use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, DeriveInput, Error, Expr, LitStr, Result};
#[proc_macro_derive(Command, attributes(command))]
pub fn derive_command(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    expand(&input)
        .unwrap_or_else(Error::into_compile_error)
        .into()
}
fn expand(input: &DeriveInput) -> Result<proc_macro2::TokenStream> {
    let attr = input
        .attrs
        .iter()
        .find(|attr| attr.path().is_ident("command"))
        .ok_or_else(|| {
            Error::new_spanned(&input.ident, "missing #[command(id = ...)] attribute")
        })?;
    let mut id: Option<proc_macro2::TokenStream> = None;
    let mut name: Option<String> = None;
    attr.parse_nested_meta(|meta| {
        if meta.path.is_ident("id") {
            let value: Expr = meta.value()?.parse()?;
            id = Some(quote!(#value));
            return Ok(());
        }
        if meta.path.is_ident("name") {
            let value: LitStr = meta.value()?.parse()?;
            name = Some(value.value());
            return Ok(());
        }
        Err(meta.error("unsupported #[command(...)] key"))
    })?;
    let id = id.ok_or_else(|| Error::new_spanned(attr, "#[command(...)] requires `id`"))?;
    let ident = &input.ident;
    let name = name.unwrap_or_else(|| ident.to_string());
    Ok(quote! {
        impl ::logic::commands::CommandMeta for #ident {
            const COMMAND_TYPE: i32 = #id;
            const NAME: &'static str = #name;
        }
        ::titan::inventory::submit! {
            ::logic::commands::CommandRegistryEntry::of::<#ident>()
        }
    })
}