Fix shortbread boundary processing in regards to disputed boundaries

The way disputed boundaries are implemented was not correct. Generally
boundaries should be processed as if disputed boundaries do not exists.
But then all boundary lines created from ways that have the disputed
flag set or that are in a relation tagged boundary=disputed will be
marked as disputed.

Note that the relation that marks a way as disputed is not the same
relation that marks a way as part of some specific admin boundary. The
first is tagged boundary=disputed, the second is tagged
boundary=administrative.

This is based on the work in #10 but rewrites the code to be (hopefully)
easier to understand.

Note that this only fixes the version for shortbread_v1, the version for
shortbread_v1_gen also needs updating which will come later.

Author: joto

themes/shortbread_v1/topics/boundaries.lua

@@ -12,7 +12,7 @@ themepark:add_table{
     ids_type = 'way',
     geom = 'linestring',
     columns = themepark:columns({
-        { column = 'admin_level', type = 'int' },
+        { column = 'admin_level', type = 'int', not_null = true },
         { column = 'maritime', type = 'bool' },
         { column = 'disputed', type = 'bool' },
     }),
@@ -29,27 +29,23 @@ themepark:add_table{
     }
 }
 
-local rinfos = {}
-
 -- ---------------------------------------------------------------------------
+-- Storage of information from boundary relations for use by boundary ways
+-- (two-stage processing).
 
--- 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
+-- Minimum admin level of all relations that reference a way id
+local min_admin_level = {}
 
-    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
+-- For all way ids that are in a relation tagged boundary=disputed
+local ways_in_disputed_boundary_relation = {}
+
+-- ---------------------------------------------------------------------------
 
--- 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
+-- Shortbread is only interested in level 2 and level 4 admin boundaries.
+local function is_admin_boundary(tags)
+    return (tags.type == 'boundary' or tags.type == 'multipolygon')
+           and tags.boundary == 'administrative'
+           and (tags.admin_level == '2' or tags.admin_level == '4')
 end
 
 -- ---------------------------------------------------------------------------
@@ -59,45 +55,45 @@ themepark:add_proc('way', function(object, data)
         return
     end
 
-    local info = rinfos[object.id]
-    if not info then
+    local admin_level = min_admin_level[object.id]
+    if not admin_level then
         return
     end
 
     local t = object.tags
     local a = {
-        admin_level = info.admin_level,
+        admin_level = admin_level,
         maritime = (t.maritime and (t.maritime == 'yes' or t.natural == 'coastline')),
-        disputed = info.disputed or (t.disputed and t.disputed == 'yes'),
+        disputed = (t.disputed and t.disputed == 'yes') or ways_in_disputed_boundary_relation[object.id],
         geom = object:as_linestring()
     }
 
     themepark:insert('boundaries', a, t)
 end)
 
 themepark:add_proc('select_relation_members', function(relation)
-    if valid_admin_level(get_admin_level(relation.tags)) then
+    if is_admin_boundary(relation.tags) then
         return { ways = osm2pgsql.way_member_ids(relation) }
     end
 end)
 
 themepark:add_proc('relation', function(object, data)
-    local t = object.tags
+    if is_admin_boundary(object.tags) then
+        local admin_level = tonumber(object.tags.admin_level)
 
-    local admin_level = get_admin_level(t)
+        for _, id in ipairs(osm2pgsql.way_member_ids(object)) do
+            if not min_admin_level[id] or min_admin_level[id] > admin_level then
+                min_admin_level[id] = admin_level
+            end
+        end
 
-    if not valid_admin_level(admin_level) then
         return
     end
 
-    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')
+    -- All ways in relations tagged boundary=disputed are flagged as disputed
+    if object.tags.boundary == 'disputed' then
+        for _, id in ipairs(osm2pgsql.way_member_ids(object)) do
+            ways_in_disputed_boundary_relation[id] = true
         end
     end
 end)