use syn::{
    parse::{ParseStream, Parser},
    spanned::Spanned,
};

#[derive(Debug)]
pub enum ExportScope {
    PubOnly,
    Prefix(String),
    All,
}

impl Default for ExportScope {
    fn default() -> ExportScope {
        ExportScope::PubOnly
    }
}

pub trait ExportedParams: Sized {
    fn parse_stream(args: ParseStream) -> syn::Result<Self>;
    fn no_attrs() -> Self;
    fn from_info(info: ExportInfo) -> syn::Result<Self>;
}

pub struct AttrItem {
    pub key: proc_macro2::Ident,
    pub value: Option<syn::LitStr>,
    pub span: proc_macro2::Span,
}

pub struct ExportInfo {
    pub item_span: proc_macro2::Span,
    pub items: Vec<AttrItem>,
}

pub fn parse_attr_items(args: ParseStream) -> syn::Result<ExportInfo> {
    if args.is_empty() {
        return Ok(ExportInfo {
            item_span: args.span(),
            items: Vec::new(),
        });
    }
    let arg_list = args
        .call(syn::punctuated::Punctuated::<syn::Expr, syn::Token![,]>::parse_separated_nonempty)?;

    parse_punctuated_items(arg_list)
}

pub fn parse_punctuated_items(
    arg_list: syn::punctuated::Punctuated<syn::Expr, syn::Token![,]>,
) -> syn::Result<ExportInfo> {
    let list_span = arg_list.span();

    let mut attrs: Vec<AttrItem> = Vec::new();
    for arg in arg_list {
        let arg_span = arg.span();
        let (key, value) = match arg {
            syn::Expr::Assign(syn::ExprAssign {
                ref left,
                ref right,
                ..
            }) => {
                let attr_name: syn::Ident = match left.as_ref() {
                    syn::Expr::Path(syn::ExprPath {
                        path: attr_path, ..
                    }) => attr_path.get_ident().cloned().ok_or_else(|| {
                        syn::Error::new(attr_path.span(), "expecting attribute name")
                    })?,
                    x => return Err(syn::Error::new(x.span(), "expecting attribute name")),
                };
                let attr_value = match right.as_ref() {
                    syn::Expr::Lit(syn::ExprLit {
                        lit: syn::Lit::Str(string),
                        ..
                    }) => string.clone(),
                    x => return Err(syn::Error::new(x.span(), "expecting string literal")),
                };
                (attr_name, Some(attr_value))
            }
            syn::Expr::Path(syn::ExprPath {
                path: attr_path, ..
            }) => attr_path
                .get_ident()
                .cloned()
                .map(|a| (a, None))
                .ok_or_else(|| syn::Error::new(attr_path.span(), "expecting attribute name"))?,
            x => return Err(syn::Error::new(x.span(), "expecting identifier")),
        };
        attrs.push(AttrItem {
            key,
            value,
            span: arg_span,
        });
    }

    Ok(ExportInfo {
        item_span: list_span,
        items: attrs,
    })
}

pub(crate) fn outer_item_attributes<T: ExportedParams>(
    args: proc_macro2::TokenStream,
    _attr_name: &str,
) -> syn::Result<T> {
    if args.is_empty() {
        return Ok(T::no_attrs());
    }

    let parser = syn::punctuated::Punctuated::<syn::Expr, syn::Token![,]>::parse_separated_nonempty;
    let arg_list = parser.parse2(args)?;

    let export_info = parse_punctuated_items(arg_list)?;
    T::from_info(export_info)
}

pub(crate) fn inner_item_attributes<T: ExportedParams>(
    attrs: &mut Vec<syn::Attribute>,
    attr_name: &str,
) -> syn::Result<T> {
    // Find the #[rhai_fn] attribute which will turn be read for the function parameters.
    if let Some(rhai_fn_idx) = attrs
        .iter()
        .position(|a| a.path.get_ident().map(|i| *i == attr_name).unwrap_or(false))
    {
        let rhai_fn_attr = attrs.remove(rhai_fn_idx);
        rhai_fn_attr.parse_args_with(T::parse_stream)
    } else {
        Ok(T::no_attrs())
    }
}

pub(crate) fn deny_cfg_attr(attrs: &Vec<syn::Attribute>) -> syn::Result<()> {
    if let Some(cfg_attr) = attrs
        .iter()
        .find(|a| a.path.get_ident().map(|i| *i == "cfg").unwrap_or(false))
    {
        Err(syn::Error::new(
            cfg_attr.span(),
            "cfg attributes not allowed on this item",
        ))
    } else {
        Ok(())
    }
}