Add script to copy & paste metadata between images

This not only takes care of tags (we already have a script for that in
contrib) but also color labels, rating and the things from the metadata
module.

official/copy_paste_metadata.lua

@@ -0,0 +1,128 @@
+--[[
+    This file is part of darktable,
+    copyright (c) 2016 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/>.
+]]
+--[[
+ADD SUPPORT FOR COPYING METADATA+RATING+COLOR LABELS+TAGS BETWEEN IMAGES
+This script adds keyboard shortcuts and buttons to copy/paste metadata between images.
+
+USAGE
+  * require this script from your main lua file
+  * it adds buttons to the selected images module
+  * it adds two keyboard shortcuts
+]]
+
+local dt = require "darktable"
+
+dt.configuration.check_version(...,{3,0,0})
+
+-- set this to "false" if you don't want to overwrite metadata fields
+-- (title, description, creator, publisher and rights) that are already set
+local overwrite = true
+
+local have_data = false
+local rating = 1
+local red = false
+local green = false
+local yellow = false
+local blue = false
+local purple = false
+local title = ""
+local description = ""
+local creator = ""
+local publisher = ""
+local rights = ""
+local tags = {}
+
+local function copy(image)
+  if not image then
+    have_data = false
+  else
+    have_data = true
+    rating = image.rating
+    red = image.red
+    green = image.green
+    yellow = image.yellow
+    blue = image.blue
+    purple = image.purple
+    title = image.title
+    description = image.description
+    creator = image.creator
+    publisher = image.publisher
+    rights = image.rights
+    tags = {}
+    for _, tag in ipairs(image:get_tags()) do
+      if not (string.sub(tag.name, 1, string.len("darktable|")) == "darktable|") then
+        table.insert(tags, tag)
+      end
+    end
+  end
+end
+
+local function paste(images)
+  if have_data then
+    for _, image in ipairs(images) do
+      image.rating = rating
+      image.red = red
+      image.green = green
+      image.yellow = yellow
+      image.blue = blue
+      image.purple = purple
+      if image.title == "" or overwrite then
+        image.title = title
+      end
+      if image.description == "" or overwrite then
+        image.description = description
+      end
+      if image.creator == "" or overwrite then
+        image.creator = creator
+      end
+      if image.publisher == "" or overwrite then
+        image.publisher = publisher
+      end
+      if image.rights == "" or overwrite then
+        image.rights = rights
+      end
+      for _, tag in ipairs(tags) do
+        image:attach_tag(tag)
+      end
+    end
+  end
+end
+
+dt.gui.libs.image.register_action(
+  "copy metadata",
+  function(event, images) copy(images[1]) end,
+  "copy metadata of the first selected image"
+)
+
+dt.gui.libs.image.register_action(
+  "paste metadata",
+  function(event, images) paste(images) end,
+  "paste metadata to the selected images"
+)
+
+dt.register_event(
+  "shortcut",
+  function(event, shortcut) copy(dt.gui.action_images[1]) end,
+  "copy metadata"
+)
+
+dt.register_event(
+  "shortcut",
+  function(event, shortcut) paste(dt.gui.action_images) end,
+  "paste metadata"
+)