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//! # Dither
//! # Written by Efron Licht. Available under the MIT license. Hire me!
//!
//!
//! Inspired by: <http://www.tannerhelland.com/4660/dithering-eleven-algorithms-source-code/>
//! and the game "Return of the Obra Dinn"

/// handling of color modes & [color::rgb::RGB].
pub mod color;
pub mod ditherer;
mod error;
mod img;
mod opts;
pub mod prelude;
pub use self::error::Error;
pub use self::error::Result;

use self::prelude::*;
#[cfg(test)]
mod tests;

/// quantize to n bits. See the [bit_depth][crate::opts::Opt] option.
/// ```
/// # use dither::prelude::*;
/// # use dither::create_quantize_n_bits_func;
/// let one_bit = create_quantize_n_bits_func(1).unwrap();
/// let want = 0;
/// assert_eq!(one_bit(100.), (0., 100.));
/// assert_eq!(one_bit(250.), (255., -5.));
///
/// ```
pub fn create_quantize_n_bits_func(n: u8) -> Result<impl Fn(f64) -> (f64, f64)> {
    if n == 0 || n > 7 {
        Err(Error::BadBitDepth(n))
    } else {
        let step_size: f64 = 255. / f64::from(n);
        let quantize = move |x: f64| {
            debug_assert!(x.is_normal());
            let y = x / step_size;
            let (floor, ceil) = (y.floor() * step_size, y.ceil() * step_size);
            let (floor_rem, ceil_rem) = (x - floor, ceil - x);
            if floor_rem < ceil_rem {
                let quot = f64::max(floor, 0.0);
                (quot, floor_rem)
            } else {
                let quot = f64::min(255.0, ceil);
                (quot, -ceil_rem)
            }
        };
        Ok(quantize)
    }
}

/// clamp a f64 to the closest u8, rounding non-integers.
/// ```
/// # use dither::clamp_f64_to_u8;
/// assert_eq!(clamp_f64_to_u8(255.2), 255);
/// assert_eq!(clamp_f64_to_u8(2.8), 3);
/// ```
pub fn clamp_f64_to_u8(n: f64) -> u8 {
    match n {
        n if n > 255.0 => 255,
        n if n < 0.0 => 0,
        n => n.round() as u8,
    }
}
/// run dither using the provided options.
pub fn exec(opts: &Opt) -> Result<()> {
    let (input, output) = (&opts.input, opts.output_path()?);
    if opts.verbose {
        eprintln!(
            concat!(
                "running dither in VERBOSE mode:\n\t",
                "INPUT: {input}\n\t",
                "OUTPUT: {output}\n\t",
                "DITHERER: {dither}\n\t",
                "BIT_DEPTH: {depth}\n\t",
                "COLOR_MODE: {mode}"
            ),
            input = input.display(),
            output = output.display(),
            dither = opts.ditherer,
            depth = opts.bit_depth,
            mode = opts.color_mode,
        );
    }
    let img: Img<RGB<f64>> =
        Img::<RGB<u8>>::load(&input)?.convert_with(|rgb| rgb.convert_with(f64::from));

    if opts.verbose {
        eprintln!("image loaded from \"{}\".\ndithering...", input.display())
    }
    let quantize = create_quantize_n_bits_func(opts.bit_depth)?;

    let output_img = match &opts.color_mode {
        color::Mode::Palette { .. } if opts.bit_depth > 1 => {
            return Err(Error::CustomPaletteIncompatibleWithDepth);
        }

        color::Mode::Color => opts
            .ditherer
            .dither(img, RGB::map_across(quantize))
            .convert_with(|rgb| rgb.convert_with(clamp_f64_to_u8)),

        color::Mode::Palette { palette: p, .. } => opts
            .ditherer
            .dither(img, color::palette::quantize(p))
            .convert_with(|rgb| rgb.convert_with(clamp_f64_to_u8)),

        color::Mode::BlackAndWhite => {
            let bw_img = img.convert_with(|rgb| rgb.to_chroma_corrected_black_and_white());
            opts.ditherer
                .dither(bw_img, quantize)
                .convert_with(RGB::from_chroma_corrected_black_and_white)
        }

        color::Mode::SingleColor(color) => {
            if opts.verbose {
                eprintln!("single_color mode: {:x}", color)
            }

            let bw_img = img.convert_with(|rgb| rgb.to_chroma_corrected_black_and_white());
            let RGB(r, g, b) = *color;
            opts.ditherer
                .dither(bw_img, quantize)
                .convert_with(|x: f64| {
                    RGB(
                        clamp_f64_to_u8(f64::from(r) / 255. * x),
                        clamp_f64_to_u8(f64::from(g) / 255. * x),
                        clamp_f64_to_u8(f64::from(b) / 255. * x),
                    )
                })
        }
    };
    if opts.verbose {
        eprintln!("dithering complete.\nsaving...");
    }
    output_img.save(&output)?;
    if opts.verbose {
        eprintln!("program finished");
    }
    Ok(())
}