//! Nyash EncodingBox Plugin - UTF-8/Base64/Hex helpers

use once_cell::sync::Lazy;
use std::collections::HashMap;
use std::sync::{Mutex, atomic::{AtomicU32, Ordering}};

const OK: i32 = 0;
const E_SHORT: i32 = -1;
const E_TYPE: i32 = -2;
const E_METHOD: i32 = -3;
const E_ARGS: i32 = -4;
const E_PLUGIN: i32 = -5;
const E_HANDLE: i32 = -8;

const M_BIRTH: u32 = 0;           // constructor (stateless)
const M_TO_UTF8_BYTES: u32 = 1;   // toUtf8Bytes(s) -> bytes
const M_FROM_UTF8_BYTES: u32 = 2; // fromUtf8Bytes(bytes) -> string
const M_BASE64_ENC: u32 = 3;      // base64Encode(s|bytes) -> string
const M_BASE64_DEC: u32 = 4;      // base64Decode(str) -> bytes
const M_HEX_ENC: u32 = 5;         // hexEncode(s|bytes) -> string
const M_HEX_DEC: u32 = 6;         // hexDecode(str) -> bytes
const M_FINI: u32 = u32::MAX;

// Assign an unused type id
const TYPE_ID_ENCODING: u32 = 53;

struct EncInstance; // stateless

static INST: Lazy<Mutex<HashMap<u32, EncInstance>>> = Lazy::new(|| Mutex::new(HashMap::new()));
static NEXT_ID: AtomicU32 = AtomicU32::new(1);

#[no_mangle]
pub extern "C" fn nyash_plugin_abi() -> u32 { 1 }

#[no_mangle]
pub extern "C" fn nyash_plugin_init() -> i32 { OK }

#[no_mangle]
pub extern "C" fn nyash_plugin_invoke(
    type_id: u32,
    method_id: u32,
    instance_id: u32,
    args: *const u8,
    args_len: usize,
    result: *mut u8,
    result_len: *mut usize,
) -> i32 {
    if type_id != TYPE_ID_ENCODING { return E_TYPE; }
    unsafe {
        match method_id {
            M_BIRTH => {
                if result_len.is_null() { return E_ARGS; }
                if preflight(result, result_len, 4) { return E_SHORT; }
                let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
                if let Ok(mut m) = INST.lock() { m.insert(id, EncInstance); } else { return E_PLUGIN; }
                let b = id.to_le_bytes(); std::ptr::copy_nonoverlapping(b.as_ptr(), result, 4); *result_len = 4; OK
            }
            M_FINI => { if let Ok(mut m) = INST.lock() { m.remove(&instance_id); OK } else { E_PLUGIN } }
            M_TO_UTF8_BYTES => {
                let s = match read_arg_string(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                write_tlv_bytes(s.as_bytes(), result, result_len)
            }
            M_FROM_UTF8_BYTES => {
                let bytes = match read_arg_bytes(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                match String::from_utf8(bytes) { Ok(s) => write_tlv_string(&s, result, result_len), Err(_) => write_tlv_string("", result, result_len) }
            }
            M_BASE64_ENC => {
                if let Some(b) = read_arg_bytes(args, args_len, 0) { let s = base64::encode(b); return write_tlv_string(&s, result, result_len); }
                let s = match read_arg_string(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                let enc = base64::encode(s.as_bytes());
                write_tlv_string(&enc, result, result_len)
            }
            M_BASE64_DEC => {
                let s = match read_arg_string(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                match base64::decode(s.as_bytes()) { Ok(b) => write_tlv_bytes(&b, result, result_len), Err(_) => write_tlv_bytes(&[], result, result_len) }
            }
            M_HEX_ENC => {
                if let Some(b) = read_arg_bytes(args, args_len, 0) { let s = hex::encode(b); return write_tlv_string(&s, result, result_len); }
                let s = match read_arg_string(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                let enc = hex::encode(s.as_bytes());
                write_tlv_string(&enc, result, result_len)
            }
            M_HEX_DEC => {
                let s = match read_arg_string(args, args_len, 0) { Some(v) => v, None => return E_ARGS };
                match hex::decode(s.as_bytes()) { Ok(b) => write_tlv_bytes(&b, result, result_len), Err(_) => write_tlv_bytes(&[], result, result_len) }
            }
            _ => E_METHOD,
        }
    }
}

fn preflight(result: *mut u8, result_len: *mut usize, needed: usize) -> bool {
    unsafe { if result_len.is_null() { return false; } if result.is_null() || *result_len < needed { *result_len = needed; return true; } }
    false
}
fn write_tlv_result(payloads: &[(u8, &[u8])], result: *mut u8, result_len: *mut usize) -> i32 {
    if result_len.is_null() { return E_ARGS; }
    let mut buf: Vec<u8> = Vec::with_capacity(4 + payloads.iter().map(|(_,p)| 4 + p.len()).sum::<usize>());
    buf.extend_from_slice(&1u16.to_le_bytes()); buf.extend_from_slice(&(payloads.len() as u16).to_le_bytes());
    for (tag, payload) in payloads { buf.push(*tag); buf.push(0); buf.extend_from_slice(&(payload.len() as u16).to_le_bytes()); buf.extend_from_slice(payload); }
    unsafe { let needed = buf.len(); if result.is_null() || *result_len < needed { *result_len = needed; return E_SHORT; } std::ptr::copy_nonoverlapping(buf.as_ptr(), result, needed); *result_len = needed; }
    OK
}
fn write_tlv_string(s: &str, result: *mut u8, result_len: *mut usize) -> i32 { write_tlv_result(&[(6u8, s.as_bytes())], result, result_len) }
fn write_tlv_bytes(b: &[u8], result: *mut u8, result_len: *mut usize) -> i32 { write_tlv_result(&[(7u8, b)], result, result_len) }

fn read_arg_string(args: *const u8, args_len: usize, n: usize) -> Option<String> {
    if args.is_null() || args_len < 4 { return None; }
    let buf = unsafe { std::slice::from_raw_parts(args, args_len) };
    let mut off = 4usize; for i in 0..=n { if buf.len() < off + 4 { return None; } let tag = buf[off]; let size = u16::from_le_bytes([buf[off+2], buf[off+3]]) as usize; if buf.len() < off + 4 + size { return None; } if i == n { if tag == 6 || tag == 7 { return Some(String::from_utf8_lossy(&buf[off+4..off+4+size]).to_string()); } else { return None; } } off += 4 + size; }
    None
}
fn read_arg_bytes(args: *const u8, args_len: usize, n: usize) -> Option<Vec<u8>> {
    if args.is_null() || args_len < 4 { return None; }
    let buf = unsafe { std::slice::from_raw_parts(args, args_len) };
    let mut off = 4usize; for i in 0..=n { if buf.len() < off + 4 { return None; } let tag = buf[off]; let size = u16::from_le_bytes([buf[off+2], buf[off+3]]) as usize; if buf.len() < off + 4 + size { return None; } if i == n { if tag == 7 || tag == 6 { return Some(buf[off+4..off+4+size].to_vec()); } else { return None; } } off += 4 + size; }
    None
}