Source File: ex50.cpp

#include <fmt/core.h>
#include <string>
#include <random>
#include <memory>
#include <algorithm>
#include <unordered_map>
#include <vector>
#include <ranges>

using std::shared_ptr, std::make_shared, std::string;

std::random_device RNG;
std::mt19937 GENERATOR(RNG());

struct Combatant {
  string name;
  int damage{0};
  int hp{0};
  bool dead{false};
};

/*
 * This is a dumb idea, but for education we'll try it.
 */
struct Player {
  string name;
  int damage{0};
  int hp{0};
  bool dead{false};
};

using ArenaID = int;
using Arena = std::unordered_map<ArenaID, shared_ptr<Combatant>>;
using CombatQueue = std::vector<size_t>;

int random_number(int from, int to) {
  std::uniform_int_distribution rand(from, to);
  return rand(GENERATOR);
}

void fight(auto attacker, auto defender) {
  using namespace fmt;

  int damage = random_number(0, attacker->damage);

  if(damage > 0) {
    defender->hp -= damage;
    println("{} hit {} for {}. {} now has {} hp",
        attacker->name, defender->name, damage,
        defender->name, defender->hp);
  } else {
    println("{} missed {}!",
        attacker->name, defender->name);
  }

  if(defender->hp <= 0) {
    fmt::println("{} died. {} wins! {} has {} HP",
        defender->name, attacker->name,
        attacker->name, attacker->hp);
  }
}

void fill_arena(Arena& arena, int combatants) {
  using namespace std::ranges;

  for(auto arena_id : views::iota(0, combatants)) {
    string name = fmt::format("Giant Rat #{}", arena_id);
    int hp = random_number(5,20);
    int damage = random_number(2,10);
    arena.try_emplace(arena_id, make_shared<Combatant>(name, damage, hp, 1.4f));
  }
}

bool combat_active(Arena& arena, shared_ptr<Combatant> player) {
  return !arena.empty() && player->hp > 0;
}

CombatQueue queue_combat(Arena& arena) {
  using namespace std::ranges;

  auto queue = arena | views::keys | to<CombatQueue>();
  shuffle(queue, GENERATOR);

  return queue;
}

void run_combat(auto combat_a, auto combat_b) {
  int winner = random_number(0,1);

  // need to explain this
  auto attacker = winner == 1 ? combat_a : combat_b;
  auto defender = winner == 0 ? combat_a : combat_b;

  fight(attacker, defender);

  if(defender->hp <= 0) {
    defender->dead = true;
  }
}

void cull_the_dead(Arena& arena) {
  using namespace std::ranges;

  auto is_dead = [&](auto& tuple) -> bool { return tuple.second->dead; };

  auto dead = arena | views::filter(is_dead) | views::elements<0> | to<CombatQueue>();

  for(auto id : dead) {
    arena.erase(id);
  }
}

int main(int argc, char* argv[]) {
  using namespace std::ranges;

  Arena arena;
  auto player = make_shared<Combatant>("Player", 20, 50, 1.4f);

  fill_arena(arena, 10);

  // now with multiple combatants we have to keep going until the player dies
  while(combat_active(arena, player)) {
    auto whos_next = queue_combat(arena);

    for_each(whos_next, [&](auto enemy_id) {
      run_combat(player, arena[enemy_id]);
    });

    cull_the_dead(arena);
  }

  if(arena.empty()) {
    fmt::println("The Player Wins! You defeated all of the rats.");
  } else {
    fmt::println("You Died! The Rats Win.");
  }
}