use super::*;

use super::optimize_bytes::*;

use super::Error;

use super::Result;

// inspired by  https://github.com/openexr/openexr/blob/master/OpenEXR/IlmImf/ImfRle.cpp

const MIN_RUN_LENGTH : usize = 3;

const MAX_RUN_LENGTH : usize = 127;

pub fn decompress_bytes(

    channels: &ChannelList,

    compressed: ByteVec,

    rectangle: IntegerBounds,

    expected_byte_size: usize,

    pedantic: bool,

) -> Result<ByteVec> {

    let mut remaining = compressed.as_slice();

    let mut decompressed = Vec::with_capacity(expected_byte_size.min(8*2048));

    while !remaining.is_empty() && decompressed.len() != expected_byte_size {

        let count = take_1(&mut remaining)? as i8 as i32;

        if count < 0 {

            // take the next '-count' bytes as-is

            let values = take_n(&mut remaining, (-count) as usize)?;

            decompressed.extend_from_slice(values);

        }

        else {

            // repeat the next value 'count + 1' times

            let value = take_1(&mut remaining)?;

            decompressed.resize(decompressed.len() + count as usize + 1, value);

        }

    }

    if pedantic && !remaining.is_empty() {

        return Err(Error::invalid("data amount"));

    }

    differences_to_samples(&mut decompressed);

    interleave_byte_blocks(&mut decompressed);

    Ok(super::convert_little_endian_to_current(decompressed, channels, rectangle))// TODO no alloc

}

pub fn compress_bytes(channels: &ChannelList, uncompressed: ByteVec, rectangle: IntegerBounds) -> Result<ByteVec> {

    // see https://github.com/AcademySoftwareFoundation/openexr/blob/3bd93f85bcb74c77255f28cdbb913fdbfbb39dfe/OpenEXR/IlmImf/ImfTiledOutputFile.cpp#L750-L842

    let mut data = super::convert_current_to_little_endian(uncompressed, channels, rectangle);// TODO no alloc

    separate_bytes_fragments(&mut data);

    samples_to_differences(&mut data);

    let mut compressed = Vec::with_capacity(data.len());

    let mut run_start = 0;

    let mut run_end = 1;

    while run_start < data.len() {

        while

            run_end < data.len()

                && data[run_start] == data[run_end]

                && (run_end - run_start) as i32 - 1 < MAX_RUN_LENGTH as i32

            {

                run_end += 1;

            }

        if run_end - run_start >= MIN_RUN_LENGTH {

            compressed.push(((run_end - run_start) as i32 - 1) as u8);

            compressed.push(data[run_start]);

            run_start = run_end;

        } else {

            while

                run_end < data.len() && (

                    (run_end + 1 >= data.len() || data[run_end] != data[run_end + 1])

                        || (run_end + 2 >= data.len() || data[run_end + 1] != data[run_end + 2])

                ) && run_end - run_start < MAX_RUN_LENGTH

                {

                    run_end += 1;

                }

            compressed.push((run_start as i32 - run_end as i32) as u8);

            compressed.extend_from_slice(&data[run_start .. run_end]);

            run_start = run_end;

            run_end += 1;

        }

    }

    Ok(compressed)

}

fn take_1(slice: &mut &[u8]) -> Result<u8> {

    if !slice.is_empty() {

        let result = slice[0];

        *slice = &slice[1..];

        Ok(result)

    } else {

        Err(Error::invalid("compressed data"))

    }

}

fn take_n<'s>(slice: &mut &'s [u8], n: usize) -> Result<&'s [u8]> {

    if n <= slice.len() {

        let (front, back) = slice.split_at(n);

        *slice = back;

        Ok(front)

    } else {

        Err(Error::invalid("compressed data"))

    }

}