use wasmi::{
        Error as InterpreterError, Externals, FuncInstance, FuncRef, HostError, ImportsBuilder,
        ModuleImportResolver, ModuleInstance, ModuleRef, RuntimeArgs, RuntimeValue, Signature, Trap,
        ValueType,
    };
use crate::{print, println};

pub fn run() {
    use alloc::vec::Vec;

    let bytes = include_bytes!("../../data/h.wasm");
    let b: Vec<u8> = bytes.iter().cloned().collect();
    println!("loaded wasm into a Vec");

    let module = wasmi::Module::from_buffer(&b).unwrap();
    let mut imports = ImportsBuilder::new();
    imports.push_resolver("h", &H);

    let instance = ModuleInstance::new(&module, &imports)
        .expect("failed to load wasm module")
        .assert_no_start();

    println!("invoking export");
    let _ = instance.invoke_export("h", &[], &mut H);
}

struct H;
const H_FUNC: usize = 0;

impl Externals for H {
    fn invoke_index(
        &mut self,
        index: usize,
        args: RuntimeArgs,
    ) -> Result<Option<RuntimeValue>, Trap> {
        use core::char::from_u32;
        match index {
            H_FUNC => {
                let ch_t: i32 = args.nth(0);
                let ch = from_u32(ch_t as u32);
                print!("{}", ch.unwrap());
                Ok(None)
            }

            _ => panic!("unknown function called"),
        }
    }
}

impl ModuleImportResolver for H {
    fn resolve_func(
        &self,
        field_name: &str,
        _signature: &Signature,
    ) -> Result<FuncRef, InterpreterError> {
        let func_ref = match field_name {
            "h" => FuncInstance::alloc_host(
                Signature::new(&[ValueType::I32][..], None),
                H_FUNC,
            ),
            _ => panic!("unknwon function asked for"),
        };

        Ok(func_ref)
    }
}