define(function() {
  
  /*
  SyncFS is a crappy way to use chrome.storage.sync for entries larger than 4KB.
  This will work until chrome.syncFileSystem is more offline-friendly.
  Entries are set with a string if they're less than 3KB, otherwise the keyed entry
  stores the number of 3KB chunks used, and those are stored at key + chunkNumber.
  */
  
  var cache = null;
  var requests = [];
  var pending = false;
  
  var decode = function(key) {
    //extracts multiple entries from a single key
    //presumes cache is set first
    var seed = cache[key];
    if (!seed) return null;
    if (typeof seed == "string") return seed;
    var pieces = [];
    for (var i = 0; i < seed; i++) {
      pieces.push(cache[key + i]);
    }
    var whole = pieces.join("");
    return whole;
  };
  
  return {
    get: function(key) {
      if (cache) {
        var result = decode(key);
        return Promise.resolve(result);
      }
      
      var only = function(data) {
        return decode(key);
      }
      
      var fetch = function() {
        return new Promise(function(ok) {
          chrome.storage.sync.get(function(all) {
            cache = all;
            ok(all);
            pending = null;
          });
        });
      };
      if (!pending) {
        pending = fetch();
      }
      return pending.then(only);
    },
    set: function(key, data) {
      cache = null;
      return new Promise(function(ok, fail) {
        if (data.length < 3000) {
          var hash = {};
          hash[key] = data;
          chrome.storage.sync.set(hash, ok);
        } else {
          var chunks = [];
          for (var i = 0; i < data.length; i += 3000) {
            chunks.push(data.substr(i, i + 3000));
          }
          var hash = {};
          hash[key] = chunks.length;
          chunks.map(function(chunk, i) {
            hash[key + i] = chunk;
          });
          chrome.storage.sync.set(hash, ok)
        }
      });
    },
    remove: function(key) {
      var seed = cache[key];
      return new Promise(function(ok) {
        if (typeof seed == "number") {
          var waiting = [];
          var p = Promise.all(new Array(seed).map(function(i) {
            new Promise(function(ok) {
              chrome.storage.sync.remove(key + i, ok);
            });
          }));
          return p.then(ok);
        }
        cache = null;
        chrome.storage.sync.remove(key, ok);
      });
    }
  }
  
  
});