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// Copyright 2020 ZomboDB, LLC <zombodb@gmail.com>. All rights reserved. Use of this source code is
// governed by the MIT license that can be found in the LICENSE file.

//! Helper functions for working with Postgres `ItemPointerData` (`tid`) type

use crate::{pg_sys, PgBox};

/// ## Safety
///
/// This function s unsafe becuase it does not check that the specified ItemPointerData pointer
/// might be null
#[inline]
pub unsafe fn item_pointer_get_block_number(
    ctid: *const pg_sys::ItemPointerData,
) -> pg_sys::BlockNumber {
    assert!(item_pointer_is_valid(ctid));
    item_pointer_get_block_number_no_check(*ctid)
}

/// ## Safety
///
/// This function s unsafe becuase it does not check that the specified ItemPointerData pointer
/// might be null
#[inline]
pub unsafe fn item_pointer_get_offset_number(
    ctid: *const pg_sys::ItemPointerData,
) -> pg_sys::OffsetNumber {
    assert!(item_pointer_is_valid(ctid));
    item_pointer_get_offset_number_no_check(*ctid)
}

/// ## Safety
///
/// This function is unsafe because it does not check that the specified ItemPointerData pointer
/// might be null
#[inline]
pub unsafe fn item_pointer_get_block_number_no_check(
    ctid: pg_sys::ItemPointerData,
) -> pg_sys::BlockNumber {
    let block_id = ctid.ip_blkid;
    (((block_id.bi_hi as u32) << 16) | (block_id.bi_lo as u32)) as pg_sys::BlockNumber
}

/// ## Safety
///
/// This function is unsafe because it does not check that the specified ItemPointerData pointer
/// might be null
#[inline]
pub unsafe fn item_pointer_get_offset_number_no_check(
    ctid: pg_sys::ItemPointerData,
) -> pg_sys::OffsetNumber {
    ctid.ip_posid
}

#[inline]
pub fn item_pointer_get_both(
    ctid: pg_sys::ItemPointerData,
) -> (pg_sys::BlockNumber, pg_sys::OffsetNumber) {
    unsafe {
        (
            item_pointer_get_block_number_no_check(ctid),
            item_pointer_get_offset_number_no_check(ctid),
        )
    }
}

#[inline]
pub fn item_pointer_set_all(
    tid: &mut pg_sys::ItemPointerData,
    blockno: pg_sys::BlockNumber,
    offno: pg_sys::OffsetNumber,
) {
    use std::convert::TryInto;
    tid.ip_posid = offno;
    tid.ip_blkid.bi_hi = (blockno >> 16).try_into().unwrap();
    tid.ip_blkid.bi_lo = (blockno & 0xffff).try_into().unwrap();
}

/// Convert an `ItemPointerData` struct into a `u64`
#[inline]
pub fn item_pointer_to_u64(ctid: pg_sys::ItemPointerData) -> u64 {
    let (blockno, offno) = item_pointer_get_both(ctid);
    let blockno = blockno as u64;
    let offno = offno as u64;

    (blockno << 32) | offno
}

/// Deconstruct a `u64` into an otherwise uninitialized `ItemPointerData` struct
#[inline]
pub fn u64_to_item_pointer(value: u64, tid: &mut pg_sys::ItemPointerData) {
    let blockno = (value >> 32) as pg_sys::BlockNumber;
    let offno = value as pg_sys::OffsetNumber;
    item_pointer_set_all(tid, blockno, offno);
}

#[inline]
pub fn u64_to_item_pointer_parts(value: u64) -> (pg_sys::BlockNumber, pg_sys::OffsetNumber) {
    let blockno = (value >> 32) as pg_sys::BlockNumber;
    let offno = value as pg_sys::OffsetNumber;
    (blockno, offno)
}

#[allow(clippy::not_unsafe_ptr_arg_deref)] // this is okay b/c we guard against ctid being null
#[inline]
pub fn item_pointer_is_valid(ctid: *const pg_sys::ItemPointerData) -> bool {
    if ctid.is_null() {
        false
    } else {
        unsafe { *ctid }.ip_posid != pg_sys::InvalidOffsetNumber
    }
}

#[inline]
pub fn new_item_pointer(
    blockno: pg_sys::BlockNumber,
    offno: pg_sys::OffsetNumber,
) -> PgBox<pg_sys::ItemPointerData> {
    let mut tid = PgBox::<pg_sys::ItemPointerData>::alloc();
    tid.ip_blkid.bi_hi = (blockno >> 16) as u16;
    tid.ip_blkid.bi_lo = (blockno & 0xffff) as u16;
    tid.ip_posid = offno;
    tid
}