Improve boundary processing in shortbread topic

More consistent processing of boundaries in shortbread_v1. Deciding when
something is a boundary is now done only in one place. And the code is
more robust, checking that the way info is there before using it.

(This is now the same as in the shortbread_v1_gen code which already had
those changes.)

See #2

themes/shortbread_v1/topics/boundaries.lua

@@ -33,13 +33,38 @@ local rinfos = {}
 
 -- ---------------------------------------------------------------------------
 
+-- Check if this looks like a boundary and return admin_level as number
+-- Return nil if this is not a valid boundary.
+local function get_admin_level(tags)
+    local type = tags.type
+
+    if type == 'boundary' or type == 'multipolygon' then
+        local boundary = tags.boundary
+        if boundary == 'administrative' or boundary == 'disputed' then
+            return tonumber(tags.admin_level)
+        end
+    end
+end
+
+-- Check the (numeric) admin level. Change this depending on which admin
+-- levels you want to process. Shortbread only shows 2 and 4.
+local function valid_admin_level(level)
+    return level == 2 or level == 4
+end
+
+-- ---------------------------------------------------------------------------
+
 themepark:add_proc('way', function(object, data)
     if osm2pgsql.stage == 1 then
         return
     end
 
-    local t = object.tags
     local info = rinfos[object.id]
+    if not info then
+        return
+    end
+
+    local t = object.tags
     local a = {
         admin_level = info.admin_level,
         maritime = (t.maritime and (t.maritime == 'yes' or t.natural == 'coastline')),
@@ -51,32 +76,28 @@ themepark:add_proc('way', function(object, data)
 end)
 
 themepark:add_proc('select_relation_members', function(relation)
-    local t = relation.tags
-    -- Only interested in relations with type=boundary, boundary=administrative
-    if t.type == 'boundary' and t.boundary == 'administrative'
-       and (t.admin_level == '2' or t.admin_level == '4') then
+    if valid_admin_level(get_admin_level(relation.tags)) then
         return { ways = osm2pgsql.way_member_ids(relation) }
     end
 end)
 
 themepark:add_proc('relation', function(object, data)
     local t = object.tags
-    if t.type ~= 'boundary' then
+
+    local admin_level = get_admin_level(t)
+
+    if not valid_admin_level(admin_level) then
         return
     end
 
-    if (t.boundary == 'administrative' or t.boundary == 'disputed')
-       and (t.admin_level == '2' or t.admin_level == '4') then
-        local admin_level = tonumber(t.admin_level)
-        for _, member in ipairs(object.members) do
-            if member.type == 'w' then
-                if not rinfos[member.ref] then
-                    rinfos[member.ref] = { admin_level = admin_level }
-                elseif rinfos[member.ref].admin_level > admin_level then
-                    rinfos[member.ref].admin_level = admin_level
-                end
-                rinfos[member.ref].disputed = t.boundary == 'disputed'
+    for _, member in ipairs(object.members) do
+        if member.type == 'w' then
+            if not rinfos[member.ref] then
+                rinfos[member.ref] = { admin_level = admin_level }
+            elseif rinfos[member.ref].admin_level > admin_level then
+                rinfos[member.ref].admin_level = admin_level
             end
+            rinfos[member.ref].disputed = (t.boundary == 'disputed')
         end
     end
 end)