mod delta;
mod io_ext;
pub mod manager;
mod path;
mod state;

use delta::Delta;
pub use manager::Manager;
pub use manager::ManagerConfig;
pub use manager::MetaManager;
pub use state::State;

use chrono::Utc;
use flate2::read::GzDecoder;
use flate2::write::GzEncoder;
use flate2::Compression;
use path::PathExt;
use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::fmt;
use std::fs::File;
use std::io;
use std::path::{Path, PathBuf};

const BYTE_SUFFIXES: [&str; 5] = ["B", "KiB", "MiB", "GiB", "TiB"];

#[derive(Debug, PartialEq, Serialize, Deserialize)]
pub enum BackupType {
    Full,
    Incremental,
}

/// Represents a successful backup
#[derive(Serialize, Deserialize, Debug)]
pub struct Backup<T: Clone> {
    /// When the backup was started (also corresponds to the name)
    pub start_time: chrono::DateTime<Utc>,
    /// When the backup finished
    pub end_time: chrono::DateTime<Utc>,
    pub size: usize,
    /// Type of the backup
    pub type_: BackupType,
    pub delta: Delta,
    /// Additional metadata that can be associated with a given backup
    pub metadata: Option<T>,
}

impl Backup<()> {
    pub const FILENAME_FORMAT: &str = "%Y-%m-%d_%H-%M-%S.tar.gz";

    /// Return the path to a backup file by properly formatting the data.
    pub fn path<P: AsRef<Path>>(backup_dir: P, start_time: chrono::DateTime<Utc>) -> PathBuf {
        let backup_dir = backup_dir.as_ref();

        let filename = format!("{}", start_time.format(Self::FILENAME_FORMAT));
        backup_dir.join(filename)
    }

    /// Extract an archive.
    ///
    /// # Arguments
    ///
    /// * `backup_path` - Path to the archive to extract
    /// * `dirs` - list of tuples `(path_in_tar, dst_dir)` with `dst_dir` the directory on-disk
    ///     where the files stored under `path_in_tar` inside the tarball should be extracted to.
    pub fn extract_archive<P: AsRef<Path>>(
        archive_path: P,
        dirs: &Vec<(PathBuf, PathBuf)>,
    ) -> io::Result<()> {
        let tar_gz = File::open(archive_path)?;
        let enc = GzDecoder::new(tar_gz);
        let mut ar = tar::Archive::new(enc);

        // Unpack each file by matching it with one of the destination directories and extracting
        // it to the right path
        for entry in ar.entries()? {
            let mut entry = entry?;
            let entry_path_in_tar = entry.path()?.to_path_buf();

            for (path_in_tar, dst_dir) in dirs {
                if entry_path_in_tar.starts_with(path_in_tar) {
                    let dst_path =
                        dst_dir.join(entry_path_in_tar.strip_prefix(path_in_tar).unwrap());

                    // Ensure all parent directories are present
                    std::fs::create_dir_all(dst_path.parent().unwrap())?;

                    entry.unpack(dst_path)?;

                    break;
                }
            }
        }

        Ok(())
    }
}

impl<T: Clone> Backup<T> {
    /// Set the backup's metadata.
    pub fn set_metadata(&mut self, metadata: T) {
        self.metadata = Some(metadata);
    }

    /// Create a new Full backup, populated with the given directories.
    ///
    /// # Arguments
    ///
    /// * `backup_dir` - Directory to store archive in
    /// * `dirs` - list of tuples `(path_in_tar, src_dir)` with `path_in_tar` the directory name
    ///     under which `src_dir`'s contents should be stored in the archive
    ///
    /// # Returns
    ///
    /// The `Backup` instance describing this new backup.
    pub fn create<P: AsRef<Path>>(
        backup_dir: P,
        dirs: &Vec<(PathBuf, PathBuf)>,
    ) -> io::Result<Self> {
        let start_time = chrono::offset::Utc::now();

        let path = Backup::path(backup_dir, start_time);
        let tar_gz = io_ext::CountingWrite::new(File::create(path)?);
        let enc = GzEncoder::new(tar_gz, Compression::default());
        let mut ar = tar::Builder::new(enc);

        let mut delta = Delta::new();

        for (dir_in_tar, src_dir) in dirs {
            let mut added_files: HashSet<PathBuf> = HashSet::new();

            for entry in src_dir.read_dir_recursive()?.ignored("cache").files() {
                let path = entry?.path();
                let stripped = path.strip_prefix(src_dir).unwrap();

                ar.append_path_with_name(&path, dir_in_tar.join(stripped))?;
                added_files.insert(stripped.to_path_buf());
            }

            delta.added.insert(dir_in_tar.to_path_buf(), added_files);
        }

        let mut enc = ar.into_inner()?;

        // The docs recommend running try_finish before unwrapping using finish
        enc.try_finish()?;
        let tar_gz = enc.finish()?;

        Ok(Backup {
            type_: BackupType::Full,
            start_time,
            end_time: chrono::Utc::now(),
            size: tar_gz.bytes_written(),
            delta,
            metadata: None,
        })
    }

    /// Create a new Incremental backup from the given state, populated with the given directories.
    ///
    /// # Arguments
    ///
    /// * `previous_state` - State the file system was in during the previous backup in the chain
    /// * `previous_start_time` - Start time of the previous backup; used to filter files
    /// * `backup_dir` - Directory to store archive in
    /// * `dirs` - list of tuples `(path_in_tar, src_dir)` with `path_in_tar` the directory name
    ///     under which `src_dir`'s contents should be stored in the archive
    ///
    /// # Returns
    ///
    /// The `Backup` instance describing this new backup.
    pub fn create_from<P: AsRef<Path>>(
        previous_state: State,
        previous_start_time: chrono::DateTime<Utc>,
        backup_dir: P,
        dirs: &Vec<(PathBuf, PathBuf)>,
    ) -> io::Result<Self> {
        let start_time = chrono::offset::Utc::now();

        let path = Backup::path(backup_dir, start_time);
        let tar_gz = io_ext::CountingWrite::new(File::create(path)?);
        let enc = GzEncoder::new(tar_gz, Compression::default());
        let mut ar = tar::Builder::new(enc);

        let mut delta = Delta::new();

        for (dir_in_tar, src_dir) in dirs {
            let mut all_files: HashSet<PathBuf> = HashSet::new();
            let mut added_files: HashSet<PathBuf> = HashSet::new();

            for entry in src_dir.read_dir_recursive()?.ignored("cache").files() {
                let path = entry?.path();
                let stripped = path.strip_prefix(src_dir).unwrap();

                if !path.not_modified_since(previous_start_time) {
                    ar.append_path_with_name(&path, dir_in_tar.join(stripped))?;
                    added_files.insert(stripped.to_path_buf());
                }

                all_files.insert(stripped.to_path_buf());
            }

            delta.added.insert(dir_in_tar.clone(), added_files);

            if let Some(previous_files) = previous_state.get(dir_in_tar) {
                delta.removed.insert(
                    dir_in_tar.to_path_buf(),
                    previous_files.difference(&all_files).cloned().collect(),
                );
            }
        }

        let mut enc = ar.into_inner()?;

        // The docs recommend running try_finish before unwrapping using finish
        enc.try_finish()?;
        let tar_gz = enc.finish()?;

        Ok(Backup {
            type_: BackupType::Incremental,
            start_time,
            end_time: chrono::Utc::now(),
            size: tar_gz.bytes_written(),
            delta,
            metadata: None,
        })
    }

    /// Restore the backup by extracting its contents to the respective directories.
    ///
    /// # Arguments
    ///
    /// * `backup_dir` - Backup directory where the file is stored
    /// * `dirs` - list of tuples `(path_in_tar, dst_dir)` with `dst_dir` the directory on-disk
    ///     where the files stored under `path_in_tar` inside the tarball should be extracted to.
    pub fn restore<P: AsRef<Path>>(
        &self,
        backup_dir: P,
        dirs: &Vec<(PathBuf, PathBuf)>,
    ) -> io::Result<()> {
        let backup_path = Backup::path(backup_dir, self.start_time);
        Backup::extract_archive(backup_path, dirs)?;

        // Remove any files
        for (path_in_tar, dst_dir) in dirs {
            if let Some(removed) = self.delta.removed.get(path_in_tar) {
                for path in removed {
                    let dst_path = dst_dir.join(path);
                    std::fs::remove_file(dst_path)?;
                }
            }
        }

        Ok(())
    }

    pub fn open<P: AsRef<Path>>(&self, backup_dir: P) -> io::Result<tar::Archive<GzDecoder<File>>> {
        let path = Backup::path(backup_dir, self.start_time);
        let tar_gz = File::open(path)?;
        let enc = GzDecoder::new(tar_gz);
        Ok(tar::Archive::new(enc))
    }

    /// Open this backup's archive and append all its files that are part of the provided state to
    /// the archive file.
    pub fn append<P: AsRef<Path>>(
        &self,
        backup_dir: P,
        state: &State,
        ar: &mut tar::Builder<GzEncoder<File>>,
    ) -> io::Result<()> {
        let mut own_ar = self.open(backup_dir)?;

        for entry in own_ar.entries()? {
            let entry = entry?;
            let entry_path_in_tar = entry.path()?.to_path_buf();

            if state.contains(&entry_path_in_tar) {
                let header = entry.header().clone();
                ar.append(&header, entry)?;
            }
        }

        Ok(())
    }
}

impl<T: Clone> fmt::Display for Backup<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let letter = match self.type_ {
            BackupType::Full => 'F',
            BackupType::Incremental => 'I',
        };

        // Pretty-print size
        // If your backup is a petabyte or larger, this will crash and you need to re-evaluate your
        // life choices
        let index = self.size.ilog(1024) as usize;
        let size = self.size as f64 / (1024.0_f64.powi(index as i32));
        let duration = self.end_time - self.start_time;

        write!(
            f,
            "{} ({}, {}m{}s, {:.2}{}, {})",
            self.start_time.format(Backup::FILENAME_FORMAT),
            letter,
            duration.num_seconds() / 60,
            duration.num_seconds() % 60,
            size,
            BYTE_SUFFIXES[index],
            self.delta
        )
    }
}