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// Copyright 2016 MaidSafe.net limited.
//
// This SAFE Network Software is licensed to you under (1) the MaidSafe.net Commercial License,
// version 1.0 or later, or (2) The General Public License (GPL), version 3, depending on which
// licence you accepted on initial access to the Software (the "Licences").
//
// By contributing code to the SAFE Network Software, or to this project generally, you agree to be
// bound by the terms of the MaidSafe Contributor Agreement.  This, along with the Licenses can be
// found in the root directory of this project at LICENSE, COPYING and CONTRIBUTOR.
//
// Unless required by applicable law or agreed to in writing, the SAFE Network Software distributed
// under the GPL Licence is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.
//
// Please review the Licences for the specific language governing permissions and limitations
// relating to use of the SAFE Network Software.

//! Helpers to work with extern "C" callbacks.

use super::FfiResult;
use std::os::raw::c_void;
use std::ptr;

/// This trait allows us to treat callbacks with different number and type of
/// arguments uniformly.
pub trait Callback {
    /// Arguments for the callback. Should be a tuple.
    type Args: CallbackArgs;

    /// Call the callback, passing the user data pointer, error code and any
    /// additional arguments.
    fn call(&self, user_data: *mut c_void, error: FfiResult, args: Self::Args);
}

impl Callback for extern "C" fn(user_data: *mut c_void, result: FfiResult) {
    type Args = ();
    fn call(&self, user_data: *mut c_void, error: FfiResult, _args: Self::Args) {
        self(user_data, error)
    }
}

impl<T: CallbackArgs> Callback for extern "C" fn(user_data: *mut c_void, result: FfiResult, a: T) {
    type Args = T;
    fn call(&self, user_data: *mut c_void, error: FfiResult, args: Self::Args) {
        self(user_data, error, args)
    }
}

impl<T: CallbackArgs> Callback
    for unsafe extern "C" fn(user_data: *mut c_void, result: FfiResult, a: T) {
    type Args = T;
    fn call(&self, user_data: *mut c_void, error: FfiResult, args: Self::Args) {
        unsafe { self(user_data, error, args) }
    }
}

impl<T0: CallbackArgs, T1: CallbackArgs> Callback
    for extern "C" fn(user_data: *mut c_void, result: FfiResult, a0: T0, a1: T1) {
    type Args = (T0, T1);
    fn call(&self, user_data: *mut c_void, error: FfiResult, args: Self::Args) {
        self(user_data, error, args.0, args.1)
    }
}

impl<T0: CallbackArgs, T1: CallbackArgs, T2: CallbackArgs> Callback
    for extern "C" fn(user_data: *mut c_void,
                  result: FfiResult,
                  a0: T0,
                  a1: T1,
                  a2: T2) {
    type Args = (T0, T1, T2);
    fn call(&self, user_data: *mut c_void, error: FfiResult, args: Self::Args) {
        self(user_data, error, args.0, args.1, args.2)
    }
}

/// Trait for arguments to callbacks. This is similar to `Default`, but allows
/// us to implement it for foreign types that don't already implement `Default`.
pub trait CallbackArgs {
    /// Return default value for the type, used when calling the callback with error.
    fn default() -> Self;
}

impl CallbackArgs for () {
    fn default() -> Self {
        ()
    }
}

impl CallbackArgs for bool {
    fn default() -> Self {
        false
    }
}

impl CallbackArgs for u32 {
    fn default() -> Self {
        0
    }
}

impl CallbackArgs for i32 {
    fn default() -> Self {
        0
    }
}

impl CallbackArgs for i64 {
    fn default() -> Self {
        0
    }
}

impl CallbackArgs for u64 {
    fn default() -> Self {
        0
    }
}

impl CallbackArgs for usize {
    fn default() -> Self {
        0
    }
}

impl<T> CallbackArgs for *const T {
    fn default() -> Self {
        ptr::null()
    }
}

impl<T> CallbackArgs for *mut T {
    fn default() -> Self {
        ptr::null_mut()
    }
}

impl CallbackArgs for [u8; 32] {
    fn default() -> Self {
        [0; 32]
    }
}

impl<T0: CallbackArgs, T1: CallbackArgs> CallbackArgs for (T0, T1) {
    fn default() -> Self {
        (CallbackArgs::default(), CallbackArgs::default())
    }
}

impl<T0: CallbackArgs, T1: CallbackArgs, T2: CallbackArgs> CallbackArgs for (T0, T1, T2) {
    fn default() -> Self {
        (
            CallbackArgs::default(),
            CallbackArgs::default(),
            CallbackArgs::default(),
        )
    }
}

impl<T0: CallbackArgs, T1: CallbackArgs, T2: CallbackArgs, T3: CallbackArgs> CallbackArgs
    for (T0, T1, T2, T3) {
    fn default() -> Self {
        (
            CallbackArgs::default(),
            CallbackArgs::default(),
            CallbackArgs::default(),
            CallbackArgs::default(),
        )
    }
}