libwebnovel-storage 0.3.2

#![deny(
    rustdoc::broken_intra_doc_links,
    rustdoc::private_intra_doc_links,
    rustdoc::bare_urls,
    missing_docs
)]
#![warn(rustdoc::unescaped_backticks)]
//! [![Crates.io Version](https://img.shields.io/crates/v/libwebnovel-storage)](https://crates.io/crates/libwebnovel-storage)
//! [![docs.rs](https://img.shields.io/docsrs/libwebnovel-storage)](https://docs.rs/libwebnovel-storage)
//!
//! This is an implementation of a local repository of webnovels. It downloads
//! webnovels & places them in a coherent manner on the filesystem. It is also
//! capable of generating ebooks from these downloaded webnovels.
//!
//! ## What this does
//!
//! Basically, it provides data structures and method easing the work of
//! implementing a program using [`libwebnovel`](https://crates.io/crates/libwebnovel). Said program would only have to make the "glue" between UI and this library's functions.
//!
//! ## Example
//!
//! ```rust,no_run
//! use libwebnovel_storage::{LibraryError, LocalLibrary};
//! fn main() -> Result<(), LibraryError> {
//!     let library_path = ".config/my_library/config.toml";
//!     let mut library = LocalLibrary::load(library_path)?;
//!     // Add to watchlist & download
//!     library.add("https://www.royalroad.com/fiction/21220/mother-of-learning")?;
//!
//!     // update all novels
//!     let errors = library.update();
//!     // or, if you want to have more control over the update process
//!     // (for instance, printing a progress bar):
//!     for novel in library.novels_mut() {
//!         let novel_title = novel.title()?.clone();
//!         for (i, result) in novel.update_iter().enumerate() {
//!             if result.is_err() {
//!                 eprintln!(
//!                     "Encountered an error while updating novel {}: {}",
//!                     novel_title,
//!                     result.unwrap_err()
//!                 );
//!             }
//!             println!("novel {}: updated chapter {}", novel_title, i + 1);
//!         }
//!         #[cfg(feature = "epub")]
//!         println!(
//!             "Generated ebook path: {}",
//!             novel.generate_epub().unwrap().display()
//!         );
//!     }
//!
//!     Ok(())
//! }
//! ```
//!
//! # `cargo` features
//!
//! By default, the `epub` feature is active. If you do not wish to use this
//! feature, use the following in your `Cargo.toml`:
//!
//! ```toml
//! # Cargo.toml
//! [dependencies.libwebnovel-storage]
//! version = '0'
//! default-features = false
//! ```
//!
//! # TODO
//!
//! - [x] a local filesystem representation for a novel library
//! - [x] bulk updates
//!   - [x] bulk updates with an iterator, to offer control over looping and get
//!     update information while they happen
//! - [x] add epub generation
//!
//! ## Legal
//!
//! Without explicit refutation in the header of any file in this repository,
//! all files in this repository are considered under the terms of the AGPL-3
//! license (of which a copy can be found in the LICENSE file at the root of
//! this repository) and bearing the mention "Copyright (c) 2024 paulollivier &
//! contributors".
//!
//! Basically, please do not use this code without crediting its writer(s) or
//! for a commercial project.

use std::fmt::{format, Debug, Formatter};
use std::fs;
use std::fs::{create_dir_all, File};
use std::io::{Cursor, Read, Write};
use std::path::{Path, PathBuf};

use directories::BaseDirs;
#[cfg(feature = "epub")]
use epub_builder::{EpubBuilder, Error, ZipLibrary};
use fs_extra::dir::{move_dir, CopyOptions};
#[cfg(feature = "epub")]
use image::EncodableLayout;
use image::{ImageError, ImageFormat};
use libwebnovel::backends::BackendError;
use libwebnovel::{Backend, Backends, Chapter, ChapterParseError};
use log::{debug, error, info, trace, warn};
use serde::{Deserialize, Serialize};
use thiserror::Error;
use url::Url;

/// Represents an error that can happen during Library operations
#[derive(Error, Debug)]
pub enum LibraryError {
    /// Wraps a [`std::io::Error`]
    #[error(transparent)]
    IoError(#[from] std::io::Error),
    /// Wraps a [`toml::de::Error`]
    #[error(transparent)]
    TomlDeserializationError(#[from] toml::de::Error),
    /// Wraps a [`toml::ser::Error`]
    #[error(transparent)]
    TomlSerializationError(#[from] toml::ser::Error),
    /// Wraps an [`url::ParseError`]
    #[error(transparent)]
    UrlParseError(#[from] url::ParseError),
    /// Wraps a [`ChapterParseError`]
    #[error(transparent)]
    ChapterParseError(#[from] ChapterParseError),
    /// Wraps a [`BackendError`]
    #[error(transparent)]
    BackendError(#[from] BackendError),
    /// Wraps a [`ImageError`]
    #[error(transparent)]
    ImageError(#[from] ImageError),
    /// Needed for accepting convert error with ?.
    #[error(transparent)]
    Infallible(#[from] std::convert::Infallible),
    /// Wraps an error from fs_extra
    #[error(transparent)]
    FsError(#[from] fs_extra::error::Error),
    /// Returned when attempting to delete a fiction
    #[error("No novel with URL \"{0}\"was found.")]
    NoSuchNovel(Url),
    /// A generic error encountered when parsing something
    #[error("{0}")]
    ParseError(String),
    /// Returned when trying to add a novel that is already watched
    #[error("Novel at url {0} is already in our watchlist")]
    NovelAlreadyPresent(Url),
}

/// A local disk storage.
/// ```rust
/// use tempfile::tempdir;
/// use libwebnovel_storage::LocalLibrary;
///
/// // Dummy path to a config file. If the path does not exist, a default configuration will be created
/// let config_path = "path/to/toml_config";
/// # let tempdir = tempdir().unwrap();
/// # let config_path = tempdir.path().join(env!("CARGO_PKG_NAME"));
///
/// let mut library = LocalLibrary::load(config_path).unwrap();
/// // Add & download a given URL
/// library
///     .add("https://www.royalroad.com/fiction/21220/mother-of-learning")
///     .unwrap();
/// let novel_urls_list = library.list();
/// assert_eq!(novel_urls_list.len(), 1);
/// assert_eq!(
///     &novel_urls_list[0].to_string(),
///     "https://www.royalroad.com/fiction/21220/mother-of-learning"
/// );
/// ```
#[derive(Serialize, Deserialize, Debug)]
pub struct LocalLibrary {
    #[serde(skip)]
    config_path: PathBuf,
    library_base_path: PathBuf,
    novels: Vec<Novel>,
}

impl Default for LocalLibrary {
    fn default() -> Self {
        let dirs = BaseDirs::new().unwrap();
        Self {
            config_path: dirs.config_dir().join(env!("CARGO_PKG_NAME")).to_path_buf(),
            library_base_path: dirs.data_dir().join(env!("CARGO_PKG_NAME")),
            novels: Vec::new(),
        }
    }
}

impl LocalLibrary {
    /// Attempts to create a new [`Self`] from a config file.
    /// ```rust
    /// use directories::BaseDirs;
    /// use libwebnovel_storage::LocalLibrary;
    ///
    /// let config_path = "path/to/config.toml";
    /// let library = LocalLibrary::load(config_path).unwrap(); // If the path doesn't exist, a
    ///                                                         // default configuration will be
    ///                                                         // loaded
    /// // Get the default data directory on this platform
    /// let basedirs = BaseDirs::new().unwrap();
    /// let data_dir = basedirs.data_dir().join(env!["CARGO_PKG_NAME"]);
    /// assert_eq!(library.base_path(), data_dir);
    /// ```
    pub fn load(config_path: impl Into<PathBuf>) -> Result<Self, LibraryError> {
        let config_path = config_path.into();
        if !config_path.exists() {
            info!("Could not find a configuration file, creating one with default values.");
            return Ok(Self {
                config_path,
                ..Default::default()
            });
        }
        let mut config_file = File::open(&config_path)?;
        let mut config_str = String::new();
        config_file.read_to_string(&mut config_str)?;
        let mut config: Self = toml::from_str(&config_str)?;
        config.config_path = config_path;
        Ok(config)
    }

    /// Changes the library base data path, moving existing content if
    /// necessary.
    pub fn set_base_path(
        &mut self,
        base_path: impl Into<PathBuf> + AsRef<Path>,
    ) -> Result<(), LibraryError> {
        if self.library_base_path.is_dir() {
            // Then we need to move the content of the directory to the new one given in
            // parameter
            create_dir_all(&base_path)?;
            move_dir(
                &self.library_base_path,
                &base_path,
                &CopyOptions {
                    overwrite: true,
                    ..CopyOptions::default()
                },
            )?;
        }
        self.library_base_path = base_path.into();
        for novel in self.novels.iter_mut() {
            novel.path = self
                .library_base_path
                .join(novel.backend.immutable_identifier()?);
        }
        self.persist()?;
        Ok(())
    }

    /// Saves the current config to disk.
    /// ```rust
    /// use std::path::Path;
    ///
    /// use libwebnovel_storage::LocalLibrary;
    ///
    /// let config_path_str = "/tmp/libwebnovel/config.toml";
    /// let config_path = Path::new(config_path_str);
    /// # use tempfile::tempdir;
    /// # let tempdir = tempdir().unwrap();
    /// # let config_path_str = tempdir.path().join(env!("CARGO_PKG_NAME")).join("config.toml");
    /// let library = LocalLibrary::load(config_path_str.clone()).unwrap();
    ///
    /// let config_path = Path::new(&config_path_str);
    /// assert!(!config_path.exists());
    /// library.persist().unwrap();
    /// # println!("config_path: {:?}", config_path.display());
    /// # println!("library: {:?}", library);
    /// assert!(config_path.exists());
    /// ```
    pub fn persist(&self) -> Result<(), LibraryError> {
        info!("Saving file to disk at path {}", self.config_path.display());
        let toml = toml::to_string(self)?;
        create_dir_all(self.config_path.parent().unwrap())?;
        let mut file = File::create(&self.config_path)?;
        file.write_all(toml.as_bytes())?;
        Ok(())
    }

    /// Returns the base path of the library storage
    pub fn base_path(&self) -> &Path {
        self.library_base_path.as_path()
    }

    /// Adds a new webnovel to watch. Won't call [`self.update()`]. Returns the
    /// title of the novel.
    pub fn add(&mut self, url: &str) -> Result<String, LibraryError> {
        let url = url.parse::<Url>()?;
        if self.novels.iter().any(|n| n.url == url) {
            return Err(LibraryError::NovelAlreadyPresent(url));
        }
        let novel = Novel::new(url, self.base_path())?;
        let novel_title = novel.title()?;
        self.novels.push(novel);
        self.persist()?;
        Ok(novel_title)
    }

    /// Returns a list of webnovels currently watched
    pub fn list(&self) -> Vec<Url> {
        self.novels.iter().map(|novel| novel.url.clone()).collect()
    }

    /// Updates all watched novels. If at least one error has been encountered
    /// during update.
    pub fn update(&mut self) -> Result<(), Vec<LibraryError>> {
        let mut errors = Vec::new();
        for novel in self.novels.iter_mut() {
            match novel.update() {
                Ok(()) => {}
                Err(e) => {
                    errors.push(e);
                }
            }
        }
        if !errors.is_empty() {
            return Err(errors);
        }
        Ok(())
    }

    /// Removes a webnovel from the watchlist and deletes local content. If
    /// there are duplicates in the novels list, only the first found will be
    /// removed and deleted.
    pub fn remove(&mut self, url: &str) -> Result<(), LibraryError> {
        let url = Url::parse(url)?;
        self.novels.retain(|novel| {
            if novel.url == url {
                let path = novel.novel_path();
                if let Err(e) = fs::remove_dir_all(path) {
                    warn!("Failed to remove directory {}: {}", path.display(), e);
                }
                return false;
            }
            true
        });
        Ok(())
    }

    /// Returns a reference to the internal novels vector.
    pub fn novels(&self) -> &Vec<Novel> {
        &self.novels
    }

    /// Returns a mutable reference to the internal novels vector
    pub fn novels_mut(&mut self) -> &mut Vec<Novel> {
        &mut self.novels
    }
}

/// Represents a novel.
/// Stored on disk at the following path: <base_library_path>/<novel.title()>/
///
/// TODO: Detect remote novel title changes
#[derive(Serialize, Deserialize)]
#[serde(try_from = "NovelConfig", into = "NovelConfig")]
pub struct Novel {
    url: Url,
    path: PathBuf,
    backend: Backends,
    chapters: Vec<Chapter>,
}

impl Debug for Novel {
    #[allow(dead_code)]
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        #[derive(Debug)]
        struct Novel<'a> {
            url: String,
            path: &'a PathBuf,
            backend: &'a Backends,
            chapters: &'a Vec<Chapter>,
        }
        let Self {
            url,
            path,
            backend,
            chapters,
        } = self;
        Debug::fmt(
            &Novel {
                url: url.to_string(),
                path,
                backend,
                chapters,
            },
            f,
        )
    }
}

impl Clone for Novel {
    fn clone(&self) -> Self {
        Self {
            url: self.url.clone(),
            path: self.path.clone(),
            backend: Backends::new(self.url.as_ref()).unwrap(),
            chapters: self.chapters.clone(),
        }
    }
}

/// An iterator over the update operation of a chapter. Used to be able to
/// monitor progress from your code.
///
/// ```rust
/// # use std::thread::sleep;
/// use std::time::Duration;
///
/// use libwebnovel_storage::{LibraryError, Novel};
/// use tempfile::tempdir;
/// use url::Url;
/// let path = "random/path";
/// # let dir = tempdir().unwrap();
/// # let path = dir.path();
/// let mut novel = Novel::new(
///     "https://www.royalroad.com/fiction/21220/mother-of-learning"
///         .parse::<Url>()
///         .unwrap(),
///     path,
/// )
/// .unwrap();
/// for (i, chapter_result) in novel.update_iter().enumerate() {
///     sleep(Duration::from_micros(500)); // throttleing requests
///     match chapter_result {
///         Ok(_chapter_title) => {
///             println!(":) Chapter update succeded!")
///         }
///         Err(e) => {
///             println!(":'( chapter update failed: {e}")
///         }
///     }
/// }
/// assert_eq!(novel.get_local_chapter_count().unwrap(), 109);
/// ```
pub struct NovelChapterUpdateIter<'a> {
    novel: &'a mut Novel,
    missing_chapters: Vec<usize>,
    current_chapter_index: usize,
}
impl Debug for NovelChapterUpdateIter<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "NovelChapterUpdateIter {}/{}:\n  Chapter_Index={},\n  Novel={},\n  base_dir={}",
            self.current_chapter_index,
            self.missing_chapters.len(),
            if self.current_chapter_index >= self.missing_chapters.len() {
                "Out of bounds (may be normal if end of iter)".to_string()
            } else {
                self.missing_chapters[self.current_chapter_index].to_string()
            },
            self.novel.url,
            self.novel.path.display(),
        )
    }
}

impl<'a> Iterator for NovelChapterUpdateIter<'a> {
    type Item = Result<String, LibraryError>;

    fn next(&mut self) -> Option<Self::Item> {
        trace!("{:?}", self);
        if self.current_chapter_index >= self.missing_chapters.len() {
            return None;
        }
        let r = match self
            .novel
            .backend
            .get_chapter(self.missing_chapters[self.current_chapter_index])
        {
            Ok(v) => match Novel::persist_chapter(&self.novel.path, &v) {
                Ok(_) => {
                    let title = v.title().clone().unwrap();
                    self.novel.chapters.push(v);
                    Some(Ok(title))
                }
                Err(e) => Some(Err(e)),
            },
            Err(e) => Some(Err(LibraryError::from(e))),
        };
        self.current_chapter_index += 1;
        r
    }
}

impl<'a> ExactSizeIterator for NovelChapterUpdateIter<'a> {
    fn len(&self) -> usize {
        self.missing_chapters.len()
    }
}

impl Novel {
    /// Returns a new Novel from the given URL. Functionally equivalent to
    /// [`Novel::try_from(Url)`].
    pub fn new(url: impl Into<Url>, library_path: &Path) -> Result<Self, LibraryError> {
        let url = url.into();
        let mut novel = Self {
            url: url.clone(),
            path: Default::default(),
            backend: Backends::new(url.as_ref())?,
            chapters: vec![],
        };
        novel.path = library_path.join(novel.backend.immutable_identifier()?);
        Ok(novel)
    }

    /// Returns the url of the novel
    pub fn url(&self) -> &Url {
        &self.url
    }

    /// Returns the title of the novel
    pub fn title(&self) -> Result<String, LibraryError> {
        Ok(self.backend.title()?)
    }

    /// returns where all the chapters are stored. static alternative to
    /// [`self.chapter_storage_path()`].
    pub fn get_chapter_storage_path(novel_path: &Path) -> PathBuf {
        novel_path.join("chapters")
    }

    /// returns where the cover image is stored. static alternative to
    /// [`self.cover_storage_path`].
    pub fn get_cover_storage_path(novel_path: &Path) -> PathBuf {
        novel_path.join("cover.png")
    }

    /// Returns where all the chapters are stored. Alternative to the static
    /// [`Self::get_chapter_storage_path`].
    pub fn chapter_storage_path(&self) -> PathBuf {
        Self::get_chapter_storage_path(&self.path)
    }

    /// Returns where the cover image is stored. Alternative to the static
    /// [`Self::get_cover_storage_path`].
    pub fn cover_storage_path(&self) -> PathBuf {
        Self::get_cover_storage_path(&self.path)
    }

    fn persist_chapter(novel_path: &Path, chapter: &Chapter) -> Result<(), LibraryError> {
        let path = Self::get_chapter_storage_path(novel_path);
        if !path.exists() {
            create_dir_all(&path)?;
        }
        let chapter_file_name = match chapter.title() {
            None => {
                format!("{}.html", chapter.index())
            }
            Some(title) => {
                format!("{}-{}.html", chapter.index(), title)
            }
        };
        let chapter_path = path.join(chapter_file_name);
        let mut file = File::create(chapter_path)?;
        file.write_all(chapter.to_string().as_bytes())?;
        Ok(())
    }

    /// Downloads the cover file and places it in [`self.cover_image_path`],
    /// performing appropriate image format conversions if necessary.
    pub fn download_cover(&self) -> Result<(), LibraryError> {
        let cover_path = self.path.join("cover.png");
        if !cover_path.is_file() {
            if !self.path.exists() {
                create_dir_all(&self.path)?;
            } else if cover_path.is_dir() {
                warn!(
                    "{} is a directory! we will delete it in order to create the cover file",
                    cover_path.display()
                );
                // There's no sense it being a directory. let's delete this shit.
                fs::remove_dir_all(&cover_path)?;
            }
            let cover_data = self.backend.cover()?;
            let data = match image::guess_format(&cover_data) {
                Ok(format) => match format {
                    ImageFormat::Png => cover_data,
                    iformat => {
                        info!(
                            "Cover image is in {}. Converting to png.",
                            iformat.extensions_str()[0]
                        );
                        let cursor = Cursor::new(cover_data);
                        let img = image::load(cursor, iformat)?;
                        let mut buffer = Vec::new();
                        img.write_to(&mut Cursor::new(&mut buffer), ImageFormat::Png)?;
                        buffer
                    }
                },
                Err(e) => {
                    // Then, attempt to guess from the URL filename?
                    // for now, let's just return the data.
                    warn!("Error trying to guess image: {}", e);
                    cover_data
                }
            };
            let mut f = File::create(cover_path)?;
            f.write_all(&data)?;
        }
        Ok(())
    }

    /// Fetch remote chapters & saves them locally. Will attempt to fix
    /// duplicates, ordering, and detect collisions.
    pub fn update(&mut self) -> Result<(), LibraryError> {
        self.load_local_chapters()?;

        // TODO: check errors, not only print them. For instance, if the source is a
        //       http 429 or equivalent, it may be worthwhile to retry.
        let _errors = self
            .update_iter()
            .filter(Result::is_err)
            .map(|r| {
                let err = r.unwrap_err();
                warn!("{}", err);
                err
            })
            .collect::<Vec<_>>();
        self.consolidate_chapter_collection();
        // TODO: Check for remaining duplicates/index collisions
        // Write all chapters to disk
        for chapter in &self.chapters {
            Self::persist_chapter(&self.path, chapter)?;
        }
        Ok(())
    }

    /// Sorts, dedups and tries to fix chapter indexes in the current "live"
    /// chapter list.
    pub fn consolidate_chapter_collection(&mut self) {
        // …sort them…
        self.chapters.sort_by(self.backend.get_ordering_function());
        // … and remove duplicates. There should not be any.
        self.chapters.dedup();
        // update the indexes accordingly, as it may happen when some chapters have been
        // deleted from the source.
        for (i, chapter) in self.chapters.iter_mut().enumerate() {
            // enumerate is 0-indexed so we must add 1 :p
            let chapter_index = i + 1;
            if *chapter.index() != chapter_index {
                warn!("There could be a conflict in chapter {}: index was expected to be {} but was {}. Setting chapter index to expectation",
                    chapter.title().clone().unwrap_or("<title_not_found>".to_string()),
                    chapter_index,
                    chapter.index()
                );
                chapter.set_index(chapter_index);
            }
        }
    }

    /// Returns an iterator that will fetch the chapters, returning a Result for
    /// each operation. See [`NovelChapterUpdateIter::next`] for more info.
    /// Will not attempt to handle duplicates & other stuff.
    ///
    /// # Panics
    ///
    /// Panics when:
    /// - [`self.get_missing_chapters_indexes`] panics
    pub fn update_iter(&mut self) -> NovelChapterUpdateIter {
        let missing_chapters = self.get_missing_chapters_indexes().unwrap();
        debug!("Missing chapters: {:?}", missing_chapters);

        NovelChapterUpdateIter {
            novel: self,
            missing_chapters,
            current_chapter_index: 0,
        }
    }

    /// Returns chapter indexes that are present in the source but not locally.
    pub fn get_missing_chapters_indexes(&self) -> Result<Vec<usize>, LibraryError> {
        // Get the local chapters
        let local_chapters_tuples: Vec<(usize, String)> = self
            .get_local_chapters()?
            .iter()
            .map(|c| c.try_into().unwrap())
            .collect();
        debug!("local chapters: {:?}", local_chapters_tuples);
        // then get the list of chapters from the backend
        let available_chapters = self.backend.get_chapter_list()?;
        debug!("available chapters: {:?}", available_chapters);
        // Extract a list of all chapters present on the source but not locally
        Ok(available_chapters
            .iter()
            .filter(|c| {
                for lc in &local_chapters_tuples {
                    if c.0 == lc.0 {
                        // That means we have an index match, let's check the
                        // title match.
                        if c.1 == lc.1 {
                            // they are the same, no need to download this one.
                            return false;
                        }
                        // if we are here, it means we have the same index but
                        // the title differs. Tomfoolery is afoot.
                        warn!("distant chapter {:?} and local chapter {:?} have the same index but different titles! I won't download them.", c, lc);
                        return false;
                    }
                }
                // if they don't have the same index, consider them missing
                debug!("Will download chapter {}: {}", c.0, c.1);
                true
            })
            .map(|c| c.0)
            .collect::<Vec<_>>())
    }

    /// Returns the count of locally-saved chapters
    pub fn get_local_chapter_count(&self) -> Result<usize, LibraryError> {
        let path = self.chapter_storage_path();
        if !path.exists() {
            return Ok(0);
        }
        // count the number of chapters in self.novel_dir()
        Ok(fs::read_dir(path)?.count())
    }

    /// returns the total count of remote chapters
    pub fn get_remote_chapter_count(&self) -> Result<usize, LibraryError> {
        Ok(self.backend.get_chapter_count()?)
    }

    /// Loads local chapters and saves them in `self.chapters`. Overrides any
    /// currently loaded chapters.
    pub fn load_local_chapters(&mut self) -> Result<(), LibraryError> {
        self.chapters = self.get_local_chapters()?;
        Ok(())
    }

    /// Returns a vector of all local [`Chapter`].
    pub fn get_local_chapters(&self) -> Result<Vec<Chapter>, LibraryError> {
        let path = self.chapter_storage_path();
        if !path.exists() {
            debug!(
                "path {} doesn't exist, returning empty local chapter list",
                path.display()
            );
            return Ok(Vec::new());
        }
        let mut chapters: Vec<Chapter> = Vec::new();
        trace!("Reading directory {} contents", path.display());
        let chapter_files = fs::read_dir(&path)?;
        for chapter_file in chapter_files {
            let chapter_file = chapter_file?;
            let chapter_path = chapter_file.path();
            trace!("looking at file {}", chapter_path.display());
            let mut file = File::open(&chapter_path)?;
            let mut content = String::new();
            file.read_to_string(&mut content)?;
            trace!("Parsing chapter from file {}", chapter_path.display());
            let chapter = content.parse()?;
            chapters.push(chapter);
        }
        Ok(chapters)
    }

    /// Returns the root path of where this novel stores its files.
    pub fn novel_path(&self) -> &Path {
        &self.path
    }

    /// Generates an epub from this novel and its currently loaded chapters,
    /// returning the path it has been saved to.
    #[cfg(feature = "epub")]
    pub fn generate_epub(&self) -> Result<PathBuf, EpubGenerationError> {
        const TITLE_PAGE_HTML: &str = r#"
        <html>
            <head>
                <style>

                </style>
            </head>
            <body style="width: 30em; margin: auto; text-align: center;">
                <h1>FICTION_TITLE</h1>
                <p><img src="/cover.png"/></p>
            </body>
        </html>
        "#;
        let mut builder =
            EpubBuilder::new(ZipLibrary::new()?).map_err(|e| EpubGenerationError::EpubError {
                msg: "Could not create new builder".to_string(),
                cause: e,
            })?;
        builder
            .metadata("title", self.title()?)
            .map_err(|e| EpubGenerationError::EpubError {
                msg: "Could not set title".to_string(),
                cause: e,
            })?
            .metadata("author", self.backend.get_authors()?.join(", "))
            .map_err(|e| EpubGenerationError::EpubError {
                msg: "could not set author metadata".to_string(),
                cause: e,
            })?
            .epub_version(epub_builder::EpubVersion::V30);
        builder.add_content(
            epub_builder::EpubContent::new(
                "cover.xhtml",
                TITLE_PAGE_HTML
                    .replace("FICTION_TITLE", &self.title().unwrap())
                    .as_bytes(),
            )
            .reftype(epub_builder::ReferenceType::Cover),
        )?;
        let cover_path = self.cover_storage_path();
        if !cover_path.is_file() {
            self.download_cover()?;
        }
        let mut f = File::open(cover_path)?;
        let mut data = Vec::new();
        f.read_to_end(&mut data)?;
        builder.add_cover_image("cover.png", data.as_bytes(), "image/png")?;
        drop(data);
        for chapter in &self.chapters {
            let title = chapter.title().clone().unwrap();
            builder.add_content(
                epub_builder::EpubContent::new(
                    format!("{}.xhtml", title),
                    chapter.content().as_bytes(),
                )
                .title(format!("ch{}: {}", chapter.index(), title))
                .reftype(epub_builder::ReferenceType::Text),
            )?;
        }
        builder.inline_toc();
        let epub_path = self.novel_path().join(format!("{}.epub3", self.title()?));
        let mut f = File::create(&epub_path)?;
        builder.generate(&mut f)?;
        Ok(epub_path)
    }
}

/// An error on epub generation
#[cfg(feature = "epub")]
#[derive(Error, Debug)]
pub enum EpubGenerationError {
    /// Returned when an error related to library management occured
    #[error(transparent)]
    LibraryError(#[from] LibraryError),
    /// Returned when an error related to epub generation occured
    #[error("{msg}: {cause:?}")]
    EpubError {
        /// A human message describing the issue
        msg: String,
        /// The underlying error
        cause: epub_builder::Error,
    },
    /// Returned when a filesystem-related error occurs
    #[error("{msg}: {cause:?}")]
    IoError {
        /// A human message describing the issue
        msg: String,
        /// The underlying error
        cause: std::io::Error,
    },
}

#[cfg(feature = "epub")]
impl From<epub_builder::Error> for EpubGenerationError {
    fn from(value: Error) -> Self {
        Self::EpubError {
            msg: String::new(),
            cause: value,
        }
    }
}
#[cfg(feature = "epub")]
impl From<BackendError> for EpubGenerationError {
    fn from(value: BackendError) -> Self {
        EpubGenerationError::LibraryError(LibraryError::BackendError(value))
    }
}
#[cfg(feature = "epub")]
impl From<std::io::Error> for EpubGenerationError {
    fn from(value: std::io::Error) -> Self {
        Self::IoError {
            msg: value.to_string(),
            cause: value,
        }
    }
}

impl TryFrom<Url> for Novel {
    type Error = LibraryError;

    /// WARNING: returns an uninitialized Novel.path!
    fn try_from(value: Url) -> Result<Self, Self::Error> {
        Self::try_from(NovelConfig {
            url: value,
            path: Default::default(),
        })
    }
}

impl TryFrom<NovelConfig> for Novel {
    type Error = LibraryError;

    fn try_from(value: NovelConfig) -> Result<Self, Self::Error> {
        let novel = Self {
            url: value.url.clone(),
            path: value.path.clone(),
            backend: Backends::new(value.url.as_str())?,
            chapters: vec![],
        };
        Ok(novel)
    }
}

/// A type not destined to be used directly, but rather by serde.
#[derive(Serialize, Deserialize, Clone, Debug)]
struct NovelConfig {
    url: Url,
    path: PathBuf,
}

impl From<Novel> for NovelConfig {
    fn from(value: Novel) -> Self {
        Self {
            url: value.url,
            path: value.path,
        }
    }
}