From e469020cb0b3ca113065ee1b68d12315e679c7c3 Mon Sep 17 00:00:00 2001
From: Karl Hallsby <karl@hallsby.com>
Date: Fri, 26 Jun 2020 18:32:47 +0200
Subject: [PATCH] mbsync: write function to generate group-channel blocks

This function takes in a set of groups, and their consituent
channels and writes the appropriate .mbsyncrc block. The block is as
shown below:

      Group groupName1
      Channel channelName1
      Channel channelName2

      Group groupName2
      Channel channelName3

Each group must have a unique name, no matter which account it is
declared under. The same holds true for channels. However, if there is
a group that shares the same name as the channel, the channel will
effectively be "shadowed" by the group, and mbsync will default to
working with the group in that case.
---
 modules/programs/mbsync.nix | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/modules/programs/mbsync.nix b/modules/programs/mbsync.nix
index f2814b39..2ed0c6d0 100644
--- a/modules/programs/mbsync.nix
+++ b/modules/programs/mbsync.nix
@@ -78,6 +78,27 @@ let
         Expunge = masterSlaveMapping.${mbsync.expunge};
         SyncState = "*";
       } // mbsync.extraConfig.channel) + "\n";
+  # Given the attr set of groups, return a string of channels to put into each group.
+  # 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, construct the "Group <grpName>" header, and construct
+      # each of the channels.
+      genGroupChannelString = group:
+        [("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 consituent channels.
+      genGroupsStrings = mapAttrsToList (name: info: concatStringsSep "\n"
+        (genGroupChannelString groups.${name})) groups;
+    in (concatStringsSep "\n\n" genGroupsStrings) # Put all strings together.
+       # 2 \n needed in concatStringsSep because last element genGroupsStrings
+       # has no \n.
+       + "\n\n"; # Additional spacing after this account's group setup.
 
   genGroupConfig = name: channels:
     let