unitval-derive 0.2.0

use proc_macro2::TokenStream;
use quote::{quote_spanned, ToTokens};
use std::{collections::HashSet, convert::TryFrom};
use syn::DataEnum;

use crate::unit::Unit;

pub struct Tokens {
    pub as_tokens: AsUnitValTokens,
    pub from_tokens: FromUnitValTokens,
}

impl TryFrom<&DataEnum> for Tokens {
    type Error = TokenStream;

    fn try_from(value: &DataEnum) -> Result<Self, Self::Error> {
        let mut as_tokens = vec![];
        let mut from_tokens = vec![];
        let mut seen_values = HashSet::new();

        for variant in &value.variants {
            let unit = Unit::try_from(variant)?;
            if seen_values.contains(&unit.unitval) {
                return Err(quote_spanned! {
                    variant.ident.span() =>
                    compile_error!("Enum variant contains duplicate unitval value");
                });
            }
            as_tokens.push(unit.as_unitval_tokens());
            from_tokens.push(unit.from_unitval_tokens());
            seen_values.insert(unit.unitval);
        }
        Ok(Tokens {
            as_tokens: AsUnitValTokens(as_tokens),
            from_tokens: FromUnitValTokens(from_tokens),
        })
    }
}

pub struct AsUnitValTokens(Vec<TokenStream>);

impl ToTokens for AsUnitValTokens {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.0.clone().into_iter().for_each(|t| tokens.extend(t))
    }
}

pub struct FromUnitValTokens(Vec<TokenStream>);

impl ToTokens for FromUnitValTokens {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.0.clone().into_iter().for_each(|t| tokens.extend(t))
    }
}