//! Image widgets for [Ratatui]
//!
//! **⚠️ THIS CRATE IS EXPERIMENTAL**
//!
//! Render images with graphics protocols in the terminal with [Ratatui].
//!
//! ```rust
//! # use ratatui::{backend::{Backend, TestBackend}, Terminal, terminal::Frame, layout::Rect};
//! # use ratatu_image::{
//! #   picker::{Picker, BackendType},
//! #   Resize, FixedImage, backend::FixedBackend,
//! # };
//! struct App {
//!     image: Box<dyn FixedBackend>,
//! }
//!
//! fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     let font_size = (7, 16); // Or use Picker::from_termios, or let user provide it.
//!     let mut picker = Picker::new(
//!         font_size,
//! #        #[cfg(feature = "sixel")]
//!         BackendType::Sixel,
//! #        #[cfg(not(feature = "sixel"))]
//! #        BackendType::Halfblocks,
//!         None,
//!     )?;
//!     let dyn_img = image::io::Reader::open("./assets/Ada.png")?.decode()?;
//!     let image = picker.new_static_fit(dyn_img, Rect::new(0, 0, 30, 20), Resize::Fit)?;
//!     let mut app = App { image };
//!
//!     let backend = TestBackend::new(80, 30);
//!     let mut terminal = Terminal::new(backend)?;
//!
//!     // loop:
//!     terminal.draw(|f| ui(f, &mut app))?;
//!
//!     Ok(())
//! }
//!
//! fn ui<B: Backend>(f: &mut Frame<B>, app: &mut App) {
//!     let image = FixedImage::new(app.image.as_ref());
//!     f.render_widget(image, f.size());
//! }
//! ```
//!
//! # TUIs
//! TUI application revolve around columns and rows of text naturally without the need of any
//! notions of pixel sizes. [Ratatui] is based on "immediate rendering with intermediate buffers".
//!
//! At each frame, widgets are constructed and rendered into some character buffer, and any changes
//! from respect to the last frame are then diffed and written to the terminal screen.
//!
//! # Terminal graphic protocols
//! Some protocols allow to output image data to terminals that support it.
//!
//! The [Sixel] protocol mechanism is, in a nutshell, just printing an escape sequence.
//! The image will be "dumped" at the cursor position, and the implementation may add enough
//! carriage returns to scroll the output.
//!
//! # Problem
//! Simply "dumping" an image into a [Ratatui] buffer is not enough. At best, the buffer diff might
//! not overwrite any characters that are covered by the image in some instances, but the diff
//! might change at any time due to screen/area resizing or simply other widget's contents
//! changing. Then the graphics would inmediately get overwritten by the underlying character data.
//!
//! # Solution
//! First it is necessary to suppress the covered character cells' rendering, which is addressed in
//! a [Ratatui PR for cell skipping].
//!
//! Second it is then necessary to get the image's size in columns and rows, which is done by
//! querying the terminal for it's pixel size and dividing by columns/rows to get the font size in
//! pixels. Currently this is implemented with `rustix::termios`, but this is subject to change for
//! a [Ratatui PR for getting window size].
//!
//! # Implementation
//!
//! The images are always resized so that they fit their nearest rectangle in columns/rows.
//! This is so that the image shall be drawn in the same "render pass" as all surrounding text, and
//! cells under the area of the image skip the draw on the ratatui buffer level, so there is no way
//! to "clear" previous drawn text. This would leave artifacts around the image's right and bottom
//! borders.
//!
//! # Example
//!
//! See the [crate::picker::Picker] helper and [`examples/demo`](./examples/demo/main.rs).
//!
//! [Ratatui]: https://github.com/ratatui-org/ratatui
//! [Sixel]: https://en.wikipedia.org/wiki/Sixel
//! [Ratatui PR for cell skipping]: https://github.com/ratatui-org/ratatui/pull/215
//! [Ratatui PR for getting window size]: https://github.com/ratatui-org/ratatui/pull/276
use std::{
    cmp::{max, min},
    collections::hash_map::DefaultHasher,
    error::Error,
    hash::{Hash, Hasher},
};

use backend::{FixedBackend, ResizeBackend};
use image::{
    imageops::{self, FilterType},
    DynamicImage, ImageBuffer, Rgb,
};
use ratatui::{
    buffer::Buffer,
    layout::Rect,
    widgets::{StatefulWidget, Widget},
};

pub mod backend;
pub mod picker;

type Result<T> = std::result::Result<T, Box<dyn Error>>;

/// The terminal's font size in `(width, height)`
pub type FontSize = (u16, u16);

#[derive(Clone)]
/// Image source for [crate::backend::ResizeBackend]s
///
/// A `[ResizeBackend]` needs to resize the ImageSource to its state when the available area
/// changes. A `[FixedBackend]` only needs it once.
///
/// # Examples
/// ```text
/// use image::{DynamicImage, ImageBuffer, Rgb};
/// use ratatu_image::ImageSource;
///
/// let image: ImageBuffer::from_pixel(300, 200, Rgb::<u8>([255, 0, 0])).into();
/// let source = ImageSource::new(image, "filename.png", (7, 14));
/// assert_eq!((43, 14), (source.rect.width, source.rect.height));
/// ```
///
pub struct ImageSource {
    /// The original image without resizing
    pub image: DynamicImage,
    /// The font size of the terminal
    pub font_size: FontSize,
    /// The area that the [`ImageSource::image`] covers, but not necessarily fills
    pub desired: Rect,
    pub hash: u64,
}

impl ImageSource {
    /// Create a new image source
    pub fn new(image: DynamicImage, font_size: FontSize) -> ImageSource {
        let desired =
            ImageSource::round_pixel_size_to_cells(image.width(), image.height(), font_size);

        let mut state = DefaultHasher::new();
        image.as_bytes().hash(&mut state);
        let hash = state.finish();

        ImageSource {
            image,
            font_size,
            desired,
            hash,
        }
    }
    /// Round an image pixel size to the nearest matching cell size, given a font size.
    fn round_pixel_size_to_cells(
        img_width: u32,
        img_height: u32,
        (char_width, char_height): FontSize,
    ) -> Rect {
        let width = (img_width as f32 / char_width as f32).ceil() as u16;
        let height = (img_height as f32 / char_height as f32).ceil() as u16;
        Rect::new(0, 0, width, height)
    }
}

/// Fixed size image widget that uses [FixedBackend].
///
/// The widget does *not* react to area resizes, and is not even guaranteed to **not** overdraw.
/// Its advantage is that the [FixedBackend] it uses needs only one initial resize.
///
/// ```rust
/// # use ratatui::{backend::Backend, terminal::Frame};
/// # use ratatu_image::{Resize, FixedImage, backend::FixedBackend};
/// struct App {
///     image_static: Box<dyn FixedBackend>,
/// }
/// fn ui<B: Backend>(f: &mut Frame<B>, app: &mut App) {
///     let image = FixedImage::new(app.image_static.as_ref());
///     f.render_widget(image, f.size());
/// }
/// ```
pub struct FixedImage<'a> {
    image: &'a dyn FixedBackend,
}

impl<'a> FixedImage<'a> {
    pub fn new(image: &'a dyn FixedBackend) -> FixedImage<'a> {
        FixedImage { image }
    }
}

impl<'a> Widget for FixedImage<'a> {
    fn render(self, area: Rect, buf: &mut Buffer) {
        if area.width == 0 || area.height == 0 {
            return;
        }

        self.image.render(area, buf);
    }
}

/// Resizeable image widget that uses an [ImageSource] and [ResizeBackend] state.
///
/// This stateful widget reacts to area resizes and resizes its image data accordingly.
///
/// ```rust
/// # use ratatui::{backend::Backend, terminal::Frame};
/// # use ratatu_image::{ImageSource, Resize, ResizeImage, backend::ResizeBackend};
/// struct App {
///     image_source: ImageSource,
///     image_state: Box<dyn ResizeBackend>,
/// }
/// fn ui<B: Backend>(f: &mut Frame<B>, app: &mut App) {
///     let image = ResizeImage::new(&app.image_source, None).resize(Resize::Crop);
///     f.render_stateful_widget(
///         image,
///         f.size(),
///         &mut app.image_state,
///     );
/// }
/// ```
pub struct ResizeImage<'a> {
    image: &'a ImageSource,
    resize: Resize,
    background_color: Option<Rgb<u8>>,
}

impl<'a> ResizeImage<'a> {
    pub fn new(image: &'a ImageSource, background_color: Option<Rgb<u8>>) -> ResizeImage<'a> {
        ResizeImage {
            image,
            resize: Resize::Fit,
            background_color,
        }
    }
    pub fn resize(mut self, resize: Resize) -> ResizeImage<'a> {
        self.resize = resize;
        self
    }
}

impl<'a> StatefulWidget for ResizeImage<'a> {
    type State = Box<dyn ResizeBackend>;
    fn render(self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
        state.render(self.image, &self.resize, self.background_color, area, buf)
    }
}

#[derive(Debug)]
/// Resize method
pub enum Resize {
    /// Fit to area.
    ///
    /// If the width or height is smaller than the area, the image will be resized maintaining
    /// proportions.
    Fit,
    /// Crop to area.
    ///
    /// If the width or height is smaller than the area, the image will be cropped.
    /// The behaviour is the same as using [`FixedImage`] widget with the overhead of resizing,
    /// but some terminals might misbehave when overdrawing characters over graphics.
    /// For example, the sixel branch of Alacritty never draws text over a cell that is currently
    /// being rendered by some sixel sequence, not necessarily originating from the same cell.
    Crop,
}

impl Resize {
    /// Resize if [`ImageSource`]'s "desired" doesn't fit into `area`, or is different than `current`
    fn resize(
        &self,
        source: &ImageSource,
        current: Rect,
        area: Rect,
        background_color: Option<Rgb<u8>>,
        force: bool,
    ) -> Option<(DynamicImage, Rect)> {
        self.needs_resize(source, current, area, force).map(|rect| {
            let width = (rect.width * source.font_size.0) as u32;
            let height = (rect.height * source.font_size.1) as u32;
            // Resize/Crop/etc. but not necessarily fitting cell size
            let mut image = self.resize_image(source, width, height);
            // Pad to cell size
            if image.width() != width || image.height() != height {
                static DEFAULT_BACKGROUND: Rgb<u8> = Rgb([0, 0, 0]);
                let color = background_color.unwrap_or(DEFAULT_BACKGROUND);
                let mut bg: DynamicImage = ImageBuffer::from_pixel(width, height, color).into();
                imageops::overlay(&mut bg, &image, 0, 0);
                image = bg;
            }
            (image, rect)
        })
    }

    /// Check if [`ImageSource`]'s "desired" fits into `area` and is different than `current`.
    fn needs_resize(
        &self,
        image: &ImageSource,
        current: Rect,
        area: Rect,
        force: bool,
    ) -> Option<Rect> {
        let desired = image.desired;
        // Check if resize is needed at all.
        if desired.width <= area.width && desired.height <= area.height && desired == current {
            let width = (desired.width * image.font_size.0) as u32;
            let height = (desired.height * image.font_size.1) as u32;
            if !force && (image.image.width() == width || image.image.height() == height) {
                return None;
            }
        }

        let rect = self.needs_resize_rect(desired, area);
        if force || rect != current {
            return Some(rect);
        }
        None
    }

    fn resize_image(&self, source: &ImageSource, width: u32, height: u32) -> DynamicImage {
        match self {
            Self::Fit => source.image.resize(width, height, FilterType::Nearest),
            Self::Crop => source.image.crop_imm(0, 0, width, height),
        }
    }

    fn needs_resize_rect(&self, desired: Rect, area: Rect) -> Rect {
        match self {
            Self::Fit => {
                let (width, height) = resize_pixels(
                    desired.width,
                    desired.height,
                    min(area.width, desired.width),
                    min(area.height, desired.height),
                );
                Rect::new(0, 0, width, height)
            }
            Self::Crop => Rect::new(
                0,
                0,
                min(desired.width, area.width),
                min(desired.height, area.height),
            ),
        }
    }
}

/// Ripped from https://github.com/image-rs/image/blob/master/src/math/utils.rs#L12
/// Calculates the width and height an image should be resized to.
/// This preserves aspect ratio, and based on the `fill` parameter
/// will either fill the dimensions to fit inside the smaller constraint
/// (will overflow the specified bounds on one axis to preserve
/// aspect ratio), or will shrink so that both dimensions are
/// completely contained within the given `width` and `height`,
/// with empty space on one axis.
fn resize_pixels(width: u16, height: u16, nwidth: u16, nheight: u16) -> (u16, u16) {
    let wratio = nwidth as f64 / width as f64;
    let hratio = nheight as f64 / height as f64;

    let ratio = f64::min(wratio, hratio);

    let nw = max((width as f64 * ratio).round() as u64, 1);
    let nh = max((height as f64 * ratio).round() as u64, 1);

    if nw > u64::from(u16::MAX) {
        let ratio = u16::MAX as f64 / width as f64;
        (u16::MAX, max((height as f64 * ratio).round() as u16, 1))
    } else if nh > u64::from(u16::MAX) {
        let ratio = u16::MAX as f64 / height as f64;
        (max((width as f64 * ratio).round() as u16, 1), u16::MAX)
    } else {
        (nw as u16, nh as u16)
    }
}

#[cfg(test)]
mod tests {
    use image::{ImageBuffer, Rgb};

    use super::*;

    const FONT_SIZE: FontSize = (10, 10);

    fn s(w: u16, h: u16) -> ImageSource {
        let image: DynamicImage =
            ImageBuffer::from_pixel(w as _, h as _, Rgb::<u8>([255, 0, 0])).into();
        ImageSource::new(image, FONT_SIZE)
    }

    fn r(w: u16, h: u16) -> Rect {
        Rect::new(0, 0, w, h)
    }

    #[test]
    fn needs_resize_fit() {
        let resize = Resize::Fit;

        let to = resize.needs_resize(&s(100, 100), r(10, 10), r(10, 10), false);
        assert_eq!(None, to);

        let to = resize.needs_resize(&s(101, 101), r(10, 10), r(10, 10), false);
        assert_eq!(None, to);

        let to = resize.needs_resize(&s(80, 100), r(8, 10), r(10, 10), false);
        assert_eq!(None, to);

        let to = resize.needs_resize(&s(100, 100), r(99, 99), r(8, 10), false);
        assert_eq!(Some(r(8, 8)), to);

        let to = resize.needs_resize(&s(100, 100), r(99, 99), r(10, 8), false);
        assert_eq!(Some(r(8, 8)), to);

        let to = resize.needs_resize(&s(100, 50), r(99, 99), r(4, 4), false);
        assert_eq!(Some(r(4, 2)), to);

        let to = resize.needs_resize(&s(50, 100), r(99, 99), r(4, 4), false);
        assert_eq!(Some(r(2, 4)), to);

        let to = resize.needs_resize(&s(100, 100), r(8, 8), r(11, 11), false);
        assert_eq!(Some(r(10, 10)), to);

        let to = resize.needs_resize(&s(100, 100), r(10, 10), r(11, 11), false);
        assert_eq!(None, to);
    }

    #[test]
    fn needs_resize_crop() {
        let resize = Resize::Crop;

        let to = resize.needs_resize(&s(100, 100), r(10, 10), r(10, 10), false);
        assert_eq!(None, to);

        let to = resize.needs_resize(&s(80, 100), r(8, 10), r(10, 10), false);
        assert_eq!(None, to);

        let to = resize.needs_resize(&s(100, 100), r(10, 10), r(8, 10), false);
        assert_eq!(Some(r(8, 10)), to);

        let to = resize.needs_resize(&s(100, 100), r(10, 10), r(10, 8), false);
        assert_eq!(Some(r(10, 8)), to);
    }
}