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    //! Common types shared between the encoder and decoder
    use filter;

    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    #[repr(u8)]
    pub enum ColorType {
        Grayscale = 0,
        RGB = 2,
        Indexed = 3,
        GrayscaleAlpha = 4,
        RGBA = 6
    }

    impl ColorType {
        /// Returns the number of samples used per pixel of `ColorType`
        pub fn samples(&self) -> usize {
            use self::ColorType::*;
            match *self {
                Grayscale | Indexed => 1,
                RGB => 3,
                GrayscaleAlpha => 2,
                RGBA => 4
            }
        }

        /// u8 -> Self. Temporary solution until Rust provides a canonical one.
        pub fn from_u8(n: u8) -> Option<ColorType> {
            match n {
                0 => Some(ColorType::Grayscale),
                2 => Some(ColorType::RGB),
                3 => Some(ColorType::Indexed),
                4 => Some(ColorType::GrayscaleAlpha),
                6 => Some(ColorType::RGBA),
                _ => None
            }
        }
    }

    /// Bit depth of the png file
    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    #[repr(u8)]
    pub enum BitDepth {
        One     = 1,
        Two     = 2,
        Four    = 4,
        Eight   = 8,
        Sixteen = 16,
    }

    impl BitDepth {
        /// u8 -> Self. Temporary solution until Rust provides a canonical one.
        pub fn from_u8(n: u8) -> Option<BitDepth> {
            match n {
                1 => Some(BitDepth::One),
                2 => Some(BitDepth::Two),
                4 => Some(BitDepth::Four),
                8 => Some(BitDepth::Eight),
                16 => Some(BitDepth::Sixteen),
                _ => None
            }
        }
    }

    /// Pixel dimensions information
    #[derive(Clone, Copy, Debug)]
    pub struct PixelDimensions {
        /// Pixels per unit, X axis
        pub xppu: u32,
        /// Pixels per unit, Y axis
        pub yppu: u32,
        /// Either *Meter* or *Unspecified*
        pub unit: Unit,
    }

    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    #[repr(u8)]
    /// Physical unit of the pixel dimensions
    pub enum Unit {
        Unspecified = 0,
        Meter = 1,
    }

    impl Unit {
        /// u8 -> Self. Temporary solution until Rust provides a canonical one.
        pub fn from_u8(n: u8) -> Option<Unit> {
            match n {
                0 => Some(Unit::Unspecified),
                1 => Some(Unit::Meter),
                _ => None
            }
        }
    }

    /// Frame control information
    #[derive(Clone, Debug)]
    pub struct FrameControl {
        /// Sequence number of the animation chunk, starting from 0
        pub sequence_number: u32,
        /// Width of the following frame
        pub width: u32,
        /// Height of the following frame
        pub height: u32,
        /// X position at which to render the following frame
        pub x_offset: u32,
        /// Y position at which to render the following frame
        pub y_offset: u32,
        /// Frame delay fraction numerator
        pub delay_num: u16,
        /// Frame delay fraction denominator
        pub delay_den: u16,
        /// Type of frame area disposal to be done after rendering this frame
        pub dispose_op: u8,
        /// Type of frame area rendering for this frame
        pub blend_op: u8,
    }

    /// Animation control information
    #[derive(Clone, Copy, Debug)]
    pub struct AnimationControl {
        /// Number of frames
        pub num_frames: u32,
        /// Number of times to loop this APNG.  0 indicates infinite looping.
        pub num_plays: u32,
    }

    #[derive(Debug, Clone)]
    pub enum Compression {
        /// Default level
        Default,
        /// Fast minimal compression
        Fast,
        /// Higher compression level
        ///
        /// Best in this context isn't actually the highest possible level
        /// the encoder can do, but is meant to emulate the `Best` setting in the `Flate2`
        /// library.
        Best,
        Huffman,
        Rle,
    }

    /// PNG info struct
    #[derive(Debug)]
    pub struct Info {
        pub width: u32,
        pub height: u32,
        pub bit_depth: BitDepth,
        pub color_type: ColorType,
        pub interlaced: bool,
        pub trns: Option<Vec<u8>>,
        pub pixel_dims: Option<PixelDimensions>,
        pub palette: Option<Vec<u8>>,
        pub frame_control: Option<FrameControl>,
        pub animation_control: Option<AnimationControl>,
        pub compression: Compression,
        pub filter: filter::FilterType,
    }

    impl Default for Info {
        fn default() -> Info {
            Info {
                width: 0,
                height: 0,
                bit_depth: BitDepth::Eight,
                color_type: ColorType::Grayscale,
                interlaced: false,
                palette: None,
                trns: None,
                pixel_dims: None,
                frame_control: None,
                animation_control: None,
                // Default to `deflate::Compresion::Fast` and `filter::FilterType::Sub`
                // to maintain backward compatible output.
                compression: Compression::Fast,
                filter: filter::FilterType::Sub,
            }
        }
    }

    impl Info {
        /// Size of the image
        pub fn size(&self) -> (u32, u32) {
            (self.width, self.height)
        }

        /// Returns true if the image is an APNG image.
        pub fn is_animated(&self) -> bool {
            self.frame_control.is_some() && self.animation_control.is_some()
        }

        /// Returns the frame control information of the image
        pub fn animation_control(&self) -> Option<&AnimationControl> {
            self.animation_control.as_ref()
        }

        /// Returns the frame control information of the current frame
        pub fn frame_control(&self) -> Option<&FrameControl> {
            self.frame_control.as_ref()
        }

        /// Returns the bits per pixel
        pub fn bits_per_pixel(&self) -> usize {
            self.color_type.samples() * self.bit_depth as usize
        }

        /// Returns the bytes per pixel
        pub fn bytes_per_pixel(&self) -> usize {
            self.color_type.samples() * ((self.bit_depth as usize + 7) >> 3)
        }

        /// Returns the number of bytes needed for one deinterlaced image
        pub fn raw_bytes(&self) -> usize {
            self.height as usize * self.raw_row_length()
        }

        /// Returns the number of bytes needed for one deinterlaced row
        pub fn raw_row_length(&self) -> usize {
            let bits = self.width as usize * self.color_type.samples() * self.bit_depth as usize;
            let extra = bits % 8;
            bits/8
            + match extra { 0 => 0, _ => 1 }
            + 1 // filter method
        }

        /// Returns the number of bytes needed for one deinterlaced row of width `width`
        pub fn raw_row_length_from_width(&self, width: u32) -> usize {
            let bits = width as usize * self.color_type.samples() * self.bit_depth as usize;
            let extra = bits % 8;
            bits/8
            + match extra { 0 => 0, _ => 1 }
            + 1 // filter method
        }
    }

    bitflags! {
        /// # Output transformations
        ///
        /// Only `IDENTITY` and `TRANSFORM_EXPAND | TRANSFORM_STRIP_ALPHA` can be used at the moment.
        pub struct Transformations: u32 {
            /// No transformation
            const IDENTITY            = 0x0000; // read and write */
            /// Strip 16-bit samples to 8 bits
            const STRIP_16            = 0x0001; // read only */
            /// Discard the alpha channel
            const STRIP_ALPHA         = 0x0002; // read only */
            /// Expand 1; 2 and 4-bit samples to bytes
            const PACKING             = 0x0004; // read and write */
            /// Change order of packed pixels to LSB first
            const PACKSWAP            = 0x0008; // read and write */
            /// Expand paletted images to RGB; expand grayscale images of
            /// less than 8-bit depth to 8-bit depth; and expand tRNS chunks
            /// to alpha channels.
            const EXPAND              = 0x0010; // read only */
            /// Invert monochrome images
            const INVERT_MONO         = 0x0020; // read and write */
            /// Normalize pixels to the sBIT depth
            const SHIFT               = 0x0040; // read and write */
            /// Flip RGB to BGR; RGBA to BGRA
            const BGR                 = 0x0080; // read and write */
            /// Flip RGBA to ARGB or GA to AG
            const SWAP_ALPHA          = 0x0100; // read and write */
            /// Byte-swap 16-bit samples
            const SWAP_ENDIAN         = 0x0200; // read and write */
            /// Change alpha from opacity to transparency
            const INVERT_ALPHA        = 0x0400; // read and write */
            const STRIP_FILLER        = 0x0800; // write only */
            const STRIP_FILLER_BEFORE = 0x0800; // write only
            const STRIP_FILLER_AFTER  = 0x1000; // write only */
            const GRAY_TO_RGB         = 0x2000; // read only */
            const EXPAND_16           = 0x4000; // read only */
            const SCALE_16            = 0x8000; // read only */
        }
    }

    /// Mod to encapsulate the converters depending on the `deflate` crate.
    ///
    /// Since this only contains trait impls, there is no need to make this public, they are simply
    /// available when the mod is compiled as well.
    #[cfg(feature = "png-encoding")]
    mod deflate_convert {
        extern crate deflate;
        use super::Compression;

        impl From<deflate::Compression> for Compression {
            fn from(c: deflate::Compression) -> Self {
                match c {
                    deflate::Compression::Default => Compression::Default,
                    deflate::Compression::Fast => Compression::Fast,
                    deflate::Compression::Best => Compression::Best,
                }
            }
        }

        impl From<Compression> for deflate::CompressionOptions {
            fn from(c: Compression) -> Self {
                match c {
                    Compression::Default => deflate::CompressionOptions::default(),
                    Compression::Fast => deflate::CompressionOptions::fast(),
                    Compression::Best => deflate::CompressionOptions::high(),
                    Compression::Huffman => deflate::CompressionOptions::huffman_only(),
                    Compression::Rle => deflate::CompressionOptions::rle(),
                }
            }
        }
    }

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