trait Sealed {}

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
#[repr(u8)]
pub enum PixelFormat {
    A8,
    Abgr32,
    Bgr24,
    Bgr32,
    Rgb24,
    Rgb32,
    Rgba32,
}

pub(crate) const NUM_PIXEL_FORMATS: usize = 7;
pub(crate) const MAX_PIXEL_WIDTH: usize = 4;

#[derive(Clone, PartialEq, Debug, Default)]
pub struct PackedLocation(Option<u8>);

impl PackedLocation {
    const fn empty() -> Self {
        Self(None)
    }
    const fn select_byte(index: u8) -> Self {
        Self(Some(index))
    }

    pub const fn index(&self) -> Option<u8> {
        self.0
    }
}

#[allow(private_bounds)]
pub trait PixelFormatSpec: Sealed + Clone + Copy + PartialEq {
    const FORMAT_ENUM: PixelFormat;
    const CHANNELS: usize;
    const PIXEL_WIDTH: usize;

    const NAME: &'static str;

    const RED_PACK: PackedLocation;
    const GREEN_PACK: PackedLocation;
    const BLUE_PACK: PackedLocation;
    const ALPHA_PACK: PackedLocation;
}

//-----------------------------------------------------------------------------
// Pixel formats
//-----------------------------------------------------------------------------

/// 8-bit alpha map
#[derive(Clone, Copy, PartialEq)]
pub struct A8;
impl Sealed for A8 {}
impl PixelFormatSpec for A8 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::A8;
    const CHANNELS: usize = 1;
    const PIXEL_WIDTH: usize = 1;

    const NAME: &'static str = "A8";

    const RED_PACK: PackedLocation = PackedLocation::empty();
    const GREEN_PACK: PackedLocation = PackedLocation::empty();
    const BLUE_PACK: PackedLocation = PackedLocation::empty();
    const ALPHA_PACK: PackedLocation = PackedLocation::select_byte(0);
}

/// RGBA with 8 bits per channel, stored big-endian
///
/// This assumes the following memory layout:
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  A | B | G | R | A | B | G | R | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Abgr32;

impl Sealed for Abgr32 {}
impl PixelFormatSpec for Abgr32 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Abgr32;
    const CHANNELS: usize = 4;
    const PIXEL_WIDTH: usize = 4;

    const NAME: &'static str = "Abgr32";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(3);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(2);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(1);
    const ALPHA_PACK: PackedLocation = PackedLocation::select_byte(0);
}

/// 24bpp colour densly packed into 24-bit words
///
/// This assumes the following memory layout:
///
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  R | G | B | R | G | B | R | G | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Bgr24;
impl Sealed for Bgr24 {}
impl PixelFormatSpec for Bgr24 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Bgr24;
    const CHANNELS: usize = 3;
    const PIXEL_WIDTH: usize = 3;

    const NAME: &'static str = "Bgr24";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(0);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(1);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(2);
    const ALPHA_PACK: PackedLocation = PackedLocation::empty();
}

/// 24bpp colour packed into 32-bit words
///
/// This assumes the following memory layout:
///
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  R | G | B | - | R | G | B | - | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Bgr32;
impl Sealed for Bgr32 {}
impl PixelFormatSpec for Bgr32 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Bgr32;
    const CHANNELS: usize = 3;
    const PIXEL_WIDTH: usize = 4;

    const NAME: &'static str = "Bgr32";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(2);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(1);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(0);
    const ALPHA_PACK: PackedLocation = PackedLocation::empty();
}

/// 24bpp colour densly packed into 24-bit words
///
/// This assumes the following memory layout:
///
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  B | G | R | B | G | R | B | G | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Rgb24;
impl Sealed for Rgb24 {}
impl PixelFormatSpec for Rgb24 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Rgb24;
    const CHANNELS: usize = 3;
    const PIXEL_WIDTH: usize = 3;

    const NAME: &'static str = "Rgb24";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(2);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(1);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(0);
    const ALPHA_PACK: PackedLocation = PackedLocation::empty();
}

/// 24bpp colour packed into 32-bit words
///
/// This assumes the following memory layout:
///
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  B | G | R | - | B | G | R | - | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Rgb32;
impl Sealed for Rgb32 {}
impl PixelFormatSpec for Rgb32 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Rgb32;
    const CHANNELS: usize = 3;
    const PIXEL_WIDTH: usize = 4;

    const NAME: &'static str = "Rgb32";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(2);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(1);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(0);
    const ALPHA_PACK: PackedLocation = PackedLocation::empty();
}

/// RGBA with 8 bits per channel, stored little-endian
///
/// This assumes the following memory layout:
/// ```text
///  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ...
/// ---+---+---+---+---+---+---+---+---
///  R | G | B | A | R | G | B | A | ...
/// ```
#[derive(Clone, Copy, PartialEq)]
pub struct Rgba32;

impl Sealed for Rgba32 {}
impl PixelFormatSpec for Rgba32 {
    const FORMAT_ENUM: PixelFormat = PixelFormat::Rgba32;
    const CHANNELS: usize = 4;
    const PIXEL_WIDTH: usize = 4;

    const NAME: &'static str = "Rgba32";

    const RED_PACK: PackedLocation = PackedLocation::select_byte(0);
    const GREEN_PACK: PackedLocation = PackedLocation::select_byte(1);
    const BLUE_PACK: PackedLocation = PackedLocation::select_byte(2);
    const ALPHA_PACK: PackedLocation = PackedLocation::select_byte(3);
}