//! Lossy compression for F32 data, but lossless compression for U32 and F16 data.

// see https://github.com/AcademySoftwareFoundation/openexr/blob/master/OpenEXR/IlmImf/ImfPxr24Compressor.cpp

// This compressor is based on source code that was contributed to

// OpenEXR by Pixar Animation Studios. The compression method was

// developed by Loren Carpenter.

//  The compressor preprocesses the pixel data to reduce entropy, and then calls zlib.

//  Compression of HALF and UINT channels is lossless, but compressing

//  FLOAT channels is lossy: 32-bit floating-point numbers are converted

//  to 24 bits by rounding the significand to 15 bits.

//

//  When the compressor is invoked, the caller has already arranged

//  the pixel data so that the values for each channel appear in a

//  contiguous block of memory.  The compressor converts the pixel

//  values to unsigned integers: For UINT, this is a no-op.  HALF

//  values are simply re-interpreted as 16-bit integers.  FLOAT

//  values are converted to 24 bits, and the resulting bit patterns

//  are interpreted as integers.  The compressor then replaces each

//  value with the difference between the value and its left neighbor.

//  This turns flat fields in the image into zeroes, and ramps into

//  strings of similar values.  Next, each difference is split into

//  2, 3 or 4 bytes, and the bytes are transposed so that all the

//  most significant bytes end up in a contiguous block, followed

//  by the second most significant bytes, and so on.  The resulting

//  string of bytes is compressed with zlib.

use super::*;

use crate::error::Result;

use lebe::io::ReadPrimitive;

// scanline decompression routine, see https://github.com/openexr/openexr/blob/master/OpenEXR/IlmImf/ImfScanLineInputFile.cpp

// 1. Uncompress the data, if necessary (If the line is uncompressed, it's in XDR format, regardless of the compressor's output format.)

// 3. Convert one scan line's worth of pixel data back from the machine-independent representation

// 4. Fill the frame buffer with pixel data, respective to sampling and whatnot

#[cfg_attr(target_endian = "big", allow(unused, unreachable_code))]

pub fn compress(channels: &ChannelList, remaining_bytes: ByteVec, area: IntegerBounds) -> Result<ByteVec> {

    #[cfg(target_endian = "big")] {

        return Err(Error::unsupported(

            "PXR24 compression method not supported yet on big endian processor architecture"

        ))

    }

    if remaining_bytes.is_empty() { return Ok(Vec::new()); }

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

    let remaining_bytes = super::convert_current_to_little_endian(remaining_bytes, channels, area);

    let mut remaining_bytes = remaining_bytes.as_slice(); // TODO less allocation

    let bytes_per_pixel: usize = channels.list.iter()

        .map(|channel| match channel.sample_type {

            SampleType::F16 => 2, SampleType::F32 => 3, SampleType::U32 => 4,

        })

        .sum();

    let mut raw = vec![0_u8; bytes_per_pixel * area.size.area()];

    {

        let mut write = raw.as_mut_slice();

        // TODO this loop should be an iterator in the `IntegerBounds` class, as it is used in all compressio methods

        for y in area.position.1..area.end().1 {

            for channel in &channels.list {

                if mod_p(y, usize_to_i32(channel.sampling.1)) != 0 { continue; }

                // this apparently can't be a closure in Rust 1.43 due to borrowing ambiguity

                let sample_count_x = channel.subsampled_resolution(area.size).0;

                macro_rules! split_off_write_slice { () => {{

                    let (slice, rest) = write.split_at_mut(sample_count_x);

                    write = rest;

                    slice

                }}; }

                let mut previous_pixel: u32 = 0;

                match channel.sample_type {

                    SampleType::F16 => {

                        let out_byte_tuples = split_off_write_slice!().iter_mut()

                            .zip(split_off_write_slice!());

                        for (out_byte_0, out_byte_1) in out_byte_tuples {

                            let pixel = u16::read_from_native_endian(&mut remaining_bytes).unwrap() as u32;

                            let [byte_1, byte_0] = (pixel.wrapping_sub(previous_pixel) as u16).to_ne_bytes();

                            *out_byte_0 = byte_0;

                            *out_byte_1 = byte_1;

                            previous_pixel = pixel;

                        }

                    },

                    SampleType::U32 => {

                        let out_byte_quadruplets = split_off_write_slice!().iter_mut()

                            .zip(split_off_write_slice!())

                            .zip(split_off_write_slice!())

                            .zip(split_off_write_slice!());

                        for (((out_byte_0, out_byte_1), out_byte_2), out_byte_3) in out_byte_quadruplets {

                            let pixel = u32::read_from_native_endian(&mut remaining_bytes).unwrap();

                            let [byte_3, byte_2, byte_1, byte_0] = pixel.wrapping_sub(previous_pixel).to_ne_bytes();

                            *out_byte_0 = byte_0;

                            *out_byte_1 = byte_1;

                            *out_byte_2 = byte_2;

                            *out_byte_3 = byte_3;

                            previous_pixel = pixel;

                        }

                    },

                    SampleType::F32 => {

                        let out_byte_triplets = split_off_write_slice!().iter_mut()

                            .zip(split_off_write_slice!())

                            .zip(split_off_write_slice!());

                        for ((out_byte_0, out_byte_1), out_byte_2) in out_byte_triplets {

                            let pixel = f32_to_f24(f32::read_from_native_endian(&mut remaining_bytes).unwrap());

                            let [byte_2, byte_1, byte_0, _] = pixel.wrapping_sub(previous_pixel).to_ne_bytes();

                            previous_pixel = pixel;

                            *out_byte_0 = byte_0;

                            *out_byte_1 = byte_1;

                            *out_byte_2 = byte_2;

                        }

                    },

                }

            }

        }

        debug_assert_eq!(write.len(), 0, "bytes left after compression");

    }

    Ok(miniz_oxide::deflate::compress_to_vec_zlib(raw.as_slice(), 4))

}

#[cfg_attr(target_endian = "big", allow(unused, unreachable_code))]

pub fn decompress(channels: &ChannelList, bytes: ByteVec, area: IntegerBounds, expected_byte_size: usize, pedantic: bool) -> Result<ByteVec> {

    #[cfg(target_endian = "big")] {

        return Err(Error::unsupported(

            "PXR24 decompression method not supported yet on big endian processor architecture"

        ))

    }

    let options = zune_inflate::DeflateOptions::default().set_limit(expected_byte_size).set_size_hint(expected_byte_size);

    let mut decoder = zune_inflate::DeflateDecoder::new_with_options(&bytes, options);

    let raw = decoder.decode_zlib()

        .map_err(|_| Error::invalid("zlib-compressed data malformed"))?; // TODO share code with zip?

    let mut read = raw.as_slice();

    let mut out = Vec::with_capacity(expected_byte_size.min(2048*4));

    for y in area.position.1 .. area.end().1 {

        for channel in &channels.list {

            if mod_p(y, usize_to_i32(channel.sampling.1)) != 0 { continue; }

            let sample_count_x = channel.subsampled_resolution(area.size).0;

            let mut read_sample_line = ||{

                if sample_count_x > read.len() { return Err(Error::invalid("not enough data")) }

                let (samples, rest) = read.split_at(sample_count_x);

                read = rest;

                Ok(samples)

            };

            let mut pixel_accumulation: u32 = 0;

            match channel.sample_type {

                SampleType::F16 => {

                    let sample_byte_pairs = read_sample_line()?.iter()

                        .zip(read_sample_line()?);

                    for (&in_byte_0, &in_byte_1) in sample_byte_pairs {

                        let difference = u16::from_ne_bytes([in_byte_1, in_byte_0]) as u32;

                        pixel_accumulation = pixel_accumulation.overflowing_add(difference).0;

                        out.extend_from_slice(&(pixel_accumulation as u16).to_ne_bytes());

                    }

                },

                SampleType::U32 => {

                    let sample_byte_quads = read_sample_line()?.iter()

                        .zip(read_sample_line()?)

                        .zip(read_sample_line()?)

                        .zip(read_sample_line()?);

                    for (((&in_byte_0, &in_byte_1), &in_byte_2), &in_byte_3) in sample_byte_quads {

                        let difference = u32::from_ne_bytes([in_byte_3, in_byte_2, in_byte_1, in_byte_0]);

                        pixel_accumulation = pixel_accumulation.overflowing_add(difference).0;

                        out.extend_from_slice(&pixel_accumulation.to_ne_bytes());

                    }

                },

                SampleType::F32 => {

                    let sample_byte_triplets = read_sample_line()?.iter()

                        .zip(read_sample_line()?).zip(read_sample_line()?);

                    for ((&in_byte_0, &in_byte_1), &in_byte_2) in sample_byte_triplets {

                        let difference = u32::from_ne_bytes([0, in_byte_2, in_byte_1, in_byte_0]);

                        pixel_accumulation = pixel_accumulation.overflowing_add(difference).0;

                        out.extend_from_slice(&pixel_accumulation.to_ne_bytes());

                    }

                }

            }

        }

    }

    if pedantic && !read.is_empty() {

        return Err(Error::invalid("too much data"));

    }

    Ok(super::convert_little_endian_to_current(out, channels, area))

}

/// Conversion from 32-bit to 24-bit floating-point numbers.

/// Reverse conversion is just a simple 8-bit left shift.

pub fn f32_to_f24(float: f32) -> u32 {

    let bits = float.to_bits();

    let sign = bits & 0x80000000;

    let exponent = bits & 0x7f800000;

    let mantissa = bits & 0x007fffff;

    let result = if exponent == 0x7f800000 {

        if mantissa != 0 {

            // F is a NAN; we preserve the sign bit and

            // the 15 leftmost bits of the significand,

            // with one exception: If the 15 leftmost

            // bits are all zero, the NAN would turn

            // into an infinity, so we have to set at

            // least one bit in the significand.

            let mantissa = mantissa >> 8;

            (exponent >> 8) | mantissa | if mantissa == 0 { 1 } else { 0 }

        }

        else { // F is an infinity.

            exponent >> 8

        }

    }

    else { // F is finite, round the significand to 15 bits.

        let result = ((exponent | mantissa) + (mantissa & 0x00000080)) >> 8;

        if result >= 0x7f8000 {

            // F was close to FLT_MAX, and the significand was

            // rounded up, resulting in an exponent overflow.

            // Avoid the overflow by truncating the significand

            // instead of rounding it.

            (exponent | mantissa) >> 8

        }

        else {

            result

        }

    };

    return (sign >> 8) | result;

}