import logging
import os
import re
from pathlib import Path

logger = logging.getLogger(__name__)

_ENV_VAR_RE = re.compile(r"\$\{([^}]+)\}")


def resolve_env_vars(value: str) -> str:
    """Replace ${VAR} patterns with environment variable values.

    Non-recursive: if ${A} expands to a literal ${B}, ${B} is NOT resolved.
    Unknown variables are replaced with empty string and a warning is logged.
    """
    if not isinstance(value, str):
        return value

    def _replacer(match: re.Match) -> str:
        var_name = match.group(1)
        env_value = os.environ.get(var_name)
        if env_value is None:
            logger.warning("Environment variable %s is not set, using empty string", var_name)
            return ""
        return env_value

    return _ENV_VAR_RE.sub(_replacer, value)


def ensure_config_dir(path: Path | None = None) -> Path:
    """Create ~/.config/redmine-reporter/ with 0o700 permissions.

    Returns the path to the config directory.
    No-op if the directory already exists.
    """
    if path is None:
        path = Path.home() / ".config" / "redmine-reporter"
    path.mkdir(mode=0o700, parents=True, exist_ok=True)
    return path


def check_file_permissions(path: Path) -> list[str]:
    """Check that a config file has safe permissions (0o600 or stricter).

    Returns a list of warning messages. Empty list means no issues.
    """
    warnings: list[str] = []
    if not path.exists():
        return warnings

    mode = path.stat().st_mode & 0o777
    if mode > 0o600:
        warnings.append(
            f"Config file permissions are too open ({mode:04o}). "
            f"Expected 0600. Fix with: chmod 600 {path}"
        )
    return warnings


def expand_filename_template(
    template: str,
    *,
    author: str = "",
    from_date: str = "",
    to_date: str = "",
    ext: str = "",
) -> str:
    """Expand placeholders in a filename template.

    Supported placeholders:
      {author}  — author name
      {from}    — start date (YYYY-MM-DD)
      {to}      — end date (YYYY-MM-DD)
      {date}    — end date formatted as DD_MM_YYYY
      {ext}     — file extension without dot

    Unknown placeholders are left as-is.
    """
    date_dd_mm_yyyy = ""
    if to_date:
        try:
            from datetime import datetime

            dt = datetime.strptime(to_date, "%Y-%m-%d")
            date_dd_mm_yyyy = dt.strftime("%d_%m_%Y")
        except ValueError:
            date_dd_mm_yyyy = to_date

    replacements = {
        "author": author.replace(" ", "_"),
        "from": from_date,
        "to": to_date,
        "date": date_dd_mm_yyyy,
        "ext": ext,
    }

    result = template
    for key, value in replacements.items():
        result = result.replace("{" + key + "}", value)
    return result


KNOWN_FORMAT_NAMES = {"xlsx", "odt", "csv", "md", "html", "json"}


def resolve_output_path(
    output_arg: str | None,
    *,
    output_dir: str = "",
    filename_template: str = "{author}_{from}_{to}.{ext}",
    default_format: str = "xlsx",
    author: str = "",
    from_date: str = "",
    to_date: str = "",
) -> str | None:
    """Resolve the final output path from --output argument and config settings.

    Returns None if output_arg is None (meaning no file output, use console).

    Resolution rules:
      - None → None (console output)
      - Bare format name (xlsx, odt, csv, md, html, json) → use template path
      - Path without extension → append .{default_format}
      - Path with known extension → use as-is
      - Path with unknown extension → use as-is
    """
    if output_arg is None:
        return None

    arg = output_arg.strip()

    import os

    if arg.lower() in KNOWN_FORMAT_NAMES:
        ext = arg.lower()
        resolved_dir = os.path.expanduser(output_dir) if output_dir else "."
        filename = expand_filename_template(
            filename_template,
            author=author,
            from_date=from_date,
            to_date=to_date,
            ext=ext,
        )
        return os.path.join(resolved_dir, filename)

    _, ext = os.path.splitext(arg)
    if not ext:
        arg = f"{arg}.{default_format}"

    return arg