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use proc_macro2::{Span, TokenStream};
use quote::quote;
use syn::{
    parse_quote, punctuated::Punctuated, token::Comma, Data, DataStruct, DeriveInput, Field,
    Fields, FieldsNamed, FieldsUnnamed, Lifetime, Stmt,
};

use super::{
    attributes::{parse_child_attributes, parse_container_attributes},
    rename_all,
};

pub fn expand_derive_from_row(input: &DeriveInput) -> syn::Result<TokenStream> {
    match &input.data {
        Data::Struct(DataStruct {
            fields: Fields::Named(FieldsNamed { named, .. }),
            ..
        }) => expand_derive_from_row_struct(input, named),

        Data::Struct(DataStruct {
            fields: Fields::Unnamed(FieldsUnnamed { unnamed, .. }),
            ..
        }) => expand_derive_from_row_struct_unnamed(input, unnamed),

        Data::Struct(DataStruct {
            fields: Fields::Unit,
            ..
        }) => Err(syn::Error::new_spanned(
            input,
            "unit structs are not supported",
        )),

        Data::Enum(_) => Err(syn::Error::new_spanned(input, "enums are not supported")),

        Data::Union(_) => Err(syn::Error::new_spanned(input, "unions are not supported")),
    }
}

fn expand_derive_from_row_struct(
    input: &DeriveInput,
    fields: &Punctuated<Field, Comma>,
) -> syn::Result<TokenStream> {
    let ident = &input.ident;

    let generics = &input.generics;

    let (lifetime, provided) = generics
        .lifetimes()
        .next()
        .map(|def| (def.lifetime.clone(), false))
        .unwrap_or_else(|| (Lifetime::new("'a", Span::call_site()), true));

    let (_, ty_generics, _) = generics.split_for_impl();

    let mut generics = generics.clone();
    generics.params.insert(0, parse_quote!(R: ::sqlx::Row));

    if provided {
        generics.params.insert(0, parse_quote!(#lifetime));
    }

    let predicates = &mut generics.make_where_clause().predicates;

    predicates.push(parse_quote!(&#lifetime ::std::primitive::str: ::sqlx::ColumnIndex<R>));

    for field in fields {
        let ty = &field.ty;

        predicates.push(parse_quote!(#ty: ::sqlx::decode::Decode<#lifetime, R::Database>));
        predicates.push(parse_quote!(#ty: ::sqlx::types::Type<R::Database>));
    }

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

    let container_attributes = parse_container_attributes(&input.attrs)?;

    let reads = fields.iter().filter_map(|field| -> Option<Stmt> {
        let id = &field.ident.as_ref()?;
        let attributes = parse_child_attributes(&field.attrs).unwrap();
        let id_s = attributes
            .rename
            .or_else(|| Some(id.to_string().trim_start_matches("r#").to_owned()))
            .map(|s| match container_attributes.rename_all {
                Some(pattern) => rename_all(&s, pattern),
                None => s,
            })
            .unwrap();

        let ty = &field.ty;

        if attributes.default {
            Some(
                parse_quote!(let #id: #ty = row.try_get(#id_s).or_else(|e| match e {
                ::sqlx::Error::ColumnNotFound(_) => {
                    ::std::result::Result::Ok(Default::default())
                },
                e => ::std::result::Result::Err(e)
            })?;),
            )
        } else {
            Some(parse_quote!(
                let #id: #ty = row.try_get(#id_s)?;
            ))
        }
    });

    let names = fields.iter().map(|field| &field.ident);

    Ok(quote!(
        #[automatically_derived]
        impl #impl_generics ::sqlx::FromRow<#lifetime, R> for #ident #ty_generics #where_clause {
            fn from_row(row: &#lifetime R) -> ::sqlx::Result<Self> {
                #(#reads)*

                ::std::result::Result::Ok(#ident {
                    #(#names),*
                })
            }
        }
    ))
}

fn expand_derive_from_row_struct_unnamed(
    input: &DeriveInput,
    fields: &Punctuated<Field, Comma>,
) -> syn::Result<TokenStream> {
    let ident = &input.ident;

    let generics = &input.generics;

    let (lifetime, provided) = generics
        .lifetimes()
        .next()
        .map(|def| (def.lifetime.clone(), false))
        .unwrap_or_else(|| (Lifetime::new("'a", Span::call_site()), true));

    let (_, ty_generics, _) = generics.split_for_impl();

    let mut generics = generics.clone();
    generics.params.insert(0, parse_quote!(R: ::sqlx::Row));

    if provided {
        generics.params.insert(0, parse_quote!(#lifetime));
    }

    let predicates = &mut generics.make_where_clause().predicates;

    predicates.push(parse_quote!(
        ::std::primitive::usize: ::sqlx::ColumnIndex<R>
    ));

    for field in fields {
        let ty = &field.ty;

        predicates.push(parse_quote!(#ty: ::sqlx::decode::Decode<#lifetime, R::Database>));
        predicates.push(parse_quote!(#ty: ::sqlx::types::Type<R::Database>));
    }

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

    let gets = fields
        .iter()
        .enumerate()
        .map(|(idx, _)| quote!(row.try_get(#idx)?));

    Ok(quote!(
        #[automatically_derived]
        impl #impl_generics ::sqlx::FromRow<#lifetime, R> for #ident #ty_generics #where_clause {
            fn from_row(row: &#lifetime R) -> ::sqlx::Result<Self> {
                ::std::result::Result::Ok(#ident (
                    #(#gets),*
                ))
            }
        }
    ))
}