use std;
use std::io;

/// A decoded icon image.
///
/// An `Image` struct consists of a width, a height, a
/// [`PixelFormat`](enum.PixelFormat.html), and a data array encoding the image
/// pixels in that format.
///
/// Regardless of format, pixel data for an image is always stored one complete
/// pixel at a time, in row-major order (that is, the top-left pixel comes
/// first, followed by the rest of the top row from left to right; then comes
/// the second row down, again from left to right, and so on until finally the
/// bottom-right pixel comes last).
#[derive(Clone)]
pub struct Image {
    pub(crate) format: PixelFormat,
    pub(crate) width: u32,
    pub(crate) height: u32,
    pub(crate) data: Box<[u8]>,
}

impl Image {
    /// Creates a new image with all pixel data set to zero.
    pub fn new(format: PixelFormat, width: u32, height: u32) -> Image {
        let data_bits = format.bits_per_pixel() * width * height;
        let data_bytes = ((data_bits + 7) / 8) as usize;
        Image {
            format,
            width,
            height,
            data: vec![0u8; data_bytes].into_boxed_slice(),
        }
    }

    /// Creates a new image using the given pixel data.  Returns an error if
    /// the data array is not the correct length.
    pub fn from_data(
        format: PixelFormat,
        width: u32,
        height: u32,
        data: Vec<u8>,
    ) -> io::Result<Image> {
        let data_bits = format.bits_per_pixel() * width * height;
        let data_bytes = ((data_bits + 7) / 8) as usize;
        if data.len() == data_bytes {
            Ok(Image {
                format,
                width,
                height,
                data: data.into_boxed_slice(),
            })
        } else {
            let msg = format!(
                "incorrect pixel data array length for \
                               speicifed format and dimensions ({} instead \
                               of {})",
                data.len(),
                data_bytes
            );
            Err(io::Error::new(io::ErrorKind::InvalidInput, msg))
        }
    }

    /// Returns the format in which this image's pixel data is stored.
    pub fn pixel_format(&self) -> PixelFormat {
        self.format
    }

    /// Returns the width of the image, in pixels.
    pub fn width(&self) -> u32 {
        self.width
    }

    /// Returns the height of the image, in pixels.
    pub fn height(&self) -> u32 {
        self.height
    }

    /// Returns a reference to the image's pixel data.
    pub fn data(&self) -> &[u8] {
        &self.data
    }

    /// Returns a mutable reference to the image's pixel data.
    pub fn data_mut(&mut self) -> &mut [u8] {
        &mut self.data
    }

    /// Consumes the image, returning the pixel data without cloning it.
    pub fn into_data(self) -> Box<[u8]> {
        self.data
    }

    /// Creates a copy of this image by converting to the specified pixel
    /// format.  This operation always succeeds, but may lose information (e.g.
    /// converting from RGBA to RGB will silently drop the alpha channel).  If
    /// the source image is already in the requested format, this is equivalant
    /// to simply calling `clone()`.
    pub fn convert_to(&self, format: PixelFormat) -> Image {
        let new_data = match self.format {
            PixelFormat::RGBA => match format {
                PixelFormat::RGBA => self.data.clone(),
                PixelFormat::RGB => rgba_to_rgb(&self.data),
                PixelFormat::GrayAlpha => rgba_to_grayalpha(&self.data),
                PixelFormat::Gray => rgba_to_gray(&self.data),
                PixelFormat::Alpha => rgba_to_alpha(&self.data),
                PixelFormat::PNG => return self.make_png_image(),
            },
            PixelFormat::RGB => match format {
                PixelFormat::RGBA => rgb_to_rgba(&self.data),
                PixelFormat::RGB => self.data.clone(),
                PixelFormat::GrayAlpha => rgb_to_grayalpha(&self.data),
                PixelFormat::Gray => rgb_to_gray(&self.data),
                PixelFormat::Alpha => rgb_to_alpha(&self.data),
                PixelFormat::PNG => return self.make_png_image(),
            },
            PixelFormat::GrayAlpha => match format {
                PixelFormat::RGBA => grayalpha_to_rgba(&self.data),
                PixelFormat::RGB => grayalpha_to_rgb(&self.data),
                PixelFormat::GrayAlpha => self.data.clone(),
                PixelFormat::Gray => grayalpha_to_gray(&self.data),
                PixelFormat::Alpha => grayalpha_to_alpha(&self.data),
                PixelFormat::PNG => return self.make_png_image(),
            },
            PixelFormat::Gray => match format {
                PixelFormat::RGBA => gray_to_rgba(&self.data),
                PixelFormat::RGB => gray_to_rgb(&self.data),
                PixelFormat::GrayAlpha => gray_to_grayalpha(&self.data),
                PixelFormat::Gray => self.data.clone(),
                PixelFormat::Alpha => gray_to_alpha(&self.data),
                PixelFormat::PNG => return self.make_png_image(),
            },
            PixelFormat::Alpha => match format {
                PixelFormat::RGBA => alpha_to_rgba(&self.data),
                PixelFormat::RGB => alpha_to_rgb(&self.data),
                PixelFormat::GrayAlpha => alpha_to_grayalpha(&self.data),
                PixelFormat::Gray => alpha_to_gray(&self.data),
                PixelFormat::Alpha => self.data.clone(),
                PixelFormat::PNG => return self.make_png_image(),
            },
            PixelFormat::PNG => match format {
                PixelFormat::PNG => self.data.clone(),
                _ => {
                    return Image::decode_from_png(&*self.data)
                        .expect("Unable to read PNG")
                        .convert_to(format)
                }
            },
        };
        Image {
            format,
            width: self.width,
            height: self.height,
            data: new_data,
        }
    }

    fn make_png_image(&self) -> Image {
        let mut v = Vec::new();
        self.write_png(&mut v).expect("Unable to write to PNG");
        Image {
            format: PixelFormat::PNG,
            width: self.width,
            height: self.height,
            data: v.into_boxed_slice(),
        }
    }
}

/// Formats for storing pixel data in an image.
///
/// This type determines how the raw data array of an
/// [`Image`](struct.Image.html) is to be interpreted.
///
/// Regardless of format, pixel data for an image is always stored one complete
/// pixel at a time, in row-major order (that is, the top-left pixel comes
/// first, followed by the rest of the top row from left to right; then comes
/// the second row down, again from left to right, and so on until finally the
/// bottom-right pixel comes last).
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum PixelFormat {
    /// 32-bit color with alpha channel.  Each pixel is four bytes, with red
    /// first and alpha last.
    RGBA,
    /// 24-bit color with no alpha.  Each pixel is three bytes, with red
    /// first and blue last.
    RGB,
    /// 16-bit grayscale-with-alpha.  Each pixel is two bytes, with the
    /// grayscale value first and alpha second.
    GrayAlpha,
    /// 8-bit grayscale with no alpha.  Each pixel is one byte (0=black,
    /// 255=white).
    Gray,
    /// 8-bit alpha mask with no color.  Each pixel is one byte (0=transparent,
    /// 255=opaque).
    Alpha,
    /// PNG data.
    PNG,
}

impl PixelFormat {
    /// Returns the number of bits needed to store a single pixel in this
    /// format.
    pub fn bits_per_pixel(self) -> u32 {
        match self {
            PixelFormat::RGBA => 32,
            PixelFormat::RGB => 24,
            PixelFormat::GrayAlpha => 16,
            PixelFormat::Gray => 8,
            PixelFormat::Alpha => 8,
            PixelFormat::PNG => panic!("Unable to know definite number of bits per pixel for PNG"),
        }
    }
}

/// Converts RGBA image data into RGB.
fn rgba_to_rgb(rgba: &[u8]) -> Box<[u8]> {
    assert_eq!(rgba.len() % 4, 0);
    let num_pixels = rgba.len() / 4;
    let mut rgb = Vec::with_capacity(num_pixels * 3);
    for i in 0..num_pixels {
        rgb.extend_from_slice(&rgba[(4 * i)..(4 * i + 3)]);
    }
    rgb.into_boxed_slice()
}

/// Converts RGB image data into RGBA.
fn rgb_to_rgba(rgb: &[u8]) -> Box<[u8]> {
    assert_eq!(rgb.len() % 3, 0);
    let num_pixels = rgb.len() / 3;
    let mut rgba = Vec::with_capacity(num_pixels * 4);
    for i in 0..num_pixels {
        rgba.extend_from_slice(&rgb[(3 * i)..(3 * i + 3)]);
        rgba.push(std::u8::MAX);
    }
    rgba.into_boxed_slice()
}

/// Converts RGBA image data into grayscale.
fn rgba_to_gray(rgba: &[u8]) -> Box<[u8]> {
    assert_eq!(rgba.len() % 4, 0);
    let num_pixels = rgba.len() / 4;
    let mut gray = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        let red = u32::from(rgba[4 * i]);
        let green = u32::from(rgba[4 * i + 1]);
        let blue = u32::from(rgba[4 * i + 2]);
        gray.push(((red + green + blue) / 3) as u8);
    }
    gray.into_boxed_slice()
}

/// Converts RGB image data into grayscale.
fn rgb_to_gray(rgb: &[u8]) -> Box<[u8]> {
    assert_eq!(rgb.len() % 3, 0);
    let num_pixels = rgb.len() / 3;
    let mut gray = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        let red = u32::from(rgb[3 * i]);
        let green = u32::from(rgb[3 * i + 1]);
        let blue = u32::from(rgb[3 * i + 2]);
        gray.push(((red + green + blue) / 3) as u8);
    }
    gray.into_boxed_slice()
}

/// Converts RGBA image data into grayscale-with-alpha.
fn rgba_to_grayalpha(rgba: &[u8]) -> Box<[u8]> {
    assert_eq!(rgba.len() % 4, 0);
    let num_pixels = rgba.len() / 4;
    let mut grayalpha = Vec::with_capacity(num_pixels * 2);
    for i in 0..num_pixels {
        let red = u32::from(rgba[4 * i]);
        let green = u32::from(rgba[4 * i + 1]);
        let blue = u32::from(rgba[4 * i + 2]);
        let alpha = rgba[4 * i + 3];
        grayalpha.push(((red + green + blue) / 3) as u8);
        grayalpha.push(alpha);
    }
    grayalpha.into_boxed_slice()
}

/// Converts RGB image data into grayscale-with-alpha.
fn rgb_to_grayalpha(rgb: &[u8]) -> Box<[u8]> {
    assert_eq!(rgb.len() % 3, 0);
    let num_pixels = rgb.len() / 3;
    let mut gray = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        let red = u32::from(rgb[3 * i]);
        let green = u32::from(rgb[3 * i + 1]);
        let blue = u32::from(rgb[3 * i + 2]);
        gray.push(((red + green + blue) / 3) as u8);
        gray.push(std::u8::MAX);
    }
    gray.into_boxed_slice()
}

/// Converts RGBA image data into an alpha mask.
fn rgba_to_alpha(rgba: &[u8]) -> Box<[u8]> {
    assert_eq!(rgba.len() % 4, 0);
    let num_pixels = rgba.len() / 4;
    let mut alpha = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        alpha.push(rgba[4 * i + 3]);
    }
    alpha.into_boxed_slice()
}

/// Converts RGB image data into an alpha mask.
fn rgb_to_alpha(rgb: &[u8]) -> Box<[u8]> {
    assert_eq!(rgb.len() % 3, 0);
    let num_pixels = rgb.len() / 3;
    vec![std::u8::MAX; num_pixels].into_boxed_slice()
}

/// Converts grayscale-with-alpha image data into RGBA.
fn grayalpha_to_rgba(grayalpha: &[u8]) -> Box<[u8]> {
    assert_eq!(grayalpha.len() % 2, 0);
    let num_pixels = grayalpha.len() / 2;
    let mut rgba = Vec::with_capacity(num_pixels * 4);
    for i in 0..num_pixels {
        let gray = grayalpha[2 * i];
        let alpha = grayalpha[2 * i + 1];
        rgba.push(gray);
        rgba.push(gray);
        rgba.push(gray);
        rgba.push(alpha);
    }
    rgba.into_boxed_slice()
}

/// Converts grayscale-with-alpha image data into RGB.
fn grayalpha_to_rgb(grayalpha: &[u8]) -> Box<[u8]> {
    assert_eq!(grayalpha.len() % 2, 0);
    let num_pixels = grayalpha.len() / 2;
    let mut rgb = Vec::with_capacity(num_pixels * 3);
    for i in 0..num_pixels {
        let gray = grayalpha[2 * i];
        rgb.push(gray);
        rgb.push(gray);
        rgb.push(gray);
    }
    rgb.into_boxed_slice()
}

/// Converts grayscale-with-alpha image data into grayscale-without-alpha.
fn grayalpha_to_gray(grayalpha: &[u8]) -> Box<[u8]> {
    assert_eq!(grayalpha.len() % 2, 0);
    let num_pixels = grayalpha.len() / 2;
    let mut gray = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        let value = grayalpha[2 * i];
        gray.push(value);
    }
    gray.into_boxed_slice()
}

/// Converts grayscale-with-alpha image data into an alpha mask.
fn grayalpha_to_alpha(grayalpha: &[u8]) -> Box<[u8]> {
    assert_eq!(grayalpha.len() % 2, 0);
    let num_pixels = grayalpha.len() / 2;
    let mut alpha = Vec::with_capacity(num_pixels);
    for i in 0..num_pixels {
        let value = grayalpha[2 * i + 1];
        alpha.push(value);
    }
    alpha.into_boxed_slice()
}

/// Converts grayscale image data into RGBA.
fn gray_to_rgba(gray: &[u8]) -> Box<[u8]> {
    let num_pixels = gray.len();
    let mut rgba = Vec::with_capacity(num_pixels * 4);
    for &value in gray {
        rgba.push(value);
        rgba.push(value);
        rgba.push(value);
        rgba.push(std::u8::MAX);
    }
    rgba.into_boxed_slice()
}

/// Converts grayscale image data into RGB.
fn gray_to_rgb(gray: &[u8]) -> Box<[u8]> {
    let num_pixels = gray.len();
    let mut rgb = Vec::with_capacity(num_pixels * 3);
    for &value in gray {
        rgb.push(value);
        rgb.push(value);
        rgb.push(value);
    }
    rgb.into_boxed_slice()
}

/// Converts grayscale image data into grayscale-with-alpha.
fn gray_to_grayalpha(gray: &[u8]) -> Box<[u8]> {
    let num_pixels = gray.len();
    let mut grayalpha = Vec::with_capacity(num_pixels * 2);
    for &value in gray {
        grayalpha.push(value);
        grayalpha.push(std::u8::MAX);
    }
    grayalpha.into_boxed_slice()
}

/// Converts grayscale image data into an alpha mask.
fn gray_to_alpha(gray: &[u8]) -> Box<[u8]> {
    vec![std::u8::MAX; gray.len()].into_boxed_slice()
}

/// Converts alpha mask image data into RGBA.
fn alpha_to_rgba(alpha: &[u8]) -> Box<[u8]> {
    let num_pixels = alpha.len();
    let mut rgba = Vec::with_capacity(num_pixels * 4);
    for &value in alpha {
        rgba.push(0);
        rgba.push(0);
        rgba.push(0);
        rgba.push(value);
    }
    rgba.into_boxed_slice()
}

/// Converts alpha mask image data into RGB.
fn alpha_to_rgb(alpha: &[u8]) -> Box<[u8]> {
    vec![0u8; alpha.len() * 3].into_boxed_slice()
}

/// Converts alpha mask image data into grayscale-with-alpha.
fn alpha_to_grayalpha(alpha: &[u8]) -> Box<[u8]> {
    let num_pixels = alpha.len();
    let mut grayalpha = Vec::with_capacity(num_pixels * 2);
    for &value in alpha {
        grayalpha.push(0);
        grayalpha.push(value);
    }
    grayalpha.into_boxed_slice()
}

/// Converts alpha mask image data into grayscale.
fn alpha_to_gray(alpha: &[u8]) -> Box<[u8]> {
    vec![0u8; alpha.len()].into_boxed_slice()
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Cursor;

    #[test]
    fn image_from_data() {
        let data: Vec<u8> = vec![255, 0, 0, 0, 255, 0, 0, 0, 255, 95, 95, 95];
        let image = Image::from_data(PixelFormat::RGB, 2, 2, data.clone()).unwrap();
        assert_eq!(image.data(), &data as &[u8]);
    }

    #[test]
    fn image_from_data_wrong_size() {
        let data: Vec<u8> = vec![1, 2, 3];
        let result = Image::from_data(PixelFormat::Alpha, 2, 2, data);
        assert!(result.is_err());
    }

    #[test]
    fn alpha_to_gray() {
        let alpha_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut alpha_image = Image::new(PixelFormat::Alpha, 2, 2);
        alpha_image.data_mut().clone_from_slice(&alpha_data);
        let gray_image = alpha_image.convert_to(PixelFormat::Gray);
        let gray_data: Vec<u8> = vec![0, 0, 0, 0];
        assert_eq!(gray_image.data(), &gray_data as &[u8]);
    }

    #[test]
    fn alpha_to_grayalpha() {
        let alpha_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut alpha_image = Image::new(PixelFormat::Alpha, 2, 2);
        alpha_image.data_mut().clone_from_slice(&alpha_data);
        let grayalpha_image = alpha_image.convert_to(PixelFormat::GrayAlpha);
        let grayalpha_data: Vec<u8> = vec![0, 63, 0, 127, 0, 191, 0, 255];
        assert_eq!(grayalpha_image.data(), &grayalpha_data as &[u8]);
    }

    #[test]
    fn alpha_to_rgb() {
        let alpha_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut alpha_image = Image::new(PixelFormat::Alpha, 2, 2);
        alpha_image.data_mut().clone_from_slice(&alpha_data);
        let rgb_image = alpha_image.convert_to(PixelFormat::RGB);
        let rgb_data: Vec<u8> = vec![0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
        assert_eq!(rgb_image.data(), &rgb_data as &[u8]);
    }

    #[test]
    fn alpha_to_rgba() {
        let alpha_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut alpha_image = Image::new(PixelFormat::Alpha, 2, 2);
        alpha_image.data_mut().clone_from_slice(&alpha_data);
        let rgba_image = alpha_image.convert_to(PixelFormat::RGBA);
        let rgba_data: Vec<u8> = vec![0, 0, 0, 63, 0, 0, 0, 127, 0, 0, 0, 191, 0, 0, 0, 255];
        assert_eq!(rgba_image.data(), &rgba_data as &[u8]);
    }

    #[test]
    fn gray_to_alpha() {
        let gray_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut gray_image = Image::new(PixelFormat::Gray, 2, 2);
        gray_image.data_mut().clone_from_slice(&gray_data);
        let alpha_image = gray_image.convert_to(PixelFormat::Alpha);
        let alpha_data: Vec<u8> = vec![255, 255, 255, 255];
        assert_eq!(alpha_image.data(), &alpha_data as &[u8]);
    }

    #[test]
    fn gray_to_grayalpha() {
        let gray_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut gray_image = Image::new(PixelFormat::Gray, 2, 2);
        gray_image.data_mut().clone_from_slice(&gray_data);
        let grayalpha_image = gray_image.convert_to(PixelFormat::GrayAlpha);
        let grayalpha_data: Vec<u8> = vec![63, 255, 127, 255, 191, 255, 255, 255];
        assert_eq!(grayalpha_image.data(), &grayalpha_data as &[u8]);
    }

    #[test]
    fn gray_to_rgb() {
        let gray_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut gray_image = Image::new(PixelFormat::Gray, 2, 2);
        gray_image.data_mut().clone_from_slice(&gray_data);
        let rgb_image = gray_image.convert_to(PixelFormat::RGB);
        let rgb_data: Vec<u8> = vec![63, 63, 63, 127, 127, 127, 191, 191, 191, 255, 255, 255];
        assert_eq!(rgb_image.data(), &rgb_data as &[u8]);
    }

    #[test]
    fn gray_to_rgba() {
        let gray_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut gray_image = Image::new(PixelFormat::Gray, 2, 2);
        gray_image.data_mut().clone_from_slice(&gray_data);
        let rgba_image = gray_image.convert_to(PixelFormat::RGBA);
        assert_eq!(rgba_image.pixel_format(), PixelFormat::RGBA);
        assert_eq!(rgba_image.width(), 2);
        assert_eq!(rgba_image.height(), 2);
        let rgba_data: Vec<u8> = vec![
            63, 63, 63, 255, 127, 127, 127, 255, 191, 191, 191, 255, 255, 255, 255, 255,
        ];
        assert_eq!(rgba_image.data(), &rgba_data as &[u8]);
    }

    #[test]
    fn grayalpha_to_alpha() {
        let grayalpha_data: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8];
        let mut grayalpha_image = Image::new(PixelFormat::GrayAlpha, 2, 2);
        grayalpha_image.data_mut().clone_from_slice(&grayalpha_data);
        let alpha_image = grayalpha_image.convert_to(PixelFormat::Alpha);
        let alpha_data: Vec<u8> = vec![2, 4, 6, 8];
        assert_eq!(alpha_image.data(), &alpha_data as &[u8]);
    }

    #[test]
    fn grayalpha_to_gray() {
        let grayalpha_data: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8];
        let mut grayalpha_image = Image::new(PixelFormat::GrayAlpha, 2, 2);
        grayalpha_image.data_mut().clone_from_slice(&grayalpha_data);
        let gray_image = grayalpha_image.convert_to(PixelFormat::Gray);
        let gray_data: Vec<u8> = vec![1, 3, 5, 7];
        assert_eq!(gray_image.data(), &gray_data as &[u8]);
    }

    #[test]
    fn grayalpha_to_rgb() {
        let grayalpha_data: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8];
        let mut grayalpha_image = Image::new(PixelFormat::GrayAlpha, 2, 2);
        grayalpha_image.data_mut().clone_from_slice(&grayalpha_data);
        let rgb_image = grayalpha_image.convert_to(PixelFormat::RGB);
        let rgb_data: Vec<u8> = vec![1, 1, 1, 3, 3, 3, 5, 5, 5, 7, 7, 7];
        assert_eq!(rgb_image.data(), &rgb_data as &[u8]);
    }

    #[test]
    fn grayalpha_to_rgba() {
        let grayalpha_data: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8];
        let mut grayalpha_image = Image::new(PixelFormat::GrayAlpha, 2, 2);
        grayalpha_image.data_mut().clone_from_slice(&grayalpha_data);
        let rgba_image = grayalpha_image.convert_to(PixelFormat::RGBA);
        let rgba_data: Vec<u8> = vec![1, 1, 1, 2, 3, 3, 3, 4, 5, 5, 5, 6, 7, 7, 7, 8];
        assert_eq!(rgba_image.data(), &rgba_data as &[u8]);
    }

    #[test]
    fn rgb_to_alpha() {
        let rgb_data: Vec<u8> = vec![30, 0, 0, 0, 60, 0, 0, 0, 90, 40, 40, 40];
        let mut rgb_image = Image::new(PixelFormat::RGB, 2, 2);
        rgb_image.data_mut().clone_from_slice(&rgb_data);
        let alpha_image = rgb_image.convert_to(PixelFormat::Alpha);
        let alpha_data: Vec<u8> = vec![255, 255, 255, 255];
        assert_eq!(alpha_image.data(), &alpha_data as &[u8]);
    }

    #[test]
    fn rgb_to_gray() {
        let rgb_data: Vec<u8> = vec![30, 0, 0, 0, 60, 0, 0, 0, 90, 40, 40, 40];
        let mut rgb_image = Image::new(PixelFormat::RGB, 2, 2);
        rgb_image.data_mut().clone_from_slice(&rgb_data);
        let gray_image = rgb_image.convert_to(PixelFormat::Gray);
        let gray_data: Vec<u8> = vec![10, 20, 30, 40];
        assert_eq!(gray_image.data(), &gray_data as &[u8]);
    }

    #[test]
    fn rgb_to_grayalpha() {
        let rgb_data: Vec<u8> = vec![30, 0, 0, 0, 60, 0, 0, 0, 90, 40, 40, 40];
        let mut rgb_image = Image::new(PixelFormat::RGB, 2, 2);
        rgb_image.data_mut().clone_from_slice(&rgb_data);
        let grayalpha_image = rgb_image.convert_to(PixelFormat::GrayAlpha);
        let grayalpha_data: Vec<u8> = vec![10, 255, 20, 255, 30, 255, 40, 255];
        assert_eq!(grayalpha_image.data(), &grayalpha_data as &[u8]);
    }

    #[test]
    fn rgb_to_rgba() {
        let rgb_data: Vec<u8> = vec![255, 0, 0, 0, 255, 0, 0, 0, 255, 127, 127, 127];
        let mut rgb_image = Image::new(PixelFormat::RGB, 2, 2);
        rgb_image.data_mut().clone_from_slice(&rgb_data);
        let rgba_image = rgb_image.convert_to(PixelFormat::RGBA);
        assert_eq!(rgba_image.pixel_format(), PixelFormat::RGBA);
        assert_eq!(rgba_image.width(), 2);
        assert_eq!(rgba_image.height(), 2);
        let rgba_data: Vec<u8> = vec![
            255, 0, 0, 255, 0, 255, 0, 255, 0, 0, 255, 255, 127, 127, 127, 255,
        ];
        assert_eq!(rgba_image.data(), &rgba_data as &[u8]);
    }

    #[test]
    fn rgba_to_alpha() {
        let rgba_data: Vec<u8> = vec![30, 0, 0, 200, 0, 60, 0, 150, 0, 0, 90, 100, 40, 40, 40, 50];
        let mut rgba_image = Image::new(PixelFormat::RGBA, 2, 2);
        rgba_image.data_mut().clone_from_slice(&rgba_data);
        let alpha_image = rgba_image.convert_to(PixelFormat::Alpha);
        let alpha_data: Vec<u8> = vec![200, 150, 100, 50];
        assert_eq!(alpha_image.data(), &alpha_data as &[u8]);
    }

    #[test]
    fn rgba_to_gray() {
        let rgba_data: Vec<u8> = vec![30, 0, 0, 200, 0, 60, 0, 150, 0, 0, 90, 100, 40, 40, 40, 50];
        let mut rgba_image = Image::new(PixelFormat::RGBA, 2, 2);
        rgba_image.data_mut().clone_from_slice(&rgba_data);
        let gray_image = rgba_image.convert_to(PixelFormat::Gray);
        let gray_data: Vec<u8> = vec![10, 20, 30, 40];
        assert_eq!(gray_image.data(), &gray_data as &[u8]);
    }

    #[test]
    fn rgba_to_grayalpha() {
        let rgba_data: Vec<u8> = vec![30, 0, 0, 200, 0, 60, 0, 150, 0, 0, 90, 100, 40, 40, 40, 50];
        let mut rgba_image = Image::new(PixelFormat::RGBA, 2, 2);
        rgba_image.data_mut().clone_from_slice(&rgba_data);
        let grayalpha_image = rgba_image.convert_to(PixelFormat::GrayAlpha);
        let grayalpha_data: Vec<u8> = vec![10, 200, 20, 150, 30, 100, 40, 50];
        assert_eq!(grayalpha_image.data(), &grayalpha_data as &[u8]);
    }

    #[test]
    fn rgba_to_rgb() {
        let rgba_data: Vec<u8> = vec![30, 0, 0, 200, 0, 60, 0, 150, 0, 0, 90, 100, 40, 40, 40, 50];
        let mut rgba_image = Image::new(PixelFormat::RGBA, 2, 2);
        rgba_image.data_mut().clone_from_slice(&rgba_data);
        let rgb_image = rgba_image.convert_to(PixelFormat::RGB);
        let rgb_data: Vec<u8> = vec![30, 0, 0, 0, 60, 0, 0, 0, 90, 40, 40, 40];
        assert_eq!(rgb_image.data(), &rgb_data as &[u8]);
    }

    #[test]
    #[cfg(feature = "pngio")]
    fn write_grayscale_png() {
        let gray_data: Vec<u8> = vec![63, 127, 191, 255];
        let mut image = Image::new(PixelFormat::Gray, 2, 2);
        image.data_mut().clone_from_slice(&gray_data);
        let mut output: Vec<u8> = Vec::new();
        image.write_png(&mut output).expect("failed to write PNG");
        let expected: Vec<u8> = vec![
            137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 2, 0, 0, 0, 2,
            8, 0, 0, 0, 0, 87, 221, 82, 248, 0, 0, 0, 14, 73, 68, 65, 84, 120, 156, 99, 180, 119,
            96, 220, 239, 0, 0, 4, 8, 1, 129, 134, 46, 201, 141, 0, 0, 0, 0, 73, 69, 78, 68, 174,
            66, 96, 130,
        ];
        assert_eq!(output, expected);
    }

    #[test]
    #[cfg(feature = "pngio")]
    fn write_rgb_png() {
        let rgb_data: Vec<u8> = vec![255, 0, 0, 0, 255, 0, 0, 0, 255, 127, 127, 127];
        let mut image = Image::new(PixelFormat::RGB, 2, 2);
        image.data_mut().clone_from_slice(&rgb_data);
        let mut output: Vec<u8> = Vec::new();
        image.write_png(&mut output).expect("failed to write PNG");
        let expected: Vec<u8> = vec![
            137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 2, 0, 0, 0, 2,
            8, 2, 0, 0, 0, 253, 212, 154, 115, 0, 0, 0, 20, 73, 68, 65, 84, 120, 156, 99, 252, 207,
            192, 0, 196, 140, 12, 12, 255, 235, 235, 27, 0, 29, 14, 4, 127, 253, 15, 140, 153, 0,
            0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
        ];
        assert_eq!(output, expected);
    }

    #[test]
    #[cfg(feature = "pngio")]
    fn write_rgba_png() {
        let rgba_data: Vec<u8> = vec![
            255, 0, 0, 63, 0, 255, 0, 127, 0, 0, 255, 191, 127, 127, 127, 255,
        ];
        let mut image = Image::new(PixelFormat::RGBA, 2, 2);
        image.data_mut().clone_from_slice(&rgba_data);
        let mut output: Vec<u8> = Vec::new();
        image.write_png(&mut output).expect("failed to write PNG");
        let expected: Vec<u8> = vec![
            137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 2, 0, 0, 0, 2,
            8, 6, 0, 0, 0, 114, 182, 13, 36, 0, 0, 0, 25, 73, 68, 65, 84, 120, 156, 99, 252, 207,
            192, 96, 15, 36, 28, 24, 25, 24, 254, 239, 175, 175, 111, 112, 0, 0, 49, 125, 5, 253,
            88, 193, 178, 240, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
        ];
        assert_eq!(output, expected);
    }

    #[test]
    #[cfg(feature = "pngio")]
    fn read_rgba_png() {
        let png: Vec<u8> = vec![
            137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 2, 0, 0, 0, 2,
            8, 6, 0, 0, 0, 114, 182, 13, 36, 0, 0, 0, 29, 73, 68, 65, 84, 120, 1, 1, 18, 0, 237,
            255, 1, 255, 0, 0, 63, 1, 255, 0, 64, 1, 0, 0, 255, 191, 127, 127, 128, 64, 49, 125, 5,
            253, 198, 70, 247, 56, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
        ];
        let image = Image::read_png(Cursor::new(&png)).expect("failed to read PNG");
        assert_eq!(image.data(), &png as &[u8]);
        let image = image.convert_to(PixelFormat::RGBA);
        assert_eq!(image.pixel_format(), PixelFormat::RGBA);
        assert_eq!(image.width(), 2);
        assert_eq!(image.height(), 2);
        let rgba_data: Vec<u8> = vec![
            255, 0, 0, 63, 0, 255, 0, 127, 0, 0, 255, 191, 127, 127, 127, 255,
        ];
        assert_eq!(image.data(), &rgba_data as &[u8]);
    }

    #[test]
    #[cfg(feature = "pngio")]
    fn png_round_trip() {
        let rgba_data: Vec<u8> = vec![
            127, 0, 0, 63, 0, 191, 0, 127, 0, 0, 255, 191, 127, 127, 127, 255,
        ];
        let mut rgba_image = Image::new(PixelFormat::RGBA, 2, 2);
        rgba_image.data_mut().clone_from_slice(&rgba_data);
        let pixel_formats = [
            PixelFormat::RGBA,
            PixelFormat::RGB,
            PixelFormat::GrayAlpha,
            PixelFormat::Gray,
            PixelFormat::Alpha,
        ];
        for &format in pixel_formats.iter() {
            // For each pixel format, try writing a PNG from an image in that
            // format.
            let image_1 = rgba_image.convert_to(format);
            let mut png_data = Vec::<u8>::new();
            image_1
                .write_png(&mut png_data)
                .expect("failed to write PNG");
            // We should be able to read the PNG back in successfully.
            let mut image_2 = Image::read_png(Cursor::new(&png_data)).expect("failed to read PNG");
            // We may get the image back in a different pixel format.  However,
            // in such cases we should be able to convert back to the original
            // pixel format and still get back exactly the same data.
            if image_2.pixel_format() != image_1.pixel_format() {
                image_2 = image_2.convert_to(image_1.pixel_format());
            }
            assert_eq!(image_1.data(), image_2.data());
        }
    }
}