#include "recv_append_entries.h"

#include "../tracing.h"
#include "assert.h"
#include "convert.h"
#include "entry.h"
#include "flags.h"
#include "heap.h"
#include "log.h"
#include "recv.h"
#include "replication.h"

static void recvSendAppendEntriesResultCb(struct raft_io_send *req, int status)
{
	(void)status;
	RaftHeapFree(req);
}

int recvAppendEntries(struct raft *r,
		      raft_id id,
		      const char *address,
		      const struct raft_append_entries *args)
{
	struct raft_io_send *req;
	struct raft_message message;
	struct raft_append_entries_result *result =
	    &message.append_entries_result;
	int match;
	bool async;
	int rv;

	assert(r != NULL);
	assert(id > 0);
	assert(args != NULL);
	assert(address != NULL);
	tracef(
	    "self:%llu from:%llu@%s leader_commit:%llu n_entries:%d "
	    "prev_log_index:%llu prev_log_term:%llu, term:%llu",
	    r->id, id, address, args->leader_commit, args->n_entries,
	    args->prev_log_index, args->prev_log_term, args->term);

	result->rejected = args->prev_log_index;
	result->last_log_index = logLastIndex(r->log);
	result->version = RAFT_APPEND_ENTRIES_RESULT_VERSION;
	result->features = RAFT_DEFAULT_FEATURE_FLAGS;

	rv = recvEnsureMatchingTerms(r, args->term, &match);
	if (rv != 0) {
		return rv;
	}

	/* From Figure 3.1:
	 *
	 *   AppendEntries RPC: Receiver implementation: Reply false if term <
	 *   currentTerm.
	 */
	if (match < 0) {
		tracef("local term is higher -> reject ");
		goto reply;
	}

	/* If we get here it means that the term in the request matches our
	 * current term or it was higher and we have possibly stepped down,
	 * because we discovered the current leader:
	 *
	 * From Figure 3.1:
	 *
	 *   Rules for Servers: Candidates: if AppendEntries RPC is received
	 * from new leader: convert to follower.
	 *
	 * From Section 3.4:
	 *
	 *   While waiting for votes, a candidate may receive an AppendEntries
	 * RPC from another server claiming to be leader. If the leader's term
	 *   (included in its RPC) is at least as large as the candidate's
	 * current term, then the candidate recognizes the leader as legitimate
	 * and returns to follower state. If the term in the RPC is smaller than
	 * the candidate's current term, then the candidate rejects the RPC and
	 *   continues in candidate state.
	 *
	 * From state diagram in Figure 3.3:
	 *
	 *   [candidate]: discovers current leader -> [follower]
	 *
	 * Note that it should not be possible for us to be in leader state,
	 * because the leader that is sending us the request should have either
	 * a lower term (and in that case we reject the request above), or a
	 * higher term (and in that case we step down). It can't have the same
	 * term because at most one leader can be elected at any given term.
	 */
	assert(r->state == RAFT_FOLLOWER || r->state == RAFT_CANDIDATE);
	assert(r->current_term == args->term);

	if (r->state == RAFT_CANDIDATE) {
		/* The current term and the peer one must match, otherwise we
		 * would have either rejected the request or stepped down to
		 * followers. */
		assert(match == 0);
		tracef("discovered leader -> step down ");
		convertToFollower(r);
	}

	assert(r->state == RAFT_FOLLOWER);

	/* Update current leader because the term in this AppendEntries RPC is
	 * up to date. */
	rv = recvUpdateLeader(r, id, address);
	if (rv != 0) {
		return rv;
	}

	/* Reset the election timer. */
	r->election_timer_start = r->io->time(r->io);

	/* If we are installing a snapshot, ignore these entries. TODO: we
	 * should do something smarter, e.g. buffering the entries in the I/O
	 * backend, which should be in charge of serializing everything. */
	if (replicationInstallSnapshotBusy(r) && args->n_entries > 0) {
		tracef("ignoring AppendEntries RPC during snapshot install");
		entryBatchesDestroy(args->entries, args->n_entries);
		return 0;
	}

	rv = replicationAppend(r, args, &result->rejected, &async);
	if (rv != 0) {
		return rv;
	}

	if (async) {
		return 0;
	}

	/* Echo back to the leader the point that we reached. */
	result->last_log_index = r->last_stored;

reply:
	result->term = r->current_term;

	/* Free the entries batch, if any. */
	if (args->n_entries > 0 && args->entries[0].batch != NULL) {
		raft_free(args->entries[0].batch);
	}

	if (args->entries != NULL) {
		raft_free(args->entries);
	}

	message.type = RAFT_IO_APPEND_ENTRIES_RESULT;
	message.server_id = id;
	message.server_address = address;

	req = RaftHeapMalloc(sizeof *req);
	if (req == NULL) {
		return RAFT_NOMEM;
	}
	req->data = r;

	rv = r->io->send(r->io, req, &message, recvSendAppendEntriesResultCb);
	if (rv != 0) {
		raft_free(req);
		return rv;
	}

	return 0;
}

#undef tracef
