"""File discovery and module import utilities for filesystem-based routing.

This module provides functions to:
1. Discover Python files in a directory tree
2. Import modules (as packages if __init__.py exists, else directly)
3. Extract decorated components (Tool, Resource, Prompt objects) from imported modules
"""

from __future__ import annotations

import importlib.util
import sys
from dataclasses import dataclass, field
from pathlib import Path
from types import ModuleType

from fastmcp.utilities.components import FastMCPComponent
from fastmcp.utilities.logging import get_logger

logger = get_logger(__name__)


@dataclass
class DiscoveryResult:
    """Result of filesystem discovery."""

    # Components are real objects (Tool, Resource, ResourceTemplate, Prompt)
    components: list[tuple[Path, FastMCPComponent]] = field(default_factory=list)
    failed_files: dict[Path, str] = field(default_factory=dict)  # path -> error message


def discover_files(root: Path) -> list[Path]:
    """Recursively discover all Python files under a directory.

    Excludes __init__.py files (they're for package structure, not components).

    Args:
        root: Root directory to scan.

    Returns:
        List of .py file paths, sorted for deterministic order.
    """
    if not root.exists():
        return []

    if not root.is_dir():
        # If root is a file, just return it (if it's a .py file)
        if root.suffix == ".py" and root.name != "__init__.py":
            return [root]
        return []

    files: list[Path] = []
    for path in root.rglob("*.py"):
        # Skip __init__.py files
        if path.name == "__init__.py":
            continue
        # Skip __pycache__ directories
        if "__pycache__" in path.parts:
            continue
        files.append(path)

    # Sort for deterministic discovery order
    return sorted(files)


def _is_package_dir(directory: Path) -> bool:
    """Check if a directory is a Python package (has __init__.py)."""
    return (directory / "__init__.py").exists()


def _find_package_root(file_path: Path) -> Path | None:
    """Find the root of the package containing this file.

    Walks up the directory tree until we find a directory without __init__.py.

    Returns:
        The package root directory, or None if not in a package.
    """
    current = file_path.parent
    package_root = None

    while current != current.parent:  # Stop at filesystem root
        if _is_package_dir(current):
            package_root = current
            current = current.parent
        else:
            break

    return package_root


def _compute_module_name(file_path: Path, package_root: Path) -> str:
    """Compute the dotted module name for a file within a package.

    Args:
        file_path: Path to the Python file.
        package_root: Root directory of the package.

    Returns:
        Dotted module name (e.g., "mcp.tools.greet").
    """
    relative = file_path.relative_to(package_root.parent)
    parts = list(relative.parts)
    # Remove .py extension from last part
    parts[-1] = parts[-1].removesuffix(".py")
    return ".".join(parts)


def import_module_from_file(file_path: Path) -> ModuleType:
    """Import a Python file as a module.

    If the file is part of a package (directory has __init__.py), imports
    it as a proper package member (relative imports work). Otherwise,
    imports directly using spec_from_file_location.

    Args:
        file_path: Path to the Python file.

    Returns:
        The imported module.

    Raises:
        ImportError: If the module cannot be imported.
    """
    file_path = file_path.resolve()

    # Check if this file is part of a package
    package_root = _find_package_root(file_path)

    if package_root is not None:
        # Import as part of a package
        module_name = _compute_module_name(file_path, package_root)

        # Ensure package root's parent is in sys.path
        package_parent = str(package_root.parent)
        if package_parent not in sys.path:
            sys.path.insert(0, package_parent)

        # Import using standard import machinery
        # If already imported, reload to pick up changes (for reload mode)
        try:
            if module_name in sys.modules:
                return importlib.reload(sys.modules[module_name])
            return importlib.import_module(module_name)
        except ImportError as e:
            raise ImportError(
                f"Failed to import {module_name} from {file_path}: {e}"
            ) from e
    else:
        # Import directly using spec_from_file_location
        module_name = file_path.stem

        # Ensure parent directory is in sys.path for imports
        parent_dir = str(file_path.parent)
        if parent_dir not in sys.path:
            sys.path.insert(0, parent_dir)

        spec = importlib.util.spec_from_file_location(module_name, file_path)
        if spec is None or spec.loader is None:
            raise ImportError(f"Cannot load spec for {file_path}")

        module = importlib.util.module_from_spec(spec)
        sys.modules[module_name] = module

        try:
            spec.loader.exec_module(module)
        except Exception as e:
            # Clean up sys.modules on failure
            sys.modules.pop(module_name, None)
            raise ImportError(f"Failed to execute module {file_path}: {e}") from e

        return module


def extract_components(module: ModuleType) -> list[FastMCPComponent]:
    """Extract all MCP components from a module.

    Scans all module attributes for instances of Tool, Resource,
    ResourceTemplate, or Prompt objects created by standalone decorators,
    or functions decorated with @tool/@resource/@prompt that have __fastmcp__ metadata.

    Args:
        module: The imported module to scan.

    Returns:
        List of component objects (Tool, Resource, ResourceTemplate, Prompt).
    """
    # Import here to avoid circular imports
    import inspect

    from fastmcp.decorators import get_fastmcp_meta
    from fastmcp.prompts.function_prompt import PromptMeta
    from fastmcp.prompts.prompt import Prompt
    from fastmcp.resources.function_resource import ResourceMeta
    from fastmcp.resources.resource import Resource
    from fastmcp.resources.template import ResourceTemplate
    from fastmcp.server.dependencies import without_injected_parameters
    from fastmcp.tools.function_tool import ToolMeta
    from fastmcp.tools.tool import Tool

    component_types = (Tool, Resource, ResourceTemplate, Prompt)
    components: list[FastMCPComponent] = []

    for name in dir(module):
        # Skip private/magic attributes
        if name.startswith("_"):
            continue

        try:
            obj = getattr(module, name)
        except AttributeError:
            continue

        # Check if this object is a component type
        if isinstance(obj, component_types):
            components.append(obj)
            continue

        # Check for functions with __fastmcp__ metadata
        meta = get_fastmcp_meta(obj)
        if meta is not None:
            if isinstance(meta, ToolMeta):
                resolved_task = meta.task if meta.task is not None else False
                tool = Tool.from_function(
                    obj,
                    name=meta.name,
                    title=meta.title,
                    description=meta.description,
                    icons=meta.icons,
                    tags=meta.tags,
                    output_schema=meta.output_schema,
                    annotations=meta.annotations,
                    meta=meta.meta,
                    task=resolved_task,
                    exclude_args=meta.exclude_args,
                    serializer=meta.serializer,
                    auth=meta.auth,
                )
                components.append(tool)
            elif isinstance(meta, ResourceMeta):
                resolved_task = meta.task if meta.task is not None else False
                has_uri_params = "{" in meta.uri and "}" in meta.uri
                wrapper_fn = without_injected_parameters(obj)
                has_func_params = bool(inspect.signature(wrapper_fn).parameters)

                if has_uri_params or has_func_params:
                    resource = ResourceTemplate.from_function(
                        fn=obj,
                        uri_template=meta.uri,
                        name=meta.name,
                        title=meta.title,
                        description=meta.description,
                        icons=meta.icons,
                        mime_type=meta.mime_type,
                        tags=meta.tags,
                        annotations=meta.annotations,
                        meta=meta.meta,
                        task=resolved_task,
                        auth=meta.auth,
                    )
                else:
                    resource = Resource.from_function(
                        fn=obj,
                        uri=meta.uri,
                        name=meta.name,
                        title=meta.title,
                        description=meta.description,
                        icons=meta.icons,
                        mime_type=meta.mime_type,
                        tags=meta.tags,
                        annotations=meta.annotations,
                        meta=meta.meta,
                        task=resolved_task,
                        auth=meta.auth,
                    )
                components.append(resource)
            elif isinstance(meta, PromptMeta):
                resolved_task = meta.task if meta.task is not None else False
                prompt = Prompt.from_function(
                    obj,
                    name=meta.name,
                    title=meta.title,
                    description=meta.description,
                    icons=meta.icons,
                    tags=meta.tags,
                    meta=meta.meta,
                    task=resolved_task,
                    auth=meta.auth,
                )
                components.append(prompt)

    return components


def discover_and_import(root: Path) -> DiscoveryResult:
    """Discover files, import modules, and extract components.

    This is the main entry point for filesystem-based discovery.

    Args:
        root: Root directory to scan.

    Returns:
        DiscoveryResult with components and any failed files.

    Note:
        Files that fail to import are tracked in failed_files, not logged.
        The caller is responsible for logging/handling failures.
        Files with no components are silently skipped.
    """
    result = DiscoveryResult()

    for file_path in discover_files(root):
        try:
            module = import_module_from_file(file_path)
        except ImportError as e:
            result.failed_files[file_path] = str(e)
            continue
        except Exception as e:
            result.failed_files[file_path] = str(e)
            continue

        components = extract_components(module)
        for component in components:
            result.components.append((file_path, component))

    return result