mail: Refactor imapfilter configuration

Make imapfilter configuraiton more flexible to prepare for different
filters being added.

The program will expect its configuration and filter files to be located
in XDG directory structure, within the sub-folder 'filters'.
E.g.: `/home/user/.config/imapfilter/filters`

A global `configDir` variable is available for any filters, which
describes the path to the current configuration directory.
The path to the filter directory can also be accessed through
`getFilterDir()`.

The configuration runs `accounts.lua` and expects it to return a table
with the individual imap boxes as top level entries, so that filters can
then loop through each account as needed.

Lastly, the config will automatically apply all filters found in the
filters sub-folder. A filter is a '.lua' file within the directory.
Other files can exist in the dir and will not be touched.

mail/.config/imapfilter/config.lua

@@ -12,7 +12,20 @@ options.subscribe = true
 -- How long to wait for servers response.
 options.timeout = 120
 
-accounts = loadfile(os.getenv("HOME") .. "/.config/imapfilter/accounts.lua")()
+-- will set filters to be grabbed from XDG-compliant filter directory
+-- can be overridden with env var IMAPFILTER_FILTERDIR
+function getConfigDir()
+  -- -- set directory for imapfilter files
+  local configdir
+  if os.getenv("IMAPFILTER_CONFIGDIR") then
+    configdir=os.getenv("IMAPFILTER_CONFIGDIR")
+  elseif os.getenv("XDG_CONFIG_HOME") then
+    configdir=os.getenv("XDG_CONFIG_HOME") .. "/imapfilter"
+  else
+    configdir=os.getenv("HOME") .. "/.config/imapfilter"
+  end
+  return configdir
+end
 
 -- will set filters to be grabbed from XDG-compliant filter directory
 -- can be overridden with env var IMAPFILTER_FILTERDIR
@@ -21,21 +34,26 @@ function getFilterDir()
   local imapfilterdir
   if os.getenv("IMAPFILTER_FILTERDIR") then
     imapfilterdir=os.getenv("IMAPFILTER_FILTERDIR")
-  elseif os.getenv("XDG_CONFIG_HOME") then
-    imapfilterdir=os.getenv("XDG_CONFIG_HOME") .. "/imapfilter/filters"
   else
-    imapfilterdir=os.getenv("HOME") .. "/.config/imapfilter/filters"
+    imapfilterdir=configDir .. "/filters"
   end
   return imapfilterdir
 end
 
-local filters = {}
 -- dirlist, from https://stackoverflow.com/a/25266573
 function applyFilters(dir)
-  local p = io.popen('find "'..dir..'" -type f')   --Open directory look for files, save data in p. By giving '-type f' as parameter, it returns all files.
+  local p = io.popen('find "'..dir..'" -type f -name "*.lua"')   --Open directory look for files, save data in p. By giving '-type f' as parameter, it returns all files.
   for file in p:lines() do                         --Loop through all files
     loadfile(file)()
   end
 end
 
+-- create global variable containing the configuration files
+configDir=getConfigDir()
+assert(configDir, "No configuration directory found. Ensure " .. os.getenv("HOME") .. "/.config/imapfilter exists.")
+
+-- create global variable containing account access
+accounts = loadfile(configDir .. "/accounts.lua")()
+assert(accounts, "No accounts configured. Ensure accounts.lua exists and returns a table of accounts.")
+
 applyFilters(getFilterDir())