Issues trying to Compose an image with masked channels

[pronay]

Hello,

This is my first time trying to write a Python script in GIMP so I am still learning my way around this stuff.
I am trying to implement a script by which I can perform the following steps:

1. Decompose an Image into RGBA channels (Colors->Components->Decompose->Color Model: RGBA)
2. Recompose an Image using R,G channels with B and A using Mask Value of 255 (Colors->Components->Compose->Color Model: RGBA, B and A use 255 mask value)

To do this in Python, I am attempting the following steps:

Code:

       decomposed = pdb.plug_in_decompose(img, drawable, "RGBA", 0)
   
       gimp.message("Performed Decompose")

       # Grab the name of the original image
       fileNameWithExt = pdb.gimp_item_get_name(draw)
       fileNameNoExt = fileNameWithExt.split('.')

       # Create the layers
       gimp.message("Creating new Layers")
       gimp.message("Setting up Red Layer")
       layerR = pdb.gimp_layer_new_from_drawable(pdb.gimp_image_get_active_layer(decomposed[0]), decomposed[0])
       layerName = fileNameNoExt[0] + "_RGBA_Red"
       pdb.gimp_item_set_name(layerR, layerName)
       pdb.gimp_image_insert_layer(decomposed[0], layerR, None, 0)

       gimp.message("Setting up Green Layer")
       layerG = pdb.gimp_layer_new_from_drawable(pdb.gimp_image_get_active_layer(decomposed[1]), decomposed[1])
       layerName = fileNameNoExt[0] + "_RGBA_Green"
       pdb.gimp_item_set_name(layerG, layerName)
       pdb.gimp_image_insert_layer(decomposed[1], layerG, None, 1)

       gimp.message("Setting up Blue Layer")
       layerB = pdb.gimp_layer_new_from_drawable(pdb.gimp_image_get_active_layer(decomposed[2]), decomposed[2])
       layerName = fileNameNoExt[0] + "_RGBA_Blue"
       pdb.gimp_item_set_name(layerB, layerName)
       pdb.gimp_image_insert_layer(decomposed[2], layerB, None, 2)

       gimp.message("Setting up Alpha Layer")
       layerA = pdb.gimp_layer_new_from_drawable(pdb.gimp_image_get_active_layer(decomposed[3]), decomposed[3])
       layerName = fileNameNoExt[0] + "_RGBA_Alpha"
       pdb.gimp_item_set_name(layerA, layerName)
       pdb.gimp_image_insert_layer(decomposed[3], layerA, None, 3)
   
       gimp.message("Creating Layer Mask")
       channelB = pdb.gimp_layer_create_mask(layerB, 1)
       channelA = pdb.gimp_layer_create_mask(layerA, 1)

       gimp.message("Inserting Channels to Decomposed Images")
       pdb.gimp_image_insert_channel(decomposed[2], channelB, None, 0)
       pdb.gimp_image_insert_channel(decomposed[3], channelA, None, 0)

       # Now compose the new image into the target export image
       gimp.message("Starting Compose Step for Output")
       OutImage = pdb.plug_in_compose(decomposed[0], draw, decomposed[1], decomposed[2], decomposed[3], "RGBA")
       gimp.message("Done with Composing Output")

However, when I run this script, I see that my output image is the exact same as the input. This means that the 255 masks are not being applied to the output composed image.
Is the approach I am using correct here? How should I be applying the 255 Mask Value to the B and A channels similar to the settings available for the Compose option in the UI?

Any advice here would be much appreciated.