From 6a0a7e3926264d0636afd22d03a8e48641e168f5 Mon Sep 17 00:00:00 2001
From: Celtic Minstrel <celtic.minstrel.ca@some.place>
Date: Fri, 19 Feb 2021 21:24:32 -0500
Subject: [PATCH] Implement a map iterator

---
 src/scripting/game_lua_kernel.cpp |  1 +
 src/scripting/lua_terrainmap.cpp  | 74 +++++++++++++++++++++++++++++++
 src/scripting/lua_terrainmap.hpp  |  1 +
 3 files changed, 76 insertions(+)

diff --git a/src/scripting/game_lua_kernel.cpp b/src/scripting/game_lua_kernel.cpp
index 217b31fa29fd9..6808be2c8e95e 100644
--- a/src/scripting/game_lua_kernel.cpp
+++ b/src/scripting/game_lua_kernel.cpp
@@ -4138,6 +4138,7 @@ game_lua_kernel::game_lua_kernel(game_state & gs, play_controller & pc, reports
 		{"terrain_mask", &intf_terrain_mask},
 		{"on_board", &intf_on_board},
 		{"on_border", &intf_on_border},
+		{"iter", &intf_terrainmap_iter},
 		// Shroud operations
 		{"place_shroud", &dispatch2<&game_lua_kernel::intf_shroud_op, true>},
 		{"remove_shroud", &dispatch2<&game_lua_kernel::intf_shroud_op, false>},
diff --git a/src/scripting/lua_terrainmap.cpp b/src/scripting/lua_terrainmap.cpp
index c485082ef0e78..6b36f2515c441 100644
--- a/src/scripting/lua_terrainmap.cpp
+++ b/src/scripting/lua_terrainmap.cpp
@@ -345,6 +345,80 @@ static int impl_terrainmap_set(lua_State *L)
 	return luaL_argerror(L, 2, err_msg.c_str());
 }
 
+/*
+The map iterator, when called with false as its parameter
+is roughly equivalent to the following Lua function:
+
+function map_iter()
+	local map, x, y = wesnoth.map.get(), 0, 1
+	return function()
+		if x == map.playable_width then
+			if y == map.playable_height then
+				return nil
+			else
+				x, y = 1, y + 1
+			end
+		else
+			x = x + 1
+		end
+		return x, y, map[{x, y}]
+	end
+end
+
+*/
+
+template<bool with_border>
+static int impl_terrainmap_iter(lua_State* L)
+{
+	// Retrieve the upvalues stored with the function
+	gamemap_base& tm = luaW_checkterrainmap(L, lua_upvalueindex(1));
+	map_location prev_loc = luaW_checklocation(L, lua_upvalueindex(2));
+	int w = with_border ? tm.total_width() - 1 : tm.w();
+	int h = with_border ? tm.total_height() - 1 : tm.h();
+	int x, y;
+	
+	// Given the previous location, determine the next one to be returned
+	if(prev_loc.wml_x() == w) {
+		if(prev_loc.wml_y() == h) {
+			lua_pushnil(L);
+			return 1;
+		} else {
+			x = with_border ? 0 : 1;
+			y = prev_loc.wml_y() + 1;
+		}
+	} else {
+		x = prev_loc.wml_x() + 1;
+		y = prev_loc.wml_y();
+	}
+	
+	// Assign the upvalue representing the previous location
+	map_location next_loc(x, y, wml_loc{});
+	luaW_pushlocation(L, next_loc);
+	lua_replace(L, lua_upvalueindex(2));
+	
+	// Return the new location and its terrain code
+	lua_pushinteger(L, x);
+	lua_pushinteger(L, y);
+	luaW_push_terrain(L, tm, next_loc);
+	
+	return 3;
+}
+
+static int intf_terrainmap_iter(lua_State* L)
+{
+	gamemap_base& tm = luaW_checkterrainmap(L, 1);
+	bool with_border = lua_isboolean(L, 2) ? luaW_toboolean(L, 2) : false;
+	lua_settop(L, 1);
+	luaW_pushlocation(L, map_location(with_border ? -1 : 0, 1, wml_loc{}));
+	
+	if(with_border) {
+		lua_pushcclosure(L, impl_terrainmap_iter<true>, 2);
+	} else {
+		lua_pushcclosure(L, impl_terrainmap_iter<false>, 2);
+	}
+	return 1;
+}
+
 static int intf_on_board(lua_State* L)
 {
 	gamemap_base& tm = luaW_checkterrainmap(L, 1);
diff --git a/src/scripting/lua_terrainmap.hpp b/src/scripting/lua_terrainmap.hpp
index 450b539ab2db9..7e41044487ea9 100644
--- a/src/scripting/lua_terrainmap.hpp
+++ b/src/scripting/lua_terrainmap.hpp
@@ -58,6 +58,7 @@ int intf_terrainmap_create(lua_State *L);
 int intf_terrainmap_get(lua_State *L);
 
 int intf_replace_if_failed(lua_State* L);
+int intf_terrainmap_iter(lua_State* L);
 int intf_on_board(lua_State* L);
 int intf_on_border(lua_State* L);