mdbook/src/renderer/html_handlebars/helpers/navigation.rs

use std::path::Path;
use std::collections::BTreeMap;

use serde_json;
use handlebars::{Context, Handlebars, Helper, RenderContext, RenderError, Renderable};


// Handlebars helper for navigation

pub fn previous(_h: &Helper, r: &Handlebars, rc: &mut RenderContext) -> Result<(), RenderError> {
    debug!("[fn]: previous (handlebars helper)");

    debug!("[*]: Get data from context");
    let chapters = rc.evaluate_absolute("chapters").and_then(|c| {
        serde_json::value::from_value::<Vec<BTreeMap<String, String>>>(c.clone())
            .map_err(|_| RenderError::new("Could not decode the JSON data"))
    })?;

    let current = rc.evaluate_absolute("path")?
                    .as_str()
                    .ok_or_else(|| RenderError::new("Type error for `path`, string expected"))?
                    .replace("\"", "");

    let mut previous: Option<BTreeMap<String, String>> = None;

    debug!("[*]: Search for current Chapter");
    // Search for current chapter and return previous entry
    for item in chapters {
        match item.get("path") {
            Some(path) if !path.is_empty() => {
                if path == &current {
                    debug!("[*]: Found current chapter");
                    if let Some(previous) = previous {
                        debug!("[*]: Creating BTreeMap to inject in context");
                        // Create new BTreeMap to extend the context: 'title' and 'link'
                        let mut previous_chapter = BTreeMap::new();

                        // Chapter title
                        previous.get("name")
                                .ok_or_else(|| {
                                                RenderError::new("No title found for chapter in \
                                                                  JSON data")
                                            })
                                .and_then(|n| {
                                              previous_chapter.insert("title".to_owned(), json!(n));
                                              Ok(())
                                          })?;


                        // Chapter link
                        previous.get("path")
                                .ok_or_else(|| {
                                                RenderError::new("No path found for chapter in \
                                                                  JSON data")
                                            })
                                .and_then(|p| {
                            Path::new(p).with_extension("html")
                                        .to_str()
                                        .ok_or_else(|| {
                                                        RenderError::new("Link could not be \
                                                                          converted to str")
                                                    })
                                        .and_then(|p| {
                                previous_chapter
                                            .insert("link".to_owned(), json!(p.replace("\\", "/")));
                                Ok(())
                            })
                        })?;


                        debug!("[*]: Render template");
                        // Render template
                        _h.template()
                          .ok_or_else(|| RenderError::new("Error with the handlebars template"))
                          .and_then(|t| {
                            let mut local_rc = rc.with_context(Context::wraps(&previous_chapter)?);
                            t.render(r, &mut local_rc)
                        })?;
                    }
                    break;
                } else {
                    previous = Some(item.clone());
                }
            }
            _ => continue,
        }
    }

    Ok(())
}




pub fn next(_h: &Helper, r: &Handlebars, rc: &mut RenderContext) -> Result<(), RenderError> {
    debug!("[fn]: next (handlebars helper)");

    debug!("[*]: Get data from context");
    let chapters = rc.evaluate_absolute("chapters").and_then(|c| {
        serde_json::value::from_value::<Vec<BTreeMap<String, String>>>(c.clone())
            .map_err(|_| RenderError::new("Could not decode the JSON data"))
    })?;
    let current = rc.evaluate_absolute("path")?
                    .as_str()
                    .ok_or_else(|| RenderError::new("Type error for `path`, string expected"))?
                    .replace("\"", "");

    let mut previous: Option<BTreeMap<String, String>> = None;

    debug!("[*]: Search for current Chapter");
    // Search for current chapter and return previous entry
    for item in chapters {
        match item.get("path") {
            Some(path) if !path.is_empty() => {
                if let Some(previous) = previous {
                    let previous_path = previous.get("path").ok_or_else(|| {
                        RenderError::new("No path found for chapter in JSON data")
                    })?;

                    if previous_path == &current {
                        debug!("[*]: Found current chapter");
                        debug!("[*]: Creating BTreeMap to inject in context");
                        // Create new BTreeMap to extend the context: 'title' and 'link'
                        let mut next_chapter = BTreeMap::new();

                        item.get("name")
                            .ok_or_else(|| {
                                            RenderError::new("No title found for chapter in JSON \
                                                              data")
                                        })
                            .and_then(|n| {
                                          next_chapter.insert("title".to_owned(), json!(n));
                                          Ok(())
                                      })?;

                        Path::new(path).with_extension("html")
                                       .to_str()
                                       .ok_or_else(|| {
                                                       RenderError::new("Link could not converted \
                                                                         to str")
                                                   })
                                       .and_then(|l| {
                            debug!("[*]: Inserting link: {:?}", l);
                            // Hack for windows who tends to use `\` as separator instead of `/`
                            next_chapter.insert("link".to_owned(), json!(l.replace("\\", "/")));
                            Ok(())
                        })?;

                        debug!("[*]: Render template");

                        // Render template
                        _h.template()
                          .ok_or_else(|| RenderError::new("Error with the handlebars template"))
                          .and_then(|t| {
                            let mut local_rc = rc.with_context(Context::wraps(&next_chapter)?);
                            t.render(r, &mut local_rc)
                        })?;
                        break;
                    }
                }

                previous = Some(item.clone());
            }

            _ => continue,
        }
    }
    Ok(())
}