"""
LAN file sync module.
Detects file changes, copies from LAN UNC paths to local, and determines which tables need migration.
"""

import os
import shutil


def sync_file(local_path, lan_path):
    """Sync a single file from LAN to local.

    Returns:
        (status, error_msg)
        status: 'copied' | 'updated' | 'skipped' | 'error'
    """
    try:
        if not os.path.exists(lan_path):
            return 'error', f'LAN path not accessible: {lan_path}'

        lan_mtime = os.path.getmtime(lan_path)
        local_existed = os.path.exists(local_path)

        if local_existed:
            local_mtime = os.path.getmtime(local_path)
            if local_mtime == lan_mtime:
                return 'skipped', None

        # Ensure parent directory exists
        os.makedirs(os.path.dirname(local_path), exist_ok=True)

        # Atomic copy: write to .tmp first, then os.replace
        tmp_path = local_path + '.tmp'
        try:
            shutil.copy2(lan_path, tmp_path)
            os.replace(tmp_path, local_path)
        except Exception:
            # Clean up temp file on failure
            if os.path.exists(tmp_path):
                os.remove(tmp_path)
            raise

        if not local_existed:
            return 'copied', None
        else:
            return 'updated', None

    except Exception as e:
        return 'error', str(e)


def sync_all_files(cfg, excel_dir):
    """Sync all LAN source files to local.

    Returns:
        {rel_path: (status, error_msg)}
    """
    lan_sources = cfg.get('lan_sources', {})
    results = {}

    for rel_path, lan_path in lan_sources.items():
        local_path = os.path.join(excel_dir, rel_path)
        status, error_msg = sync_file(local_path, lan_path)
        results[rel_path] = (status, error_msg)

    return results


def determine_tables_to_migrate(cfg, sync_results):
    """Determine which tables need migration based on sync results.

    A table needs migration if ANY of its source files were copied or updated.

    Returns:
        set of table names that need migration
    """
    tables_to_migrate = set()

    for table_cfg in cfg.get('tables', []):
        table_name = table_cfg['table']
        for src in table_cfg['sources']:
            file_rel = src['file']
            if file_rel in sync_results:
                status, _ = sync_results[file_rel]
                if status in ('copied', 'updated'):
                    tables_to_migrate.add(table_name)
                    break

    return tables_to_migrate