#!/usr/bin/env bash

set -euo pipefail

if [ "$#" -lt 2 ] || [ "$#" -gt 3 ]; then
  echo "Usage: $0 <template-file> <env-file> [session-secret]" >&2
  exit 1
fi

template_file="$1"
env_file="$2"
session_secret="${3:-}"

if [ ! -f "$template_file" ]; then
  echo "Template file not found: $template_file" >&2
  exit 1
fi

tmp_output="$(mktemp)"
trap 'rm -f "$tmp_output"' EXIT

if [ -f "$env_file" ]; then
  awk '
    function key_from(line, key) {
      if (line ~ /^[[:space:]]*[A-Za-z_][A-Za-z0-9_]*=/) {
        key = line
        sub(/=.*/, "", key)
        gsub(/^[[:space:]]+|[[:space:]]+$/, "", key)
        return key
      }
      return ""
    }
    FNR == NR {
      key = key_from($0)
      if (key != "") {
        existing[key] = $0
        existing_order[++existing_count] = key
      }
      next
    }
    {
      key = key_from($0)
      if (key != "") {
        template_seen[key] = 1
        if (key in existing) {
          print existing[key]
        } else {
          print $0
        }
      } else {
        print $0
      }
    }
    END {
      appended = 0
      for (i = 1; i <= existing_count; i++) {
        key = existing_order[i]
        if (!(key in template_seen)) {
          if (!appended) {
            print ""
            print "# Vorherige zusaetzliche Eintraege"
            appended = 1
          }
          print existing[key]
        }
      }
    }
  ' "$env_file" "$template_file" > "$tmp_output"
else
  cp "$template_file" "$tmp_output"
fi

if [ -n "$session_secret" ] && grep -q '^SESSION_SECRET=$' "$tmp_output"; then
  sed -i "s/^SESSION_SECRET=$/SESSION_SECRET=$session_secret/" "$tmp_output"
fi

mv "$tmp_output" "$env_file"