import pandas as pd
import json
from filelock import FileLock, Timeout
import time

# Define the path to the Excel file and the lock file
excel_file_path = "./OR-L-Interview Data.xlsx"
lock_file_path = "./OR-L-Interview Data.xlsx.lock"

def ReadDatabase():
    """ 
    Reads the database for which slots are available

    ``REQUIRES``: None
    
    ``PROMISES``: JSON (Interview Available Slots)

    ``Developed in part by``: Ahmad

    ``Contact``: ahmad.ahmad1@ucalgary.ca

    """
    # Retry parameters
    max_retries = 60  # Maximum number of retries if the file is locked
    retry_interval = 0.5  # Wait time (in seconds) between retries

    retries = 0
    while retries < max_retries:
        try:
            # Attempt to acquire a shared read (non-blocking) access
            with FileLock(lock_file_path, timeout=0):  # Non-blocking, checks if the lock exists
                # Load the Excel file into a pandas DataFrame
                df = pd.read_excel(excel_file_path)

                # Initialize the dictionary to store the structured data
                interview_data = {}

                # Group the DataFrame by Date, Start Time, and Slot for organization
                for _, row in df.iterrows():
                    date = str(row['Date'])
                    start_time = str(row['Start Time'])
                    slot = int(row['Slot']) if not pd.isna(row['Slot']) else 0

                    # Returns the number of interviewees in the slot; returns 0 if empty
                    interviewee_amount = len(str(row['Interviewee Name']).split()) if str(row['Interviewee Name']) != "nan" else 0

                    # Check if the slot is available for an interviewee to attend
                    available_slots = interviewee_amount != slot
                    if available_slots:
                        # Initialize nested structure if not present
                        if date not in interview_data:
                            interview_data[date] = {}
                        # Add the start time and duration if not present
                        if start_time not in interview_data[date]:
                            interview_data[date][start_time] = {
                                'Meeting Duration': row['Meeting Duration'],
                            }
                return interview_data  # Successfully read the database

        except Timeout:
            # File is locked; wait and retry
            retries += 1
            print(f"File is locked, retrying ({retries}/{max_retries})...")
            time.sleep(retry_interval)

    # If max retries are exceeded, raise an error
    raise RuntimeError("Unable to access the database after multiple attempts due to a file lock.")

# Example usage of the ReadDatabase function
if __name__ == "__main__":
    try:
        data = ReadDatabase()
        print(json.dumps(data, indent=4))
    except RuntimeError as e:
        print(e)