"""
Applies a reviewed batch of FileRecords to disk.

Safety rules, non-negotiable regardless of which front end calls this:
  - dry_run=True by default. Nothing is touched unless you explicitly
    pass dry_run=False.
  - Every run produces a log (same shape for dry-run and real runs), so
    a dry-run's log IS the preview of exactly what a real run would do.
  - A file is only ever touched if its status is "confirmed" — "pending"
    or "skip" rows are left completely alone.
  - If the computed target path already exists, the file is skipped with
    a clear reason rather than silently overwritten.
"""

import csv
import shutil
from datetime import datetime
from pathlib import Path
from typing import List, Optional

from .model import FileRecord


def plan_new_path(rec: FileRecord) -> Path:
    return rec.root / rec.dest_folder / rec.new_filename_preview


def apply_batch(records: List[FileRecord], dry_run: bool = True,
                 log_path: Optional[Path] = None) -> List[dict]:
    log_rows = []

    for rec in records:
        if rec.status != "confirmed":
            continue

        new_path = plan_new_path(rec)
        row = {
            "timestamp": datetime.now().isoformat(timespec="seconds"),
            "old_path": str(rec.path),
            "new_path": str(new_path),
            "dry_run": dry_run,
            "result": "",
        }

        if new_path == rec.path:
            row["result"] = "unchanged"
        elif new_path.exists():
            row["result"] = "SKIPPED - target already exists"
        elif dry_run:
            row["result"] = "would move"
        else:
            new_path.parent.mkdir(parents=True, exist_ok=True)
            shutil.move(str(rec.path), str(new_path))
            rec.path = new_path   # the record now represents the file at its NEW location —
            row["result"] = "moved"  # without this, anything using rec.path afterwards
            rec.status = "done"       # (identity, re-display, a second move) points at nothing.

        log_rows.append(row)

    if log_path and log_rows:
        with open(log_path, "w", newline="", encoding="utf-8") as f:
            writer = csv.DictWriter(f, fieldnames=list(log_rows[0].keys()))
            writer.writeheader()
            writer.writerows(log_rows)

    return log_rows