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use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
use syn;
use Bindings;

/// Field for the builder struct, implementing `quote::ToTokens`.
///
/// # Examples
///
/// Will expand to something like the following (depending on settings):
///
/// ```rust
/// # extern crate proc_macro2;
/// # #[macro_use]
/// # extern crate quote;
/// # #[macro_use]
/// # extern crate syn;
/// # #[macro_use]
/// # extern crate derive_builder_core;
/// # use derive_builder_core::{BuilderField, BuilderPattern};
/// # fn main() {
/// #    let attrs = vec![parse_quote!(#[some_attr])];
/// #    let mut field = default_builder_field!();
/// #    field.attrs = attrs.as_slice();
/// #
/// #    assert_eq!(quote!(#field).to_string(), quote!(
/// #[some_attr] pub foo: ::std::option::Option<String>,
/// #    ).to_string());
/// # }
/// ```
#[derive(Debug, Clone)]
pub struct BuilderField<'a> {
    /// Name of the target field.
    pub field_ident: &'a syn::Ident,
    /// Type of the target field.
    ///
    /// The corresonding builder field will be `Option<field_type>`.
    pub field_type: &'a syn::Type,
    /// Whether the builder implements a setter for this field.
    ///
    /// Note: We will fallback to `PhantomData` if the setter is disabled
    ///       to hack around issues with unused generic type parameters - at
    ///       least for now.
    pub field_enabled: bool,
    /// Visibility of this builder field, e.g. `syn::Visibility::Public`.
    pub field_visibility: syn::Visibility,
    /// Attributes which will be attached to this builder field.
    pub attrs: &'a [syn::Attribute],
    /// Bindings to libstd or libcore.
    pub bindings: Bindings,
}

impl<'a> ToTokens for BuilderField<'a> {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        if self.field_enabled {
            trace!("Deriving builder field for `{}`.", self.field_ident);
            let vis = &self.field_visibility;
            let ident = self.field_ident;
            let ty = self.field_type;
            let attrs = self.attrs;
            let option = self.bindings.option_ty();

            tokens.append_all(quote!(
                #(#attrs)* #vis #ident: #option<#ty>,
            ));
        } else {
            trace!(
                "Skipping builder field for `{}`, fallback to PhantomData.",
                self.field_ident
            );
            let ident = self.field_ident;
            let ty = self.field_type;
            let attrs = self.attrs;
            let phantom_data = self.bindings.phantom_data_ty();

            tokens.append_all(quote!(
                #(#attrs)* #ident: #phantom_data<#ty>,
            ));
        }
    }
}

/// Helper macro for unit tests. This is _only_ public in order to be accessible
/// from doc-tests too.
#[doc(hidden)]
#[macro_export]
macro_rules! default_builder_field {
    () => {{
        BuilderField {
            field_ident: &syn::Ident::new("foo", ::proc_macro2::Span::call_site()),
            field_type: &syn::parse_str("String").unwrap(),
            field_enabled: true,
            field_visibility: syn::parse_str("pub").unwrap(),
            attrs: &[parse_quote!(#[some_attr])],
            bindings: Default::default(),
        }
    }};
}

#[cfg(test)]
mod tests {
    #[allow(unused_imports)]
    use super::*;

    #[test]
    fn setter_enabled() {
        let field = default_builder_field!();

        assert_eq!(
            quote!(#field).to_string(),
            quote!(
                #[some_attr] pub foo: ::std::option::Option<String>,
            )
            .to_string()
        );
    }

    #[test]
    fn setter_disabled() {
        let mut field = default_builder_field!();
        field.field_enabled = false;

        assert_eq!(
            quote!(#field).to_string(),
            quote!(
                #[some_attr]
                foo: ::std::marker::PhantomData<String>,
            )
            .to_string()
        );
    }

    #[test]
    fn no_std_setter_enabled() {
        let mut field = default_builder_field!();
        field.bindings.no_std = true;

        assert_eq!(
            quote!(#field).to_string(),
            quote!(
                #[some_attr] pub foo: ::core::option::Option<String>,
            )
            .to_string()
        );
    }

    #[test]
    fn no_std_setter_disabled() {
        let mut field = default_builder_field!();
        field.bindings.no_std = true;
        field.field_enabled = false;

        assert_eq!(
            quote!(#field).to_string(),
            quote!(
                #[some_attr]
                foo: ::core::marker::PhantomData<String>,
            )
            .to_string()
        );
    }

    #[test]
    fn private_field() {
        let private = syn::Visibility::Inherited;
        let mut field = default_builder_field!();
        field.field_visibility = private;

        assert_eq!(
            quote!(#field).to_string(),
            quote!(
                #[some_attr]
                foo: ::std::option::Option<String>,
            )
            .to_string()
        );
    }
}