use Result;
use error::{ErrorKind, ResultExt};
use serde_json;
use schema::Schema;
use std::sync::Arc;
use std::borrow::BorrowMut;
use std::fmt;
use core::SegmentId;
use directory::{Directory, MmapDirectory, RAMDirectory};
use indexer::index_writer::open_index_writer;
use core::searcher::Searcher;
use std::convert::From;
use num_cpus;
use super::segment::Segment;
use core::SegmentReader;
use super::pool::Pool;
use core::SegmentMeta;
use super::pool::LeasedItem;
use std::path::Path;
use core::IndexMeta;
use indexer::DirectoryLock;
use IndexWriter;
use directory::ManagedDirectory;
use core::META_FILEPATH;
use super::segment::create_segment;
use indexer::segment_updater::save_new_metas;
use tokenizer::TokenizerManager;

const NUM_SEARCHERS: usize = 12;

fn load_metas(directory: &Directory) -> Result<IndexMeta> {
    let meta_data = directory.atomic_read(&META_FILEPATH)?;
    let meta_string = String::from_utf8_lossy(&meta_data);
    serde_json::from_str(&meta_string).chain_err(|| ErrorKind::CorruptedFile(META_FILEPATH.clone()))
}

/// Search Index
pub struct Index {
    directory: ManagedDirectory,
    schema: Schema,
    searcher_pool: Arc<Pool<Searcher>>,
    tokenizers: TokenizerManager,
}

impl Index {
    /// Creates a new index using the `RAMDirectory`.
    ///
    /// The index will be allocated in anonymous memory.
    /// This should only be used for unit tests.
    pub fn create_in_ram(schema: Schema) -> Index {
        let ram_directory = RAMDirectory::create();
        // unwrap is ok here
        let directory = ManagedDirectory::new(ram_directory).expect(
            "Creating a managed directory from a brand new RAM directory \
             should never fail.",
        );
        Index::from_directory(directory, schema).expect("Creating a RAMDirectory should never fail")
    }

    /// Creates a new index in a given filepath.
    /// The index will use the `MMapDirectory`.
    ///
    /// If a previous index was in this directory, then its meta file will be destroyed.
    pub fn create<P: AsRef<Path>>(directory_path: P, schema: Schema) -> Result<Index> {
        let mmap_directory = MmapDirectory::open(directory_path)?;
        let directory = ManagedDirectory::new(mmap_directory)?;
        Index::from_directory(directory, schema)
    }

    /// Accessor for the tokenizer manager.
    pub fn tokenizers(&self) -> &TokenizerManager {
        &self.tokenizers
    }

    /// Creates a new index in a temp directory.
    ///
    /// The index will use the `MMapDirectory` in a newly created directory.
    /// The temp directory will be destroyed automatically when the `Index` object
    /// is destroyed.
    ///
    /// The temp directory is only used for testing the `MmapDirectory`.
    /// For other unit tests, prefer the `RAMDirectory`, see: `create_in_ram`.
    pub fn create_from_tempdir(schema: Schema) -> Result<Index> {
        let mmap_directory = MmapDirectory::create_from_tempdir()?;
        let directory = ManagedDirectory::new(mmap_directory)?;
        Index::from_directory(directory, schema)
    }

    /// Creates a new index given a directory and an `IndexMeta`.
    fn create_from_metas(directory: ManagedDirectory, metas: &IndexMeta) -> Result<Index> {
        let schema = metas.schema.clone();
        let index = Index {
            directory,
            schema,
            searcher_pool: Arc::new(Pool::new()),
            tokenizers: TokenizerManager::default(),
        };
        index.load_searchers()?;
        Ok(index)
    }

    /// Create a new index from a directory.
    pub fn from_directory(mut directory: ManagedDirectory, schema: Schema) -> Result<Index> {
        save_new_metas(schema.clone(), 0, directory.borrow_mut())?;
        let metas = IndexMeta::with_schema(schema);
        Index::create_from_metas(directory, &metas)
    }

    /// Opens a new directory from an index path.
    pub fn open<P: AsRef<Path>>(directory_path: P) -> Result<Index> {
        let mmap_directory = MmapDirectory::open(directory_path)?;
        let directory = ManagedDirectory::new(mmap_directory)?;
        let metas = load_metas(&directory)?;
        Index::create_from_metas(directory, &metas)
    }

    /// Reads the index meta file from the directory.
    pub fn load_metas(&self) -> Result<IndexMeta> {
        load_metas(self.directory())
    }

    /// Open a new index writer. Attempts to acquire a lockfile.
    ///
    /// The lockfile should be deleted on drop, but it is possible
    /// that due to a panic or other error, a stale lockfile will be
    /// left in the index directory. If you are sure that no other
    /// `IndexWriter` on the system is accessing the index directory,
    /// it is safe to manually delete the lockfile.
    ///
    /// num_threads specifies the number of indexing workers that
    /// should work at the same time.
    ///
    /// # Errors
    /// If the lockfile already exists, returns `Error::FileAlreadyExists`.
    /// # Panics
    /// If the heap size per thread is too small, panics.
    pub fn writer_with_num_threads(
        &self,
        num_threads: usize,
        heap_size_in_bytes: usize,
    ) -> Result<IndexWriter> {
        let directory_lock = DirectoryLock::lock(self.directory().box_clone())?;
        open_index_writer(self, num_threads, heap_size_in_bytes, directory_lock)
    }

    /// Creates a multithreaded writer
    /// It just calls `writer_with_num_threads` with the number of cores as `num_threads`
    ///
    /// # Errors
    /// If the lockfile already exists, returns `Error::FileAlreadyExists`.
    /// # Panics
    /// If the heap size per thread is too small, panics.
    pub fn writer(&self, heap_size_in_bytes: usize) -> Result<IndexWriter> {
        self.writer_with_num_threads(num_cpus::get(), heap_size_in_bytes)
    }

    /// Accessor to the index schema
    ///
    /// The schema is actually cloned.
    pub fn schema(&self) -> Schema {
        self.schema.clone()
    }

    /// Returns the list of segments that are searchable
    pub fn searchable_segments(&self) -> Result<Vec<Segment>> {
        Ok(self.searchable_segment_metas()?
            .into_iter()
            .map(|segment_meta| self.segment(segment_meta))
            .collect())
    }

    #[doc(hidden)]
    pub fn segment(&self, segment_meta: SegmentMeta) -> Segment {
        create_segment(self.clone(), segment_meta)
    }

    /// Creates a new segment.
    pub fn new_segment(&self) -> Segment {
        let segment_meta = SegmentMeta::new(SegmentId::generate_random());
        create_segment(self.clone(), segment_meta)
    }

    /// Return a reference to the index directory.
    pub fn directory(&self) -> &ManagedDirectory {
        &self.directory
    }

    /// Return a mutable reference to the index directory.
    pub fn directory_mut(&mut self) -> &mut ManagedDirectory {
        &mut self.directory
    }

    /// Reads the meta.json and returns the list of
    /// `SegmentMeta` from the last commit.
    pub fn searchable_segment_metas(&self) -> Result<Vec<SegmentMeta>> {
        Ok(self.load_metas()?.segments)
    }

    /// Returns the list of segment ids that are searchable.
    pub fn searchable_segment_ids(&self) -> Result<Vec<SegmentId>> {
        Ok(self.searchable_segment_metas()?
            .iter()
            .map(|segment_meta| segment_meta.id())
            .collect())
    }

    /// Creates a new generation of searchers after

    /// a change of the set of searchable indexes.
    ///
    /// This needs to be called when a new segment has been
    /// published or after a merge.
    pub fn load_searchers(&self) -> Result<()> {
        let searchable_segments = self.searchable_segments()?;
        let segment_readers: Vec<SegmentReader> = searchable_segments
            .iter()
            .map(SegmentReader::open)
            .collect::<Result<_>>()?;
        let searchers = (0..NUM_SEARCHERS)
            .map(|_| Searcher::from(segment_readers.clone()))
            .collect();
        self.searcher_pool.publish_new_generation(searchers);
        Ok(())
    }

    /// Returns a searcher
    ///
    /// This method should be called every single time a search
    /// query is performed.
    /// The searchers are taken from a pool of `NUM_SEARCHERS` searchers.
    /// If no searcher is available
    /// this may block.
    ///
    /// The same searcher must be used for a given query, as it ensures
    /// the use of a consistent segment set.
    pub fn searcher(&self) -> LeasedItem<Searcher> {
        self.searcher_pool.acquire()
    }
}

impl fmt::Debug for Index {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Index({:?})", self.directory)
    }
}

impl Clone for Index {
    fn clone(&self) -> Index {
        Index {
            directory: self.directory.clone(),
            schema: self.schema.clone(),
            searcher_pool: Arc::clone(&self.searcher_pool),
            tokenizers: self.tokenizers.clone(),
        }
    }
}