# Declarative routing configuration. Usees BIRD2 underneath.
#
# The mapping from declarative configuration to BIRD is quite straightforward,
# however, we take a few liberties:
#  - we introduce an 'originate' protocol for originating prefixes (using the
#    static protocol).
#  - routing tables in the configuration are referred to by a common name for
#    IPv4 and IPv4 - while in BIRD, two tables are created (suffixed by '4' and
#    '6', following the two default 'master4' and 'master6' tables).

{ config, lib, pkgs, ... }:

with lib;
let
  cfg = config.hscloud.routing;

  originateType = af: let
    v4 = af == "ipv4";
    v6 = af == "ipv6";
    pretty = if v4 then "IPv4" else "IPv6";
  in with types; mkOption {
    type = attrsOf (submodule {
      options = {
        table = mkOption {
          type = nullOr str;
          description = "BIRD table to which session should be connected.";
        };
        address = mkOption {
          type = str;
          description = "Address part of prefix to announce.";
        };
        prefixLength = mkOption {
          type = int;
          description = "Prefix length to announce.";
        };
      };
    });
    default = {};
    description = "${pretty} prefixes to unconditionally inject into a table.";
  };

  originateRender = af: n: v: let
    name = "static_originate_${af}_${n}";
    ip = if af == "ipv4" then "4" else "6";
  in ''
    protocol static ${name} {
      ${af} {
        table ${v.table}${ip};
        import all;
        export none;
      };

      route ${v.address}/${toString v.prefixLength} blackhole;
    }
  '';

  ospfType = af: let
    v4 = af == "ipv4";
    v6 = af == "ipv6";
    pretty = if v4 then "IPv4" else "IPv6";
    ospf = if v4 then "OSPFv2" else "OSPFv3";
  in with types; mkOption {
    type = attrsOf (submodule {
      options = {
        table = mkOption {
          type = nullOr str;
          description = "BIRD table to which session should be connected.";
        };
        filterIn = mkOption {
          type = str;
          default = "accept;";
          description = "BIRD filter definition for received routes.";
        };
        filterOut = mkOption {
          type = str;
          default = "accept;";
          description = "BIRD filter definition for sent routes.";
        };
        area = mkOption {
          type = attrsOf (submodule {
            options = {
              interfaces = mkOption {
                type = attrsOf (submodule {
                  options = {
                    cost = mkOption {
                      type = int;
                      default = 10; # 1Gbps
                      description = "Interface cost (10e9/iface_speed_in_bps).";
                    };
                    type = mkOption {
                      type = enum ["bcast" "nbma" "ptp" "ptmp"];
                      description = "Interface type (dictates BIRD behaviour).";
                    };
                    stub = mkOption {
                      type = bool;
                      default = false;
                      description = "Interface is stub (do not HELLO).";
                    };
                  };
                });
                description = "Interface configuration";
              };
            };
          });
          description = "Area configuration";
        };
      };
    });
    default = {};
    description = "${ospf} configuration";
  };

  ospfRender = af: n: v: let
    v4 = af == "ipv4";
    v6 = af == "ipv6";
    ip = if v4 then "4" else "6";
    name = "ospf_${af}_${n}";

    interfaces = mapAttrsToList (iface: ifaceConfig: ''
      interface "${iface}" {
        type ${ifaceConfig.type};
        cost ${toString ifaceConfig.cost};
        ${if ifaceConfig.stub then "stub yes;" else ""}
      };
    '');
    areas = mapAttrsToList (area: areaConfig: ''
      area ${area} {
        ${concatStringsSep "\n" (interfaces areaConfig.interfaces)}
      };
    '') v.area;
  in ''
    filter ${name}_in {
      ${v.filterIn}
    };
    filter ${name}_out {
      ${v.filterOut}
    };
    protocol ospf ${if v4 then "v2" else "v3"} ${name} {
      ${af} {
        table ${v.table}${ip};
        import filter ${name}_in;
        export filter ${name}_out;
      };
      ${concatStringsSep "\n" areas}
    }
  '';

  pipeType = af: with types; mkOption {
    type = attrsOf (submodule {
      options = {
        table = mkOption {
          type = nullOr str;
          description = "BIRD table to which session should be connected.";
        };
        peerTable = mkOption {
          type = nullOr str;
          description = "BIRD 'remote' table to which session should be connected.";
        };
        filterIn = mkOption {
          type = str;
          default = "accept";
          description = "BIRD filter definition for routes received from peerTable";
        };
        filterOut = mkOption {
          type = str;
          default = "reject;";
          description = "BIRD filter definition for routes sent to peerTable";
        };
      };
    });
    default = {};
    description = "${pretty} prefixes to pipe from one table to another.";
  };

  pipeRender = af: n: v: let
    name = "pipe_${af}_${n}";
    v4 = af == "ipv4";
    v6 = af == "ipv6";
    ip = if v4 then "4" else "6";
  in ''
    filter ${name}_in {
      ${v.filterIn}
    };
    filter ${name}_out {
      ${v.filterOut}
    };
    protocol pipe ${name} {
      table ${v.table}${ip};
      peer table ${v.peerTable}${ip};
      import filter ${name}_in;
      export filter ${name}_out;
    }
  '';

  bgpSessionsType = af: let
    v4 = af == "ipv4";
    v6 = af == "ipv6";
    pretty = if v4 then "IPv4" else "IPv6";
  in with types; mkOption {
    type = attrsOf (submodule {
      options = {
        description = mkOption {
          type = str;
          description = "Session description (for BIRD).";
        };
        table = mkOption {
          type = nullOr str;
          description = "BIRD table to which session should be connected.";
        };
        local = mkOption {
          type = str;
          description = "${pretty} address of this router.";
        };
        asn = mkOption {
          type = int;
          description = "ASN of local router - will default to hscloud.routing.asn.";
          default = cfg.asn;
        };
        prepend = mkOption {
          type = int;
          default = 0;
          description = "How many times to prepend this router's ASN on the link.";
        };
        pref = mkOption {
          type = int;
          default = 100;
          description = "Preference (BGP local_pref) for routes from this session.";
        };
        direct = mkOption {
          type = nullOr bool;
          default = null;
        };
        filterIn = mkOption {
          type = str;
          default = "accept;";
          description = "BIRD filter definition for received routes.";
        };
        filterOut = mkOption {
          type = str;
          default = "accept;";
          description = "BIRD filter definition for sent routes.";
        };
        neighbors = mkOption {
          type = listOf (submodule {
            options = {
              address = mkOption {
                type = str;
                description = "${pretty} address of neighbor.";
              };
              asn = mkOption {
                type = int;
                description = "ASN of neighbor.";
              };
              password = mkOption {
                type = nullOr str;
                default = null;
                description = "BGP TCP MD5 secret.";
              };
            };
          });
          description = "BGP Neighbor configuration";
        };
      };
    });
    default = {};
    description = "BGP Sesions for ${pretty}";
  };

  bgpSessionRender = af: n: v: let
    name = "bgp_${af}_${n}";
    ip = if af == "ipv4" then "4" else "6";
    filters = ''
      filter ${name}_in {
        if bgp_path.len > 64 then reject;
        bgp_local_pref = ${toString v.pref};
        ${v.filterIn}
      }

      filter ${name}_out {
        ${if v.prepend > 0 then
          (concatStringsSep "\n" 
            (map (_: "bgp_path.prepend(${toString v.asn});") (range 0 (v.prepend - 1)))
          )
        else ""}
        ${v.filterOut}
      }
    '';
    peer = ix: peer: ''
      protocol bgp ${name}_${toString ix} {
        description "${v.description}";

        ${af} {
            table ${v.table}${ip};
            import filter ${name}_in;
            export filter ${name}_out;
        };

        local ${v.local} as ${toString v.asn};
        neighbor ${peer.address} as ${toString peer.asn};
        ${if peer.password != null then "password \"${peer.password}\";" else ""}
        ${if v.direct == true then "direct;" else ""}
      }
    '';
  in "${filters}\n${concatStringsSep "\n" (imap1 peer v.neighbors)}";

  tablesFromProtoAF =
    af: p: filter (el: el != null) (
      mapAttrsToList (_: v: "${af} table ${v.table}${if af == "ipv4" then "4" else "6"};") p);
  tablesFromProto = p: (tablesFromProtoAF "ipv4" p.v4) ++ (tablesFromProtoAF "ipv6" p.v6);
  tables =
    unique (
      (tablesFromProto cfg.bgpSessions) ++
      (tablesFromProto cfg.originate) ++
      (tablesFromProto cfg.pipe) ++
      (tablesFromProto cfg.ospf)
      # TODO(q3k): also slurp in peer tables from pipes.
    );
  tablesRender = ''
    ${concatStringsSep "\n" tables}
  '';
  tablesProgram = mapAttrsToList (n: _: n) (filterAttrs (n: v: v.program == true) cfg.tables);
  tableProgram =
    if (length tablesProgram) != 1 then
      (abort "exactly one table must be set to be programmed")
    else 
      (head tablesProgram);

in {
  options.hscloud.routing = {
    enable = mkEnableOption "declarative routing";
    routerID = mkOption {
      type = types.str;
      description = ''
        Default Router ID for dynamic routing protocols, eg. IPv4 address from
        loopback interface.
      '';
    };
    asn = mkOption {
      type = types.int;
      description = "Default ASN for BGP.";
    };
    extra = mkOption {
      type = types.lines;
      description = "Extra configuration lines.";
    };
    bgpSessions = {
      v4 = bgpSessionsType "ipv4";
      v6 = bgpSessionsType "ipv6";
    };
    originate = {
      v4 = originateType "ipv4";
      v6 = originateType "ipv6";
    };
    pipe = {
      v4 = pipeType "ipv4";
      v6 = pipeType "ipv6";
    };
    ospf = {
      v4 = ospfType "ipv4";
      v6 = ospfType "ipv6";
    };
    tables = mkOption {
      type = types.attrsOf (types.submodule {
        options = {
          program = mkOption {
            type = types.bool;
            default = false;
            description = "This is the primary table programmed in to the kernel.";
          };
          programSourceV4 = mkOption {
            type = types.nullOr types.str;
            default = null;
            description = "If set, programmed routes will have source set to this address.";
          };
          programSourceV6 = mkOption {
            type = types.nullOr types.str;
            default = null;
            description = "If set, programmed routes will have source set to this address.";
          };
        };
      });
      description = "Routing table configuration.";
    };
  };

  config = mkIf cfg.enable {
    services.bird2.enable = true;
    services.bird2.config = ''
      log syslog all;
      debug protocols { states, interfaces, events }

      router id ${cfg.routerID};

      ${cfg.extra}

      ${tablesRender}

      protocol device {
        scan time 10;
      };

      protocol kernel kernel_v4 {
        scan time 60;
        ipv4 {
          table ${tableProgram}4;
          import none;
          export filter {
            ${let src = cfg.tables."${tableProgram}".programSourceV4; in if src != null then ''
              krt_prefsrc = ${src};
            '' else ""}
            accept;
          };
        };
      }
      protocol kernel kernel_v6 {
        scan time 60;
        ipv6 {
          table ${tableProgram}6;
          import none;
          export filter {
            ${let src = cfg.tables."${tableProgram}".programSourceV6; in if src != null then ''
              krt_prefsrc = ${src};
            '' else ""}
            accept;
          };
        };
      };

      ${concatStringsSep "\n" (mapAttrsToList (bgpSessionRender "ipv4") cfg.bgpSessions.v4)}
      ${concatStringsSep "\n" (mapAttrsToList (bgpSessionRender "ipv6") cfg.bgpSessions.v6)}
      ${concatStringsSep "\n" (mapAttrsToList (originateRender "ipv4") cfg.originate.v4)}
      ${concatStringsSep "\n" (mapAttrsToList (originateRender "ipv6") cfg.originate.v6)}
      ${concatStringsSep "\n" (mapAttrsToList (pipeRender "ipv4") cfg.pipe.v4)}
      ${concatStringsSep "\n" (mapAttrsToList (pipeRender "ipv6") cfg.pipe.v6)}
      ${concatStringsSep "\n" (mapAttrsToList (ospfRender "ipv4") cfg.ospf.v4)}
      ${concatStringsSep "\n" (mapAttrsToList (ospfRender "ipv6") cfg.ospf.v6)}

    '';
  };
}