Wiki.sol

pragma solidity ^0.4.11;

contract Wiki {
  function Wiki() {

  }

  struct Diff {
    address owner;
    uint currentSwarmHash;
    uint previousSwarmHash;
  }

  uint numEdits;
  uint lastEditedBlock;
  address lastEditedBy;

  mapping (uint => uint) diffIndexes;
  Diff[] diffs;

  function update(
    uint currentDiffSwarmHash,
    uint previousDiffSwarmHash
  ) {
    uint previousIndex = diffIndexes[previousDiffSwarmHash];
    uint previousCurrentHash = diffs[previousIndex].currentSwarmHash;
    if (
      numEdits > 0
      && currentDiffSwarmHash != previousCurrentHash
    ) {
      throw;
    }

    numEdits = numEdits + 1;
    lastEditedBlock = block.number;
    lastEditedBy = msg.sender;
    diffIndexes[currentDiffSwarmHash] = diffIndexes[currentDiffSwarmHash] + 1;
    diffs.push(
      Diff(
        msg.sender,
        currentDiffSwarmHash,
        previousDiffSwarmHash
      )
    );
  }

  function getNumEdits() returns (uint) {
    return numEdits;
  }
}