Categorized ERC721 token

contracts/token/CategorizedERC721/CategorizedERC721Token.sol

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+pragma solidity ^0.4.18;
+
+import 'zeppelin-solidity/contracts/ownership/Ownable.sol';
+import 'zeppelin-solidity/contracts/token/ERC721/ERC721Token.sol';
+
+contract CategorizedERC721Token is ERC721Token, Ownable {
+
+  // event fired when a new category is created
+  event CategoryCreated(uint categoryId, uint fromTokenId, uint toTokenId);
+
+  // array with the supply of each category
+  uint[] categoriesSupply;
+
+  // mapping between the tokenId and categoryId
+  mapping (uint => uint) private tokenIdCategoryId;
+
+  // method used to create a new category and mint the tokens
+  function createCategory(uint _supply) public onlyOwner{
+    uint categoryId = categoriesSupply.push(_supply);
+
+    uint startTokenId = totalSupply();
+    uint lastTokenId = startTokenId + _supply - 1;
+    for(uint tokenId = startTokenId; tokenId <= lastTokenId; tokenId++) {
+      _mint(msg.sender, tokenId);
+      tokenIdCategoryId[tokenId] = categoryId;
+    }
+
+    CategoryCreated(categoryId, startTokenId, lastTokenId);
+  }
+  // method to extend the amount of tokens for a given category
+  function increaseCategorySupply(uint _categoryId, uint _extraSupply) public onlyOwner{
+    require(categoriesSupply[_categoryId] > 0);
+
+    uint currentSupply = categoriesSupply[_categoryId];
+
+    uint newSupply = currentSupply + _extraSupply;
+    categoriesSupply[_categoryId] = newSupply;
+
+    uint startTokenId = totalSupply();
+    uint lastTokenId = startTokenId + _extraSupply - 1;
+    for(uint tokenId = startTokenId; tokenId <= lastTokenId; tokenId++) {
+      _mint(msg.sender, tokenId);
+      tokenIdCategoryId[tokenId] = _categoryId;
+    }
+  }
+
+  // get the categoryId for a given token
+  function getCategoryId(uint _tokenId) public view returns (uint) {
+    require(_tokenId < totalSupply());
+    return tokenIdCategoryId[_tokenId];
+  }
+
+  // get the total supply for a given category
+  function getCategorySupply(uint _categoryId) public view returns (uint){
+    require(_categoryId < categoriesSupply.length);
+    return categoriesSupply[_categoryId];
+  }
+}