tplay 0.9.2

//! The `ImagePipeline` module contains a struct and implementation for converting images to ASCII
//! art. It offers a pipeline for processing images by resizing and converting them into ASCII
//! representations using a character lookup table.
use crate::common::errors::*;
use fast_image_resize as fr;
use image::DynamicImage;
#[cfg(test)]
use image::GrayImage;

/// The `ImagePipeline` struct encapsulates the process of converting an image to ASCII art. It
/// stores the target resolution (width and height) and the character lookup table used for the
/// conversion.
pub struct ImagePipeline {
    /// The target resolution (width and height) for the pipeline.
    pub target_resolution: (u32, u32),
    /// The character lookup table used for the conversion.
    pub char_map: Vec<char>,
    /// Whether to add newlines to the output at the end of each line
    pub new_lines: bool,
    /// Precomputed lookup table: lut[luminance] → character (avoids per-pixel division)
    lut: [char; 256],
}

impl ImagePipeline {
    /// Constructs a new `ImagePipeline` with the given target resolution (width and height) and
    /// character lookup table (a vector of characters).
    ///
    /// # Arguments
    ///
    /// * `target_resolution` - A tuple of two u32 integers representing the target width and
    ///   height.
    /// * `char_map` - A vector of characters to be used as the lookup table for ASCII
    ///   conversion.
    pub fn new(target_resolution: (u32, u32), char_map: Vec<char>, new_lines: bool) -> Self {
        let lut = Self::build_lut(&char_map);
        Self {
            target_resolution,
            char_map,
            new_lines,
            lut,
        }
    }

    /// Builds a 256-entry lookup table mapping luminance values directly to characters.
    fn build_lut(char_map: &[char]) -> [char; 256] {
        let mut lut = [' '; 256];
        let len = char_map.len();
        for i in 0..256 {
            lut[i] = char_map[len * i / 256];
        }
        lut
    }

    /// Rebuilds the LUT after a char_map change.
    pub fn rebuild_lut(&mut self) {
        self.lut = Self::build_lut(&self.char_map);
    }

    /// Sets the target resolution (width and height) for the pipeline and returns a mutable
    /// reference to self.
    ///
    /// # Arguments
    ///
    /// * `width` - The target width as a u32 integer.
    /// * `height` - The target height as a u32 integer.
    pub fn set_target_resolution(&mut self, width: u32, height: u32) -> &mut Self {
        self.target_resolution = (width, height);
        self
    }

    /// Resizes a given `DynamicImage` to the target resolution specified in the `self` object.
    ///
    /// This function takes a reference to a `DynamicImage` and resizes it using the nearest
    /// neighbor algorithm. The resized image is returned as a `DynamicImage`.
    ///
    /// # Arguments
    ///
    /// * `img` - A reference to the `DynamicImage` to be resized.
    ///
    /// # Returns
    ///
    /// A `Result` containing a resized `DynamicImage` if the operation is successful, or a
    /// `MyError` if an error occurs.
    ///
    /// # Errors
    ///
    /// This function may return a `MyError` if any of the following conditions are encountered:
    ///
    /// * The input image has a width or height of zero.
    /// * The target resolution has a width or height of zero.
    /// * An error occurs while creating an `fr::Image` from the input image.
    /// * An error occurs while resizing the image using the `fr::Resizer`.
    /// * An error occurs while creating an `ImageBuffer` from the resized image data.
    pub fn resize(&self, img: &DynamicImage) -> Result<DynamicImage, MyError> {
        let width = img.width();
        let height = img.height();
        let src_image = fr::images::Image::from_vec_u8(
            width,
            height,
            img.to_rgb8().into_raw(),
            fr::PixelType::U8x3,
        )
        .map_err(|err| MyError::Pipeline(format!("{ERROR_RESIZE}:{err:?}")))?;
        let mut dst_image = fr::images::Image::new(
            self.target_resolution.0,
            self.target_resolution.1,
            fr::PixelType::U8x3,
        );

        let mut resizer = fr::Resizer::new();
        resizer
            .resize(
                &src_image,
                &mut dst_image,
                &fr::ResizeOptions::new().resize_alg(fr::ResizeAlg::Nearest),
            )
            .map_err(|err| MyError::Pipeline(format!("{ERROR_RESIZE}:{err:?}")))?;

        let dst_image = dst_image.into_vec();
        let img_buff = image::ImageBuffer::<image::Rgb<u8>, _>::from_vec(
            self.target_resolution.0,
            self.target_resolution.1,
            dst_image,
        )
        .ok_or(MyError::Pipeline(ERROR_DATA.to_string()))?;
        Ok(DynamicImage::ImageRgb8(img_buff))
    }

    /// Converts the given grayscale image to ASCII art using the character lookup table stored in
    /// this `ImagePipeline`.
    ///
    /// This method iterates through the pixels of the input image and maps each pixel's grayscale
    /// value to a character from the lookup table. The resulting ASCII art is returned as a
    /// `String`.
    ///
    /// # Arguments
    ///
    /// * `input` - A reference to a `GrayImage` to be converted to ASCII art.
    ///
    /// # Returns
    ///
    /// A `String` containing the ASCII art representation of the input image.
    #[cfg(test)]
    pub fn to_ascii(&self, input: &GrayImage) -> String {
        let (width, height) = (input.width(), input.height());
        let capacity = (width + 1) * height + 1;
        let mut output = String::with_capacity(capacity as usize);

        for y in 0..height {
            output.extend((0..width).map(|x| {
                let lum = input.get_pixel(x, y)[0] as usize;
                self.lut[lum]
            }));

            if self.new_lines && y < height - 1 {
                output.push('\r');
                output.push('\n');
            }
        }

        output
    }

    /// Converts RGB pixel data directly to ASCII art, computing luminance inline.
    /// Avoids the separate grayscale conversion pass and its allocation entirely.
    pub fn to_ascii_from_rgb(&self, rgb_data: &[u8], width: u32, height: u32) -> String {
        let capacity = (width + 1) as usize * height as usize + 1;
        let mut output = String::with_capacity(capacity);

        for y in 0..height {
            let row_start = (y * width * 3) as usize;
            for x in 0..width {
                let idx = row_start + (x as usize) * 3;
                let r = rgb_data[idx] as u32;
                let g = rgb_data[idx + 1] as u32;
                let b = rgb_data[idx + 2] as u32;
                // BT.709 (sRGB) luma, matching the image crate's into_luma8():
                // 2126/10000 ≈ 0.2126, 7152/10000 ≈ 0.7152, 722/10000 ≈ 0.0722
                let lum = ((r * 2126 + g * 7152 + b * 722) / 10000) as usize;
                output.push(self.lut[lum]);
            }

            if self.new_lines && y < height - 1 {
                output.push('\r');
                output.push('\n');
            }
        }

        output
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::pipeline::char_maps::CHARS1;
    use image::{DynamicImage, ImageError};
    use reqwest;
    use std::io::Cursor;

    const TEST_IMAGE_URL: &str = "https://sipi.usc.edu/database/preview/misc/4.1.01.png";

    fn download_image(url: &str) -> Result<DynamicImage, ImageError> {
        let response = reqwest::blocking::get(url)
            .expect("Failed to download image")
            .bytes()
            .expect("Failed to get image bytes");

        let image_data = Cursor::new(response);
        image::load(image_data, image::ImageFormat::Png)
    }

    #[test]
    fn test_new() {
        let image = ImagePipeline::new((120, 80), vec!['a', 'b', 'c'], false);
        assert_eq!(image.target_resolution, (120, 80));
        assert_eq!(image.char_map, vec!['a', 'b', 'c']);
    }

    #[test]
    fn test_process() {
        let image = ImagePipeline::new((120, 80), vec!['a', 'b', 'c'], false);
        let input = download_image(TEST_IMAGE_URL).expect("Failed to download image");

        let output = image.resize(&input).expect("Failed to resize image");
        assert_eq!(output.width(), 120);
        assert_eq!(output.height(), 80);
    }

    #[test]
    fn test_to_ascii_ext() {
        let image = ImagePipeline::new((120, 80), CHARS1.chars().collect(), false);
        let input = download_image(TEST_IMAGE_URL).expect("Failed to download image");
        let output = image.to_ascii(
            &image
                .resize(&input)
                .expect("Failed to resize image")
                .into_luma8(),
        );
        assert_eq!(output.chars().count(), 120 * 80);
    }

    #[test]
    fn test_to_ascii() {
        let image = ImagePipeline::new((120, 80), vec!['a', 'b', 'c'], false);
        let input = download_image(TEST_IMAGE_URL).expect("Failed to download image");
        let output = image.to_ascii(
            &image
                .resize(&input)
                .expect("Failed to resize image")
                .into_luma8(),
        );
        assert_eq!(output.len(), 120 * 80);
    }
}