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

with lib;

let

  cfg = config.programs.mbsync;

  # Accounts for which mbsync is enabled.
  mbsyncAccounts =
    filter (a: a.mbsync.enable) (attrValues config.accounts.email.accounts);

  # Given a SINGLE group's channels attribute set, return true if ANY of the channel's
  # patterns use the invalidOption attribute set value name.
  channelInvalidOption = channels: invalidOption:
    any (c: c) (mapAttrsToList (c: hasAttr invalidOption) channels);

  # Given a SINGLE account's groups attribute set, return true if ANY of the account's group's channel's patterns use the invalidOption attribute set value name.
  groupInvalidOption = groups: invalidOption:
    any (g: g) (mapAttrsToList (groupName: groupVals:
      channelInvalidOption groupVals.channels invalidOption) groups);

  # Given all accounts (ensure that accounts passed in here ARE mbsync-using accounts)
  # return true if ANY of the account's groups' channels' patterns use the
  # invalidOption attribute set value name.
  accountInvalidOption = accounts: invalidOption:
    any (a: a)
    (map (account: groupInvalidOption account.mbsync.groups invalidOption)
      mbsyncAccounts);

  genTlsConfig = tls:
    {
      SSLType = if !tls.enable then
        "None"
      else if tls.useStartTls then
        "STARTTLS"
      else
        "IMAPS";
    } // optionalAttrs (tls.enable && tls.certificatesFile != null) {
      CertificateFile = toString tls.certificatesFile;
    };

  imports = [
    (mkRenamedOptionModule [ "programs" "mbsync" "masterSlaveMapping" ] [
      "programs"
      "mbsync"
      "nearFarMapping"
    ])
  ];

  nearFarMapping = {
    none = "None";
    imap = "Far";
    maildir = "Near";
    both = "Both";
  };

  genSection = header: entries:
    let
      escapeValue = escape [ ''"'' ];
      hasSpace = v: builtins.match ".* .*" v != null;
      genValue = n: v:
        if isList v then
          concatMapStringsSep " " (genValue n) v
        else if isBool v then
          lib.hm.booleans.yesNo v
        else if isInt v then
          toString v
        else if isString v && hasSpace v then
          ''"${escapeValue v}"''
        else if isString v then
          v
        else
          let prettyV = lib.generators.toPretty { } v;
          in throw "mbsync: unexpected value for option ${n}: '${prettyV}'";
    in ''
      ${header}
      ${concatStringsSep "\n"
      (mapAttrsToList (n: v: "${n} ${genValue n v}") entries)}
    '';

  genAccountConfig = account:
    with account;
    genSection "IMAPAccount ${name}" ({
      Host = imap.host;
      User = userName;
      PassCmd = toString passwordCommand;
    } // genTlsConfig imap.tls
      // optionalAttrs (imap.port != null) { Port = toString imap.port; }
      // mbsync.extraConfig.account) + "\n"
    + genSection "IMAPStore ${name}-remote"
    ({ Account = name; } // mbsync.extraConfig.remote) + "\n"
    + genSection "MaildirStore ${name}-local" ({
      Inbox = "${maildir.absPath}/${folders.inbox}";
    } // optionalAttrs
      (mbsync.subFolders != "Maildir++" || mbsync.flatten != null) {
        Path = "${maildir.absPath}/";
      } // optionalAttrs (mbsync.flatten == null) {
        SubFolders = mbsync.subFolders;
      } // optionalAttrs (mbsync.flatten != null) { Flatten = mbsync.flatten; }
      // mbsync.extraConfig.local) + "\n" + genChannels account;

  genChannels = account:
    with account;
    if mbsync.groups == { } then
      genAccountWideChannel account
    else
      genGroupChannelConfig name mbsync.groups + "\n"
      + genAccountGroups mbsync.groups;

  # Used when no channels are specified for this account. This will create a
  # single channel for the entire account that is then further refined within
  # the Group for synchronization.
  genAccountWideChannel = account:
    with account;
    genSection "Channel ${name}" ({
      Far = ":${name}-remote:";
      Near = ":${name}-local:";
      Patterns = mbsync.patterns;
      Create = nearFarMapping.${mbsync.create};
      Remove = nearFarMapping.${mbsync.remove};
      Expunge = nearFarMapping.${mbsync.expunge};
      SyncState = "*";
    } // mbsync.extraConfig.channel) + "\n";

  # Given the attr set of groups, return a string of channels that will direct
  # mail to the proper directories, according to the pattern used in channel's
  # "far" pattern definition.
  genGroupChannelConfig = storeName: groups:
    let
      # Given the name of the group this channel is part of and the channel
      # itself, generate the string for the desired configuration.
      genChannelString = groupName: channel:
        let
          escapeValue = escape [ ''\"'' ];
          hasSpace = v: builtins.match ".* .*" v != null;
          # Given a list of patterns, will return the string requested.
          # Only prints if the pattern is NOT the empty list, the default.
          genChannelPatterns = patterns:
            if (length patterns) != 0 then
              "Pattern " + concatStringsSep " "
              (map (pat: if hasSpace pat then escapeValue pat else pat)
                patterns) + "\n"
            else
              "";
        in genSection "Channel ${groupName}-${channel.name}" ({
          Far = ":${storeName}-remote:${channel.farPattern}";
          Near = ":${storeName}-local:${channel.nearPattern}";
        } // channel.extraConfig) + genChannelPatterns channel.patterns;
      # Given the group name, and a attr set of channels within that group,
      # Generate a list of strings for each channels' configuration.
      genChannelStrings = groupName: channels:
        optionals (channels != { })
        (mapAttrsToList (channelName: info: genChannelString groupName info)
          channels);
      # Given a group, return a string that configures all the channels within
      # the group.
      genGroupsChannels = group:
        concatStringsSep "\n" (genChannelStrings group.name group.channels);
      # Generate all channel configurations for all groups for this account.
    in concatStringsSep "\n"
    (remove "" (mapAttrsToList (name: group: genGroupsChannels group) groups));

  # Given the attr set of groups, return a string which maps channels to groups
  genAccountGroups = groups:
    let
      # Given the name of the group and the attribute set of channels, make
      # make "Channel <grpName>-<chnName>" for each channel to list os strings
      genChannelStrings = groupName: channels:
        mapAttrsToList (name: info: "Channel ${groupName}-${name}") channels;
      # Take in 1 group, if the group has channels specified, construct the
      # "Group <grpName>" header and each of the channels.
      genGroupChannelString = group:
        flatten (optionals (group.channels != { }) ([ "Group ${group.name}" ]
          ++ (genChannelStrings group.name group.channels)));
      # Given set of groups, generates list of strings, where each string is one
      # of the groups and its constituent channels.
      genGroupsStrings = mapAttrsToList (name: info:
        concatStringsSep "\n" (genGroupChannelString groups.${name})) groups;
      # Join all non-empty groups.
      combined = concatStringsSep "\n\n" (remove "" genGroupsStrings) + "\n";
    in combined;

  genGroupConfig = name: channels:
    let
      genGroupChannel = n: boxes: "Channel ${n}:${concatStringsSep "," boxes}";
    in "\n" + concatStringsSep "\n"
    ([ "Group ${name}" ] ++ mapAttrsToList genGroupChannel channels);

in {
  meta.maintainers = [ maintainers.KarlJoad ];

  options = {
    programs.mbsync = {
      enable = mkEnableOption "mbsync IMAP4 and Maildir mailbox synchronizer";

      package = mkOption {
        type = types.package;
        default = pkgs.isync;
        defaultText = literalExpression "pkgs.isync";
        example = literalExpression "pkgs.isync";
        description = "The package to use for the mbsync binary.";
      };

      groups = mkOption {
        type = types.attrsOf (types.attrsOf (types.listOf types.str));
        default = { };
        example = literalExpression ''
          {
            inboxes = {
              account1 = [ "Inbox" ];
              account2 = [ "Inbox" ];
            };
          }
        '';
        description = ''
          Definition of groups.
        '';
      };

      extraConfig = mkOption {
        type = types.lines;
        default = "";
        description = ''
          Extra configuration lines to add to the mbsync configuration.
        '';
      };
    };

    accounts.email.accounts = mkOption {
      type = with types; attrsOf (submodule (import ./mbsync-accounts.nix));
    };
  };

  config = mkIf cfg.enable (mkMerge [
    {
      assertions = let
        checkAccounts = pred: msg:
          let badAccounts = filter pred mbsyncAccounts;
          in {
            assertion = badAccounts == [ ];
            message = "mbsync: ${msg} for accounts: "
              + concatMapStringsSep ", " (a: a.name) badAccounts;
          };
      in [
        (checkAccounts (a: a.maildir == null) "Missing maildir configuration")
        (checkAccounts (a: a.imap == null) "Missing IMAP configuration")
        (checkAccounts (a: a.passwordCommand == null) "Missing passwordCommand")
        (checkAccounts (a: a.userName == null) "Missing username")
      ];
    }

    (mkIf (accountInvalidOption mbsyncAccounts "masterPattern") {
      warnings = [
        "mbsync channels no longer use masterPattern. Use farPattern in its place."
      ];
    })

    (mkIf (accountInvalidOption mbsyncAccounts "slavePattern") {
      warnings = [
        "mbsync channels no longer use slavePattern. Use nearPattern in its place."
      ];
    })

    {
      home.packages = [ cfg.package ];

      programs.notmuch.new.ignore = [ ".uidvalidity" ".mbsyncstate" ];

      home.file.".mbsyncrc".text = let
        accountsConfig = map genAccountConfig mbsyncAccounts;
        # Only generate this kind of Group configuration if there are ANY accounts
        # that do NOT have a per-account groups/channels option(s) specified.
        groupsConfig =
          if any (account: account.mbsync.groups == { }) mbsyncAccounts then
            mapAttrsToList genGroupConfig cfg.groups
          else
            [ ];
      in ''
        # Generated by Home Manager.

      ''
      + concatStringsSep "\n" (optional (cfg.extraConfig != "") cfg.extraConfig)
      + concatStringsSep "\n\n" accountsConfig
      + concatStringsSep "\n" groupsConfig;

      home.activation = mkIf (mbsyncAccounts != [ ]) {
        createMaildir =
          hm.dag.entryBetween [ "linkGeneration" ] [ "writeBoundary" ] ''
            $DRY_RUN_CMD mkdir -m700 -p $VERBOSE_ARG ${
              concatMapStringsSep " " (a: a.maildir.absPath) mbsyncAccounts
            }
          '';
      };
    }
  ]);
}
