mod builder;
mod iterator;

use std::path::Path;
use std::sync::Arc;

use anyhow::Result;
pub use builder::SsTableBuilder;
use bytes::{Buf, BufMut, Bytes};
pub use iterator::SsTableIterator;

use crate::block::Block;

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct BlockMeta {
    /// Offset of this data block.
    pub offset: usize,
    /// The first key of the data block.
    pub first_key: Bytes,
}

impl BlockMeta {
    /// Encode block meta to a buffer.
    pub fn encode_block_meta(block_meta: &[BlockMeta], buf: &mut Vec<u8>) {
        let mut estimated_size = 0;
        for meta in block_meta {
            estimated_size += std::mem::size_of::<u32>();
            estimated_size += std::mem::size_of::<u16>();
            estimated_size += meta.first_key.len();
        }
        buf.reserve(estimated_size);
        let original_len = buf.len();
        for meta in block_meta {
            buf.put_u32(meta.offset as u32);
            buf.put_u16(meta.first_key.len() as u16);
            buf.put_slice(&meta.first_key);
        }
        assert_eq!(estimated_size, buf.len() - original_len);
    }

    /// Decode block meta from a buffer.
    pub fn decode_block_meta(mut buf: impl Buf) -> Vec<BlockMeta> {
        let mut block_meta = Vec::new();
        while buf.has_remaining() {
            let offset = buf.get_u32() as usize;
            let first_key_len = buf.get_u16() as usize;
            let first_key = buf.copy_to_bytes(first_key_len);
            block_meta.push(BlockMeta { offset, first_key });
        }
        block_meta
    }
}

/// A file object.
pub struct FileObject(Bytes);

impl FileObject {
    pub fn read(&self, offset: u64, len: u64) -> Result<Vec<u8>> {
        Ok(self.0[offset as usize..(offset + len) as usize].to_vec())
    }

    pub fn size(&self) -> u64 {
        self.0.len() as u64
    }

    pub fn create(_path: &Path, data: Vec<u8>) -> Result<Self> {
        Ok(FileObject(data.into()))
    }

    pub fn open(_path: &Path) -> Result<Self> {
        unimplemented!()
    }
}

pub struct SsTable {
    file: FileObject,
    block_metas: Vec<BlockMeta>,
    block_meta_offset: usize,
}

impl SsTable {
    /// Open SSTable from a file.
    pub fn open(file: FileObject) -> Result<Self> {
        let len = file.size();
        let raw_meta_offset = file.read(len - 4, 4)?;
        let block_meta_offset = (&raw_meta_offset[..]).get_u32() as u64;
        let raw_meta = file.read(block_meta_offset, len - 4 - block_meta_offset)?;
        Ok(Self {
            file,
            block_metas: BlockMeta::decode_block_meta(&raw_meta[..]),
            block_meta_offset: block_meta_offset as usize,
        })
    }

    /// Read a block from the disk.
    pub fn read_block(&self, block_idx: usize) -> Result<Arc<Block>> {
        let offset = self.block_metas[block_idx].offset;
        let offset_end = self
            .block_metas
            .get(block_idx + 1)
            .map(|x| x.offset)
            .unwrap_or(self.block_meta_offset);
        let block_data = self
            .file
            .read(offset as u64, (offset_end - offset) as u64)?;
        Ok(Arc::new(Block::decode(&block_data[..])))
    }

    /// Find the block that may contain `key`.
    pub fn find_block_idx(&self, key: &[u8]) -> usize {
        self.block_metas
            .partition_point(|meta| meta.first_key <= key)
            .saturating_sub(1)
    }

    /// Get number of data blocks.
    pub fn num_of_blocks(&self) -> usize {
        self.block_metas.len()
    }
}

#[cfg(test)]
mod tests;