#!/usr/bin/env bash
set -euo pipefail

PROGRAM=$0
CURRENT_FILENAME=""
DESTINATION_FILENAME=""

function usage()
{
    echo 1>&2 "USAGE: ${PROGRAM} CURRENT_FILENAME DESTINATION_FILENAME"
}

while [[ $# -gt 0 ]]
do
  key="$1"

  if [[ "$CURRENT_FILENAME" == "" ]]; then
      CURRENT_FILENAME=$key
  elif [[ "$DESTINATION_FILENAME" == "" ]]; then
      DESTINATION_FILENAME=$key
  else
      usage
      exit 30  # Error during arguments parsing
  fi
  shift  # past argument or value
done

if [[ "$DESTINATION_FILENAME" == "" ]]; then
    usage
    exit 20  # Missing arguments CURRENT_FILENAME
elif [[ "$CURRENT_FILENAME" == "" ]]; then
    usage
    exit 10  # Missing arguments CURRENT_FILENAME
else
    if [ -e "$DESTINATION_FILENAME"  ]; then
        echo 1>&2 "$DESTINATION_FILENAME already exists."
        echo 1>&2 "Make sure to remove the destination first."
        exit 40
    fi

    if [[ "$DESTINATION_FILENAME" == */ ]]; then
      echo 1>&2 "$DESTINATION_FILENAME is not a file path."
      exit 80
    fi
    if [[ "$DESTINATION_FILENAME" == */* ]]; then
      DESTINATION_DIR="${DESTINATION_FILENAME%/*}"
      if ! mkdir -p "$DESTINATION_DIR"; then
        echo 1>&2 "Failed to create destination directory: $DESTINATION_DIR"
        exit 160
      fi
    fi


    echo "Copying $CURRENT_FILENAME into $DESTINATION_FILENAME"

    # Pre-check that the source and destination will work
    git mv --dry-run "${CURRENT_FILENAME}" "${DESTINATION_FILENAME}"

    # Make a new branch and switch to it
    BRANCH_NAME="git-cp-$(date +%s)"
    git checkout -b "$BRANCH_NAME"

    # Move the original file to the new destination, in this branch
    git mv "${CURRENT_FILENAME}" "${DESTINATION_FILENAME}"
    git commit -nm "--Duplicate $CURRENT_FILENAME history into $DESTINATION_FILENAME"

    # Restore the original file to keep it in the history
    git checkout HEAD~ "${CURRENT_FILENAME}"
    git commit -nm "--Restore $CURRENT_FILENAME"

    # Switch to the original branch and merge this back in.
    git checkout -
    git merge --no-ff "$BRANCH_NAME" -m "Copy $CURRENT_FILENAME into $DESTINATION_FILENAME"

    # We're now done with the branch, so delete it.
    # We shouldn't need -D here, as we've already merged it back in.
    git branch -d "$BRANCH_NAME"
fi