Solidity Smart Contract for storing IPFS hashes in Collection format. (untested, WIP)

ContentCollection.sol

pragma solidity 0.4.21;

// ContentCollection is meant to store hashes from IPFS in a "Collection" format (array of structs), per user.
contract ContentCollection {
  // Content types / Mime Types
  // 0 - deleted
  // 1 - text/plain
  // 2 - application/json
  // 3 - image/jpeg
  // 4 - image/png
  
  // Content Index corresponds to a variety of more meaningful content contexts in the application (avatar, profile data, contribution, comment, etc.)

  // Content Hash corresponds to an IPFS hash.
  struct Content {
    bytes1 contentType;
    bytes4 contentIndex;
    bytes32 contentHash;
  }

  // Mapping of Content struct arrays (collections) by user address, allows only authorized users to edit their own data
  mapping (address => Content[]) contents;
  
  // Helps listening to events, either by sender or by hash.
  event contentAdded (
    address contentOwner,
    bytes32 contentHash
  );

  // Multiple records can be added at once, but they must be added by array.
  function addContent(bytes1[] contentTypes, bytes4[] contentIndices, bytes32[] contentHashes) public {
    require(contentTypes.length == contentIndices.length && contentIndices.length == contentHashes.length);

    for (uint c = 0; c < contentTypes.length; c++) {
      contents[msg.sender].push(Content(contentTypes[c], contentIndices[c], contentHashes[c]));
    }
  }

  function transformContents(Content[] contentArray, bytes4 filterIndex) pure internal returns (bytes1[], bytes4[], bytes32[]) {
    bytes1[] memory contentTypes;
    bytes4[] memory contentIndices;
    bytes32[] memory contentHashes;
    for (uint c = 0; c < contentArray.length; c++) {
      Content memory content = contentArray[c];
      // filterIndex == 0 not the same as deleted content.
      if ((filterIndex > 0x0 && content.contentIndex == filterIndex) || filterIndex == 0x0) {
        contentTypes[c] = content.contentType;
        contentIndices[c] = content.contentIndex;
        contentHashes[c] = content.contentHash;
      }
    }
    return (contentTypes, contentIndices, contentHashes);
  }

  function getContentsByAddress(address user) public view returns (bytes1[], bytes4[], bytes32[]) {
    return transformContents(contents[user], 0);
  }

  function getContentsByAddressAndIndex(address user, bytes4 index) public view returns (bytes1[], bytes4[], bytes32[]) {
    require(index > 0x0);
    return transformContents(contents[user], index);
  }
}