//! Internal implementation details of `xtensa-lx106-rt`.
//!
//! Do not use this crate directly.

extern crate proc_macro;

use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::quote;
use std::collections::HashSet;
use syn::{
    parse, parse_macro_input, spanned::Spanned, AttrStyle, AttributeArgs, Attribute, FnArg, Ident,
    Item, ItemFn, ItemStatic, ReturnType, Stmt, Type, Visibility,
};

/// Marks a function as the main function to be called on program start
#[proc_macro_attribute]
pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
    let mut f = parse_macro_input!(input as ItemFn);

    // check the function signature
    let valid_signature = f.sig.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && f.sig.inputs.is_empty()
        && 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) => match **ty {
            Type::Never(_) => true,
            _ => false,
        },
    };

    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();
    }

    let (statics, stmts) = match extract_static_muts(f.block.stmts) {
        Err(e) => return e.to_compile_error().into(),
        Ok(x) => x,
    };

    f.sig.ident = Ident::new(
        &format!("__xtensa_lx106_rt_{}", f.sig.ident),
        Span::call_site(),
    );
    f.sig.inputs.extend(statics.iter().map(|statik| {
        let ident = &statik.ident;
        let ty = &statik.ty;
        let attrs = &statik.attrs;

        // Note that we use an explicit `'static` lifetime for the entry point arguments. This makes
        // it more flexible, and is sound here, since the entry will not be called again, ever.
        syn::parse::<FnArg>(
            quote!(#[allow(non_snake_case)] #(#attrs)* #ident: &'static mut #ty).into(),
        )
            .unwrap()
    }));
    f.block.stmts = stmts;

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

    let resource_args = statics
        .iter()
        .map(|statik| {
            let (ref cfgs, ref attrs) = extract_cfgs(statik.attrs.clone());
            let ident = &statik.ident;
            let ty = &statik.ty;
            let expr = &statik.expr;
            quote! {
                #(#cfgs)*
                {
                    #(#attrs)*
                    static mut #ident: #ty = #expr;
                    &mut #ident
                }
            }
        })
        .collect::<Vec<_>>();

    if let Err(error) = check_attr_whitelist(&f.attrs, WhiteListCaller::Entry) {
        return error;
    }

    let (ref cfgs, ref attrs) = extract_cfgs(f.attrs.clone());

    quote!(
        #(#cfgs)*
        #(#attrs)*
        #[doc(hidden)]
        #[export_name = "main"]
        pub unsafe extern "C" fn #tramp_ident() {
            #ident(
                #(#resource_args),*
            )
        }

        #[inline(always)]
        #f
    )
        .into()
}

/// Marks a function as the pre_init function. This function is called before main and *before
/// the memory is initialized*.
#[proc_macro_attribute]
pub fn pre_init(args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    // check the function signature
    let valid_signature = f.sig.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.unsafety.is_some()
        && f.sig.abi.is_none()
        && f.sig.inputs.is_empty()
        && 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(),
            _ => false,
        },
    };

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[pre_init]` 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();
    }

    if let Err(error) = check_attr_whitelist(&f.attrs, WhiteListCaller::PreInit) {
        return error;
    }

    let attrs = f.attrs;
    let ident = f.sig.ident;
    let block = f.block;

    quote!(
        #[export_name = "__pre_init"]
        #[allow(missing_docs)]  // we make a private fn public, which can trigger this lint
        #(#attrs)*
        pub unsafe fn #ident() #block
    )
        .into()
}

/// Marks a function as the exception handler
///
/// ## Example
///
/// ```ignore
/// use xtensa_lx106_rt::{exception, ExceptionContext};
///
/// #[exception]
/// fn exception_handler(cause: ExceptionCause, save_frame: &ExceptionContext) {
///     // ...
/// }
/// ```
#[proc_macro_attribute]
pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
    let mut f = parse_macro_input!(input as ItemFn);

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

    if let Err(error) = check_attr_whitelist(&f.attrs, WhiteListCaller::Exception) {
        return error;
    }

    let valid_signature = f.sig.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && f.sig.inputs.len() <= 2
        && 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,
        },
    };

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

    let args = match f.sig.inputs.len() {
        0 => quote!(),
        1 => quote!(cause),
        _ => quote!(cause, frame),
    };

    let (statics, stmts) = match extract_static_muts(f.block.stmts) {
        Err(e) => return e.to_compile_error().into(),
        Ok(x) => x,
    };

    f.sig.ident = Ident::new(&format!("__xtensa_lx_106_{}", f.sig.ident), Span::call_site());
    f.sig.inputs.extend(statics.iter().map(|statik| {
        let ident = &statik.ident;
        let ty = &statik.ty;
        let attrs = &statik.attrs;
        syn::parse::<FnArg>(quote!(#[allow(non_snake_case)] #(#attrs)* #ident: &mut #ty).into())
            .unwrap()
    }));
    f.block.stmts = stmts;

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

    let (ref cfgs, ref attrs) = extract_cfgs(f.attrs.clone());

    quote!(
        #(#cfgs)*
        #(#attrs)*
        #[doc(hidden)]
        #[export_name = "__user_exception"]
        pub unsafe extern "C" fn #tramp_ident(
            cause: xtensa_lx106_rt::ExceptionCause,
            frame: xtensa_lx106_rt::ExceptionContext
        ) {
            #ident(
                #args
            )
        }

        #[inline(always)]
        #f
    )
        .into()
}

/// Marks a function as the interrupt handler for the given interrupt type
#[proc_macro_attribute]
pub fn interrupt(args: TokenStream, input: TokenStream) -> TokenStream {
    let mut f: ItemFn = syn::parse(input).expect("`#[interrupt]` must be applied to a function");

    let attr_args = parse_macro_input!(args as AttributeArgs);

    let naked = f.attrs.iter().position(|x| eq(x, "naked")).is_some();

    if naked {
        return parse::Error::new(
            Span::call_site(),
            "#[naked] interrupt handlers are not supported",
        )
            .to_compile_error()
            .into();
    }

    if attr_args.len() != 1 {
        return parse::Error::new(
            Span::call_site(),
            "This attribute requires one arguments",
        )
            .to_compile_error()
            .into();
    }

    let ty = match &attr_args[0] {
        syn::NestedMeta::Lit(syn::Lit::Str(lit_str)) => lit_str.value(),
        syn::NestedMeta::Meta(syn::Meta::Path(path)) if path.get_ident().is_some() => path.get_ident().unwrap().to_string(),
        _ => {
            return parse::Error::new(
                Span::call_site(),
                "This attribute accepts a string attribute",
            )
                .to_compile_error()
                .into();
        }
    }.to_ascii_lowercase();

    match ty.as_str() {
        "slc" | "spi" | "gpio" | "uart" | "ccompare" | "soft" | "timer1" => (),
        _ => {
            return parse::Error::new(
                Span::call_site(),
                format!("Invalid interrupt type {}, the following types are supported:  slc, spi, gpio, uart, ccompare, soft and timer1", ty),
            )
                .to_compile_error()
                .into();
        }
    }

    if let Err(error) = check_attr_whitelist(&f.attrs, WhiteListCaller::Interrupt) {
        return error;
    }

    let ident_s = format!("__{}_interrupt", ty);

    let valid_signature = f.sig.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && ((!naked && f.sig.inputs.len() <= 1) || (naked && f.sig.inputs.len() == 0))
        && 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,
        },
    };

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[interrupt]` handlers must have signature `[unsafe] fn([u32[, &ExceptionContext]]) [-> !]`",
        )
            .to_compile_error()
            .into();
    }

    let (statics, stmts) = match extract_static_muts(f.block.stmts.iter().cloned()) {
        Err(e) => return e.to_compile_error().into(),
        Ok(x) => x,
    };

    let args = match f.sig.inputs.len() {
        0 => quote!(),
        1 => quote!(frame),
        _ => unreachable!()
    };

    f.sig.ident = Ident::new(&format!("__xtensa_lx_106_{}", f.sig.ident), Span::call_site());
    f.sig.inputs.extend(statics.iter().map(|statik| {
        let ident = &statik.ident;
        let ty = &statik.ty;
        let attrs = &statik.attrs;
        syn::parse::<FnArg>(quote!(#[allow(non_snake_case)] #(#attrs)* #ident: &mut #ty).into())
            .unwrap()
    }));
    f.block.stmts = stmts;

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

    let resource_args = statics
        .iter()
        .map(|statik| {
            let (ref cfgs, ref attrs) = extract_cfgs(statik.attrs.clone());
            let ident = &statik.ident;
            let ty = &statik.ty;
            let expr = &statik.expr;
            quote! {
                #(#cfgs)*
                {
                    #(#attrs)*
                    static mut #ident: #ty = #expr;
                    &mut #ident
                }
            }
        })
        .collect::<Vec<_>>();

    let (ref cfgs, ref attrs) = extract_cfgs(f.attrs.clone());

    quote!(
        #(#cfgs)*
        #(#attrs)*
        #[doc(hidden)]
        #[export_name = #ident_s]
        pub unsafe extern "C" fn #tramp_ident(
            frame: &xtensa_lx106_rt::exception::ExceptionContext
        ) {
                #ident(#args
                #(,#resource_args)*
            )
        }

        #[inline(always)]
        #f
    )
        .into()
}

/// Extracts `static mut` vars from the beginning of the given statements
fn extract_static_muts(
    stmts: impl IntoIterator<Item=Stmt>,
) -> Result<(Vec<ItemStatic>, Vec<Stmt>), parse::Error> {
    let mut istmts = stmts.into_iter();

    let mut seen = HashSet::new();
    let mut statics = vec![];
    let mut stmts = vec![];
    while let Some(stmt) = istmts.next() {
        match stmt {
            Stmt::Item(Item::Static(var)) => {
                if var.mutability.is_some() {
                    if seen.contains(&var.ident) {
                        return Err(parse::Error::new(
                            var.ident.span(),
                            format!("the name `{}` is defined multiple times", var.ident),
                        ));
                    }

                    seen.insert(var.ident.clone());
                    statics.push(var);
                } else {
                    stmts.push(Stmt::Item(Item::Static(var)));
                }
            }
            _ => {
                stmts.push(stmt);
                break;
            }
        }
    }

    stmts.extend(istmts);

    Ok((statics, stmts))
}

fn extract_cfgs(attrs: Vec<Attribute>) -> (Vec<Attribute>, Vec<Attribute>) {
    let mut cfgs = vec![];
    let mut not_cfgs = vec![];

    for attr in attrs {
        if eq(&attr, "cfg") {
            cfgs.push(attr);
        } else {
            not_cfgs.push(attr);
        }
    }

    (cfgs, not_cfgs)
}

#[allow(dead_code)]
enum WhiteListCaller {
    Entry,
    Exception,
    Interrupt,
    PreInit,
}

fn check_attr_whitelist(attrs: &[Attribute], caller: WhiteListCaller) -> Result<(), TokenStream> {
    let whitelist = &[
        "doc",
        "link_section",
        "cfg",
        "allow",
        "warn",
        "deny",
        "forbid",
        "cold",
        "ram",
    ];

    'o: for attr in attrs {
        for val in whitelist {
            if eq(&attr, &val) {
                continue 'o;
            }
        }

        let err_str = match caller {
            WhiteListCaller::Entry => {
                "this attribute is not allowed on a xtensa-lx106-rt entry point"
            }
            WhiteListCaller::Exception => {
                "this attribute is not allowed on an exception handler controlled by xtensa-lx106-rt"
            }
            WhiteListCaller::Interrupt => {
                if eq(&attr, "naked") {
                    continue 'o;
                }

                "this attribute is not allowed on an interrupt handler controlled by xtensa-lx106-rt"
            }
            WhiteListCaller::PreInit => {
                "this attribute is not allowed on a pre-init controlled by xtensa-lx106-rt"
            }
        };

        return Err(parse::Error::new(attr.span(), &err_str)
            .to_compile_error()
            .into());
    }

    Ok(())
}

/// Returns `true` if `attr.path` matches `name`
fn eq(attr: &Attribute, name: &str) -> bool {
    attr.style == AttrStyle::Outer && attr.path.is_ident(name)
}