class_name TaskDispatcher
extends RefCounted

## Deterministic employee/task matcher. Inventory reservation is injected so
## this layer can keep the Task/Staff pair atomic without owning stock.

const StaffRuntimeType = preload("res://scripts/staff/staff_runtime.gd")
const StaffTaskType = preload("res://scripts/staff/staff_task.gd")

const SNAPSHOT_VERSION := 1
const DISPATCH_INTERVAL_MINUTES := 5
const HIGH_PRIORITY_THRESHOLD := 90
const PRIORITY_MULTIPLIER := 10
const SKILL_FIT_MULTIPLIER := 4
const ROLE_FIT_MULTIPLIER := 100
const TRAVEL_MINUTE_PENALTY := 3
const FATIGUE_PENALTY := 2
const OVERTIME_PENALTY := 200
const INTERRUPT_COST_LEVEL_1 := 300
const INTERRUPT_COST_LEVEL_2 := 150
const INTERRUPT_COST_LEVEL_3 := 25
const MIN_SCORE := -2_147_483_648

var last_dispatch_minute := -1
var last_report: Dictionary = {}
var last_restore_error := ""

var _item_reserver := Callable()
var _item_releaser := Callable()
var _travel_estimator := Callable()
var _assignment_history: Array[Dictionary] = []


func configure_callbacks(
	item_reserver: Callable = Callable(),
	item_releaser: Callable = Callable(),
	travel_estimator: Callable = Callable()
) -> TaskDispatcher:
	_item_reserver = item_reserver
	_item_releaser = item_releaser
	_travel_estimator = travel_estimator
	return self


func should_dispatch(absolute_minute: int, has_high_priority_task := false) -> bool:
	if has_high_priority_task:
		return true
	if last_dispatch_minute < 0:
		return true
	return absolute_minute - last_dispatch_minute >= DISPATCH_INTERVAL_MINUTES


func dispatch(
	tasks: Array,
	staff_by_id: Dictionary,
	absolute_minute: int
) -> Dictionary:
	var task_by_id := _task_index(tasks)
	var pending := _sorted_open_tasks(tasks)
	var assignments: Array[Dictionary] = []
	var blocked: Array[Dictionary] = []
	var unassigned: Array[Dictionary] = []
	var interruptions: Array[Dictionary] = []
	var assigned_this_pass: Dictionary = {}

	for task: StaffTask in pending:
		var selected := _select_candidate(
			task,
			staff_by_id,
			task_by_id,
			assigned_this_pass,
			absolute_minute
		)
		if selected.is_empty():
			unassigned.append({
				&"task_id": task.task_id,
				&"reason": &"NO_ELIGIBLE_STAFF",
			})
			continue
		var staff_id: StringName = selected[&"staff_id"]
		var staff: StaffRuntime = staff_by_id[staff_id]
		var previous_task: StaffTask = selected.get(&"current_task") as StaffTask
		var result := _reserve_pair(task, staff, previous_task, absolute_minute)
		if not bool(result.get(&"ok", false)):
			var reason := StringName(result.get(&"reason", &"RESERVATION_FAILED"))
			if bool(result.get(&"blocked", false)):
				blocked.append({&"task_id": task.task_id, &"reason": reason})
			else:
				unassigned.append({&"task_id": task.task_id, &"reason": reason})
			continue
		if previous_task != null:
			interruptions.append({
				&"staff_id": staff_id,
				&"interrupted_task_id": previous_task.task_id,
				&"replacement_task_id": task.task_id,
			})
		var assignment := {
			&"task_id": task.task_id,
			&"staff_id": staff_id,
			&"score": int(selected[&"score"]),
			&"travel_minutes": int(selected[&"travel_minutes"]),
			&"assigned_at": absolute_minute,
		}
		assignments.append(assignment)
		_assignment_history.append(assignment.duplicate(true))
		assigned_this_pass[staff_id] = true

	last_dispatch_minute = absolute_minute
	last_report = {
		&"assigned": assignments,
		&"blocked": blocked,
		&"unassigned": unassigned,
		&"interruptions": interruptions,
	}
	return last_report.duplicate(true)


func score_candidate(
	task: StaffTask,
	staff: StaffRuntime,
	travel_minutes: int,
	current_task: StaffTask = null
) -> int:
	if task == null or staff == null or travel_minutes < 0:
		return MIN_SCORE
	var interrupt_cost := 0
	if current_task != null:
		match current_task.interrupt_level:
			1:
				interrupt_cost = INTERRUPT_COST_LEVEL_1
			2:
				interrupt_cost = INTERRUPT_COST_LEVEL_2
			_:
				interrupt_cost = INTERRUPT_COST_LEVEL_3
	return (
		task.priority * PRIORITY_MULTIPLIER
		+ staff.skill_fit_for(task) * SKILL_FIT_MULTIPLIER
		+ staff.role_fit_for(task) * ROLE_FIT_MULTIPLIER
		- travel_minutes * TRAVEL_MINUTE_PENALTY
		- staff.fatigue * FATIGUE_PENALTY
		- interrupt_cost
		- (OVERTIME_PENALTY if staff.is_overtime else 0)
	)


func create_snapshot() -> Dictionary:
	var history: Array[Dictionary] = []
	for assignment: Dictionary in _assignment_history:
		var serialized := assignment.duplicate(true)
		serialized[&"task_id"] = String(assignment[&"task_id"])
		serialized[&"staff_id"] = String(assignment[&"staff_id"])
		history.append(serialized)
	return {
		&"version": SNAPSHOT_VERSION,
		&"last_dispatch_minute": last_dispatch_minute,
		&"assignment_history": history,
	}


func restore_snapshot(snapshot: Dictionary) -> bool:
	last_restore_error = ""
	if int(snapshot.get(&"version", -1)) != SNAPSHOT_VERSION:
		last_restore_error = "Unsupported task dispatcher snapshot version."
		return false
	var raw_history: Variant = snapshot.get(&"assignment_history", null)
	if not raw_history is Array:
		last_restore_error = "Task dispatcher history is malformed."
		return false
	var next_history: Array[Dictionary] = []
	for raw_assignment: Variant in raw_history:
		if not raw_assignment is Dictionary:
			last_restore_error = "Task dispatcher history entry must be a Dictionary."
			return false
		var task_id := StringName(raw_assignment.get(&"task_id", ""))
		var staff_id := StringName(raw_assignment.get(&"staff_id", ""))
		if task_id.is_empty() or staff_id.is_empty():
			last_restore_error = "Task dispatcher history has an empty identifier."
			return false
		var assignment: Dictionary = raw_assignment.duplicate(true)
		assignment[&"task_id"] = task_id
		assignment[&"staff_id"] = staff_id
		next_history.append(assignment)
	var next_last_minute := int(snapshot.get(&"last_dispatch_minute", -1))
	if next_last_minute < -1:
		last_restore_error = "Task dispatcher minute is invalid."
		return false
	_assignment_history = next_history
	last_dispatch_minute = next_last_minute
	last_report = {}
	return true


func assignment_history() -> Array[Dictionary]:
	return _assignment_history.duplicate(true)


func _select_candidate(
	task: StaffTask,
	staff_by_id: Dictionary,
	task_by_id: Dictionary,
	excluded_staff_ids: Dictionary,
	absolute_minute: int
) -> Dictionary:
	var best: Dictionary = {}
	for staff_id: StringName in _sorted_names(staff_by_id.keys()):
		if excluded_staff_ids.has(staff_id):
			continue
		var staff: StaffRuntime = staff_by_id.get(staff_id) as StaffRuntime
		if staff == null or not staff.meets_task_requirements(task):
			continue
		var current_task: StaffTask = null
		if staff.current_task_id.is_empty():
			if not staff.is_available_for_dispatch():
				continue
		else:
			current_task = task_by_id.get(staff.current_task_id) as StaffTask
			if current_task == null or not current_task.can_be_interrupted_by(task):
				continue
		var travel_minutes := _travel_minutes(staff, task, absolute_minute)
		if travel_minutes < 0:
			continue
		var score := score_candidate(task, staff, travel_minutes, current_task)
		if (
			best.is_empty()
			or score > int(best[&"score"])
			or (score == int(best[&"score"]) and String(staff_id) < String(best[&"staff_id"]))
		):
			best = {
				&"staff_id": staff_id,
				&"staff": staff,
				&"current_task": current_task,
				&"travel_minutes": travel_minutes,
				&"score": score,
			}
	return best


func _reserve_pair(
	task: StaffTask,
	staff: StaffRuntime,
	previous_task: StaffTask,
	absolute_minute: int
) -> Dictionary:
	if not task.is_dispatchable() or staff == null:
		return {&"ok": false, &"reason": &"STATE_CHANGED", &"blocked": false}
	if previous_task == null and not staff.is_available_for_dispatch():
		return {&"ok": false, &"reason": &"STAFF_STATE_CHANGED", &"blocked": false}
	if previous_task != null:
		if staff.current_task_id != previous_task.task_id:
			return {&"ok": false, &"reason": &"STAFF_TASK_MISMATCH", &"blocked": false}
		if previous_task.assigned_staff_id != staff.staff_id:
			return {&"ok": false, &"reason": &"TASK_STAFF_MISMATCH", &"blocked": false}
		if not previous_task.can_be_interrupted_by(task):
			return {&"ok": false, &"reason": &"INTERRUPT_DENIED", &"blocked": false}

	var item_result := _reserve_items(task, absolute_minute)
	if not bool(item_result.get(&"ok", false)):
		var item_reason := StringName(item_result.get(&"reason", &"ITEM_RESERVATION_FAILED"))
		task.block(item_reason, absolute_minute)
		return {&"ok": false, &"reason": item_reason, &"blocked": true}
	var reservation_ids: Array[StringName] = _name_array(item_result.get(&"reservation_ids", []))

	var staff_before := {
		&"current_task_id": staff.current_task_id,
		&"state": staff.state,
		&"state_reason": staff.state_reason,
		&"state_changed_at": staff.state_changed_at,
	}
	var task_before := {
		&"state": task.state,
		&"assigned_staff_id": task.assigned_staff_id,
		&"reservation_ids": task.reservation_ids.duplicate(),
		&"state_reason": task.state_reason,
		&"state_changed_at": task.state_changed_at,
	}
	var previous_before: Dictionary = {}
	if previous_task != null:
		previous_before = {
			&"state": previous_task.state,
			&"assigned_staff_id": previous_task.assigned_staff_id,
			&"reservation_ids": previous_task.reservation_ids.duplicate(),
			&"progress_minutes": previous_task.progress_minutes,
			&"state_reason": previous_task.state_reason,
			&"state_changed_at": previous_task.state_changed_at,
		}
		previous_task.reopen(
			&"INTERRUPTED",
			absolute_minute,
			previous_task.preserve_progress_on_interrupt
		)
		staff.release_task(absolute_minute, &"TASK_INTERRUPTED")

	var task_reserved := task.reserve(staff.staff_id, reservation_ids, absolute_minute)
	var staff_reserved := task_reserved and staff.reserve_task(task.task_id, absolute_minute)
	if not task_reserved or not staff_reserved:
		_restore_pair_state(task, staff, previous_task, task_before, staff_before, previous_before)
		_release_items(reservation_ids, task, absolute_minute)
		return {&"ok": false, &"reason": &"ATOMIC_PAIR_RESERVATION_FAILED", &"blocked": false}

	if previous_task != null:
		var old_ids: Array[StringName] = _name_array(previous_before[&"reservation_ids"])
		if not _release_items(old_ids, previous_task, absolute_minute):
			_restore_pair_state(task, staff, previous_task, task_before, staff_before, previous_before)
			_release_items(reservation_ids, task, absolute_minute)
			return {&"ok": false, &"reason": &"INTERRUPT_RELEASE_FAILED", &"blocked": false}
	return {&"ok": true, &"reservation_ids": reservation_ids}


func _reserve_items(task: StaffTask, absolute_minute: int) -> Dictionary:
	if task.required_items.is_empty():
		return {&"ok": true, &"reservation_ids": []}
	if not _item_reserver.is_valid():
		return {&"ok": false, &"reason": &"ITEM_RESERVATION_UNAVAILABLE"}
	var response: Variant = _item_reserver.call(task, absolute_minute)
	if not response is Dictionary:
		return {&"ok": false, &"reason": &"ITEM_RESERVATION_INVALID_RESPONSE"}
	var result: Dictionary = response
	if not bool(result.get(&"ok", false)):
		return {
			&"ok": false,
			&"reason": StringName(result.get(&"reason", result.get(&"code", &"ITEM_RESERVATION_FAILED"))),
		}
	var reservation_ids := _name_array(result.get(&"reservation_ids", []))
	if reservation_ids.is_empty():
		return {&"ok": false, &"reason": &"ITEM_RESERVATION_IDS_MISSING"}
	return {&"ok": true, &"reservation_ids": reservation_ids}


func _release_items(
	reservation_ids: Array[StringName],
	task: StaffTask,
	absolute_minute: int
) -> bool:
	if reservation_ids.is_empty():
		return true
	if not _item_releaser.is_valid():
		return false
	var response: Variant = _item_releaser.call(reservation_ids, task, absolute_minute)
	if response is Dictionary:
		return bool(response.get(&"ok", false))
	return bool(response)


func _travel_minutes(staff: StaffRuntime, task: StaffTask, absolute_minute: int) -> int:
	if _travel_estimator.is_valid():
		return int(_travel_estimator.call(staff, task, absolute_minute))
	var delta := staff.current_cell - task.target_cell
	return absi(delta.x) + absi(delta.y) + absi(delta.z)


static func _restore_pair_state(
	task: StaffTask,
	staff: StaffRuntime,
	previous_task: StaffTask,
	task_before: Dictionary,
	staff_before: Dictionary,
	previous_before: Dictionary
) -> void:
	task.state = int(task_before[&"state"]) as StaffTask.State
	task.assigned_staff_id = task_before[&"assigned_staff_id"]
	task.reservation_ids.assign(task_before[&"reservation_ids"])
	task.state_reason = task_before[&"state_reason"]
	task.state_changed_at = int(task_before[&"state_changed_at"])
	staff.current_task_id = staff_before[&"current_task_id"]
	staff.state = int(staff_before[&"state"]) as StaffRuntime.State
	staff.state_reason = staff_before[&"state_reason"]
	staff.state_changed_at = int(staff_before[&"state_changed_at"])
	if previous_task != null:
		previous_task.state = int(previous_before[&"state"]) as StaffTask.State
		previous_task.assigned_staff_id = previous_before[&"assigned_staff_id"]
		previous_task.reservation_ids.assign(previous_before[&"reservation_ids"])
		previous_task.progress_minutes = int(previous_before[&"progress_minutes"])
		previous_task.state_reason = previous_before[&"state_reason"]
		previous_task.state_changed_at = int(previous_before[&"state_changed_at"])


static func _task_index(tasks: Array) -> Dictionary:
	var result: Dictionary = {}
	for value: Variant in tasks:
		if value is StaffTask:
			result[value.task_id] = value
	return result


static func _sorted_open_tasks(tasks: Array) -> Array[StaffTask]:
	var result: Array[StaffTask] = []
	for value: Variant in tasks:
		if value is StaffTask and value.is_dispatchable():
			result.append(value)
	result.sort_custom(func(a: StaffTask, b: StaffTask) -> bool:
		if a.priority != b.priority:
			return a.priority > b.priority
		var a_deadline := 9_223_372_036_854_775_807 if a.deadline_at < 0 else a.deadline_at
		var b_deadline := 9_223_372_036_854_775_807 if b.deadline_at < 0 else b.deadline_at
		if a_deadline != b_deadline:
			return a_deadline < b_deadline
		return String(a.task_id) < String(b.task_id)
	)
	return result


static func _sorted_names(values: Variant) -> Array[StringName]:
	var result: Array[StringName] = []
	for value: Variant in values:
		result.append(StringName(value))
	result.sort_custom(func(a: StringName, b: StringName) -> bool: return String(a) < String(b))
	return result


static func _name_array(source: Variant) -> Array[StringName]:
	var result: Array[StringName] = []
	if not source is Array:
		return result
	for value: Variant in source:
		var name := StringName(value)
		if not name.is_empty() and not result.has(name):
			result.append(name)
	result.sort_custom(func(a: StringName, b: StringName) -> bool: return String(a) < String(b))
	return result