use block::BlockIter;
use blockhandle::BlockHandle;
use filter::FilterPolicy;
use filter_block::FilterBlockReader;
use options::Options;
use table_builder::{self, Footer};
use types::{Comparator, LdbIterator};

use std::io::{Read, Seek, SeekFrom, Result};

/// Reads the table footer.
fn read_footer<R: Read + Seek>(f: &mut R, size: usize) -> Result<Footer> {
    try!(f.seek(SeekFrom::Start((size - table_builder::FULL_FOOTER_LENGTH) as u64)));
    let mut buf = [0; table_builder::FULL_FOOTER_LENGTH];
    try!(f.read_exact(&mut buf));
    Ok(Footer::decode(&buf))
}

fn read_bytes<R: Read + Seek>(f: &mut R, location: &BlockHandle) -> Result<Vec<u8>> {
    try!(f.seek(SeekFrom::Start(location.offset() as u64)));

    let mut buf = Vec::new();
    buf.resize(location.size(), 0);

    try!(f.read_exact(&mut buf[0..location.size()]));

    Ok(buf)
}

/// Reads a block at location.
fn read_block<R: Read + Seek, C: Comparator>(cmp: &C,
                                             f: &mut R,
                                             location: &BlockHandle)
                                             -> Result<BlockIter<C>> {
    let buf = try!(read_bytes(f, location));
    Ok(BlockIter::new(buf, *cmp))
}

pub struct Table<R: Read + Seek, C: Comparator, FP: FilterPolicy> {
    file: R,
    file_size: usize,

    opt: Options,
    cmp: C,

    footer: Footer,
    indexblock: BlockIter<C>,
    filters: Option<FilterBlockReader<FP>>,
}

impl<R: Read + Seek, C: Comparator, FP: FilterPolicy> Table<R, C, FP> {
    pub fn new(mut file: R, size: usize, cmp: C, fp: FP, opt: Options) -> Result<Table<R, C, FP>> {
        let footer = try!(read_footer(&mut file, size));

        let indexblock = try!(read_block(&cmp, &mut file, &footer.index));
        let mut metaindexblock = try!(read_block(&cmp, &mut file, &footer.meta_index));

        let mut filter_block_reader = None;
        let mut filter_name = "filter.".as_bytes().to_vec();
        filter_name.extend_from_slice(fp.name().as_bytes());

        metaindexblock.seek(&filter_name);
        if let Some((_key, val)) = metaindexblock.current() {
            let filter_block_location = BlockHandle::decode(&val).0;

            if filter_block_location.size() > 0 {
                let buf = try!(read_bytes(&mut file, &filter_block_location));
                filter_block_reader = Some(FilterBlockReader::new_owned(fp, buf));
            }
        }
        metaindexblock.reset();

        Ok(Table {
            file: file,
            file_size: size,
            cmp: cmp,
            opt: opt,
            footer: footer,
            filters: filter_block_reader,
            indexblock: indexblock,
        })
    }

    fn read_block_(&mut self, location: &BlockHandle) -> Result<BlockIter<C>> {
        read_block(&self.cmp, &mut self.file, location)
    }

    /// Returns the offset of the block that contains `key`.
    pub fn approx_offset_of(&self, key: &[u8]) -> usize {
        // cheap clone!
        let mut iter = self.indexblock.clone();

        iter.seek(key);

        if let Some((_, val)) = iter.current() {
            let location = BlockHandle::decode(&val).0;
            return location.offset();
        }

        return self.footer.meta_index.offset();
    }

    // Iterators read from the file; thus only one iterator can be borrowed (mutably) per scope
    fn iter<'a>(&'a mut self) -> TableIterator<'a, R, C, FP> {
        let mut iter = TableIterator {
            current_block: self.indexblock.clone(), // just for filling in here
            index_block: self.indexblock.clone(),
            table: self,
        };
        iter.skip_to_next_entry(); // initialize current_block
        iter
    }
}

/// This iterator is a "TwoLevelIterator"; it uses an index block in order to get an offset hint
/// into the data blocks.
pub struct TableIterator<'a, R: 'a + Read + Seek, C: 'a + Comparator, FP: 'a + FilterPolicy> {
    table: &'a mut Table<R, C, FP>,
    current_block: BlockIter<C>,
    index_block: BlockIter<C>,
}

impl<'a, C: Comparator, R: Read + Seek, FP: FilterPolicy> TableIterator<'a, R, C, FP> {
    // Skips to the entry referenced by the next index block.
    fn skip_to_next_entry(&mut self) -> bool {
        if let Some((_key, val)) = self.index_block.next() {
            let (new_block_h, _) = BlockHandle::decode(&val);
            if let Ok(block) = self.table.read_block_(&new_block_h) {
                self.current_block = block;
                true
            } else {
                false
            }
        } else {
            false
        }
    }
}

impl<'a, C: Comparator, R: Read + Seek, FP: FilterPolicy> Iterator for TableIterator<'a, R, C, FP> {
    type Item = (Vec<u8>, Vec<u8>);

    fn next(&mut self) -> Option<Self::Item> {
        if let Some((key, val)) = self.current_block.next() {
            Some((key, val))
        } else {
            if self.skip_to_next_entry() {
                self.next()
            } else {
                None
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use filter::BloomPolicy;
    use options::Options;
    use table_builder::TableBuilder;
    use types::StandardComparator;

    use std::io::Cursor;

    use super::*;

    fn build_data() -> Vec<(&'static str, &'static str)> {
        vec![("abc", "def"),
             ("abd", "dee"),
             ("bcd", "asa"),
             ("bsr", "a00"),
             ("xyz", "xxx"),
             ("xzz", "yyy"),
             ("zzz", "111")]
    }


    fn build_table() -> (Vec<u8>, usize) {
        let mut d = Vec::with_capacity(512);
        let mut opt = Options::default();
        opt.block_restart_interval = 2;

        {
            let mut b = TableBuilder::new(opt, StandardComparator, &mut d, BloomPolicy::new(4));
            let data = build_data();

            for &(k, v) in data.iter() {
                b.add(k.as_bytes(), v.as_bytes());
            }

            b.finish();
        }

        let size = d.len();

        (d, size)
    }

    #[test]
    fn test_table_iterator() {
        let (src, size) = build_table();
        let data = build_data();

        let mut table = Table::new(Cursor::new(&src as &[u8]),
                                   size,
                                   StandardComparator,
                                   BloomPolicy::new(4),
                                   Options::default())
            .unwrap();
        let iter = table.iter();
        let mut i = 0;

        for (k, v) in iter {
            assert_eq!((data[i].0.as_bytes(), data[i].1.as_bytes()),
                       (k.as_ref(), v.as_ref()));
            i += 1;
        }
    }
}