// Protocol Buffers - Google's data interchange format
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// https://developers.google.com/protocol-buffers/
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// Rust Protobuf runtime using the UPB kernel.

/// Represents UPB's upb_Arena.
use std::ops::Deref;
use std::ptr::NonNull;
use std::slice;

#[repr(C)]
pub struct Arena {
    _data: [u8; 0],
    _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
}

impl Arena {
    pub unsafe fn new() -> *mut Self {
        upb_Arena_New()
    }

    pub unsafe fn free(arena: *mut Self) {
        upb_Arena_Free(arena)
    }
}

extern "C" {
    pub fn upb_Arena_New() -> *mut Arena;
    pub fn upb_Arena_Free(arena: *mut Arena);
}

/// Represents serialized Protobuf wire format data. It's typically produced by
/// `<Message>.serialize()`.
#[derive(Debug)]
pub struct SerializedData {
    data: NonNull<u8>,
    len: usize,
    arena: *mut Arena,
}

impl SerializedData {
    pub unsafe fn from_raw_parts(arena: *mut Arena, data: NonNull<u8>, len: usize) -> Self {
        SerializedData { arena, data, len }
    }
}

impl Deref for SerializedData {
    type Target = [u8];
    fn deref(&self) -> &Self::Target {
        unsafe { slice::from_raw_parts(self.data.as_ptr() as *const _, self.len) }
    }
}

impl Drop for SerializedData {
    fn drop(&mut self) {
        unsafe { Arena::free(self.arena) };
    }
}

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

    #[test]
    fn test_arena_new_and_free() {
        let arena = unsafe { Arena::new() };
        unsafe { Arena::free(arena) };
    }

    #[test]
    fn test_serialized_data_roundtrip() {
        let arena = unsafe { Arena::new() };
        let original_data = b"Hello world";
        let len = original_data.len();

        let serialized_data = unsafe {
            SerializedData::from_raw_parts(
                arena,
                NonNull::new(original_data as *const _ as *mut _).unwrap(),
                len,
            )
        };
        assert_eq!(&*serialized_data, b"Hello world");
    }
}