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

with lib;

let

  cfg = config.programs.vdirsyncer;

  vdirsyncerCalendarAccounts = filterAttrs (_: v: v.vdirsyncer.enable)
    (mapAttrs' (n: v: nameValuePair ("calendar_" + n) v)
      config.accounts.calendar.accounts);

  vdirsyncerContactAccounts = filterAttrs (_: v: v.vdirsyncer.enable)
    (mapAttrs' (n: v: nameValuePair ("contacts_" + n) v)
      config.accounts.contact.accounts);

  vdirsyncerAccounts = vdirsyncerCalendarAccounts // vdirsyncerContactAccounts;

  wrap = s: ''"${s}"'';

  listString = l: "[${concatStringsSep ", " l}]";

  boolString = b: if b then "true" else "false";

  localStorage = a:
    filterAttrs (_: v: v != null)
    ((getAttrs [ "type" "fileExt" "encoding" ] a.local) // {
      path = a.local.path;
      postHook = if a.vdirsyncer.postHook != null then
        (pkgs.writeShellScriptBin "post-hook" a.vdirsyncer.postHook
          + "/bin/post-hook")
      else
        null;
    });

  remoteStorage = a:
    filterAttrs (_: v: v != null)
    ((getAttrs [ "type" "url" "userName" "passwordCommand" ] a.remote)
      // (if a.vdirsyncer == null then
        { }
      else
        getAttrs [
          "urlCommand"
          "userNameCommand"
          "itemTypes"
          "verify"
          "verifyFingerprint"
          "auth"
          "authCert"
          "userAgent"
          "tokenFile"
          "clientIdCommand"
          "clientSecretCommand"
          "timeRange"
        ] a.vdirsyncer));

  pair = a:
    with a.vdirsyncer;
    filterAttrs (k: v: k == "collections" || (v != null && v != [ ]))
    (getAttrs [ "collections" "conflictResolution" "metadata" "partialSync" ]
      a.vdirsyncer);

  pairs = mapAttrs (_: v: pair v) vdirsyncerAccounts;
  localStorages = mapAttrs (_: v: localStorage v) vdirsyncerAccounts;
  remoteStorages = mapAttrs (_: v: remoteStorage v) vdirsyncerAccounts;

  optionString = n: v:
    if (n == "type") then
      ''type = "${v}"''
    else if (n == "path") then
      ''path = "${v}"''
    else if (n == "fileExt") then
      ''fileext = "${v}"''
    else if (n == "encoding") then
      ''encoding = "${v}"''
    else if (n == "postHook") then
      ''post_hook = "${v}"''
    else if (n == "url") then
      ''url = "${v}"''
    else if (n == "urlCommand") then
      "url.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
    else if (n == "timeRange") then ''
      start_date = "${v.start}"
      end_date = "${v.end}"'' else if (n == "itemTypes") then
      "item_types = ${listString (map wrap v)}"
    else if (n == "userName") then
      ''username = "${v}"''
    else if (n == "userNameCommand") then
      "username.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
    else if (n == "password") then
      ''password = "${v}"''
    else if (n == "passwordCommand") then
      "password.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
    else if (n == "passwordPrompt") then
      ''password.fetch = ["prompt", "${v}"]''
    else if (n == "verify") then
      ''verify = "${v}"''
    else if (n == "verifyFingerprint") then
      ''verify_fingerprint = "${v}"''
    else if (n == "auth") then
      ''auth = "${v}"''
    else if (n == "authCert" && isString (v)) then
      ''auth_cert = "${v}"''
    else if (n == "authCert") then
      "auth_cert = ${listString (map wrap v)}"
    else if (n == "userAgent") then
      ''useragent = "${v}"''
    else if (n == "tokenFile") then
      ''token_file = "${v}"''
    else if (n == "clientId") then
      ''client_id = "${v}"''
    else if (n == "clientIdCommand") then
      "client_id.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
    else if (n == "clientSecret") then
      ''client_secret = "${v}"''
    else if (n == "clientSecretCommand") then
      "client_secret.fetch = ${listString (map wrap ([ "command" ] ++ v))}"
    else if (n == "metadata") then
      "metadata = ${listString (map wrap v)}"
    else if (n == "partialSync") then
      ''partial_sync = "${v}"''
    else if (n == "collections") then
      let
        contents =
          map (c: if (isString c) then ''"${c}"'' else listString (map wrap c))
          v;
      in "collections = ${
        if ((isNull v) || v == [ ]) then "null" else listString contents
      }"
    else if (n == "conflictResolution") then
      if v == "remote wins" then
        ''conflict_resolution = "a wins"''
      else if v == "local wins" then
        ''conflict_resolution = "b wins"''
      else
        "conflict_resolution = ${listString (map wrap ([ "command" ] ++ v))}"
    else
      throw "Unrecognized option: ${n}";

  attrsString = a: concatStringsSep "\n" (mapAttrsToList optionString a);

  pairString = n: v: ''
    [pair ${n}]
    a = "${n}_remote"
    b = "${n}_local"
    ${attrsString v}
  '';

  configFile = pkgs.writeText "config" ''
    [general]
    status_path = "${cfg.statusPath}"

    ### Pairs

    ${concatStringsSep "\n" (mapAttrsToList pairString pairs)}

    ### Local storages

    ${concatStringsSep "\n\n"
    (mapAttrsToList (n: v: "[storage ${n}_local]" + "\n" + attrsString v)
      localStorages)}

    ### Remote storages

    ${concatStringsSep "\n\n"
    (mapAttrsToList (n: v: "[storage ${n}_remote]" + "\n" + attrsString v)
      remoteStorages)}
  '';

in {
  options = {
    programs.vdirsyncer = {
      enable = mkEnableOption "vdirsyncer";

      package = mkOption {
        type = types.package;
        default = pkgs.vdirsyncer;
        defaultText = "pkgs.vdirsyncer";
        description = ''
          vdirsyncer package to use.
        '';
      };

      statusPath = mkOption {
        type = types.str;
        default = "${config.xdg.dataHome}/vdirsyncer/status";
        defaultText = "$XDG_DATA_HOME/vdirsyncer/status";
        description = ''
          A directory where vdirsyncer will store some additional data for the next sync.

          For more information, see the
          [vdirsyncer manual](https://vdirsyncer.pimutils.org/en/stable/config.html#general-section).
        '';
      };
    };
  };

  config = mkIf cfg.enable {
    assertions = let

      mutuallyExclusiveOptions =
        [ [ "url" "urlCommand" ] [ "userName" "userNameCommand" ] ];

      requiredOptions = t:
        if (t == "caldav" || t == "carddav" || t == "http") then
          [ "url" ]
        else if (t == "filesystem") then [
          "path"
          "fileExt"
        ] else if (t == "singlefile") then
          [ "path" ]
        else if (t == "google_calendar" || t == "google_contacts") then [
          "tokenFile"
          "clientId"
          "clientSecret"
        ] else
          throw "Unrecognized storage type: ${t}";

      allowedOptions = let
        remoteOptions = [
          "urlCommand"
          "userName"
          "userNameCommand"
          "password"
          "passwordCommand"
          "passwordPrompt"
          "verify"
          "verifyFingerprint"
          "auth"
          "authCert"
          "userAgent"
        ];
      in t:
      if (t == "caldav") then
        [ "timeRange" "itemTypes" ] ++ remoteOptions
      else if (t == "carddav" || t == "http") then
        remoteOptions
      else if (t == "filesystem") then [
        "fileExt"
        "encoding"
        "postHook"
      ] else if (t == "singlefile") then
        [ "encoding" ]
      else if (t == "google_calendar") then [
        "timeRange"
        "itemTypes"
        "clientIdCommand"
        "clientSecretCommand"
      ] else if (t == "google_contacts") then [
        "clientIdCommand"
        "clientSecretCommand"
      ] else
        throw "Unrecognized storage type: ${t}";

      assertStorage = n: v:
        let allowed = allowedOptions v.type ++ (requiredOptions v.type);
        in mapAttrsToList (a: v':
          [{
            assertion = (elem a allowed);
            message = ''
              Storage ${n} is of type ${v.type}. Option
              ${a} is not allowed for this type.
            '';
          }] ++ (let
            required =
              filter (a: !hasAttr "${a}Command" v) (requiredOptions v.type);
          in map (a: [{
            assertion = hasAttr a v;
            message = ''
              Storage ${n} is of type ${v.type}, but required
              option ${a} is not set.
            '';
          }]) required) ++ map (attrs:
            let
              defined = attrNames (filterAttrs (n: v: v != null)
                (genAttrs attrs (a: v.${a} or null)));
            in {
              assertion = length defined <= 1;
              message = "Storage ${n} has mutually exclusive options: ${
                  concatStringsSep ", " defined
                }";
            }) mutuallyExclusiveOptions) (removeAttrs v [ "type" "_module" ]);

      storageAssertions = flatten (mapAttrsToList assertStorage localStorages)
        ++ flatten (mapAttrsToList assertStorage remoteStorages);

    in storageAssertions;
    home.packages = [ cfg.package ];
    xdg.configFile."vdirsyncer/config".source = configFile;
  };
}