//! Details of the `#[ruma_api(...)]` attributes.

use syn::{
    parse::{Parse, ParseStream},
    Ident, Token,
};

/// Like syn::MetaNameValue, but expects an identifier as the value. Also, we don't care about the
/// the span of the equals sign, so we don't have the `eq_token` field from syn::MetaNameValue.
pub struct MetaNameValue {
    /// The part left of the equals sign
    pub name: Ident,
    /// The part right of the equals sign
    pub value: Ident,
}

/// Like syn::Meta, but only parses ruma_api attributes
pub enum Meta {
    /// A single word, like `query` in `#[ruma_api(query)]`
    Word(Ident),
    /// A name-value pair, like `header = CONTENT_TYPE` in `#[ruma_api(header = CONTENT_TYPE)]`
    NameValue(MetaNameValue),
}

impl Meta {
    /// Check if the given attribute is a ruma_api attribute. If it is, parse it.
    ///
    /// # Panics
    ///
    /// Panics if the given attribute is a ruma_api attribute, but fails to parse.
    pub fn from_attribute(attr: &syn::Attribute) -> syn::Result<Option<Self>> {
        if attr.path.is_ident("ruma_api") {
            attr.parse_args().map(Some)
        } else {
            Ok(None)
        }
    }
}

impl Parse for Meta {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let ident = input.parse()?;

        if input.peek(Token![=]) {
            let _ = input.parse::<Token![=]>();
            Ok(Meta::NameValue(MetaNameValue { name: ident, value: input.parse()? }))
        } else {
            Ok(Meta::Word(ident))
        }
    }
}