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use syn::{Field, DeriveInput, Data, Lit, Meta, Fields, FieldsNamed};

pub fn symbol_name(field: &Field) -> String {
    match find_str_attr_val(field, "dlopen_name") {
        Some(val) => val,
        None => //not found, so use field name
            match field.ident {
                Some(ref val) => val.to_string(),
                None => panic!("All structure fields need to be identifiable")
            }
    }
}

pub fn find_str_attr_val<'a>(field: &'a Field, attr_name: &str) -> Option<String> {
    for attr in field.attrs.iter() {
        match attr.parse_meta() {
            Ok(Meta::NameValue(ref meta)) => {
                if meta.ident == attr_name {
                    return match &meta.lit {
                        &Lit::Str(ref val, ..) => {
                            Some(val.value())
                        },
                        _ => panic!("{} attribute must be a string", attr_name)
                    }
                }
            },
            _ => continue
        }
    }
    None
}

pub fn has_marker_attr(field :&Field, attr_name: &str) -> bool {
    for attr in field.attrs.iter() {
        match attr.parse_meta() {
            Ok(Meta::Word(ref val)) => if val == attr_name{
              return true;
            },
            _ => continue
        }
    }
    false
}

pub fn get_fields<'a>(ast: &'a DeriveInput, trait_name: &str) -> &'a FieldsNamed {
    let vd = match ast.data {
        Data::Enum(_) | Data::Union(_) => panic ! ("{} can be only implemented for structures", trait_name),
        Data::Struct( ref val) => val
    };
    match &vd.fields {
        & Fields::Named( ref f) => f,
        & Fields::Unnamed(_) | &Fields::Unit => panic ! ("{} can be only implemented for structures", trait_name)
    }
}