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use wasmer::*;

pub use anyhow::Result;

fn _ipcs_arg_count(ctx: &mut Ctx) -> u32 {
    println!("_ipcs_arg_count");
    let data = ctx.data.cast::<IoData>();
    (unsafe { &*data }).args.len() as _
}

fn _ipcs_arg_len(ctx: &mut Ctx, idx: u32) -> u32 {
    println!("_ipcs_arg_len: {}", idx);
    let data = ctx.data.cast::<IoData>();
    (unsafe { &*data }).args[idx as usize].len() as u32
}

fn _ipcs_arg_read(ctx: &mut Ctx, idx: u32, ptr: u32, offset: u32, len: u32) -> u32 {
    println!("_ipcs_arg_read: {}, {}, {}, {}", idx, ptr, offset, len);
    let data = ctx.data.cast::<IoData>();
    let arg = (unsafe { &*data }).args[idx as usize];

    let mem = ctx.memory(0);
    let view = mem.view::<u8>();

    let iter = arg[offset as usize..(offset + len) as usize]
        .iter()
        .zip(view[ptr as usize..(ptr + len) as usize].iter());

    let mut count = 0;
    for (src, dst) in iter {
        dst.set(*src);
        count += 1;
    }
    count
}

fn _ipcs_ret(ctx: &mut Ctx, ptr: u32, len: u32) {
    let data = ctx.data.cast::<IoData>();
    let mem = ctx.memory(0).view::<u8>();
    for v in &mem[ptr as usize..(ptr + len) as usize] {
        unsafe {
            (&mut *data).ret.push(v.get());
        }
    }
}

struct IoData<'a> {
    ret: Vec<u8>,
    args: &'a [&'a [u8]],
}

/// Execute wasm module (which is expected to conform to ipcs platform
/// along with a list of arguments (arguments provided here are raw buffers). At this layer we don't care about IPFS
/// TODO: Introduce file-like abstraction to support streaming processing of data.
pub fn exec(wasm: &[u8], args: &[&[u8]]) -> Result<Vec<u8>, wasmer::error::Error> {
    let imports = imports! {
        "_ipcs" => {
            "_ipcs_arg_count" => func!(_ipcs_arg_count),
            "_ipcs_arg_len" => func!(_ipcs_arg_len),
            "_ipcs_arg_read" => func!(_ipcs_arg_read),
            "_ipcs_ret" => func!(_ipcs_ret),
        },
    };

    let mut instance = instantiate(wasm, &imports)?;

    let mut io_data = IoData { ret: vec![], args };

    instance.context_mut().data = &mut io_data as *mut _ as *mut _;

    let entrypoint = format!("_ipcs_start");

    let main = instance.dyn_func(&entrypoint)?;
    assert_eq!(main.signature().params().len(), 0);
    instance.call(&entrypoint, &[])?;
    return Ok(io_data.ret);
}