{ pkgs, config, lib, ... }:
let
  cfg = config.myServices.databasesReplication.postgresql;
in
{
  options.myServices.databasesReplication.postgresql = {
    enable = lib.mkEnableOption "Enable postgresql replication";
    base = lib.mkOption {
      type = lib.types.path;
      description = ''
        Base path to put the replications
        '';
    };
    hosts = lib.mkOption {
      default = {};
      description = ''
        Hosts to backup
        '';
      type = lib.types.attrsOf (lib.types.submodule {
        options = {
          package = lib.mkOption {
            type = lib.types.package;
            default = pkgs.postgresql;
            description = ''
              Postgresql package for this host
            '';
          };
          slot = lib.mkOption {
            type = lib.types.str;
            description = ''
              Slot to use for replication
            '';
          };
          connection = lib.mkOption {
            type = lib.types.str;
            description = ''
              Connection string to access the psql master
            '';
          };
        };
      });
    };
  };

  config = lib.mkIf cfg.enable {
    nixpkgs.overlays = [ (self: super: {
      postgresql = self.postgresql_11_custom;
    }) ];

    users.users.postgres = {
      name = "postgres";
      uid = config.ids.uids.postgres;
      group = "postgres";
      description = "PostgreSQL server user";
      home = "/var/lib/postgresql";
      useDefaultShell = true;
      extraGroups = [ "keys" ];
    };
    users.groups.postgres.gid = config.ids.gids.postgres;
    environment.systemPackages = [ pkgs.postgresql ];

    secrets.keys = lib.flatten (lib.mapAttrsToList (name: hcfg: [
      {
        dest = "postgresql_replication/${name}/recovery.conf";
        user = "postgres";
        group = "postgres";
        permissions = "0400";
        text = ''
          standby_mode = on
          primary_conninfo = '${hcfg.connection}?sslmode=require'
          primary_slot_name = '${hcfg.slot}'
          '';
      }
      {
        dest = "postgresql_replication/${name}/connection_string";
        user = "postgres";
        group = "postgres";
        permissions = "0400";
        text = hcfg.connection;
      }
      {
        dest = "postgresql_replication/${name}/postgresql.conf";
        user = "postgres";
        group = "postgres";
        permissions = "0400";
        text = let
          dataDir = "${cfg.base}/${name}/postgresql";
        in ''
          listen_addresses = '''
          unix_socket_directories = '${dataDir}'
          data_directory = '${dataDir}'
          wal_level = logical
          '';
      }
    ]) cfg.hosts);

    services.cron = {
      enable = true;
      systemCronJobs = lib.flatten (lib.mapAttrsToList (name: hcfg:
        let
          dataDir = "${cfg.base}/${name}/postgresql";
          backupDir = "${cfg.base}/${name}/postgresql_backup";
          backup_script = pkgs.writeScript "backup_psql_${name}" ''
              #!${pkgs.stdenv.shell}

              set -euo pipefail

              resume_replication() {
                ${hcfg.package}/bin/psql -h ${dataDir} -c "SELECT pg_wal_replay_resume();" >/dev/null || echo "impossible to resume replication"
              }

              trap resume_replication EXIT

              ${hcfg.package}/bin/psql -h ${dataDir} -c "SELECT pg_wal_replay_pause();" >/dev/null || (echo "impossible to pause replication" && false)

              ${hcfg.package}/bin/pg_dumpall -h ${dataDir} -f ${backupDir}/$(${pkgs.coreutils}/bin/date -Iseconds).sql
            '';
          u = pkgs.callPackage ./utils.nix {};
          cleanup_script = pkgs.writeScript "cleanup_postgresql_${name}" (u.keepLastNDumps backupDir 12);
        in [
          "0 22,4,10,16 * * * postgres ${backup_script}"
          "0 3 * * * postgres ${cleanup_script}"
        ]) cfg.hosts);
    };

    system.activationScripts = lib.attrsets.mapAttrs' (name: hcfg:
      lib.attrsets.nameValuePair "psql_replication_${name}" {
        deps = [ "users" ];
        text = ''
          install -m 0700 -o postgres -g postgres -d ${cfg.base}/${name}/postgresql
          install -m 0700 -o postgres -g postgres -d ${cfg.base}/${name}/postgresql_backup
          '';
      }) cfg.hosts;

    systemd.services = lib.attrsets.mapAttrs' (name: hcfg:
      let
        dataDir = "${cfg.base}/${name}/postgresql";
      in
      lib.attrsets.nameValuePair "postgresql_backup_${name}" {
        description = "Postgresql replication for ${name}";
        wantedBy = [ "multi-user.target" ];
        after = [ "network.target" ];

        environment.PGDATA = dataDir;
        path = [ hcfg.package ];

        preStart = ''
          if ! test -e ${dataDir}/PG_VERSION; then
            mkdir -m 0700 -p ${dataDir}
            chown -R postgres:postgres ${dataDir}
          fi
          '';
        script = let
          fp = n: config.secrets.fullPaths."postgresql_replication/${name}/${n}";
        in ''
          if ! test -e ${dataDir}/PG_VERSION; then
            pg_basebackup -d $(cat ${fp "connection_string"}) -D ${dataDir} -S ${hcfg.slot}
          fi
          ln -sfn ${fp "recovery.conf"} ${dataDir}/recovery.conf
          ln -sfn ${fp "postgresql.conf"} ${dataDir}/postgresql.conf

          exec postgres
          '';

        serviceConfig = {
          ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
          User = "postgres";
          Group = "postgres";
          PermissionsStartOnly = true;
          RuntimeDirectory = "postgresql";
          Type = "notify";

          KillSignal = "SIGINT";
          KillMode = "mixed";
          # basebackup can take a long time
          TimeoutStartSec="infinity";
          TimeoutStopSec = 120;
        };
        unitConfig.RequiresMountsFor = dataDir;
    }) cfg.hosts;
  };
}