{ config, lib, pkgs, ... }:
with lib;
let
  cfg = config.services.erpnext;
  pkg = cfg.package;
  defaultUser = "erpnext";
in
{
  # interface
  options.services.erpnext = {
    enable = mkOption {
      type = lib.types.bool;
      default = false;
      description = lib.mdDoc ''
        Enable ERPNext.

        When started, the ERPNext database is automatically created if it doesn't
        exist.
      '';
    };

    domain = mkOption {
      type = types.str;
      default = "localhost";
      description = lib.mdDoc ''
        Domain name of your server.
      '';
    };

    workDir = mkOption {
      type = types.str;
      default = "/var/lib/erpnext";
      description = lib.mdDoc "Working directory of ERPNext.";
    };

    benchDir = mkOption {
      type = types.str;
      default = "${cfg.workDir}/bench";
      description = lib.mdDoc "Bench directory for ERPNext.";
    };

    adminPasswordFile = mkOption {
      type = types.nullOr types.path;
      default = null;
      example = "/run/secrets/erpnext-admin-password";
      description = lib.mdDoc ''
        A file containing the Administrator user password.
      '';
    };

    database = {
      host = mkOption {
        type = types.str;
        default = "localhost";
        description = lib.mdDoc "Database host address.";
      };
      port = mkOption {
        type = types.port;
        default = 3306;
        description = lib.mdDoc "Database host port.";
      };
      name = mkOption {
        type = types.str;
        default = "erpnext";
        description = lib.mdDoc "Database name.";
      };
      user = mkOption {
        type = types.str;
        default = "erpnext";
        description = lib.mdDoc "Database username.";
      };
      userPasswordFile = mkOption {
        type = types.nullOr types.path;
        default = null;
        example = "/run/secrets/erpnext-db-user-password";
        description = lib.mdDoc ''
          A file containing the MariaDB erpnext user password.
        '';
      };
      rootPasswordFile = mkOption {
        type = types.nullOr types.path;
        default = null;
        example = "/run/secrets/erpnext-db-root-password";
        description = lib.mdDoc ''
          A file containing the MariaDB root user password.
        '';
      };
      createLocally = mkOption {
        type = types.bool;
        default = true;
        description = lib.mdDoc "Create the database and database user locally.";
      };
      automaticMigrations = mkEnableOption
        (lib.mdDoc "automatic migrations for database schema and data") // {
          default = true;
        };
    };

    redis = {
      host = mkOption {
        type = types.str;
        default = "localhost";
        description = lib.mdDoc "Redis host address.";
      };
      port = mkOption {
        type = types.port;
        default = 6379;
        description = lib.mdDoc "Redis host port.";
      };
      createLocally = mkOption {
        type = types.bool;
        default = true;
        description = lib.mdDoc "Create the redis server locally.";
      };
    };

    webserver = {
      bindAddress = mkOption {
        type = types.str;
        default = "localhost";
        description = lib.mdDoc "Web interface address.";
      };
      bindPort = mkOption {
        type = types.port;
        default = 9090;
        description = lib.mdDoc "Web interface port.";
      };
    };

    caddy = mkOption {
      type = types.nullOr types.attrs;
      default = null;
      example = lib.literalExpression ''
        {
          serverAliases = [
            "erpnext.your.domain"
            "erp.your.domain"
          ];
          # Disable access logs
          logFormat = ''
            output discard
          '';
        }
      '';
      description = lib.mdDoc ''
          With this option, you can customize a caddy virtual host.
          Set to {} if you do not need any customization to the virtual host.
          If enabled, then by default, the {option}`hostName` is
          `''${domain}`,
          TLS is active by default, and handled by caddy.

          Additionally, you probably want to set the caddy email option, when
          enabling this: {option}`services.caddy.email

          If this is set to null (the default), no caddy virtualHost will be
          configured.
      '';
    };

    user = mkOption {
      type = types.str;
      default = defaultUser;
      description = lib.mdDoc "User under which ERPNext runs.";
    };

    package = mkOption {
      type = types.package;
      default = pkgs.python3.pkgs.erpnext;
      defaultText = literalExpression "pkgs.python3.pkgs.erpnext";
      description = lib.mdDoc "The ERPNext package to use.";
    };
  };

  # implementation
  config =
  let
    penv = pkgs.python3.buildEnv.override {
      extraLibs = [
        pkgs.python3.pkgs.frappe
        pkgs.python3.pkgs.erpnext
        pkgs.python3.pkgs.bench
      ];
    };
    appsFile = pkgs.writeText "erpnext-apps.txt" ''
      frappe
      erpnext
    '';
    # In a module, this could be provided by a use as a file as it could
    # contain secrets and we don't want this in the nix-store. But here it
    # is OK.
    commonSiteConfig = {
      db_host = "${cfg.database.host}";
      db_port = "${toString cfg.database.port}";
      db_name = "${cfg.database.name}";
      db_password = "#NIXOS_ERPNEXT_DB_USER_PASSWORD#";
      redis_cache = "redis://${cfg.redis.host}:${toString cfg.redis.port}?db=0";
      redis_queue = "redis://${cfg.redis.host}:${toString cfg.redis.port}?db=1";
    };
    commonSiteConfigFile = pkgs.writeText "erpnext-common_site_config.json" (builtins.toJSON commonSiteConfig);

    defaultServiceConfig = {
      User = cfg.user;
      NoNewPrivileges = true;
      Type = "simple";
      BindReadOnlyPaths = [
        "/etc/hosts:/etc/hosts"
        "/etc/resolv.conf:/etc/resolv.conf"
        "/etc/ssl:/etc/ssl"
        "/etc/static/ssl:/etc/static/ssl"
        "/run/agenix:/run/agenix"
        "${pkgs.frappe-app}:${pkgs.frappe-app}"
        "${pkgs.frappe-app}/share/apps/frappe:${cfg.benchDir}/apps/frappe"
        "${pkgs.erpnext-app}:${pkgs.erpnext-app}"
        "${pkgs.erpnext-app}/share/apps/erpnext:${cfg.benchDir}/apps/erpnext"
        "${pkgs.frappe-erpnext-assets}/share/sites/assets:${cfg.benchDir}/sites/assets"
        "${appsFile}:${cfg.benchDir}/sites/apps.txt"
        "${penv}:${cfg.benchDir}/env"
      ];
      WorkingDirectory = "${cfg.benchDir}";
      # Expands to /var/lib/erpnext, see: 'man 5 systemd.exec'
      StateDirectory = "erpnext";
    };
  in mkIf cfg.enable
  {
    services.mysql = mkIf cfg.database.createLocally {
      enable = true;
      package = pkgs.mariadb;
      ensureUsers = [{
        name = "root";
        ensurePermissions = {
          "*.*" = "ALL PRIVILEGES";
        };
      }];
      ensureDatabases = [ "root" ];
    };

    services.redis.servers = mkIf cfg.redis.createLocally {
      # Queue, naming it "" makes it use default values.
      "".enable = true;
    };

    users = optionalAttrs (cfg.user == defaultUser) {
      users.${defaultUser} = {
        description = "User to run ERPNext";
        group = defaultUser;
        uid = 327;
        # TODO assign an appropriate ID when merging this into nixos/nixpkgs
        #uid = config.ids.uids.erpnext;
        home = cfg.workDir;
      };

      groups.${defaultUser} = {
        gid = 327;
        # TODO assign an appropriate ID when merging this into nixos/nixpkgs
        #gid = config.ids.gids.erpnext;
      };
    };

    systemd.services.erpnext-setup-mysql = mkIf cfg.database.createLocally {
      enable = true;
      before = [ "erpnext-web.service" ];
      after = [ "mysql.service" ];
      wantedBy = [ "erpnext-web.service" ];
      partOf = [ "erpnext-web.service" ];
      script = ''
        ${pkgs.mariadb-client}/bin/mysql -e "SET PASSWORD FOR 'root'@'localhost' = PASSWORD('$(cat "${cfg.database.rootPasswordFile}")')";
      '';
      serviceConfig = {
        RemainAfterExit = true;
        Type = "oneshot";
      };
    };

    systemd.tmpfiles.rules = [
      "d '${cfg.benchDir}/apps' 0750 ${cfg.user} ${config.users.users.${cfg.user}.group}"
      "d '${cfg.benchDir}/config/pids' 0750 ${cfg.user} ${config.users.users.${cfg.user}.group}"
      "d '${cfg.benchDir}/logs' 0750 ${cfg.user} ${config.users.users.${cfg.user}.group}"
      "d '${cfg.benchDir}/sites' 0750 ${cfg.user} ${config.users.users.${cfg.user}.group}"
    ];

    services.caddy.enable = mkIf (cfg.caddy != null) true;
    services.caddy.virtualHosts."${cfg.domain}" = mkIf (cfg.caddy != null) (lib.mkMerge [
      cfg.caddy
      ({
        extraConfig = ''
          handle /assets/* {
            root * ${pkgs.frappe-erpnext-assets}/share/sites
            file_server
          }

          reverse_proxy :${toString cfg.webserver.bindPort}
        '';
      })
    ]);

    systemd.services.erpnext-web = {
      enable = true;
      wantedBy = [ "multi-user.target" ];
      after = [
        "mysql.service"
        "redis.service"
        "systemd-tmpfiles-setup.service"
      ];
      description = "ERPNext web server";
      confinement = {
        enable = true;
        # pkgs listed here get added to the services' BindReadOnlyPaths
        # The same is true for pkgs referred to in ExecStartPre, ExecStart, etc.
        # Explicitily listing these pkgs here for visibility
        packages = [
          penv
          pkgs.coreutils
          # Dependency for 'bench new-site' subcommand
          pkgs.mariadb-client
          pkgs.replace-secret
        ];
      };
      path = [
        pkgs.bash
        pkgs.mariadb-client
      ];
      environment = {
        PYTHON_PATH = "${penv}/${pkgs.python3.sitePackages}";
      };
      unitConfig = {
        StartLimitBurst = "5";
        StartLimitIntervalSec = "30";
      };
      serviceConfig = defaultServiceConfig // {
        TimeoutStartSec = "600s";
        Restart = "on-failure";
        RestartSec = "5s";
        ExecStartPre = assert cfg.adminPasswordFile != null && cfg.database.rootPasswordFile != null; pkgs.writeScript "erpnext-web-init" ''
          #!/bin/sh
          if ! test -e ${escapeShellArg "${cfg.workDir}/.db-created"}; then
            # Fail on error
            set -e

            ${pkgs.coreutils}/bin/install -m0600 ${commonSiteConfigFile} ${cfg.benchDir}/sites/common_site_config.json
            ${pkgs.replace-secret}/bin/replace-secret \
              '#NIXOS_ERPNEXT_DB_USER_PASSWORD#' \
              ${cfg.database.userPasswordFile} \
              ${cfg.benchDir}/sites/common_site_config.json

            ADMIN_PASSWORD="$(${pkgs.coreutils}/bin/cat "${cfg.adminPasswordFile}")"
            DB_ROOT_PASSWORD="$(${pkgs.coreutils}/bin/cat "${cfg.database.rootPasswordFile}")"

            # Upstream initializes the database with this command
            ${penv}/bin/bench new-site ${cfg.domain} \
              --mariadb-root-password "$DB_ROOT_PASSWORD" \
              --admin-password "$ADMIN_PASSWORD" \
              --install-app erpnext

            ${pkgs.coreutils}/bin/touch ${escapeShellArg "${cfg.workDir}/.db-created"}
          fi

          ${lib.optionalString cfg.database.automaticMigrations ''
            # Migrate the database
            ${penv}/bin/bench --site ${cfg.domain} migrate
        ''}
        '';
        ExecStart = ''
          ${penv}/bin/gunicorn \
            --chdir="${cfg.benchDir}/sites" \
            --bind=${cfg.webserver.bindAddress}:${toString cfg.webserver.bindPort} \
            --threads=4 \
            --workers=2 \
            --worker-class=gthread \
            --worker-tmp-dir=/dev/shm \
            --timeout=120 \
            --preload \
            frappe.app:application
        '';
      };
    };
    systemd.services.erpnext-queue-short = {
      enable = true;
      after = [ "erpnext-web.service" ];
      wantedBy = [ "erpnext-web.service" ];
      partOf = [ "erpnext-web.service" ];
      description = "ERPNext short queue server";
      confinement = {
        enable = true;
        packages = [ penv ];
      };
      serviceConfig = defaultServiceConfig // {
        ExecStart = ''
          ${penv}/bin/bench worker --queue short
        '';
      };
    };
    systemd.services.erpnext-queue-long = {
      enable = true;
      after = [ "erpnext-web.service" ];
      wantedBy = [ "erpnext-web.service" ];
      partOf = [ "erpnext-web.service" ];
      description = "ERPNext long queue server";
      confinement = {
        enable = true;
        packages = [ penv ];
      };
      serviceConfig = defaultServiceConfig // {
        ExecStart = ''
          ${penv}/bin/bench worker --queue long
        '';
      };
    };
    systemd.services.erpnext-scheduler = {
      enable = true;
      after = [ "erpnext-web.service" ];
      wantedBy = [ "erpnext-web.service" ];
      partOf = [ "erpnext-web.service" ];
      description = "ERPNext scheduler server";
      confinement = {
        enable = true;
        packages = [ penv ];
      };
      serviceConfig = defaultServiceConfig // {
        ExecStart = ''
          ${penv}/bin/bench schedule
        '';
      };
    };
  };
}