"""Filename generation with collision avoidance.

Pattern: YYYY-MM-DD-slugified-title.md
Slug: lowercase alphanumeric + hyphens only.
Appends numeric suffix (-2, -3, ...) if file already exists.
"""

import logging
from datetime import datetime, timezone
from pathlib import Path

from slugify import slugify

logger = logging.getLogger(__name__)


def generate_filename(title: str, date: str | None = None) -> str:
    """Generate a filename from title and optional date.

    Args:
        title: The note title to slugify.
        date: Optional date string (YYYY-MM-DD). Uses today if not provided.

    Returns:
        Filename in format YYYY-MM-DD-slugified-title.md
    """
    if date is None:
        date = datetime.now(timezone.utc).strftime("%Y-%m-%d")

    # Ensure date is just the date portion (handle ISO datetime strings)
    date_part = date[:10] if len(date) >= 10 else date

    slug = slugify(title, max_length=80)
    if not slug:
        slug = "untitled"

    return f"{date_part}-{slug}.md"


def resolve_collision(target_dir: Path, filename: str) -> Path:
    """Resolve filename collisions by appending numeric suffix.

    Args:
        target_dir: Directory where the file will be written.
        filename: Desired filename (e.g., 2024-03-15-meeting-notes.md).

    Returns:
        Full path with unique filename (appends -2, -3, etc. if needed).
    """
    target = Path(target_dir) / filename

    if not target.exists():
        return target

    # Split filename to insert suffix before .md
    stem = filename.rsplit(".md", 1)[0]
    suffix_num = 2

    while True:
        new_filename = f"{stem}-{suffix_num}.md"
        new_target = Path(target_dir) / new_filename
        if not new_target.exists():
            logger.debug("Collision resolved: %s → %s", filename, new_filename)
            return new_target
        suffix_num += 1