use std::{
    fs,
    io,
    iter,
    path,
    collections::BTreeMap,
};

use crate::{
    input,
    folders,
    manage::Specification,
};

use anyhow::Context;

use sanitise_file_name::sanitise;

struct Playlist<'a> {
    root: &'a path::Path,
    files: BTreeMap<chrono::NaiveDateTime, Vec<m3u::Entry>>,
}

impl<'a> Playlist<'a> {
    fn new(root: &'a path::Path) -> Self {
        Self {
            root,
            files: BTreeMap::new(),
        }
    }

    /// Writes the playlist file based on the specified filename.
    ///
    /// Output boolean indicates if the playlist was written (if it was
    /// different from the existing file)
    fn write_as(
        &self,
        name: &str,
        reverse: bool,
    ) -> anyhow::Result<bool> {
        let playlists_folder = self.root.join(folders::LOCAL_PLAYLISTS_DIR);
        if !playlists_folder.exists() {
            fs::create_dir(&playlists_folder)
                .context(format!("failed to create output directory for playlists"))?;
        }
        let mut path = playlists_folder.join(sanitise(name));
        path.set_extension("m3u");

        let mut output = io::BufWriter::new(Vec::new());
        let mut writer = m3u::Writer::new(&mut output);
        let entries =
            self
            .files
            .values()
            .map(|entries| entries.iter())
            .flatten();

        if reverse {
            for entry in entries.rev() {
                writer.write_entry(entry)?;
            }
        } else {
            for entry in entries {
                writer.write_entry(entry)?;
            }
        };

        drop(writer);
        let output = output.into_inner()?;
        if fs::read(&path)? != output {
            fs::write(path, output.as_slice())?;
            Ok(true)
        } else {
            Ok(false)
        }

    }
    
    fn insert(
        &mut self,
        published: chrono::NaiveDateTime,
        absolute_path: &path::Path,
    ) {
        let entry = m3u::path_entry({
            let relative = absolute_path.strip_prefix(
                &self.root.join(folders::LOCAL_PODCASTS_DIR)
            ).unwrap();
            path::Path::new(folders::IPOD_PODCASTS_DIR).join(relative)
        });

        match self.files.get_mut(&published) {
            Some(existing) => {
                existing.push(entry)
            },
            None => {
                self.files.insert(
                    published,
                    vec![entry]
                );
            }
        }
    }
}

pub(crate) fn generate_master_m3u(
    config: &input::Config,
    root: &path::Path,
) -> anyhow::Result<()> {
    let mut playlist = Playlist::new(root);

    for (podcast, _) in &config.podcasts {
        let output = folders::podcast_folder(root, podcast.as_str());
        let spec_file = output.join(folders::SPEC_FILE);
        let spec = Specification::read_from(&spec_file)?;

        let (feed, files) = spec.into_feed_and_files();

        for (published, episodes) in feed {
            for episode in episodes {
                let path = output.join(
                    files.get(episode.id()).unwrap()
                );

                playlist.insert(
                    published,
                    &path
                )
            }
        }
    }

    if playlist.write_as(folders::MASTER_PLAYLIST_PATH, true)? {
        println!("[info] generated master playlist");
    }

    Ok(())
}


pub(crate) fn generate_podcast_m3u(
    alias: &str,
    root: &path::Path,
    unlistened_only: bool,
) -> anyhow::Result<()> {
    let mut playlist = Playlist::new(root);

    let output = folders::podcast_folder(root, alias);
    let spec_file = output.join(folders::SPEC_FILE);
    let spec = Specification::read_from(&spec_file)?;

    let episodes =
        spec
        .feed_iter()
        .map(|(published, eps)|
            iter::repeat(published).zip(eps.iter())
        )
        .flatten()
        .filter(|episode|
            !unlistened_only || (unlistened_only && !episode.1.listened)
        );

    for (published, episode) in episodes {
        let path = output.join(
            spec.path_from_id(episode.id()).unwrap()
        );
        playlist.insert(
            published.clone(),
            &path,
        );
    }

    let written = if unlistened_only {
        playlist.write_as(&format!("[PC] {} (unlistened)", alias), false)
    } else {
        playlist.write_as(&format!("[PC] {}", alias), false)
    }?;

    if written {
        println!("[info] generated playlist for podcast {:?}.", alias);
    }

    Ok(())
}