# =============================================================================
# USAGE EXAMPLES (run from any directory)
# -----------------------------------------------------------------------------
#   python file.py -scan C:\Users\User\Desktop\debugrem
#   python file.py -scan "D:\My Data\Projects"
#   python file.py --scan .
#   python file.py -scan C:\Windows\Temp -j 32
#
# FLAGS
#   -scan, --scan PATH   Root folder to scan (required). Only direct children
#                        of PATH are listed; folder sizes are total bytes of
#                        all nested files (recursive).
#   -j, --jobs N         Parallel workers for sizing top-level folders
#                        (default: min(32, CPU count * 4)).
#
# OUTPUT FORMAT (columns separated by two spaces)
#   <name>  <path>  <size_KB>
#   Paths use OS separators; directories end with a separator.
#   Rows are sorted by size_KB descending (largest first); ties by name.
# =============================================================================

from __future__ import annotations

import argparse
import os
import sys
from concurrent.futures import ThreadPoolExecutor, as_completed
from os import scandir, stat_result


def _bytes_to_kb(n: int) -> int:
    return (n + 1023) // 1024 if n else 0


def _tree_size_bytes(root: str) -> int:
    """Sum st_size of all regular files under root (iterative, no recursion limit)."""
    total = 0
    stack = [root]
    push = stack.append
    pop = stack.pop

    while stack:
        d = pop()
        try:
            with scandir(d) as it:
                for ent in it:
                    try:
                        if ent.is_file(follow_symlinks=False):
                            st: stat_result = ent.stat(follow_symlinks=False)
                            total += st.st_size
                        elif ent.is_dir(follow_symlinks=False):
                            push(ent.path)
                    except OSError:
                        continue
        except OSError:
            continue
    return total


def _format_line(name: str, path_for_display: str, size_kb: int) -> str:
    return f"{name}  {path_for_display}  {size_kb}"


def scan_root(root: str, jobs: int) -> None:
    root = os.path.abspath(os.path.normpath(root))
    if not os.path.isdir(root):
        print(f"Not a directory: {root}", file=sys.stderr)
        sys.exit(2)

    sep = os.sep
    entries: list[tuple[str, str, bool]] = []
    try:
        with scandir(root) as it:
            for ent in it:
                try:
                    is_dir = ent.is_dir(follow_symlinks=False)
                except OSError:
                    continue
                entries.append((ent.name, ent.path, is_dir))
    except OSError as e:
        print(f"Cannot read directory {root}: {e}", file=sys.stderr)
        sys.exit(1)

    files_ready: list[tuple[str, str, int]] = []
    dir_jobs: list[tuple[str, str]] = []

    for name, fullpath, is_dir in entries:
        if is_dir:
            display = fullpath if fullpath.endswith(sep) else fullpath + sep
            dir_jobs.append((name, fullpath))
        else:
            try:
                st = os.stat(fullpath, follow_symlinks=False)
                sz = st.st_size
            except OSError:
                sz = 0
            display = fullpath
            files_ready.append((name, display, _bytes_to_kb(sz)))

    dirs_ready: list[tuple[str, str, int]] = []
    if dir_jobs:
        workers = max(1, min(jobs, len(dir_jobs)))
        with ThreadPoolExecutor(max_workers=workers) as ex:
            futs = {
                ex.submit(_tree_size_bytes, p): (n, p)
                for n, p in dir_jobs
            }
            for fut in as_completed(futs):
                name, fullpath = futs[fut]
                display = fullpath if fullpath.endswith(sep) else fullpath + sep
                try:
                    b = fut.result()
                except Exception:
                    b = 0
                dirs_ready.append((name, display, _bytes_to_kb(b)))

    out: list[tuple[str, str, int]] = [*files_ready, *dirs_ready]
    out.sort(key=lambda row: (-row[2], row[0].lower()))

    for name, path_disp, kb in out:
        print(_format_line(name, path_disp, kb))


def main() -> None:
    p = argparse.ArgumentParser(
        description="List direct children of PATH with sizes (folders = recursive total).",
    )
    p.add_argument(
        "-scan",
        "--scan",
        dest="root",
        metavar="PATH",
        required=True,
        help="Root directory to scan",
    )
    p.add_argument(
        "-j",
        "--jobs",
        type=int,
        default=max(1, min(32, (os.cpu_count() or 4) * 4)),
        metavar="N",
        help="Thread workers for parallel folder sizing",
    )
    args = p.parse_args()
    scan_root(args.root, args.jobs)


if __name__ == "__main__":
    main()