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

with lib;

let

  cfg = config.services.squid;


  squidConfig = pkgs.writeText "squid.conf"
    (if cfg.configText != null then cfg.configText else
    ''
    #
    # Recommended minimum configuration (3.5):
    #

    # Example rule allowing access from your local networks.
    # Adapt to list your (internal) IP networks from where browsing
    # should be allowed
    acl localnet src 10.0.0.0/8     # RFC 1918 possible internal network
    acl localnet src 172.16.0.0/12  # RFC 1918 possible internal network
    acl localnet src 192.168.0.0/16 # RFC 1918 possible internal network
    acl localnet src 169.254.0.0/16 # RFC 3927 link-local (directly plugged) machines
    acl localnet src fc00::/7       # RFC 4193 local private network range
    acl localnet src fe80::/10      # RFC 4291 link-local (directly plugged) machines

    acl SSL_ports port 443          # https
    acl Safe_ports port 80          # http
    acl Safe_ports port 21          # ftp
    acl Safe_ports port 443         # https
    acl Safe_ports port 70          # gopher
    acl Safe_ports port 210         # wais
    acl Safe_ports port 1025-65535  # unregistered ports
    acl Safe_ports port 280         # http-mgmt
    acl Safe_ports port 488         # gss-http
    acl Safe_ports port 591         # filemaker
    acl Safe_ports port 777         # multiling http
    acl CONNECT method CONNECT

    #
    # Recommended minimum Access Permission configuration:
    #
    # Deny requests to certain unsafe ports
    http_access deny !Safe_ports

    # Deny CONNECT to other than secure SSL ports
    http_access deny CONNECT !SSL_ports

    # Only allow cachemgr access from localhost
    http_access allow localhost manager
    http_access deny manager

    # We strongly recommend the following be uncommented to protect innocent
    # web applications running on the proxy server who think the only
    # one who can access services on "localhost" is a local user
    http_access deny to_localhost

    # Application logs to syslog, access and store logs have specific files
    cache_log       syslog
    access_log      stdio:/var/log/squid/access.log
    cache_store_log stdio:/var/log/squid/store.log

    # Required by systemd service
    pid_filename    /run/squid.pid

    # Run as user and group squid
    cache_effective_user squid squid

    #
    # INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
    #
    ${cfg.extraConfig}

    # Example rule allowing access from your local networks.
    # Adapt localnet in the ACL section to list your (internal) IP networks
    # from where browsing should be allowed
    http_access allow localnet
    http_access allow localhost

    # And finally deny all other access to this proxy
    http_access deny all

    # Squid normally listens to port 3128
    http_port ${
      optionalString (cfg.proxyAddress != null) "${cfg.proxyAddress}:"
    }${toString cfg.proxyPort}

    # Leave coredumps in the first cache dir
    coredump_dir /var/cache/squid

    #
    # Add any of your own refresh_pattern entries above these.
    #
    refresh_pattern ^ftp:           1440    20%     10080
    refresh_pattern ^gopher:        1440    0%      1440
    refresh_pattern -i (/cgi-bin/|\?) 0     0%      0
    refresh_pattern .               0       20%     4320
  '');

in

{

  options = {

    services.squid = {

      enable = mkOption {
        type = types.bool;
        default = false;
        description = "Whether to run squid web proxy.";
      };

      proxyAddress = mkOption {
        type = types.nullOr types.str;
        default = null;
        description = "IP address on which squid will listen.";
      };

      proxyPort = mkOption {
        type = types.int;
        default = 3128;
        description = "TCP port on which squid will listen.";
      };

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

      configText = mkOption {
        type = types.nullOr types.lines;
        default = null;
        description = ''
          Verbatim contents of squid.conf. If null (default), use the
          autogenerated file from NixOS instead.
        '';
      };

    };

  };

  config = mkIf cfg.enable {

    users.users.squid = {
      isSystemUser = true;
      group = "squid";
      home = "/var/cache/squid";
      createHome = true;
    };

    users.groups.squid = {};

    systemd.services.squid = {
      description = "Squid caching web proxy";
      after = [ "network.target" "nss-lookup.target" ];
      wantedBy = [ "multi-user.target"];
      preStart = ''
        mkdir -p "/var/log/squid"
        chown squid:squid "/var/log/squid"
      '';
      serviceConfig = {
        Type="forking";
        PIDFile="/run/squid.pid";
        ExecStart  = "${pkgs.squid}/bin/squid -YCs -f ${squidConfig}";
      };
    };

  };

}