Bluetooth headset - switch between quality sound + no mic (A2DP) and crappy sound and mic (HSP/HFP)

switchHeadphones.sh

#!/bin/bash

####  Restart Bluetooth
if [ "$1" == "resetBT" ] ; then
  sudo rfkill block bluetooth && sleep 0.1 && sudo rfkill unblock bluetooth;
  exit;
fi;

#### Toggle listen/speak
if [ "$1" == "" -o "$1" == "toggle" ] ; then
  LINE=`pacmd list-sinks  | grep '\(name:\|alias\)' | grep -B1 F5A  | head -1`
  if [ "$LINE" == "" ] ; then echo "F5A headset not found."; $0 reset; sleep 2; exit; fi

  SINK_NAME="bluez_sink.00_19_5D_25_6F_6C.a2dp_sink"
  if $(echo "$LINE" | grep $SINK_NAME &> /dev/null) ; then
    echo "Detected quality sound output, that means we can't speak; switch that."
    $0 speak;
  else
    echo "Quality sound not found, switch to the good sound."
    $0 listen;
  fi
fi

#### Change the output to F5A
if [ "$1" == "listen" ] ; then
  LINE=`pacmd list-sinks  | grep '\(name:\|alias\)' | grep -B1 F5A  | head -1`
  if [ "$LINE" == "" ] ; then echo "F5A phones not found."; $0 reset; sleep 2; exit; fi
  #        name: <bluez_sink.00_19_5D_25_6F_6C.headset_head_unit>

  ## Get what's between <...>
  SINK_NAME=`echo "$LINE" | tr '>' '<' | cut -d'<' -f2`;

  ## The above gives an ID according to the active profile.
  ## To set manually:
  #SINK_NAME="bluez_sink.00_19_5D_25_6F_6C.headset_head_unit"
  #SINK_NAME="bluez_sink.00_19_5D_25_6F_6C.a2dp_sink"

  ## Switch the output to that.
  echo "Switching audio output to $SINK_NAME";
  pacmd set-default-sink "$SINK_NAME"

  #### Change profile to quality output + no mic. From `pacmd list-cards`:
  CARD="bluez_card.00_19_5D_25_6F_6C"
  PROFILE="a2dp_sink"	
  echo "Switching audio profile to $PROFILE";
  pacmd set-card-profile $CARD $PROFILE
  exit;
fi;

#### Input
if [ "$1" == "speak" ] ; then
  ## Change profile to crappy output + mic. From `pacmd list-cards`:
  CARD="bluez_card.00_19_5D_25_6F_6C"
  pacmd set-card-profile $CARD headset_head_unit

  LINE=`pacmd list-sources | grep '\(name:\|alias\)' | grep -B1 F5A  | head -1`
  if [ "$LINE" == "" ] ; then echo "F5A mic not found."; $0 reset; sleep 2; exit; fi
  SOURCE_NAME=`echo "$LINE" | tr '>' '<' | cut -d'<' -f2`;
  #SOURCE_NAME="bluez_source.00_19_5D_25_6F_6C.headset_head_unit"
  #SOURCE_NAME="bluez_sink.00_19_5D_25_6F_6C.a2dp_sink.monitor"
  echo "Switching audio input to $SOURCE_NAME";
  pacmd set-default-source "$SOURCE_NAME" || echo 'Try `pacmd list-sources`.';
fi;


####  Resources:

##  Why this is needed
# https://jimshaver.net/2015/03/31/going-a2dp-only-on-linux/

##  My original question
# https://askubuntu.com/questions/1004712/audio-profile-changes-automatically-to-hsp-bad-quality-when-i-change-input-to/1009156#1009156

##  Script to monitor plugged earphones and switch when unplugged (Ubuntu does that, but nice script):
# https://github.com/freundTech/linux-helper-scripts/blob/master/padevswitch/padevswitch

@JustinFrost47 I never did figure it out but now having read your answer, it seems so obvious what the problem was. Looks like I hadn't skimmed the code back then to find out what prompted the error message.

I've since moved to a newer machine running Windows 10 (which is posing its own set of BT-related challenges). I'm now inspired to dust off the old laptop and give it another go for an undeserved sense of accomplishment. Thanks for the help, cheers.