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//! Pure C ABI for the Bex WASM Plugin Engine.
//!
//! This module exports `extern "C"` functions that match the declarations in
//! `bex_engine.h`. The architecture is callback-driven:
//!
//! 1. C++ calls `bex_submit_search(engine, plugin_id, query, callback, user_data)`
//! 2. Rust spawns a Tokio task that does the work
//! 3. On completion, Rust invokes `callback(user_data, request_id, success, payload, len)`
//!    from the Tokio background thread
//! 4. C++ receives the result and can parse/copy it before the callback returns
//!
//! There is NO event queue, NO polling, NO cxx dependency.
//! This is a clean, high-performance Pure C ABI boundary.

use std::ffi::{CStr, CString};
use std::os::raw::{c_char, c_void};
use std::path::PathBuf;
use std::sync::atomic::{AtomicU64, Ordering};


use bex_core::EngineConfig;
use bex_types::BexError;

use crate::runtime::BexRuntime;

// ── Opaque Engine Handle ──────────────────────────────────────────────

/// The internal representation behind the opaque `BexEngine*` pointer.
pub struct BexEngineInner {
    runtime: BexRuntime,
    next_request_id: AtomicU64,
    /// Stores the last error message from a sync operation.
    last_error: parking_lot::Mutex<Option<CString>>,
}

// ── Callback type matching bex_engine.h ───────────────────────────────

type ResultCallback = unsafe extern "C" fn(
    user_data: *mut c_void,
    request_id: u64,
    success: bool,
    payload: *const u8,
    payload_len: usize,
);

// ── FFI-visible structs ───────────────────────────────────────────────

/// FFI-visible BexPluginInfo struct — must match the C header exactly.
#[repr(C)]
pub struct BexPluginInfo {
    pub id: *mut c_char,
    pub name: *mut c_char,
    pub version: *mut c_char,
    pub capabilities: u32,
    pub enabled: bool,
    pub description: *mut c_char,
    pub author: *mut c_char,
    pub homepage: *mut c_char,
}

/// FFI-visible BexPluginInfoList — must match the C header exactly.
#[repr(C)]
pub struct BexPluginInfoList {
    pub items: *mut BexPluginInfo,
    pub count: usize,
}

// ── Helper functions ──────────────────────────────────────────────────

fn set_last_error(inner: &BexEngineInner, msg: &str) {
    if let Ok(c) = CString::new(msg) {
        *inner.last_error.lock() = Some(c);
    }
}

fn clear_last_error(inner: &BexEngineInner) {
    *inner.last_error.lock() = None;
}

fn error_to_code(inner: &BexEngineInner, e: &BexError) -> i32 {
    let msg = e.to_string();
    set_last_error(inner, &msg);
    match e {
        BexError::PluginNotFound(_) => 2,
        BexError::PluginDisabled(_) => 3,
        BexError::NotReady => 4,
        BexError::Storage(_) => 5,
        BexError::Internal(_) => 6,
        _ => -1,
    }
}

fn str_to_cstring(s: &str) -> *mut c_char {
    CString::new(s)
        .map(|c| c.into_raw())
        .unwrap_or(std::ptr::null_mut())
}

fn plugin_info_to_ffi(info: &bex_types::plugin_info::PluginInfo) -> BexPluginInfo {
    BexPluginInfo {
        id: str_to_cstring(&info.id),
        name: str_to_cstring(&info.name),
        version: str_to_cstring(&info.version),
        capabilities: info.capabilities,
        enabled: info.enabled,
        description: str_to_cstring(""),
        author: str_to_cstring(""),
        homepage: str_to_cstring(""),
    }
}

fn error_code_short(err: &BexError) -> &'static str {
    match err {
        BexError::AbiMismatch { .. } => "ABI_MISMATCH",
        BexError::ManifestInvalid(_) => "INVALID_MANIFEST",
        BexError::HashMismatch { .. } => "HASH_MISMATCH",
        BexError::PluginNotFound(_) => "NOT_FOUND",
        BexError::PluginDisabled(_) => "DISABLED",
        BexError::Unsupported(_) => "UNSUPPORTED",
        BexError::NetworkBlocked(_) => "NETWORK_BLOCKED",
        BexError::Timeout { .. } => "TIMEOUT",
        BexError::FuelExhausted => "FUEL_EXHAUSTED",
        BexError::Cancelled => "CANCELLED",
        BexError::PluginFault(_) => "PLUGIN_FAULT",
        BexError::PluginError(_) => "PLUGIN_ERROR",
        BexError::Network(_) => "NETWORK",
        BexError::Storage(_) => "STORAGE",
        BexError::NotReady => "NOT_READY",
        BexError::Internal(_) => "INTERNAL",
        _ => "UNKNOWN",
    }
}

/// Helper to convert a C string pointer to a Rust String.
/// Returns None if the pointer is null or invalid UTF-8.
unsafe fn cstr_to_string(ptr: *const c_char) -> Option<String> {
    if ptr.is_null() {
        return None;
    }
    CStr::from_ptr(ptr).to_str().ok().map(|s| s.to_string())
}

// ══════════════════════════════════════════════════════════════════════
// FFI-exported functions — must match bex_engine.h exactly
// ══════════════════════════════════════════════════════════════════════

// ── Lifecycle ─────────────────────────────────────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_engine_new(data_dir: *const c_char) -> *mut BexEngineInner {
    if data_dir.is_null() {
        return std::ptr::null_mut();
    }

    let data_dir_str = match cstr_to_string(data_dir) {
        Some(s) => s,
        None => return std::ptr::null_mut(),
    };

    let config = EngineConfig {
        data_dir: PathBuf::from(data_dir_str),
        ..Default::default()
    };

    match BexRuntime::new(config) {
        Ok(runtime) => {
            let inner = Box::new(BexEngineInner {
                runtime,
                next_request_id: AtomicU64::new(1),
                last_error: parking_lot::Mutex::new(None),
            });
            Box::into_raw(inner)
        }
        Err(e) => {
            tracing::error!("Failed to create BexEngine: {}", e);
            std::ptr::null_mut()
        }
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_free(engine: *mut BexEngineInner) {
    if engine.is_null() {
        return;
    }
    let inner = Box::from_raw(engine);
    inner.runtime.shutdown();
}

// ── Plugin Management (synchronous) ──────────────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_engine_install(
    engine: *mut BexEngineInner,
    path: *const c_char,
) -> i32 {
    if engine.is_null() || path.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let path_str = match cstr_to_string(path) {
        Some(s) => s,
        None => {
            set_last_error(inner, "Invalid UTF-8 in path");
            return -1;
        }
    };

    match inner.runtime.install_plugin(std::path::Path::new(&path_str)) {
        Ok(_) => 0,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_uninstall(
    engine: *mut BexEngineInner,
    id: *const c_char,
) -> i32 {
    if engine.is_null() || id.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let id_str = match cstr_to_string(id) {
        Some(s) => s,
        None => {
            set_last_error(inner, "Invalid UTF-8 in id");
            return -1;
        }
    };

    match inner.runtime.uninstall_plugin(&id_str) {
        Ok(_) => 0,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_list_plugins(
    engine: *mut BexEngineInner,
) -> BexPluginInfoList {
    if engine.is_null() {
        return BexPluginInfoList {
            items: std::ptr::null_mut(),
            count: 0,
        };
    }
    let inner = &*engine;
    let plugins = inner.runtime.list_plugins();
    let count = plugins.len();

    if count == 0 {
        return BexPluginInfoList {
            items: std::ptr::null_mut(),
            count: 0,
        };
    }

    // Allocate array of BexPluginInfo
    let layout = std::alloc::Layout::array::<BexPluginInfo>(count).unwrap();
    let items_ptr = std::alloc::alloc(layout) as *mut BexPluginInfo;
    if items_ptr.is_null() {
        return BexPluginInfoList {
            items: std::ptr::null_mut(),
            count: 0,
        };
    }

    for (i, info) in plugins.iter().enumerate() {
        let ffi_info = plugin_info_to_ffi(info);
        std::ptr::write(items_ptr.add(i), ffi_info);
    }

    BexPluginInfoList { items: items_ptr, count }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_plugin_info(
    engine: *mut BexEngineInner,
    id: *const c_char,
    out: *mut BexPluginInfo,
) -> i32 {
    if engine.is_null() || id.is_null() || out.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let id_str = match cstr_to_string(id) {
        Some(s) => s,
        None => {
            set_last_error(inner, "Invalid UTF-8 in id");
            return -1;
        }
    };

    match inner.runtime.get_plugin_info(&id_str) {
        Some(info) => {
            std::ptr::write(out, plugin_info_to_ffi(&info));
            0
        }
        None => {
            set_last_error(inner, &format!("Plugin not found: {}", id_str));
            2
        }
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_enable(
    engine: *mut BexEngineInner,
    id: *const c_char,
) -> i32 {
    if engine.is_null() || id.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let id_str = match cstr_to_string(id) {
        Some(s) => s,
        None => return -1,
    };

    match inner.runtime.enable_plugin(&id_str) {
        Ok(_) => 0,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_disable(
    engine: *mut BexEngineInner,
    id: *const c_char,
) -> i32 {
    if engine.is_null() || id.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let id_str = match cstr_to_string(id) {
        Some(s) => s,
        None => return -1,
    };

    match inner.runtime.disable_plugin(&id_str) {
        Ok(_) => 0,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_plugin_info_list_free(list: BexPluginInfoList) {
    if list.items.is_null() || list.count == 0 {
        return;
    }

    for i in 0..list.count {
        let info = &*list.items.add(i);
        if !info.id.is_null() { let _ = CString::from_raw(info.id); }
        if !info.name.is_null() { let _ = CString::from_raw(info.name); }
        if !info.version.is_null() { let _ = CString::from_raw(info.version); }
        if !info.description.is_null() { let _ = CString::from_raw(info.description); }
        if !info.author.is_null() { let _ = CString::from_raw(info.author); }
        if !info.homepage.is_null() { let _ = CString::from_raw(info.homepage); }
    }

    let layout = std::alloc::Layout::array::<BexPluginInfo>(list.count).unwrap();
    std::alloc::dealloc(list.items as *mut u8, layout);
}

#[no_mangle]
pub unsafe extern "C" fn bex_plugin_info_free(info: BexPluginInfo) {
    if !info.id.is_null() { let _ = CString::from_raw(info.id); }
    if !info.name.is_null() { let _ = CString::from_raw(info.name); }
    if !info.version.is_null() { let _ = CString::from_raw(info.version); }
    if !info.description.is_null() { let _ = CString::from_raw(info.description); }
    if !info.author.is_null() { let _ = CString::from_raw(info.author); }
    if !info.homepage.is_null() { let _ = CString::from_raw(info.homepage); }
}

// ── API Key / Secret Management (synchronous) ────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_engine_secret_set(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    key: *const c_char,
    value: *const c_char,
) -> i32 {
    if engine.is_null() || plugin_id.is_null() || key.is_null() || value.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return -1 };
    let k = match cstr_to_string(key) { Some(s) => s, None => return -1 };
    let v = match cstr_to_string(value) { Some(s) => s, None => return -1 };

    match inner.runtime.secret_set(&pid, &k, &v) {
        Ok(_) => 0,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_secret_get(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    key: *const c_char,
    out_buf: *mut c_char,
    out_buf_len: *mut usize,
) -> i32 {
    if engine.is_null() || plugin_id.is_null() || key.is_null()
        || out_buf.is_null() || out_buf_len.is_null()
    {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return -1 };
    let k = match cstr_to_string(key) { Some(s) => s, None => return -1 };

    match inner.runtime.secret_get(&pid, &k) {
        Ok(Some(val)) => {
            let buf_size = *out_buf_len;
            let val_bytes = val.as_bytes();
            let copy_len = val_bytes.len().min(buf_size - 1);
            if copy_len < val_bytes.len() {
                set_last_error(inner, "Output buffer too small");
                *out_buf_len = val_bytes.len() + 1;
                return -2;
            }
            std::ptr::copy_nonoverlapping(val_bytes.as_ptr(), out_buf as *mut u8, copy_len);
            *out_buf.add(copy_len) = 0;
            *out_buf_len = copy_len;
            0
        }
        Ok(None) => {
            set_last_error(inner, &format!("Secret '{}' not found for plugin '{}'", k, pid));
            1
        }
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_secret_delete(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    key: *const c_char,
) -> i32 {
    if engine.is_null() || plugin_id.is_null() || key.is_null() {
        return -1;
    }
    let inner = &*engine;
    clear_last_error(inner);

    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return -1 };
    let k = match cstr_to_string(key) { Some(s) => s, None => return -1 };

    match inner.runtime.secret_remove(&pid, &k) {
        Ok(true) => 0,
        Ok(false) => 1,
        Err(e) => error_to_code(inner, &e),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_engine_secret_keys(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
) -> *mut c_char {
    if engine.is_null() || plugin_id.is_null() {
        return std::ptr::null_mut();
    }
    let inner = &*engine;

    let pid = match cstr_to_string(plugin_id) {
        Some(s) => s,
        None => return std::ptr::null_mut(),
    };

    match inner.runtime.secret_keys(&pid) {
        Ok(keys) => {
            let joined = keys.join(",");
            str_to_cstring(&joined)
        }
        Err(_) => std::ptr::null_mut(),
    }
}

#[no_mangle]
pub unsafe extern "C" fn bex_string_free(s: *mut c_char) {
    if !s.is_null() {
        let _ = CString::from_raw(s);
    }
}

// ── Async Operations ─────────────────────────────────────────────────
//
// Each submit function:
// 1. Converts all C strings to owned Rust Strings BEFORE creating the closure
// 2. Generates a request_id
// 3. Spawns a Tokio task that executes the work and invokes the callback
//
// The closure captures only owned types (String, Arc<Engine>, etc.) —
// no raw pointers, making it Send-safe.

#[no_mangle]
pub unsafe extern "C" fn bex_submit_search(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    query: *const c_char,
    callback: ResultCallback,
    user_data: *mut c_void,
) -> u64 {
    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return 0 };
    let query_str = match cstr_to_string(query) { Some(s) => s, None => return 0 };

    submit_async(engine, pid, callback, user_data, move |engine, pid| {
        engine.call_search_json(pid, &query_str)
            .map(|s| s.into_bytes())
    })
}

#[no_mangle]
pub unsafe extern "C" fn bex_submit_home(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    callback: ResultCallback,
    user_data: *mut c_void,
) -> u64 {
    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return 0 };

    submit_async(engine, pid, callback, user_data, move |engine, pid| {
        engine.call_get_home_json(pid)
            .map(|s| s.into_bytes())
    })
}

#[no_mangle]
pub unsafe extern "C" fn bex_submit_info(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    media_id: *const c_char,
    callback: ResultCallback,
    user_data: *mut c_void,
) -> u64 {
    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return 0 };
    let mid = match cstr_to_string(media_id) { Some(s) => s, None => return 0 };

    submit_async(engine, pid, callback, user_data, move |engine, pid| {
        engine.call_get_info_json(pid, &mid)
            .map(|s| s.into_bytes())
    })
}

#[no_mangle]
pub unsafe extern "C" fn bex_submit_servers(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    id: *const c_char,
    callback: ResultCallback,
    user_data: *mut c_void,
) -> u64 {
    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return 0 };
    let id_str = match cstr_to_string(id) { Some(s) => s, None => return 0 };

    submit_async(engine, pid, callback, user_data, move |engine, pid| {
        engine.call_get_servers_json(pid, &id_str)
            .map(|s| s.into_bytes())
    })
}

#[no_mangle]
pub unsafe extern "C" fn bex_submit_stream(
    engine: *mut BexEngineInner,
    plugin_id: *const c_char,
    server_json: *const c_char,
    callback: ResultCallback,
    user_data: *mut c_void,
) -> u64 {
    let pid = match cstr_to_string(plugin_id) { Some(s) => s, None => return 0 };
    let server_str = match cstr_to_string(server_json) { Some(s) => s, None => return 0 };

    submit_async(engine, pid, callback, user_data, move |engine, pid| {
        engine.call_resolve_stream_json(pid, &server_str)
            .map(|s| s.into_bytes())
    })
}

// ── Cancellation ─────────────────────────────────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_cancel_request(
    engine: *mut BexEngineInner,
    request_id: u64,
) -> bool {
    if engine.is_null() {
        return false;
    }
    let inner = &*engine;
    inner.runtime.cancel_request(request_id)
}

// ── Engine Stats ─────────────────────────────────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_engine_stats(
    engine: *mut BexEngineInner,
) -> *mut c_char {
    if engine.is_null() {
        return std::ptr::null_mut();
    }
    let inner = &*engine;
    let stats = inner.runtime.stats();
    match serde_json::to_string(&stats) {
        Ok(json) => str_to_cstring(&json),
        Err(_) => std::ptr::null_mut(),
    }
}

// ── Last Error ───────────────────────────────────────────────────────

#[no_mangle]
pub unsafe extern "C" fn bex_engine_last_error(
    engine: *mut BexEngineInner,
) -> *mut c_char {
    if engine.is_null() {
        return std::ptr::null_mut();
    }
    let inner = &*engine;
    match inner.last_error.lock().as_ref() {
        Some(cstr) => {
            let bytes = cstr.as_bytes();
            let dup = CString::from_vec_unchecked(bytes.to_vec());
            dup.into_raw()
        }
        None => std::ptr::null_mut(),
    }
}

// ══════════════════════════════════════════════════════════════════════
// Internal async submit helper
// ══════════════════════════════════════════════════════════════════════

/// Common implementation for all async submit functions.
///
/// - `engine`: raw pointer to BexEngineInner
/// - `pid`: owned String (plugin_id, already converted from C)
/// - `callback`: C function pointer
/// - `user_data`: opaque pointer from C++
/// - `work`: closure that takes `&bex_core::Engine` + `&str` (plugin_id),
///           does the work, and returns `Result<Vec<u8>, BexError>`
///
/// All C strings must be converted to Rust Strings BEFORE calling this,
/// so the closure only captures Send types.
unsafe fn submit_async<F>(
    engine: *mut BexEngineInner,
    pid: String,
    callback: ResultCallback,
    user_data: *mut c_void,
    work: F,
) -> u64
where
    F: FnOnce(&bex_core::Engine, &str) -> Result<Vec<u8>, BexError> + Send + 'static,
{
    if engine.is_null() {
        return 0;
    }

    let inner = &*engine;
    let request_id = inner.next_request_id.fetch_add(1, Ordering::Relaxed);

    // Clone the engine (Arc-based, cheap) for the spawned task
    let engine_clone = inner.runtime.clone_engine();

    // Store callback and user_data as usize for Send-safety across threads.
    // The callback is a function pointer (inherently Send), and user_data
    // is an opaque pointer that C++ guarantees remains valid until callback
    // is invoked.
    let callback_addr = callback as usize;
    let user_data_addr = user_data as usize;

    // Get cancellation token
    let cancel_token = tokio_util::sync::CancellationToken::new();
    inner.runtime.insert_cancellation(request_id, cancel_token.clone());

    // Spawn on the BexRuntime's internal Tokio runtime
    let rt_handle = inner.runtime.tokio_handle();

    rt_handle.spawn(async move {
        // Check cancellation before starting
        if cancel_token.is_cancelled() {
            invoke_callback(callback_addr, user_data_addr, request_id, false,
                format!("CANCELLED: Request {} was cancelled", request_id).as_bytes());
            return;
        }

        // Execute the work using spawn_blocking since bex-core Engine
        // internally uses its own Tokio runtime for HTTP/WASM operations.
        let result = tokio::task::spawn_blocking(move || {
            work(&engine_clone, &pid)
        }).await;

        match result {
            Ok(Ok(payload)) => {
                invoke_callback(callback_addr, user_data_addr, request_id, true, &payload);
            }
            Ok(Err(e)) => {
                let err_msg = format!("{}: {}", error_code_short(&e), e);
                invoke_callback(callback_addr, user_data_addr, request_id, false, err_msg.as_bytes());
            }
            Err(_) => {
                invoke_callback(callback_addr, user_data_addr, request_id, false,
                    b"INTERNAL: Worker thread panicked");
            }
        }
    });

    request_id
}

/// Invoke the C callback with a byte payload.
unsafe fn invoke_callback(
    callback_addr: usize,
    user_data_addr: usize,
    request_id: u64,
    success: bool,
    payload: &[u8],
) {
    let cb: ResultCallback = std::mem::transmute(callback_addr);
    let ud = user_data_addr as *mut c_void;
    cb(ud, request_id, success, payload.as_ptr(), payload.len());
}