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// Copyright 2020 TiKV Project Authors. Licensed under Apache-2.0.

use std::collections::BTreeMap;
use std::io::Read;
use std::ops::{Deref, DerefMut};
use tikv_util::codec::number::{self, NumberEncoder};
use tikv_util::codec::Result;

#[derive(Clone, Debug, Default)]
pub struct IndexHandle {
    pub size: u64,   // The size of the stored block
    pub offset: u64, // The offset of the block in the file
}

#[derive(Debug, Default)]
pub struct IndexHandles(BTreeMap<Vec<u8>, IndexHandle>);

impl Deref for IndexHandles {
    type Target = BTreeMap<Vec<u8>, IndexHandle>;
    fn deref(&self) -> &BTreeMap<Vec<u8>, IndexHandle> {
        &self.0
    }
}

impl DerefMut for IndexHandles {
    fn deref_mut(&mut self) -> &mut BTreeMap<Vec<u8>, IndexHandle> {
        &mut self.0
    }
}

impl IndexHandles {
    pub fn new() -> IndexHandles {
        IndexHandles(BTreeMap::new())
    }

    pub fn into_map(self) -> BTreeMap<Vec<u8>, IndexHandle> {
        self.0
    }

    pub fn add(&mut self, key: Vec<u8>, index_handle: IndexHandle) {
        self.0.insert(key, index_handle);
    }

    // Format: | klen | k | v.size | v.offset |
    pub fn encode(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(1024);
        for (k, v) in &self.0 {
            buf.encode_u64(k.len() as u64).unwrap();
            buf.extend(k);
            buf.encode_u64(v.size).unwrap();
            buf.encode_u64(v.offset).unwrap();
        }
        buf
    }

    pub fn decode(mut buf: &[u8]) -> Result<IndexHandles> {
        let mut res = BTreeMap::new();
        while !buf.is_empty() {
            let klen = number::decode_u64(&mut buf)?;
            let mut k = vec![0; klen as usize];
            buf.read_exact(&mut k)?;
            let v = IndexHandle {
                size: number::decode_u64(&mut buf)?,
                offset: number::decode_u64(&mut buf)?,
            };
            res.insert(k, v);
        }
        Ok(IndexHandles(res))
    }
}

pub trait DecodeProperties {
    fn decode(&self, k: &str) -> Result<&[u8]>;

    fn decode_u64(&self, k: &str) -> Result<u64> {
        let mut buf = self.decode(k)?;
        number::decode_u64(&mut buf)
    }

    fn decode_handles(&self, k: &str) -> Result<IndexHandles> {
        let buf = self.decode(k)?;
        IndexHandles::decode(buf)
    }
}