General developer forum

I've been working on a mod plugin that is a UI for students. The teacher can upload a text file (it's presently going to a cloud service), and the plugin uses it to generate the interface. The interface is intended to be used by several different courses.

Can I use the File API to store and retrieve the text file "locally?"

1. From my limited understanding of moodle, the contextid would provide a unique element for any given file as the context would be specific to that particular interface and that particular course. Is this understanding correct?
2. If a teacher was using the interface on 3 separate courses, their upload creating that interface would be unique to each course?
3. As well, since I only want one text file for a specific course, can I hardcode in the itemid, so that the file gets replaced every time the teacher uploads a new one for that course? 
4. Finally, since there might be several files uploaded for several different courses, can I use a variable that takes in the user's original file name (or code that creates a unique one) to populate the filename?

$fs = get_file_storage();

// Prepare file record object
$fileinfo = array(
    'contextid' => $context->id, // ID of context
    'component' => 'mod_mymodule',     // usually = table name
    'filearea' => 'myarea',     // usually = table name
    'itemid' => 0,               // usually = ID of row in table
    'filepath' => '/',           // any path beginning and ending in /
    'filename' => 'myfile.txt'); // any filename

// Create file containing text 'hello world'
$fs->create_file_from_string($fileinfo, 'hello world');

The filearea is also somewhat confusing to me. Looking at the snippet below, the filearea in this case would be "post."
For my purposes, could I make a folder mod/mymodule/interface_files to store the txt files (in filepath) and then call the 'filearea' value 'interface_files'?
$url = $CFG->wwwroot/pluginfile.php/$forumcontextid/mod_forum/post/$postid/image.jpg The plugin needs to read the file every time the screen refreshes.
Can I use the Read File code, provided it's inside my mod/mymodule folder somewhere?
The moodle docs state "Please note you are allowed to do this ONLY from mod/mymodule/* code, it is not acceptable to do this anywhere else." 
I'm assuming they mean the code must be inside the folder (say in my index.php file). Is this correct?
Block 2: Read a file:

$fs = get_file_storage();

// Prepare file record object
$fileinfo = array(
    'component' => 'mod_mymodule',     // usually = table name
    'filearea' => 'myarea',     // usually = table name
    'itemid' => 0,               // usually = ID of row in table
    'contextid' => $context->id, // ID of context
    'filepath' => '/',           // any path beginning and ending in /
    'filename' => 'myfile.txt'); // any filename

// Get file
$file = $fs->get_file($fileinfo['contextid'], $fileinfo['component'], $fileinfo['filearea'],
                      $fileinfo['itemid'], $fileinfo['filepath'], $fileinfo['filename']);

// Read contents
if ($file) {
    $contents = $file->get_content();
} else {
    // file doesn't exist - do something
}