use anyhow::{bail, Context};
use serde::de::{self, Deserialize, Deserializer, Visitor};
use std::{
    fmt,
    hash::{Hash, Hasher},
};

/// Convert an RGB hex color code number to a color type
pub fn rgb(hex: u32) -> Rgba {
    let r = ((hex >> 16) & 0xFF) as f32 / 255.0;
    let g = ((hex >> 8) & 0xFF) as f32 / 255.0;
    let b = (hex & 0xFF) as f32 / 255.0;
    Rgba { r, g, b, a: 1.0 }
}

/// Convert an RGBA hex color code number to [`Rgba`]
pub fn rgba(hex: u32) -> Rgba {
    let r = ((hex >> 24) & 0xFF) as f32 / 255.0;
    let g = ((hex >> 16) & 0xFF) as f32 / 255.0;
    let b = ((hex >> 8) & 0xFF) as f32 / 255.0;
    let a = (hex & 0xFF) as f32 / 255.0;
    Rgba { r, g, b, a }
}

/// An RGBA color
#[derive(PartialEq, Clone, Copy, Default)]
pub struct Rgba {
    /// The red component of the color, in the range 0.0 to 1.0
    pub r: f32,
    /// The green component of the color, in the range 0.0 to 1.0
    pub g: f32,
    /// The blue component of the color, in the range 0.0 to 1.0
    pub b: f32,
    /// The alpha component of the color, in the range 0.0 to 1.0
    pub a: f32,
}

impl fmt::Debug for Rgba {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "rgba({:#010x})", u32::from(*self))
    }
}

impl Rgba {
    /// Create a new [`Rgba`] color by blending this and another color together
    pub fn blend(&self, other: Rgba) -> Self {
        if other.a >= 1.0 {
            other
        } else if other.a <= 0.0 {
            return *self;
        } else {
            return Rgba {
                r: (self.r * (1.0 - other.a)) + (other.r * other.a),
                g: (self.g * (1.0 - other.a)) + (other.g * other.a),
                b: (self.b * (1.0 - other.a)) + (other.b * other.a),
                a: self.a,
            };
        }
    }
}

impl From<Rgba> for u32 {
    fn from(rgba: Rgba) -> Self {
        let r = (rgba.r * 255.0) as u32;
        let g = (rgba.g * 255.0) as u32;
        let b = (rgba.b * 255.0) as u32;
        let a = (rgba.a * 255.0) as u32;
        (r << 24) | (g << 16) | (b << 8) | a
    }
}

struct RgbaVisitor;

impl<'de> Visitor<'de> for RgbaVisitor {
    type Value = Rgba;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("a string in the format #rrggbb or #rrggbbaa")
    }

    fn visit_str<E: de::Error>(self, value: &str) -> Result<Rgba, E> {
        Rgba::try_from(value).map_err(E::custom)
    }
}

impl<'de> Deserialize<'de> for Rgba {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        deserializer.deserialize_str(RgbaVisitor)
    }
}

impl From<Hsla> for Rgba {
    fn from(color: Hsla) -> Self {
        let h = color.h;
        let s = color.s;
        let l = color.l;

        let c = (1.0 - (2.0 * l - 1.0).abs()) * s;
        let x = c * (1.0 - ((h * 6.0) % 2.0 - 1.0).abs());
        let m = l - c / 2.0;
        let cm = c + m;
        let xm = x + m;

        let (r, g, b) = match (h * 6.0).floor() as i32 {
            0 | 6 => (cm, xm, m),
            1 => (xm, cm, m),
            2 => (m, cm, xm),
            3 => (m, xm, cm),
            4 => (xm, m, cm),
            _ => (cm, m, xm),
        };

        Rgba {
            r,
            g,
            b,
            a: color.a,
        }
    }
}

impl TryFrom<&'_ str> for Rgba {
    type Error = anyhow::Error;

    fn try_from(value: &'_ str) -> Result<Self, Self::Error> {
        const RGB: usize = "rgb".len();
        const RGBA: usize = "rgba".len();
        const RRGGBB: usize = "rrggbb".len();
        const RRGGBBAA: usize = "rrggbbaa".len();

        const EXPECTED_FORMATS: &str = "Expected #rgb, #rgba, #rrggbb, or #rrggbbaa";
        const INVALID_UNICODE: &str = "invalid unicode characters in color";

        let Some(("", hex)) = value.trim().split_once('#') else {
            bail!("invalid RGBA hex color: '{value}'. {EXPECTED_FORMATS}");
        };

        let (r, g, b, a) = match hex.len() {
            RGB | RGBA => {
                let r = u8::from_str_radix(
                    hex.get(0..1).with_context(|| {
                        format!("{INVALID_UNICODE}: r component of #rgb/#rgba for value: '{value}'")
                    })?,
                    16,
                )?;
                let g = u8::from_str_radix(
                    hex.get(1..2).with_context(|| {
                        format!("{INVALID_UNICODE}: g component of #rgb/#rgba for value: '{value}'")
                    })?,
                    16,
                )?;
                let b = u8::from_str_radix(
                    hex.get(2..3).with_context(|| {
                        format!("{INVALID_UNICODE}: b component of #rgb/#rgba for value: '{value}'")
                    })?,
                    16,
                )?;
                let a = if hex.len() == RGBA {
                    u8::from_str_radix(
                        hex.get(3..4).with_context(|| {
                            format!("{INVALID_UNICODE}: a component of #rgba for value: '{value}'")
                        })?,
                        16,
                    )?
                } else {
                    0xf
                };

                /// Duplicates a given hex digit.
                /// E.g., `0xf` -> `0xff`.
                const fn duplicate(value: u8) -> u8 {
                    value << 4 | value
                }

                (duplicate(r), duplicate(g), duplicate(b), duplicate(a))
            }
            RRGGBB | RRGGBBAA => {
                let r = u8::from_str_radix(
                    hex.get(0..2).with_context(|| {
                        format!(
                            "{}: r component of #rrggbb/#rrggbbaa for value: '{}'",
                            INVALID_UNICODE, value
                        )
                    })?,
                    16,
                )?;
                let g = u8::from_str_radix(
                    hex.get(2..4).with_context(|| {
                        format!(
                            "{INVALID_UNICODE}: g component of #rrggbb/#rrggbbaa for value: '{value}'"
                        )
                    })?,
                    16,
                )?;
                let b = u8::from_str_radix(
                    hex.get(4..6).with_context(|| {
                        format!(
                            "{INVALID_UNICODE}: b component of #rrggbb/#rrggbbaa for value: '{value}'"
                        )
                    })?,
                    16,
                )?;
                let a = if hex.len() == RRGGBBAA {
                    u8::from_str_radix(
                        hex.get(6..8).with_context(|| {
                            format!(
                                "{INVALID_UNICODE}: a component of #rrggbbaa for value: '{value}'"
                            )
                        })?,
                        16,
                    )?
                } else {
                    0xff
                };
                (r, g, b, a)
            }
            _ => bail!("invalid RGBA hex color: '{value}'. {EXPECTED_FORMATS}"),
        };

        Ok(Rgba {
            r: r as f32 / 255.,
            g: g as f32 / 255.,
            b: b as f32 / 255.,
            a: a as f32 / 255.,
        })
    }
}

/// An HSLA color
#[derive(Default, Copy, Clone, Debug)]
#[repr(C)]
pub struct Hsla {
    /// Hue, in a range from 0 to 1
    pub h: f32,

    /// Saturation, in a range from 0 to 1
    pub s: f32,

    /// Lightness, in a range from 0 to 1
    pub l: f32,

    /// Alpha, in a range from 0 to 1
    pub a: f32,
}

impl PartialEq for Hsla {
    fn eq(&self, other: &Self) -> bool {
        self.h
            .total_cmp(&other.h)
            .then(self.s.total_cmp(&other.s))
            .then(self.l.total_cmp(&other.l).then(self.a.total_cmp(&other.a)))
            .is_eq()
    }
}

impl PartialOrd for Hsla {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for Hsla {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.h
            .total_cmp(&other.h)
            .then(self.s.total_cmp(&other.s))
            .then(self.l.total_cmp(&other.l).then(self.a.total_cmp(&other.a)))
    }
}

impl Eq for Hsla {}

impl Hash for Hsla {
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_u32(u32::from_be_bytes(self.h.to_be_bytes()));
        state.write_u32(u32::from_be_bytes(self.s.to_be_bytes()));
        state.write_u32(u32::from_be_bytes(self.l.to_be_bytes()));
        state.write_u32(u32::from_be_bytes(self.a.to_be_bytes()));
    }
}

/// Construct an [`Hsla`] object from plain values
pub fn hsla(h: f32, s: f32, l: f32, a: f32) -> Hsla {
    Hsla {
        h: h.clamp(0., 1.),
        s: s.clamp(0., 1.),
        l: l.clamp(0., 1.),
        a: a.clamp(0., 1.),
    }
}

/// Pure black in [`Hsla`]
pub fn black() -> Hsla {
    Hsla {
        h: 0.,
        s: 0.,
        l: 0.,
        a: 1.,
    }
}

/// Transparent black in [`Hsla`]
pub fn transparent_black() -> Hsla {
    Hsla {
        h: 0.,
        s: 0.,
        l: 0.,
        a: 0.,
    }
}

/// Transparent black in [`Hsla`]
pub fn transparent_white() -> Hsla {
    Hsla {
        h: 0.,
        s: 0.,
        l: 1.,
        a: 0.,
    }
}

/// Opaque grey in [`Hsla`], values will be clamped to the range [0, 1]
pub fn opaque_grey(lightness: f32, opacity: f32) -> Hsla {
    Hsla {
        h: 0.,
        s: 0.,
        l: lightness.clamp(0., 1.),
        a: opacity.clamp(0., 1.),
    }
}

/// Pure white in [`Hsla`]
pub fn white() -> Hsla {
    Hsla {
        h: 0.,
        s: 0.,
        l: 1.,
        a: 1.,
    }
}

/// The color red in [`Hsla`]
pub fn red() -> Hsla {
    Hsla {
        h: 0.,
        s: 1.,
        l: 0.5,
        a: 1.,
    }
}

/// The color blue in [`Hsla`]
pub fn blue() -> Hsla {
    Hsla {
        h: 0.6,
        s: 1.,
        l: 0.5,
        a: 1.,
    }
}

/// The color green in [`Hsla`]
pub fn green() -> Hsla {
    Hsla {
        h: 0.33,
        s: 1.,
        l: 0.5,
        a: 1.,
    }
}

/// The color yellow in [`Hsla`]
pub fn yellow() -> Hsla {
    Hsla {
        h: 0.16,
        s: 1.,
        l: 0.5,
        a: 1.,
    }
}

impl Hsla {
    /// Converts this HSLA color to an RGBA color.
    pub fn to_rgb(self) -> Rgba {
        self.into()
    }

    /// The color red
    pub fn red() -> Self {
        red()
    }

    /// The color green
    pub fn green() -> Self {
        green()
    }

    /// The color blue
    pub fn blue() -> Self {
        blue()
    }

    /// The color black
    pub fn black() -> Self {
        black()
    }

    /// The color white
    pub fn white() -> Self {
        white()
    }

    /// The color transparent black
    pub fn transparent_black() -> Self {
        transparent_black()
    }

    /// Returns true if the HSLA color is fully transparent, false otherwise.
    pub fn is_transparent(&self) -> bool {
        self.a == 0.0
    }

    /// Blends `other` on top of `self` based on `other`'s alpha value. The resulting color is a combination of `self`'s and `other`'s colors.
    ///
    /// If `other`'s alpha value is 1.0 or greater, `other` color is fully opaque, thus `other` is returned as the output color.
    /// If `other`'s alpha value is 0.0 or less, `other` color is fully transparent, thus `self` is returned as the output color.
    /// Else, the output color is calculated as a blend of `self` and `other` based on their weighted alpha values.
    ///
    /// Assumptions:
    /// - Alpha values are contained in the range [0, 1], with 1 as fully opaque and 0 as fully transparent.
    /// - The relative contributions of `self` and `other` is based on `self`'s alpha value (`self.a`) and `other`'s  alpha value (`other.a`), `self` contributing `self.a * (1.0 - other.a)` and `other` contributing its own alpha value.
    /// - RGB color components are contained in the range [0, 1].
    /// - If `self` and `other` colors are out of the valid range, the blend operation's output and behavior is undefined.
    pub fn blend(self, other: Hsla) -> Hsla {
        let alpha = other.a;

        if alpha >= 1.0 {
            other
        } else if alpha <= 0.0 {
            return self;
        } else {
            let converted_self = Rgba::from(self);
            let converted_other = Rgba::from(other);
            let blended_rgb = converted_self.blend(converted_other);
            return Hsla::from(blended_rgb);
        }
    }

    /// Returns a new HSLA color with the same hue, and lightness, but with no saturation.
    pub fn grayscale(&self) -> Self {
        Hsla {
            h: self.h,
            s: 0.,
            l: self.l,
            a: self.a,
        }
    }

    /// Fade out the color by a given factor. This factor should be between 0.0 and 1.0.
    /// Where 0.0 will leave the color unchanged, and 1.0 will completely fade out the color.
    pub fn fade_out(&mut self, factor: f32) {
        self.a *= 1.0 - factor.clamp(0., 1.);
    }
}

impl From<Rgba> for Hsla {
    fn from(color: Rgba) -> Self {
        let r = color.r;
        let g = color.g;
        let b = color.b;

        let max = r.max(g.max(b));
        let min = r.min(g.min(b));
        let delta = max - min;

        let l = (max + min) / 2.0;
        let s = if l == 0.0 || l == 1.0 {
            0.0
        } else if l < 0.5 {
            delta / (2.0 * l)
        } else {
            delta / (2.0 - 2.0 * l)
        };

        let h = if delta == 0.0 {
            0.0
        } else if max == r {
            ((g - b) / delta).rem_euclid(6.0) / 6.0
        } else if max == g {
            ((b - r) / delta + 2.0) / 6.0
        } else {
            ((r - g) / delta + 4.0) / 6.0
        };

        Hsla {
            h,
            s,
            l,
            a: color.a,
        }
    }
}

impl<'de> Deserialize<'de> for Hsla {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        // First, deserialize it into Rgba
        let rgba = Rgba::deserialize(deserializer)?;

        // Then, use the From<Rgba> for Hsla implementation to convert it
        Ok(Hsla::from(rgba))
    }
}

#[cfg(test)]
mod tests {
    use serde_json::json;

    use super::*;

    #[test]
    fn test_deserialize_three_value_hex_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!("#f09")).unwrap();

        assert_eq!(actual, rgba(0xff0099ff))
    }

    #[test]
    fn test_deserialize_four_value_hex_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!("#f09f")).unwrap();

        assert_eq!(actual, rgba(0xff0099ff))
    }

    #[test]
    fn test_deserialize_six_value_hex_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!("#ff0099")).unwrap();

        assert_eq!(actual, rgba(0xff0099ff))
    }

    #[test]
    fn test_deserialize_eight_value_hex_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!("#ff0099ff")).unwrap();

        assert_eq!(actual, rgba(0xff0099ff))
    }

    #[test]
    fn test_deserialize_eight_value_hex_with_padding_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!(" #f5f5f5ff   ")).unwrap();

        assert_eq!(actual, rgba(0xf5f5f5ff))
    }

    #[test]
    fn test_deserialize_eight_value_hex_with_mixed_case_to_rgba() {
        let actual: Rgba = serde_json::from_value(json!("#DeAdbEeF")).unwrap();

        assert_eq!(actual, rgba(0xdeadbeef))
    }
}