//! Rendering the *body* of a node: markdown for text nodes, previews for file
//! nodes, the target of link nodes.

use std::collections::HashMap;
use std::path::{Path, PathBuf};

use eframe::egui::{self, Align, Layout, RichText, Ui};

use crate::markdown;
use crate::model::{Node, NodeKind, file_name};
use crate::theme::Palette;

/// Files larger than this are not previewed as text.
const MAX_PREVIEW_BYTES: usize = 64 * 1024;

/// What a file node points at.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum FileKind {
    Image,
    Text,
    Other,
}

pub fn file_kind(path: &str) -> FileKind {
    let ext = Path::new(path)
        .extension()
        .map(|e| e.to_string_lossy().to_ascii_lowercase())
        .unwrap_or_default();
    match ext.as_str() {
        "png" | "jpg" | "jpeg" | "gif" | "bmp" | "webp" | "ico" | "tiff" => FileKind::Image,
        "md" | "markdown" | "txt" | "text" | "canvas" | "json" | "toml" | "yaml" | "yml"
        | "csv" | "log" | "rs" | "py" | "js" | "ts" | "html" | "css" | "sh" => FileKind::Text,
        _ => FileKind::Other,
    }
}

/// Cache for the text previews of file nodes, so the disk is not hit per frame.
#[derive(Default)]
pub struct PreviewCache {
    text: HashMap<PathBuf, Result<String, String>>,
}

impl PreviewCache {
    pub fn clear(&mut self) {
        self.text.clear();
    }

    fn text_preview(&mut self, path: &Path) -> &Result<String, String> {
        self.text.entry(path.to_path_buf()).or_insert_with(|| {
            match std::fs::read(path) {
                Ok(bytes) => {
                    let truncated = bytes.len() > MAX_PREVIEW_BYTES;
                    let head = &bytes[..bytes.len().min(MAX_PREVIEW_BYTES)];
                    let mut text = String::from_utf8_lossy(head).into_owned();
                    if truncated {
                        text.push_str("\n\n…");
                    }
                    Ok(text)
                }
                Err(err) => Err(format!("{err}")),
            }
        })
    }
}

/// Resolves a node path against the folder the canvas lives in.
pub fn resolve_path(base_dir: Option<&Path>, raw: &str) -> PathBuf {
    let path = Path::new(raw);
    match base_dir {
        Some(base) if path.is_relative() => base.join(path),
        _ => path.to_path_buf(),
    }
}

/// A `file://` URI for egui's image loader.
///
/// On Windows the loader wants the `file:///C:/dir/file.png` form: without the
/// third slash it reads the drive letter as a UNC host name. It does not
/// percent-decode, so nothing here is escaped.
pub fn file_uri(path: &Path) -> String {
    let text = path.to_string_lossy().replace('\\', "/");
    if cfg!(windows) {
        format!("file:///{}", text.trim_start_matches('/'))
    } else {
        format!("file://{text}")
    }
}

/// Everything the body renderer needs from the outside world.
pub struct BodyContext<'a> {
    pub palette: &'a Palette,
    pub base_dir: Option<&'a Path>,
    pub cache: &'a mut PreviewCache,
    /// Current canvas scale, used to skip detail when zoomed far out.
    pub scale: f32,
}

/// Draws the contents of `node` inside `ui`, returning a link/file the user
/// activated by clicking.
pub fn render_body(ui: &mut Ui, node: &Node, ctx: &mut BodyContext<'_>) -> Option<String> {
    match &node.kind {
        NodeKind::Text { text } => render_text(ui, text, ctx),
        NodeKind::File { file, subpath } => render_file(ui, file, subpath.as_deref(), ctx),
        NodeKind::Link { url } => render_link(ui, url, ctx),
        NodeKind::Group { .. } => None,
        NodeKind::Unknown { type_name } => {
            ui.label(
                RichText::new(format!("Unsupported node type “{type_name}”"))
                    .size(13.0)
                    .color(ctx.palette.text_muted)
                    .italics(),
            );
            ui.label(
                RichText::new("Its data is preserved when the file is saved.")
                    .size(11.0)
                    .color(ctx.palette.text_muted),
            );
            None
        }
    }
}

fn render_text(ui: &mut Ui, text: &str, ctx: &mut BodyContext<'_>) -> Option<String> {
    if text.trim().is_empty() {
        ui.label(
            RichText::new("Empty note")
                .size(13.0)
                .italics()
                .color(ctx.palette.text_muted),
        );
        return None;
    }
    let blocks = markdown::parse(text);
    markdown::render(ui, &blocks, ctx.palette, 14.0)
}

fn render_file(
    ui: &mut Ui,
    file: &str,
    subpath: Option<&str>,
    ctx: &mut BodyContext<'_>,
) -> Option<String> {
    let palette = ctx.palette;
    let path = resolve_path(ctx.base_dir, file);
    let kind = file_kind(file);
    let mut activated = None;

    // Header: the file name, plus the subpath when the node points inside a file.
    ui.horizontal(|ui| {
        ui.spacing_mut().item_spacing.x = 4.0;
        let icon = match kind {
            FileKind::Image => "IMG",
            FileKind::Text => "DOC",
            FileKind::Other => "FILE",
        };
        ui.label(RichText::new(icon).size(10.0).color(palette.text_muted));
        if ui
            .link(
                RichText::new(file_name(file))
                    .size(13.0)
                    .strong()
                    .color(palette.text),
            )
            .on_hover_text(path.display().to_string())
            .clicked()
        {
            activated = Some(file.to_owned());
        }
        if let Some(subpath) = subpath {
            ui.label(
                RichText::new(subpath)
                    .size(12.0)
                    .color(palette.text_muted),
            );
        }
    });

    if ctx.scale < 0.4 {
        return activated;
    }

    if !path.exists() {
        ui.add_space(4.0);
        ui.label(
            RichText::new("File not found")
                .size(12.0)
                .italics()
                .color(palette.danger),
        );
        return activated;
    }

    ui.add_space(4.0);
    match kind {
        FileKind::Image => {
            ui.add(
                egui::Image::new(file_uri(&path))
                    .maintain_aspect_ratio(true)
                    .fit_to_exact_size(ui.available_size())
                    .corner_radius(4.0),
            );
        }
        FileKind::Text => match ctx.cache.text_preview(&path) {
            Ok(text) => {
                let excerpt = excerpt_for(text, subpath);
                let blocks = markdown::parse(&excerpt);
                if let Some(link) = markdown::render(ui, &blocks, palette, 13.0) {
                    activated = Some(link);
                }
            }
            Err(err) => {
                ui.label(
                    RichText::new(format!("Could not read the file: {err}"))
                        .size(12.0)
                        .color(palette.danger),
                );
            }
        },
        FileKind::Other => {
            ui.label(
                RichText::new("No preview available")
                    .size(12.0)
                    .italics()
                    .color(palette.text_muted),
            );
        }
    }
    activated
}

/// The part of a text file a file node shows: the whole file, or the section a
/// `subpath` (`#heading`) points at.
fn excerpt_for(text: &str, subpath: Option<&str>) -> String {
    let Some(heading) = subpath.and_then(|s| s.strip_prefix('#')) else {
        return text.to_owned();
    };
    let heading = heading.trim().to_ascii_lowercase();
    let mut out = Vec::new();
    let mut level = 0usize;
    for line in text.lines() {
        let hashes = line.chars().take_while(|c| *c == '#').count();
        let is_heading = (1..=6).contains(&hashes) && line[hashes..].starts_with(' ');
        if level == 0 {
            if is_heading && line[hashes..].trim().to_ascii_lowercase() == heading {
                level = hashes;
                out.push(line.to_owned());
            }
        } else {
            if is_heading && hashes <= level {
                break;
            }
            out.push(line.to_owned());
        }
    }
    if out.is_empty() {
        format!("*Section “{heading}” not found*")
    } else {
        out.join("\n")
    }
}

fn render_link(ui: &mut Ui, url: &str, ctx: &mut BodyContext<'_>) -> Option<String> {
    let palette = ctx.palette;
    let mut activated = None;
    ui.with_layout(Layout::top_down(Align::Min), |ui| {
        ui.horizontal(|ui| {
            ui.spacing_mut().item_spacing.x = 4.0;
            ui.label(RichText::new("URL").size(10.0).color(palette.text_muted));
            ui.label(
                RichText::new(host_of(url))
                    .size(13.0)
                    .strong()
                    .color(palette.text),
            );
        });
        ui.add_space(2.0);
        if ui
            .link(RichText::new(url).size(12.0).color(palette.accent))
            .on_hover_text("Open in the default browser")
            .clicked()
        {
            activated = Some(url.to_owned());
        }
    });
    activated
}

/// The host part of a URL, for the link node header.
fn host_of(url: &str) -> &str {
    let rest = url
        .split_once("://")
        .map(|(_, rest)| rest)
        .unwrap_or(url);
    let host = rest.split(['/', '?', '#']).next().unwrap_or(rest);
    if host.is_empty() { url } else { host }
}

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

    #[test]
    fn recognises_file_kinds() {
        assert_eq!(file_kind("a/b/photo.PNG"), FileKind::Image);
        assert_eq!(file_kind("notes.md"), FileKind::Text);
        assert_eq!(file_kind("archive.zip"), FileKind::Other);
        assert_eq!(file_kind("no-extension"), FileKind::Other);
    }

    #[test]
    fn resolves_relative_paths_against_the_canvas_folder() {
        let base = Path::new("/vault/boards");
        assert_eq!(
            resolve_path(Some(base), "notes/a.md"),
            PathBuf::from("/vault/boards/notes/a.md")
        );
        // Absolute paths are left alone.
        let absolute = if cfg!(windows) { "C:\\tmp\\a.md" } else { "/tmp/a.md" };
        assert_eq!(
            resolve_path(Some(base), absolute),
            PathBuf::from(absolute)
        );
    }

    #[test]
    fn a_subpath_selects_one_section() {
        let text = "# One\nalpha\n\n## Two\nbeta\n\n# Three\ngamma";
        assert_eq!(excerpt_for(text, Some("#Two")), "## Two\nbeta\n");
        assert!(excerpt_for(text, Some("#Missing")).contains("not found"));
        assert_eq!(excerpt_for(text, None), text);
    }

    #[test]
    fn image_uris_use_the_form_the_loader_expects() {
        let uri = file_uri(Path::new(if cfg!(windows) {
            "C:\\vault\\a b.png"
        } else {
            "/vault/a b.png"
        }));
        if cfg!(windows) {
            assert_eq!(uri, "file:///C:/vault/a b.png");
        } else {
            assert_eq!(uri, "file:///vault/a b.png");
        }
    }

    #[test]
    fn shows_the_host_of_a_link() {
        assert_eq!(host_of("https://jsoncanvas.org/spec/1.0/"), "jsoncanvas.org");
        assert_eq!(host_of("example.com"), "example.com");
    }
}