//! Provides the SVG template for rendering terminal output in a visual format.
//!
//! # Examples
//!
//! See [`Template`] for examples of usage.

use handlebars::{Handlebars, RenderError};
use serde::{Deserialize, Serialize};

use std::{fmt::Write as _, io::Write};

mod palette;

pub use self::palette::{NamedPalette, NamedPaletteParseError, Palette, TermColors};
pub use crate::utils::{RgbColor, RgbColorParseError};
use crate::{TermError, Transcript, UserInput};

const MAIN_TEMPLATE_NAME: &str = "main";
const TEMPLATE: &str = include_str!("default.svg.handlebars");

/// Configurable options of a [`Template`].
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TemplateOptions {
    /// Width of the rendered terminal window in pixels. The default value is `720`.
    pub width: usize,
    /// Palette of terminal colors. The default value of [`Palette`] is used by default.
    pub palette: Palette,
    /// Font family specification in the CSS format. Should be monospace.
    pub font_family: String,
    /// Indicates whether to display a window frame around the shell. Default value is `false`.
    pub window_frame: bool,
    /// Options for the scroll animation. If set to `None` (which is the default),
    /// no scrolling will be enabled, and the height of the generated image is not limited.
    pub scroll: Option<ScrollOptions>,
    /// Text wrapping options. The default value of [`WrapOptions`] is used by default.
    pub wrap: Option<WrapOptions>,
}

impl Default for TemplateOptions {
    fn default() -> Self {
        Self {
            width: 720,
            palette: Palette::default(),
            font_family: "SFMono-Regular, Consolas, Liberation Mono, Menlo, monospace".to_owned(),
            window_frame: false,
            scroll: None,
            wrap: Some(WrapOptions::default()),
        }
    }
}

/// Options that influence the scrolling animation.
///
/// The animation is only displayed if the console exceeds [`Self::max_height`]. In this case,
/// the console will be scrolled vertically with the interval of [`Self::interval`] seconds
/// between every frame. The view is moved 4 lines of text per scroll.
#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct ScrollOptions {
    /// Maximum height of the console, in pixels. The default value allows to fit 19 lines
    /// of text into the view (potentially, slightly less because of vertical margins around
    /// user inputs).
    pub max_height: usize,
    /// Interval between keyframes in seconds. The default value is `4`.
    pub interval: f32,
}

impl Default for ScrollOptions {
    fn default() -> Self {
        Self {
            max_height: Template::LINE_HEIGHT * 19,
            interval: 4.0,
        }
    }
}

/// Text wrapping options.
#[derive(Debug, Clone, Deserialize, Serialize)]
#[non_exhaustive]
pub enum WrapOptions {
    /// Perform a hard break at the specified width of output. The [`Default`] implementation
    /// returns this variant with width 80.
    HardBreakAt(usize),
}

impl Default for WrapOptions {
    fn default() -> Self {
        Self::HardBreakAt(80)
    }
}

/// Template for rendering [`Transcript`]s into an [SVG] image.
///
/// [SVG]: https://developer.mozilla.org/en-US/docs/Web/SVG
///
/// # Examples
///
/// ```
/// use term_transcript::{svg::*, Transcript, UserInput};
///
/// # fn main() -> anyhow::Result<()> {
/// let mut transcript = Transcript::new();
/// transcript.add_interaction(
///     UserInput::command("test"),
///     "Hello, \u{1b}[32mworld\u{1b}[0m!",
/// );
///
/// let template_options = TemplateOptions {
///     palette: NamedPalette::Dracula.into(),
///     ..TemplateOptions::default()
/// };
/// let mut buffer = vec![];
/// Template::new(template_options).render(&transcript, &mut buffer)?;
/// let buffer = String::from_utf8(buffer)?;
/// assert!(buffer.contains(r#"Hello, <span class="fg2">world</span>!"#));
/// # Ok(())
/// # }
/// ```
#[derive(Debug)]
pub struct Template {
    options: TemplateOptions,
    handlebars: Handlebars<'static>,
}

impl Default for Template {
    fn default() -> Self {
        Self::new(TemplateOptions::default())
    }
}

impl Template {
    /// Bottom margin for each input or output block.
    const BLOCK_MARGIN: usize = 6;
    /// Additional padding for each user input block.
    const USER_INPUT_PADDING: usize = 4;
    /// Padding within the rendered terminal window in pixels.
    const WINDOW_PADDING: usize = 10;
    /// Line height in pixels.
    const LINE_HEIGHT: usize = 18;
    /// Height of the window frame.
    const WINDOW_FRAME_HEIGHT: usize = 22;
    /// Pixels scrolled vertically per each animation frame.
    const PIXELS_PER_SCROLL: usize = Self::LINE_HEIGHT * 4;
    /// Right offset of the scrollbar relative to the right border of the frame.
    const SCROLLBAR_RIGHT_OFFSET: usize = 7;
    /// Height of the scrollbar in pixels.
    const SCROLLBAR_HEIGHT: usize = 40;

    /// Initializes the template based on provided `options`.
    pub fn new(options: TemplateOptions) -> Self {
        let mut handlebars = Handlebars::new();
        handlebars.set_strict_mode(true);
        handlebars
            .register_template_string(MAIN_TEMPLATE_NAME, TEMPLATE)
            .expect("Default template should be valid");

        Self {
            options,
            handlebars,
        }
    }

    /// Renders the `transcript` as an SVG image.
    ///
    /// # Errors
    ///
    /// Returns a Handlebars rendering error, if any. Normally, the only errors could be
    /// related to I/O (e.g., the image cannot be written to a file).
    pub fn render<W: Write>(
        &self,
        transcript: &Transcript,
        destination: W,
    ) -> Result<(), RenderError> {
        let rendered_outputs = self
            .render_outputs(transcript)
            .map_err(|err| RenderError::from_error("content", err))?;

        let content_height = Self::compute_content_height(transcript, &rendered_outputs);
        let scroll_animation = self.scroll_animation(content_height);
        let screen_height = if scroll_animation.is_some() {
            self.options
                .scroll
                .as_ref()
                .map_or(content_height, |scroll| scroll.max_height)
        } else {
            content_height
        };

        let mut height = screen_height + 2 * Self::WINDOW_PADDING;
        if self.options.window_frame {
            height += Self::WINDOW_FRAME_HEIGHT;
        }

        let data = HandlebarsData {
            creator: CreatorData::default(),
            height,
            content_height,
            screen_height,
            interactions: transcript
                .interactions()
                .iter()
                .zip(rendered_outputs)
                .map(|(interaction, output_html)| SerializedInteraction {
                    input: interaction.input(),
                    output_html,
                })
                .collect(),
            options: &self.options,
            scroll_animation,
        };

        self.handlebars
            .render_to_write(MAIN_TEMPLATE_NAME, &data, destination)
    }

    fn render_outputs(&self, transcript: &Transcript) -> Result<Vec<String>, TermError> {
        let max_width = self
            .options
            .wrap
            .as_ref()
            .map(|wrap_options| match wrap_options {
                WrapOptions::HardBreakAt(width) => *width,
            });

        transcript
            .interactions
            .iter()
            .map(|interaction| {
                let output = interaction.output();
                let mut buffer = String::with_capacity(output.as_ref().len());
                output.write_as_html(&mut buffer, max_width)?;
                Ok(buffer)
            })
            .collect()
    }

    fn compute_content_height(transcript: &Transcript, rendered_outputs: &[String]) -> usize {
        let line_count: usize = transcript
            .interactions
            .iter()
            .zip(rendered_outputs)
            .map(|(interaction, output_html)| {
                Self::count_lines_in_input(interaction.input().as_ref())
                    + Self::count_lines_in_output(output_html)
            })
            .sum();
        let margin_count = transcript
            .interactions
            .iter()
            .map(|interaction| {
                if interaction.output().as_ref().is_empty() {
                    1
                } else {
                    2
                }
            })
            .sum::<usize>()
            .saturating_sub(1); // The last margin is not displayed.
        line_count * Self::LINE_HEIGHT
            + margin_count * Self::BLOCK_MARGIN
            + transcript.interactions.len() * Self::USER_INPUT_PADDING
    }

    fn count_lines_in_input(input_str: &str) -> usize {
        let mut input_lines = bytecount::count(input_str.as_bytes(), b'\n');
        if !input_str.is_empty() && !input_str.ends_with('\n') {
            input_lines += 1;
        }
        input_lines
    }

    fn count_lines_in_output(output_html: &str) -> usize {
        let mut output_lines =
            bytecount::count(output_html.as_bytes(), b'\n') + output_html.matches("<br/>").count();

        if !output_html.is_empty() && !output_html.ends_with('\n') {
            output_lines += 1;
        }
        output_lines
    }

    #[allow(clippy::cast_precision_loss)] // no loss with sane amount of `steps`
    fn scroll_animation(&self, content_height: usize) -> Option<ScrollAnimationConfig> {
        fn div_ceil(x: usize, y: usize) -> usize {
            (x + y - 1) / y
        }

        let scroll_options = self.options.scroll.as_ref()?;
        let max_height = scroll_options.max_height;
        let max_offset = content_height.checked_sub(max_height)?;
        let steps = div_ceil(max_offset, Self::PIXELS_PER_SCROLL);
        debug_assert!(steps > 0);

        let mut view_box = (0..=steps).fold(String::new(), |mut acc, i| {
            let y = (Self::PIXELS_PER_SCROLL as f32 * i as f32).round();
            write!(
                &mut acc,
                "0 {y} {width} {height};",
                y = y,
                width = self.options.width,
                height = max_height
            )
            .unwrap(); // safe; writing to a string is infallible
            acc
        });
        view_box.pop(); // trim the last ';'

        let y_step = (max_height - Self::SCROLLBAR_HEIGHT) as f32 / steps as f32;
        let mut scrollbar_y = (0..=steps).fold(String::new(), |mut acc, i| {
            let y = (y_step * i as f32).round();
            write!(&mut acc, "0 {};", y).unwrap();
            acc
        });
        scrollbar_y.pop(); // trim the last ';'

        Some(ScrollAnimationConfig {
            duration: scroll_options.interval * steps as f32,
            view_box,
            scrollbar_x: self.options.width - Self::SCROLLBAR_RIGHT_OFFSET,
            scrollbar_y,
        })
    }
}

/// Root data structure sent to the Handlebars template.
#[derive(Debug, Serialize)]
struct HandlebarsData<'r> {
    creator: CreatorData,
    height: usize,
    screen_height: usize,
    content_height: usize,
    interactions: Vec<SerializedInteraction<'r>>,
    #[serde(flatten)]
    options: &'r TemplateOptions,
    scroll_animation: Option<ScrollAnimationConfig>,
}

#[derive(Debug, Serialize)]
struct CreatorData {
    name: &'static str,
    version: &'static str,
    repo: &'static str,
}

impl Default for CreatorData {
    fn default() -> Self {
        Self {
            name: env!("CARGO_PKG_NAME"),
            version: env!("CARGO_PKG_VERSION"),
            repo: env!("CARGO_PKG_REPOSITORY"),
        }
    }
}

#[derive(Debug, Serialize)]
struct SerializedInteraction<'a> {
    input: &'a UserInput,
    output_html: String,
}

#[derive(Debug, Serialize)]
struct ScrollAnimationConfig {
    duration: f32,
    view_box: String,
    scrollbar_x: usize,
    scrollbar_y: String,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn rendering_simple_transcript() {
        let mut transcript = Transcript::new();
        transcript.add_interaction(
            UserInput::command("test"),
            "Hello, \u{1b}[32mworld\u{1b}[0m!",
        );

        let mut buffer = vec![];
        Template::new(TemplateOptions::default())
            .render(&transcript, &mut buffer)
            .unwrap();
        let buffer = String::from_utf8(buffer).unwrap();
        assert!(buffer.contains(r#"Hello, <span class="fg2">world</span>!"#));
        assert!(!buffer.contains("<circle"));
    }

    #[test]
    fn rendering_transcript_with_frame() {
        let mut transcript = Transcript::new();
        transcript.add_interaction(
            UserInput::command("test"),
            "Hello, \u{1b}[32mworld\u{1b}[0m!",
        );

        let mut buffer = vec![];
        let options = TemplateOptions {
            window_frame: true,
            ..TemplateOptions::default()
        };
        Template::new(options)
            .render(&transcript, &mut buffer)
            .unwrap();
        let buffer = String::from_utf8(buffer).unwrap();
        assert!(buffer.contains("<circle"));
    }

    #[test]
    fn rendering_transcript_with_animation() {
        let mut transcript = Transcript::new();
        transcript.add_interaction(
            UserInput::command("test"),
            "Hello, \u{1b}[32mworld\u{1b}[0m!\n".repeat(22),
        );

        let mut buffer = vec![];
        let options = TemplateOptions {
            scroll: Some(ScrollOptions {
                max_height: 240,
                interval: 3.0,
            }),
            ..TemplateOptions::default()
        };
        Template::new(options)
            .render(&transcript, &mut buffer)
            .unwrap();
        let buffer = String::from_utf8(buffer).unwrap();

        assert!(buffer.contains(r#"viewBox="0 0 720 260""#), "{}", buffer);
        assert!(buffer.contains("<animateTransform"), "{}", buffer);
    }

    #[test]
    fn rendering_transcript_with_wraps() {
        let mut transcript = Transcript::new();
        transcript.add_interaction(
            UserInput::command("test"),
            "Hello, \u{1b}[32mworld\u{1b}[0m!",
        );

        let mut buffer = vec![];
        let options = TemplateOptions {
            wrap: Some(WrapOptions::HardBreakAt(5)),
            ..TemplateOptions::default()
        };
        Template::new(options)
            .render(&transcript, &mut buffer)
            .unwrap();
        let buffer = String::from_utf8(buffer).unwrap();

        assert!(buffer.contains(r#"viewBox="0 0 720 102""#), "{}", buffer);
        assert!(buffer.contains("<br/>"), "{}", buffer);
    }
}