Add checksum to Logger.

Closes #479.

logger.js

@@ -8,9 +8,11 @@ var cadence = require('cadence/redux')
 var Queue = require('./queue')
 var Script = require('./script')
 var Scribe = require('./scribe')
+var checksum = require('./checksum')
 
-function Logger (directory, sheaf) {
-    this._directory = directory
+function Logger (options, sheaf) {
+    this._directory = options.directory
+    this._checksum = checksum(options.checksum)
     // todo: remove when page can slice
     this._sheaf = sheaf
 }
@@ -27,7 +29,7 @@ Logger.prototype.writeEntry = function (options) {
 
     entry = options.header.slice()
     json = JSON.stringify(entry)
-    var hash = this._sheaf.checksum()
+    var hash = this._checksum()
     hash.update(json)
 
     length = 0

sheaf.js

@@ -28,22 +28,6 @@ function Sheaf (options) {
     this.comparator = options.comparator || compare
     this.player = options.player
     this.logger = options.logger
-    this.checksum = (function () {
-        if (typeof options.checksum == 'function') return options.checksum
-        var algorithm
-        switch (algorithm = options.checksum || 'sha1') {
-        case 'none':
-            return function () {
-                return {
-                    update: function () {},
-                    digest: function () { return '0' }
-                }
-            }
-        default:
-            var crypto = require('crypto')
-            return function (m) { return crypto.createHash(algorithm) }
-        }
-    })()
     this.serialize = options.serialize || function (object) { return new Buffer(JSON.stringify(object)) }
     this.deserialize = options.deserialize || function (buffer) { return JSON.parse(buffer.toString()) }
     this.lengths = {}

strata.js

@@ -25,7 +25,7 @@ function extend(to, from) {
 
 function Strata (options) {
     options.player = new Player(options)
-    options.logger = new Logger(options.directory, this.sheaf)
+    options.logger = new Logger(options, this.sheaf)
     options.logger._sheaf = this.sheaf = new Sheaf(options)
 }