use crate::IxArg;
use anyhow::Result;
use heck::CamelCase;
use quote::quote;

// Namespace for calculating instruction sighash signatures for any instruction
// not affecting program state.
pub const SIGHASH_GLOBAL_NAMESPACE: &str = "global";

// We don't technically use sighash, because the input arguments aren't given.
// Rust doesn't have method overloading so no need to use the arguments.
// However, we do namespace methods in the preeimage so that we can use
// different traits with the same method name.
pub fn sighash(namespace: &str, name: &str) -> [u8; 8] {
    let preimage = format!("{namespace}:{name}");

    let mut sighash = [0u8; 8];
    sighash.copy_from_slice(&crate::hash::hash(preimage.as_bytes()).to_bytes()[..8]);
    sighash
}

pub fn gen_discriminator(namespace: &str, name: impl ToString) -> proc_macro2::TokenStream {
    let discriminator = sighash(namespace, name.to_string().as_str());
    format!("&{discriminator:?}").parse().unwrap()
}

pub fn generate_ix_variant(name: &str, args: &[IxArg]) -> Result<proc_macro2::TokenStream> {
    let ix_arg_names: Vec<&syn::Ident> = args.iter().map(|arg| &arg.name).collect();
    let ix_name_camel = generate_ix_variant_name(name)?;

    let variant = if args.is_empty() {
        quote! {
            #ix_name_camel
        }
    } else {
        quote! {
            #ix_name_camel {
                #(#ix_arg_names),*
            }
        }
    };
    Ok(variant)
}

pub fn generate_ix_variant_name(name: &str) -> Result<syn::Ident> {
    Ok(syn::parse_str(&name.to_camel_case())?)
}
