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    //! Encoding of PNM Images
    use std::fmt;
    use std::io;

    use std::io::Write;

    use super::AutoBreak;
    use super::{ArbitraryHeader, ArbitraryTuplType, BitmapHeader, GraymapHeader, PixmapHeader};
    use super::{HeaderRecord, PNMHeader, PNMSubtype, SampleEncoding};
    use color::{num_components, ColorType};

    use byteorder::{BigEndian, WriteBytesExt};

    enum HeaderStrategy {
        Dynamic,
        Subtype(PNMSubtype),
        Chosen(PNMHeader),
    }

    #[derive(Clone, Copy)]
    pub enum FlatSamples<'a> {
        U8(&'a [u8]),
        U16(&'a [u16]),
    }

    /// Encodes images to any of the `pnm` image formats.
    pub struct PNMEncoder<W: Write> {
        writer: W,
        header: HeaderStrategy,
    }

    /// Encapsulate the checking system in the type system. Non of the fields are actually accessed
    /// but requiring them forces us to validly construct the struct anyways.
    struct CheckedImageBuffer<'a> {
        _image: FlatSamples<'a>,
        _width: u32,
        _height: u32,
        _color: ColorType,
    }

    // Check the header against the buffer. Each struct produces the next after a check.
    struct UncheckedHeader<'a> {
        header: &'a PNMHeader,
    }

    struct CheckedDimensions<'a> {
        unchecked: UncheckedHeader<'a>,
        width: u32,
        height: u32,
    }

    struct CheckedHeaderColor<'a> {
        dimensions: CheckedDimensions<'a>,
        color: ColorType,
    }

    struct CheckedHeader<'a> {
        color: CheckedHeaderColor<'a>,
        encoding: TupleEncoding<'a>,
        _image: CheckedImageBuffer<'a>,
    }

    enum TupleEncoding<'a> {
        PbmBits {
            samples: FlatSamples<'a>,
            width: u32,
        },
        Ascii {
            samples: FlatSamples<'a>,
        },
        Bytes {
            samples: FlatSamples<'a>,
        },
    }

    impl<W: Write> PNMEncoder<W> {
        /// Create new PNMEncoder from the `writer`.
        ///
        /// The encoded images will have some `pnm` format. If more control over the image type is
        /// required, use either one of `with_subtype` or `with_header`. For more information on the
        /// behaviour, see `with_dynamic_header`.
        pub fn new(writer: W) -> Self {
            PNMEncoder {
                writer,
                header: HeaderStrategy::Dynamic,
            }
        }

        /// Encode a specific pnm subtype image.
        ///
        /// The magic number and encoding type will be chosen as provided while the rest of the header
        /// data will be generated dynamically. Trying to encode incompatible images (e.g. encoding an
        /// RGB image as Graymap) will result in an error.
        ///
        /// This will overwrite the effect of earlier calls to `with_header` and `with_dynamic_header`.
        pub fn with_subtype(self, subtype: PNMSubtype) -> Self {
            PNMEncoder {
                writer: self.writer,
                header: HeaderStrategy::Subtype(subtype),
            }
        }

        /// Enforce the use of a chosen header.
        ///
        /// While this option gives the most control over the actual written data, the encoding process
        /// will error in case the header data and image parameters do not agree. It is the users
        /// obligation to ensure that the width and height are set accordingly, for example.
        ///
        /// Choose this option if you want a lossless decoding/encoding round trip.
        ///
        /// This will overwrite the effect of earlier calls to `with_subtype` and `with_dynamic_header`.
        pub fn with_header(self, header: PNMHeader) -> Self {
            PNMEncoder {
                writer: self.writer,
                header: HeaderStrategy::Chosen(header),
            }
        }

        /// Create the header dynamically for each image.
        ///
        /// This is the default option upon creation of the encoder. With this, most images should be
        /// encodable but the specific format chosen is out of the users control. The pnm subtype is
        /// chosen arbitrarily by the library.
        ///
        /// This will overwrite the effect of earlier calls to `with_subtype` and `with_header`.
        pub fn with_dynamic_header(self) -> Self {
            PNMEncoder {
                writer: self.writer,
                header: HeaderStrategy::Dynamic,
            }
        }

        /// Encode an image whose samples are represented as `u8`.
        ///
        /// Some `pnm` subtypes are incompatible with some color options, a chosen header most
        /// certainly with any deviation from the original decoded image.
        pub fn encode<'s, S>(
            &mut self,
            image: S,
            width: u32,
            height: u32,
            color: ColorType,
        ) -> io::Result<()>
        where
            S: Into<FlatSamples<'s>>,
        {
            let image = image.into();
            match self.header {
                HeaderStrategy::Dynamic => self.write_dynamic_header(image, width, height, color),
                HeaderStrategy::Subtype(subtype) => {
                    self.write_subtyped_header(subtype, image, width, height, color)
                }
                HeaderStrategy::Chosen(ref header) => {
                    Self::write_with_header(&mut self.writer, header, image, width, height, color)
                }
            }
        }

        /// Choose any valid pnm format that the image can be expressed in and write its header.
        ///
        /// Returns how the body should be written if successful.
        fn write_dynamic_header(
            &mut self,
            image: FlatSamples,
            width: u32,
            height: u32,
            color: ColorType,
        ) -> io::Result<()> {
            let depth = num_components(color) as u32;
            let (maxval, tupltype) = match color {
                ColorType::Gray(1) => (1, ArbitraryTuplType::BlackAndWhite),
                ColorType::GrayA(1) => (1, ArbitraryTuplType::BlackAndWhiteAlpha),
                ColorType::Gray(n @ 1...16) => ((1 << n) - 1, ArbitraryTuplType::Grayscale),
                ColorType::GrayA(n @ 1...16) => ((1 << n) - 1, ArbitraryTuplType::GrayscaleAlpha),
                ColorType::RGB(n @ 1...16) => ((1 << n) - 1, ArbitraryTuplType::RGB),
                ColorType::RGBA(n @ 1...16) => ((1 << n) - 1, ArbitraryTuplType::RGBAlpha),
                _ => {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        &format!("Encoding colour type {:?} is not supported", color)[..],
                    ))
                }
            };

            let header = PNMHeader {
                decoded: HeaderRecord::Arbitrary(ArbitraryHeader {
                    width,
                    height,
                    depth,
                    maxval,
                    tupltype: Some(tupltype),
                }),
                encoded: None,
            };

            Self::write_with_header(&mut self.writer, &header, image, width, height, color)
        }

        /// Try to encode the image with the chosen format, give its corresponding pixel encoding type.
        fn write_subtyped_header(
            &mut self,
            subtype: PNMSubtype,
            image: FlatSamples,
            width: u32,
            height: u32,
            color: ColorType,
        ) -> io::Result<()> {
            let header = match (subtype, color) {
                (PNMSubtype::ArbitraryMap, color) => {
                    return self.write_dynamic_header(image, width, height, color)
                }
                (PNMSubtype::Pixmap(encoding), ColorType::RGB(8)) => PNMHeader {
                    decoded: HeaderRecord::Pixmap(PixmapHeader {
                        encoding,
                        width,
                        height,
                        maxval: 255,
                    }),
                    encoded: None,
                },
                (PNMSubtype::Graymap(encoding), ColorType::Gray(8)) => PNMHeader {
                    decoded: HeaderRecord::Graymap(GraymapHeader {
                        encoding,
                        width,
                        height,
                        maxwhite: 255,
                    }),
                    encoded: None,
                },
                (PNMSubtype::Bitmap(encoding), ColorType::Gray(8))
                | (PNMSubtype::Bitmap(encoding), ColorType::Gray(1)) => PNMHeader {
                    decoded: HeaderRecord::Bitmap(BitmapHeader {
                        encoding,
                        width,
                        height,
                    }),
                    encoded: None,
                },
                (_, _) => {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "Color type can not be represented in the chosen format",
                    ))
                }
            };

            Self::write_with_header(&mut self.writer, &header, image, width, height, color)
        }

        /// Try to encode the image with the chosen header, checking if values are correct.
        ///
        /// Returns how the body should be written if successful.
        fn write_with_header(
            writer: &mut Write,
            header: &PNMHeader,
            image: FlatSamples,
            width: u32,
            height: u32,
            color: ColorType,
        ) -> io::Result<()> {
            let unchecked = UncheckedHeader { header };

            unchecked
                .check_header_dimensions(width, height)?
                .check_header_color(color)?
                .check_sample_values(image)?
                .write_header(writer)?
                .write_image(writer)
        }
    }

    impl<'a> CheckedImageBuffer<'a> {
        fn check(
            image: FlatSamples<'a>,
            width: u32,
            height: u32,
            color: ColorType,
        ) -> io::Result<CheckedImageBuffer<'a>> {
            let components = num_components(color);
            let uwidth = width as usize;
            let uheight = height as usize;
            match Some(components)
                .and_then(|v| v.checked_mul(uwidth))
                .and_then(|v| v.checked_mul(uheight))
            {
                None => Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    &format!(
                        "Image dimensions invalid: {}×{}×{} (w×h×d)",
                        width, height, components
                    )[..],
                )),
                Some(v) if v == image.len() => Ok(CheckedImageBuffer {
                    _image: image,
                    _width: width,
                    _height: height,
                    _color: color,
                }),
                Some(_) => Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    &"Image buffer does not correspond to size and colour".to_string()[..],
                )),
            }
        }
    }

    impl<'a> UncheckedHeader<'a> {
        fn check_header_dimensions(self, width: u32, height: u32) -> io::Result<CheckedDimensions<'a>> {
            if self.header.width() != width || self.header.height() != height {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    "Chosen header does not match Image dimensions",
                ));
            }

            Ok(CheckedDimensions {
                unchecked: self,
                width,
                height,
            })
        }
    }

    impl<'a> CheckedDimensions<'a> {
        // Check color compatibility with the header. This will only error when we are certain that
        // the comination is bogus (e.g. combining Pixmap and Palette) but allows uncertain
        // combinations (basically a ArbitraryTuplType::Custom with any color of fitting depth).
        fn check_header_color(self, color: ColorType) -> io::Result<CheckedHeaderColor<'a>> {
            let components = match color {
                ColorType::Gray(_) => 1,
                ColorType::GrayA(_) => 2,
                ColorType::Palette(_) | ColorType::RGB(_) | ColorType::BGR(_)=> 3,
                ColorType::RGBA(_) | ColorType::BGRA(_) => 4,
            };

            match *self.unchecked.header {
                PNMHeader {
                    decoded: HeaderRecord::Bitmap(_),
                    ..
                } => match color {
                    ColorType::Gray(_) => (),
                    _ => {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidInput,
                            "PBM format only support ColorType::Gray",
                        ))
                    }
                },
                PNMHeader {
                    decoded: HeaderRecord::Graymap(_),
                    ..
                } => match color {
                    ColorType::Gray(_) => (),
                    _ => {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidInput,
                            "PGM format only support ColorType::Gray",
                        ))
                    }
                },
                PNMHeader {
                    decoded: HeaderRecord::Pixmap(_),
                    ..
                } => match color {
                    ColorType::RGB(_) => (),
                    _ => {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidInput,
                            "PPM format only support ColorType::RGB",
                        ))
                    }
                },
                PNMHeader {
                    decoded:
                        HeaderRecord::Arbitrary(ArbitraryHeader {
                            depth,
                            ref tupltype,
                            ..
                        }),
                    ..
                } => match (tupltype, color) {
                    (&Some(ArbitraryTuplType::BlackAndWhite), ColorType::Gray(_)) => (),
                    (&Some(ArbitraryTuplType::BlackAndWhiteAlpha), ColorType::GrayA(_)) => (),

                    (&Some(ArbitraryTuplType::Grayscale), ColorType::Gray(_)) => (),
                    (&Some(ArbitraryTuplType::GrayscaleAlpha), ColorType::GrayA(_)) => (),

                    (&Some(ArbitraryTuplType::RGB), ColorType::RGB(_)) => (),
                    (&Some(ArbitraryTuplType::RGBAlpha), ColorType::RGBA(_)) => (),

                    (&None, _) if depth == components => (),
                    (&Some(ArbitraryTuplType::Custom(_)), _) if depth == components => (),
                    _ if depth != components => {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidInput,
                            format!("Depth mismatch: header {} vs. color {}", depth, components),
                        ))
                    }
                    _ => {
                        return Err(io::Error::new(
                            io::ErrorKind::InvalidInput,
                            "Invalid color type for selected PAM color type",
                        ))
                    }
                },
            }

            Ok(CheckedHeaderColor {
                dimensions: self,
                color,
            })
        }
    }

    impl<'a> CheckedHeaderColor<'a> {
        fn check_sample_values(self, image: FlatSamples<'a>) -> io::Result<CheckedHeader<'a>> {
            let header_maxval = match self.dimensions.unchecked.header.decoded {
                HeaderRecord::Bitmap(_) => 1,
                HeaderRecord::Graymap(GraymapHeader { maxwhite, .. }) => maxwhite,
                HeaderRecord::Pixmap(PixmapHeader { maxval, .. }) => maxval,
                HeaderRecord::Arbitrary(ArbitraryHeader { maxval, .. }) => maxval,
            };

            // We trust the image color bit count to be correct at least.
            let max_sample = match self.color {
                // Protects against overflows from shifting and gives a better error.
                ColorType::Gray(n)
                | ColorType::GrayA(n)
                | ColorType::Palette(n)
                | ColorType::RGB(n)
                | ColorType::RGBA(n)
                | ColorType::BGR(n)
                | ColorType::BGRA(n) if n > 16 =>
                {
                    return Err(io::Error::new(
                        io::ErrorKind::InvalidInput,
                        "Encoding colors with a bit depth greater 16 not supported",
                    ))
                }
                ColorType::Gray(n)
                | ColorType::GrayA(n)
                | ColorType::Palette(n)
                | ColorType::RGB(n)
                | ColorType::RGBA(n)
                | ColorType::BGR(n)
                | ColorType::BGRA(n) => (1 << n) - 1,
            };

            // Avoid the performance heavy check if possible, e.g. if the header has been chosen by us.
            if header_maxval < max_sample && !image.all_smaller(header_maxval) {
                return Err(io::Error::new(
                    io::ErrorKind::InvalidInput,
                    "Sample value greater than allowed for chosen header",
                ));
            }

            let encoding = image.encoding_for(&self.dimensions.unchecked.header.decoded);

            let image = CheckedImageBuffer::check(
                image,
                self.dimensions.width,
                self.dimensions.height,
                self.color,
            )?;

            Ok(CheckedHeader {
                color: self,
                encoding,
                _image: image,
            })
        }
    }

    impl<'a> CheckedHeader<'a> {
        fn write_header(self, writer: &mut Write) -> io::Result<TupleEncoding<'a>> {
            self.header().write(writer)?;
            Ok(self.encoding)
        }

        fn header(&self) -> &PNMHeader {
            self.color.dimensions.unchecked.header
        }
    }

    struct SampleWriter<'a>(&'a mut Write);

    impl<'a> SampleWriter<'a> {
        fn write_samples_ascii<V>(self, samples: V) -> io::Result<()>
        where
            V: Iterator,
            V::Item: fmt::Display,
        {
            let mut auto_break_writer = AutoBreak::new(self.0, 70);
            for value in samples {
                write!(auto_break_writer, "{} ", value)?;
            }
            auto_break_writer.flush()
        }

        fn write_pbm_bits<V>(self, samples: &[V], width: u32) -> io::Result<()>
        /* Default gives 0 for all primitives. TODO: replace this with `Zeroable` once it hits stable */
        where
            V: Default + Eq + Copy,
        {
            // The length of an encoded scanline
            let line_width = (width - 1) / 8 + 1;

            // We'll be writing single bytes, so buffer
            let mut line_buffer = Vec::with_capacity(line_width as usize);

            for line in samples.chunks(width as usize) {
                for byte_bits in line.chunks(8) {
                    let mut byte = 0u8;
                    for i in 0..8 {
                        // Black pixels are encoded as 1s
                        if let Some(&v) = byte_bits.get(i) {
                            if v == V::default() {
                                byte |= 1u8 << (7 - i)
                            }
                        }
                    }
                    line_buffer.push(byte)
                }
                self.0.write_all(line_buffer.as_slice())?;
                line_buffer.clear();
            }

            self.0.flush()
        }
    }

    impl<'a> FlatSamples<'a> {
        fn len(&self) -> usize {
            match *self {
                FlatSamples::U8(arr) => arr.len(),
                FlatSamples::U16(arr) => arr.len(),
            }
        }

        fn all_smaller(&self, max_val: u32) -> bool {
            match *self {
                FlatSamples::U8(arr) => arr.iter().any(|&val| u32::from(val) > max_val),
                FlatSamples::U16(arr) => arr.iter().any(|&val| u32::from(val) > max_val),
            }
        }

        fn encoding_for(&self, header: &HeaderRecord) -> TupleEncoding<'a> {
            match *header {
                HeaderRecord::Bitmap(BitmapHeader {
                    encoding: SampleEncoding::Binary,
                    width,
                    ..
                }) => TupleEncoding::PbmBits {
                    samples: *self,
                    width,
                },

                HeaderRecord::Bitmap(BitmapHeader {
                    encoding: SampleEncoding::Ascii,
                    ..
                }) => TupleEncoding::Ascii { samples: *self },

                HeaderRecord::Arbitrary(_) => TupleEncoding::Bytes { samples: *self },

                HeaderRecord::Graymap(GraymapHeader {
                    encoding: SampleEncoding::Ascii,
                    ..
                })
                | HeaderRecord::Pixmap(PixmapHeader {
                    encoding: SampleEncoding::Ascii,
                    ..
                }) => TupleEncoding::Ascii { samples: *self },

                HeaderRecord::Graymap(GraymapHeader {
                    encoding: SampleEncoding::Binary,
                    ..
                })
                | HeaderRecord::Pixmap(PixmapHeader {
                    encoding: SampleEncoding::Binary,
                    ..
                }) => TupleEncoding::Bytes { samples: *self },
            }
        }
    }

    impl<'a> From<&'a [u8]> for FlatSamples<'a> {
        fn from(samples: &'a [u8]) -> Self {
            FlatSamples::U8(samples)
        }
    }

    impl<'a> From<&'a [u16]> for FlatSamples<'a> {
        fn from(samples: &'a [u16]) -> Self {
            FlatSamples::U16(samples)
        }
    }

    impl<'a> TupleEncoding<'a> {
        fn write_image(&self, writer: &mut Write) -> io::Result<()> {
            match *self {
                TupleEncoding::PbmBits {
                    samples: FlatSamples::U8(samples),
                    width,
                } => SampleWriter(writer).write_pbm_bits(samples, width),
                TupleEncoding::PbmBits {
                    samples: FlatSamples::U16(samples),
                    width,
                } => SampleWriter(writer).write_pbm_bits(samples, width),

                TupleEncoding::Bytes {
                    samples: FlatSamples::U8(samples),
                } => writer.write_all(samples),
                TupleEncoding::Bytes {
                    samples: FlatSamples::U16(samples),
                } => samples
                    .iter()
                    .map(|&sample| writer.write_u16::<BigEndian>(sample))
                    .collect(),

                TupleEncoding::Ascii {
                    samples: FlatSamples::U8(samples),
                } => SampleWriter(writer).write_samples_ascii(samples.iter()),
                TupleEncoding::Ascii {
                    samples: FlatSamples::U16(samples),
                } => SampleWriter(writer).write_samples_ascii(samples.iter()),
            }
        }
    }

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

        #[test]
        fn custom_header_and_color() {
            let data: [u8; 12] = [0, 0, 0, 1, 1, 1, 255, 255, 255, 0, 0, 0];

            let header = ArbitraryHeader {
                width: 2,
                height: 2,
                depth: 3,
                maxval: 255,
                tupltype: Some(ArbitraryTuplType::Custom("Palette".to_string())),
            };

            let mut output = Vec::new();

            PNMEncoder::new(&mut output)
                .with_header(header.into())
                .encode(&data[..], 2, 2, ColorType::Palette(8))
                .expect("Failed encoding custom color value");
        }
    }

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