/*
 * This file is part of the uutils coreutils package.
 *
 * (c) Roman Gafiyatullin <r.gafiyatullin@me.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

//!
//! The following tokens are present in the expr grammar:
//! * integer literal;
//! * string literal;
//! * infix binary operators;
//! * prefix operators.
//!
//! According to the man-page of expr we have expression split into tokens (each token -- separate CLI-argument).
//! Hence all we need is to map the strings into the Token structures, except for some ugly fiddling with +-escaping.
//!

#[derive(Debug)]
#[derive(Clone)]
pub enum Token {
    Value{ value: String },

    ParOpen,
    ParClose,

    InfixOp {
        precedence: u8,
        left_assoc: bool,
        value: String
    },

    PrefixOp {
        arity: usize,
        value: String
    },
}
impl Token {
    fn new_infix_op( v: &String, left_assoc: bool, precedence: u8 ) -> Self {
        Token::InfixOp{
            left_assoc: left_assoc,
            precedence: precedence,
            value: v.clone()
        }
    }
    fn new_value( v: &String ) -> Self {
        Token::Value{
            value: v.clone()
        }
    }

    fn is_infix_plus( &self ) -> bool {
        match *self {
            Token::InfixOp{ ref value, .. } => value == "+",
            _ => false
        }
    }
    fn is_a_number( &self ) -> bool {
        match *self {
            Token::Value{ ref value, .. } =>
                match value.parse::<i64>() {
                    Ok( _ ) => true,
                    Err( _ ) => false
                },
            _ => false,
        }
    }
    fn is_a_close_paren( &self ) -> bool {
        match *self {
            Token::ParClose => true,
            _ => false,
        }
    }
}

pub fn strings_to_tokens( strings: &[String] ) -> Result< Vec<(usize, Token)>, String > {
    let mut tokens_acc = Vec::with_capacity( strings.len() );
    let mut tok_idx = 1;

    for s in strings {
        let token_if_not_escaped =
            match s.as_ref() {
                "(" => Token::ParOpen,
                ")" => Token::ParClose,

                "^" => Token::new_infix_op( &s, false, 7 ),

                ":" => Token::new_infix_op( &s, true, 6 ),

                "*" => Token::new_infix_op( &s, true, 5 ),
                "/" => Token::new_infix_op( &s, true, 5 ),
                "%" => Token::new_infix_op( &s, true, 5 ),

                "+" => Token::new_infix_op( &s, true, 4 ),
                "-" => Token::new_infix_op( &s, true, 4 ),

                "=" => Token::new_infix_op( &s, true, 3 ),
                "!=" => Token::new_infix_op( &s, true, 3 ),
                "<" => Token::new_infix_op( &s, true, 3 ),
                ">" => Token::new_infix_op( &s, true, 3 ),
                "<=" => Token::new_infix_op( &s, true, 3 ),
                ">=" => Token::new_infix_op( &s, true, 3 ),

                "&" => Token::new_infix_op( &s, true, 2 ),

                "|" => Token::new_infix_op( &s, true, 1 ),

                "match" => Token::PrefixOp{ arity: 2, value: s.clone() },
                "substr" => Token::PrefixOp{ arity: 3, value: s.clone() },
                "index" => Token::PrefixOp{ arity: 2, value: s.clone() },
                "length" => Token::PrefixOp{ arity: 1, value: s.clone() },

                _ => Token::new_value( &s ),
            };
        push_token_if_not_escaped( &mut tokens_acc, tok_idx, token_if_not_escaped, &s );
        tok_idx += 1;
    }
    maybe_dump_tokens_acc( &tokens_acc );

    Ok( tokens_acc )
}

fn maybe_dump_tokens_acc( tokens_acc: &[(usize, Token)] ) {
    use std::env;

    if let Ok(debug_var) = env::var( "EXPR_DEBUG_TOKENS" ) {
        if debug_var == "1" {
            println!("EXPR_DEBUG_TOKENS");
            for token in tokens_acc {
                println!("\t{:?}", token);
            }
        }
    }
}

fn push_token_if_not_escaped( acc: &mut Vec<(usize, Token)>, tok_idx: usize, token: Token, s: &String ) {
    // Smells heuristics... :(
    let prev_is_plus =
        match acc.last() {
            None => false,
            Some( ref t )  => t.1.is_infix_plus(),
        };
    let should_use_as_escaped =
        if prev_is_plus && acc.len() >= 2 {
            let pre_prev = &acc[acc.len() - 2];
            ! ( pre_prev.1.is_a_number() || pre_prev.1.is_a_close_paren() )
        }
        else {
            prev_is_plus 
        };

    if should_use_as_escaped {
        acc.pop();
        acc.push( (tok_idx, Token::new_value( s )) )
    }
    else {
        acc.push( (tok_idx, token) )
    }
}