"""
Invoice Emailing Utility.

Provides a web interface for managing invoice emailing configurations.
Handles HTTP GET (view) and POST (update) at '/data' for configuration data, and serves the main app page at '/'.

Author: Isaak Buslovich
Date: 2023-12-21
"""
from flask import Flask, request, jsonify, send_from_directory
import yaml
from pathlib import Path
import logging

app = Flask(__name__, static_folder='.', static_url_path='')
logging.basicConfig(level=logging.INFO)

DATA_FILE = 'config.yaml'


def read_yaml():
    """
    Reads data from YAML file specified by DATA_FILE. Returns a tuple containing the data and error message.
    On success: Returns (data_dict, None), where data_dict contains 'email' and 'email_template'.
    On file not found: Logs a message and returns ({'email': {}, 'email_template': ''}, None).
    On error: Logs the specific error and returns (None, error_message), where error_message explains the issue.
    """
    file_path = Path(DATA_FILE)
    try:
        if not file_path.is_file():
            logging.info("YAML file not found. Returning empty data.")
            return {'email': {}, 'email_template': ''}, None
        with file_path.open() as file:
            data = yaml.safe_load(file) or {}
            return {
                'email': data.get('email', {}),
                'email_template': data.get('email_template', '')
            }, None
    except yaml.YAMLError as e:
        logging.error(f"YAML Error: {e}", exc_info=True)
        return None, f"YAML parsing error: {e}"
    except IOError as e:
        logging.error(f"IO Error: {e}", exc_info=True)
        return None, f"File I/O error: {e}"
    except Exception as e:
        logging.error(f"Unexpected Error: {e}", exc_info=True)
        return None, f"Unexpected error: {e}"


def write_yaml(email_data, email_template_data):
    """
    Writes email and template data to the YAML file defined by DATA_FILE.

    Args:
        email_data (dict): Email configuration settings.
        email_template_data (str): Email template content.

    Returns:
        tuple: (bool, str) indicating success status and an error message if any.

    Raises:
        Exception: Logs and returns error details upon failure.
    """
    file_path = Path(DATA_FILE)
    try:
        with file_path.open('w') as file:
            yaml.dump({
                'email': email_data,
                'email_template': email_template_data
            }, file)
            return True, None
    except Exception as e:
        logging.error(f"Error writing YAML file: {e}", exc_info=True)
        return False, f"Error writing file: {e}"


@app.route('/data', methods=['GET', 'POST'])
def handle_data():
    """
    Flask route handler function for '/data', accepting both GET and POST methods. - GET method: Reads and outputs
    data from the YAML configuration file. In case of errors, it returns a 500 status code with an error message. -
    POST method: Gets 'email' and 'email_template' data from the request, writes it to the YAML configuration file.
    In case of write errors, it returns a 500 status code with an error message. Otherwise, it returns a message
    stating the file was saved successfully with a 200 status code.
    """
    if request.method == 'GET':
        data, error = read_yaml()
        if error:
            return jsonify({'success': False, 'message': error}), 500
        return jsonify(data), 200
    elif request.method == 'POST':
        email_data = request.json.get('email', {})
        email_template_data = request.json.get('email_template', '')
        success, error = write_yaml(email_data, email_template_data)
        if error:
            return jsonify({'success': False, 'message': error}), 500
        return jsonify({'success': True, 'message': "File saved successfully"}), 200


@app.route('/')
def index():
    """
    Serves the main index HTML page.

    Returns:
        HTML content of the main page.
    """
    return send_from_directory('.', 'index.html')


if __name__ == '__main__':
    app.run(debug=True)