# @File (label = "Output directory", style = "directory") output_directory
import os
import csv
from ij.gui import YesNoCancelDialog
from java.awt import Frame


def main():
    """ImageJ Jython script testing for the existence of an output file before
    writing to that file location.
    Graceful exit if user chooses to cancel the operation.
    """
    try:
        output_filename = begin_output_file(output_directory)
    except KeyboardInterrupt:
        print("User cancelled script \
                to avoid overwriting existing output file")
        return
    # program continues...


def begin_output_file(output_directory):
    """Writes output file, with option to cancel if overwriting existing file.
    Parameters
    ----------
    output_csv_directory : String directory path for the output file location.
    Returns
    -------
    csv_filename : String filepath to the output csv file.
    Raises
    ------
    KeyboardInterrupt
        User cancellation of analysis script
        to avoid overwriting existing output files.
    """
    csv_filename = os.path.join(str(output_directory), 'csv_filename.csv')
    error_msg = "User cancelled script to avoid \
                overwriting existing output files."
    if os.path.exists(csv_filename) is False:  # file does not yet exist
        # write new file
        headers = ["header_1", "header_2", "header_3", "header_4"]
        with open(csv_filename, 'wb') as f:
            writer = csv.writer(f)
            writer.writerow(headers)
        return csv_filename
    elif os.path.exists(csv_filename) is True:  # file already exists
        overwrite_files_dialog = YesNoCancelDialog(
            Frame(),
            "Overwrite file?",
            "Do you want to overwrite the existing csv file?"
        )
        if overwrite_files_dialog.yesPressed():
            print("Overwriting existing file...")
            # write new empty csv file
            with open(csv_filename, 'wb') as f:
                writer = csv.writer(f)
                writer.writerow(headers)
            return csv_filename
        elif overwrite_files_dialog.cancelPressed():
            raise KeyboardInterrupt(error_msg)
        else:
            raise KeyboardInterrupt(error_msg)
    return


main()
print("Finished")