//! The documentation for these bindings is a mix from GNUStep's and Apple's
//! sources, but the [ABI specification][ABI] is really the place you should
//! be looking!
//!
//! [ABI]: https://clang.llvm.org/docs/Block-ABI-Apple.html
#![allow(unused)]

use core::ffi::{c_char, c_int, c_ulong, c_void};
use core::fmt;
use core::mem::MaybeUninit;
use core::ops::{BitAnd, BitOr};

use alloc::format;

use crate::ffi::Class;

/// Block descriptor flags.
#[repr(transparent)]
#[derive(Clone, Copy, PartialEq, Eq)]
pub(crate) struct BlockFlags(pub(crate) c_int);

impl BlockFlags {
    pub(crate) const EMPTY: Self = Self(0);

    /// Note: Not public ABI.
    const BLOCK_DEALLOCATING: Self = Self(0x0001);

    /// Note: Not public ABI.
    const BLOCK_REFCOUNT_MASK: Self = Self(if cfg!(feature = "gnustep-1-7") {
        // Mask for the reference count in byref structure's flags field. The low
        // 3 bytes are reserved for the reference count, the top byte for the flags.
        0x00ffffff
    } else if cfg!(any(feature = "compiler-rt", feature = "unstable-objfw")) {
        0xffff
    } else if cfg!(target_vendor = "apple") {
        0xfffe // runtime
    } else {
        0
    });

    /// Note: Not public ABI.
    const BLOCK_INLINE_LAYOUT_STRING: Self = Self(1 << 21);

    /// Note: Not public ABI.
    const BLOCK_SMALL_DESCRIPTOR: Self = Self(1 << 22);

    pub(crate) const BLOCK_IS_NOESCAPE: Self = Self(1 << 23);

    /// Note: Not public ABI.
    const BLOCK_NEEDS_FREE: Self = Self(1 << 24);

    /// The block descriptor contains copy and dispose helpers.
    pub(crate) const BLOCK_HAS_COPY_DISPOSE: Self = Self(1 << 25);

    /// Helpers have C++ code.
    #[doc(alias = "BLOCK_HAS_CXX_OBJ")]
    pub(crate) const BLOCK_HAS_CTOR: Self = Self(1 << 26);

    /// Note: Not public ABI.
    const BLOCK_IS_GC: Self = Self(1 << 27);

    /// Block is stored in global memory and does not need to be copied.
    pub(crate) const BLOCK_IS_GLOBAL: Self = Self(1 << 28);

    /// Block function uses a calling convention that returns a structure via a
    /// pointer passed in by the caller.
    ///
    /// match (BLOCK_USE_STRET, BLOCK_HAS_SIGNATURE) {
    ///     (false, false) => 10.6.ABI, no signature field available
    ///     (true, false)  => 10.6.ABI, no signature field available
    ///     (false, true)  => ABI.2010.3.16, regular calling convention, presence of signature field
    ///     (true, true)   => ABI.2010.3.16, stret calling convention, presence of signature field,
    /// }
    ///
    /// See <https://clang.llvm.org/docs/Block-ABI-Apple.html#high-level>
    #[doc(alias = "BLOCK_USE_SRET")]
    #[doc(alias = "BLOCK_HAS_DESCRIPTOR")]
    pub(crate) const BLOCK_USE_STRET: Self = Self(1 << 29);

    /// Block has an Objective-C type encoding.
    pub(crate) const BLOCK_HAS_SIGNATURE: Self = Self(1 << 30);

    /// Note: Not public ABI.
    const BLOCK_HAS_EXTENDED_LAYOUT: Self = Self(1 << 31);

    /// `const` version of [`PartialEq`].
    pub(crate) const fn equals(self, other: Self) -> bool {
        self.0 == other.0
    }

    /// `const` version of [`BitOr`]: adds the flags together.
    pub(crate) const fn union(self, other: Self) -> Self {
        Self(self.0 | other.0)
    }

    /// `const` version of [`BitAnd`]: only keeps the common flags.
    pub(crate) const fn intersect(self, other: Self) -> Self {
        Self(self.0 & other.0)
    }

    /// Returns `true` if and only if all the flags from `other` are enabled,
    /// i.e. `self & other == other`.
    pub(crate) const fn has(self, other: Self) -> bool {
        self.intersect(other).equals(other)
    }
}

/// See [`BlockFlags::union`].
impl BitOr for BlockFlags {
    type Output = Self;

    fn bitor(self, other: Self) -> Self {
        self.union(other)
    }
}

/// See [`BlockFlags::intersect`].
impl BitAnd for BlockFlags {
    type Output = Self;

    fn bitand(self, other: Self) -> Self {
        self.intersect(other)
    }
}

impl fmt::Debug for BlockFlags {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut f = f.debug_struct("BlockFlags");
        f.field("value", &format!("{:032b}", self.0));

        macro_rules! test_flags {
            {$(
                $(#[$m:meta])?
                $name:ident: $flag:ident
            );* $(;)?} => ($(
                $(#[$m])?
                f.field(stringify!($name), &self.has(Self::$flag));
            )*)
        }
        test_flags! {
            #[cfg(target_vendor = "apple")]
            deallocating: BLOCK_DEALLOCATING;
            #[cfg(target_vendor = "apple")]
            inline_layout_string: BLOCK_INLINE_LAYOUT_STRING;
            #[cfg(target_vendor = "apple")]
            small_descriptor: BLOCK_SMALL_DESCRIPTOR;
            #[cfg(target_vendor = "apple")]
            is_noescape: BLOCK_IS_NOESCAPE;
            #[cfg(target_vendor = "apple")]
            needs_free: BLOCK_NEEDS_FREE;
            has_copy_dispose: BLOCK_HAS_COPY_DISPOSE;
            has_ctor: BLOCK_HAS_CTOR;
            #[cfg(target_vendor = "apple")]
            is_gc: BLOCK_IS_GC;
            is_global: BLOCK_IS_GLOBAL;
            use_stret: BLOCK_USE_STRET;
            has_signature: BLOCK_HAS_SIGNATURE;
            #[cfg(target_vendor = "apple")]
            has_extended_layout: BLOCK_HAS_EXTENDED_LAYOUT;
        }

        f.field("over_referenced", &self.has(Self::BLOCK_REFCOUNT_MASK));
        f.field(
            "reference_count",
            &((*self & Self::BLOCK_REFCOUNT_MASK).0 >> 1),
        );

        f.finish_non_exhaustive()
    }
}

/// The value is of some id-like type, and should be copied as an Objective-C
/// object: i.e. by sending -retain or via the GC assign functions in GC mode
/// (not yet supported).
///
/// id, NSObject, __attribute__((NSObject)), block, ...
pub(crate) const BLOCK_FIELD_IS_OBJECT: c_int = 3;

/// The field is a block.  This must be copied by the block copy functions.
///
/// a block variable
pub(crate) const BLOCK_FIELD_IS_BLOCK: c_int = 7;

/// The field is an indirect reference to a variable declared with the __block
/// storage qualifier.
///
/// the on stack structure holding the __block variable
pub(crate) const BLOCK_FIELD_IS_BYREF: c_int = 8;

/// The field is an indirect reference to a variable declared with the __block
/// storage qualifier.
///
/// declared __weak, only used in byref copy helpers
pub(crate) const BLOCK_FIELD_IS_WEAK: c_int = 16;

/// The field is an indirect reference to a variable declared with the __block
/// storage qualifier.
///
/// called from __block (byref) copy/dispose support routines.
pub(crate) const BLOCK_BYREF_CALLER: c_int = 128;

/// The expected header of every block.
#[repr(C)]
#[doc(alias = "__block_literal")]
#[doc(alias = "Block_layout")]
#[doc(alias = "Block_basic")]
#[allow(missing_debug_implementations)]
#[derive(Clone, Copy)]
pub struct BlockHeader {
    /// Class pointer.
    ///
    /// Always initialised to &_NSConcreteStackBlock for blocks that are
    /// created on the stack or &_NSConcreteGlobalBlock for blocks that are
    /// created in global storage.
    pub isa: *const Class,
    /// Flags.
    ///
    /// See the `BlockFlags` enumerated type for possible values.
    ///
    /// Contains reference count in Apple's and ObjFW's runtime.
    #[doc(alias = "Block_flags")]
    pub(crate) flags: BlockFlags,
    /// Reserved.
    ///
    /// Initialized to 0 by the compiler, but is said to be uninitialized in
    /// the specification.
    ///
    /// Used for the reference count in GNUStep's and WinObjC's runtime.
    #[doc(alias = "Block_size")]
    pub(crate) reserved: MaybeUninit<c_int>,
    /// The function that implements the block.
    ///
    /// The first parameter is a pointer to this structure, the subsequent
    /// parameters are the block's explicit parameters.
    ///
    /// If the BLOCK_USE_SRET & BLOCK_HAS_SIGNATURE flag is set, there is an
    /// additional hidden parameter, which is a pointer to the space on the
    /// stack allocated to hold the return value.
    pub invoke: Option<unsafe extern "C-unwind" fn()>,
    /// The block's descriptor.
    pub(crate) descriptor: BlockDescriptorPtr,
}

/// The type of this is:
/// ```pseudo-code
/// match (BLOCK_HAS_COPY_DISPOSE, BLOCK_HAS_SIGNATURE) {
///     (false, false) => BlockDescriptor,
///     (true, false) => BlockDescriptorCopyDispose,
///     (false, true) => BlockDescriptorSignature,
///     (true, true) => BlockDescriptorCopyDisposeSignature,
/// }
/// ```
///
/// Since all of these start with `BlockDescriptor`, it is always safe to
/// use the `basic` field.
//
// Note: We use an union on top of the pointer, since otherwise the descriptor
// would be forced to have a greater size than is actually required.
#[repr(C)]
#[derive(Clone, Copy)]
pub(crate) union BlockDescriptorPtr {
    pub(crate) basic: *const BlockDescriptor,
    pub(crate) with_copy_dispose: *const BlockDescriptorCopyDispose,
    pub(crate) with_signature: *const BlockDescriptorSignature,
    pub(crate) with_copy_dispose_signature: *const BlockDescriptorCopyDisposeSignature,
}

/// Basic block descriptor.
#[repr(C)]
#[doc(alias = "__block_descriptor")]
#[doc(alias = "Block_descriptor_1")]
#[derive(Clone, Copy, Debug)]
pub(crate) struct BlockDescriptor {
    /// Reserved for future use. Currently always 0.
    pub(crate) reserved: c_ulong,
    /// Size of the block.
    pub(crate) size: c_ulong,
}

/// Block descriptor that contains copy and dispose operations.
///
/// Requires BLOCK_HAS_COPY_DISPOSE.
#[repr(C)]
#[doc(alias = "__block_descriptor")]
#[doc(alias = "Block_descriptor_2")]
#[derive(Clone, Copy, Debug)]
pub(crate) struct BlockDescriptorCopyDispose {
    /// Reserved for future use. Currently always 0.
    pub(crate) reserved: c_ulong,
    /// Size of the block.
    pub(crate) size: c_ulong,

    /// Helper to copy the block if it contains nontrivial copy operations.
    ///
    /// This may be NULL since macOS 11.0.1 in Apple's runtime, but this
    /// should not be relied on.
    pub(crate) copy: Option<unsafe extern "C-unwind" fn(dst: *mut c_void, src: *const c_void)>,
    /// Helper to destroy the block after being copied.
    ///
    /// This may be NULL since macOS 11.0.1 in Apple's runtime, but this
    /// should not be relied on.
    pub(crate) dispose: Option<unsafe extern "C-unwind" fn(src: *mut c_void)>,
}

/// Block descriptor that has an encoding / a signature.
///
/// Requires BLOCK_HAS_SIGNATURE.
#[repr(C)]
#[doc(alias = "__block_descriptor")]
#[doc(alias = "Block_descriptor_3")]
#[derive(Clone, Copy, Debug)]
pub(crate) struct BlockDescriptorSignature {
    /// Reserved for future use. Currently always 0.
    pub(crate) reserved: c_ulong,
    /// Size of the block.
    pub(crate) size: c_ulong,

    /// Objective-C type encoding of the block.
    #[doc(alias = "signature")]
    pub(crate) encoding: *const c_char,
}

/// Block descriptor that contains copy and dispose operations, and which
/// has an encoding / a signature.
///
/// Requires BLOCK_HAS_COPY_DISPOSE and BLOCK_HAS_SIGNATURE.
#[repr(C)]
#[doc(alias = "__block_descriptor")]
#[doc(alias = "Block_descriptor_2")]
#[doc(alias = "Block_descriptor_3")]
#[derive(Clone, Copy, Debug)]
pub(crate) struct BlockDescriptorCopyDisposeSignature {
    /// Reserved for future use. Currently always 0.
    pub(crate) reserved: c_ulong,
    /// Size of the block.
    pub(crate) size: c_ulong,

    /// Helper to copy the block if it contains nontrivial copy operations.
    ///
    /// This may be NULL since macOS 11.0.1 in Apple's runtime, but this
    /// should not be relied on.
    pub(crate) copy: Option<unsafe extern "C-unwind" fn(dst: *mut c_void, src: *const c_void)>,
    /// Helper to destroy the block after being copied.
    ///
    /// This may be NULL since macOS 11.0.1 in Apple's runtime, but this
    /// should not be relied on.
    pub(crate) dispose: Option<unsafe extern "C-unwind" fn(src: *mut c_void)>,

    /// Objective-C type encoding of the block.
    #[doc(alias = "signature")]
    pub(crate) encoding: *const c_char,
}

#[cfg(test)]
mod tests {
    use super::*;

    fn assert_no_trailing_padding<T>() {
        struct AddU8<T> {
            t: T,
            extra: u8,
        }
        assert_ne!(core::mem::size_of::<T>(), core::mem::size_of::<AddU8<T>>());
    }

    #[test]
    fn no_types_have_padding() {
        assert_no_trailing_padding::<BlockHeader>();
        assert_no_trailing_padding::<BlockDescriptorPtr>();
        assert_no_trailing_padding::<BlockDescriptor>();
        assert_no_trailing_padding::<BlockDescriptorCopyDispose>();
        assert_no_trailing_padding::<BlockDescriptorSignature>();
        assert_no_trailing_padding::<BlockDescriptorCopyDisposeSignature>();
    }
}