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

use std::marker::PhantomData;

use engine_traits::{KvEngine, Snapshot, ALL_CFS, CF_RAFT};
use kvproto::metapb::Region;

use crate::{
    coprocessor::{ConsistencyCheckMethod, Coprocessor},
    Result,
};

pub trait ConsistencyCheckObserver<E: KvEngine>: Coprocessor {
    /// Update context. Return `true` if later observers should be skiped.
    fn update_context(&self, context: &mut Vec<u8>) -> bool;

    /// Compute hash for `region`. The policy is extracted from `context`.
    fn compute_hash(
        &self,
        region: &Region,
        context: &mut &[u8],
        snap: &E::Snapshot,
    ) -> Result<Option<u32>>;
}

#[derive(Clone)]
pub struct Raw<E: KvEngine>(PhantomData<E>);

impl<E: KvEngine> Coprocessor for Raw<E> {}

impl<E: KvEngine> Default for Raw<E> {
    fn default() -> Raw<E> {
        Raw(Default::default())
    }
}

impl<E: KvEngine> ConsistencyCheckObserver<E> for Raw<E> {
    fn update_context(&self, context: &mut Vec<u8>) -> bool {
        context.push(ConsistencyCheckMethod::Raw as u8);
        // Raw consistency check is the most heavy and strong one.
        // So all others can be skiped.
        true
    }

    fn compute_hash(
        &self,
        region: &kvproto::metapb::Region,
        context: &mut &[u8],
        snap: &E::Snapshot,
    ) -> Result<Option<u32>> {
        if context.is_empty() {
            return Ok(None);
        }
        assert_eq!(context[0], ConsistencyCheckMethod::Raw as u8);
        *context = &context[1..];
        compute_hash_on_raw(region, snap).map(Some)
    }
}

fn compute_hash_on_raw<S: Snapshot>(region: &Region, snap: &S) -> Result<u32> {
    let region_id = region.get_id();
    let mut digest = crc32fast::Hasher::new();

    let start_key = keys::enc_start_key(region);
    let end_key = keys::enc_end_key(region);
    for cf in ALL_CFS {
        snap.scan(cf, &start_key, &end_key, false, |k, v| {
            digest.update(k);
            digest.update(v);
            Ok(true)
        })?;
    }

    // Computes the hash from the Region state too.
    let region_state_key = keys::region_state_key(region_id);
    digest.update(&region_state_key);
    match snap.get_value_cf(CF_RAFT, &region_state_key) {
        Err(e) => return Err(e.into()),
        Ok(Some(v)) => digest.update(&v),
        Ok(None) => {}
    }
    Ok(digest.finalize())
}

#[cfg(test)]
mod tests {
    use engine_test::kv::KvTestEngine;

    use super::*;

    #[test]
    fn test_update_context() {
        let mut context = Vec::new();
        let observer = Raw::<KvTestEngine>::default();
        assert!(observer.update_context(&mut context));
        assert_eq!(context.len(), 1);
        assert_eq!(context[0], ConsistencyCheckMethod::Raw as u8);
    }
}