//! Apple process boundary: only the safe WASM interpreter sees remote updates.
use std::panic::{catch_unwind, AssertUnwindSafe};
use wasmi::{Config, Engine, Instance, Linker, Memory, Module, Store, StoreLimits, StoreLimitsBuilder};
const MAX_BYTES: usize = 8 * 1024 * 1024 + 1;
const FUEL: u64 = 40_000_000;
const WASM: &[u8] = include_bytes!("../../crdt/target/wasm32-unknown-unknown/release/docs_native_crdt.wasm");
pub struct Host {
    store: Store<StoreLimits>,
    instance: Instance,
    memory: Memory,
    output: Vec<u8>,
    failed: bool,
}
impl Host {
    pub fn new() -> Result<Self, &'static str> {
        let mut config = Config::default();
        config.consume_fuel(true);
        let engine = Engine::new(&config);
        let module = Module::new(&engine, WASM).map_err(|_| "invalid_module")?;
        // No imports are supplied: CRDT must remain independent of host JS,
        // filesystem, entropy and clock functions. Identity is an input.
        let linker = Linker::new(&engine);
        let limits = StoreLimitsBuilder::new().memory_size(64 * 1024 * 1024).instances(1).memories(1).tables(1).build();
        let mut store = Store::new(&engine, limits);
        store.limiter(|limits| limits);
        store.set_fuel(FUEL).map_err(|_| "fuel")?;
        let instance = linker.instantiate(&mut store, &module).map_err(|_| "invalid_module")?.start(&mut store).map_err(|_| "module_trap")?;
        let memory = instance.get_memory(&store, "memory").ok_or("invalid_module")?;
        Ok(Self {store, instance, memory, output: Vec::new(), failed: false})
    }
    pub fn call(&mut self, request: &[u8]) -> Result<&[u8], &'static str> {
        if self.failed || request.len() > MAX_BYTES { return Err("replica_unavailable"); }
        // Any failed mutation can have partially modified the WASM state. Once
        // failed, discard the replica; never let callers continue using it.
        self.failed = true;
        self.store.set_fuel(FUEL).map_err(|_| "fuel")?;
        let alloc = self.instance.get_typed_func::<u32, u32>(&self.store, "docs_editor_alloc").map_err(|_| "invalid_abi")?;
        let ptr = alloc.call(&mut self.store, request.len() as u32).map_err(|_| "module_trap")?;
        if ptr == 0 { return Err("allocation"); }
        self.memory.write(&mut self.store, ptr as usize, request).map_err(|_| "invalid_memory")?;
        let call = self.instance.get_typed_func::<(u32,u32), i32>(&self.store, "docs_editor_call").map_err(|_| "invalid_abi")?;
        let status = call.call(&mut self.store, (ptr, request.len() as u32)).map_err(|_| "module_trap")?;
        let free = self.instance.get_typed_func::<(u32,u32), ()>(&self.store, "docs_editor_free").map_err(|_| "invalid_abi")?;
        free.call(&mut self.store, (ptr, request.len() as u32)).map_err(|_| "module_trap")?;
        if status != 0 {
            // Report only a fixed whitelist of engine error codes, never content.
            let len = self.instance.get_typed_func::<(),u32>(&self.store, "docs_editor_output_len").map_err(|_| "invalid_abi")?.call(&mut self.store, ()).map_err(|_| "module_trap")? as usize;
            let start = self.instance.get_typed_func::<(),u32>(&self.store, "docs_editor_output_ptr").map_err(|_| "invalid_abi")?.call(&mut self.store, ()).map_err(|_| "module_trap")? as usize;
            let mut code = [0u8; 64];
            if len <= code.len() && self.memory.read(&self.store,start,&mut code[..len]).is_ok() {
                return Err(match &code[..len] { b"unknown_command" => "unknown_command", b"invalid_range" => "invalid_range", b"invalid_anchor" => "invalid_anchor", b"missing_node" => "missing_node", _ => "rejected_command" });
            }
            return Err("rejected_command");
        }
        let length = self.instance.get_typed_func::<(),u32>(&self.store, "docs_editor_output_len").map_err(|_| "invalid_abi")?.call(&mut self.store, ()).map_err(|_| "module_trap")? as usize;
        let start = self.instance.get_typed_func::<(),u32>(&self.store, "docs_editor_output_ptr").map_err(|_| "invalid_abi")?.call(&mut self.store, ()).map_err(|_| "module_trap")? as usize;
        if length > MAX_BYTES { return Err("oversized_output"); }
        self.output.resize(length, 0);
        self.memory.read(&self.store, start, &mut self.output).map_err(|_| "invalid_memory")?;
        self.failed = false;
        Ok(&self.output)
    }
}
#[no_mangle]
pub extern "C" fn docs_host_new() -> *mut Host {
    catch_unwind(|| Host::new().map(|h| Box::into_raw(Box::new(h))).unwrap_or(std::ptr::null_mut())).unwrap_or(std::ptr::null_mut())
}
/// # Safety
/// `host` must be returned by docs_host_new, uniquely owned, and freed once.
#[no_mangle]
pub unsafe extern "C" fn docs_host_free(host: *mut Host) {
    if !host.is_null() { let _ = catch_unwind(AssertUnwindSafe(|| drop(Box::from_raw(host)))); }
}
/// # Safety
/// Host/input/output must be valid for their stated lengths. The caller serializes calls.
#[no_mangle]
pub unsafe extern "C" fn docs_host_call(host: *mut Host, input: *const u8, length: usize, output: *mut u8, capacity: usize) -> i64 {
    if host.is_null() || input.is_null() || output.is_null() || length > MAX_BYTES || capacity > MAX_BYTES { return -1; }
    catch_unwind(AssertUnwindSafe(|| {
        let host = &mut *host;
        let bytes = std::slice::from_raw_parts(input, length);
        match host.call(bytes) {
            Ok(result) if result.len() <= capacity => {
                std::ptr::copy_nonoverlapping(result.as_ptr(), output, result.len()); result.len() as i64
            },
            _ => { host.failed = true; -1 },
        }
    })).unwrap_or_else(|_| { (*host).failed = true; -1 })
}