use std::error::Error;
use std::fmt;
use std::io;
use std::mem;
use std::ops::{Deref, DerefMut};

use buffer::{ImageBuffer, Pixel};
use color;
use color::ColorType;

use animation::{Frame, Frames};
use dynimage::decoder_to_image;

#[cfg(feature = "pnm")]
use pnm::PNMSubtype;

/// An enumeration of Image errors
#[derive(Debug)]
pub enum ImageError {
    /// The Image is not formatted properly
    FormatError(String),

    /// The Image's dimensions are either too small or too large
    DimensionError,

    /// The Decoder does not support this image format
    UnsupportedError(String),

    /// The Decoder does not support this color type
    UnsupportedColor(ColorType),

    /// Not enough data was provided to the Decoder
    /// to decode the image
    NotEnoughData,

    /// An I/O Error occurred while decoding the image
    IoError(io::Error),

    /// The end of the image has been reached
    ImageEnd,
}

impl fmt::Display for ImageError {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match *self {
            ImageError::FormatError(ref e) => write!(fmt, "Format error: {}", e),
            ImageError::DimensionError => write!(
                fmt,
                "The Image's dimensions are either too \
                 small or too large"
            ),
            ImageError::UnsupportedError(ref f) => write!(
                fmt,
                "The Decoder does not support the \
                 image format `{}`",
                f
            ),
            ImageError::UnsupportedColor(ref c) => write!(
                fmt,
                "The decoder does not support \
                 the color type `{:?}`",
                c
            ),
            ImageError::NotEnoughData => write!(
                fmt,
                "Not enough data was provided to the \
                 Decoder to decode the image"
            ),
            ImageError::IoError(ref e) => e.fmt(fmt),
            ImageError::ImageEnd => write!(fmt, "The end of the image has been reached"),
        }
    }
}

impl Error for ImageError {
    fn description(&self) -> &str {
        match *self {
            ImageError::FormatError(..) => "Format error",
            ImageError::DimensionError => "Dimension error",
            ImageError::UnsupportedError(..) => "Unsupported error",
            ImageError::UnsupportedColor(..) => "Unsupported color",
            ImageError::NotEnoughData => "Not enough data",
            ImageError::IoError(..) => "IO error",
            ImageError::ImageEnd => "Image end",
        }
    }

    fn cause(&self) -> Option<&Error> {
        match *self {
            ImageError::IoError(ref e) => Some(e),
            _ => None,
        }
    }
}

impl From<io::Error> for ImageError {
    fn from(err: io::Error) -> ImageError {
        ImageError::IoError(err)
    }
}

/// Result of an image decoding/encoding process
pub type ImageResult<T> = Result<T, ImageError>;

/// Result of a decoding process
#[derive(Debug)]
pub enum DecodingResult {
    /// A vector of unsigned bytes
    U8(Vec<u8>),
    /// A vector of unsigned words
    U16(Vec<u16>),
}

/// An enumeration of supported image formats.
/// Not all formats support both encoding and decoding.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum ImageFormat {
    /// An Image in PNG Format
    PNG,

    /// An Image in JPEG Format
    JPEG,

    /// An Image in GIF Format
    GIF,

    /// An Image in WEBP Format
    WEBP,

    /// An Image in general PNM Format
    PNM,

    /// An Image in TIFF Format
    TIFF,

    /// An Image in TGA Format
    TGA,

    /// An Image in BMP Format
    BMP,

    /// An Image in ICO Format
    ICO,

    /// An Image in Radiance HDR Format
    HDR,
}

/// An enumeration of supported image formats for encoding.
#[derive(Clone, PartialEq, Eq, Debug)]
pub enum ImageOutputFormat {
    #[cfg(feature = "png_codec")]
    /// An Image in PNG Format
    PNG,

    #[cfg(feature = "jpeg")]
    /// An Image in JPEG Format with specified quality
    JPEG(u8),

    #[cfg(feature = "pnm")]
    /// An Image in one of the PNM Formats
    PNM(PNMSubtype),

    #[cfg(feature = "gif_codec")]
    /// An Image in GIF Format
    GIF,

    #[cfg(feature = "ico")]
    /// An Image in ICO Format
    ICO,

    #[cfg(feature = "bmp")]
    /// An Image in BMP Format
    BMP,

    /// A value for signalling an error: An unsupported format was requested
    // Note: When TryFrom is stabilized, this value should not be needed, and
    // a TryInto<ImageOutputFormat> should be used instead of an Into<ImageOutputFormat>.
    Unsupported(String),
}

impl From<ImageFormat> for ImageOutputFormat {
    fn from(fmt: ImageFormat) -> Self {
        match fmt {
            #[cfg(feature = "png_codec")]
            ImageFormat::PNG => ImageOutputFormat::PNG,
            #[cfg(feature = "jpeg")]
            ImageFormat::JPEG => ImageOutputFormat::JPEG(75),
            #[cfg(feature = "pnm")]
            ImageFormat::PNM => ImageOutputFormat::PNM(PNMSubtype::ArbitraryMap),
            #[cfg(feature = "gif_codec")]
            ImageFormat::GIF => ImageOutputFormat::GIF,
            #[cfg(feature = "ico")]
            ImageFormat::ICO => ImageOutputFormat::ICO,
            #[cfg(feature = "bmp")]
            ImageFormat::BMP => ImageOutputFormat::BMP,

            f => ImageOutputFormat::Unsupported(format!(
                "Image format {:?} not supported for encoding.",
                f
            )),
        }
    }
}

/// The trait that all decoders implement
pub trait ImageDecoder: Sized {
    /// Returns a tuple containing the width and height of the image
    fn dimensions(&mut self) -> ImageResult<(u32, u32)>;

    /// Returns the color type of the image e.g. RGB(8) (8bit RGB)
    fn colortype(&mut self) -> ImageResult<ColorType>;

    /// Returns the length in bytes of one decoded row of the image
    fn row_len(&mut self) -> ImageResult<usize>;

    /// Reads one row from the image into ```buf``` and returns the row index
    fn read_scanline(&mut self, buf: &mut [u8]) -> ImageResult<u32>;

    /// Decodes the entire image and return it as a Vector
    fn read_image(&mut self) -> ImageResult<DecodingResult>;

    /// Returns true if the image is animated
    fn is_animated(&mut self) -> ImageResult<bool> {
        // since most image formats do not support animation
        // just return false by default
        Ok(false)
    }

    /// Returns the frames of the image
    ///
    /// If the image is not animated it returns a single frame
    #[allow(unused)]
    fn into_frames(mut self) -> ImageResult<Frames> {
        Ok(Frames::new(vec![Frame::new(
            try!(decoder_to_image(self)).to_rgba(),
        )]))
    }

    /// Decodes a specific region of the image, represented by the rectangle
    /// starting from ```x``` and ```y``` and having ```length``` and ```width```
    fn load_rect(&mut self, x: u32, y: u32, length: u32, width: u32) -> ImageResult<Vec<u8>> {
        let (w, h) = try!(self.dimensions());

        if length > h || width > w || x > w || y > h {
            return Err(ImageError::DimensionError);
        }

        let c = try!(self.colortype());

        let bpp = color::bits_per_pixel(c) / 8;

        let rowlen = try!(self.row_len());

        let mut buf = vec![0u8; length as usize * width as usize * bpp];
        let mut tmp = vec![0u8; rowlen];

        loop {
            let row = try!(self.read_scanline(&mut tmp));

            if row - 1 == y {
                break;
            }
        }

        for i in 0..length as usize {
            {
                let from = &tmp[x as usize * bpp..width as usize * bpp];

                let to = &mut buf[i * width as usize * bpp..width as usize * bpp];

                ::copy_memory(from, to);
            }

            let _ = try!(self.read_scanline(&mut tmp));
        }

        Ok(buf)
    }
}

/// Immutable pixel iterator
pub struct Pixels<'a, I: ?Sized + 'a> {
    image: &'a I,
    x: u32,
    y: u32,
    width: u32,
    height: u32,
}

impl<'a, I: GenericImageView> Iterator for Pixels<'a, I> {
    type Item = (u32, u32, I::Pixel);

    fn next(&mut self) -> Option<(u32, u32, I::Pixel)> {
        if self.x >= self.width {
            self.x = 0;
            self.y += 1;
        }

        if self.y >= self.height {
            None
        } else {
            let pixel = self.image.get_pixel(self.x, self.y);
            let p = (self.x, self.y, pixel);

            self.x += 1;

            Some(p)
        }
    }
}

/// Mutable pixel iterator
///
/// DEPRECATED: It is currently not possible to create a safe iterator for this in Rust. You have to use an iterator over the image buffer instead.
pub struct MutPixels<'a, I: ?Sized + 'a> {
    image: &'a mut I,
    x: u32,
    y: u32,
    width: u32,
    height: u32,
}

impl<'a, I: GenericImage + 'a> Iterator for MutPixels<'a, I>
where
    I::Pixel: 'a,
    <I::Pixel as Pixel>::Subpixel: 'a,
{
    type Item = (u32, u32, &'a mut I::Pixel);

    fn next(&mut self) -> Option<(u32, u32, &'a mut I::Pixel)> {
        if self.x >= self.width {
            self.x = 0;
            self.y += 1;
        }

        if self.y >= self.height {
            None
        } else {
            let tmp = self.image.get_pixel_mut(self.x, self.y);

            // NOTE: This is potentially dangerous. It would require the signature fn next(&'a mut self) to be safe.
            // error: lifetime of `self` is too short to guarantee its contents can be safely reborrowed...
            let ptr = unsafe { mem::transmute(tmp) };

            let p = (self.x, self.y, ptr);

            self.x += 1;

            Some(p)
        }
    }
}

/// Trait to inspect an image.
pub trait GenericImageView {
    /// The type of pixel.
    type Pixel: Pixel;

    /// Underlying image type. This is mainly used by SubImages in order to
    /// always have a reference to the original image. This allows for less
    /// indirections and it eases the use of nested SubImages.
    type InnerImageView: GenericImageView<Pixel = Self::Pixel>;

    /// The width and height of this image.
    fn dimensions(&self) -> (u32, u32);

    /// The width of this image.
    fn width(&self) -> u32 {
        let (w, _) = self.dimensions();
        w
    }

    /// The height of this image.
    fn height(&self) -> u32 {
        let (_, h) = self.dimensions();
        h
    }

    /// The bounding rectangle of this image.
    fn bounds(&self) -> (u32, u32, u32, u32);

    /// Returns true if this x, y coordinate is contained inside the image.
    fn in_bounds(&self, x: u32, y: u32) -> bool {
        let (ix, iy, iw, ih) = self.bounds();
        x >= ix && x < ix + iw && y >= iy && y < iy + ih
    }

    /// Returns the pixel located at (x, y)
    ///
    /// # Panics
    ///
    /// Panics if `(x, y)` is out of bounds.
    ///
    /// TODO: change this signature to &P
    fn get_pixel(&self, x: u32, y: u32) -> Self::Pixel;

    /// Returns the pixel located at (x, y)
    ///
    /// This function can be implemented in a way that ignores bounds checking.
    unsafe fn unsafe_get_pixel(&self, x: u32, y: u32) -> Self::Pixel {
        self.get_pixel(x, y)
    }

    /// Returns an Iterator over the pixels of this image.
    /// The iterator yields the coordinates of each pixel
    /// along with their value
    fn pixels(&self) -> Pixels<Self> {
        let (width, height) = self.dimensions();

        Pixels {
            image: self,
            x: 0,
            y: 0,
            width,
            height,
        }
    }

    /// Returns a reference to the underlying image.
    fn inner(&self) -> &Self::InnerImageView;

    /// Returns an subimage that is an immutable view into this image.
    fn view(&self, x: u32, y: u32, width: u32, height: u32) -> SubImage<&Self::InnerImageView> {
        SubImage::new(self.inner(), x, y, width, height)
    }
}

/// A trait for manipulating images.
pub trait GenericImage: GenericImageView {
    /// Underlying image type. This is mainly used by SubImages in order to
    /// always have a reference to the original image. This allows for less
    /// indirections and it eases the use of nested SubImages.
    type InnerImage: GenericImage<Pixel = Self::Pixel>;

    /// Gets a reference to the mutable pixel at location `(x, y)`
    ///
    /// # Panics
    ///
    /// Panics if `(x, y)` is out of bounds.
    fn get_pixel_mut(&mut self, x: u32, y: u32) -> &mut Self::Pixel;

    /// Put a pixel at location (x, y)
    ///
    /// # Panics
    ///
    /// Panics if `(x, y)` is out of bounds.
    fn put_pixel(&mut self, x: u32, y: u32, pixel: Self::Pixel);

    /// Puts a pixel at location (x, y)
    ///
    /// This function can be implemented in a way that ignores bounds checking.
    unsafe fn unsafe_put_pixel(&mut self, x: u32, y: u32, pixel: Self::Pixel) {
        self.put_pixel(x, y, pixel);
    }

    /// Put a pixel at location (x, y), taking into account alpha channels
    ///
    /// DEPRECATED: This method will be removed. Blend the pixel directly instead.
    fn blend_pixel(&mut self, x: u32, y: u32, pixel: Self::Pixel);

    /// Returns an Iterator over mutable pixels of this image.
    /// The iterator yields the coordinates of each pixel
    /// along with a mutable reference to them.
    #[deprecated(
        note = "This cannot be implemented safely in Rust. Please use the image buffer directly."
    )]
    fn pixels_mut(&mut self) -> MutPixels<Self> {
        let (width, height) = self.dimensions();

        MutPixels {
            image: self,
            x: 0,
            y: 0,
            width,
            height,
        }
    }

    /// Copies all of the pixels from another image into this image.
    ///
    /// The other image is copied with the top-left corner of the
    /// other image placed at (x, y).
    ///
    /// In order to copy only a piece of the other image, use `sub_image`.
    ///
    /// # Returns
    /// `true` if the copy was successful, `false` if the image could not
    /// be copied due to size constraints.
    fn copy_from<O>(&mut self, other: &O, x: u32, y: u32) -> bool
    where
        O: GenericImageView<Pixel = Self::Pixel>,
    {
        // Do bounds checking here so we can use the non-bounds-checking
        // functions to copy pixels.
        if self.width() < other.width() + x || self.height() < other.height() + y {
            return false;
        }

        for i in 0..other.width() {
            for k in 0..other.height() {
                unsafe {
                    let p = other.unsafe_get_pixel(i, k);
                    self.unsafe_put_pixel(i + x, k + y, p);
                }
            }
        }
        true
    }

    /// Returns a mutable reference to the underlying image.
    fn inner_mut(&mut self) -> &mut Self::InnerImage;

    /// Returns a subimage that is a view into this image.
    fn sub_image(
        &mut self,
        x: u32,
        y: u32,
        width: u32,
        height: u32,
    ) -> SubImage<&mut Self::InnerImage> {
        SubImage::new(self.inner_mut(), x, y, width, height)
    }
}

/// A View into another image
pub struct SubImage<I> {
    image: I,
    xoffset: u32,
    yoffset: u32,
    xstride: u32,
    ystride: u32,
}

/// Alias to access Pixel behind a reference
type DerefPixel<I> = <<I as Deref>::Target as GenericImageView>::Pixel;

/// Alias to access Subpixel behind a reference
type DerefSubpixel<I> = <DerefPixel<I> as Pixel>::Subpixel;

impl<I> SubImage<I> {
    /// Construct a new subimage
    pub fn new(image: I, x: u32, y: u32, width: u32, height: u32) -> SubImage<I> {
        SubImage {
            image,
            xoffset: x,
            yoffset: y,
            xstride: width,
            ystride: height,
        }
    }

    /// Change the coordinates of this subimage.
    pub fn change_bounds(&mut self, x: u32, y: u32, width: u32, height: u32) {
        self.xoffset = x;
        self.yoffset = y;
        self.xstride = width;
        self.ystride = height;
    }

    /// Convert this subimage to an ImageBuffer
    pub fn to_image(
        &self,
    ) -> ImageBuffer<DerefPixel<I>, Vec<DerefSubpixel<I>>,
    >
    where
        I: Deref,
        I::Target: GenericImage + 'static,
    {
        let mut out = ImageBuffer::new(self.xstride, self.ystride);
        let borrowed = self.image.deref();

        for y in 0..self.ystride {
            for x in 0..self.xstride {
                let p = borrowed.get_pixel(x + self.xoffset, y + self.yoffset);
                out.put_pixel(x, y, p);
            }
        }

        out
    }
}

#[allow(deprecated)]
impl<I> GenericImageView for SubImage<I>
where
    I: Deref,
    I::Target: GenericImageView + Sized,
{
    type Pixel = DerefPixel<I>;
    type InnerImageView = I::Target;

    fn dimensions(&self) -> (u32, u32) {
        (self.xstride, self.ystride)
    }

    fn bounds(&self) -> (u32, u32, u32, u32) {
        (self.xoffset, self.yoffset, self.xstride, self.ystride)
    }

    fn get_pixel(&self, x: u32, y: u32) -> Self::Pixel {
        self.image.get_pixel(x + self.xoffset, y + self.yoffset)
    }

    fn view(&self, x: u32, y: u32, width: u32, height: u32) -> SubImage<&Self::InnerImageView> {
        let x = self.xoffset + x;
        let y = self.yoffset + y;
        SubImage::new(self.inner(), x, y, width, height)
    }

    fn inner(&self) -> &Self::InnerImageView {
        &self.image
    }
}

#[allow(deprecated)]
impl<I> GenericImage for SubImage<I>
where
    I: DerefMut,
    I::Target: GenericImage + Sized,
{
    type InnerImage = I::Target;

    fn get_pixel_mut(&mut self, x: u32, y: u32) -> &mut Self::Pixel {
        self.image.get_pixel_mut(x + self.xoffset, y + self.yoffset)
    }

    fn put_pixel(&mut self, x: u32, y: u32, pixel: Self::Pixel) {
        self.image
            .put_pixel(x + self.xoffset, y + self.yoffset, pixel)
    }

    /// DEPRECATED: This method will be removed. Blend the pixel directly instead.
    fn blend_pixel(&mut self, x: u32, y: u32, pixel: Self::Pixel) {
        self.image
            .blend_pixel(x + self.xoffset, y + self.yoffset, pixel)
    }

    fn sub_image(
        &mut self,
        x: u32,
        y: u32,
        width: u32,
        height: u32,
    ) -> SubImage<&mut Self::InnerImage> {
        let x = self.xoffset + x;
        let y = self.yoffset + y;
        SubImage::new(self.inner_mut(), x, y, width, height)
    }

    fn inner_mut(&mut self) -> &mut Self::InnerImage {
        &mut self.image
    }
}

#[cfg(test)]
mod tests {

    use super::{GenericImage, GenericImageView};
    use buffer::ImageBuffer;
    use color::Rgba;

    #[test]
    /// Test that alpha blending works as expected
    fn test_image_alpha_blending() {
        let mut target = ImageBuffer::new(1, 1);
        target.put_pixel(0, 0, Rgba([255u8, 0, 0, 255]));
        assert!(*target.get_pixel(0, 0) == Rgba([255, 0, 0, 255]));
        target.blend_pixel(0, 0, Rgba([0, 255, 0, 255]));
        assert!(*target.get_pixel(0, 0) == Rgba([0, 255, 0, 255]));

        // Blending an alpha channel onto a solid background
        target.blend_pixel(0, 0, Rgba([255, 0, 0, 127]));
        assert!(*target.get_pixel(0, 0) == Rgba([127, 127, 0, 255]));

        // Blending two alpha channels
        target.put_pixel(0, 0, Rgba([0, 255, 0, 127]));
        target.blend_pixel(0, 0, Rgba([255, 0, 0, 127]));
        assert!(*target.get_pixel(0, 0) == Rgba([169, 85, 0, 190]));
    }

    #[test]
    fn test_in_bounds() {
        let mut target = ImageBuffer::new(2, 2);
        target.put_pixel(0, 0, Rgba([255u8, 0, 0, 255]));

        assert!(target.in_bounds(0, 0));
        assert!(target.in_bounds(1, 0));
        assert!(target.in_bounds(0, 1));
        assert!(target.in_bounds(1, 1));

        assert!(!target.in_bounds(2, 0));
        assert!(!target.in_bounds(0, 2));
        assert!(!target.in_bounds(2, 2));
    }

    #[test]
    fn test_can_subimage_clone_nonmut() {
        let mut source = ImageBuffer::new(3, 3);
        source.put_pixel(1, 1, Rgba([255u8, 0, 0, 255]));

        // A non-mutable copy of the source image
        let source = source.clone();

        // Clone a view into non-mutable to a separate buffer
        let cloned = source.view(1, 1, 1, 1).to_image();

        assert!(cloned.get_pixel(0, 0) == source.get_pixel(1, 1));
    }

    #[test]
    fn test_can_nest_views() {
        let mut source = ImageBuffer::from_pixel(3, 3, Rgba([255u8, 0, 0, 255]));

        {
            let mut sub1 = source.sub_image(0, 0, 2, 2);
            let mut sub2 = sub1.sub_image(1, 1, 1, 1);
            sub2.put_pixel(0, 0, Rgba([0, 0, 0, 0]));
        }

        assert_eq!(*source.get_pixel(1, 1), Rgba([0, 0, 0, 0]));

        let view1 = source.view(0, 0, 2, 2);
        assert_eq!(*source.get_pixel(1, 1), view1.get_pixel(1, 1));

        let view2 = view1.view(1, 1, 1, 1);
        assert_eq!(*source.get_pixel(1, 1), view2.get_pixel(0, 0));
    }
}