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// ---------------------------------------------------------------------------
// Copyright:   (c) 2021 ff. Michael Amrhein (michael@adrhinum.de)
// License:     This program is part of a larger application. For license
//              details please read the file LICENSE.TXT provided together
//              with the application.
// ---------------------------------------------------------------------------
// $Source: fpdec-macros/src/lib.rs $
// $Revision: 2022-08-17T18:32:32+02:00 $

#![doc = include_str ! ("../README.md")]

use ::proc_macro::TokenStream;
use ::quote::quote;
use fpdec_core::{str_to_dec, ParseDecimalError, MAX_N_FRAC_DIGITS};

/// Macro used to convert a number literal into a `Decimal`.
///
/// The literal must be in the form
/// \[+|-]\<int\>\[.\<frac\>]\[<e|E>\[+|-]\<exp\>] or
/// \[+|-].\<frac\>\[<e|E>\[+|-]\<exp\>].
///
/// The resulting number of fractional digits is determined by the number of
/// digits in the fractional part of the literal minus the value of the signed
/// exponent.
///
/// The resulting value must not exceed the limits given by the internal
/// representaion of `Decimal`:
/// * The coefficient must fit into an `i128`.
/// * The number of fractional digits must not exceed the constant
///   `MAX_N_FRAC_DIGITS`.
///
/// # Panics
///
/// The macro panics if the conditions listed above are not met!
///
/// # Examples
///
/// ```ignore
/// let d = Dec!(17.5);
/// assert_eq!(d.to_string(), "17.5");
///
/// let d = Dec!(-170.5e-2);
/// assert_eq!(d.to_string(), "-1.705");
/// ```
#[allow(non_snake_case)]
#[proc_macro]
pub fn Dec(input: TokenStream) -> TokenStream {
    let mut src = input.to_string();
    // "-" and "+" get separated by a blank => remove it
    if src.starts_with("- ") || src.starts_with("+ ") {
        src.remove(1);
    }
    match str_to_dec(&src) {
        Err(e) => panic!("{}", e),
        Ok((mut coeff, mut exponent)) => {
            if -exponent > (MAX_N_FRAC_DIGITS as isize) {
                panic!("{}", ParseDecimalError::FracDigitLimitExceeded)
            }
            if exponent > 38 {
                // 10 ^ 39 > int128::MAX
                panic!("{}", ParseDecimalError::InternalOverflow);
            }
            if exponent > 0 {
                match coeff.checked_mul(10i128.pow(exponent as u32)) {
                    None => panic!("{}", ParseDecimalError::InternalOverflow),
                    Some(val) => {
                        coeff = val;
                    }
                }
                exponent = 0;
            }
            let n_frac_digits = -exponent as u8;
            quote!(
                Decimal::new_raw(#coeff, #n_frac_digits)
            )
            .into()
        }
    }
}