DiD S04 Todo: Add snow

Lifted code from HttT to add snow coverage.

data/campaigns/Descent_Into_Darkness/scenarios/04_Beginning_of_the_Revenge.cfg

@@ -133,7 +133,53 @@
             [/gold_carryover]
         [/objectives]
 
-        # TODO: manually add snow detritus
+        [lua]
+            code=<<
+-- For prime-time use the filter terrain needs to come in and the convert
+-- table needs to be VERY complete. Or, rename this to morph_terrain and
+-- have the conversion table come in as an argument, too.
+
+local locations = wesnoth.get_locations{terrain = 'Ce,Chr,Co,Gg,Gg^Efm,Gg^Vc,Gg^Vo,Gs^Fds,Gs^Fms,Gs^Fmw,Gs^Fp,Hh,Hh^Vhh,Hh^Vo,Ke,Khr,Ko,Mm,Mm^Xm'}
+
+local coverage = 0.15
+-- Constant 15% random coverage.
+-- Valid range is (0.0 .. 1.0)
+-- Do not raise too high or player may not be able to make it in the time allotted.
+
+local snowNeeded = (#locations * coverage)
+
+local convert = {
+    ['Ce'] = 'Cea',
+    ['Chr'] = 'Cha',
+    ['Co'] = 'Coa',
+    ['Gg'] = 'Aa',
+    ['Gg^Efm'] = 'Aa',
+    ['Gg^Vc'] = 'Aa^Vca',
+    ['Gg^Vo'] = 'Aa^Voa',
+    ['Gs^Fds'] = 'Aa^Fda',
+    ['Gs^Fms'] = 'Aa^Fma',
+    ['Gs^Fmw'] = 'Aa^Fma',
+    ['Gs^Fp'] = 'Aa^Fpa',
+    ['Hh'] = 'Ha',
+    ['Hh^Vhh'] = 'Ha^Vha',
+    ['Hh^Vo'] = 'Ha^Voa',
+    ['Ke'] = 'Kea',
+    ['Khr'] = 'Kha',
+    ['Ko'] = 'Koa',
+    ['Mm'] = 'Ms',
+    ['Mm^Xm'] = 'Ms^Xm'
+}
+
+local loopCounter
+for loopCounter = 1, snowNeeded do
+    local locationsIndex = wesnoth.random(#locations)
+    local coordinate = locations[locationsIndex]
+    local terrainCode = wesnoth.get_terrain(coordinate[1], coordinate[2])
+    wesnoth.set_terrain(coordinate[1], coordinate[2], (convert[terrainCode] or terrainCode))
+    table.remove(locations, locationsIndex)
+end
+            >>
+        [/lua]
 
         [recall]
             id=Darken Volk