//! Utility functions related to handling of

//! [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm).

/// Describes which stage of

/// [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm)

/// applies to a decoded row.

///

/// See also [Reader.next_interlaced_row](crate::decoder::Reader::next_interlaced_row).

#[derive(Clone, Copy, Debug, PartialEq, Eq)]

pub struct Adam7Info {

    pub(crate) pass: u8,

    pub(crate) line: u32,

    pub(crate) width: u32,

}

impl Adam7Info {

    /// Creates a new `Adam7Info`.  May panic if the arguments are out of range (e.g. if `pass` is

    /// 0 or greater than 8).

    ///

    /// * `pass` corresponds to a pass of the

    ///   [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm)

    /// * `line` is the number of a line within a pass (starting with 0).  For example,

    ///   in an image of height 8, `line` can be beteween `0..4` in the 7th `pass`

    ///   (those 4 interlaced rows correspond to 2nd, 4th, 6th, and 8th row of the full image).

    /// * `width` describes how many pixels are in an interlaced row.  For example,

    ///   in the 7th `pass`, the `width` is be the same as full image width, but in

    ///   in the 1st `pass`, the `width` is be 1/8th of the image width (rounded up as

    ///   necessary).

    ///

    /// Note that in typical usage, `Adam7Info`s are returned by [Reader.next_interlaced_row]

    /// and there is no need to create them by calling `Adam7Info::new`.  `Adam7Info::new` is

    /// nevertheless exposed as a public API, because it helps to provide self-contained example

    /// usage of [expand_interlaced_row](crate::expand_interlaced_row).

    pub fn new(pass: u8, line: u32, width: u32) -> Self {

        assert!(1 <= pass && pass <= 7);

        assert!(width > 0);

        Self { pass, line, width }

    }

}

/// This iterator iterates over the different passes of an image Adam7 encoded

/// PNG image

/// The pattern is:

///     16462646

///     77777777

///     56565656

///     77777777

///     36463646

///     77777777

///     56565656

///     77777777

///

#[derive(Clone)]

pub(crate) struct Adam7Iterator {

    line: u32,

    lines: u32,

    line_width: u32,

    current_pass: u8,

    width: u32,

    height: u32,

}

impl Adam7Iterator {

    pub fn new(width: u32, height: u32) -> Adam7Iterator {

        let mut this = Adam7Iterator {

            line: 0,

            lines: 0,

            line_width: 0,

            current_pass: 1,

            width,

            height,

        };

        this.init_pass();

        this

    }

    /// Calculates the bounds of the current pass

    fn init_pass(&mut self) {

        let w = f64::from(self.width);

        let h = f64::from(self.height);

        let (line_width, lines) = match self.current_pass {

            1 => (w / 8.0, h / 8.0),

            2 => ((w - 4.0) / 8.0, h / 8.0),

            3 => (w / 4.0, (h - 4.0) / 8.0),

            4 => ((w - 2.0) / 4.0, h / 4.0),

            5 => (w / 2.0, (h - 2.0) / 4.0),

            6 => ((w - 1.0) / 2.0, h / 2.0),

            7 => (w, (h - 1.0) / 2.0),

            _ => unreachable!(),

        };

        self.line_width = line_width.ceil() as u32;

        self.lines = lines.ceil() as u32;

        self.line = 0;

    }

}

/// Iterates over `Adam7Info`s.

impl Iterator for Adam7Iterator {

    type Item = Adam7Info;

    fn next(&mut self) -> Option<Self::Item> {

        if self.line < self.lines && self.line_width > 0 {

            let this_line = self.line;

            self.line += 1;

            Some(Adam7Info {

                pass: self.current_pass,

                line: this_line,

                width: self.line_width,

            })

        } else if self.current_pass < 7 {

            self.current_pass += 1;

            self.init_pass();

            self.next()

        } else {

            None

        }

    }

}

fn subbyte_pixels(scanline: &[u8], bits_pp: usize) -> impl Iterator<Item = u8> + '_ {

    (0..scanline.len() * 8)

        .step_by(bits_pp)

        .map(move |bit_idx| {

            let byte_idx = bit_idx / 8;

            // sub-byte samples start in the high-order bits

            let rem = 8 - bit_idx % 8 - bits_pp;

            match bits_pp {

                // evenly divides bytes

                1 => (scanline[byte_idx] >> rem) & 1,

                2 => (scanline[byte_idx] >> rem) & 3,

                4 => (scanline[byte_idx] >> rem) & 15,

                _ => unreachable!(),

            }

        })

}

/// Given `row_stride`, interlace `info`, and bits-per-pixel, produce an iterator of bit positions

/// of pixels to copy from the input scanline to the image buffer.  The positions are expressed as

/// bit offsets from position (0,0) in the frame that is currently being decoded.

fn expand_adam7_bits(

    row_stride_in_bytes: usize,

    info: &Adam7Info,

    bits_pp: usize,

) -> impl Iterator<Item = usize> {

    let line_no = info.line as usize;

    let pass = info.pass;

    let interlaced_width = info.width as usize;

    let (line_mul, line_off, samp_mul, samp_off) = match pass {

        1 => (8, 0, 8, 0),

        2 => (8, 0, 8, 4),

        3 => (8, 4, 4, 0),

        4 => (4, 0, 4, 2),

        5 => (4, 2, 2, 0),

        6 => (2, 0, 2, 1),

        7 => (2, 1, 1, 0),

        _ => {

            // `Adam7Info.pass` is a non-`pub`lic field.  `InterlaceInfo` is expected

            // to maintain an invariant that `pass` is valid.

            panic!("Invalid `Adam7Info.pass`");

        }

    };

    // the equivalent line number in progressive scan

    let prog_line = line_mul * line_no + line_off;

    let line_start = prog_line * row_stride_in_bytes * 8;

    (0..interlaced_width)

        .map(move |i| i * samp_mul + samp_off)

        .map(move |i| i * bits_pp)

        .map(move |bits_offset| bits_offset + line_start)

}

/// Copies pixels from `interlaced_row` into the right location in `img`.

///

/// First bytes of `img` should belong to the top-left corner of the currently decoded frame.

///

/// `img_row_stride` specifies an offset in bytes between subsequent rows of `img`.

/// This can be the width of the current frame being decoded, but this is not required - a bigger

/// stride may be useful if the frame being decoded is a sub-region of `img`.

///

/// `interlaced_row` and `interlace_info` typically come from

/// [crate::decoder::Reader::next_interlaced_row], but this is not required.  In particular, before

/// calling `expand_interlaced_row` one may need to expand the decoded row, so that its format and

/// `bits_per_pixel` matches that of `img`.  Note that in initial Adam7 passes the `interlaced_row`

/// may contain less pixels that the width of the frame being decoded (e.g. it contains only 1/8th

/// of pixels in the initial pass).

///

/// Example:

///

/// ```

/// use png::{expand_interlaced_row, Adam7Info};

/// let info = Adam7Info::new(5, 0, 4);  // 1st line of 5th pass has 4 pixels.

/// let mut img = vec![0; 8 * 8];

/// let row = vec![1, 2, 3, 4];

/// expand_interlaced_row(&mut img, 8, &row, &info, 8);

/// assert_eq!(&img, &[

///     0, 0, 0, 0, 0, 0, 0, 0,

///     0, 0, 0, 0, 0, 0, 0, 0,

///     1, 0, 2, 0, 3, 0, 4, 0,  // <= this is where the 1st line of 5s appears

///     0, 0, 0, 0, 0, 0, 0, 0,  //    in the schematic drawing of the passes at

///     0, 0, 0, 0, 0, 0, 0, 0,  //    https://en.wikipedia.org/wiki/Adam7_algorithm

///     0, 0, 0, 0, 0, 0, 0, 0,

///     0, 0, 0, 0, 0, 0, 0, 0,

///     0, 0, 0, 0, 0, 0, 0, 0,

/// ]);

/// ```

pub fn expand_pass(

    img: &mut [u8],

    img_row_stride: usize,

    interlaced_row: &[u8],

    interlace_info: &Adam7Info,

    bits_per_pixel: u8,

) {

    let bits_pp = bits_per_pixel as usize;

    let bit_indices = expand_adam7_bits(img_row_stride, interlace_info, bits_pp);

    if bits_pp < 8 {

        for (pos, px) in bit_indices.zip(subbyte_pixels(interlaced_row, bits_pp)) {

            let rem = 8 - pos % 8 - bits_pp;

            img[pos / 8] |= px << rem as u8;

        }

    } else {

        let bytes_pp = bits_pp / 8;

        for (bitpos, px) in bit_indices.zip(interlaced_row.chunks(bytes_pp)) {

            for (offset, val) in px.iter().enumerate() {

                img[bitpos / 8 + offset] = *val;

            }

        }

    }

}

#[test]

fn test_adam7() {

    /*

        1646

        7777

        5656

        7777

    */

    let it = Adam7Iterator::new(4, 4);

    let passes: Vec<_> = it.collect();

    assert_eq!(

        &*passes,

        &[

            Adam7Info {

                pass: 1,

                line: 0,

                width: 1

            },

            Adam7Info {

                pass: 4,

                line: 0,

                width: 1

            },

            Adam7Info {

                pass: 5,

                line: 0,

                width: 2

            },

            Adam7Info {

                pass: 6,

                line: 0,

                width: 2

            },

            Adam7Info {

                pass: 6,

                line: 1,

                width: 2

            },

            Adam7Info {

                pass: 7,

                line: 0,

                width: 4

            },

            Adam7Info {

                pass: 7,

                line: 1,

                width: 4

            }

        ]

    );

}

#[test]

fn test_subbyte_pixels() {

    let scanline = &[0b10101010, 0b10101010];

    let pixels = subbyte_pixels(scanline, 1).collect::<Vec<_>>();

    assert_eq!(pixels.len(), 16);

    assert_eq!(pixels, [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0]);

}

#[test]

fn test_expand_adam7_bits() {

    let width = 32;

    let bits_pp = 1;

    let stride = width / 8;

    let info = |pass, line, img_width| create_adam7_info_for_tests(pass, line as u32, img_width);

    let expected = |offset: usize, step: usize, count: usize| {

        (0..count)

            .map(move |i| step * i + offset)

            .collect::<Vec<_>>()

    };

    for line_no in 0..8 {

        let start = 8 * line_no * width;

        assert_eq!(

            expand_adam7_bits(stride, &info(1, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 8, 4)

        );

        let start = start + 4;

        assert_eq!(

            expand_adam7_bits(stride, &info(2, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 8, 4)

        );

        let start = (8 * line_no + 4) * width;

        assert_eq!(

            expand_adam7_bits(stride, &info(3, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 4, 8)

        );

    }

    for line_no in 0..16 {

        let start = 4 * line_no * width + 2;

        assert_eq!(

            expand_adam7_bits(stride, &info(4, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 4, 8)

        );

        let start = (4 * line_no + 2) * width;

        assert_eq!(

            expand_adam7_bits(stride, &info(5, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 2, 16)

        )

    }

    for line_no in 0..32 {

        let start = 2 * line_no * width + 1;

        assert_eq!(

            expand_adam7_bits(stride, &info(6, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 2, 16),

            "line_no: {}",

            line_no

        );

        let start = (2 * line_no + 1) * width;

        assert_eq!(

            expand_adam7_bits(stride, &info(7, line_no, width), bits_pp).collect::<Vec<_>>(),

            expected(start, 1, 32)

        );

    }

}

#[test]

fn test_expand_adam7_bits_independent_row_stride() {

    let pass = 1;

    let line_no = 1;

    let width = 32;

    let bits_pp = 8;

    let info = create_adam7_info_for_tests;

    {

        let stride = width;

        assert_eq!(

            expand_adam7_bits(stride, &info(pass, line_no, width), bits_pp).collect::<Vec<_>>(),

            vec![2048, 2112, 2176, 2240],

        );

    }

    {

        let stride = 10000;

        assert_eq!(

            expand_adam7_bits(stride, &info(pass, line_no, width), bits_pp).collect::<Vec<_>>(),

            vec![640000, 640064, 640128, 640192],

        );

    }

}

#[test]

fn test_expand_pass_subbyte() {

    let mut img = [0u8; 8];

    let width = 8;

    let stride = width / 8;

    let bits_pp = 1;

    let info = create_adam7_info_for_tests;

    expand_pass(&mut img, stride, &[0b10000000], &info(1, 0, width), bits_pp);

    assert_eq!(img, [0b10000000u8, 0, 0, 0, 0, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b10000000], &info(2, 0, width), bits_pp);

    assert_eq!(img, [0b10001000u8, 0, 0, 0, 0, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b11000000], &info(3, 0, width), bits_pp);

    assert_eq!(img, [0b10001000u8, 0, 0, 0, 0b10001000, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b11000000], &info(4, 0, width), bits_pp);

    assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10001000, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b11000000], &info(4, 1, width), bits_pp);

    assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10101010, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b11110000], &info(5, 0, width), bits_pp);

    assert_eq!(img, [0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0, 0]);

    expand_pass(&mut img, stride, &[0b11110000], &info(5, 1, width), bits_pp);

    assert_eq!(

        img,

        [0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]

    );

    expand_pass(&mut img, stride, &[0b11110000], &info(6, 0, width), bits_pp);

    assert_eq!(

        img,

        [0b11111111u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]

    );

    expand_pass(&mut img, stride, &[0b11110000], &info(6, 1, width), bits_pp);

    assert_eq!(

        img,

        [0b11111111u8, 0, 0b11111111, 0, 0b10101010, 0, 0b10101010, 0]

    );

    expand_pass(&mut img, stride, &[0b11110000], &info(6, 2, width), bits_pp);

    assert_eq!(

        img,

        [0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b10101010, 0]

    );

    expand_pass(&mut img, stride, &[0b11110000], &info(6, 3, width), bits_pp);

    assert_eq!(

        [0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b11111111, 0],

        img

    );

    expand_pass(&mut img, stride, &[0b11111111], &info(7, 0, width), bits_pp);

    assert_eq!(

        [

            0b11111111u8,

            0b11111111,

            0b11111111,

            0,

            0b11111111,

            0,

            0b11111111,

            0

        ],

        img

    );

    expand_pass(&mut img, stride, &[0b11111111], &info(7, 1, width), bits_pp);

    assert_eq!(

        [

            0b11111111u8,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0,

            0b11111111,

            0

        ],

        img

    );

    expand_pass(&mut img, stride, &[0b11111111], &info(7, 2, width), bits_pp);

    assert_eq!(

        [

            0b11111111u8,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0

        ],

        img

    );

    expand_pass(&mut img, stride, &[0b11111111], &info(7, 3, width), bits_pp);

    assert_eq!(

        [

            0b11111111u8,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111,

            0b11111111

        ],

        img

    );

}

#[cfg(test)]

fn create_adam7_info_for_tests(pass: u8, line: u32, img_width: usize) -> Adam7Info {

    let width = {

        let img_height = 8;

        Adam7Iterator::new(img_width as u32, img_height)

            .filter(|info| info.pass == pass)

            .map(|info| info.width)

            .next()

            .unwrap()

    };

    Adam7Info { pass, line, width }

}