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use core::convert::TryFrom;

use crate::error::{Error, Result};
use crate::utils::unlikely;

/// Image color space.
///
/// Note: the color space is purely informative. Although it is saved to the
/// file header, it does not affect encoding/decoding in any way.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
#[repr(u8)]
pub enum ColorSpace {
    /// sRGB with linear alpha
    Srgb = 0,
    /// All channels are linear
    Linear = 1,
}

impl ColorSpace {
    /// Returns true if the color space is sRGB with linear alpha.
    pub const fn is_srgb(self) -> bool {
        matches!(self, Self::Srgb)
    }

    /// Returns true is all channels are linear.
    pub const fn is_linear(self) -> bool {
        matches!(self, Self::Linear)
    }

    /// Converts to an integer (0 if sRGB, 1 if all linear).
    pub const fn as_u8(self) -> u8 {
        self as u8
    }
}

impl Default for ColorSpace {
    fn default() -> Self {
        Self::Srgb
    }
}

impl From<ColorSpace> for u8 {
    #[inline]
    fn from(colorspace: ColorSpace) -> Self {
        colorspace as Self
    }
}

impl TryFrom<u8> for ColorSpace {
    type Error = Error;

    #[inline]
    fn try_from(colorspace: u8) -> Result<Self> {
        if unlikely(colorspace | 1 != 1) {
            Err(Error::InvalidColorSpace { colorspace })
        } else {
            Ok(if colorspace == 0 { Self::Srgb } else { Self::Linear })
        }
    }
}

/// Number of 8-bit channels in a pixel.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
#[repr(u8)]
pub enum Channels {
    /// Three 8-bit channels (RGB)
    Rgb = 3,
    /// Four 8-bit channels (RGBA)
    Rgba = 4,
}

impl Channels {
    /// Returns true if there are 3 channels (RGB).
    pub const fn is_rgb(self) -> bool {
        matches!(self, Self::Rgb)
    }

    /// Returns true if there are 4 channels (RGBA).
    pub const fn is_rgba(self) -> bool {
        matches!(self, Self::Rgba)
    }

    /// Converts to an integer (3 if RGB, 4 if RGBA).
    pub const fn as_u8(self) -> u8 {
        self as u8
    }
}

impl Default for Channels {
    fn default() -> Self {
        Self::Rgb
    }
}

impl From<Channels> for u8 {
    #[inline]
    fn from(channels: Channels) -> Self {
        channels as Self
    }
}

impl TryFrom<u8> for Channels {
    type Error = Error;

    #[inline]
    fn try_from(channels: u8) -> Result<Self> {
        if unlikely(channels != 3 && channels != 4) {
            Err(Error::InvalidChannels { channels })
        } else {
            Ok(if channels == 3 { Self::Rgb } else { Self::Rgba })
        }
    }
}