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

with lib;

let
    libDir = "/var/lib/burp";
    clientCertDir = "${libDir}/CA-client";
    cfg = config.services.burp;

    clientConf = pkgs.writeText "burp.conf" ''
        mode = client
        pidfile = /run/burp/burp.pid
        port = ${toString cfg.client.port}
        status_port = ${toString cfg.client.statusPort}
        server = ${cfg.client.server}
        password = ${if (cfg.client.passwordFile != null) then "#PASSWORD#" else cfg.client.password}
        cname = ${cfg.client.clientName}
        ca_burp_ca = ${cfg.package}/bin/burp_ca
        ca_csr_dir = ${clientCertDir}
        ssl_cert_ca = ${libDir}/ssl_cert_ca.pem
        ssl_cert = ${libDir}/ssl_cert-client.pem
        ssl_key = ${libDir}/ssl_cert-client.key
        ssl_key_password = ${if (cfg.client.sslKeyPasswordFile != null) then "#SSL_KEY_PASSWORD#" else cfg.client.sslKeyPassword}
        ssl_peer_cn = burpserver
        ${concatMapStringsSep "\n" (x: "include = " + x) cfg.client.includes}
        ${concatMapStringsSep "\n" (x: "exclude = " + x) cfg.client.excludes}
        nobackup = .nobackup
        ${optionalString (cfg.client.encryptionPasswordFile != null) ''
        encryption_password = #ENCRYPTION_PASSWORD#
        ''}
        ${cfg.client.extraConfig}
    '';

    serverHome = "/var/lib/burp";
    serverClientConfDir = serverHome + "/clientconfdir";

    serverCaConf = pkgs.writeText "CA.cnf" ''
        CA_DIR                  = ${serverHome}/CA

        [ ca ]
        dir                     = $ENV::CA_DIR
        database                = $dir/index.txt
        serial                  = $dir/serial.txt
        certs                   = $dir/certs
        new_certs_dir           = $dir/newcerts
        crlnumber               = $dir/crlnumber.txt

        unique_subject          = no

        default_md              = sha256
        default_days            = 7300
        default_crl_days        = 7300

        #????
        name_opt                = ca_default
        cert_opt                = ca_default

        x509_extensions         = usr_cert
        copy_extensions         = copy
        policy                  = policy_anything

        [ usr_cert ]
        basicConstraints        = CA:FALSE

        [ policy_anything ]
        commonName              = supplied
    '';

    serverConf = pkgs.writeText "burp-server.conf" ''
        mode = server
        pidfile = /run/burp/burp-server.pid
        listen = ${cfg.server.listen}
        max_children = 5;
        listen_status = ${cfg.server.listenStatus}
        max_status_children = 5;

        user = burp
        group = burp
        umask = 0022
        clientconfdir = ${serverClientConfDir}
        directory = ${cfg.server.dataDirectory}

        ca_conf = ${serverCaConf}
        ca_name = burpCA
        ca_server_name = burpserver
        ca_burp_ca = ${cfg.package}/bin/burp_ca
        ca_crl_check = 1
        ssl_cert_ca = ${serverHome}/ssl_cert_ca.pem
        ssl_cert = ${serverHome}/ssl_cert-server.pem
        ssl_key = ${serverHome}/ssl_cert-server.key
        ssl_dhfile = ${serverHome}/dhfile.pem
        ssl_key_password = ${if (cfg.server.sslKeyPasswordFile != null) then "#SSL_KEY_PASSWORD#" else cfg.server.sslKeyPassword}

        ${concatMapStringsSep "\n" (x: "keep = " + toString x) cfg.server.keep}
        timer_script = ${cfg.server.timerScript}
        ${concatMapStringsSep "\n" (x: "timer_arg = " + x) cfg.server.timerArgs}

        dedup_group = global
        working_dir_recovery_method = ${cfg.server.workingDirRecoveryMethod}
        max_resume_attempts = ${toString cfg.server.maxResumeAttempts}

        ${concatMapStringsSep "\n" (x: "super_client = " + x) cfg.server.superClients}
        ${concatMapStringsSep "\n" (x: "restore_client = " + x) cfg.server.restoreClients}

        ${cfg.server.extraConfig}
    '';

    clientConfigs = lib.attrsets.mapAttrs (name: config: (pkgs.writeText name ''
        password = ${if (config.passwordFile != null) then "#PASSWORD#" else config.password}
        ${config.extraConfig}
    '')) cfg.server.clients;

in {
    options = {
        services.burp.package = mkOption {
            type = types.package;
            default = pkgs.burp;
            description = ''
                The package which is used as a burp server/client.
            '';
        };

        services.burp.server = {
            enable = mkEnableOption "Burp server";

            listen = mkOption {
                type = types.str;
                default = ":::4971";
                description = ''
                    Listen address used for backup communication.
                '';
            };

            listenStatus = mkOption {
                type = types.str;
                default = ":::4972";
                description = ''
                    Listen address used for querying backup and server status.
                '';
            };

            dataDirectory = mkOption {
                type = types.str;
                default = "/var/spool/burp";
                description = ''
                    Where the backup data is stored.
                '';
            };

            sslKeyPassword = mkOption {
                type = types.str;
                default = "change-this-password";
                description = ''
                    SSL key password for loading a certificate with encryption.
                '';
            };
            sslKeyPasswordFile = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = mdDoc ''
                    File to load an SSL key password for loading a certificate with encryption from.
                    Takes preference over `sslKeyPassword`.
                '';
            };

            keep = mkOption {
                type = types.listOf types.int;
                default = [ 7 ];
                description = ''
                    How many backups to keep.
                '';
            };

            timerScript = mkOption {
                type = types.str;
                default = "${cfg.package}/share/burp/scripts/timer_script";
                description = ''
                    Timer script used to evaluate if it's backup time.
                '';
            };

            timerArgs = mkOption {
                type = types.listOf types.str;
                default = [
                    "20h"
                    "Mon,Tue,Wed,Thu,Fri,00,01,02,03,04,05,19,20,21,22,23"
                    "Sat,Sun,00,01,02,03,04,05,06,07,08,17,18,19,20,21,22,23"
                ];
                description = ''
                    How often should backups be triggered.
                '';
            };

            superClients = mkOption {
                type = types.listOf types.str;
                default = [];
                description = ''
                    Clients that are permitted to list, verify, restore, delete, and diff files belonging to any other client, according to the super_client's client_can permissions (eg, 'client_can_list'). If this is too permissive, you may set a super_client for individual original clients in the individual clientconfdir files, or look at the 'restoreClients' option.
                '';
            };

            restoreClients = mkOption {
                type = types.listOf types.str;
                default = [];
                description = ''
                     Clients that are permitted to list, verify, restore, delete, and diff files belonging to any other client, according to  the client_can permissions on both the restore_client and the original_client (eg, 'client_can_list'). If this is too permissive, you may set a restoreClient for individual original clients in the individual clientconfdir files.
                '';
            };

            workingDirRecoveryMethod = mkOption {
                type = types.str;
                default = "delete";
                description = ''
                    This option tells the server what to do when it finds the working directory of an interrupted backup (perhaps somebody pulled the plug on the server, or something). This can be overridden by the client configurations files in clientconfdir on the server. Options are...

                    delete: Just delete the old working directory.

                    resume: Continue the previous backup from the point at which it left off. NOTE: If the client has changed its include/exclude configuration since the backup was interrupted, the recovery method will automatically switch to 'delete'. See also the 'resume attempts' option.
                '';
            };

            maxResumeAttempts = mkOption {
                type = types.int;
                default = 0;
                description = ''
                    If  workingDirRecoveryMethod  is 'resume', this option tells the server how many times to attempt to resume before giving up and deleting the working directory. The default is 0, which means to never give up.
                '';
            };

            clients = mkOption {
                type = types.attrsOf (types.submodule ({ ... }: {
                    options = {
                        password = mkOption {
                            type = types.str;
                            default = "change-this-password";
                            description = ''
                                Password used by the client for first contact with the server.
                            '';
                        };
                        passwordFile = mkOption {
                            type = types.nullOr types.str;
                            default = null;
                            description = mdDoc ''
                                File to load a password for the first contact from client to server from.
                                Takes preference over `password`.
                            '';
                        };

                        extraConfig = mkOption {
                            type = types.lines;
                            default = "";
                            description = ''
                                Extra configuration for burp client. Contents will be added verbatim to the
                                configuration file.
                            '';
                        };
                    };
                }));
            };

            extraConfig = mkOption {
                type = types.lines;
                default = "";
                description = ''
                    Extra configuration for burp client. Contents will be added verbatim to the
                    configuration file.
                '';
            };
        };

        services.burp.client = {
            enable = mkEnableOption "Burp client";

            frequency = mkOption {
                type = types.str;
                default = "hourly";
                description = ''
                    Controls how frequently the systemd timer is triggered and a backup
                    is attempted.
                    Backup frequency is still determined by the server, this
                    controls only how often the client tries.
                '';
            };

            server = mkOption {
                type = types.str;
                default = "127.0.0.1";
                description = ''
                    Address of burp server the client should contact.
                '';
            };

            port = mkOption {
                type = types.port;
                default = 4971;
                description = ''
                    Port used for backup communication.
                '';
            };

            statusPort = mkOption {
                type = types.port;
                default = 4972;
                description = ''
                    Port used for querying backup and server status.
                '';
            };

            clientName = mkOption {
                type = types.str;
                default = "${config.networking.hostName}";
                description = ''
                    Name the client should use to identify itself to the server.
                '';
            };

            password = mkOption {
                type = types.str;
                default = "change-this-password";
                description = ''
                    Password used by the client for first contact with the server.
                '';
            };
            passwordFile = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = mdDoc ''
                    File to load a password for the first contact from client to server from.
                    Takes preference over `password`.
                '';
            };

            sslKeyPassword = mkOption {
                type = types.str;
                default = "change-this-password";
                description = ''
                    SSL key password for loading a certificate with encryption.
                '';
            };
            sslKeyPasswordFile = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = mdDoc ''
                    File to load an SSL key password for loading a certificate with encryption from.
                    Takes preference over `sslKeyPassword`.
                '';
            };

            includes = mkOption {
                type = types.listOf types.str;
                default = [ "/etc" "/root" "/var" "/home" ];
                description = ''
                    List of locations to include in backups.
                '';
            };

            excludes = mkOption {
                type = types.listOf types.str;
                default = [ libDir ];
                description = ''
                    List of locations to exclude from the backup.
                '';
            };

            encryptionPasswordFile = mkOption {
                type = types.nullOr types.str;
                default = null;
                description = ''
                    File with a password for encrypted backups.
                '';
            };

            extraConfig = mkOption {
                type = types.lines;
                default = "";
                description = ''
                    Extra configuration for burp client. Contents will be added verbatim to the
                    configuration file.
                '';
            };
        };
    };

    config = {
        environment.systemPackages = mkIf cfg.client.enable [ cfg.package ];

        systemd.timers.burp-client = mkIf cfg.client.enable {
            description = "Timer for triggering Burp client and start a backup";
            wantedBy = [ "timers.target" ];
            timerConfig = {
                OnCalendar = cfg.client.frequency;
                Unit = "burp-client.service";
            };
        };

        systemd.services.burp-client = mkIf cfg.client.enable {
            description = "Burp client";
            after = [ "network.target" ];
            path = [ cfg.package pkgs.nettools pkgs.openssl ];

            preStart = let
                configFile = "${libDir}/burp.conf";
                replaceSecret = "${pkgs.replace-secret}/bin/replace-secret";
            in ''
                prepare_config()
                {
                    umask 027
                    install -Dm640 ${clientConf} '${configFile}'

                    ${optionalString (cfg.client.passwordFile != null) ''
                        ${replaceSecret} '#PASSWORD#' '${cfg.client.passwordFile}' '${configFile}'
                    ''}
                    ${optionalString (cfg.client.sslKeyPasswordFile != null) ''
                        ${replaceSecret} '#SSL_KEY_PASSWORD#' '${cfg.client.sslKeyPasswordFile}' '${configFile}'
                    ''}
                    ${optionalString (cfg.client.encryptionPasswordFile != null) ''
                        ${replaceSecret} '#ENCRYPTION_PASSWORD#' '${cfg.client.encryptionPasswordFile}' '${configFile}'
                    ''}
                }

                if [ ! -d "${libDir}" ]; then
                    mkdir -m 0750 -p ${libDir}
                    mkdir -m 0700 -p ${clientCertDir}
                    prepare_config
                    ${cfg.package}/bin/burp -c '${configFile}' -g
                else
                    prepare_config
                fi
            '';

            serviceConfig = {
                Type = "simple";
                ExecStart = "${cfg.package}/bin/burp -c ${libDir}/burp.conf -a t";
                SuccessExitStatus = "3";
            };
        };

        users = mkIf cfg.server.enable {
            users.burp = {
                group = "burp";
                uid = 497;
                home = "${serverHome}";
                createHome = true;
                description = "Burp Server user";
                shell = "${pkgs.bash}/bin/bash";
                isSystemUser = true;
            };
            groups.burp = {
                gid = 497;
            };
        };

        systemd.services.burp-server = mkIf cfg.server.enable {
            description = "Burp Server";
            after = [ "network.target" ];
            wantedBy = [ "multi-user.target" ];
            path = [ cfg.package pkgs.nettools pkgs.openssl ];

            serviceConfig = let
                configFile = "${serverHome}/burp-server.conf";
                replaceSecret = "${pkgs.replace-secret}/bin/replace-secret";
                preStartScript = pkgs.writeScript "burp-server-prestart" ''
                    #!/${pkgs.bash}/bin/bash

                    prepare_data_directory()
                    {
                        if ! [ -d "${cfg.server.dataDirectory}" ] ; then
                            mkdir -p "${cfg.server.dataDirectory}"
                        fi
                        chown burp:burp "${cfg.server.dataDirectory}" "${serverClientConfDir}"
                        chmod 700 "${cfg.server.dataDirectory}"
                    }

                    prepare_config()
                    {
                        install -Dm640 -o burp -g burp '${serverConf}' '${configFile}'

                        ${optionalString (cfg.server.sslKeyPasswordFile != null) ''
                            ${replaceSecret} '#SSL_KEY_PASSWORD#' '${cfg.server.sslKeyPasswordFile}' '${configFile}'
                        ''}
                    }

                    prepare_client_configs()
                    {
                        umask 077

                        if ! [ -d "${serverClientConfDir}" ] ; then
                            mkdir -p "${serverClientConfDir}"
                        fi

                        rm -f "${serverClientConfDir}"/*

                        ${concatStringsSep "\n" (mapAttrsToList(name: file: ''
                            install -Dm640 -o burp -g burp '${file}' '${serverClientConfDir}/${name}'
                            ${optionalString (cfg.server.clients.${name}.passwordFile != null) ''
                                ${replaceSecret} '#PASSWORD#' '${cfg.server.clients.${name}.passwordFile}' '${serverClientConfDir}/${name}'
                            ''}
                        '') clientConfigs)}
                    }

                    prepare_data_directory
                    prepare_config
                    prepare_client_configs
                '';
            in {
                ExecStart = "${cfg.package}/bin/burp -F -v -c ${configFile}";
                ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";

                User = "burp";
                Group = "burp";
                UMask = "0077";
                RuntimeDirectory = "burp";
                PrivateTmp = true;
                PrivateDevices = true;
                ProtectSystem = true;
                ProtectHome = true;
                NoNewPrivileges = true;
                ReadWriteDirectories = [
                    cfg.server.dataDirectory
                    serverHome
                ];

                ExecStartPre = "+${preStartScript}";

                Nice = 19;
                IOSchedulingClass = "idle";
                CPUSchedulingPolicy = "idle";
            };
        };
    };
}