imag/libimagstore/src/store.rs

use std::collections::HashMap;
use std::fs::{File, remove_file};
use std::ops::Drop;
use std::path::PathBuf;
use std::result::Result as RResult;
use std::sync::Arc;
use std::sync::RwLock;

use fs2::FileExt;

use entry::Entry;
use error::{StoreError, StoreErrorKind};
use storeid::StoreId;

/// The Result Type returned by any interaction with the store that could fail
pub type Result<T> = RResult<T, StoreError>;

#[derive(PartialEq)]
enum StoreEntryPresence {
    Present,
    Borrowed
}

/// A store entry, depending on the option type it is either borrowed currently
/// or not.
struct StoreEntry {
    file: File,
    entry: StoreEntryPresence
}


impl StoreEntry {
    /// The entry is currently borrowed, meaning that some thread is currently
    /// mutating it
    fn is_borrowed(&self) -> bool {
        self.entry == StoreEntryPresence::Borrowed
    }
}

/// The Store itself, through this object one can interact with IMAG's entries
pub struct Store {
    location: PathBuf,

    /**
     * Internal Path->File cache map
     *
     * Caches the files, so they remain flock()ed
     *
     * Could be optimized for a threadsafe HashMap
     */
    entries: Arc<RwLock<HashMap<StoreId, StoreEntry>>>,
}

impl Store {

    /// Create a new Store object
    pub fn new(location: PathBuf) -> Store {
        use std::fs::create_dir_all;

        if !location.exists() {
            create_dir_all(location.clone()).ok(); // TODO: Error handling?
        }

        // TODO: Path exists, but is a file? What now?

        Store {
            location: location,
            entries: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Creates the Entry at the given location (inside the entry)
    pub fn create(&self, entry: Entry) -> Result<()> {
        unimplemented!();
    }

    /// Borrow a given Entry. When the `FileLockEntry` is either `update`d or
    /// dropped, the new Entry is written to disk
    pub fn retrieve<'a>(&'a self, id: StoreId) -> Result<FileLockEntry<'a>> {
        unimplemented!();
    }

    /// Return the `FileLockEntry` and write to disk
    pub fn update<'a>(&'a self, entry: FileLockEntry<'a>) -> Result<()> {
        self._update(&entry)
    }

    /// Internal method to write to the filesystem store.
    ///
    /// # Assumptions
    /// This method assumes that entry is dropped _right after_ the call, hence
    /// it is not public.
    fn _update<'a>(&'a self, entry: &FileLockEntry<'a>) -> Result<()> {
        unimplemented!();
    }

    /// Retrieve a copy of a given entry, this cannot be used to mutate
    /// the one on disk
    pub fn retrieve_copy(&self, id: StoreId) -> Result<Entry> {
        unimplemented!();
    }

    /// Delete an entry
    pub fn delete(&self, id: StoreId) -> Result<()> {
        let mut entries_lock = self.entries.write();
        let mut entries = entries_lock.unwrap();

        // if the entry is currently modified by the user, we cannot drop it
        if entries.get(&id).map(|e| e.is_borrowed()).unwrap_or(false) {
            return Err(StoreError::new(StoreErrorKind::IdLocked, None));
        }

        // remove the entry first, then the file
        entries.remove(&id);
        remove_file(&id).map_err(|e| StoreError::new(StoreErrorKind::FileError, Some(Box::new(e))))
    }
}

impl Drop for Store {

    /**
     * Unlock all files on drop
     *
     * TODO: Error message when file cannot be unlocked?
     */
    fn drop(&mut self) {
        self.entries.write().unwrap()
            .iter().map(|f| f.1.file.unlock());
    }

}

/// A struct that allows you to borrow an Entry
pub struct FileLockEntry<'a> {
    store: &'a Store,
    entry: Entry,
    key: StoreId,
}

impl<'a> FileLockEntry<'a, > {
    fn new(store: &'a Store, entry: Entry, key: StoreId) -> FileLockEntry<'a> {
        FileLockEntry {
            store: store,
            entry: entry,
            key: key,
        }
    }
}

impl<'a> ::std::ops::Deref for FileLockEntry<'a> {
    type Target = Entry;

    fn deref(&self) -> &Self::Target {
        &self.entry
    }
}

impl<'a> ::std::ops::DerefMut for FileLockEntry<'a> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.entry
    }
}

impl<'a> Drop for FileLockEntry<'a> {
    fn drop(&mut self) {
        self.store._update(self).unwrap()
    }
}