lua_pathfind_cost_calculator.hpp

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#pragma once
#include "lua/lua.h"
#include "map/location.hpp"
#include "scripting/lua_api.hpp"
#include "pathfind/pathfind.hpp"

/**
 * Cost function object relying on a Lua function.
 * @note The stack index of the Lua function must be valid each time the cost is computed.
 */
struct lua_pathfind_cost_calculator : pathfind::cost_calculator
{
    lua_State *L;
    int index;
    /// @param i the stack position of the lua function to calculate the cost.
    lua_pathfind_cost_calculator(lua_State *L_, int i): L(L_), index(i) {}
    double cost(const map_location &loc, const double so_far) const
    {
        // Copy the user function and push the location and current cost.
        lua_pushvalue(L, index);
        lua_pushinteger(L, loc.x + 1);
        lua_pushinteger(L, loc.y + 1);
        lua_pushnumber(L, so_far);
        // Execute the user function.
        if (!luaW_pcall(L, 3, 1)) {
            return 1.;
        }
        // Return a cost of at least 1 mp to avoid issues in pathfinder.
        // (Condition is inverted to detect NaNs.)
        double cost = lua_tonumber(L, -1);
        lua_pop(L, 1);
        return !(cost >= 1.) ? 1. : cost;
    }
};