Re Construction of php for reading and sending json response - php

Question

I've got a new project, it was left uncompleted by the previous developer. I'm trying to rebuild the action.php
$.ajax({
type: "POST",
url: "action.php",
data: {action:'upload',
image:data, //data is data:image/png;base64 uri
count:uploadNum,
uniqid:uniqid}
}).done(function(o) {
var data = $.parseJSON(o);
if (!data || data === null) {
toggleError(true);
}else{
if(data.status==true){
uploadLoopCount++;
if(uploadLoopCount < upload_arr.length){
uploadImage();
}else{
readySave = true;
toggleShareButtons('ready');
var loc = location.href
loc = loc.substring(0, loc.lastIndexOf("/") + 1);
loc += '?id='+uniqid;
$('#shareLink').val(loc);
}
}else{
toggleError(true);
}
}
});
and
$.ajax({
type: "POST",
url: "action.php",
data: {action:'save',
profiledata1:JSON.stringify(userdata_arr[0]),
profiledata2:JSON.stringify(userdata_arr[1]),
profiledata3:JSON.stringify(userdata_arr[2]),
profiledata4:JSON.stringify(userdata_arr[3]),
profiledata5:JSON.stringify(userdata_arr[4])}
}).done(function(o) {
var data = $.parseJSON(o);
if (!data || data === null) {
toggleError(true);
}else{
if(data.status==true){
uniqid = data.uniqid;
checkImageUpload();
}else{
toggleError(true);
}
}
});
I've tried creating the action.php, the upload function will upload the image into some directory and there would be some data base links. and the load section would return contents from database. I'm confused with the json part of php.
this is the raw action.php
<?php
if ($_POST['action']=='load') {
$uid=$_POST['uniqid'];
// fetch contents from db with $uid;
header("content-type:application/json");
$data[] = array('status' =>'true','profile1_data' =>'green','profile2_data' =>'blue','profile3_data' =>'orange','profile4_data' =>'green','profile5_data' =>'red' ,'upload' =>'http://localhost/img/', 'format' =>'jpeg' );
$j = json_encode($data);
echo $j;
}
if ($_POST['action']=='upload') {
header("content-type:application/json");
//confused with reading json response
// upload the contents
$data[]= array('status' =>'true' );
$j=json_encode($data);
echo $j;
} ?>
I'm confused with reading the json response and the response as json. Help me to rebuild the action.php. Thanks in advance