loggin tab, initial work on IO

tabs/logging.js

@@ -0,0 +1,83 @@
+function tab_initialize_logging() {
+    ga_tracker.sendAppView('Logging');
+    GUI.active_tab = 'logging';
+
+    $('#content').load("./tabs/logging.html", process_html);
+
+    function process_html() {
+        // translate to user-selected language
+        localize();
+
+        // UI hooks
+        $('a.log_file').click(prepare_file);
+
+        $('a.logging').click(function() {
+            if (fileEntry.isFile) {
+                // TODO:
+                // grab enabled properties
+                // grab refresh rate
+                // start data polling timer
+                // start buffer flushing sequence & timer (keep fileWriter.readyState in mind)
+            }
+        });
+    }
+
+    // IO related methods
+    var fileEntry = null;
+    var fileWriter = null;
+
+    function prepare_file() {
+        // create or load the file
+        chrome.fileSystem.chooseEntry({type: 'saveFile', suggestedName: 'bf_data_log', accepts: [{extensions: ['csv']}]}, function(entry) {
+            if (!entry) {
+                console.log('No file selected');
+                return;
+            }
+
+            fileEntry = entry;
+
+            // echo/console log path specified
+            chrome.fileSystem.getDisplayPath(fileEntry, function(path) {
+                console.log('Log file path: ' + path);
+            });
+
+            // change file entry from read only to read/write
+            chrome.fileSystem.getWritableEntry(fileEntry, function(fileEntryWritable) {
+                // check if file is writable
+                chrome.fileSystem.isWritableEntry(fileEntryWritable, function(isWritable) {
+                    if (isWritable) {
+                        fileEntry = fileEntryWritable;
+
+                        prepare_writer();
+                    } else {
+                        console.log('File appears to be read only, sorry.');
+                    }
+                });
+            });
+        });
+    }
+
+    function prepare_writer() {
+        fileEntry.createWriter(function(writer) {
+            fileWriter = writer;
+
+            fileWriter.onerror = function(e) {
+                console.error(e);
+            };
+
+            fileWriter.onwriteend = function() {
+                // console.log('Data written');
+            };
+        }, function(e) {
+            console.error(e);
+        });
+    }
+
+    function append_to_file(data) {
+        if (fileWriter.position < fileWriter.length) {
+            fileWriter.seek(fileWriter.length);
+        }
+
+        fileWriter.write(new Blob([data + '\n'], {type: 'text/plain'}));
+    }
+}