abom_struct.bash

# A struct, which is a set of key/value pairs, is represented as a string.
# Each key/value pair is separated from others with an ASCII RS (record
# separator) character, hex 1e. The key and value in each pair is separated by
# an ASCII US (unit separator) character, hex 1f.
#
# Empty keys cause undefined behavior. Empty values are not supported; setting
# an empty value deletes its key.

# make_struct builds a new struct as a string and and echoes it. Pass it
# alternating keys and values.
#
# my_struct=$(make_struct key1 val1 key2 val2)
make_struct() {
  local s=""
  local argct=$#
  local i
  for (( i = 0; i < argct; i += 2 )); do
    local key=$1
    local value=$2
    if [[ -z $value ]]; then
      continue
    fi
    if [[ -n $s ]]; then
      s=$(printf '%s\x1e' "${s}")
    fi
    s=$(printf '%s%s\x1f%s' "$s" "$key" "$value")
    shift 2
  done

  echo "$s"
}

# struct_get looks up the value for a key in a struct and echoes it. Pass it the
# struct and the key. If the key is not present, an empty string is echoed.
#
# value=$(struct_get "$my_struct" key1) # val1
struct_get() {
  local s=$1
  local k=$2

  while [[ ! $s =~ ^$k$'\x1f' ]]; do
    local nexts=${s#*$'\x1e'}
    if [[ $nexts == "$s" ]]; then
      s=""
      break
    fi
    s=$nexts
  done
  if [[ -z $s ]]; then
    echo
  else
    local pair=${s%%$'\x1e'*}
    echo "${pair#*$'\x1f'}"
  fi
}

# struct_set sets a value for a key in a struct and echoes the new struct. Pass
# it the struct, key, and value. If the key is present in the struct, its old
# value is replaced; otherwise, it is added. If the value is empty, the key is
# removed from the struct. Remember to store the output from this function as
# the new struct.
#
# my_struct=$(struct_set "$my_struct" key3 val3)
struct_set() {
  local s=$1
  local k=$2
  local v=$3

  local news=()
  local found=
  while [[ -n $s ]]; do
    local thiskv=${s%%$'\x1e'*}
    local thisk=${thiskv%%$'\x1f'*}
    if [[ $thisk == "$k" ]]; then
      if [[ -n $v ]]; then
        news+=( "$thisk" "$v" )
      fi
      found=1
    else
      local thisv=${thiskv#*$'\x1f'}
      news+=( "$thisk" "$thisv" )
    fi

    if [[ $thiskv == "$s" ]]; then
      break
    fi
    s=${s#*$'\x1e'}
  done

  if [[ -z $found ]]; then
    news+=( "$k" "$v" )
  fi

  make_struct "${news[@]}"
}

# struct_del deletes a key from a struct and echoes the new struct. Pass it the
# struct and key. This is a convenience function for calling struct_set with an
# empty value.
#
# my_struct=$(struct_del "$my_struct" key3)
struct_del() {
  local s=$1
  local k=$2

  struct_set "$s" "$k" ""
}