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use proc_macro2::{Ident, Span};
use proc_macro_error::proc_macro_error;
use syn::{
    parse, parse_macro_input, spanned::Spanned, ItemFn, PathArguments, ReturnType, Type, Visibility,
};

use proc_macro::TokenStream;
use quote::quote;

#[proc_macro_attribute]
pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    // check the function arguments
    if !f.sig.inputs.is_empty() {
        return parse::Error::new(
            f.sig.inputs.last().unwrap().span(),
            "`#[entry]` function accepts no arguments",
        )
        .to_compile_error()
        .into();
    }

    // check the function signature
    let valid_signature = f.sig.constness.is_none()
        && f.sig.asyncness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && f.sig.generics.params.is_empty()
        && f.sig.generics.where_clause.is_none()
        && f.sig.variadic.is_none()
        && match f.sig.output {
            ReturnType::Default => false,
            ReturnType::Type(_, ref ty) => matches!(**ty, Type::Never(_)),
        };

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[entry]` function must have signature `[unsafe] fn() -> !`",
        )
        .to_compile_error()
        .into();
    }

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let unsafety = f.sig.unsafety;
    let args = f.sig.inputs;
    let stmts = f.block.stmts;

    quote!(
        #[allow(non_snake_case)]
        #[export_name = "main"]
        #(#attrs)*
        pub #unsafety fn __risc_v_rt__main(#args) -> ! {
            #(#stmts)*
        }
    )
    .into()
}

#[allow(unused)]
fn is_simple_type(ty: &Type, name: &str) -> bool {
    if let Type::Path(p) = ty {
        if p.qself.is_none() && p.path.leading_colon.is_none() && p.path.segments.len() == 1 {
            let segment = p.path.segments.first().unwrap();
            if segment.ident == name && segment.arguments == PathArguments::None {
                return true;
            }
        }
    }
    false
}

/// This attribute allows placing functions into ram.
#[proc_macro_attribute]
#[proc_macro_error]
pub fn highcode(_args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    let section = quote! {
        #[link_section = ".highcode"]
        #[inline(never)] // make certain function is not inlined
    };

    quote!(
        #section
        #f
    )
    .into()
}

/// Marks a function as an interrupt handler
#[proc_macro_attribute]
pub fn interrupt(_args: TokenStream, input: TokenStream) -> TokenStream {
    let mut f = parse_macro_input!(input as ItemFn);

    // check the function arguments
    if !f.sig.inputs.is_empty() {
        return parse::Error::new(
            f.sig.inputs.last().unwrap().span(),
            "`#[interrupt]` function accepts no arguments",
        )
        .to_compile_error()
        .into();
    }

    let ident = f.sig.ident.clone();
    let ident_s = &ident.clone();

    let valid_signature = f.sig.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && f.sig.generics.params.is_empty()
        && f.sig.generics.where_clause.is_none()
        && f.sig.variadic.is_none()
        && match f.sig.output {
            ReturnType::Default => true,
            ReturnType::Type(_, ref ty) => match **ty {
                Type::Tuple(ref tuple) => tuple.elems.is_empty(),
                Type::Never(..) => true,
                _ => false,
            },
        }
        && f.sig.inputs.len() <= 1;

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[interrupt]` handlers must have signature `[unsafe] fn() [-> !]`",
        )
        .to_compile_error()
        .into();
    }

    let inner_fn_export_name = format!("__ch32v_rt_internal_{}", f.sig.ident);
    f.sig.ident = Ident::new(&inner_fn_export_name, proc_macro2::Span::call_site());

    // let ident = &f.sig.ident;
    let interrupt_name = ident_s.to_string();

    //let attrs = f.attrs;
    //let unsafety = f.sig.unsafety;

    // global asm to add mret instruction at the end of the interrupt handler
    let asm_src = format!(
        r#"
        .section .trap, "ax"
        .global {0}
    {0}:
        addi sp, sp, -4
        sw ra, 0(sp)
        jal {1}
        lw ra, 0(sp)
        addi sp, sp, 4
        mret
    "#,
        interrupt_name, inner_fn_export_name
    );

    quote!(
        core::arch::global_asm!(#asm_src);

        #[link_section = ".trap"]
        #[export_name = #inner_fn_export_name]
        #[allow(non_snake_case)]
        #f
    )
    .into()
}