waterbot: add WIP water renewing bot

At the moment it can just give you a list of water sources that can be bucketed without having a net loss of water.
Next is to make an automatic bucket filler hack using that.

clientmods/mods.conf

@@ -42,3 +42,4 @@ load_mod_muse = true
 load_mod_optimize = true
 load_mod_render = true
 load_mod_combat = true
+load_mod_waterbot = true

clientmods/waterbot/init.lua

@@ -0,0 +1,106 @@
+-- CC0/Unlicense Emilia 2020
+waterbot = {}
+
+-- Lua doesnt have enums and tables look gross
+-- should still be a table tho
+local WATER_USABLE = 0  -- water source
+local WATER_STABLE = 1  -- water source used for refreshing other sources
+local WATER_USED = 2    -- water source that can be bucketed
+local AIR = 3           -- something that water can flow into and renew
+local SOLID = 4         -- something that water cannot flow into and renew
+
+local function get_offset(pos, radius)
+    return vector.round({
+        x = pos.x - radius - 1,
+        y = pos.y - radius - 1,
+        z = pos.z - radius - 1
+    })
+end
+
+-- returns {{{n n n} {n n n} ...} {...} ...}
+local function get_intarr(pos, radius)
+    local offset = get_offset(pos, radius)
+    local out = {}
+    local diameter = radius * 2 + 1
+
+    for z = 1, diameter do
+        table.insert(out, {})
+        for y = 1, diameter do
+            table.insert(out[#out], {})
+            for x = 1, diameter do
+                local npos = {x = x, y = y, z = z}
+                local node = minetest.get_node_or_nil(vector.add(offset, npos))
+                local v = SOLID
+                if node then
+                    if node.name == "mcl_core:water_source" then
+                        v = WATER_USABLE
+                    elseif node.name == "air" then
+                        v = AIR
+                    end
+                end
+                table.insert(out[#out][#out[#out]], v)
+            end
+        end
+    end
+
+    return out
+end
+
+local function coord_valid(coord, width, height)
+    return ((coord[1] > 0) and (coord[2] > 0)) and ((coord[1] <= width) and (coord[2] <= height))
+end
+
+-- returns modified list and safe sources
+-- table is [z][y][x] accessed
+-- safe sources is a coordinate list
+-- this is like cellular automata but the state is mogrified in place
+local function mogrify_stable(t, offset)
+    local safe = {}
+
+    -- indented like this because this is necessary and full indent would be ugly
+    for zi, zv in ipairs(t) do
+     for yi, yv in ipairs(zv) do
+      for xi, xv in ipairs(yv) do
+       if xv == WATER_USABLE then
+            local nhood = {
+                {xi - 1, zi},
+                {xi, zi - 1},
+                {xi + 1, zi},
+                {xi, zi + 1}
+            }
+
+            local last
+            local applied = false
+
+            for i, v in ipairs(nhood) do
+                if not applied and coord_valid(v, #yv, #t) then
+                    local check = t[v[2]][yi][v[1]]
+                    if check == WATER_USABLE or check == WATER_STABLE then
+                        if not last then
+                            last = v
+                        else
+                            t[   v[2]][yi][   v[1]] = WATER_STABLE
+                            t[last[2]][yi][last[1]] = WATER_STABLE
+                            yv[xi] = WATER_USED
+                            table.insert(safe,
+                                vector.add(offset,
+                                    {x = xi, y = yi, z = zi}))
+                            applied = true
+                        end
+                    end
+                end
+            end
+       end
+      end
+     end
+    end
+
+    return t, safe
+end
+
+function waterbot.find_renewable_water_near(pos, radius)
+    local int = get_intarr(pos, radius)
+    local offset = get_offset(pos, radius)
+    local mint, safe = mogrify_stable(int, offset)
+    return safe
+end