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

/// Usage: brainfuck!("++>-[].,")
#[proc_macro]
pub fn brainfuck(input: TokenStream) -> TokenStream {
    let lit = parse_macro_input!(input as LitStr);
    let s = lit.value();

    // Map characters -> OpCode tokens
    let mut ops = Vec::new();
    for ch in s.chars() {
        let token = match ch {
            '>' => Some(quote! { OpCode::IncrementPointer }),
            '<' => Some(quote! { OpCode::DecrementPointer }),
            '+' => Some(quote! { OpCode::Increment }),
            '-' => Some(quote! { OpCode::Decrement }),
            '.' => Some(quote! { OpCode::Write }),
            ',' => Some(quote! { OpCode::Read }),
            '[' => Some(quote! { OpCode::LoopBegin }),
            ']' => Some(quote! { OpCode::LoopEnd }),
            _ => None, // ignore comments/whitespace
        };
        if let Some(t) = token {
            ops.push(t);
        }
    }

    let n = ops.len();
    // Expand to a const array; the caller gets a [OpCode; N]
    let expanded = quote! {
        {
            const __BF_OPS: [OpCode; #n] = [ #(#ops),* ];
            __BF_OPS
        }
    };
    expanded.into()
}