wiljmorales / blockchain-todo

PrivaTO-DO

This api is a TODO list and note-taking. The main difference of this app is that the tasks are stored in a blockchain that creates a history with all the changes and modifications of the different notes/tasks.

How it works?

This api allows the user add new notes and mark them as completed. The flow is always the same, first we need to add new note/task and then these are saved on the Blockchain. In order to make the blockchain data persistent we need to store Blockchain in a file.

You could find the API description on the OpenAPI description file

Workflow

The workflow of the api is as follows:

1. Send request to the API to add or mark as completed any task
2. Load the Blockchain data from the file, if exists
3. Create a Block with the new todo/task data
4. Add the new Block to the Blockchain
5. Save the Blockchain with the new data on a file

Technical Considerations

Keep in mind the following:

1. Related with the blockchain:
   1. Every Block has multiple properties:
      1. timestamp: the timestamp for the moment when the block was created
      2. lastHash: hash of the previous block on the Blockchain
      3. data: information we want to store in the block (in our case the description of the task)
      4. hash: a SHA256 string for the block, calculated concatenating the timestamp, lastHash and data.
   2. The implementation of the Blockchain must follow these contract:

   interface Blockchain {
     /** Adds new block to blockchain */
     addBlock(block: Block): Block
     /**
      * Validates the chain by checking if:
      * - every element's last hash value matches previous block's hash
      * - data hasn't been tampered (which will produce a different hash value)
      */
     isValid(blockchain: Blockchain): boolean
     /** The new blockchain that is a candidate for replacing the current blockchain */
     replace(blockchain: Blockchain): boolean
   }
   
   interface Block {
     /** Generate the hash for the given block */
     static generateHashFromBlock(block: Block): string
   }
   

Tips

• You can think about the Blockchain as a sort of Linked List, which have some extra properties to ensure the validity of the items and the list as a whole.
• When you have to update a task or note of the application (i.e. when mark it as completed), you will have to create a new Block with this information, but the previous one will remain in the Blockchain with the outdated information.

Technical requirements

• Create a clean, maintainable and well-designed code. We expect to see a good and clear architecture that allows to add or modify the solution without so much troubles.
• Test your code until you are comfortable with it. We don't expect a 100% of Code Coverage but some tests that helps to have a more stable and confident base code.

To understand how you take decisions during the implementation, please write a COMMENTS.md file explaining some of the most important parts of the application. You would also be able to defend your code through Rviewer, once you submit your solution.

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How to submit your solution

• Push your code to the devel branch - we encourage you to commit regularly to show your thinking process was.
• Create a new Pull Request to main branch & merge it.

Once merged you won't be able to change or add anything to your solution, so double-check that everything is as you expected!

Remember that there is no countdown, so take your time and implement a solution that you are proud!

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If you have any feedback or problem, let us know! 🤘

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