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// Rust language amplification derive library providing multiple generic trait
// implementations, type wrappers, derive macros and other language enhancements
//
// Written in 2019-2021 by
//     Dr. Maxim Orlovsky <orlovsky@pandoracore.com>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the MIT License
// along with this software.
// If not, see <https://opensource.org/licenses/MIT>.

use syn::parse::{Parse, Result, ParseBuffer};
use syn::{Path, Lit};
use syn::ext::IdentExt;
use proc_macro2::{Ident, TokenStream};
use quote::ToTokens;

use crate::ArgValue;

/// Drop-in replacement for [`syn::NestedMeta`], which allows to parse
/// attributes which can have arguments made of either literal, path or
/// [`MetaArgNameValue`] expressions.
pub enum MetaArgs {
    /// Attribute argument in form of literal
    Literal(Lit),

    /// Attribute argument in form of a path
    Path(Path),

    /// Attribute argument in form of `name = value` expression, where value
    /// can be any [`ArgValue`]-representable data
    NameValue(MetaArgNameValue),
}

impl Parse for MetaArgs {
    fn parse(input: &ParseBuffer) -> Result<Self> {
        if input.peek2(Token![=]) {
            input.parse().map(MetaArgs::NameValue)
        } else if input.peek(Ident::peek_any)
            || input.peek(Token![::]) && input.peek3(Ident::peek_any)
        {
            input.parse().map(MetaArgs::Path)
        } else {
            input.parse().map(MetaArgs::Literal)
        }
    }
}

impl ToTokens for MetaArgs {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        match self {
            MetaArgs::Literal(lit) => lit.to_tokens(tokens),
            MetaArgs::Path(path) => path.to_tokens(tokens),
            MetaArgs::NameValue(meta) => meta.to_tokens(tokens),
        }
    }
}

/// Drop-in replacement for [`syn::MetaNameValue`] used for parsing named
/// arguments inside attributes which name is always an [`proc_macro2::Ident`]
/// (and not [`syn::Path`]) and value can be not only a literal, but of any
/// valid rust type.
pub struct MetaArgNameValue {
    /// Argument name
    pub name: Ident,
    /// Token placeholder
    pub eq_token: Token![=],
    /// Argument value
    pub value: ArgValue,
}

impl Parse for MetaArgNameValue {
    fn parse(input: &ParseBuffer) -> Result<Self> {
        Ok(MetaArgNameValue {
            name: input.parse()?,
            eq_token: input.parse()?,
            value: input.parse()?,
        })
    }
}

impl ToTokens for MetaArgNameValue {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.name.to_tokens(tokens);
        self.eq_token.to_tokens(tokens);
        self.value.to_tokens(tokens);
    }
}

impl Parse for ArgValue {
    fn parse(input: &ParseBuffer) -> Result<Self> {
        if input.peek(Lit) {
            input.parse().map(ArgValue::Literal)
        } else {
            input.parse().map(ArgValue::Type)
        }
    }
}

impl ToTokens for ArgValue {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        match self {
            ArgValue::Literal(lit) => lit.to_tokens(tokens),
            ArgValue::Type(ty) => ty.to_tokens(tokens),
            ArgValue::None => quote! { ! }.to_tokens(tokens),
        }
    }
}