use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, ItemFn};

/// Run test case when the environment variable is set.
/// ```
/// #[cfg(test)]
/// mod tests {
///
///     // PWD environment variable exists
///     #[test_with::env(PWD)]
///     fn test_works() {
///         assert!(true);
///     }
///
///     // NOTHING environment variable does not exist
///     #[test_with::env(NOTHING)]
///     fn test_ignored() {
///         panic!("should be ignored")
///     }
///
///     // NOT_SAYING environment variable does not exist
///     #[test_with::env(PWD, NOT_SAYING)]
///     fn test_ignored_too() {
///         panic!("should be ignored")
///     }
/// }
/// ```
#[proc_macro_attribute]
pub fn env(attr: TokenStream, stream: TokenStream) -> TokenStream {
    let input = parse_macro_input!(stream as ItemFn);
    let ItemFn {
        attrs,
        vis,
        sig,
        block,
    } = input;
    let attr_str = attr.to_string().replace(" ", "");
    let var_names: Vec<&str> = attr_str.split(',').collect();
    let mut all_var_exist = true;
    let mut ignore_msg = "because following variable not found:".to_string();
    for var in var_names.iter() {
        if std::env::var(var).is_err() {
            all_var_exist = false;
            ignore_msg.push(' ');
            ignore_msg.push_str(var);
        }
    }
    return if all_var_exist {
        quote! {
            #(#attrs)*
            #[test]
            #vis #sig #block
        }
        .into()
    } else {
        quote! {
           #(#attrs)*
           #[test]
           #[ignore = #ignore_msg ]
           #vis #sig #block
        }
        .into()
    };
}