tangara-fw/src/lua/property.cpp

/*
 * Copyright 2023 jacqueline <me@jacqueline.id.au>
 *
 * SPDX-License-Identifier: GPL-3.0-only
 */

#include "property.hpp"

#include <memory>
#include <string>

#include "lua.h"
#include "lua.hpp"
#include "lvgl.h"
#include "service_locator.hpp"

namespace lua {

static const char kMetatableName[] = "property";
static const char kBindingsTable[] = "bindings";

static auto check_property(lua_State* state) -> Property* {
  void* data = luaL_checkudata(state, 1, kMetatableName);
  luaL_argcheck(state, data != NULL, 1, "`property` expected");
  return *reinterpret_cast<Property**>(data);
}

static auto property_get(lua_State* state) -> int {
  Property* p = check_property(state);
  p->PushValue(*state);
  return 1;
}

static auto property_set(lua_State* state) -> int {
  Property* p = check_property(state);
  luaL_argcheck(state, p->IsTwoWay(), 1, "property is read-only");
  bool valid = p->PopValue(*state);
  lua_pushboolean(state, valid);
  return 1;
}

static auto property_bind(lua_State* state) -> int {
  Property* p = check_property(state);
  luaL_checktype(state, 2, LUA_TFUNCTION);

  // Copy the function, as we need to invoke it then store our reference.
  lua_pushvalue(state, 2);
  // ...and another copy, since we return the original closure.
  lua_pushvalue(state, 2);

  // FIXME: This should ideally be lua_pcall, for safety.
  p->PushValue(*state);
  lua_call(state, 1, 0);  // Invoke the initial binding.

  lua_pushstring(state, kBindingsTable);
  lua_gettable(state, LUA_REGISTRYINDEX);  // REGISTRY[kBindingsTable]
  lua_insert(state, -2);          // Move bindings to the bottom, with fn above.
  int ref = luaL_ref(state, -2);  // bindings[ref] = fn

  p->AddLuaBinding(state, ref);

  // Pop the bindings table, leaving one of the copiesw of the callback fn at
  // the top of the stack.
  lua_pop(state, 1);

  return 1;
}

static const struct luaL_Reg kPropertyBindingFuncs[] = {{"get", property_get},
                                                        {"set", property_set},
                                                        {"bind", property_bind},
                                                        {NULL, NULL}};

PropertyBindings::PropertyBindings(lua_State& s) {
  // Create the metatable responsible for the Property API.
  luaL_newmetatable(&s, kMetatableName);

  lua_pushliteral(&s, "__index");
  lua_pushvalue(&s, -2);
  lua_settable(&s, -3);  // metatable.__index = metatable

  // Add our binding funcs (get, set, bind) to the metatable.
  luaL_setfuncs(&s, kPropertyBindingFuncs, 0);

  // Create a weak table in the registry to hold live bindings.
  lua_pushstring(&s, kBindingsTable);
  lua_newtable(&s);  // bindings = {}

  // Metatable for the weak table. Values are weak.
  lua_newtable(&s);  // meta = {}
  lua_pushliteral(&s, "__mode");
  lua_pushliteral(&s, "v");
  lua_settable(&s, -3);      // meta.__mode='v'
  lua_setmetatable(&s, -2);  // setmetatable(bindings, meta)

  lua_settable(&s, LUA_REGISTRYINDEX);  // REGISTRY[kBindingsTable] = bindings
}

auto PropertyBindings::Register(lua_State* s, Property* prop) -> void {
  Property** data =
      reinterpret_cast<Property**>(lua_newuserdata(s, sizeof(Property*)));
  *data = prop;

  luaL_setmetatable(s, kMetatableName);
}

template <class... Ts>
inline constexpr bool always_false_v = false;

Property::Property(const LuaValue& val) : value_(val), cb_() {}

Property::Property(const LuaValue& val,
                   std::function<bool(const LuaValue& val)> cb)
    : value_(val), cb_(cb) {}

auto Property::PushValue(lua_State& s) -> int {
  std::visit(
      [&](auto&& arg) {
        using T = std::decay_t<decltype(arg)>;
        if constexpr (std::is_same_v<T, std::monostate>) {
          lua_pushnil(&s);
        } else if constexpr (std::is_same_v<T, int>) {
          lua_pushinteger(&s, arg);
        } else if constexpr (std::is_same_v<T, float>) {
          lua_pushnumber(&s, arg);
        } else if constexpr (std::is_same_v<T, bool>) {
          lua_pushboolean(&s, arg);
        } else if constexpr (std::is_same_v<T, std::string>) {
          lua_pushstring(&s, arg.c_str());
        } else {
          static_assert(always_false_v<T>, "PushValue missing type");
        }
      },
      value_);
  return 1;
}

auto Property::PopValue(lua_State& s) -> bool {
  LuaValue new_val;
  switch (lua_type(&s, 2)) {
    case LUA_TNIL:
      new_val = std::monostate{};
      break;
    case LUA_TNUMBER:
      if (lua_isinteger(&s, 2)) {
        new_val = lua_tointeger(&s, 2);
      } else {
        new_val = lua_tonumber(&s, 2);
      }
      break;
    case LUA_TBOOLEAN:
      new_val = lua_toboolean(&s, 2);
      break;
    case LUA_TSTRING:
      new_val = lua_tostring(&s, 2);
      break;
    default:
      return false;
  }

  if (cb_ && std::invoke(*cb_, new_val)) {
    Update(new_val);
    return true;
  }
  return false;
}

auto Property::Update(const LuaValue& v) -> void {
  value_ = v;

  for (int i = bindings_.size() - 1; i >= 0; i--) {
    auto& b = bindings_[i];

    lua_pushstring(b.first, kBindingsTable);
    lua_gettable(b.first, LUA_REGISTRYINDEX);       // REGISTRY[kBindingsTable]
    int type = lua_rawgeti(b.first, -1, b.second);  // push bindings[i]

    // Has closure has been GCed?
    if (type == LUA_TNIL) {
      // Clean up after ourselves.
      lua_pop(b.first, 1);
      // Remove the binding.
      bindings_.erase(bindings_.begin() + i);
      continue;
    }

    PushValue(*b.first);      // push the argument
    lua_call(b.first, 1, 0);  // invoke the closure
  }
}

auto Property::AddLuaBinding(lua_State* state, int ref) -> void {
  bindings_.push_back({state, ref});
}

}  // namespace lua