"""Edit log helpers for change tracking."""
import json
from datetime import datetime, timezone


def compute_diff(old: dict, new: dict, exclude: set = None) -> dict:
    """Compare old and new values, return {field: [old, new]} for changed fields."""
    if exclude is None:
        exclude = {"edit_log", "updated_at", "created_at", "id"}
    changes = {}
    for key, new_val in new.items():
        if key in exclude:
            continue
        old_val = old.get(key)
        # Normalize for comparison
        old_str = str(old_val) if old_val is not None else ""
        new_str = str(new_val) if new_val is not None else ""
        if old_str != new_str:
            changes[key] = [old_str, new_str]
    return changes


def append_entry(record, editor_name: str, changes: dict, reason: str = None):
    """Append an edit log entry to a record's edit_log JSON list."""
    log = list(record.edit_log) if record.edit_log else []
    entry = {
        "editor": editor_name,
        "time": datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ"),
        "changes": changes,
    }
    if reason:
        entry["reason"] = reason
    log.append(entry)
    record.edit_log = log


def init_entry(record, creator_name: str):
    """Initialize edit_log with a creation entry."""
    record.edit_log = [{
        "editor": creator_name,
        "time": datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ"),
        "changes": {},
    }]