use core::cell::Cell;

/// make_decode_table_entry() creates a decode table entry for the given symbol

/// by combining the static part 'decode_results[sym]' with the dynamic part

/// 'len', which is the remaining codeword length (the codeword length for main

/// table entries, or the codeword length minus TABLEBITS for subtable entries).

///

/// In all cases, we add 'len' to each of the two low-order bytes to create the

/// appropriately-formatted decode table entry.  See the definitions of the

/// *_decode_results[] arrays below, where the entry format is described.

pub(crate) fn make_decode_table_entry(decode_results: &[u32], sym: usize, len: u32) -> u32

{

    decode_results[sym] + (len << 8) + len

}

/// A safe version of src.copy_within that helps me because I tend to always

/// confuse the arguments

pub fn fixed_copy_within<const SIZE: usize>(dest: &mut [u8], src_offset: usize, dest_offset: usize)

{

    // for debug builds ensure we don't go out of bounds

    debug_assert!(

        dest_offset + SIZE <= dest.len(),

        "[dst]: End position {} out of range for slice of length {}",

        dest_offset + SIZE,

        dest.len()

    );

    dest.copy_within(src_offset..src_offset + SIZE, dest_offset);

}

#[inline(always)]

pub fn copy_rep_matches(dest: &mut [u8], offset: usize, dest_offset: usize, length: usize)

{

    // This is a slightly complicated rep match copier that has

    // no bounds check.

    // The only invariant we need to uphold is dest[dest_offset] should

    // copy from dest[offset]

    // i.e in the first iteration, the first entry in the window will point

    // to dest[offset] and the

    // last entry will point to dest[dest_offset]

    // it's easy to prove dest[offset] since we take our slice

    // from offset.

    // but proving dest[dest_offset] is trickier

    // If we were at offset, to get to dest_offset, we could

    // 1. Get difference between dest_offset and offset

    // 2. Add that difference to offset.

    //

    let diff = dest_offset - offset + 1;

    // note

    for window in Cell::from_mut(&mut dest[offset..dest_offset + length + 2])

        .as_slice_of_cells()

        .windows(diff)

    {

        window.last().unwrap().set(window[0].get());

    }

}

/// Return the minimum of two usizes in a const context

#[rustfmt::skip]

pub const fn const_min_usize(a: usize, b: usize) -> usize

{

    if a < b { a } else { b }

}

/// Calculate the adler hash of a piece of data.

#[inline(never)]

#[cfg(feature = "zlib")]

pub fn calc_adler_hash(data: &[u8]) -> u32

{

    use simd_adler32::Adler32;

    let mut hasher = Adler32::new();

    hasher.write(data);

    hasher.finish()

}