use proc_macro2::{Ident, TokenStream};
use quote::{format_ident, quote, ToTokens};
use syn::punctuated::Punctuated;
use syn::token::Brace;
use syn::{
    AngleBracketedGenericArguments,
    Attribute,
    BareFnArg,
    Field,
    Fields,
    FieldsNamed,
    FnArg,
    GenericArgument,
    GenericParam,
    Generics,
    ImplItemMethod,
    ItemStruct,
    Lifetime,
    Path,
    PathSegment,
    Receiver,
    ReturnType,
    Token,
    Type,
    TypeBareFn,
    TypePath,
    TypeReference,
    Visibility,
};

use crate::syn_ext::{
    AngleBracketedGenericArgumentsExt,
    AttributeExt,
    AttributeStyle,
    BareFnArgExt,
    GenericsExt,
    IsMut,
    LifetimeExt,
    PathExt,
    PathSegmentExt,
    TypeBareFnExt,
    TypePathExt,
    TypeReferenceExt,
    VisibilityExt,
    WithColons,
    WithLeadingColons,
};
use crate::util::{create_path, create_unit_type_tuple};

pub struct Expectation
{
    ident: Ident,
    method_generics: Generics,
    generic_params: Punctuated<GenericParam, Token![,]>,
    receiver: Option<Receiver>,
    mock: Ident,
    arg_types: Vec<Type>,
    return_type: ReturnType,
    phantom_fields: Vec<PhantomField>,
}

impl Expectation
{
    pub fn new(
        mock: &Ident,
        item_method: &ImplItemMethod,
        generic_params: Punctuated<GenericParam, Token![,]>,
    ) -> Self
    {
        let ident = create_expectation_ident(mock, &item_method.sig.ident);

        let phantom_fields = Self::create_phantom_fields(
            &item_method
                .sig
                .generics
                .params
                .clone()
                .into_iter()
                .chain(generic_params.clone())
                .collect(),
        );

        let receiver =
            item_method
                .sig
                .inputs
                .first()
                .and_then(|first_arg| match first_arg {
                    FnArg::Receiver(receiver) => Some(receiver.clone()),
                    FnArg::Typed(_) => None,
                });

        let arg_types = item_method
            .sig
            .inputs
            .iter()
            .filter_map(|arg| match arg {
                FnArg::Typed(typed_arg) => Some(*typed_arg.ty.clone()),
                FnArg::Receiver(_) => None,
            })
            .collect::<Vec<_>>();

        let return_type = item_method.sig.output.clone();

        Self {
            ident,
            method_generics: item_method.sig.generics.clone(),
            generic_params,
            receiver,
            mock: mock.clone(),
            arg_types,
            return_type,
            phantom_fields,
        }
    }

    fn create_phantom_fields(
        generic_params: &Punctuated<GenericParam, Token![,]>,
    ) -> Vec<PhantomField>
    {
        generic_params
            .iter()
            .filter_map(|generic_param| match generic_param {
                GenericParam::Type(type_param) => {
                    let type_param_ident = &type_param.ident;

                    let field_ident = create_phantom_field_ident(
                        type_param_ident,
                        &PhantomFieldKind::Type,
                    );

                    let ty = create_phantom_data_type_path([GenericArgument::Type(
                        Type::Path(TypePath::new(Path::new(
                            WithLeadingColons::No,
                            [PathSegment::new(type_param_ident.clone(), None)],
                        ))),
                    )]);

                    Some(PhantomField {
                        field: field_ident,
                        type_path: ty,
                    })
                }
                GenericParam::Lifetime(lifetime_param) => {
                    let lifetime = &lifetime_param.lifetime;

                    let field_ident = create_phantom_field_ident(
                        &lifetime.ident,
                        &PhantomFieldKind::Lifetime,
                    );

                    let ty = create_phantom_data_type_path([GenericArgument::Type(
                        Type::Reference(TypeReference::new(
                            Some(lifetime.clone()),
                            IsMut::No,
                            Type::Tuple(create_unit_type_tuple()),
                        )),
                    )]);

                    Some(PhantomField {
                        field: field_ident,
                        type_path: ty,
                    })
                }
                GenericParam::Const(_) => None,
            })
            .collect()
    }
}

impl ToTokens for Expectation
{
    fn to_tokens(&self, tokens: &mut TokenStream)
    {
        let generics = {
            let mut generics = self.method_generics.clone();

            generics.params.extend(self.generic_params.clone());

            generics
        };

        let generic_params = &generics.params;

        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

        let bogus_generics = create_bogus_generics(generic_params);

        let opt_self_type = receiver_to_mock_self_type(&self.receiver, self.mock.clone());

        let ident = &self.ident;
        let phantom_fields = &self.phantom_fields;

        let returning_fn = Type::BareFn(TypeBareFn::new(
            opt_self_type
                .iter()
                .chain(self.arg_types.iter())
                .map(|ty| BareFnArg::new(ty.clone())),
            self.return_type.clone(),
        ));

        let expectation_struct = ItemStruct {
            attrs: vec![Attribute::new(
                AttributeStyle::Outer,
                create_path!(allow),
                quote! { (non_camel_case_types, non_snake_case) },
            )],
            vis: Visibility::new_pub_crate(),
            struct_token: <Token![struct]>::default(),
            ident: self.ident.clone(),
            generics: generics.clone().without_where_clause(),
            fields: Fields::Named(FieldsNamed {
                brace_token: Brace::default(),
                named: [Field {
                    attrs: vec![],
                    vis: Visibility::Inherited,
                    ident: Some(format_ident!("returning")),
                    colon_token: Some(<Token![:]>::default()),
                    ty: Type::Path(TypePath::new(Path::new(
                        WithLeadingColons::No,
                        [PathSegment::new(
                            format_ident!("Option"),
                            Some(AngleBracketedGenericArguments::new(
                                WithColons::No,
                                [GenericArgument::Type(returning_fn.clone())],
                            )),
                        )],
                    ))),
                }]
                .into_iter()
                .chain(phantom_fields.iter().cloned().map(Field::from))
                .collect(),
            }),
            semi_token: None,
        };

        quote! {
            #expectation_struct

            impl #impl_generics #ident #ty_generics #where_clause
            {
                fn new() -> Self {
                    Self {
                        returning: None,
                        #(#phantom_fields),*
                    }
                }

                #[allow(unused)]
                pub fn returning(
                    &mut self,
                    func: #returning_fn
                ) -> &mut Self
                {
                    self.returning = Some(func);

                    self
                }

                #[allow(unused)]
                fn strip_generic_params(
                    self,
                ) -> #ident<#(#bogus_generics),*>
                {
                    unsafe { std::mem::transmute(self) }
                }
            }

            impl #ident<#(#bogus_generics),*> {
                #[allow(unused)]
                fn with_generic_params<#generic_params>(
                    &self,
                ) -> &#ident #ty_generics
                {
                    // SAFETY: self is a pointer to a sane place, Rustc guarantees that
                    // by it being a reference. The generic parameters doesn't affect
                    // the size of self in any way, as they are only used in the function
                    // pointer field "returning"
                    unsafe { &*(self as *const Self).cast() }
                }

                #[allow(unused)]
                fn with_generic_params_mut<#generic_params>(
                    &mut self,
                ) -> &mut #ident #ty_generics
                {
                    // SAFETY: self is a pointer to a sane place, Rustc guarantees that
                    // by it being a reference. The generic parameters doesn't affect
                    // the size of self in any way, as they are only used in the function
                    // pointer field "returning"
                    unsafe { &mut *(self as *mut Self).cast() }
                }
            }
        }
        .to_tokens(tokens);
    }
}

pub fn create_expectation_ident(mock: &Ident, method: &Ident) -> Ident
{
    format_ident!("{mock}Expectation_{method}")
}

#[derive(Clone)]
struct PhantomField
{
    field: Ident,
    type_path: TypePath,
}

impl ToTokens for PhantomField
{
    fn to_tokens(&self, tokens: &mut TokenStream)
    {
        self.field.to_tokens(tokens);

        <Token![:]>::default().to_tokens(tokens);

        self.type_path.to_tokens(tokens);
    }
}

impl From<PhantomField> for Field
{
    fn from(phantom_field: PhantomField) -> Self
    {
        Self {
            attrs: vec![],
            vis: Visibility::Inherited,
            ident: Some(phantom_field.field.clone()),
            colon_token: Some(<Token![:]>::default()),
            ty: Type::Path(phantom_field.type_path),
        }
    }
}

fn create_phantom_field_ident(ident: &Ident, kind: &PhantomFieldKind) -> Ident
{
    match kind {
        PhantomFieldKind::Type => format_ident!("{ident}_phantom"),
        PhantomFieldKind::Lifetime => format_ident!("{ident}_lt_phantom"),
    }
}

enum PhantomFieldKind
{
    Type,
    Lifetime,
}

fn create_phantom_data_type_path(
    generic_args: impl IntoIterator<Item = GenericArgument>,
) -> TypePath
{
    TypePath::new(Path::new(
        WithLeadingColons::Yes,
        [
            PathSegment::new(format_ident!("std"), None),
            PathSegment::new(format_ident!("marker"), None),
            PathSegment::new(
                format_ident!("PhantomData"),
                Some(AngleBracketedGenericArguments::new(
                    WithColons::Yes,
                    generic_args,
                )),
            ),
        ],
    ))
}

fn create_bogus_generics(
    generic_params: &Punctuated<GenericParam, Token![,]>,
) -> Vec<GenericArgument>
{
    generic_params
        .iter()
        .filter_map(|generic_param| match generic_param {
            GenericParam::Type(_) => {
                Some(GenericArgument::Type(Type::Tuple(create_unit_type_tuple())))
            }
            GenericParam::Lifetime(_) => Some(GenericArgument::Lifetime(
                Lifetime::create(format_ident!("static")),
            )),
            GenericParam::Const(_) => None,
        })
        .collect()
}

fn receiver_to_mock_self_type(receiver: &Option<Receiver>, mock: Ident) -> Option<Type>
{
    receiver.as_ref().map(|receiver| {
        let self_type = Type::Path(TypePath::new(Path::new(
            WithLeadingColons::No,
            [PathSegment::new(mock, None)],
        )));

        if let Some((_, lifetime)) = &receiver.reference {
            return Type::Reference(TypeReference::new(
                lifetime.clone(),
                receiver.mutability.into(),
                self_type,
            ));
        }

        self_type
    })
}