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use crate::ast::{self, kw};
use crate::parser::{Parse, Parser, Result};

/// A WebAssembly event directive, part of the exception handling proposal.
#[derive(Debug)]
pub struct Event<'a> {
    /// Where this event was defined
    pub span: ast::Span,
    /// An optional name by which to refer to this event in name resolution.
    pub id: Option<ast::Id<'a>>,
    /// Optional export directives for this event.
    pub exports: ast::InlineExport<'a>,
    /// The type of event that is defined.
    pub ty: EventType<'a>,
}

/// Listing of various types of events that can be defined in a wasm module.
#[derive(Clone, Debug)]
pub enum EventType<'a> {
    /// An exception event, where the payload is the type signature of the event
    /// (constructor parameters, etc).
    Exception(ast::TypeUse<'a, ast::FunctionType<'a>>),
}

impl<'a> Parse<'a> for Event<'a> {
    fn parse(parser: Parser<'a>) -> Result<Self> {
        let span = parser.parse::<kw::event>()?.0;
        let id = parser.parse()?;
        let exports = parser.parse()?;
        let ty = parser.parse()?;
        Ok(Event {
            span,
            id,
            exports,
            ty,
        })
    }
}

impl<'a> Parse<'a> for EventType<'a> {
    fn parse(parser: Parser<'a>) -> Result<Self> {
        Ok(EventType::Exception(parser.parse()?))
    }
}