"""Filesystem operations service.

Provides unified filesystem operations including file discovery, size
calculation, and path management. Consolidates common filesystem patterns
used across quantisation and conversion workflows.
"""

from __future__ import annotations

import json
import subprocess
from pathlib import Path
from typing import Any

from helpers.logger import logger

BYTES_PER_UNIT = 1024.0


class FilesystemService:
    """Handles filesystem operations with consistent error handling.

    Provides methods for file discovery, size formatting, and JSON loading
    with proper error handling and logging. Ensures consistent behaviour
    across different tools and workflows.
    """

    @staticmethod
    def get_file_size(file_path: Path) -> str:
        """Get human-readable file size using system utilities.

        Attempts to use `du -h` for human-readable output, falling back to
        Python calculation if the system command fails. Provides consistent
        size formatting across the toolset.

        Returns:
            Human-readable file size string (e.g., "1.5G", "750M").
        """
        try:
            result = subprocess.run(
                ["du", "-h", str(file_path)], capture_output=True, text=True, check=True
            )
            return result.stdout.split()[0]
        except (subprocess.CalledProcessError, FileNotFoundError):
            # Fallback to Python calculation

            try:
                size_bytes: float = float(file_path.stat().st_size)
                for unit in ["B", "K", "M", "G", "T"]:
                    if size_bytes < BYTES_PER_UNIT:
                        return f"{size_bytes:.1f}{unit}"
                    size_bytes /= BYTES_PER_UNIT
            except Exception:
                return "Unknown"
            else:
                return f"{size_bytes:.1f}P"

    @staticmethod
    def load_json_config(config_path: Path) -> dict[str, Any]:
        """Load and parse JSON configuration file.

        Provides consistent JSON loading with proper error handling and
        encoding specification. Used for loading model configurations,
        tokeniser settings, and other JSON-based metadata.

        Returns:
            Parsed JSON content as dictionary.

        Raises:
            FileNotFoundError: If config file doesn't exist.
        """
        if not config_path.exists():
            msg = f"Configuration file not found: {config_path}"
            raise FileNotFoundError(msg)

        with Path(config_path).open(encoding="utf-8") as f:
            return json.load(f)

    @staticmethod
    def find_safetensor_files(model_path: Path) -> list[Path]:
        """Find all SafeTensor files in model directory using priority search.

        Searches for tensor files in order of preference: single model.safetensors,
        sharded model-*-of-*.safetensors files, then any *.safetensors files. This
        approach handles both single-file and multi-shard model distributions whilst
        ensuring predictable file ordering for conversion consistency.

        Returns:
            List of SafeTensor file paths in priority order.

        Raises:
            FileNotFoundError: If no SafeTensor files are found.
        """
        # Check for single file
        single_file = model_path / "model.safetensors"
        if single_file.exists():
            return [single_file]

        # Check for sharded files
        pattern = "model-*-of-*.safetensors"
        sharded_files = sorted(model_path.glob(pattern))
        if sharded_files:
            return sharded_files

        # Check for any safetensor files
        any_files = sorted(model_path.glob("*.safetensors"))
        if any_files:
            return any_files

        msg = f"No SafeTensor files found in {model_path}"
        raise FileNotFoundError(msg)

    @staticmethod
    def find_gguf_files(model_path: Path, pattern: str | None = None) -> list[Path]:
        """Find GGUF files in directory, optionally filtered by pattern.

        Searches for GGUF files with optional pattern matching. Prioritises
        multi-part files (00001-of-*) over single files for proper handling
        of large models split across multiple files.

        Returns:
            List of GGUF file paths, sorted with multi-part files first.
        """
        if pattern:
            gguf_files = list(model_path.glob(f"*{pattern}*.gguf"))
        else:
            gguf_files = list(model_path.glob("*.gguf"))

        # Sort to prioritise 00001-of-* files
        gguf_files.sort(
            key=lambda x: (
                "00001-of-" not in x.name,  # False sorts before True
                x.name,
            )
        )

        return gguf_files

    @staticmethod
    def ensure_directory(path: Path) -> Path:
        """Ensure directory exists, creating if necessary.

        Creates directory and all parent directories if they don't exist.
        Returns the path for method chaining convenience.

        Returns:
            The directory path.
        """
        path.mkdir(parents=True, exist_ok=True)
        return path

    @staticmethod
    def cleanup_directory(path: Path, pattern: str = "*") -> int:
        """Remove files matching pattern from directory.

        Safely removes files matching the specified glob pattern. Returns
        count of files removed for logging purposes.

        Returns:
            Number of files removed.
        """
        if not path.exists():
            return 0

        files_removed = 0
        for file_path in path.glob(pattern):
            if file_path.is_file():
                try:
                    file_path.unlink()
                    files_removed += 1
                except Exception as e:
                    logger.warning(f"Failed to remove {file_path}: {e}")

        return files_removed