repl.sh

#!/usr/bin/env bash

[[ -v REPL_FILES ]] || declare -a REPL_FILES=()
[[ -v REPL_CHECKSUM ]] || declare REPL_CHECKSUM

repl.install() {
  local command
  declare -ga PROMPT_COMMAND
  for command in "${PROMPT_COMMAND[@]}"; do
    if [[ "$command" == "repl.load_if_changed" ]]; then
      return
    fi
  done

  PROMPT_COMMAND+=(repl.load_if_changed)
  repl.install_prompt
}

repl.watch() {
  local f r

  for f in "$@"; do
    for r in "${REPL_FILES[@]}"; do
      if [[ "$r" == "$f" ]]; then
        continue 2
      fi
    done

    REPL_FILES+=("$f")
    printf "repl.watch: %s\n" "$f" >&2
    repl.load "$f"
  done
  REPL_CHECKSUM=$(repl.checksum)
}

repl.checksum() {
  if [[ "${#REPL_FILES[@]}" -eq 0 ]]; then
    return
  fi
  sha1sum "${REPL_FILES[@]}" 2>/dev/null
}

repl.parse_checksum() {
  local sha1 filename
  local -n destination_dict="$1"
  while read sha1 filename; do
    [[ -z "$filename" ]] && continue
    destination_dict["$filename"]="$sha1"
  done
}

repl.load() {
  printf "repl.load: %s\n" "$1" >&2
  source "$1"
}

repl.load_if_changed() {
  local filename new_checksum
  local -A old new
  new_checksum=$(repl.checksum)
  repl.parse_checksum old <<<"${REPL_CHECKSUM}"
  repl.parse_checksum new <<<"$new_checksum"

  for filename in "${!new[@]}"; do
    if [[ "${new[$filename]}" != "${old[$filename]:-}" ]]; then
      repl.load "$filename"
    fi
  done

  REPL_CHECKSUM="$new_checksum"
}

repl.install_prompt() {
  if [[ "$PS1" =~ repl: ]]; then
    return
  fi

  PS1="\[repl:\$(repl.prompt_info)\] $PS1"
}

repl.prompt_info() {
  local IFS=,
  printf '[%s]' "${REPL_FILES[*]}"
}

repl.enter() {
  bash --rcfile <(printf "%s\n" \
    "$(< $HOME/.bashrc)" \
    'source repl.sh' \
    'repl.install' \
  ) -i
}

case ${0##*/} in
  repl.sh) repl.enter;;
  -bash) repl.install;;
esac