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extern crate proc_macro;
use heck::{CamelCase, ShoutySnakeCase};
use proc_macro::{Ident, Span, TokenStream, TokenTree};

/// Expands an input `ident` as UPPERCASE
#[proc_macro]
pub fn upper(input: TokenStream) -> TokenStream {
    let ident = Ident::new(&input.to_string().to_uppercase(), Span::call_site());
    TokenStream::from(TokenTree::Ident(ident))
}

/// Expands an input `ident` as lowercase
#[proc_macro]
pub fn lower(input: TokenStream) -> TokenStream {
    let ident = Ident::new(&input.to_string().to_lowercase(), Span::call_site());
    TokenStream::from(TokenTree::Ident(ident))
}

/// Expands an input `ident` as snake_case
/// e.g. `HelloWorld` -> `hello_world`
#[proc_macro]
pub fn snake(input: TokenStream) -> TokenStream {
    let raw_ident = &input.to_string();
    let mut s = String::new();
    for (i, c) in raw_ident.chars().enumerate() {
        if c.is_uppercase() || c.is_numeric() {
            if i > 0 {
                s.push('_');
            }
            s.push(c.to_lowercase().to_string().chars().next().unwrap());
        } else {
            s.push(c)
        }
    }
    let ident = Ident::new(&s, Span::call_site());
    TokenStream::from(TokenTree::Ident(ident))
}

/// Expands an input `ident` as CamelCase
/// e.g. `helloWorld` -> `HelloWorld`
#[proc_macro]
pub fn camel(input: TokenStream) -> TokenStream {
    let ident = Ident::new(&input.to_string().to_camel_case(), Span::call_site());
    TokenStream::from(TokenTree::Ident(ident))
}

/// Expands an input `ident` as SHOUTY_CASE
/// e.g. `HelloWorld` -> `HELLO_WORLD`
#[proc_macro]
pub fn shouty(input: TokenStream) -> TokenStream {
    let ident = Ident::new(&input.to_string().to_shouty_snake_case(), Span::call_site());
    TokenStream::from(TokenTree::Ident(ident))
}