use crate::limits::{MAX_WASM_FUNCTION_RETURNS, MAX_WASM_START_ARGS};

use crate::prelude::*;

use crate::{BinaryReader, FromReader, Result};

/// Represents the start function in a WebAssembly component.

#[derive(Debug, Clone)]

pub struct ComponentStartFunction {

    /// The index to the start function.

    pub func_index: u32,

    /// The start function arguments.

    ///

    /// The arguments are specified by value index.

    pub arguments: Box<[u32]>,

    /// The number of expected results for the start function.

    pub results: u32,

}

impl<'a> FromReader<'a> for ComponentStartFunction {

    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {

        let func_index = reader.read_var_u32()?;

        let arguments = reader

            .read_iter(MAX_WASM_START_ARGS, "start function arguments")?

            .collect::<Result<_>>()?;

        let results = reader.read_size(MAX_WASM_FUNCTION_RETURNS, "start function results")? as u32;

        Ok(ComponentStartFunction {

            func_index,

            arguments,

            results,

        })

    }

}