docs: [AXM-686] ADR for Offline Mode application

openedx/features/offline_mode/docs/001-offline-mode.rst

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+===================================================
+Offline Mode content generation for mobile OeX app
+===================================================
+
+Status
+------
+
+Proposed
+
+Context and Problem Statement
+-----------------------------
+
+The primary goal is to enable offline access to course content in the Open edX mobile application.
+This will allow users to download course materials when they have internet access and access them
+later without an internet connection. This feature is crucial for learners in areas with unreliable
+internet connectivity or those who prefer to study on the go without using mobile data.
+
+Decision Drivers
+----------------
+
+* **User Convenience**: Improve the learning experience by allowing access to course materials anytime, anywhere.
+* **Accessibility**: Ensure learners in regions with limited or no internet connectivity can still benefit from the educational content.
+* **Platform Compatibility**: Maintain compatibility with existing Open edX infrastructure and mobile applications.
+* **Performance**: Ensure that the offline mode does not degrade the performance of the mobile application.
+
+Considered Options
+------------------
+
+* **Implement of a mechanism for generating and storing on a server or external storage**: The course content should be pre-generated and saved to the storage for later download.
+    * **Render content**: Generate HTML content of block as it does for LMS.
+    * **Replace static and media**: Save static and media assets files used in block to temporary directory and replace their static paths with local paths.
+    * **Archive and store content**: Archive the generated content and store it on the server or external storage.
+* **Mechanism for updating the generated data**: When updating course blocks (namely when publishing) the content that has been changed should be re-generated.
+    * **Track course publishing events on CMS side**: Signal in the CMS that makes request to LMS to update course content.
+    * **Track course publishing events on LMS side**: API endpoint to receive the signal from CMS and update course content.
+    * **Update archive**: Check generated archive creation date and update it if less than course publishing date.
+* **Implement a Mobile Local Storage Mechanism**: Use the device's local storage to save course content for offline access.
+    * **Extend blocks API**: Add links to download blocks content and  where it is possible.
+* **Sync Mechanism**: Periodically synchronize local data with the server when the device is online.
+    * **Sync on app side**: On course outline screen, check if the course content is up to date and update it if necessary.
+* **Selective Download**: Allow users to choose specific content to download for offline use.
+* **Full Course Download**: Provide an option to download entire courses for offline access.
+
+Consequences
+------------
+
+* Enhanced learner experience with flexible access to course materials.
+* Increased accessibility for learners in regions with poor internet connectivity.
+* Improved engagement and completion rates due to uninterrupted access to content.
+* Potential increase in app size due to locally stored content.
+* Increased complexity in managing content synchronization and updates.
+* Need for continuous monitoring and updates to handle new content types and formats.
+
+Rejected Solutions
+------------------
+
+Store common .js and .css files of blocks in a separate folder:
+    * This solution was rejected because it is unclear how to track potential changes to these files and re-generate the content of the blocks.
+
+Generate content on the fly when the user requests it:
+    * This solution was rejected because it would require a significant amount of processing power and time to generate content for each block when requested.