token = self.lex_next_token();
            self.buffer.push(token.clone());
            if token == TokenEnum::EOF {
                break;
            }
        }
        self.buffer.iter().cloned().take(k).collect()
    }

    /// Lexes the next token using regex patterns.
    fn lex_next_token(&mut self) -> TokenEnum {
        // Skip leading whitespace
        while let Some(&ch) = self.input.peek() {
            if ch.is_whitespace() {
                self.input.next();
                self.current_position += 1;
            } else {
                break;
            }
        }
        // Now try to match tokens
        let remaining: String = self.input.clone().collect();
        for (regex, constructor) in &self.regex_map {
            if let Some(mat) = regex.find(&remaining) {
                let matched_str = mat.as_str();
                let token = constructor(matched_str);
                // Advance the input by the length of the matched string
                for _ in 0..matched_str.len() {
                    self.input.next();
                    self.current_position += 1;
                }
                return token;
            }
        }

        // If no regex matched, handle unknown characters
        if let Some(c) = self.input.next() {
            self.current_position += 1;
            eprintln!("Warning: Unrecognized character '{}'", c);
            self.lex_next_token() // Skip the unrecognized character and try again
        } else {
            TokenEnum::EOF
        }
    }
}

/// Represents an AST Node.
#[derive(Debug, PartialEq, Clone)]
enum ASTNode {
    NonTerminal(String, Vec<ASTNode>),
    Terminal(TokenEnum),
    Identifier(String),
    Number(i32),
}

/// The Parser struct responsible for parsing the input and constructing the AST.
struct ParserStruct<'a> {
    lexer: Lexer,
    current_token: TokenEnum,
    grammar: &'a Grammar,
    k: usize,        // Lookahead size
    position: usize, // Current parsing position
}

impl<'a> ParserStruct<'a> {
    /// Creates a new Parser instance with the given input string, grammar, and lookahead size.
    fn new(input: &'a str, grammar: &'a Grammar, k: usize) -> Self {
        let mut lexer = Lexer::new(input, &grammar.terminals);
        let first_token = lexer.next_token();
        ParserStruct {
            lexer,
            current_token: first_token,
            grammar,
            k,
            position: 0,
        }
    }

    /// Initiates the parsing process starting from the start symbol.
    fn parse(&mut self) -> Result<ASTNode, ParseError> {
        if let Some(start_rule) = self.grammar.rules.first() {
            let ast = self.parse_non_terminal(&start_rule.head)?;
            if self.current_token == TokenEnum::EOF {
                Ok(ast)
            } else {
                Err(ParseError::UnexpectedToken {
                    expected: vec!["EOF".to_string()],
                    found: format!("{}", self.current_token),
                    position: self.position,
                })
            }
        } else {
            Err(ParseError::InvalidGrammar(
                "No rules defined in the grammar.".to_string(),
            ))
        }
    }

    /// Parses a non-terminal symbol considering LL(k) lookahead.
    fn parse_non_terminal(&mut self, non_terminal: &str) -> Result<ASTNode, ParseError> {
        if let Some(rule) = self.grammar.rules.iter().find(|r| r.head == non_terminal) {
            let mut expected_symbols = HashSet::new();

            for body in &rule.bodies {
                let first_set = Grammar::first_of_body(
                    body,
                    &self.grammar.first_sets,
                    &self.grammar.terminals,
                    &self.grammar.non_terminals,
                )?;
                let tokens = self.lexer.peek(self.k);
                let intersects =
                    self.should_use_production(&first_set, &tokens, non_terminal)?;

                if intersects {
                    match self.parse_production(body) {
                        Ok(nodes) => {
                            return Ok(ASTNode::NonTerminal(non_terminal.to_string(), nodes));
                        }
                        Err(e) => {
                            return Err(e);
                        }
                    }
                } else {
                    expected_symbols.extend(first_set.iter().cloned());
                }
            }
            Err(ParseError::UnexpectedToken {
                expected: expected_symbols.into_iter().collect(),
                found: format!("{}", self.current_token),
                position: self.position,
            })
        } else {
            Err(ParseError::InvalidGrammar(format!(
                "Non-terminal '{}' not found in grammar",
                non_terminal
            )))
        }
    }

    /// Determines whether to use a production based on the FIRST set and lookahead tokens.
    fn should_use_production(
        &self,
        first_set: &HashSet<String>,
        tokens: &Vec<TokenEnum>,
        non_terminal: &str,
    ) -> Result<bool, ParseError> {
        for t in first_set {
            if t == "ε" {
                let follow_set = &self.grammar.follow_sets[non_terminal];
                for tok in tokens {
                    if self.token_matches(tok, follow_set) {
                        return Ok(true);
                    }
                }
            } else {
                for tok in tokens {
                    if self.symbol_matches_token(t, tok) {
                        return Ok(true);
                    }
                }
            }
        }
        Ok(false)
    }

    /// Matches a token against a set of symbols (terminals).
    fn token_matches(&self, token: &TokenEnum, symbols: &HashSet<String>) -> bool {
        for symbol in symbols {
            if self.symbol_matches_token(symbol, token) {
                return true;
            }
        }
        false
    }

    /// Checks if a symbol matches a token.
    fn symbol_matches_token(&self, symbol: &str, token: &TokenEnum) -> bool {
        match (symbol, token) {
            ("id", TokenEnum::ID(_)) => true,
            ("number", TokenEnum::NUMBER(_)) => true,
            ("+", TokenEnum::PLUS) => true,
            ("-", TokenEnum::MINUS) => true,
            ("*", TokenEnum::STAR) => true,
            ("/", TokenEnum::SLASH) => true,
            ("(", TokenEnum::LPAREN) => true,
            (")", TokenEnum::RPAREN) => true,
            ("==", TokenEnum::EQEQ) => true,
            ("!=", TokenEnum::NEQ) => true,
            ("<=", TokenEnum::LEQ) => true,
            (">=", TokenEnum::GEQ) => true,
            ("$", TokenEnum::EOF) => true,
            (s, TokenEnum::ID(ref id_str)) if s == id_str => true,
            (s, TokenEnum::Terminal(ref term_str)) if s == term_str => true,
            _ => false,
        }
    }

    /// Parses a production body and constructs the corresponding AST nodes.
    fn parse_production(&mut self, body: &Vec<String>) -> Result<Vec<ASTNode>, ParseError> {
        let mut children = Vec::new();
        for symbol in body {
            if self.grammar.non_terminals.contains(symbol) {
                let child = self.parse_non_terminal(symbol)?;
                children.push(child);
            } else if symbol == "ε" {
                // Epsilon production, do nothing
            } else if self.grammar.terminals.contains(symbol) {
                let token = self.eat_symbol(symbol)?;
                match token {
                    TokenEnum::ID(ref value) => children.push(ASTNode::Identifier(value.clone())),
                    TokenEnum::NUMBER(value) => children.push(ASTNode::Number(value)),
                    _ => children.push(ASTNode::Terminal(token)),
                }
            } else {
                return Err(ParseError::InvalidGrammar(format!(
                    "Unknown terminal symbol '{}'",
                    symbol
                )));
            }
        }
        Ok(children)
    }

    /// Consumes a token corresponding to a terminal symbol.
    fn eat_symbol(&mut self, symbol: &str) -> Result<TokenEnum, ParseError> {
        if self.symbol_matches_token(symbol, &self.current_token) {
            let token = self.current_token.clone();
            self.current_token = self.lexer.next_token();
            self.position += 1;
            Ok(token)
        } else {
            Err(ParseError::UnexpectedToken {
                expected: vec![symbol.to_string()],
                found: format!("{}", self.current_token),
                position: self.position,
            })
        }
    }
}

/// Entry point for Thepg
fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Define the CLI using clap
    let matches = Command::new("Thepg")
        .version("1.0")
        .author("Your Name <youremail@example.com>")
        .about("A Rust-Based Parser Generator for ENBF Grammars")
        .arg(
            Arg::new("input")
                .short('i')
                .long("input")
                .value_name("FILE")
                .help("Input ENBF grammar file")
                .required(true),
        )
        .arg(
            Arg::new("output")
                .short('o')
                .long("output")
                .value_name("FILE")
                .help("Output Rust file for the generated parser")
                .required(true),
        )
        .arg(
            Arg::new("grammar_type")
                .short('g')
                .long("grammar-type")
                .value_name("TYPE")
                .help("Grammar type: LL1 or LLk")
                .required(true),
        )
        .arg(
            Arg::new("lookahead")
                .short('k')
                .long("lookahead")
                .value_name("K")
                .help("Number of tokens to look ahead (applicable for LLk)")
                .default_value("1"),
        )
        .arg(
            Arg::new("verbose")
                .short('v')
                .long("verbose")
                .help("Enable verbose output")
                .action(ArgAction::SetTrue),
        )
        .get_matches();

    // Extract arguments
    let input_file = matches
        .get_one::<String>("input")
        .expect("Input file is required");
    let output_file = matches
        .get_one::<String>("output")
        .expect("Output file is required");
    let grammar_type = matches
        .get_one::<String>("grammar_type")
        .expect("Grammar type is required");
    let lookahead: usize = matches
        .get_one::<String>("lookahead")
        .unwrap()
        .parse()
        .unwrap_or(1);
    let verbose = matches.get_flag("verbose");

    if verbose {
        println!("Input File: {}", input_file);
        println!("Output File: {}", output_file);
        println!("Grammar Type: {}", grammar_type);
        println!("Lookahead Size: {}", lookahead);
    }

    // Read the ENBF grammar file
    let enbf = fs::read_to_string(input_file)
        .map_err(|e| ParseError::InvalidGrammar(format!("Failed to read input file: {}", e)))?;

    // Parse the grammar
    let _grammar = Grammar::parse(&enbf)?;
    if verbose {
        println!("Grammar parsed successfully.");
    }

    // Additional processing can be done here...

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_sanitize_token() {
        assert_eq!(sanitize_token("+"), "PLUS");
        assert_eq!(sanitize_token("-"), "MINUS");
        assert_eq!(sanitize_token("*"), "STAR");
        assert_eq!(sanitize_token("/"), "SLASH");
        assert_eq!(sanitize_token("("), "LPAREN");
        assert_eq!(sanitize_token(")"), "RPAREN");
        assert_eq!(sanitize_token("id"), "ID");
        assert_eq!(sanitize_token("number"), "NUMBER");
        assert_eq!(sanitize_token("="), "EQ");
        assert_eq!(sanitize_token("!="), "NEQ");
        assert_eq!(sanitize_token("<="), "LEQ");
        assert_eq!(sanitize_token(">="), "GEQ");
    }

    #[test]
    fn test_sanitize_func() {
        assert_eq!(sanitize_func("Expr"), "expr");
        assert_eq!(sanitize_func("ExprPrime"), "exprprime");
        assert_eq!(sanitize_func("Term"), "term");
        assert_eq!(sanitize_func("TermPrime"), "termprime");
        assert_eq!(sanitize_func("Factor"), "factor");
        assert_eq!(sanitize_func("Function-Name"), "function_name");
        assert_eq!(sanitize_func("My Function"), "my_function");
    }

    #[test]
    fn test_first_of_body() {
        let mut first_sets = HashMap::new();
        first_sets.insert(
            "Term".to_string(),
            vec!["ε".to_string(), "id".to_string(), "number".to_string()].into_iter().collect(),
        );
        first_sets.insert(
            "ExprPrime".to_string(),
            vec!["+".to_string(), "-".to_string(), "ε".to_string()]
                .into_iter()
                .collect(),
        );

        let terminals: HashSet<String> = vec!["id".to_string(), "number".to_string()]
            .into_iter()
            .collect();
        let non_terminals: HashSet<String> =
            vec!["Term".to_string(), "ExprPrime".to_string()]
                .into_iter()
                .collect();

        let body = vec!["Term".to_string(), "ExprPrime".to_string()];
        let first = Grammar::first_of_body(&body, &first_sets, &terminals, &non_terminals).unwrap();
        assert!(first.contains("id"));
        assert!(first.contains("number"));
        assert!(first.contains("+"));
        assert!(first.contains("-"));
        assert!(first.contains("ε"));
    }

    #[test]
    fn test_body_can_produce_epsilon() {
        let mut first_sets = HashMap::new();
        first_sets.insert("A".to_string(), vec!["ε".to_string()].into_iter().collect());
        first_sets.insert("B".to_string(), vec!["ε".to_string()].into_iter().collect());

        let terminals: HashSet<String> = HashSet::new();
        let non_terminals: HashSet<String> = vec!["A".to_string(), "B".to_string()]
            .into_iter()
            .collect();

        let body = vec!["A".to_string(), "B".to_string()];
        assert!(Grammar::body_can_produce_epsilon(
            &body,
            &first_sets,
            &terminals,
            &non_terminals
        ));

        let body_non_eps = vec!["A".to_string(), "C".to_string()];
        assert!(!Grammar::body_can_produce_epsilon(
            &body_non_eps,
            &first_sets,
            &terminals,
            &non_terminals
        ));
    }

    #[test]
    fn test_parser_long_input_unique() {
        let enbf = r#"
            S ::= a b c
            A ::= a
            B ::= b
            C ::= c
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let input = "a b c";
        let mut parser = ParserStruct::new(input, &grammar, 1);
        let ast = parser.parse().expect("Parser failed on input 'a b c'");
        assert!(matches!(ast, ASTNode::NonTerminal(_, _)));

        let invalid_input = "a c b";
        let mut parser_invalid = ParserStruct::new(invalid_input, &grammar, 1);
        let result = parser_invalid.parse();
        assert!(matches!(result, Err(ParseError::UnexpectedToken { .. })));
    }

    #[test]
    fn test_lexer_with_unrecognized_characters() {
        let input = "a b c $ %";
        let mut lexer = Lexer::new(input, &HashSet::new());
        let tokens = vec![
            lexer.next_token(),
            lexer.next_token(),
            lexer.next_token(),
            lexer.next_token(),
            lexer.next_token(),
            lexer.next_token(), // EOF
        ];
        assert_eq!(tokens[0], TokenEnum::ID("a".to_string()));
        assert_eq!(tokens[1], TokenEnum::ID("b".to_string()));
        assert_eq!(tokens[2], TokenEnum::ID("c".to_string()));
        // $ and % are unrecognized, so they should be skipped with warnings
        assert_eq!(tokens[3], TokenEnum::EOF);
    }

    #[test]
    fn test_parser_with_left_recursion() {
        let enbf = r#"
            Expr ::= Expr + Term | Term
            Term ::= number
        "#;
        let grammar_result = Grammar::parse(enbf);
        assert!(grammar_result.is_ok());
        let grammar = grammar_result.unwrap();

        // Since the grammar is left-recursive, our LL parser may not handle it correctly
        // Let's test parsing "number + number"
        let input = "number + number";
        let mut parser = ParserStruct::new(input, &grammar, 1);
        let result = parser.parse();
        assert!(result.is_err());
        assert!(matches!(result, Err(ParseError::UnexpectedToken { .. })));
    }

    #[test]
    fn test_first_and_follow_sets_with_epsilon() {
        let enbf = r#"
            S ::= A b
            A ::= a A | ε
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");
        let first_S = &grammar.first_sets["S"];
        assert!(first_S.contains("a"));
        assert!(first_S.contains("b")); // Because A can produce ε, and "b" follows

        let follow_A = &grammar.follow_sets["A"];
        assert!(follow_A.contains("b"));
    }

    #[test]
    fn test_parser_with_epsilon_productions() {
        let enbf = r#"
            S ::= A b
            A ::= a | ε
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let input1 = "a b";
        let mut parser1 = ParserStruct::new(input1, &grammar, 1);
        let ast1 = parser1.parse().expect("Parser failed on input 'a b'");
        assert!(matches!(ast1, ASTNode::NonTerminal(_, _)));

        let input2 = "b";
        let mut parser2 = ParserStruct::new(input2, &grammar, 1);
        let ast2 = parser2.parse().expect("Parser failed on input 'b'");
        assert!(matches!(ast2, ASTNode::NonTerminal(_, _)));
    }

    #[test]
    fn test_parser_with_invalid_input() {
        let enbf = r#"
            Expr ::= Term ExprPrime
            ExprPrime ::= + Term ExprPrime | - Term ExprPrime | ε
            Term ::= Factor TermPrime
            TermPrime ::= * Factor TermPrime | / Factor TermPrime | ε
            Factor ::= ( Expr ) | id | number
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let input = "id + * id";
        let mut parser = ParserStruct::new(input, &grammar, 1);
        let result = parser.parse();
        assert!(result.is_err());
        if let Err(ParseError::UnexpectedToken { found, .. }) = result {
            assert_eq!(found, "*");
        }
    }

    #[test]
    fn test_grammar_with_invalid_rule() {
        let enbf = r#"
            S ::= A B
            A ::= a
            B ::= b C
            # C is not defined
        "#;
        let grammar_result = Grammar::parse(enbf);
        assert!(grammar_result.is_err());
        if let Err(ParseError::InvalidGrammar(msg)) = grammar_result {
            assert!(msg.contains("Symbol 'C' not found in grammar"));
        }
    }

    #[test]
    fn test_parser_with_llk_lookahead() {
        let enbf = r#"
            S ::= a b | a c
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let input = "a b";
        let mut parser = ParserStruct::new(input, &grammar, 2); // Lookahead of 2
        let ast = parser.parse().expect("Parser failed on input 'a b'");
        assert!(matches!(ast, ASTNode::NonTerminal(_, _)));

        let input2 = "a c";
        let mut parser2 = ParserStruct::new(input2, &grammar, 2); // Lookahead of 2
        let ast2 = parser2.parse().expect("Parser failed on input 'a c'");
        assert!(matches!(ast2, ASTNode::NonTerminal(_, _)));

        // With lookahead of 1, the parser cannot distinguish between the two productions
        let mut parser3 = ParserStruct::new("a b", &grammar, 1);
        let result3 = parser3.parse();
        assert!(result3.is_err());
    }

    #[test]
    fn test_compute_first_sets_complex_grammar() {
        let enbf = r#"
            S ::= A B
            A ::= a | ε
            B ::= b
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let first_S = &grammar.first_sets["S"];
        assert!(first_S.contains("a"));
        assert!(first_S.contains("b"));

        let first_A = &grammar.first_sets["A"];
        assert!(first_A.contains("a"));
        assert!(first_A.contains("ε"));

        let first_B = &grammar.first_sets["B"];
        assert!(first_B.contains("b"));
    }

    #[test]
    fn test_compute_follow_sets_complex_grammar() {
        let enbf = r#"
            S ::= A C
            A ::= a | ε
            C ::= c
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let follow_S = &grammar.follow_sets["S"];
        assert!(follow_S.contains("$"));

        let follow_A = &grammar.follow_sets["A"];
        assert!(follow_A.contains("c"));

        let follow_C = &grammar.follow_sets["C"];
        assert!(follow_C.contains("$"));
    }

    #[test]
    fn test_parse_error_reporting() {
        let enbf = r#"
            S ::= a b
        "#;
        let grammar = Grammar::parse(enbf).expect("Failed to parse grammar");

        let input = "a c";
        let mut parser = ParserStruct::new(input, &grammar, 1);
        let result = parser.parse();
        assert!(result.is_err());
        if let Err(ParseError::UnexpectedToken { expected, found, position }) = result {
            assert_eq!(expected, vec!["b".to_string()]);
            assert_eq!(found, "c");
            assert_eq!(position, 1);
        }
    }
}