/*
 * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
 *
 * This program is free software: you can use, redistribute, and/or modify
 * it under the terms of the GNU Affero General Public License, version 3
 * or later ("AGPL"), as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#define _DEFAULT_SOURCE
#include "syncAppendEntries.h"
#include "syncMessage.h"
#include "syncRaftLog.h"
#include "syncRaftStore.h"

// TLA+ Spec
// HandleAppendEntriesRequest(i, j, m) ==
//    LET logOk == \/ m.mprevLogIndex = 0
//                 \/ /\ m.mprevLogIndex > 0
//                    /\ m.mprevLogIndex <= Len(log[i])
//                    /\ m.mprevLogTerm = log[i][m.mprevLogIndex].term
//    IN /\ m.mterm <= currentTerm[i]
//       /\ \/ /\ \* reject request
//                \/ m.mterm < currentTerm[i]
//                \/ /\ m.mterm = currentTerm[i]
//                   /\ state[i] = Follower
//                   /\ \lnot logOk
//             /\ Reply([mtype           |-> AppendEntriesResponse,
//                       mterm           |-> currentTerm[i],
//                       msuccess        |-> FALSE,
//                       mmatchIndex     |-> 0,
//                       msource         |-> i,
//                       mdest           |-> j],
//                       m)
//             /\ UNCHANGED <<serverVars, logVars>>
//          \/ \* return to follower state
//             /\ m.mterm = currentTerm[i]
//             /\ state[i] = Candidate
//             /\ state' = [state EXCEPT ![i] = Follower]
//             /\ UNCHANGED <<currentTerm, votedFor, logVars, messages>>
//          \/ \* accept request
//             /\ m.mterm = currentTerm[i]
//             /\ state[i] = Follower
//             /\ logOk
//             /\ LET index == m.mprevLogIndex + 1
//                IN \/ \* already done with request
//                       /\ \/ m.mentries = << >>
//                          \/ /\ m.mentries /= << >>
//                             /\ Len(log[i]) >= index
//                             /\ log[i][index].term = m.mentries[1].term
//                          \* This could make our commitIndex decrease (for
//                          \* example if we process an old, duplicated request),
//                          \* but that doesn't really affect anything.
//                       /\ commitIndex' = [commitIndex EXCEPT ![i] =
//                                              m.mcommitIndex]
//                       /\ Reply([mtype           |-> AppendEntriesResponse,
//                                 mterm           |-> currentTerm[i],
//                                 msuccess        |-> TRUE,
//                                 mmatchIndex     |-> m.mprevLogIndex +
//                                                     Len(m.mentries),
//                                 msource         |-> i,
//                                 mdest           |-> j],
//                                 m)
//                       /\ UNCHANGED <<serverVars, log>>
//                   \/ \* conflict: remove 1 entry
//                       /\ m.mentries /= << >>
//                       /\ Len(log[i]) >= index
//                       /\ log[i][index].term /= m.mentries[1].term
//                       /\ LET new == [index2 \in 1..(Len(log[i]) - 1) |->
//                                          log[i][index2]]
//                          IN log' = [log EXCEPT ![i] = new]
//                       /\ UNCHANGED <<serverVars, commitIndex, messages>>
//                   \/ \* no conflict: append entry
//                       /\ m.mentries /= << >>
//                       /\ Len(log[i]) = m.mprevLogIndex
//                       /\ log' = [log EXCEPT ![i] =
//                                      Append(log[i], m.mentries[1])]
//                       /\ UNCHANGED <<serverVars, commitIndex, messages>>
//       /\ UNCHANGED <<candidateVars, leaderVars>>
//

int32_t syncNodeFollowerCommit(SSyncNode* ths, SyncIndex newCommitIndex) {
  if (ths->state != TAOS_SYNC_STATE_FOLLOWER) {
    sNTrace(ths, "can not do follower commit");
    return -1;
  }

  // maybe update commit index, leader notice me
  if (newCommitIndex > ths->commitIndex) {
    // has commit entry in local
    if (newCommitIndex <= ths->pLogStore->syncLogLastIndex(ths->pLogStore)) {
      // advance commit index to sanpshot first
      SSnapshot snapshot;
      ths->pFsm->FpGetSnapshotInfo(ths->pFsm, &snapshot);
      if (snapshot.lastApplyIndex >= 0 && snapshot.lastApplyIndex > ths->commitIndex) {
        SyncIndex commitBegin = ths->commitIndex;
        SyncIndex commitEnd = snapshot.lastApplyIndex;
        ths->commitIndex = snapshot.lastApplyIndex;
        sNTrace(ths, "commit by snapshot from index:%" PRId64 " to index:%" PRId64, commitBegin, commitEnd);
      }

      SyncIndex beginIndex = ths->commitIndex + 1;
      SyncIndex endIndex = newCommitIndex;

      // update commit index
      ths->commitIndex = newCommitIndex;

      // call back Wal
      int32_t code = ths->pLogStore->syncLogUpdateCommitIndex(ths->pLogStore, ths->commitIndex);
      ASSERT(code == 0);

      code = syncNodeDoCommit(ths, beginIndex, endIndex, ths->state);
      ASSERT(code == 0);
    }
  }

  return 0;
}

int32_t syncNodeOnAppendEntries(SSyncNode* ths, SyncAppendEntries* pMsg) {
  // if already drop replica, do not process
  if (!syncNodeInRaftGroup(ths, &(pMsg->srcId))) {
    syncLogRecvAppendEntries(ths, pMsg, "not in my config");
    goto _IGNORE;
  }

  // prepare response msg
  SyncAppendEntriesReply* pReply = syncAppendEntriesReplyBuild(ths->vgId);
  pReply->srcId = ths->myRaftId;
  pReply->destId = pMsg->srcId;
  pReply->term = ths->pRaftStore->currentTerm;
  pReply->success = false;
  // pReply->matchIndex = ths->pLogStore->syncLogLastIndex(ths->pLogStore);
  pReply->matchIndex = SYNC_INDEX_INVALID;
  pReply->lastSendIndex = pMsg->prevLogIndex + 1;
  pReply->startTime = ths->startTime;

  if (pMsg->term < ths->pRaftStore->currentTerm) {
    syncLogRecvAppendEntries(ths, pMsg, "reject, small term");
    goto _SEND_RESPONSE;
  }

  if (pMsg->term > ths->pRaftStore->currentTerm) {
    pReply->term = pMsg->term;
  }

  syncNodeStepDown(ths, pMsg->term);
  syncNodeResetElectTimer(ths);

  SyncIndex startIndex = ths->pLogStore->syncLogBeginIndex(ths->pLogStore);
  SyncIndex lastIndex = ths->pLogStore->syncLogLastIndex(ths->pLogStore);

  if (pMsg->prevLogIndex > lastIndex) {
    syncLogRecvAppendEntries(ths, pMsg, "reject, index not match");
    goto _SEND_RESPONSE;
  }

  if (pMsg->prevLogIndex >= startIndex) {
    SyncTerm myPreLogTerm = syncNodeGetPreTerm(ths, pMsg->prevLogIndex + 1);
    ASSERT(myPreLogTerm != SYNC_TERM_INVALID);

    if (myPreLogTerm != pMsg->prevLogTerm) {
      syncLogRecvAppendEntries(ths, pMsg, "reject, pre-term not match");
      goto _SEND_RESPONSE;
    }
  }

  // accept
  pReply->success = true;
  bool hasAppendEntries = pMsg->dataLen > 0;
  if (hasAppendEntries) {
    SSyncRaftEntry* pAppendEntry = syncEntryBuildFromAppendEntries(pMsg);
    ASSERT(pAppendEntry != NULL);

    SyncIndex       appendIndex = pMsg->prevLogIndex + 1;
    SSyncRaftEntry* pLocalEntry = NULL;
    int32_t         code = ths->pLogStore->syncLogGetEntry(ths->pLogStore, appendIndex, &pLocalEntry);
    if (code == 0) {
      if (pLocalEntry->term == pAppendEntry->term) {
        // do nothing
        sNTrace(ths, "log match, do nothing, index:%" PRId64, appendIndex);
      } else {
        // truncate
        code = ths->pLogStore->syncLogTruncate(ths->pLogStore, appendIndex);
        if (code != 0) {
          char logBuf[128];
          snprintf(logBuf, sizeof(logBuf), "ignore, truncate error, append-index:%" PRId64, appendIndex);
          syncLogRecvAppendEntries(ths, pMsg, logBuf);

          syncEntryDestory(pLocalEntry);
          syncEntryDestory(pAppendEntry);
          goto _IGNORE;
        }

        // append
        code = ths->pLogStore->syncLogAppendEntry(ths->pLogStore, pAppendEntry);
        if (code != 0) {
          char logBuf[128];
          snprintf(logBuf, sizeof(logBuf), "ignore, append error, append-index:%" PRId64, appendIndex);
          syncLogRecvAppendEntries(ths, pMsg, logBuf);

          syncEntryDestory(pLocalEntry);
          syncEntryDestory(pAppendEntry);
          goto _IGNORE;
        }
      }

    } else {
      if (terrno == TSDB_CODE_WAL_LOG_NOT_EXIST) {
        // log not exist

        // truncate
        code = ths->pLogStore->syncLogTruncate(ths->pLogStore, appendIndex);
        if (code != 0) {
          char logBuf[128];
          snprintf(logBuf, sizeof(logBuf), "ignore, log not exist, truncate error, append-index:%" PRId64, appendIndex);
          syncLogRecvAppendEntries(ths, pMsg, logBuf);

          syncEntryDestory(pLocalEntry);
          syncEntryDestory(pAppendEntry);
          goto _IGNORE;
        }

        // append
        code = ths->pLogStore->syncLogAppendEntry(ths->pLogStore, pAppendEntry);
        if (code != 0) {
          char logBuf[128];
          snprintf(logBuf, sizeof(logBuf), "ignore, log not exist, append error, append-index:%" PRId64, appendIndex);
          syncLogRecvAppendEntries(ths, pMsg, logBuf);

          syncEntryDestory(pLocalEntry);
          syncEntryDestory(pAppendEntry);
          goto _IGNORE;
        }

      } else {
        // error
        char logBuf[128];
        snprintf(logBuf, sizeof(logBuf), "ignore, get local entry error, append-index:%" PRId64 " err:%d", appendIndex,
                 terrno);
        syncLogRecvAppendEntries(ths, pMsg, logBuf);

        syncEntryDestory(pLocalEntry);
        syncEntryDestory(pAppendEntry);
        goto _IGNORE;
      }
    }

    // update match index
    pReply->matchIndex = pAppendEntry->index;

    syncEntryDestory(pLocalEntry);
    syncEntryDestory(pAppendEntry);

  } else {
    // no append entries, do nothing
    // maybe has extra entries, no harm

    // update match index
    pReply->matchIndex = pMsg->prevLogIndex;
  }

  // maybe update commit index, leader notice me
  syncNodeFollowerCommit(ths, pMsg->commitIndex);

  syncLogRecvAppendEntries(ths, pMsg, "accept");
  goto _SEND_RESPONSE;

_IGNORE:
  syncAppendEntriesReplyDestroy(pReply);
  return 0;

_SEND_RESPONSE:
  // msg event log
  syncLogSendAppendEntriesReply(ths, pReply, "");

  // send response
  SRpcMsg rpcMsg;
  syncAppendEntriesReply2RpcMsg(pReply, &rpcMsg);
  syncNodeSendMsgById(&pReply->destId, ths, &rpcMsg);
  syncAppendEntriesReplyDestroy(pReply);

  return 0;
}