Add a manager for import filters + 2 examples

This adds a new callback to darktable:
darktable.register_import_filter(name, callback)

official/import_filter_manager.lua

@@ -0,0 +1,79 @@
+--[[
+    This file is part of darktable,
+    copyright (c) 2015 Tobias Ellinghaus
+
+    darktable is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    darktable is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
+]]
+--[[
+IMPORT FILTER MANAGER
+This script adds a dropdown list with import filters to the import dialog.
+Scripts can add new filters by registering them with
+  darktable.register_import_filter(name, callback)
+The callback has type function(event, images), i.e., it is the same as when
+directly registering the pre-import event.
+
+
+USAGE
+* require this script from your main lua file
+* also require some files with import filters, for example import_filters.lua.
+  it is important to add them AFTER this one!
+]]
+
+local dt = require "darktable"
+
+local import_filter_list = {}
+local n_import_filters = 1
+
+-- allow changing the filter from the preferences
+dt.preferences.register("import_filter_manager", "active_filter", "string",
+  "import filter", "the name of the filter used for importing images", "")
+
+
+-- the dropdown to select the active filter from the import dialog
+local filter_dropdown = dt.new_widget("combobox")
+{
+  label = "import filter",
+  editable = false,
+
+  changed_callback = function(widget)
+    dt.preferences.write("import_filter_manager", "active_filter", "string", widget.value)
+  end,
+
+  "" -- the first entry in the list is hard coded to "" so it's possible to have no filter
+}
+dt.gui.libs.import.register_widget(filter_dropdown)
+
+
+-- this is just a wrapper which calls the active import filter
+dt.register_event("pre-import", function(event, images)
+  local active_filter = dt.preferences.read("import_filter_manager", "active_filter", "string")
+  if active_filter == "" then return end
+  local callback = import_filter_list[active_filter]
+  if callback then callback(event, images) end
+end)
+
+
+-- add a new global function to register import filters
+dt.register_import_filter = function(name, callback)
+  local active_filter = dt.preferences.read("import_filter_manager", "active_filter", "string")
+  dt.print_error("registering import filter `" .. name .. "'")
+  import_filter_list[name] = callback
+  n_import_filters = n_import_filters  + 1
+  filter_dropdown[n_import_filters] = name
+  if name == active_filter then filter_dropdown.value = n_import_filters end
+end
+
+
+-- vim: shiftwidth=2 expandtab tabstop=2 cindent
+-- kate: tab-indents: off; indent-width 2; replace-tabs on; remove-trailing-space on;

official/import_filters.lua

@@ -0,0 +1,80 @@
+--[[
+    This file is part of darktable,
+    copyright (c) 2015 Tobias Ellinghaus
+
+    darktable is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    darktable is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
+]]
+--[[
+EXAMPLE IMPORT FILTERS
+This script goes along with the import filter manager. It adds two filters:
+* ignore jpegs: this one does the same as the existing option in the import dialog
+                and just skips all JPEGs during import.
+* prefer raw over jpeg: this one is a bit more elaborate, it ignores JPEGs when there
+                        is also another file with the same basename, otherwise it
+                        allows JPEGs, too.
+
+USAGE
+* require this script from your main lua file AFTER import_filter_manager.lua
+]]
+
+local dt = require "darktable"
+
+-- we get fed a sorted list of filenames. just setting images to ignore to nil is enough
+
+-- ignore jpeg
+dt.register_import_filter("ignore jpegs", function(event, images)
+  dt.print_error("ignoring all jpegs")
+  for i, img in ipairs(images) do
+    local extension = img:match("[^.]*$"):upper()
+    if (extension == "JPG") or (extension == "JPEG") then
+      images[i] = nil
+    end
+  end
+end)
+
+
+-- ignore jpeg iff another format for the image is found
+dt.register_import_filter("prefer raw over jpeg", function(event, images)
+  dt.print_error("prefering raw over jpeg")
+  local current_base = ""
+  local jpg_indices = {}
+  local other_format_found = false
+  for i, img in ipairs(images) do
+    local extension = img:match("[^.]*$"):upper()
+    local base = img:match("^.*[.]")
+
+    if base ~= current_base then
+      -- we are done with the base name, act according to what we found out
+      if other_format_found then
+        for _, jpg in ipairs(jpg_indices) do
+          images[jpg] = nil
+        end
+      end
+      current_base = base
+      other_format_found = false
+      for k,_ in pairs(jpg_indices) do jpg_indices[k] = nil end
+    end
+
+    -- remember what we have here to act accordingly after all instances of this base name were checked
+    if (extension == "JPG") or (extension == "JPEG") then
+      table.insert(jpg_indices, i)
+    else
+      other_format_found = true
+    end
+
+  end
+end)
+
+-- vim: shiftwidth=2 expandtab tabstop=2 cindent
+-- kate: tab-indents: off; indent-width 2; replace-tabs on; remove-trailing-space on;