// Copyright (c) 2017-present PyO3 Project and Contributors

use std::collections::HashSet;

use crate::{
    konst::{ConstAttributes, ConstSpec},
    pyfunction::PyFunctionOptions,
    pymethod,
};
use proc_macro2::TokenStream;
use pymethod::GeneratedPyMethod;
use quote::quote;
use syn::spanned::Spanned;

/// The mechanism used to collect `#[pymethods]` into the type object
pub enum PyClassMethodsType {
    Specialization,
    Inventory,
}

pub fn build_py_methods(
    ast: &mut syn::ItemImpl,
    methods_type: PyClassMethodsType,
) -> syn::Result<TokenStream> {
    if let Some((_, path, _)) = &ast.trait_ {
        bail_spanned!(path.span() => "#[pymethods] cannot be used on trait impl blocks");
    } else if ast.generics != Default::default() {
        bail_spanned!(
            ast.generics.span() =>
            "#[pymethods] cannot be used with lifetime parameters or generics"
        );
    } else {
        impl_methods(&ast.self_ty, &mut ast.items, methods_type)
    }
}

pub fn impl_methods(
    ty: &syn::Type,
    impls: &mut Vec<syn::ImplItem>,
    methods_type: PyClassMethodsType,
) -> syn::Result<TokenStream> {
    let mut trait_impls = Vec::new();
    let mut proto_impls = Vec::new();
    let mut methods = Vec::new();

    let mut implemented_proto_fragments = HashSet::new();

    for iimpl in impls.iter_mut() {
        match iimpl {
            syn::ImplItem::Method(meth) => {
                let options = PyFunctionOptions::from_attrs(&mut meth.attrs)?;
                match pymethod::gen_py_method(ty, &mut meth.sig, &mut meth.attrs, options)? {
                    GeneratedPyMethod::Method(token_stream) => {
                        let attrs = get_cfg_attributes(&meth.attrs);
                        methods.push(quote!(#(#attrs)* #token_stream));
                    }
                    GeneratedPyMethod::TraitImpl(token_stream) => {
                        let attrs = get_cfg_attributes(&meth.attrs);
                        trait_impls.push(quote!(#(#attrs)* #token_stream));
                    }
                    GeneratedPyMethod::SlotTraitImpl(method_name, token_stream) => {
                        implemented_proto_fragments.insert(method_name);
                        let attrs = get_cfg_attributes(&meth.attrs);
                        trait_impls.push(quote!(#(#attrs)* #token_stream));
                    }
                    GeneratedPyMethod::Proto(token_stream) => {
                        let attrs = get_cfg_attributes(&meth.attrs);
                        proto_impls.push(quote!(#(#attrs)* #token_stream))
                    }
                }
            }
            syn::ImplItem::Const(konst) => {
                let attributes = ConstAttributes::from_attrs(&mut konst.attrs)?;
                if attributes.is_class_attr {
                    let spec = ConstSpec {
                        rust_ident: konst.ident.clone(),
                        attributes,
                    };
                    let attrs = get_cfg_attributes(&konst.attrs);
                    let meth = gen_py_const(ty, &spec);
                    methods.push(quote!(#(#attrs)* #meth));
                }
            }
            _ => (),
        }
    }

    add_shared_proto_slots(ty, &mut proto_impls, implemented_proto_fragments);

    Ok(match methods_type {
        PyClassMethodsType::Specialization => {
            let methods_registration = impl_py_methods(ty, methods);
            let protos_registration = impl_protos(ty, proto_impls);

            quote! {
                #(#trait_impls)*

                #protos_registration

                #methods_registration
            }
        }
        PyClassMethodsType::Inventory => {
            let inventory = submit_methods_inventory(ty, methods, proto_impls);
            quote! {
                #(#trait_impls)*

                #inventory
            }
        }
    })
}

fn gen_py_const(cls: &syn::Type, spec: &ConstSpec) -> TokenStream {
    let member = &spec.rust_ident;
    let deprecations = &spec.attributes.deprecations;
    let python_name = &spec.null_terminated_python_name();
    quote! {
        ::pyo3::class::PyMethodDefType::ClassAttribute({
            ::pyo3::class::PyClassAttributeDef::new(
                #python_name,
                ::pyo3::class::methods::PyClassAttributeFactory({
                    fn __wrap(py: ::pyo3::Python<'_>) -> ::pyo3::PyObject {
                        #deprecations
                        ::pyo3::IntoPy::into_py(#cls::#member, py)
                    }
                    __wrap
                })
            )
        })
    }
}

fn impl_py_methods(ty: &syn::Type, methods: Vec<TokenStream>) -> TokenStream {
    quote! {
        impl ::pyo3::class::impl_::PyMethods<#ty>
            for ::pyo3::class::impl_::PyClassImplCollector<#ty>
        {
            fn py_methods(self) -> &'static [::pyo3::class::methods::PyMethodDefType] {
                static METHODS: &[::pyo3::class::methods::PyMethodDefType] = &[#(#methods),*];
                METHODS
            }
        }
    }
}

fn add_shared_proto_slots(
    ty: &syn::Type,
    proto_impls: &mut Vec<TokenStream>,
    mut implemented_proto_fragments: HashSet<String>,
) {
    macro_rules! try_add_shared_slot {
        ($first:literal, $second:literal, $slot:ident) => {{
            let first_implemented = implemented_proto_fragments.remove($first);
            let second_implemented = implemented_proto_fragments.remove($second);
            if first_implemented || second_implemented {
                proto_impls.push(quote! { ::pyo3::$slot!(#ty) })
            }
        }};
    }

    try_add_shared_slot!("__setattr__", "__delattr__", generate_pyclass_setattr_slot);
    try_add_shared_slot!("__set__", "__delete__", generate_pyclass_setdescr_slot);
    try_add_shared_slot!("__setitem__", "__delitem__", generate_pyclass_setitem_slot);
    try_add_shared_slot!("__add__", "__radd__", generate_pyclass_add_slot);
    try_add_shared_slot!("__sub__", "__rsub__", generate_pyclass_sub_slot);
    try_add_shared_slot!("__mul__", "__rmul__", generate_pyclass_mul_slot);
    try_add_shared_slot!("__mod__", "__rmod__", generate_pyclass_mod_slot);
    try_add_shared_slot!("__divmod__", "__rdivmod__", generate_pyclass_divmod_slot);
    try_add_shared_slot!("__lshift__", "__rlshift__", generate_pyclass_lshift_slot);
    try_add_shared_slot!("__rshift__", "__rrshift__", generate_pyclass_rshift_slot);
    try_add_shared_slot!("__and__", "__rand__", generate_pyclass_and_slot);
    try_add_shared_slot!("__or__", "__ror__", generate_pyclass_or_slot);
    try_add_shared_slot!("__xor__", "__rxor__", generate_pyclass_xor_slot);
    try_add_shared_slot!("__matmul__", "__rmatmul__", generate_pyclass_matmul_slot);
    try_add_shared_slot!("__truediv__", "__rtruediv__", generate_pyclass_truediv_slot);
    try_add_shared_slot!(
        "__floordiv__",
        "__rfloordiv__",
        generate_pyclass_floordiv_slot
    );
    try_add_shared_slot!("__pow__", "__rpow__", generate_pyclass_pow_slot);

    assert!(implemented_proto_fragments.is_empty());
}

fn impl_protos(ty: &syn::Type, proto_impls: Vec<TokenStream>) -> TokenStream {
    quote! {
        impl ::pyo3::class::impl_::PyMethodsProtocolSlots<#ty>
            for ::pyo3::class::impl_::PyClassImplCollector<#ty>
        {
            fn methods_protocol_slots(self) -> &'static [::pyo3::ffi::PyType_Slot] {
                &[#(#proto_impls),*]
            }
        }
    }
}

fn submit_methods_inventory(
    ty: &syn::Type,
    methods: Vec<TokenStream>,
    proto_impls: Vec<TokenStream>,
) -> TokenStream {
    quote! {
        ::pyo3::inventory::submit! {
            #![crate = ::pyo3] {
                type Inventory = <#ty as ::pyo3::class::impl_::HasMethodsInventory>::Methods;
                <Inventory as ::pyo3::class::impl_::PyMethodsInventory>::new(::std::vec![#(#methods),*], ::std::vec![#(#proto_impls),*])
            }
        }
    }
}

fn get_cfg_attributes(attrs: &[syn::Attribute]) -> Vec<&syn::Attribute> {
    attrs
        .iter()
        .filter(|attr| attr.path.is_ident("cfg"))
        .collect()
}