#!/usr/bin/env bash

_date_format_repo_root() {
  cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd
}

_date_format_env_file() {
  printf '%s/.env\n' "$(_date_format_repo_root)"
}

_read_env_value() {
  local key="$1"
  local env_file
  env_file="$(_date_format_env_file)"

  if [ ! -f "$env_file" ]; then
    return 1
  fi

  awk -F= -v key="$key" '
    $1 == key {
      value = substr($0, index($0, "=") + 1)
      gsub(/^["'"'"']|["'"'"']$/, "", value)
      print value
      exit
    }
  ' "$env_file"
}

_resolve_display_locale() {
  if [ -n "${SYSTEM_LOCALE:-}" ]; then
    printf '%s\n' "$SYSTEM_LOCALE"
    return
  fi

  local env_locale
  env_locale="$(_read_env_value SYSTEM_LOCALE 2>/dev/null || true)"
  if [ -n "$env_locale" ]; then
    printf '%s\n' "$env_locale"
    return
  fi

  env_locale="${DISPLAY_LOCALE:-$(_read_env_value DISPLAY_LOCALE 2>/dev/null || true)}"
  if [ -n "$env_locale" ]; then
    printf '%s.UTF-8\n' "$(printf '%s' "$env_locale" | tr '-' '_')"
    return
  fi

  if [ -n "${LANG:-}" ]; then
    printf '%s\n' "$LANG"
    return
  fi

  printf 'C.UTF-8\n'
}

_resolve_display_timezone() {
  if [ -n "${TZ:-}" ]; then
    printf '%s\n' "$TZ"
    return
  fi

  local env_tz
  env_tz="$(_read_env_value TZ 2>/dev/null || true)"
  if [ -n "$env_tz" ]; then
    printf '%s\n' "$env_tz"
    return
  fi

  printf 'UTC\n'
}

_read_now_parts() {
  local locale tz output
  locale="$(_resolve_display_locale)"
  tz="$(_resolve_display_timezone)"

  if output=$(LC_TIME="$locale" TZ="$tz" date '+%d %b %Y %H %M %S' 2>/dev/null); then
    printf '%s\n' "$output"
    return
  fi

  TZ="$tz" date '+%d %b %Y %H %M %S'
}

format_display_date_now() {
  local day month year hour minute second
  read -r day month year hour minute second <<<"$(_read_now_parts)"
  month="${month%.}"
  printf '%s.%s.%s\n' "$day" "$month" "$year"
}

format_display_timestamp_now() {
  local day month year hour minute second
  read -r day month year hour minute second <<<"$(_read_now_parts)"
  month="${month%.}"
  printf '%s.%s.%s %s:%s:%s\n' \
    "$day" "$month" "$year" "$hour" "$minute" "$second"
}

format_snapshot_stamp_now() {
  local day month year hour minute second
  read -r day month year hour minute second <<<"$(_read_now_parts)"
  month="${month%.}"
  printf '%s.%s.%s-%s%s\n' \
    "$day" "$month" "$year" "$hour" "$minute"
}

if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
  set -euo pipefail
  case "${1:-}" in
    display-date)
      format_display_date_now
      ;;
    display-ts)
      format_display_timestamp_now
      ;;
    snapshot-stamp)
      format_snapshot_stamp_now
      ;;
    *)
      echo "Usage: $0 {display-date|display-ts|snapshot-stamp}" >&2
      exit 1
      ;;
  esac
fi