import ./make-test-python.nix ({pkgs, lib, ...}:

let
  # Settings for both servers and agents
  webUi = true;
  retry_interval = "1s";
  raft_multiplier = 1;

  defaultExtraConfig = {
    inherit retry_interval;
    performance = {
      inherit raft_multiplier;
    };
  };

  allConsensusServerHosts = [
    "192.168.1.1"
    "192.168.1.2"
    "192.168.1.3"
  ];

  allConsensusClientHosts = [
    "192.168.2.1"
    "192.168.2.2"
  ];

  firewallSettings = {
    # See https://www.consul.io/docs/install/ports.html
    allowedTCPPorts = [ 8301 8302 8600 8500 8300 ];
    allowedUDPPorts = [ 8301 8302 8600 ];
  };

  client = index: { pkgs, ... }:
    let
      ip = builtins.elemAt allConsensusClientHosts index;
    in
      {
        environment.systemPackages = [ pkgs.consul ];

        networking.interfaces.eth1.ipv4.addresses = pkgs.lib.mkOverride 0 [
          { address = ip; prefixLength = 16; }
        ];
        networking.firewall = firewallSettings;

        services.consul = {
          enable = true;
          inherit webUi;
          extraConfig = defaultExtraConfig // {
            server = false;
            retry_join = allConsensusServerHosts;
            bind_addr = ip;
          };
        };
      };

  server = index: { pkgs, ... }:
    let
      numConsensusServers = builtins.length allConsensusServerHosts;
      thisConsensusServerHost = builtins.elemAt allConsensusServerHosts index;
      ip = thisConsensusServerHost; # since we already use IPs to identify servers
    in
      {
        networking.interfaces.eth1.ipv4.addresses = pkgs.lib.mkOverride 0 [
          { address = ip; prefixLength = 16; }
        ];
        networking.firewall = firewallSettings;

        services.consul =
          assert builtins.elem thisConsensusServerHost allConsensusServerHosts;
          {
            enable = true;
            inherit webUi;
            extraConfig = defaultExtraConfig // {
              server = true;
              bootstrap_expect = numConsensusServers;
              # Tell Consul that we never intend to drop below this many servers.
              # Ensures to not permanently lose consensus after temporary loss.
              # See https://github.com/hashicorp/consul/issues/8118#issuecomment-645330040
              autopilot.min_quorum = numConsensusServers;
              retry_join =
                # If there's only 1 node in the network, we allow self-join;
                # otherwise, the node must not try to join itself, and join only the other servers.
                # See https://github.com/hashicorp/consul/issues/2868
                if numConsensusServers == 1
                  then allConsensusServerHosts
                  else builtins.filter (h: h != thisConsensusServerHost) allConsensusServerHosts;
              bind_addr = ip;
            };
          };
      };
in {
  name = "consul";

  nodes = {
    server1 = server 0;
    server2 = server 1;
    server3 = server 2;

    client1 = client 0;
    client2 = client 1;
  };

  testScript = ''
    servers = [server1, server2, server3]
    machines = [server1, server2, server3, client1, client2]

    for m in machines:
        m.wait_for_unit("consul.service")


    def wait_for_healthy_servers():
        # See https://github.com/hashicorp/consul/issues/8118#issuecomment-645330040
        # for why the `Voter` column of `list-peers` has that info.
        # TODO: The `grep true` relies on the fact that currently in
        #       the output like
        #           # consul operator raft list-peers
        #           Node     ID   Address           State     Voter  RaftProtocol
        #           server3  ...  192.168.1.3:8300  leader    true   3
        #           server2  ...  192.168.1.2:8300  follower  true   3
        #           server1  ...  192.168.1.1:8300  follower  false  3
        #       `Voter`is the only boolean column.
        #       Change this to the more reliable way to be defined by
        #       https://github.com/hashicorp/consul/issues/8118
        #       once that ticket is closed.
        for m in machines:
            m.wait_until_succeeds(
                "[ $(consul operator raft list-peers | grep true | wc -l) == 3 ]"
            )


    def wait_for_all_machines_alive():
        """
        Note that Serf-"alive" does not mean "Raft"-healthy;
        see `wait_for_healthy_servers()` for that instead.
        """
        for m in machines:
            m.wait_until_succeeds("[ $(consul members | grep -o alive | wc -l) == 5 ]")


    wait_for_healthy_servers()
    # Also wait for clients to be alive.
    wait_for_all_machines_alive()

    client1.succeed("consul kv put testkey 42")
    client2.succeed("[ $(consul kv get testkey) == 42 ]")


    def rolling_reboot_test(proper_rolling_procedure=True):
        """
        Tests that the cluster can tolearate failures of any single server,
        following the recommended rolling upgrade procedure from
        https://www.consul.io/docs/upgrading#standard-upgrades.

        Optionally, `proper_rolling_procedure=False` can be given
        to wait only for each server to be back `Healthy`, not `Stable`
        in the Raft consensus, see Consul setting `ServerStabilizationTime` and
        https://github.com/hashicorp/consul/issues/8118#issuecomment-645330040.
        """

        for server in servers:
            server.crash()

            # For each client, wait until they have connection again
            # using `kv get -recurse` before issuing commands.
            client1.wait_until_succeeds("consul kv get -recurse")
            client2.wait_until_succeeds("consul kv get -recurse")

            # Do some consul actions while one server is down.
            client1.succeed("consul kv put testkey 43")
            client2.succeed("[ $(consul kv get testkey) == 43 ]")
            client2.succeed("consul kv delete testkey")

            # Restart crashed machine.
            server.start()

            if proper_rolling_procedure:
                # Wait for recovery.
                wait_for_healthy_servers()
            else:
                # NOT proper rolling upgrade procedure, see above.
                wait_for_all_machines_alive()

            # Wait for client connections.
            client1.wait_until_succeeds("consul kv get -recurse")
            client2.wait_until_succeeds("consul kv get -recurse")

            # Do some consul actions with server back up.
            client1.succeed("consul kv put testkey 44")
            client2.succeed("[ $(consul kv get testkey) == 44 ]")
            client2.succeed("consul kv delete testkey")


    def all_servers_crash_simultaneously_test():
        """
        Tests that the cluster will eventually come back after all
        servers crash simultaneously.
        """

        for server in servers:
            server.crash()

        for server in servers:
            server.start()

        # Wait for recovery.
        wait_for_healthy_servers()

        # Wait for client connections.
        client1.wait_until_succeeds("consul kv get -recurse")
        client2.wait_until_succeeds("consul kv get -recurse")

        # Do some consul actions with servers back up.
        client1.succeed("consul kv put testkey 44")
        client2.succeed("[ $(consul kv get testkey) == 44 ]")
        client2.succeed("consul kv delete testkey")


    # Run the tests.

    print("rolling_reboot_test()")
    rolling_reboot_test()

    print("all_servers_crash_simultaneously_test()")
    all_servers_crash_simultaneously_test()

    print("rolling_reboot_test(proper_rolling_procedure=False)")
    rolling_reboot_test(proper_rolling_procedure=False)
  '';
})