Calendar Logger with Zoho and Google Calendar Integration

This Python desktop application provides a calendar interface to create and manage events, with a specific feature to log time spent on Zoho Projects. It also syncs with your Google Calendar to display your events.

Table of Contents

1. Features
2. Technologies Used
3. Project Structure
4. Key Logic Implemented
   • Calendar Rendering
   • Zoho API and Authentication Management
   • Google Calendar Integration
   • Secure Credential Storage
5. Installation and Startup
6. Initial Configuration
7. Automated Build and Release
8. Possible Future Improvements

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Features

• Calendar View: Displays a weekly grid from Monday to Friday, with configurable time slots.
• Complete CRUD for Events: You can Create, Read, Modify, and Delete events.
• Local Persistence: All events are saved in a local SQLite database (events.db), ensuring that data is not lost between sessions.
• Integration with Zoho Projects: For completed events, you can log time directly to Zoho Projects through a dedicated form.
• Google Calendar Sync: Automatically fetches and displays events from your primary Google Calendar.
• Immutability of Logged Events: Once an event is logged to Zoho, it is locked and can no longer be modified or deleted.
• Settings Panel: A dedicated window to securely enter and save Zoho and Google API credentials.
• Secure Credential Management: API keys are not stored in plain text but are entrusted to the operating system's credential manager.

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Technologies Used

• Python 3: Main programming language.
• CustomTkinter: Library chosen for the GUI. It offers modern widgets and a more pleasing appearance than standard Tkinter.
• SQLite 3: Database engine. SQLite was chosen because it is integrated into Python and is perfect for single-user desktop applications.
• Requests: De-facto standard library for making HTTP calls, used for all communications with the Zoho APIs.
• Keyring: A fundamental library for security. It interfaces with the native credential manager of the operating system (e.g., Windows Credential Manager, macOS Keychain) to save and retrieve sensitive data.
• Google API Client Library for Python: Used to interact with the Google Calendar API.
• PyInstaller: To create the application executable.

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Project Structure

The code is organized in a package structure to improve maintainability and clarity.

• main.py: (Root) The application's entry point.
• calendar_logger/: (Package) Contains all the application's source code.
  • __init__.py: Makes the folder a Python package.
  • app.py: The heart of the application, manages the GUI and main logic.
  • database.py: Manages data persistence on SQLite.
  • settings_manager.py: Manages the secure saving and loading of credentials.
  • zoho_api.py: Contains all the logic for communicating with the Zoho APIs.
  • google_calendar.py: Handles integration with the Google Calendar API.
• scripts/: Contains accessory scripts.
  • build.py: Script to create the application executable via PyInstaller.
• .github/workflows/: Contains the CI/CD pipeline.
  • release.yml: A GitHub Actions workflow that automatically builds and releases executables for Linux, macOS, and Windows when a new tag is pushed.
• requirements.txt: Lists the Python dependencies.
• .gitignore: Specifies the files to be ignored in version control.

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Key Logic Implemented

Calendar Rendering

The display of events is handled in the refresh_events() method in app.py. The logic is as follows:

1. Cleanup: All previously drawn event widgets are destroyed to avoid duplicates.
2. Fetch: All events are retrieved from the local database and Google Calendar.
3. Iteration and Drawing: For each event, its position in the grid (row and column) is calculated based on date and time.

Zoho API and Authentication Management

The logic resides in zoho_api.py and follows the OAuth 2.0 flow with Refresh Token.

1. Token Refresh: The refresh_access_token() function is responsible for requesting a new access_token from Zoho.
2. API Call with Automatic Retry: The log_time_to_zoho() function is robust: it automatically retries the API call with a new token if the current one is expired.

Google Calendar Integration

The google_calendar.py module handles the connection to the Google Calendar API.

1. OAuth 2.0 Authentication: On the first run, it guides the user through an authentication process to grant the application read-only access to their calendar.
2. Token Storage: The obtained credentials are securely stored in a token.json file for subsequent sessions.
3. Event Fetching: The get_events_for_week function retrieves all events for the displayed week.

Secure Credential Storage

In settings_manager.py, the keyring library is used to never expose credentials in the code or in text files.

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Installation and Startup

1. Make sure you have Python 3 installed.
2. It is advisable to create a virtual environment: python -m venv venv and activate it.
3. Install the dependencies: pip install -r requirements.txt.
4. Start the application from the project root folder: python main.py.

Create the Executable

To create a standalone .exe file, run the build script from the root folder:

python scripts/build.py

The compiled application will be in dist/CalendarLogger.

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Initial Configuration

To make the integrations work, follow these steps:

1. Get Zoho credentials: Go to the Zoho API console (https://api-console.zoho.eu/) and create a new Self-Client type client. This will provide you with a Client ID, a Client Secret, and a Refresh Token.
2. Get Google Calendar credentials:
   • Go to the Google Cloud Console.
   • Create a new project.
   • Enable the "Google Calendar API".
   • Create credentials for a "Desktop app" OAuth client.
   • Download the credentials.json file and place it in the calendar_logger folder.
3. Start the app and click the "Settings" button.
4. Enter the credentials obtained in the respective fields.
5. Click "Save Settings".

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Automated Build and Release

This project uses GitHub Actions to automate the creation of executables for Windows, macOS, and Linux. The workflow, defined in .github/workflows/release.yml, is triggered every time a new tag (e.g., v1.0.1) is pushed to the repository.

The workflow automatically builds the executables and attaches them as assets to a new GitHub Release.

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Possible Future Improvements

• UI for Errors: Show error messages in dialog windows instead of on the console.
• Datepicker Widget: Replace manual date entry with a calendar widget to improve usability.
• Fetch of Projects/Tasks: Instead of manually entering project and task IDs, implement API calls that retrieve the list of existing projects and tasks and show them in a dropdown menu.
• Drag and Drop: Implement moving and resizing events with the mouse.