#!/usr/bin/env bash

# READ THIS BEFORE MAKING CHANGES:
#
# If you want to add a new pre-commit check, here are the rules:
#
#   1. Create a bash function for your check (see e.g. ui_lint below).
#      NOTE: Each function will be called in a sub-shell so you can freely
#      change directory without worrying about interference.
#   2. Add the name of the function to the CHECKS variable.
#   3. If no changes relevant to your new check are staged, then
#      do not output anything at all - this would be annoying noise.
#      In this case, call 'return 0' from your check function to return
#      early without blocking the commit.
#   4. If any non-trivial check-specific thing has to be invoked,
#      then output '==> [check description]' as the first line of
#      output. Each sub-check should output '--> [subcheck description]'
#      after it has run, indicating success or failure.
#   5. Call 'block [reason]' to block the commit. This ensures the last
#      line of output calls out that the commit was blocked - which may not
#      be obvious from random error messages generated in 4.
#
# At the moment, there are no automated tests for this hook, so please run it
# locally to check you have not broken anything - breaking this will interfere
# with other peoples' workflows significantly, so be sure, check everything twice.

set -euo pipefail

# Call block to block the commit with a message.
block() {
  echo "$@"
  echo "Commit blocked - see errors above."
  exit 1
}

# Add all check functions to this space separated list.
# They are executed in this order (see end of file).
CHECKS="ui_lint"

# Run ui linter if changes in that dir detected.
ui_lint() {
  local DIR=ui LINTER=node_modules/.bin/lint-staged

  # Silently succeed if no changes staged for $DIR
  if git diff --name-only --cached --exit-code -- $DIR/; then
    return 0
  fi

  # Silently succeed if the linter has not been installed.
  # We assume that if you're doing UI dev, you will have installed the linter
  # by running yarn.
  if [ ! -x $DIR/$LINTER ]; then
    return 0
  fi

  echo "==> Changes detected in $DIR/: Running linter..."

  # Run the linter from the UI dir.
  cd $DIR
  $LINTER || block "UI lint failed"
}

for CHECK in $CHECKS; do
  # Force each check into a subshell to avoid crosstalk.
  ( $CHECK ) || exit $?
done