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use std::iter;

use better_any::{Tid, TidAble};
use proc_macro2::{Span, TokenStream};
use quote::quote;
use syn::Ident;

use crate::{
    context::Context,
    maybe_borrowed::MaybeBorrowed,
    passed_data::{PassedData, WithData},
};

use super::Generatable;

/// A trait Generatable / Template. This asserts that some type implements some trait.
#[derive(Tid, PartialEq, Eq, PartialOrd, Ord)]
pub struct Type<'a> {
    /// The type to check the asserted type equals
    pub r#type: MaybeBorrowed<'a, Ident>,
    /// The amount of generics the type should have
    pub generics_count: usize,
}

impl<'a> Type<'a> {
    /// Creates a new type template from some type to be checked against.
    /// Takes any T that can be turned into a MaybeBorrowed type, to support
    /// references as well as owned types
    pub fn new<T>(r#type: T, generics_count: usize) -> Self
    where
        T: Into<MaybeBorrowed<'a, Ident>>,
    {
        Self {
            r#type: r#type.into(),
            generics_count,
        }
    }
}

impl<'a> Generatable<'a> for Type<'a> {
    type GeneratableData = Ident;
    type TemplateData = ();
    type Assert = syn::Ident;

    fn generatable(
        Context {
            ident_generator, ..
        }: &mut Context,
    ) -> PassedData<Self::GeneratableData> {
        let ident = ident_generator.prefixed("assert_type_eq");
        let type_eq_ident = ident_generator.prefixed("TypeEq");

        quote! {
            trait #type_eq_ident {
                type This: ?Sized;
            }
            impl<T: ?Sized> #type_eq_ident for T {
                type This = Self;
            }

            fn #ident<T, U>()
            where
                T: ?Sized + TypeEq<This = U>,
                U: ?Sized,
            {
            }
        }
        .with_data(ident)
    }

    fn assert(
        &self,
        _context: &mut Context,
        (assert_type_eq, _): (&Self::GeneratableData, &Self::TemplateData),
        to_assert: &Self::Assert,
    ) -> Option<TokenStream> {
        let type_bound = &*self.r#type;

        if self.generics_count > 0 {
            let generic_ident = Ident::new("_", Span::call_site());
            let generic_ident_iter = iter::repeat(generic_ident).take(self.generics_count);

            Some(quote! {
                #assert_type_eq::<#to_assert,#type_bound<#(#generic_ident_iter),*>>();
            })
        } else {
            Some(quote! {
                #assert_type_eq::<#to_assert,#type_bound>();
            })
        }
    }

    fn template(
        &self,
        _context: &mut Context,
        _passed: &Self::GeneratableData,
    ) -> PassedData<Self::TemplateData>
    where
        Self::TemplateData: Default,
    {
        PassedData::default()
    }
}

#[cfg(test)]
mod test {
    use crate::ident_generator::MockIdentGenerator;
    use quote::quote;
    use syn::parse_quote;

    use super::*;

    #[test]
    fn generate_generatable() {
        let mut mock_ident_gen = MockIdentGenerator::new();

        mock_ident_gen.push_ident("mock_1");

        let mut context = Context {
            ident_generator: &mut mock_ident_gen,
        };

        assert_eq!(
            Type::generatable(&mut context),
            quote! {
                trait TypeEq {
                    type This: ?Sized;
                }
                impl<T: ?Sized> TypeEq for T {
                    type This = Self;
                }

                fn assert_type_eq_mock_1<T, U>()
                where
                    T: ?Sized + TypeEq<This = U>,
                    U: ?Sized,
                {
                }
            }
            .with_data(parse_quote!(assert_type_eq_mock_1)),
        );

        assert!(mock_ident_gen.has_no_idents_remaining());
    }

    #[test]
    fn generate_template() {
        let mut mock_ident_gen = MockIdentGenerator::new();
        let mut context = Context {
            ident_generator: &mut mock_ident_gen,
        };

        assert_eq!(
            Type {
                r#type: MaybeBorrowed::Owned(parse_quote!(Type)),
                generics_count: 2,
            }
            .template(&mut context, &parse_quote!(assert_type_eq_mock_1)),
            PassedData::<()>::default(),
        );
        assert!(mock_ident_gen.was_not_called());
    }

    #[test]
    fn generate_assert() {
        let mut mock_ident_gen = MockIdentGenerator::new();
        let mut context = Context {
            ident_generator: &mut mock_ident_gen,
        };

        assert_eq!(
            Type {
                r#type: MaybeBorrowed::Owned(parse_quote!(Type)),
                generics_count: 2,
            }
            .assert(
                &mut context,
                (&parse_quote!(assert_type_eq_mock_1), &()),
                &syn::Ident::new("Test", Span::call_site())
            )
            .map(|x| x.to_string()),
            Some(quote! {
                assert_type_eq_mock_1::<Test,Type<_,_>>();
            })
            .map(|x| x.to_string())
        );
        assert!(mock_ident_gen.was_not_called());
    }
}