feat(createEvent): Implement category adding

app/src/main/java/com/p_vacho/neat_calendar/activities/CreateEventActivity.kt

@@ -25,6 +25,7 @@ import com.google.android.material.button.MaterialButton
 import com.google.android.material.button.MaterialButtonToggleGroup
 import com.google.android.material.textfield.TextInputEditText
 import com.google.gson.Gson
+import com.p_vacho.neat_calendar.MyApplication
 import com.p_vacho.neat_calendar.R
 import com.p_vacho.neat_calendar.adapters.CategoryChipAdapter
 import com.p_vacho.neat_calendar.api.RetrofitClient
@@ -78,13 +79,13 @@ class CreateEventActivity : AppCompatActivity() {
         val dateString = intent.getStringExtra("date")!!
         defaultDate = LocalDate.parse(dateString)
 
-        // TODO: Fetch the available categories from the API
         allCategories = emptyList()
-        eventCategories = mutableListOf()
+        eventCategories = mutableListOf() // start off empty
 
         initializeViews()
         setupListeners()
         updateCategoryView()
+        fetchCategories()
     }
 
     private fun initializeViews() {
@@ -153,16 +154,57 @@ class CreateEventActivity : AppCompatActivity() {
         btnClose.setOnClickListener { finish() }
     }
 
+    private fun fetchCategories() {
+        val userId = (application as MyApplication).tokenManager.userId
+
+        if (userId.isNullOrEmpty()) {
+            Toast.makeText(this, "User not authenticated. Unable to fetch categories.", Toast.LENGTH_SHORT).show()
+            finish() // Close the activity if no user is authenticated
+            return
+        }
+
+        lifecycleScope.launch(Dispatchers.IO) {
+            // Fetch categories from the API
+            val fetchedCategories = RetrofitClient.categoryService.userCategories(userId)
+
+            withContext(Dispatchers.Main) { allCategories = fetchedCategories }
+        }
+    }
+
+    /**
+     * Handle user clicking on the add button for the event categories.
+     *
+     * This will open up a modal where the user will be able to choose from
+     * the available categories (excluding the already picked ones). Once chosen,
+     * the category will be added to the categoryRecyclerView.
+     */
     private fun addCategory() {
-        // This should probably open some modal with a dropdown
-        // showing all the available categories (without the already picked ones)
+        // Create a list categories available to select (not already picked)
+        val selectableCategories = allCategories.filter { category ->
+            !eventCategories.contains(category)
+        }
 
-        var newCategory = TODO("Implement category adding")
-        if (newCategory == null) return
+        if (selectableCategories.isEmpty()) {
+            Toast.makeText(this, "No more categories to add", Toast.LENGTH_SHORT).show()
+            return
+        }
 
-        eventCategories.add(newCategory)
-        categoryRecyclerView.adapter!!.notifyItemInserted(eventCategories.size - 1)
-        updateCategoryView()
+        val categoryNames = selectableCategories.map { it.name }.toTypedArray()
+
+        val builder = android.app.AlertDialog.Builder(this)
+            .setTitle("Add Category")
+            .setItems(categoryNames) { dialog, which ->
+                val selectedCategory = selectableCategories[which]
+                eventCategories.add(selectedCategory)
+                categoryRecyclerView.adapter?.notifyItemInserted(eventCategories.size - 1)
+                updateCategoryView()
+                dialog.dismiss()
+            }
+            .setNegativeButton("Cancel") { dialog, _ ->
+                dialog.dismiss()
+            }
+
+        builder.create().show()
     }
 
     /**
@@ -170,8 +212,17 @@ class CreateEventActivity : AppCompatActivity() {
      * the category chip was clicked.
      */
     private fun onCategoryRemoved(category: CategoryResponse, position: Int) {
-        TODO("Implement category removing")
+        // We can't use the passed position, as the adapter still uses the old positions
+        // which don't necessarily match ours
+        val actualPosition = eventCategories.indexOf(category)
 
+        if (actualPosition == -1) {
+            Log.w("CreateEventActivity", "Attempted to remove a category that no longer exists.")
+            return
+        }
+
+        eventCategories.removeAt(actualPosition)
+        categoryRecyclerView.adapter!!.notifyItemRemoved(actualPosition)
         updateCategoryView()
     }
 
@@ -192,7 +243,7 @@ class CreateEventActivity : AppCompatActivity() {
         val eventRequest = EventRequest(
             title = title,
             description = description,
-            category_ids = emptyList(), // Categories will be added later
+            category_ids = eventCategories.map { it.id },
             start_time = startDateTime!!.atZone(ZoneId.systemDefault()).toOffsetDateTime(),
             end_time = endDateTime?.atZone(ZoneId.systemDefault())?.toOffsetDateTime()
                 ?: startDateTime!!.atZone(ZoneId.systemDefault()).toOffsetDateTime(),