// Radio propagation is simulated using actual living carriers and inventory.
// A manpack is the HQ uplink; short-range hops are limited to 500 m and three
// retransmissions. No virtual relay is fabricated when the network is broken.
class ERR_HQRadioNode
{
	IEntity Carrier;
	SCR_AIGroup Group;
	int UnitId;
	int Capability;
	protected float m_CheckedAt = -1;
	protected int m_LiveCapability;

	bool Valid(bool manpack = false)
	{
		ERR_GameMode factions = ERR_GameMode.Get();
		if (!Carrier || !Group || Group.GetPlayerCount(true) > 0 || !factions || Group.GetFaction() != factions.EnemyFaction() || ERR_Actors.Group(Carrier) != Group)
			return false;
		int required = 1;
		if (manpack)
			required = 2;
		float now = GetGame().GetWorld().GetWorldTime();
		if (m_CheckedAt < 0 || now < m_CheckedAt || now - m_CheckedAt >= 1000)
		{
			m_CheckedAt = now;
			m_LiveCapability = ERR_HQRadio.Capability(Carrier);
		}
		return m_LiveCapability >= required;
	}

	string Label()
	{
		return "unit " + UnitId.ToString();
	}
}

class ERR_HQRoute
{
	ref array<ref ERR_HQRadioNode> Nodes = {};
	bool Downlink;
	int Cursor;
	bool Sending;
	float Due;
	vector SentFrom;
	float StartedAt = -1;
	int MessageId;
	string Payload;
	bool Failed;

	// -1 failed, 0 travelling, 1 delivered. Each hop really gates delivery.
	int Advance(float now, ERR_HQJournal journal)
	{
		if (Failed)
			return -1;
		if (StartedAt < 0)
		{
			StartedAt = now;
			if (Downlink)
				Cursor = -1; // first leg is HQ to the manpack
		}
		if (now - StartedAt > 30000)
			return Fail(journal, "route timed out");
		int target = Cursor + 1;
		if (Sending)
		{
			if (now < Due)
				return 0;
			if (target < Nodes.Count())
			{
				if (!Nodes[target].Valid(Downlink && target == 0))
					return Fail(journal, "receiving carrier lost radio, died or changed ownership");
				if (Cursor >= 0 && vector.DistanceXZ(SentFrom, Nodes[target].Carrier.GetOrigin()) > 500)
					return Fail(journal, "receiver moved beyond the 500m link");
				journal.Write("RECEIVE", Nodes[target].Label() + " received from " + SenderLabel(), MessageId);
			}
			else
				journal.Write("RECEIVE", "HQ received from " + SenderLabel(), MessageId);
			Cursor++;
			Sending = false;
			if ((!Downlink && Cursor >= Nodes.Count()) || (Downlink && Cursor == Nodes.Count() - 1))
				return 1;
			target = Cursor + 1;
		}
		if (Nodes.IsEmpty())
			return Fail(journal, "no physical radio route");
		if (Cursor >= 0 && !Nodes[Cursor].Valid(!Downlink && Cursor == Nodes.Count() - 1))
			return Fail(journal, "transmitting carrier lost radio, died or changed ownership");
		string recipient = "HQ";
		string link = "long-range";
		if (target < Nodes.Count())
		{
			if (!Nodes[target].Valid(Downlink && target == 0))
				return Fail(journal, "next relay unavailable");
			recipient = Nodes[target].Label();
			if (Cursor >= 0)
			{
				SentFrom = Nodes[Cursor].Carrier.GetOrigin();
				float distance = vector.DistanceXZ(SentFrom, Nodes[target].Carrier.GetOrigin());
				if (distance > 500)
					return Fail(journal, "next relay beyond 500m");
				link = Math.Round(distance).ToString() + "m short-range";
			}
		}
		journal.Write("TRANSMIT", SenderLabel() + " -> " + recipient + " (" + link + ")", MessageId);
		Sending = true;
		Due = now + 2000;
		return 0;
	}

	protected string SenderLabel()
	{
		if (Cursor < 0)
			return "HQ";
		return Nodes[Cursor].Label();
	}

	protected int Fail(ERR_HQJournal journal, string reason)
	{
		Failed = true;
		journal.Write("LOST", reason + "; " + Payload, MessageId);
		return -1;
	}
}

class ERR_HQNetwork
{
	protected ref array<ref ERR_HQRadioNode> m_Nodes = {};
	protected ref array<int> m_Parents = {};
	protected ref array<int> m_Depths = {};
	protected ref map<IEntity, int> m_Indices = new map<IEntity, int>();
	protected ref map<string, ref array<int>> m_Cells = new map<string, ref array<int>>();
	bool Overflow;

	void Clear()
	{
		m_Nodes.Clear();
		m_Parents.Clear();
		m_Depths.Clear();
		m_Indices.Clear();
		m_Cells.Clear();
		Overflow = false;
	}

	protected string Cell(int x, int z)
	{
		return string.Format("%1:%2", x, z);
	}

	void Add(IEntity carrier, SCR_AIGroup group, int unitId, int capability)
	{
		if (m_Indices.Contains(carrier))
			return;
		if (m_Nodes.Count() >= 2048)
		{
			Overflow = true;
			return;
		}
		ERR_HQRadioNode node = new ERR_HQRadioNode();
		node.Carrier = carrier;
		node.Group = group;
		node.UnitId = unitId;
		node.Capability = capability;
		int index = m_Nodes.Count();
		m_Nodes.Insert(node);
		m_Indices.Insert(carrier, index);
		m_Parents.Insert(-2);
		m_Depths.Insert(99);
		vector position = carrier.GetOrigin();
		string key = Cell(Math.Floor(position[0] / 500), Math.Floor(position[2] / 500));
		array<int> cell = m_Cells.Get(key);
		if (!cell)
		{
			cell = {};
			m_Cells.Insert(key, cell);
		}
		cell.Insert(index);
	}

	void Build()
	{
		array<int> queue = {};
		int checks;
		for (int root = 0; root < m_Nodes.Count(); root++)
		{
			if (m_Nodes[root].Capability == 2)
			{
				m_Parents[root] = -1;
				m_Depths[root] = 0;
				queue.Insert(root);
			}
		}
		for (int head = 0; head < queue.Count(); head++)
		{
			int from = queue[head];
			if (m_Depths[from] >= 3)
				continue;
			vector position = m_Nodes[from].Carrier.GetOrigin();
			int x = Math.Floor(position[0] / 500);
			int z = Math.Floor(position[2] / 500);
			for (int dx = -1; dx <= 1; dx++)
			{
				for (int dz = -1; dz <= 1; dz++)
				{
					array<int> neighbors = m_Cells.Get(Cell(x + dx, z + dz));
					if (!neighbors)
						continue;
					foreach (int candidate : neighbors)
					{
						if (++checks > 100000)
						{
							Overflow = true;
							return;
						}
						if (m_Parents[candidate] != -2 || vector.DistanceXZ(position, m_Nodes[candidate].Carrier.GetOrigin()) > 500)
							continue;
						m_Parents[candidate] = from;
						m_Depths[candidate] = m_Depths[from] + 1;
						queue.Insert(candidate);
					}
				}
			}
		}
	}

	ERR_HQRoute Route(IEntity caller, bool downlink = false)
	{
		int index;
		if (!m_Indices.Find(caller, index) || m_Parents[index] == -2)
			return null;
		ERR_HQRoute route = new ERR_HQRoute();
		route.Downlink = downlink;
		while (index >= 0)
		{
			if (downlink)
				route.Nodes.InsertAt(m_Nodes[index], 0);
			else
				route.Nodes.Insert(m_Nodes[index]);
			index = m_Parents[index];
		}
		return route;
	}
}