//! Render diagram markup in a Pandoc AST into SVG
//!
//! Process a Pandoc abstract syntax tree and convert fenced code
//! blocks with diagram markup into embedded SVG images. Supported
//! diagram markup languages:
//!
//! - [pikchr](https://pikchr.org/home/doc/trunk/homepage.md)
//! - [Graphviz dot](https://graphviz.org/doc/info/lang.html)
//! - [PlantUML](https://plantuml.com/)
//! - [roadmap](https://gitlab.com/larswirzenius/roadmap)
//! - [raw SVG](https://en.wikipedia.org/wiki/Scalable_Vector_Graphics)
//!
//! The Pandoc AST has represents input as `Block` and other types of
//! nodes. This crate turns `Block::CodeBlock` nodes that carry a
//! class attribute that specifies one of the supported diagram markup
//! languages into blocks with embedded SVG graphics.
//!
//! Note that this library does not do any parsing. The
//! `pandoc_ast::filter` function does that.

use pandoc_ast::{Block, Inline, MutVisitor, Pandoc};
use std::env;
use std::ffi::OsString;
use std::io::{Read, Write};
use std::path::{Path, PathBuf};
use std::process::{Command, Stdio};

/// Represent the diagram filter.
#[derive(Debug)]
pub struct DiagramFilter {
    dot: PathBuf,
    roadmap_width: usize,
    java_path: PathBuf,
    plantuml_jar: PathBuf,
}

/// Possible errors for diagram filtering.
#[derive(Debug, thiserror::Error)]
pub enum DiagramError {
    /// When rendering a pikchr, something went wrong.
    #[error("failure rendering pikchr diagram: {0}")]
    PikchrRenderError(String),

    /// When rendering a roadmap, something went wrong.
    #[error("failure rendering roadmap diagram: {0}")]
    Roadmap(#[from] roadmap::RoadmapError),

    /// Failed to invoke a program.
    ///
    /// This Pandoc filter uses some helper programs to do some of its
    /// work. It failed to invoke such a helper program.
    #[error("failed to invoke helper program {0} (as {1}): {2}")]
    InvokeFailed(String, PathBuf, String),

    /// A helper program failed
    ///
    /// The filter uses some helper programs to implement some of its
    /// functionality, for example the GraphViz dot program. This
    /// error means that the helper program failed (exit code was not
    /// zero).
    ///
    /// This probably implies there's something wrong in the filter.
    /// Please report this error.
    #[error("helper program failed: {0} (as {1}): {2}")]
    HelperFailed(String, PathBuf, String, String),

    /// I/O error
    ///
    /// The filter did some I/O, and it failed. This is a generic
    /// wrapper for any kind of I/O error.
    #[error(transparent)]
    IoError(#[from] std::io::Error),
}

type Svg = Vec<u8>;

impl Default for DiagramFilter {
    fn default() -> Self {
        Self {
            dot: PathBuf::from("dot"),
            roadmap_width: 50,
            java_path: PathBuf::from("java"),
            plantuml_jar: PathBuf::from("/usr/share/plantuml/plantuml.jar"),
        }
    }
}

impl DiagramFilter {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn dot_path<P>(&mut self, path: P) -> &mut Self
    where
        P: AsRef<Path>,
    {
        self.dot = path.as_ref().to_path_buf();
        self
    }

    pub fn java_path<P>(&mut self, path: P) -> &mut Self
    where
        P: AsRef<Path>,
    {
        self.java_path = path.as_ref().to_path_buf();
        self
    }

    pub fn plantuml_jar<P>(&mut self, path: P) -> &mut Self
    where
        P: AsRef<Path>,
    {
        self.plantuml_jar = path.as_ref().to_path_buf();
        self
    }

    pub fn roadmap_width(&mut self, w: usize) -> &mut Self {
        self.roadmap_width = w;
        self
    }

    pub fn filter(&mut self, mut doc: Pandoc) -> Pandoc {
        self.walk_pandoc(&mut doc);
        doc
    }

    fn error_block(&self, error: DiagramError) -> Block {
        let msg = Inline::Str(format!("ERROR: {}", error.to_string()));
        let msg = vec![Inline::Strong(vec![msg])];
        Block::Para(msg)
    }

    fn svg_block(&self, svg: &[u8]) -> Block {
        let url = self.svg_as_data_url(svg);
        let attr = ("".to_string(), vec![], vec![]);
        let img = Inline::Image(attr, vec![], (url, "".to_string()));
        Block::Para(vec![img])
    }

    fn svg_as_data_url(&self, svg: &[u8]) -> String {
        let svg = base64::encode(&svg);
        format!("data:image/svg+xml;base64,{}", svg)
    }

    fn pikchr_to_svg(&self, markup: &str, _class: Option<&str>) -> Result<Svg, DiagramError> {
        let mut flags = pikchr::PikchrFlags::default();
        flags.generate_plain_errors();
        let image =
            pikchr::Pikchr::render(markup, None, flags).map_err(DiagramError::PikchrRenderError)?;
        Ok(image.as_bytes().to_vec())
    }

    fn dot_to_svg(&self, markup: &str) -> Result<Svg, DiagramError> {
        filter_via(markup, "dot", &self.dot, &["-Tsvg"], None)
    }

    fn roadmap_to_svg(&self, markup: &str) -> Result<Svg, DiagramError> {
        match roadmap::from_yaml(markup) {
            Ok(ref mut roadmap) => {
                roadmap.set_missing_statuses();
                match roadmap.format_as_dot(self.roadmap_width) {
                    Ok(dot) => self.dot_to_svg(&dot),
                    Err(e) => Err(DiagramError::Roadmap(e)),
                }
            }
            Err(err) => Err(DiagramError::Roadmap(err)),
        }
    }

    fn plantuml_to_svg(&self, markup: &str) -> Result<Svg, DiagramError> {
        let args = &[
            "-Djava.awt.headless=true",
            "-jar",
            self.plantuml_jar.to_str().unwrap(),
            "--",
            "-pipe",
            "-tsvg",
            "-v",
            "-graphvizdot",
            self.dot.to_str().unwrap(),
        ];
        filter_via(markup, "java", &self.java_path, args, build_java_path())
    }
}

// If JAVA_HOME is set, and PATH is set, then:
// Check if JAVA_HOME/bin is in PATH, if not, prepend it and return a new
// PATH
fn build_java_path() -> Option<OsString> {
    let java_home = env::var_os("JAVA_HOME")?;
    let cur_path = env::var_os("PATH")?;
    let cur_path: Vec<_> = env::split_paths(&cur_path).collect();
    let java_home = PathBuf::from(java_home);
    let java_bin = java_home.join("bin");
    if cur_path.iter().any(|v| v.as_os_str() == java_bin) {
        // No need to add JAVA_HOME/bin it's already on-path
        return None;
    }
    env::join_paths(Some(java_bin).iter().chain(cur_path.iter())).ok()
}

fn filter_via(
    markup: &str,
    name: &str,
    argv0: &Path,
    args: &[&str],
    cmdpath: Option<OsString>,
) -> Result<Svg, DiagramError> {
    // Start program without waiting for it to finish.
    let mut cmd = Command::new(argv0);
    cmd.args(args)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped());
    if let Some(p) = cmdpath {
        cmd.env("PATH", p);
    }
    let mut child = cmd.spawn()?;

    if let Some(stdin) = child.stdin.as_mut() {
        stdin.write_all(markup.as_bytes())?;
        let output = child.wait_with_output()?;
        if output.status.success() {
            Ok(output.stdout)
        } else {
            let status = if let Some(code) = output.status.code() {
                format!("{}", code)
            } else {
                String::from("terminated by signal")
            };
            let stderr = String::from_utf8_lossy(&output.stderr);
            Err(DiagramError::HelperFailed(
                name.to_string(),
                argv0.to_path_buf(),
                status,
                stderr.into_owned(),
            ))
        }
    } else {
        // Something went wrong when we invoked the program. Read stderr.
        let mut error_message = vec![];
        if let Some(mut stderr) = child.stderr {
            stderr.read_to_end(&mut error_message)?;
        }
        Err(DiagramError::InvokeFailed(
            name.to_string(),
            argv0.to_path_buf(),
            String::from_utf8_lossy(&error_message).into_owned(),
        ))
    }
}

impl MutVisitor for DiagramFilter {
    fn visit_block(&mut self, block: &mut Block) {
        match block {
            Block::CodeBlock((_id, classes, _kv), text) => match DiagramKind::from(classes) {
                DiagramKind::GraphvizDot => match self.dot_to_svg(text) {
                    Err(err) => *block = self.error_block(err),
                    Ok(svg) => *block = self.svg_block(&svg),
                },
                DiagramKind::Roadmap => match self.roadmap_to_svg(text) {
                    Err(err) => *block = self.error_block(err),
                    Ok(svg) => *block = self.svg_block(&svg),
                },
                DiagramKind::Plantuml => match self.plantuml_to_svg(text) {
                    Err(err) => *block = self.error_block(err),
                    Ok(svg) => *block = self.svg_block(&svg),
                },
                DiagramKind::Pikchr => match self.pikchr_to_svg(text, None) {
                    Err(err) => *block = self.error_block(err),
                    Ok(svg) => *block = self.svg_block(&svg),
                },
                DiagramKind::Svg => *block = self.svg_block(text.as_bytes()),
                DiagramKind::Other => (),
            },
            _ => {
                self.walk_block(block);
            }
        }
    }
}

enum DiagramKind {
    GraphvizDot,
    Pikchr,
    Plantuml,
    Roadmap,
    Svg,
    Other,
}

impl DiagramKind {
    fn from(classes: &[String]) -> Self {
        if has_class(classes, "pikchr") {
            Self::Pikchr
        } else if has_class(classes, "dot") {
            Self::GraphvizDot
        } else if has_class(classes, "roadmap") {
            Self::Roadmap
        } else if has_class(classes, "plantuml") {
            Self::Plantuml
        } else if has_class(classes, "svg") {
            Self::Svg
        } else {
            Self::Other
        }
    }
}

fn has_class(classes: &[String], wanted: &str) -> bool {
    classes.iter().any(|s| s == wanted)
}