Convert file to PNG using Firefox's headless screenshot feature

firefox-screenshot.sh

#!/usr/bin/env bash

# Render a local file (or URL) to PNG using Firefox headless screenshot.
# This is often a high-fidelity rasterizer for SVG/HTML/CSS compared to some converters.

set -o errtrace -o errexit -o pipefail
[[ "${TRACE:-0}" == "1" ]] && set -o xtrace
if [[ "${BASH_VERSINFO:-0}" -gt 4 || ( "${BASH_VERSINFO[0]}" -eq 4 && "${BASH_VERSINFO[1]}" -ge 4 ) ]]; then
  shopt -s inherit_errexit
fi

PS4='+\t '
[[ ! -t 0 ]] && [[ -n "${DBUS_SESSION_BUS_ADDRESS:-}" ]] && command -v notify-send >/dev/null 2>&1 && notify=1

error_handler() {
  local line="$1" bash_lineno="$2" cmd="$3" status="$4"
  local start=$(( line > 3 ? line - 3 : 1 ))
  local summary="Error: In ${BASH_SOURCE[0]}, Line ${line}, Command ${cmd} exited with Status ${status}"
  local body
  body="$(pr -tn "${BASH_SOURCE[0]}" | tail -n+"$start" | head -n7 | sed '4s/^[[:space:]]*/>> /')"
  echo >&2 -e "${summary}\n${body}"
  [[ -z "${notify:+x}" ]] || notify-send --urgency=critical "$summary" "$body"
  exit "$status"
}
trap 'error_handler "$LINENO" "${BASH_LINENO[0]:-?}" "$BASH_COMMAND" "$?"' ERR

usage() {
  cat <<'TXT'
firefox-screenshot.sh: Render an input in Firefox headless mode and save a PNG screenshot.

Usage:
  firefox-screenshot.sh [-o output.png] [-s width,height] <input>

Arguments:
  <input>  Local path or URL.

Options:
  -o, --output  Output PNG path.
  -s, --size    Window size as "width,height", e.g. "1920,1080".
  -h, --help    Show help.

Rules:
  If <input> is a local path and -o is omitted, derive output as "<input-without-last-extension>.png".
  If <input> is a URL, require -o.
TXT
}

abs_path() {
  local p="$1"
  if command -v realpath >/dev/null 2>&1; then
    realpath -- "$p"
  elif command -v python3 >/dev/null 2>&1; then
    python3 - <<'PY' "$p"
import os,sys
print(os.path.realpath(sys.argv[1]))
PY
  else
    (cd -- "$(dirname -- "$p")" && printf '%s/%s\n' "$PWD" "$(basename -- "$p")")
  fi
}

default_output_for_file() {
  local in="$1" base
  base="$(basename -- "$in")"
  if [[ "$base" == *.* && "$base" != .* ]]; then
    printf '%s.png\n' "${in%.*}"
  else
    printf '%s.png\n' "$in"
  fi
}

main() {
  command -v firefox >/dev/null 2>&1 || { echo "Firefox is required but not found." >&2; return 1; }

  local output="" size="" input=""
  while [[ $# -gt 0 ]]; do
    case "$1" in
      -h|--help) usage; return 0 ;;
      -o|--output) output="${2-}"; shift 2 ;;
      -s|--size) size="${2-}"; shift 2 ;;
      --) shift; break ;;
      -*) echo "Unknown option: $1" >&2; usage >&2; return 2 ;;
      *) input="$1"; shift; break ;;
    esac
  done
  [[ -n "$input" ]] || { usage >&2; return 2; }

  local uri
  if [[ "$input" =~ ^[a-zA-Z][a-zA-Z0-9+.-]*:// ]]; then
    uri="$input"
    [[ -n "$output" ]] || { echo "Output path is required for URL input." >&2; return 2; }
  else
    [[ -f "$input" ]] || { echo "Input path not found: $input" >&2; return 1; }
    uri="file://$(abs_path "$input")"
    [[ -n "$output" ]] || output="$(default_output_for_file "$input")"
  fi

  local dir="${XDG_CACHE_HOME:-$HOME/.cache}"
  mkdir -p -- "$dir"
  local temp
  temp="$(mktemp -d -- "$dir/firefox-XXXXXX")"
  trap 'rm -rf -- "$temp"' INT TERM EXIT

  local args=(--profile "$temp" --headless --new-instance --screenshot "$output")
  [[ -n "$size" ]] && args+=(--window-size "$size")

  firefox "${args[@]}" "$uri"
}

main "$@"