use proc_macro::TokenStream;
use proc_macro2::{Span, TokenStream as TokenStream2};
use proc_macro_error::{abort, proc_macro_error};
use quote::{format_ident, quote, ToTokens};
use syn::{
    parse::Result as ParseResult, parse_macro_input, spanned::Spanned, Attribute, Fields, Ident,
    Meta, NestedMeta,
};

/// extract traits from attribute
///  `#[services(Piano,Tuba)]` returns vec![ Piano, Tuba ]
///  items in the vec are syn::Path, and may have more than one path segment,
///    as in instruments::Piano
///
fn attr_traits(attr: &Attribute, key: &str) -> Vec<syn::Path> {
    let mut traits = Vec::new();
    if attr.path.is_ident(key) {
        if let Ok(Meta::List(ref ml)) = attr.parse_meta() {
            for n in ml.nested.iter() {
                if let NestedMeta::Meta(Meta::Path(p)) = n {
                    traits.push(p.clone())
                }
            }
        }
    }
    traits
}

#[allow(dead_code)]
struct ReceiverDef {
    attrs: Vec<Attribute>,
    attrs_span: Span,
    ident: Ident,
    ident_span: Span,
    fields: Fields,
}

impl syn::parse::Parse for ReceiverDef {
    fn parse(input: syn::parse::ParseStream) -> ParseResult<Self> {
        let derive_input: syn::DeriveInput = input.parse()?;
        let attrs_span = derive_input.span();
        let syn::DeriveInput { attrs, ident, data, .. } = derive_input;
        let ident_span = ident.span();
        let fields = match data {
            syn::Data::Struct(data) => data.fields,
            _ => {
                return Err(syn::Error::new(
                    ident_span,
                    "derive macro only works for structs",
                ))
            }
        };
        Ok(ReceiverDef {
            attrs,
            attrs_span,
            ident,
            ident_span,
            fields,
        })
    }
}

#[proc_macro_error]
#[proc_macro_derive(Actor, attributes(services))]
pub fn derive_actor(input: TokenStream) -> TokenStream {
    let actor_receiver = parse_macro_input!(input as ReceiverDef);

    let mut traits = Vec::new();
    for attr in actor_receiver.attrs.iter() {
        traits.extend(attr_traits(attr, "services"));
    }
    if traits.is_empty() {
        abort!(
            actor_receiver.attrs_span,
            "Missing list of traits. try `#[services(Trait1,Trait2)]`"
        );
    }
    let actor_ident = actor_receiver.ident;
    let dispatch_impl = gen_dispatch(&traits, &actor_ident);

    let output = quote!(

    // version of the host-actor api
    pub const HOST_API_VERSION : u32 = 1;

    #[link(wasm_import_module = "wasmbus")]
    #[cfg(target_arch = "wasm32")]
    extern "C" {
        pub fn __guest_response(ptr: *const u8, len: usize);
        pub fn __guest_error(ptr: *const u8, len: usize);
        pub fn __guest_request(op_ptr: *const u8, ptr: *const u8);
    }

    #[no_mangle]
    pub extern "C" fn __wasmbus_rpc_version() -> u32 {
        HOST_API_VERSION
    }

    #[no_mangle]
    #[cfg(target_arch = "wasm32")]
    pub extern "C" fn __guest_call(op_len: i32, req_len: i32) -> i32 {
        use std::slice;

        let buf: Vec<u8> = Vec::with_capacity(req_len as _);
        let req_ptr = buf.as_ptr();

        let opbuf: Vec<u8> = Vec::with_capacity(op_len as _);
        let op_ptr = opbuf.as_ptr();

        let (slice, op) = unsafe {
            __guest_request(op_ptr, req_ptr);
            (
                slice::from_raw_parts(req_ptr, req_len as _),
                slice::from_raw_parts(op_ptr, op_len as _),
            )
        };
        let method = String::from_utf8_lossy(op);
        let context = wasmbus_rpc::common::Context::default();
        let actor = #actor_ident ::default();
        let resp = futures::executor::block_on({
            wasmbus_rpc::common::MessageDispatch::dispatch(
                &actor,
                &context,
                wasmbus_rpc::common::Message {
                    method: &method,
                    arg: std::borrow::Cow::Borrowed(slice),
                },
            )
        });
        match resp {
            Ok(data) => {
                unsafe {
                    __guest_response(data.as_ptr(), data.len() as _);
                }
                1
            }
            Err(e) => {
                let errmsg = format!("Guest call failed for method {}: {}",
                        &method, e);
                unsafe {
                    __guest_error(errmsg.as_ptr(), errmsg.len() as _);
                }
                0
            }
        }
    }

       #dispatch_impl
    ); // end quote

    // struct #actor_ident { #fields }
    output.into()
}

#[proc_macro_derive(ActorHealthResponder)]
pub fn derive_health_responder(input: TokenStream) -> TokenStream {
    let actor_receiver = parse_macro_input!(input as ReceiverDef);
    let actor_ident = actor_receiver.ident;
    let output = quote!(

        #[async_trait]
        impl Actor for #actor_ident {
            async fn health_request(
                &self,
                ctx: &wasmbus_rpc::common::Context,
                arg: &wasmbus_rpc::core::HealthCheckRequest,
            ) -> wasmbus_rpc::error::RpcResult<wasmbus_rpc::core::HealthCheckResponse> {
                Ok(wasmbus_rpc::core::HealthCheckResponse {
                    healthy: true,
                    message: None,
                })
            }
        }
    ); // end quote
    output.into()
}

fn gen_dispatch(traits: &[syn::Path], ident: &Ident) -> TokenStream2 {
    let mut methods = Vec::new();
    let mut trait_receiver_impl = Vec::new();

    for path in traits.iter() {
        let path_str = path.segments.to_token_stream().to_string();
        let id = format_ident!("{}Receiver", &path_str);
        methods.push(quote!(
            #path_str => #id::dispatch(self, ctx, message).await
        ));
        trait_receiver_impl.push(quote!(
            impl #id for #ident { }
        ));
    }

    quote!(
        #[async_trait]
        impl wasmbus_rpc::common::MessageDispatch for #ident {
            async fn dispatch(
                &self,
                ctx: &wasmbus_rpc::common::Context,
                message: wasmbus_rpc::common::Message<'_>,
            ) -> std::result::Result<Vec<u8>, wasmbus_rpc::error::RpcError> {
                let (trait_name, trait_method) = message
                    .method
                    .rsplit_once('.')
                    .unwrap_or(("_", message.method));
                let message = wasmbus_rpc::common::Message {
                    method: trait_method,
                    arg: message.arg,
                };
                match trait_name {
                   #( #methods, )*
                    _ => Err(wasmbus_rpc::error::RpcError::MethodNotHandled(
                            format!("{}.{} - unknown method", trait_name,message.method)))
                }
            }
        }

      #( #trait_receiver_impl )*
    )
}

// for providers that do not implement any Service Receivers
// (for example, HttpServer that sends only)
// implement MessageDispatch that always return error if we receive rpc
fn gen_empty_dispatch(ident: &Ident) -> TokenStream2 {
    quote!(
        #[async_trait]
        impl wasmbus_rpc::common::MessageDispatch for #ident {
            async fn dispatch(&self, _ctx: &wasmbus_rpc::common::Context, message: wasmbus_rpc::common::Message<'_>) -> std::result::Result<Vec<u8>, wasmbus_rpc::error::RpcError> {
                Err(wasmbus_rpc::error::RpcError::MethodNotHandled(message.method.to_string()))
            }
        }
    )
}

#[proc_macro_error]
#[proc_macro_derive(Provider, attributes(services))]
pub fn derive_provider(input: TokenStream) -> TokenStream {
    let provider_receiver = parse_macro_input!(input as ReceiverDef);

    let mut traits = Vec::new();
    for attr in provider_receiver.attrs.iter() {
        traits.extend(attr_traits(attr, "services"));
    }
    let ident = provider_receiver.ident;
    let output = if traits.is_empty() {
        gen_empty_dispatch(&ident)
    } else {
        gen_dispatch(&traits, &ident)
    };
    output.into()
}