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//! Infrastructure for parsing fields from text.
use proc_macro2::{Span, TokenStream};

use quote::{quote, quote_spanned};
use syn::{spanned::Spanned, *};

use crate::error_message::ParentRef;

use super::{Field, FieldParsePart};

/// A field parsed from a XML text.
///
/// Maps to `#[xml(text)]`.
#[derive(Debug)]
pub(crate) struct TextField {
    /// The codec implementation to use.
    ///
    /// If set, parsing does not use the `FromXmlText` / `IntoXmlText` traits
    /// but instead uses the `TextCodec` trait on the given type.
    pub(super) codec: Option<Type>,
}

impl TextField {
    /// Construct a new `#[xml(text)]` field.
    ///
    /// `codec` must be the value of the `codec = ..` option, which, if given
    /// overrides how the text is converted to a rust value.
    ///
    /// `attr_span` is used for emitting error messages when no better span
    /// can be constructed. This should point at the `#[xml(..)]` meta of the
    /// field or another closely-related object.
    pub(super) fn new(_attr_span: &Span, codec: Option<Type>) -> Result<Self> {
        Ok(Self { codec })
    }
}

impl Field for TextField {
    fn is_text(&self) -> bool {
        true
    }

    fn build_try_from_element(
        &self,
        _container_name: &ParentRef,
        _container_namespace_expr: &Expr,
        tempname: Ident,
        _member: &Member,
        ty: &Type,
    ) -> Result<FieldParsePart> {
        let decode = match self.codec {
            Some(ref codec_ty) => {
                let codec_ty_decode = quote_spanned! {codec_ty.span()=> <#codec_ty as ::xso::TextCodec::<#ty>>::decode};
                quote! {
                    #codec_ty_decode(&residual.text())?
                }
            }
            None => {
                let ty_from_xml_text =
                    quote_spanned! {ty.span()=> <#ty as ::xso::FromXmlText>::from_xml_text};
                quote! {
                    #ty_from_xml_text(&residual.text())?
                }
            }
        };

        Ok(FieldParsePart {
            tempinit: quote! {
                let #tempname: #ty = #decode;
            },
            value: quote! { #tempname },
            ..FieldParsePart::default()
        })
    }

    fn build_into_element(
        &self,
        _container_name: &ParentRef,
        _container_namespace_expr: &Expr,
        _member: &Member,
        ty: &Type,
        access: Expr,
    ) -> Result<TokenStream> {
        let encode = match self.codec {
            Some(ref codec_ty) => {
                let codec_ty_encode = quote_spanned! {codec_ty.span()=> <#codec_ty as ::xso::TextCodec::<#ty>>::encode};
                quote! {
                    #codec_ty_encode(#access).unwrap_or_else(String::new)
                }
            }
            None => {
                let ty_into_xml_text =
                    quote_spanned! {ty.span()=> <#ty as ::xso::IntoXmlText>::into_xml_text};
                quote! {
                    #ty_into_xml_text(#access)
                }
            }
        };

        Ok(quote! {
            {
                let __text = #encode;
                if __text.len() > 0 {
                    builder.append(::xso::exports::minidom::Node::Text(__text))
                } else {
                    builder
                }
            }
        })
    }

    fn build_set_namespace(
        &self,
        _input: &Ident,
        _ty: &Type,
        _access: Expr,
    ) -> Result<TokenStream> {
        Ok(TokenStream::default())
    }
}