use std::convert::TryInto;
use std::num::NonZeroUsize;
use std::{cmp, io};

use byteorder::{BigEndian, WriteBytesExt};

use crate::block_writer::BlockWriter;
use crate::compression::{compress, CompressionType};
use crate::count_write::CountWrite;
use crate::metadata::{FileVersion, Metadata};

const DEFAULT_BLOCK_SIZE: usize = 8192;
const MIN_BLOCK_SIZE: usize = 1024;

/// A struct that is used to configure a [`Writer`].
pub struct WriterBuilder {
    compression_type: CompressionType,
    compression_level: u32,
    index_key_interval: Option<NonZeroUsize>,
    index_levels: u8,
    block_size: usize,
}

impl Default for WriterBuilder {
    fn default() -> WriterBuilder {
        WriterBuilder {
            compression_type: CompressionType::None,
            compression_level: 0,
            index_key_interval: None,
            index_levels: 0,
            block_size: DEFAULT_BLOCK_SIZE,
        }
    }
}

impl WriterBuilder {
    /// Creates a [`WriterBuilder`], it can be used to
    /// configure your [`Writer`] to better fit your needs.
    pub fn new() -> WriterBuilder {
        WriterBuilder::default()
    }

    /// Defines the [`CompressionType`] that will be used to compress the writer blocks.
    pub fn compression_type(&mut self, compression_type: CompressionType) -> &mut Self {
        self.compression_type = compression_type;
        self
    }

    /// Defines the copression level of the defined [`CompressionType`]
    /// that will be used to compress the writer blocks.
    pub fn compression_level(&mut self, level: u32) -> &mut Self {
        self.compression_level = level;
        self
    }

    /// Defines the size of the blocks that the writer will writer.
    ///
    /// The bigger the blocks are the better they are compressed
    /// but the more time it takes to compress and decompress them.
    pub fn block_size(&mut self, size: usize) -> &mut Self {
        self.block_size = cmp::max(MIN_BLOCK_SIZE, size);
        self
    }

    /// The interval at which we store the index of a key in the
    /// index footer, used to seek into a block.
    pub fn index_key_interval(&mut self, interval: NonZeroUsize) -> &mut Self {
        self.index_key_interval = Some(interval);
        self
    }

    /// The number of levels/indirection we will use to write the index footer.
    ///
    /// An indirection of 1 or 2 is sufficient to reduce the impact of
    /// decompressing/reading the index block footer.
    ///
    /// The default is 0 which means that the index block footer values directly specifies
    /// the block where the requested data entries can be found. The disavantage of this
    /// is that the index block can be quite big and take time to be decompressed and read.
    pub fn index_levels(&mut self, levels: u8) -> &mut Self {
        self.index_levels = levels;
        self
    }

    /// Creates the [`Writer`] that will write into the provided [`io::Write`] type.
    pub fn build<W: io::Write>(&self, writer: W) -> Writer<W> {
        let mut block_writer_builder = BlockWriter::builder();
        if let Some(interval) = self.index_key_interval {
            block_writer_builder.index_key_interval(interval);
        }

        let mut index_block_writer_builder = BlockWriter::builder();
        if let Some(interval) = self.index_key_interval {
            index_block_writer_builder.index_key_interval(interval);
        }
        let index_block_writer = index_block_writer_builder.build();

        Writer {
            block_writer: block_writer_builder.build(),
            index_block_writers: vec![index_block_writer; self.index_levels as usize + 1],
            compression_type: self.compression_type,
            compression_level: self.compression_level,
            block_size: self.block_size,
            entries_count: 0,
            writer: CountWrite::new(writer),
        }
    }

    /// Creates the [`Writer`] that will write into a [`Vec`] of bytes.
    pub fn memory(&self) -> Writer<Vec<u8>> {
        self.build(Vec::new())
    }
}

/// A struct you can use to write entries into any [`io::Write`] type,
/// entries must be inserted in key-order.
pub struct Writer<W> {
    /// The block writer that is currently storing the key/values entries.
    block_writer: BlockWriter,
    /// The block writers that associates the offset (big endian u64) of the
    /// blocks in the file with the last key of these given blocks.
    index_block_writers: Vec<BlockWriter>,
    /// The compression method used to compress individual blocks.
    compression_type: CompressionType,
    /// The compression level used to compress individual blocks.
    compression_level: u32,
    /// The amount of bytes to reach before dumping this block on disk.
    block_size: usize,
    /// The amount of key already inserted.
    entries_count: u64,
    /// The writer in which we write the block, index footer blocks and footer metadata.
    writer: CountWrite<W>,
}

impl Writer<Vec<u8>> {
    /// Creates a [`Writer`] that will write into a [`Vec`] of bytes.
    pub fn memory() -> Writer<Vec<u8>> {
        WriterBuilder::new().memory()
    }
}

impl Writer<()> {
    /// Creates a [`WriterBuilder`], it can be used to configure your [`Writer`].
    pub fn builder() -> WriterBuilder {
        WriterBuilder::default()
    }
}

impl<W: io::Write> Writer<W> {
    /// Gets a reference to the underlying writer.
    pub fn as_ref(&self) -> &W {
        self.writer.as_ref()
    }
}

impl<W: io::Write> Writer<W> {
    /// Creates a [`Writer`] that will write into the provided [`io::Write`] type.
    pub fn new(writer: W) -> Writer<W> {
        WriterBuilder::new().build(writer)
    }

    /// Writes the provided entry into the underlying [`io::Write`] type,
    /// key-values must be given in key-order.
    pub fn insert<A, B>(&mut self, key: A, val: B) -> io::Result<()>
    where
        A: AsRef<[u8]>,
        B: AsRef<[u8]>,
    {
        self.block_writer.insert(key.as_ref(), val.as_ref());
        self.entries_count += 1;

        if self.block_writer.current_size_estimate() >= self.block_size {
            // Only write a block if there is at least a key in it.
            if let Some(last_key) = self.block_writer.last_key() {
                if let Some(index_block_writer) = self.index_block_writers.last_mut() {
                    // Get the current offset and last key of the current block,
                    // write it in the index block writer.
                    let offset = self.writer.count();
                    index_block_writer.insert(last_key, &offset.to_be_bytes());

                    compress_and_write_block(
                        &mut self.writer,
                        &mut self.block_writer,
                        self.compression_type,
                        self.compression_level,
                    )?;
                }

                // We iterate recursively on the index blocks and dumps the blocks that reached
                // the size limit, saving the offsets in the parent block. We skip the first index
                // block as it is the main one and must only be dumped at the end.
                let mut index_block_writers = &mut self.index_block_writers.as_mut_slice()[1..];
                while let Some((last_block_writer, head)) = index_block_writers.split_last_mut() {
                    if last_block_writer.current_size_estimate() >= self.block_size {
                        // Only write a block if there is at least a key in it.
                        if let Some(last_key) = last_block_writer.last_key() {
                            if let Some(index_block_writer) = head.last_mut() {
                                let offset = self.writer.count();
                                index_block_writer.insert(last_key, &offset.to_be_bytes());

                                compress_and_write_block(
                                    &mut self.writer,
                                    last_block_writer,
                                    self.compression_type,
                                    self.compression_level,
                                )?;
                            }
                        }
                    }

                    index_block_writers = head;
                }
            }
        }

        Ok(())
    }

    /// Consumes this [`Writer`] and write the latest block currently being built.
    ///
    /// You must call this method before using the underlying [`io::Write`] type.
    pub fn finish(self) -> io::Result<()> {
        self.into_inner().map(drop)
    }

    /// Consumes this [`Writer`] and write the latest block currenty being built.
    ///
    /// Returns the underlying [`io::Write`] provided type.
    pub fn into_inner(mut self) -> io::Result<W> {
        // Write the last block only if it is not empty.
        if let Some(last_key) = self.block_writer.last_key() {
            if let Some(index_block_writer) = self.index_block_writers.last_mut() {
                // Get the current offset and last key of the current block,
                // write it in the index block writer.
                let offset = self.writer.count();
                index_block_writer.insert(last_key, &offset.to_be_bytes());

                compress_and_write_block(
                    &mut self.writer,
                    &mut self.block_writer,
                    self.compression_type,
                    self.compression_level,
                )?;
            }
        }

        // We must write the index block levels to the file.
        let mut index_block_offset = self.writer.count();
        let mut index_block_writers = self.index_block_writers.as_mut_slice();
        while let Some((last_block_writer, head)) = index_block_writers.split_last_mut() {
            // Get the offset where we are in the file.
            index_block_offset = self.writer.count();

            match last_block_writer.last_key() {
                // Write the index block only if it is not empty.
                Some(last_key) => {
                    // Get the last_key of the index block we are writing and
                    // put that last_key into the index block of the level above.
                    if let Some(pre_last_block_writer) = head.last_mut() {
                        pre_last_block_writer.insert(last_key, &index_block_offset.to_be_bytes());
                    }

                    compress_and_write_block(
                        &mut self.writer,
                        last_block_writer,
                        self.compression_type,
                        self.compression_level,
                    )?;
                }
                // Or if this is the main index block.
                None => {
                    if head.is_empty() {
                        compress_and_write_block(
                            &mut self.writer,
                            last_block_writer,
                            self.compression_type,
                            self.compression_level,
                        )?;
                    }
                }
            }

            index_block_writers = head;
        }

        // Then we can write the metadata that specifies where the index block is stored.
        let metadata = Metadata {
            file_version: FileVersion::FormatV2,
            index_block_offset,
            compression_type: self.compression_type,
            entries_count: self.entries_count,
            index_levels: self.index_block_writers.len() as u8 - 1,
        };

        metadata.write_into(&mut self.writer)?;
        self.writer.into_inner()
    }
}

/// Compress and write the block into the writer prefixed by the length of it as an `u64`.
fn compress_and_write_block<W: io::Write>(
    mut writer: W,
    block_writer: &mut BlockWriter,
    compression_type: CompressionType,
    compression_level: u32,
) -> io::Result<()> {
    let buffer = block_writer.finish();

    // Compress, write the length of the compressed block then the block itself.
    let buffer = compress(compression_type, compression_level, buffer.as_ref())?;
    let block_len = buffer.len().try_into().unwrap();
    writer.write_u64::<BigEndian>(block_len)?;
    writer.write_all(&buffer)?;

    Ok(())
}

#[cfg(test)]
mod tests {
    use std::io::Cursor;

    use super::*;
    use crate::Reader;

    #[test]
    #[cfg_attr(miri, ignore)]
    fn no_compression() {
        let wb = Writer::builder();
        let mut writer = wb.build(Vec::new());

        for x in 0..2000u32 {
            let x = x.to_be_bytes();
            writer.insert(&x, &x).unwrap();
        }

        let bytes = writer.into_inner().unwrap();
        assert_ne!(bytes.len(), 0);
    }

    #[test]
    #[cfg_attr(miri, ignore)]
    fn no_compression_index_levels_2() {
        let mut wb = Writer::builder();
        wb.index_levels(2);
        let mut writer = wb.build(Vec::new());

        for x in 0..2000u32 {
            let x = x.to_be_bytes();
            writer.insert(&x, &x).unwrap();
        }

        let bytes = writer.into_inner().unwrap();
        assert_ne!(bytes.len(), 0);
    }

    #[test]
    #[cfg_attr(miri, ignore)]
    #[cfg(feature = "snappy")]
    fn snappy_compression() {
        let mut wb = Writer::builder();
        wb.compression_type(CompressionType::Snappy);
        let mut writer = wb.build(Vec::new());

        for x in 0..2000u32 {
            let x = x.to_be_bytes();
            writer.insert(&x, &x).unwrap();
        }

        let bytes = writer.into_inner().unwrap();
        assert_ne!(bytes.len(), 0);
    }

    #[test]
    #[cfg_attr(miri, ignore)]
    #[cfg(feature = "snappy")]
    fn backward_compatibility_0_4_snappy_compression() {
        let mut writer = grenad_0_4::Writer::builder()
            .compression_type(grenad_0_4::CompressionType::Snappy)
            .memory();

        let total: u32 = 156_000;

        for x in 0..total {
            let x = x.to_be_bytes();
            writer.insert(&x, &x).unwrap();
        }

        let bytes = writer.into_inner().unwrap();
        assert_ne!(bytes.len(), 0);

        let reader = Reader::new(Cursor::new(bytes.as_slice())).unwrap();
        let mut cursor = reader.into_cursor().unwrap();
        let mut x = 0u32;

        while let Some((k, v)) = cursor.move_on_next().unwrap() {
            let k = k.try_into().map(u32::from_be_bytes).unwrap();
            let v = v.try_into().map(u32::from_be_bytes).unwrap();
            assert_eq!(k, x);
            assert_eq!(v, x);
            x += 1;
        }

        for x in 0..total {
            let (k, v) =
                cursor.move_on_key_greater_than_or_equal_to(x.to_be_bytes()).unwrap().unwrap();
            let k = k.try_into().map(u32::from_be_bytes).unwrap();
            let v = v.try_into().map(u32::from_be_bytes).unwrap();
            assert_eq!(k, x);
            assert_eq!(v, x);
        }

        assert_eq!(x, total);
    }
}