use crate::attrs::AttributeSpanWrapper;
use crate::field::Field;
use crate::model::Model;
use crate::util::{inner_of_option_ty, is_option_ty, wrap_in_dummy_mod};
use proc_macro2::TokenStream;
use quote::quote;
use quote::quote_spanned;
use syn::parse_quote;
use syn::spanned::Spanned as _;
use syn::{DeriveInput, Expr, Path, Result, Type};

pub fn derive(item: DeriveInput) -> Result<TokenStream> {
    let model = Model::from_item(&item, false, true)?;

    let tokens = model
        .table_names()
        .iter()
        .map(|table_name| derive_into_single_table(&item, &model, table_name))
        .collect::<Result<Vec<_>>>()?;

    Ok(wrap_in_dummy_mod(quote! {
        use diesel::insertable::Insertable;
        use diesel::internal::derives::insertable::UndecoratedInsertRecord;
        use diesel::prelude::*;

        #(#tokens)*
    }))
}

fn derive_into_single_table(
    item: &DeriveInput,
    model: &Model,
    table_name: &Path,
) -> Result<TokenStream> {
    let treat_none_as_default_value = model.treat_none_as_default_value();
    let struct_name = &item.ident;

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

    let mut generate_borrowed_insert = true;

    let mut direct_field_ty = Vec::with_capacity(model.fields().len());
    let mut direct_field_assign = Vec::with_capacity(model.fields().len());
    let mut ref_field_ty = Vec::with_capacity(model.fields().len());
    let mut ref_field_assign = Vec::with_capacity(model.fields().len());

    for field in model.fields() {
        // skip this field while generating the insertion
        if field.skip_insertion() {
            continue;
        }
        // Use field-level attr. with fallback to the struct-level one.
        let treat_none_as_default_value = match &field.treat_none_as_default_value {
            Some(attr) => {
                if let Some(embed) = &field.embed {
                    return Err(syn::Error::new(
                        embed.attribute_span,
                        "`embed` and `treat_none_as_default_value` are mutually exclusive",
                    ));
                }

                if !is_option_ty(&field.ty) {
                    return Err(syn::Error::new(
                        field.ty.span(),
                        "expected `treat_none_as_default_value` field to be of type `Option<_>`",
                    ));
                }

                attr.item
            }
            None => treat_none_as_default_value,
        };

        match (field.serialize_as.as_ref(), field.embed()) {
            (None, true) => {
                direct_field_ty.push(field_ty_embed(field, None));
                direct_field_assign.push(field_expr_embed(field, None));
                ref_field_ty.push(field_ty_embed(field, Some(quote!(&'insert))));
                ref_field_assign.push(field_expr_embed(field, Some(quote!(&))));
            }
            (None, false) => {
                direct_field_ty.push(field_ty(
                    field,
                    table_name,
                    None,
                    treat_none_as_default_value,
                )?);
                direct_field_assign.push(field_expr(
                    field,
                    table_name,
                    None,
                    treat_none_as_default_value,
                )?);
                ref_field_ty.push(field_ty(
                    field,
                    table_name,
                    Some(quote!(&'insert)),
                    treat_none_as_default_value,
                )?);
                ref_field_assign.push(field_expr(
                    field,
                    table_name,
                    Some(quote!(&)),
                    treat_none_as_default_value,
                )?);
            }
            (Some(AttributeSpanWrapper { item: ty, .. }), false) => {
                direct_field_ty.push(field_ty_serialize_as(
                    field,
                    table_name,
                    ty,
                    treat_none_as_default_value,
                )?);
                direct_field_assign.push(field_expr_serialize_as(
                    field,
                    table_name,
                    ty,
                    treat_none_as_default_value,
                )?);

                generate_borrowed_insert = false; // as soon as we hit one field with #[diesel(serialize_as)] there is no point in generating the impl of Insertable for borrowed structs
            }
            (Some(AttributeSpanWrapper { attribute_span, .. }), true) => {
                return Err(syn::Error::new(
                    *attribute_span,
                    "`#[diesel(embed)]` cannot be combined with `#[diesel(serialize_as)]`",
                ));
            }
        }
    }

    let insert_owned = quote! {
        impl #impl_generics Insertable<#table_name::table> for #struct_name #ty_generics
            #where_clause
        {
            type Values = <(#(#direct_field_ty,)*) as Insertable<#table_name::table>>::Values;

            fn values(self) -> <(#(#direct_field_ty,)*) as Insertable<#table_name::table>>::Values {
                (#(#direct_field_assign,)*).values()
            }
        }
    };

    let insert_borrowed = if generate_borrowed_insert {
        let mut impl_generics = item.generics.clone();
        impl_generics.params.push(parse_quote!('insert));
        let (impl_generics, ..) = impl_generics.split_for_impl();

        quote! {
            impl #impl_generics Insertable<#table_name::table>
                for &'insert #struct_name #ty_generics
            #where_clause
            {
                type Values = <(#(#ref_field_ty,)*) as Insertable<#table_name::table>>::Values;

                fn values(self) -> <(#(#ref_field_ty,)*) as Insertable<#table_name::table>>::Values {
                    (#(#ref_field_assign,)*).values()
                }
            }
        }
    } else {
        quote! {}
    };

    Ok(quote! {
        #[allow(unused_qualifications)]
        #insert_owned

        #[allow(unused_qualifications)]
        #insert_borrowed

        impl #impl_generics UndecoratedInsertRecord<#table_name::table>
                for #struct_name #ty_generics
            #where_clause
        {
        }
    })
}

fn field_ty_embed(field: &Field, lifetime: Option<TokenStream>) -> TokenStream {
    let field_ty = &field.ty;
    let span = field.span;
    quote_spanned!(span=> #lifetime #field_ty)
}

fn field_expr_embed(field: &Field, lifetime: Option<TokenStream>) -> TokenStream {
    let field_name = &field.name;
    quote!(#lifetime self.#field_name)
}

fn field_ty_serialize_as(
    field: &Field,
    table_name: &Path,
    ty: &Type,
    treat_none_as_default_value: bool,
) -> Result<TokenStream> {
    let column_name = field.column_name()?.to_ident()?;
    let span = field.span;
    if treat_none_as_default_value {
        let inner_ty = inner_of_option_ty(ty);

        Ok(quote_spanned! {span=>
            std::option::Option<diesel::dsl::Eq<
                #table_name::#column_name,
                #inner_ty,
            >>
        })
    } else {
        Ok(quote_spanned! {span=>
            diesel::dsl::Eq<
                #table_name::#column_name,
                #ty,
            >
        })
    }
}

fn field_expr_serialize_as(
    field: &Field,
    table_name: &Path,
    ty: &Type,
    treat_none_as_default_value: bool,
) -> Result<TokenStream> {
    let field_name = &field.name;
    let column_name = field.column_name()?.to_ident()?;
    let column = quote!(#table_name::#column_name);
    if treat_none_as_default_value {
        if is_option_ty(ty) {
            Ok(quote!(::std::convert::Into::<#ty>::into(self.#field_name).map(|v| #column.eq(v))))
        } else {
            Ok(
                quote!(std::option::Option::Some(#column.eq(::std::convert::Into::<#ty>::into(self.#field_name)))),
            )
        }
    } else {
        Ok(quote!(#column.eq(::std::convert::Into::<#ty>::into(self.#field_name))))
    }
}

fn field_ty(
    field: &Field,
    table_name: &Path,
    lifetime: Option<TokenStream>,
    treat_none_as_default_value: bool,
) -> Result<TokenStream> {
    let column_name = field.column_name()?.to_ident()?;
    let span = field.span;
    if treat_none_as_default_value {
        let inner_ty = inner_of_option_ty(&field.ty);

        Ok(quote_spanned! {span=>
            std::option::Option<diesel::dsl::Eq<
                #table_name::#column_name,
                #lifetime #inner_ty,
            >>
        })
    } else {
        let inner_ty = &field.ty;

        Ok(quote_spanned! {span=>
            diesel::dsl::Eq<
                #table_name::#column_name,
                #lifetime #inner_ty,
            >
        })
    }
}

fn field_expr(
    field: &Field,
    table_name: &Path,
    lifetime: Option<TokenStream>,
    treat_none_as_default_value: bool,
) -> Result<TokenStream> {
    let field_name = &field.name;
    let column_name = field.column_name()?.to_ident()?;

    let column: Expr = parse_quote!(#table_name::#column_name);
    if treat_none_as_default_value {
        if is_option_ty(&field.ty) {
            if lifetime.is_some() {
                Ok(quote!(self.#field_name.as_ref().map(|x| #column.eq(x))))
            } else {
                Ok(quote!(self.#field_name.map(|x| #column.eq(x))))
            }
        } else {
            Ok(quote!(std::option::Option::Some(#column.eq(#lifetime self.#field_name))))
        }
    } else {
        Ok(quote!(#column.eq(#lifetime self.#field_name)))
    }
}