diff --git a/to-m4b.sh b/to-m4b.sh
old mode 100644
new mode 100755
index 658765f..f92d736
--- a/to-m4b.sh
+++ b/to-m4b.sh
@@ -3,28 +3,126 @@ set -x
 set -eufo pipefail
 
 # CONSTANTS
-declare -r m4b-tool="nix run github:sandreas/m4b-tool#m4b-tool-libfdk -- "
 declare -r script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 # VARS
 LEADING_ZEROES=2
-MAIN_SRC="${SRC:${script_dir}/src}"
-MAIN_OUT="${OUT:${script_dir}/out}"
+SRC="${script_dir}/src"
+OUT="${script_dir}/out"
 
 # FUNCTIONS
 parse-vars() {
-  # TODO implement parsing the directory structure of the passed directory, to fill in missing vars and return them
   # Series structure: ${SRC}/<author>/<series>/Book <part> - <year> - <book> {<narrator>}/
   # Standalone structure: ${SRC}/<author>/<year> - <book> {<narrator>}/
-  # Return the <part> wihh leading zeros based on the LEADING_ZEROES variable
+  # Return variables as key=value lines; <part> zero-padded to LEADING_ZEROES as series_index
+  local dir="${1%/}"
+  local leaf="${dir##*/}"
+  local parent="${dir%/*}"
+  local grandparent="${parent%/*}"
+
+  local author=""
+  local series=""
+  local title=""
+  local year=""
+  local narrator=""
+  local part=""
+  local series_index=""
+  local rest=""
+
+  # Helper: trim leading/trailing whitespace
+  trim() { local s="$1"; s="${s#${s%%[![:space:]]*}}"; s="${s%${s##*[![:space:]]}}"; printf '%s' "$s"; }
+
+  # Detect pattern and extract fields
+  if [[ "$leaf" =~ ^[Bb]ook[[:space:]]+([0-9]+)[[:space:]]*-[[:space:]]*([0-9]{4})[[:space:]]*-[[:space:]]*(.+)$ ]]; then
+    part="${BASH_REMATCH[1]}"
+    year="${BASH_REMATCH[2]}"
+    rest="${BASH_REMATCH[3]}"
+    if [[ "$rest" =~ ^(.+)[[:space:]]*\{([^}]*)\}[[:space:]]*$ ]]; then
+      title="${BASH_REMATCH[1]}"
+      narrator="${BASH_REMATCH[2]}"
+    else
+      title="$rest"
+    fi
+    series="${parent##*/}"
+    author="${grandparent##*/}"
+  elif [[ "$leaf" =~ ^([0-9]{4})[[:space:]]*-[[:space:]]*(.+)$ ]]; then
+    year="${BASH_REMATCH[1]}"
+    rest="${BASH_REMATCH[2]}"
+    if [[ "$rest" =~ ^(.+)[[:space:]]*\{([^}]*)\}[[:space:]]*$ ]]; then
+      title="${BASH_REMATCH[1]}"
+      narrator="${BASH_REMATCH[2]}"
+    else
+      title="$rest"
+    fi
+    author="${parent##*/}"
+  else
+    # Fallback best-effort parsing
+    rest="$leaf"
+    if [[ "$rest" =~ \{([^}]*)\}[[:space:]]*$ ]]; then
+      narrator="${BASH_REMATCH[1]}"
+      rest="${rest%\{${narrator}\}*}"
+    fi
+    if [[ "$rest" =~ ^([0-9]{4})[[:space:]]*-[[:space:]]*(.+)$ ]]; then
+      year="${BASH_REMATCH[1]}"
+      title="${BASH_REMATCH[2]}"
+    else
+      title="$rest"
+    fi
+    author="${parent##*/}"
+  fi
+
+  # Normalize whitespace
+  title="$(trim "$title")"
+  author="$(trim "$author")"
+  series="$(trim "$series")"
+  narrator="$(trim "$narrator")"
+
+  # Zero-pad part for series_index if available
+  if [[ -n "$part" ]]; then
+    part="${part//[^0-9]/}"
+    series_index=$(printf "%0*d" "$LEADING_ZEROES" "$part")
+  fi
+
+  printf 'author=%q\n' "$author"
+  printf 'series=%q\n' "$series"
+  printf 'series_index=%q\n' "$series_index"
+  printf 'title=%q\n' "$title"
+  printf 'year=%q\n' "$year"
+  printf 'narrator=%q\n' "$narrator"
 }
 
 get-book-directories() {
-  # TODO implemet getting the book directoris based on the ${SRC} path
-  # find the directories that contains the books files and return them as an array
-  # Example book directory:
-  # /path/to/src/Author/Series/Book Part - Year - Book {Narrator}/
-  # /path/to/src/Author/Year - Book {Narrator}/
+  # Discover book directories under ${SRC} (or ${script_dir}/src if unset)
+  # Matches:
+  # - ${SRC}/<author>/<series>/Book <part> - <year> - <title> {<narrator>}/
+  # - ${SRC}/<author>/<year> - <title> {<narrator>}/
+  # Prints matched directories, one per line
+  local src_root="${1}"
+  local -a results=()
+  local dir leaf
+
+  # Iterate candidate depths using fast globbing (avoids slow full-recursive find)
+  for dir in "${src_root}"/*/*/ "${src_root}"/*/*/*/; do
+    [[ -d "$dir" ]] || continue
+    leaf="${dir%/}"; leaf="${leaf##*/}"
+
+    # Match standalone: "YYYY - Title {Narrator}" or similar
+    if [[ "$leaf" =~ ^[0-9]{4}[[:space:]]*-[[:space:]]*.+$ ]]; then
+      :
+    # Match series: "Book N - YYYY - Title {Narrator}" (Book/book, flexible spaces)
+    elif [[ "$leaf" =~ ^[Bb]ook[[:space:]]+[0-9]+[[:space:]]*-[[:space:]]*[0-9]{4}[[:space:]]*-[[:space:]]*.+$ ]]; then
+      :
+    else
+      continue
+    fi
+
+    # Quick check: directory contains at least one likely audio file
+    if compgen -G "$dir"*.{mp3,m4a,m4b,aac,flac,wav} >/dev/null 2>&1; then
+      results+=("${dir%/}")
+    fi
+  done
+
+  printf '%s\n' "${results[@]}"
 }
 
 m4b-merge() {
@@ -38,7 +136,7 @@ m4b-merge() {
   local series_index=${8}
 
   mkdir -p "$(dirname "${output_file}")"
-  "${m4b-tool}" \
+  nix run github:sandreas/m4b-tool#m4b-tool-libfdk -- \
     merge \
       -v \
       --jobs=6 \
@@ -55,7 +153,32 @@ m4b-merge() {
 }
 
 main() {
+  local src_root="${SRC:-${script_dir}/src}"
+  local out_root="${OUT:-${script_dir}/out}"
+  local dir author narrator title year series series_index output_file
 
+  mapfile -t dirs < <(get-book-directories "${src_root}")
+
+  for dir in "${dirs[@]}"; do
+    eval "$(parse-vars "$dir")"
+    if [[ -z "$title" ]]; then
+      echo "Skipping '$dir': could not parse title" >&2
+      continue
+    fi
+    if [[ -z "$author" ]]; then
+      echo "Skipping '$dir': could not parse author" >&2
+      continue
+    fi
+    # Construct output path: ${OUT}/<author>/<series or standalone>/<series_index - >title {narrator}.m4b
+    if [[ -n "$series" ]]; then
+      output_file="${out_root}/${author}/${series}/${series_index:+${series_index} - }${title}${narrator:+ {${narrator}}}.m4b"
+    else
+      output_file="${out_root}/${author}/${year:+${year} - }${title}${narrator:+ {${narrator}}}.m4b"
+    fi
+
+    echo "Processing '$dir' -> '$output_file'"
+    # m4b-merge "$output_file" "$dir" "$author" "$narrator" "$title" "$year" "$series" "$series_index"
+  done
 }
 
 main "$@"