extends Node

signal data_changed

func get_row_count() -> int:
	return int(pow(2, 53) - 1)

func get_headers() -> Array:
	return ["#", "text", "int"]

func get_rows(row_start: int, size: int) -> Array:
	size = min(size, get_row_count() - row_start)
	return range(0, size).map(func(n): return _get_row(n + row_start))


const _arr = ["foo", "bar", "hello", "world"]
func _get_row(row_index: int) -> Array:
	return [row_index, _arr[hash(row_index)%_arr.size()], str(row_index)]

extends Node

signal data_changed

## Instance of the SQLite class for database interactions.
var database: SQLite = SQLite.new()

## Database path and query constants.
const DATABASE_PATH = "user://data2.db"
const QUERY_SELECT = "SELECT * FROM Card JOIN CardData ON Card.cardDataId = CardData.id WHERE language IN ('English', 'French')"

## Variables to store headers, placeholder rows, and total row count.
var headers = []
var placeholder_row = []
var total_row_count = 0

## Threading-related variables for synchronization and thread management.
var mutex: Mutex = Mutex.new()
var semaphore: Semaphore = Semaphore.new()
var worker_thread: Thread = Thread.new()
var requested_row_range := [0, 0]
var pending_tasks_count := 0
var should_exit_thread := false

## Constants and variables for row caching.
const ROWS_BATCH_SIZE = 1000
var cached_row_range := [-1, -1]
var cached_rows := []

## Called when the node is added to the scene. Initializes the database and starts the worker thread.
func _ready():
	_initialize_database()
	_start_worker_thread()

## Called when the node is about to be removed from the scene. Terminates the worker thread.
func _exit_tree():
	_terminate_worker_thread()

## Initializes the database by opening it and querying for headers and total row count.
func _initialize_database():
	database.path = DATABASE_PATH
	database.open_db()
	if not database.query(QUERY_SELECT + " LIMIT 1") or database.query_result.size() == 0:
		return
	headers = database.query_result[0].keys()
	placeholder_row = headers.map(func(header): return "-")
	
	var query_count = "SELECT COUNT(*) as count FROM (%s)" % QUERY_SELECT
	if not database.query(query_count) or database.query_result.size() == 0:
		return
	total_row_count = database.query_result[0].count
	print(total_row_count)

## Starts the worker thread which handles background data fetching.
func _start_worker_thread():
	worker_thread.start(_thread_function)

## Worker thread function that waits for tasks, fetches data from the database, and updates the cache.
func _thread_function():
	while true:
		semaphore.wait()
		
		mutex.lock()
		var exit_thread = should_exit_thread
		var row_range = requested_row_range.duplicate()
		pending_tasks_count -= 1
		mutex.unlock()
		
		if exit_thread:
			return
		
		var limit_clause = "LIMIT %d, %d" % row_range
		if not database.query(QUERY_SELECT + " " + limit_clause) or database.query_result.size() == 0:
			print("Error querying database.")
		else:
			var data = database.query_result_by_reference.map(func(record): return record.values())
			call_deferred("_on_rows_fetched", row_range, data)

## Signals the worker thread to exit and waits for it to finish.
func _terminate_worker_thread():
	mutex.lock()
	should_exit_thread = true
	mutex.unlock()
	semaphore.post()
	worker_thread.wait_to_finish()

## Requests rows from the database by updating the requested range and signaling the semaphore if needed.
func _request_rows(from, size):
	from = max(from, 0)
	var should_post_semaphore = false
	
	mutex.lock()
	if requested_row_range != [from, size]:
		requested_row_range = [from, size]
		if pending_tasks_count == 0:
			pending_tasks_count += 1
			should_post_semaphore = true
	mutex.unlock()
	
	if should_post_semaphore:
		semaphore.post()

## Callback function when rows are fetched by the worker thread. Updates the cache and emits the data_changed signal.
func _on_rows_fetched(row_range, data):
	cached_row_range = row_range
	cached_rows = data
	data_changed.emit()

## Returns the total number of rows in the database.
func get_row_count() -> int:
	return total_row_count

## Returns the headers of the database table.
func get_headers() -> Array:
	return headers

## Checks if the requested row range is within the cached range.
func is_range_within_cached_range(requested_range: Array) -> bool:
	var cached_start = cached_row_range[0]
	var cached_end = cached_row_range[0] + cached_row_range[1]
	var requested_start = requested_range[0]
	var requested_end = requested_range[0] + requested_range[1]
	return cached_start <= requested_start and requested_end <= cached_end

## Returns the requested rows if they are cached, otherwise returns placeholder rows and initiates a data fetch.
func get_rows(row_start: int, size: int) -> Array:
	size = clamp(size, 0, total_row_count - row_start)
	
	if is_range_within_cached_range([row_start, size]):
		return cached_rows.slice(row_start - cached_row_range[0], row_start - cached_row_range[0] + size)
	
	_request_rows(row_start - ROWS_BATCH_SIZE / 2, ROWS_BATCH_SIZE)
	
	return range(size).map(func(n): return placeholder_row)