"""
CRUD operations for GUARDIAN, STUDENT and ATTENDANCE.

Every function takes an open mysql-connector-python connection as its first
argument and manages its own commit/rollback. All functions return plain
data (dicts/lists/bool) so this module has no dependency on the UI layer.
"""

import mysql.connector


class CrudError(Exception):
	"""Raised for expected, user-facing data errors (bad FK, duplicate key, etc)."""
	pass


def _run(conn, sql, params=None, fetch=None):
	"""
	Helper: execute a statement, commit, and optionally fetch results.
	fetch: None (no fetch), 'one', or 'all'
	Translates common MySQL errors into CrudError with a friendly message.
	"""
	cur = conn.cursor(dictionary=True)
	try:
		cur.execute(sql, params or ())
		result = None
		if fetch == "one":
			result = cur.fetchone()
		elif fetch == "all":
			result = cur.fetchall()
		conn.commit()
		return result if fetch else cur.rowcount
	except mysql.connector.errors.IntegrityError as e:
		conn.rollback()
		if e.errno == 1062:
			raise CrudError("A record with that primary/unique key already exists.")
		if e.errno in (1451, 1452):
			raise CrudError(
				"That operation violates a foreign key constraint "
				"(referenced record missing, or still referenced by other rows)."
			)
		raise CrudError(f"Database integrity error: {e}")
	except mysql.connector.errors.DataError as e:
		conn.rollback()
		raise CrudError(f"Invalid data for one or more fields: {e}")
	except mysql.connector.Error as e:
		conn.rollback()
		raise CrudError(f"Database error: {e}")
	finally:
		cur.close()


# ---------------------------------------------------------------- GUARDIAN --

def create_guardian(conn, guid, gname, gphone, gaddress):
	_run(
		conn,
		"INSERT INTO GUARDIAN (GUID, GName, GPhone, GAddress) VALUES (%s, %s, %s, %s)",
		(guid, gname, gphone, gaddress),
	)


def get_guardian(conn, guid):
	return _run(conn, "SELECT * FROM GUARDIAN WHERE GUID = %s", (guid,), fetch="one")


def list_guardians(conn):
	return _run(conn, "SELECT * FROM GUARDIAN ORDER BY GUID", fetch="all")


def update_guardian(conn, guid, gname=None, gphone=None, gaddress=None):
	fields, params = [], []
	if gname is not None:
		fields.append("GName = %s")
		params.append(gname)
	if gphone is not None:
		fields.append("GPhone = %s")
		params.append(gphone)
	if gaddress is not None:
		fields.append("GAddress = %s")
		params.append(gaddress)
	if not fields:
		return 0
	params.append(guid)
	return _run(conn, f"UPDATE GUARDIAN SET {', '.join(fields)} WHERE GUID = %s", params)


def delete_guardian(conn, guid):
	return _run(conn, "DELETE FROM GUARDIAN WHERE GUID = %s", (guid,))


# ----------------------------------------------------------------- STUDENT --

def create_student(conn, roll_number, sname, sdateofbirth, guid):
	_run(
		conn,
		"INSERT INTO STUDENT (RollNumber, SName, SDateofBirth, GUID) VALUES (%s, %s, %s, %s)",
		(roll_number, sname, sdateofbirth, guid),
	)


def get_student(conn, roll_number):
	return _run(conn, "SELECT * FROM STUDENT WHERE RollNumber = %s", (roll_number,), fetch="one")


def list_students(conn):
	return _run(
		conn,
		"""
		SELECT s.RollNumber, s.SName, s.SDateofBirth, s.GUID, g.GName AS GuardianName
		FROM STUDENT s
		LEFT JOIN GUARDIAN g ON s.GUID = g.GUID
		ORDER BY s.RollNumber
		""",
		fetch="all",
	)


def update_student(conn, roll_number, sname=None, sdateofbirth=None, guid=None):
	fields, params = [], []
	if sname is not None:
		fields.append("SName = %s")
		params.append(sname)
	if sdateofbirth is not None:
		fields.append("SDateofBirth = %s")
		params.append(sdateofbirth)
	if guid is not None:
		fields.append("GUID = %s")
		params.append(guid)
	if not fields:
		return 0
	params.append(roll_number)
	return _run(conn, f"UPDATE STUDENT SET {', '.join(fields)} WHERE RollNumber = %s", params)


def delete_student(conn, roll_number):
	return _run(conn, "DELETE FROM STUDENT WHERE RollNumber = %s", (roll_number,))


# --------------------------------------------------------------- ATTENDANCE --

def mark_attendance(conn, attendance_date, roll_number, status):
	"""Insert attendance; if a record for that date+student exists, update it instead."""
	existing = _run(
		conn,
		"SELECT 1 FROM ATTENDANCE WHERE AttendanceDate = %s AND RollNumber = %s",
		(attendance_date, roll_number),
		fetch="one",
	)
	if existing:
		_run(
			conn,
			"UPDATE ATTENDANCE SET AttendanceStatus = %s "
			"WHERE AttendanceDate = %s AND RollNumber = %s",
			(status, attendance_date, roll_number),
		)
		return "updated"
	else:
		_run(
			conn,
			"INSERT INTO ATTENDANCE (AttendanceDate, RollNumber, AttendanceStatus) "
			"VALUES (%s, %s, %s)",
			(attendance_date, roll_number, status),
		)
		return "created"


def get_attendance(conn, attendance_date, roll_number):
	return _run(
		conn,
		"SELECT * FROM ATTENDANCE WHERE AttendanceDate = %s AND RollNumber = %s",
		(attendance_date, roll_number),
		fetch="one",
	)


def list_attendance_by_date(conn, attendance_date):
	return _run(
		conn,
		"""
		SELECT a.AttendanceDate, a.RollNumber, s.SName, a.AttendanceStatus
		FROM ATTENDANCE a
		JOIN STUDENT s ON a.RollNumber = s.RollNumber
		WHERE a.AttendanceDate = %s
		ORDER BY a.RollNumber
		""",
		(attendance_date,),
		fetch="all",
	)


def list_attendance_by_student(conn, roll_number):
	return _run(
		conn,
		"SELECT * FROM ATTENDANCE WHERE RollNumber = %s ORDER BY AttendanceDate",
		(roll_number,),
		fetch="all",
	)


def delete_attendance(conn, attendance_date, roll_number):
	return _run(
		conn,
		"DELETE FROM ATTENDANCE WHERE AttendanceDate = %s AND RollNumber = %s",
		(attendance_date, roll_number),
	)