Add ImportHistory class and RecordStorage class.

ui/file_manager/file_manager/background/js/import_history.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+/**
+ * @constructor
+ *
+ * @param {!RecordStorage} storage
+ */
+function ImportHistory(storage) {
+
+  /** @private {!RecordStorage} */
+  this.storage_ = storage;
+
+  /** @private {!Object.<string, !Array.<string>>} */
+  this.history_ = {};
+};

[mtomasz, 2014/10/29 01:10:41]

nit: ; seems redundant here.

[Steve McKay, 2014/10/29 16:57:21]

Done.

+
+/**
+ * Prints an error to the console.
+ *
+ * @param  {!Error} error
+ * @private
+ */
+ImportHistory.handleError_ = function(error) {
+  console.error(error.stack || error);
+};
+
+/**
+ * Use this factory method to get a fully ready instance of ImportHistory.
+ *
+ * @param {!RecordStorage} storage
+ *
+ * @return {!Promise.<!ImportHistory>} Resolves when history instance is ready.
+ */
+ImportHistory.load = function(storage) {
+  var history = new ImportHistory(storage);
+  return history.reload().then(
+    function() {
+      return history;
+    });
+};
+
+/**
+ * Reloads history from disk. Should be called when the file
+ * is synced.
+ *
+ * @return {!Promise} Resolves when history has been loaded.
+ */
+ImportHistory.prototype.reload = function() {
+  this.history_ = {};
+  return this.storage_.readAll()
+      .then(
+          function(entries) {
+            entries.forEach(
+                function(entry) {
+                  this.updateHistoryRecord_(entry[0], entry[1]);
+                }.bind(this));
+          }.bind(this))
+      .catch(ImportHistory.handleError_);
+};
+
+/**
+ * Adds a history entry to the in-memory history model.
+ * @param {string} key
+ * @param {string} destination
+ */
+ImportHistory.prototype.updateHistoryRecord_ = function(key, destination) {
+  if (key in this.history_) {
+    this.history_[key].push(destination);
+  } else {
+    this.history_[key] = [destination];
+  }
+};
+
+/**
+ * @param {!FileEntry} entry
+ * @param {string} destination
+ * @return {!Promise.<boolean>} Settles with true if the FileEntry
+ *     was previously imported to the specified destination.
+ */
+ImportHistory.prototype.wasImported = function(entry, destination) {
+  return this.createKey_(entry)
+      .then(
+          function(key) {
+            return this.getDestinations_(key).indexOf(destination) >= 0;
+          }.bind(this))
+      .catch(ImportHistory.handleError_);
+};
+
+/**
+ * @param {!FileEntry} entry
+ * @param {string} destination
+ * @return {!Promise.<boolean>} Settles with true if the FileEntry
+ *     was previously imported to the specified destination.
+ */
+ImportHistory.prototype.markImported = function(entry, destination) {
+  return this.createKey_(entry)
+      .then(this.addDestination_.bind(this, destination))
+      .catch(ImportHistory.handleError_);
+};
+
+/**
+ * @param {string} key
+ * @return {!Array.<string>} The list of previously noted
+ *     destinations, or an empty array, if none.
+ */
+ImportHistory.prototype.getDestinations_ = function(key) {
+  return key in this.history_ ? this.history_[key] : [];
+};
+
+/**
+ * @param {string} destination
+ * @param {string} key
+ * @return {!Promise}
+ */
+ImportHistory.prototype.addDestination_ = function(destination, key) {
+  this.updateHistoryRecord_(key, destination);
+  return this.storage_.write([key, destination]);
+};
+
+/**
+ * @param {!FileEntry} entry
+ * @return {!Promise.<string>} Settles with a the key is available.
+ */
+ImportHistory.prototype.createKey_ = function(fileEntry) {
+  var entry = new FileEntryWrapper(fileEntry);
+  return new Promise(
+      function(resolve, reject) {
+        entry.getMetadata()
+            .then(
+                function(metadata) {
+                  if (!('modificationTime' in metadata)) {
+                    reject('File entry missing "modificationTime" field.');
+                  } else if (!('size' in metadata)) {
+                    reject('File entry missing "size" field.');
+                  } else {
+                    resolve(
+                      metadata['modificationTime'] + '_' + metadata['size']);
+                  }
+                }.bind(this));
+      }.bind(this));
+};
+
+/**
+ * An simple record storage mechanism.
+ *
+ * @interface
+ */
+function RecordStorage(entry) {};
+
+/**
+ * Adds a new record.
+ *
+ * @param {!Array.<*>} record
+ * @return {!Promise} Resolves when record is added.
+ */
+RecordStorage.prototype.write;

[mtomasz, 2014/10/29 01:10:41]

Will this compile? We used to write an empty method implementation in
interfaces, like RS.prototype.write = function(record) {}. I'm fine with this,
as long as it compiles.

[Steve McKay, 2014/10/29 16:57:21]

This is purely in anticipation of Closure compilation. The @interface isn't used
at all in uncompiled code (referenced only by @implements). It'll be used by the
Closure Compiler during type checking && Closure Compiler will strip it from
builds.

+
+/**
+ * Reads all records.
+ *
+ * @return {!Promise.<!Array.<!Array.<*>>>}
+ */
+RecordStorage.prototype.readAll;
+
+/**
+ * A {@code RecordStore} that persists data in a {@code FileEntry}.
+ *
+ * @param {!FileEntry} entry
+ *
+ * @constructor
+ * @implements {RecordStorage}
+ */
+function FileEntryRecordStorage(entry) {
+  /** @private {!FileEntryWrapper} */
+  this.entry_ = new FileEntryWrapper(entry);
+};
+
+/**
+ * Prints an error to the console.
+ *
+ * @param  {!Error} error
+ * @private
+ */
+FileEntryRecordStorage.handleError_ = function(error) {
+  console.error(error.stack || error);
+};
+
+/** @override */
+FileEntryRecordStorage.prototype.write = function(record) {
+  // TODO(smckay): should we make an effort to reuse a file writer?
+  return this.entry_.createWriter()
+      .then(this.writeRecord_.bind(this, record))
+      .catch(FileEntryRecordStorage.handleError_);
+};
+
+/**
+ * Appends a new record to the end of the file.
+ *
+ * @param {!Object} record
+ * @param {!FileWriter} writer
+ * @return {!Promise} Resolves when write is complete.
+ * @private
+ */
+FileEntryRecordStorage.prototype.writeRecord_ = function(record, writer) {
+  return new Promise(
+      function(resolve, reject) {
+        var blob = new Blob(
+            [JSON.stringify(record) + ',\n'],
+            {type: 'application/json; charset=utf-8'});

[mtomasz, 2014/10/29 01:10:41]

It's not really a valid json. How about simply plain/text mime type?

[Steve McKay, 2014/10/29 16:57:21]

Done. text/plain; charset=UTF-8

+
+        writer.onwriteend = function() {
+          resolve();
+        };
+        writer.onerror = function() {
+          reject();
+        };
+
+        writer.seek(writer.length);
+        writer.write(blob);
+      }.bind(this));
+};
+
+/** @override */
+FileEntryRecordStorage.prototype.readAll = function() {
+  return this.entry_.file()
+      .then(this.readFileAsText_.bind(this), function() { return '';})

[mtomasz, 2014/10/29 01:10:41]

nit: space after ; missing.

[Steve McKay, 2014/10/29 16:57:21]

Done.

+      .then(this.parse_.bind(this))
+      .then(
+          function(entries) {
+            return entries;
+          })
+      .catch(FileEntryRecordStorage.handleError_);
+};
+
+/**
+ * Reads all lines from the entry.
+ *
+ * @param {!File} file
+ * @return {!Promise.<!Array.<string>>}
+ * @private
+ */
+FileEntryRecordStorage.prototype.readFileAsText_ = function(file) {
+  return new Promise(
+      function(resolve, reject) {
+
+        var reader = new FileReader();
+
+        reader.onloadend = function() {
+          if (!!reader.error) {
+            FileEntryRecordStorage.handleError_(reader.error);
+            resolve('');
+          } else {
+            resolve(reader.result);
+          }
+        };
+
+        reader.onerror = function(error) {
+          FileEntryRecordStorage.handleError_(error);
+          reject(e);
+        };
+
+        reader.readAsText(file);
+      }.bind(this));
+};
+
+/**
+ * Parses the text.
+ *
+ * @param {string} text
+ * @return {!Promise.<!Array.<!Object>>}
+ * @private
+ */
+FileEntryRecordStorage.prototype.parse_ = function(text) {
+  return new Promise(
+      function(resolve, reject) {
+        if (text.length == 0) {
+          resolve([]);
+        } else {
+          // Dress up the contents of the file like an array,
+          // so the JSON object can parse it using JSON.parse.
+          // That means we need to both:
+          //   1) Strip the trailing ',\n' from the last record
+          //   2) Surround the whole string in brackets.
+          // NOTE: JSON.parse is WAY faster than parsing this
+          // ourselves in javascript.
+          var json = '[' + text.substring(0, text.length - 2) + ']';
+          resolve(JSON.parse(json));

[mtomasz, 2014/10/29 01:10:41]

Date objects will not deserialize properly from json. Shall we add a comment
about it, or add a special logic for creating Date objects when deserializing?

[Steve McKay, 2014/10/29 16:57:22]

The value is just a string. There's no need to parse the date. We just need a
string for opaque comparison. The value used in this entry is provided by the
fileEntry from the getMetadata call (lastModifiedTime or something like that).

And since this is a first line of defence, best-effort type of operation, we
don't really need to worry about a user who is switching locales. That would be
a self-rectifying situation after a single import + the media would still be
deduplicated at the content based deduplication phase.

+        }
+      }.bind(this));
+};
+
+/**
+ * An Object storage mechanism built on top of a FileEntry.
+ *
+ * @param {!FileEntry} entry
+ *
+ * @constructor
+ * @private
+ */
+function FileEntryWrapper(entry) {
+  /** @private {!FileEntry} */
+  this.entry_ = entry;
+};
+
+/**
+ * A "Promisary" wrapper around entry.getWriter.
+ * @return {!Promise.<!FileWriter>}
+ */
+FileEntryWrapper.prototype.createWriter = function() {
+  return new Promise(this.entry_.createWriter.bind(this.entry_));
+};
+
+/**
+ * A "Promisary" wrapper around entry.file.
+ * @return {!Promise.<!File>}
+ */
+FileEntryWrapper.prototype.file = function() {
+  return new Promise(this.entry_.file.bind(this.entry_));
+};
+
+/**
+ * @return {!Promise.<!Object>} Data format not yet verified.
+ *     Either a string, or an object.
+ */
+FileEntryWrapper.prototype.getMetadata = function() {
+  return new Promise(this.entry_.getMetadata.bind(this.entry_));
+};