import os
import re
from pathlib import Path

# Virtual path prefix seen by agents inside the sandbox
VIRTUAL_PATH_PREFIX = "/mnt/user-data"

_SAFE_THREAD_ID_RE = re.compile(r"^[A-Za-z0-9_\-]+$")


class Paths:
    """
    Centralized path configuration for DeerFlow application data.

    Directory layout (host side):
        {base_dir}/
        ├── memory.json
        ├── USER.md          <-- global user profile (injected into all agents)
        ├── agents/
        │   └── {agent_name}/
        │       ├── config.yaml
        │       ├── SOUL.md  <-- agent personality/identity (injected alongside lead prompt)
        │       └── memory.json
        └── threads/
            └── {thread_id}/
                └── user-data/         <-- mounted as /mnt/user-data/ inside sandbox
                    ├── workspace/     <-- /mnt/user-data/workspace/
                    ├── uploads/       <-- /mnt/user-data/uploads/
                    └── outputs/       <-- /mnt/user-data/outputs/

    BaseDir resolution (in priority order):
        1. Constructor argument `base_dir`
        2. DEER_FLOW_HOME environment variable
        3. Local dev fallback: cwd/.deer-flow  (when cwd is the backend/ dir)
        4. Default: $HOME/.deer-flow
    """

    def __init__(self, base_dir: str | Path | None = None) -> None:
        self._base_dir = Path(base_dir).resolve() if base_dir is not None else None

    @property
    def base_dir(self) -> Path:
        """Root directory for all application data."""
        if self._base_dir is not None:
            return self._base_dir

        if env_home := os.getenv("DEER_FLOW_HOME"):
            return Path(env_home).resolve()

        cwd = Path.cwd()
        if cwd.name == "backend" or (cwd / "pyproject.toml").exists():
            return cwd / ".deer-flow"

        return Path.home() / ".deer-flow"

    @property
    def memory_file(self) -> Path:
        """Path to the persisted memory file: `{base_dir}/memory.json`."""
        return self.base_dir / "memory.json"

    @property
    def user_md_file(self) -> Path:
        """Path to the global user profile file: `{base_dir}/USER.md`."""
        return self.base_dir / "USER.md"

    @property
    def agents_dir(self) -> Path:
        """Root directory for all custom agents: `{base_dir}/agents/`."""
        return self.base_dir / "agents"

    def agent_dir(self, name: str) -> Path:
        """Directory for a specific agent: `{base_dir}/agents/{name}/`."""
        return self.agents_dir / name.lower()

    def agent_memory_file(self, name: str) -> Path:
        """Per-agent memory file: `{base_dir}/agents/{name}/memory.json`."""
        return self.agent_dir(name) / "memory.json"

    def thread_dir(self, thread_id: str) -> Path:
        """
        Host path for a thread's data: `{base_dir}/threads/{thread_id}/`

        This directory contains a `user-data/` subdirectory that is mounted
        as `/mnt/user-data/` inside the sandbox.

        Raises:
            ValueError: If `thread_id` contains unsafe characters (path separators
                        or `..`) that could cause directory traversal.
        """
        if not _SAFE_THREAD_ID_RE.match(thread_id):
            raise ValueError(f"Invalid thread_id {thread_id!r}: only alphanumeric characters, hyphens, and underscores are allowed.")
        return self.base_dir / "threads" / thread_id

    def sandbox_work_dir(self, thread_id: str) -> Path:
        """
        Host path for the agent's workspace directory.
        Host: `{base_dir}/threads/{thread_id}/user-data/workspace/`
        Sandbox: `/mnt/user-data/workspace/`
        """
        return self.thread_dir(thread_id) / "user-data" / "workspace"

    def sandbox_uploads_dir(self, thread_id: str) -> Path:
        """
        Host path for user-uploaded files.
        Host: `{base_dir}/threads/{thread_id}/user-data/uploads/`
        Sandbox: `/mnt/user-data/uploads/`
        """
        return self.thread_dir(thread_id) / "user-data" / "uploads"

    def sandbox_outputs_dir(self, thread_id: str) -> Path:
        """
        Host path for agent-generated artifacts.
        Host: `{base_dir}/threads/{thread_id}/user-data/outputs/`
        Sandbox: `/mnt/user-data/outputs/`
        """
        return self.thread_dir(thread_id) / "user-data" / "outputs"

    def sandbox_user_data_dir(self, thread_id: str) -> Path:
        """
        Host path for the user-data root.
        Host: `{base_dir}/threads/{thread_id}/user-data/`
        Sandbox: `/mnt/user-data/`
        """
        return self.thread_dir(thread_id) / "user-data"

    def ensure_thread_dirs(self, thread_id: str) -> None:
        """Create all standard sandbox directories for a thread."""
        self.sandbox_work_dir(thread_id).mkdir(parents=True, exist_ok=True)
        self.sandbox_uploads_dir(thread_id).mkdir(parents=True, exist_ok=True)
        self.sandbox_outputs_dir(thread_id).mkdir(parents=True, exist_ok=True)

    def resolve_virtual_path(self, thread_id: str, virtual_path: str) -> Path:
        """Resolve a sandbox virtual path to the actual host filesystem path.

        Args:
            thread_id: The thread ID.
            virtual_path: Virtual path as seen inside the sandbox, e.g.
                          ``/mnt/user-data/outputs/report.pdf``.
                          Leading slashes are stripped before matching.

        Returns:
            The resolved absolute host filesystem path.

        Raises:
            ValueError: If the path does not start with the expected virtual
                        prefix or a path-traversal attempt is detected.
        """
        stripped = virtual_path.lstrip("/")
        prefix = VIRTUAL_PATH_PREFIX.lstrip("/")

        # Require an exact segment-boundary match to avoid prefix confusion
        # (e.g. reject paths like "mnt/user-dataX/...").
        if stripped != prefix and not stripped.startswith(prefix + "/"):
            raise ValueError(f"Path must start with /{prefix}")

        relative = stripped[len(prefix) :].lstrip("/")
        base = self.sandbox_user_data_dir(thread_id).resolve()
        actual = (base / relative).resolve()

        try:
            actual.relative_to(base)
        except ValueError:
            raise ValueError("Access denied: path traversal detected")

        return actual


# ── Singleton ────────────────────────────────────────────────────────────

_paths: Paths | None = None


def get_paths() -> Paths:
    """Return the global Paths singleton (lazy-initialized)."""
    global _paths
    if _paths is None:
        _paths = Paths()
    return _paths


def resolve_path(path: str) -> Path:
    """Resolve *path* to an absolute ``Path``.

    Relative paths are resolved relative to the application base directory.
    Absolute paths are returned as-is (after normalisation).
    """
    p = Path(path)
    if not p.is_absolute():
        p = get_paths().base_dir / path
    return p.resolve()