class_name ManaNetworkService
extends RefCounted

## Deterministic Mana graph, allocation, storage and brownout simulation.
##
## The graph is intentionally separate from the walking graph. Authoritative
## values are integers so save/load and repeated simulations produce the same
## result on every platform.

signal consumer_state_changed(consumer_id: StringName, previous_state: int, next_state: int, reasons: Array[StringName])

enum NodeKind {
	SOURCE,
	CONSUMER,
	CONNECTOR,
	STORAGE,
}

enum ConsumerPriority {
	LUXURY = 0,
	NORMAL = 50,
	ESSENTIAL = 100,
}

enum ConsumerState {
	ACTIVE,
	DEGRADED,
	NO_POWER,
	DISABLED,
}

const SNAPSHOT_VERSION := 1
const EVALUATION_INTERVAL_MINUTES := 10
const MINIMUM_OFF_HOLD_MINUTES := 10
const DEGRADED_THRESHOLD_PERCENT := 75

var revision := 0
var last_evaluation_minute := -1
var last_error := ""

var _nodes: Dictionary = {}
var _adjacency: Dictionary = {}
var _last_report: Dictionary = {}


func register_source(node_id: StringName, output: int, enabled := true) -> bool:
	if output < 0:
		return _fail("Source output cannot be negative.")
	return _register_node(node_id, NodeKind.SOURCE, {
		&"output": output,
		&"enabled": enabled,
	})


func register_consumer(
	node_id: StringName,
	demand: int,
	priority := ConsumerPriority.NORMAL,
	enabled := true
) -> bool:
	if demand < 0:
		return _fail("Consumer demand cannot be negative.")
	return _register_node(node_id, NodeKind.CONSUMER, {
		&"demand": demand,
		&"priority": priority,
		&"enabled": enabled,
		&"allocated": 0,
		&"state": ConsumerState.NO_POWER if enabled else ConsumerState.DISABLED,
		&"state_reasons": [&"awaiting_evaluation"] if enabled else [&"disabled"],
		&"hold_until": 0,
	})


func register_connector(node_id: StringName, enabled := true) -> bool:
	return _register_node(node_id, NodeKind.CONNECTOR, {&"enabled": enabled})


func register_storage(
	node_id: StringName,
	capacity: int,
	current: int,
	max_flow: int,
	enabled := true
) -> bool:
	if capacity < 0 or current < 0 or current > capacity or max_flow < 0:
		return _fail("Storage values must satisfy 0 <= current <= capacity and max_flow >= 0.")
	return _register_node(node_id, NodeKind.STORAGE, {
		&"capacity": capacity,
		&"current": current,
		&"max_flow": max_flow,
		&"enabled": enabled,
	})


func unregister_node(node_id: StringName) -> bool:
	if not _nodes.has(node_id):
		return _fail("Unknown Mana node: %s" % node_id)
	var neighbors: Array = _adjacency.get(node_id, {}).keys()
	for neighbor: Variant in neighbors:
		_adjacency[neighbor].erase(node_id)
	_adjacency.erase(node_id)
	_nodes.erase(node_id)
	revision += 1
	last_error = ""
	return true


func connect_nodes(first_id: StringName, second_id: StringName) -> bool:
	if first_id == second_id:
		return _fail("A Mana node cannot connect to itself.")
	if not _nodes.has(first_id) or not _nodes.has(second_id):
		return _fail("Both Mana nodes must exist before they are connected.")
	if _adjacency[first_id].has(second_id):
		last_error = ""
		return true
	_adjacency[first_id][second_id] = true
	_adjacency[second_id][first_id] = true
	revision += 1
	last_error = ""
	return true


func disconnect_nodes(first_id: StringName, second_id: StringName) -> bool:
	if not _adjacency.has(first_id) or not _adjacency[first_id].has(second_id):
		return _fail("Mana edge does not exist.")
	_adjacency[first_id].erase(second_id)
	_adjacency[second_id].erase(first_id)
	revision += 1
	last_error = ""
	return true


func set_node_enabled(node_id: StringName, enabled: bool) -> bool:
	if not _nodes.has(node_id):
		return _fail("Unknown Mana node: %s" % node_id)
	var node: Dictionary = _nodes[node_id]
	if bool(node[&"enabled"]) == enabled:
		last_error = ""
		return true
	node[&"enabled"] = enabled
	if int(node[&"kind"]) == NodeKind.CONSUMER and not enabled:
		node[&"allocated"] = 0
		_set_consumer_state(node_id, node, ConsumerState.DISABLED, [&"disabled"])
	_nodes[node_id] = node
	revision += 1
	last_error = ""
	return true


func set_source_output(node_id: StringName, output: int) -> bool:
	if output < 0 or not _is_kind(node_id, NodeKind.SOURCE):
		return _fail("A valid source and non-negative output are required.")
	var node: Dictionary = _nodes[node_id]
	node[&"output"] = output
	_nodes[node_id] = node
	revision += 1
	last_error = ""
	return true


func set_consumer_demand(node_id: StringName, demand: int) -> bool:
	if demand < 0 or not _is_kind(node_id, NodeKind.CONSUMER):
		return _fail("A valid consumer and non-negative demand are required.")
	var node: Dictionary = _nodes[node_id]
	node[&"demand"] = demand
	_nodes[node_id] = node
	revision += 1
	last_error = ""
	return true


func set_consumer_priority(node_id: StringName, priority: int) -> bool:
	if not _is_kind(node_id, NodeKind.CONSUMER):
		return _fail("A valid consumer is required.")
	var node: Dictionary = _nodes[node_id]
	node[&"priority"] = priority
	_nodes[node_id] = node
	revision += 1
	last_error = ""
	return true


func advance_one_minute(absolute_minute: int) -> Dictionary:
	if absolute_minute < 0:
		return {&"evaluated": false, &"error": "Minute cannot be negative."}
	if absolute_minute % EVALUATION_INTERVAL_MINUTES != 0 \
		or absolute_minute == last_evaluation_minute:
		return {&"evaluated": false, &"minute": absolute_minute}
	return evaluate_now(absolute_minute)


func evaluate_now(absolute_minute: int) -> Dictionary:
	if absolute_minute < 0:
		return {&"evaluated": false, &"error": "Minute cannot be negative."}
	var changes: Array = []
	var component_reports: Array = []
	for component: Array[StringName] in _connected_components():
		component_reports.append(_evaluate_component(component, absolute_minute, changes))
	last_evaluation_minute = absolute_minute
	_last_report = {
		&"evaluated": true,
		&"minute": absolute_minute,
		&"components": component_reports,
		&"state_changes": changes,
	}
	last_error = ""
	return _last_report.duplicate(true)


func get_node(node_id: StringName) -> Dictionary:
	if not _nodes.has(node_id):
		return {}
	return (_nodes[node_id] as Dictionary).duplicate(true)


func get_consumer_state(node_id: StringName) -> int:
	if not _is_kind(node_id, NodeKind.CONSUMER):
		return -1
	return int(_nodes[node_id][&"state"])


func get_allocated_mana(node_id: StringName) -> int:
	if not _is_kind(node_id, NodeKind.CONSUMER):
		return 0
	return int(_nodes[node_id][&"allocated"])


func get_storage_current(node_id: StringName) -> int:
	if not _is_kind(node_id, NodeKind.STORAGE):
		return 0
	return int(_nodes[node_id][&"current"])


## Upkeep demand of every registered consumer, including disabled ones,
## except the given consumer ids (for example destroyed facilities).
func get_total_consumer_demand(excluded_ids: Array = []) -> int:
	var total := 0
	for node_id: StringName in _nodes:
		if int(_nodes[node_id][&"kind"]) == NodeKind.CONSUMER and not node_id in excluded_ids:
			total += int(_nodes[node_id][&"demand"])
	return total


func get_last_report() -> Dictionary:
	return _last_report.duplicate(true)


func node_count() -> int:
	return _nodes.size()


func edge_count() -> int:
	var doubled := 0
	for neighbors: Variant in _adjacency.values():
		doubled += (neighbors as Dictionary).size()
	return doubled / 2


func validate_invariants() -> Dictionary:
	var errors: Array[String] = []
	for node_id: Variant in _sorted_ids(_nodes.keys()):
		var node: Dictionary = _nodes[node_id]
		if not _adjacency.has(node_id):
			errors.append("Node %s has no adjacency entry." % node_id)
		if int(node[&"kind"]) == NodeKind.STORAGE:
			var current := int(node[&"current"])
			var capacity := int(node[&"capacity"])
			if current < 0 or current > capacity:
				errors.append("Storage %s is outside its capacity." % node_id)
		if int(node[&"kind"]) == NodeKind.CONSUMER:
			var allocation := int(node[&"allocated"])
			if allocation < 0 or allocation > int(node[&"demand"]):
				errors.append("Consumer %s has an invalid allocation." % node_id)
	for first_id: Variant in _adjacency:
		for second_id: Variant in _adjacency[first_id]:
			if not _adjacency.has(second_id) or not _adjacency[second_id].has(first_id):
				errors.append("Edge %s-%s is not symmetric." % [first_id, second_id])
	return {&"valid": errors.is_empty(), &"errors": errors}


func create_snapshot() -> Dictionary:
	var serialized_nodes: Array = []
	for node_id: StringName in _sorted_ids(_nodes.keys()):
		var node: Dictionary = (_nodes[node_id] as Dictionary).duplicate(true)
		node[&"id"] = String(node_id)
		var serialized_reasons: Array[String] = []
		for reason: Variant in node.get(&"state_reasons", []):
			serialized_reasons.append(String(reason))
		if node.has(&"state_reasons"):
			node[&"state_reasons"] = serialized_reasons
		serialized_nodes.append(node)

	var edges: Array = []
	for first_id: StringName in _sorted_ids(_adjacency.keys()):
		for second_id: StringName in _sorted_ids(_adjacency[first_id].keys()):
			if String(first_id) < String(second_id):
				edges.append([String(first_id), String(second_id)])
	return {
		&"version": SNAPSHOT_VERSION,
		&"revision": revision,
		&"last_evaluation_minute": last_evaluation_minute,
		&"nodes": serialized_nodes,
		&"edges": edges,
	}


func restore_snapshot(snapshot: Dictionary) -> bool:
	if int(snapshot.get(&"version", 0)) != SNAPSHOT_VERSION:
		return _fail("Unsupported Mana snapshot version.")
	var raw_nodes: Variant = snapshot.get(&"nodes", null)
	var raw_edges: Variant = snapshot.get(&"edges", null)
	if not raw_nodes is Array or not raw_edges is Array:
		return _fail("Mana snapshot nodes and edges must be Arrays.")

	var next_nodes: Dictionary = {}
	var next_adjacency: Dictionary = {}
	for raw_node: Variant in raw_nodes:
		var normalization := _normalize_saved_node(raw_node)
		if not normalization[&"ok"]:
			return _fail(normalization[&"error"])
		var node: Dictionary = normalization[&"node"]
		var node_id: StringName = node[&"id"]
		if next_nodes.has(node_id):
			return _fail("Duplicate Mana node in snapshot: %s" % node_id)
		next_nodes[node_id] = node
		next_adjacency[node_id] = {}

	for raw_edge: Variant in raw_edges:
		if not raw_edge is Array or raw_edge.size() != 2:
			return _fail("Mana snapshot edge must contain two node ids.")
		var first_id := StringName(raw_edge[0])
		var second_id := StringName(raw_edge[1])
		if first_id == second_id or not next_nodes.has(first_id) or not next_nodes.has(second_id):
			return _fail("Mana snapshot contains an invalid edge.")
		next_adjacency[first_id][second_id] = true
		next_adjacency[second_id][first_id] = true

	_nodes = next_nodes
	_adjacency = next_adjacency
	revision = maxi(int(snapshot.get(&"revision", 0)), 0)
	last_evaluation_minute = int(snapshot.get(&"last_evaluation_minute", -1))
	_last_report = {}
	last_error = ""
	var validation := validate_invariants()
	if not validation[&"valid"]:
		return _fail("Restored Mana state violates its invariants.")
	return true


func _register_node(node_id: StringName, kind: int, fields: Dictionary) -> bool:
	if node_id.is_empty():
		return _fail("Mana node id cannot be empty.")
	if _nodes.has(node_id):
		return _fail("Duplicate Mana node: %s" % node_id)
	var node := {
		&"id": node_id,
		&"kind": kind,
		&"enabled": true,
	}
	for key: Variant in fields:
		node[key] = fields[key]
	_nodes[node_id] = node
	_adjacency[node_id] = {}
	revision += 1
	last_error = ""
	return true


func _evaluate_component(
	component: Array[StringName],
	absolute_minute: int,
	changes: Array
) -> Dictionary:
	var generation := 0
	var consumers: Array[StringName] = []
	var storages: Array[StringName] = []
	for node_id: StringName in component:
		var node: Dictionary = _nodes[node_id]
		if not bool(node[&"enabled"]):
			if int(node[&"kind"]) == NodeKind.CONSUMER:
				node[&"allocated"] = 0
				_record_state_change(node_id, node, ConsumerState.DISABLED, [&"disabled"], changes)
				_nodes[node_id] = node
			continue
		match int(node[&"kind"]):
			NodeKind.SOURCE:
				generation += int(node[&"output"])
			NodeKind.CONSUMER:
				consumers.append(node_id)
			NodeKind.STORAGE:
				storages.append(node_id)
	consumers.sort_custom(Callable(self, "_consumer_precedes"))
	storages = _sorted_ids(storages)

	var eligible_demand := 0
	for consumer_id: StringName in consumers:
		var consumer: Dictionary = _nodes[consumer_id]
		if absolute_minute >= int(consumer[&"hold_until"]):
			eligible_demand += int(consumer[&"demand"])

	var discharged := 0
	var shortage := maxi(eligible_demand - generation, 0)
	for storage_id: StringName in storages:
		if shortage <= 0:
			break
		var storage: Dictionary = _nodes[storage_id]
		var amount := mini(shortage, mini(int(storage[&"current"]), int(storage[&"max_flow"])))
		storage[&"current"] = int(storage[&"current"]) - amount
		_nodes[storage_id] = storage
		shortage -= amount
		discharged += amount

	var remaining := generation + discharged
	var allocated_total := 0
	for consumer_id: StringName in consumers:
		var consumer: Dictionary = _nodes[consumer_id]
		var demand := int(consumer[&"demand"])
		if absolute_minute < int(consumer[&"hold_until"]):
			consumer[&"allocated"] = 0
			_record_state_change(consumer_id, consumer, ConsumerState.NO_POWER, [&"minimum_off_hold"], changes)
			_nodes[consumer_id] = consumer
			continue
		var allocation := mini(demand, remaining)
		remaining -= allocation
		allocated_total += allocation
		consumer[&"allocated"] = allocation
		var next_state := ConsumerState.ACTIVE
		var reasons: Array[StringName] = []
		if demand > 0 and allocation < demand:
			if allocation * 100 >= demand * DEGRADED_THRESHOLD_PERCENT:
				next_state = ConsumerState.DEGRADED
				reasons = [&"brownout"]
			else:
				next_state = ConsumerState.NO_POWER
				reasons = [&"insufficient_supply"]
				consumer[&"hold_until"] = absolute_minute + MINIMUM_OFF_HOLD_MINUTES
		_record_state_change(consumer_id, consumer, next_state, reasons, changes)
		_nodes[consumer_id] = consumer

	var charged := 0
	for storage_id: StringName in storages:
		if remaining <= 0:
			break
		var storage: Dictionary = _nodes[storage_id]
		var headroom := int(storage[&"capacity"]) - int(storage[&"current"])
		var amount := mini(remaining, mini(headroom, int(storage[&"max_flow"])))
		storage[&"current"] = int(storage[&"current"]) + amount
		_nodes[storage_id] = storage
		remaining -= amount
		charged += amount

	return {
		&"component_id": String(component[0]) if not component.is_empty() else "",
		&"generation": generation,
		&"discharged": discharged,
		&"charged": charged,
		&"allocated": allocated_total,
		&"unused": remaining,
		&"nodes": _string_ids(component),
	}


func _record_state_change(
	consumer_id: StringName,
	consumer: Dictionary,
	next_state: int,
	reasons: Array[StringName],
	changes: Array
) -> void:
	var previous_state := int(consumer[&"state"])
	var previous_reasons: Array = consumer.get(&"state_reasons", [])
	consumer[&"state"] = next_state
	consumer[&"state_reasons"] = reasons.duplicate()
	if previous_state == next_state and previous_reasons == reasons:
		return
	changes.append({
		&"consumer_id": String(consumer_id),
		&"previous_state": previous_state,
		&"state": next_state,
		&"reasons": _string_ids(reasons),
	})
	consumer_state_changed.emit(consumer_id, previous_state, next_state, reasons)


func _set_consumer_state(
	consumer_id: StringName,
	consumer: Dictionary,
	next_state: int,
	reasons: Array[StringName]
) -> void:
	var ignored_changes: Array = []
	_record_state_change(consumer_id, consumer, next_state, reasons, ignored_changes)


func _connected_components() -> Array[Array]:
	var components: Array[Array] = []
	var visited: Dictionary = {}
	for start_id: StringName in _sorted_ids(_nodes.keys()):
		if visited.has(start_id) or not bool(_nodes[start_id][&"enabled"]):
			continue
		var component: Array[StringName] = []
		var frontier: Array[StringName] = [start_id]
		visited[start_id] = true
		while not frontier.is_empty():
			var current: StringName = frontier.pop_front()
			component.append(current)
			for neighbor: StringName in _sorted_ids(_adjacency[current].keys()):
				if visited.has(neighbor) or not bool(_nodes[neighbor][&"enabled"]):
					continue
				visited[neighbor] = true
				frontier.append(neighbor)
		component = _sorted_ids(component)
		components.append(component)
	return components


func _consumer_precedes(first_id: StringName, second_id: StringName) -> bool:
	var first_priority := int(_nodes[first_id][&"priority"])
	var second_priority := int(_nodes[second_id][&"priority"])
	if first_priority != second_priority:
		return first_priority > second_priority
	return String(first_id) < String(second_id)


func _normalize_saved_node(raw_node: Variant) -> Dictionary:
	if not raw_node is Dictionary:
		return {&"ok": false, &"error": "Mana snapshot node must be a Dictionary."}
	var node_id := StringName(raw_node.get(&"id", ""))
	var kind := int(raw_node.get(&"kind", -1))
	if node_id.is_empty() or kind < NodeKind.SOURCE or kind > NodeKind.STORAGE:
		return {&"ok": false, &"error": "Mana snapshot node id or kind is invalid."}
	var node: Dictionary = raw_node.duplicate(true)
	node[&"id"] = node_id
	node[&"kind"] = kind
	node[&"enabled"] = bool(node.get(&"enabled", true))
	match kind:
		NodeKind.SOURCE:
			if int(node.get(&"output", -1)) < 0:
				return {&"ok": false, &"error": "Mana source output is invalid."}
		NodeKind.CONSUMER:
			var demand := int(node.get(&"demand", -1))
			var allocated := int(node.get(&"allocated", -1))
			var state := int(node.get(&"state", -1))
			if demand < 0 or allocated < 0 or allocated > demand \
				or state < ConsumerState.ACTIVE or state > ConsumerState.DISABLED:
				return {&"ok": false, &"error": "Mana consumer values are invalid."}
			var reasons: Array[StringName] = []
			for raw_reason: Variant in node.get(&"state_reasons", []):
				reasons.append(StringName(raw_reason))
			node[&"state_reasons"] = reasons
			node[&"priority"] = int(node.get(&"priority", ConsumerPriority.NORMAL))
			node[&"hold_until"] = maxi(int(node.get(&"hold_until", 0)), 0)
		NodeKind.STORAGE:
			var capacity := int(node.get(&"capacity", -1))
			var current := int(node.get(&"current", -1))
			if capacity < 0 or current < 0 or current > capacity or int(node.get(&"max_flow", -1)) < 0:
				return {&"ok": false, &"error": "Mana storage values are invalid."}
	return {&"ok": true, &"node": node}


func _is_kind(node_id: StringName, kind: int) -> bool:
	return _nodes.has(node_id) and int(_nodes[node_id][&"kind"]) == kind


func _sorted_ids(raw_ids: Array) -> Array[StringName]:
	var ids: Array[StringName] = []
	for raw_id: Variant in raw_ids:
		ids.append(StringName(raw_id))
	ids.sort_custom(func(first: StringName, second: StringName) -> bool:
		return String(first) < String(second)
	)
	return ids


func _string_ids(raw_ids: Array) -> Array[String]:
	var result: Array[String] = []
	for raw_id: Variant in raw_ids:
		result.append(String(raw_id))
	return result


func _fail(message: String) -> bool:
	last_error = message
	return false