from __future__ import annotations

from dataclasses import dataclass
from pathlib import Path

from backend.app.api.errors import AppError


@dataclass(frozen=True)
class ResolvedPath:
    alias: str
    relative: str
    absolute: Path


class PathGuard:
    def __init__(self, root_aliases: dict[str, str]):
        normalized: dict[str, Path] = {}
        for alias, root in root_aliases.items():
            normalized[alias] = Path(root).resolve()
        self._roots = normalized

    def resolve_directory_path(self, input_path: str) -> ResolvedPath:
        resolved = self.resolve_path(input_path)
        if not resolved.absolute.exists():
            raise AppError(
                code="path_not_found",
                message="Requested path was not found",
                status_code=404,
                details={"path": input_path},
            )
        if not resolved.absolute.is_dir():
            raise AppError(
                code="path_type_conflict",
                message="Requested path is not a directory",
                status_code=409,
                details={"path": input_path},
            )
        return resolved

    def resolve_existing_path(self, input_path: str) -> ResolvedPath:
        resolved = self.resolve_path(input_path)
        if not resolved.absolute.exists():
            raise AppError(
                code="path_not_found",
                message="Requested path was not found",
                status_code=404,
                details={"path": input_path},
            )
        return resolved

    def resolve_path(self, input_path: str) -> ResolvedPath:
        alias, rel_segments, candidate = self.resolve_lexical_path(input_path)
        root = self._roots[alias]

        # Resolve symlinks for existing prefixes; for not-yet-existing tails strict=False keeps
        # path normalization while still enabling containment check.
        resolved_candidate = candidate.resolve(strict=False)
        if not self._is_under_root(resolved_candidate, root):
            raise AppError(
                code="path_outside_whitelist",
                message="Requested path is outside allowed roots",
                status_code=403,
                details={"path": input_path},
            )

        return ResolvedPath(
            alias=alias,
            relative=self._format_relative(alias, rel_segments),
            absolute=resolved_candidate,
        )

    def resolve_lexical_path(self, input_path: str) -> tuple[str, list[str], Path]:
        normalized_input = (input_path or "").strip().strip("/")
        if not normalized_input:
            raise AppError(
                code="invalid_request",
                message="Query parameter 'path' is required",
                status_code=400,
            )

        segments = [seg for seg in normalized_input.split("/") if seg]
        alias = segments[0] if segments else ""
        if alias not in self._roots:
            raise AppError(
                code="invalid_root_alias",
                message="Unknown root alias",
                status_code=403,
                details={"path": input_path},
            )

        rel_segments = segments[1:]
        if any(seg == ".." for seg in rel_segments):
            raise AppError(
                code="path_traversal_detected",
                message="Path traversal is not allowed",
                status_code=403,
                details={"path": input_path},
            )

        root = self._roots[alias]
        candidate = root.joinpath(*rel_segments)
        return alias, rel_segments, candidate

    def validate_name(self, name: str, field: str) -> str:
        normalized = (name or "").strip()
        if not normalized or normalized in {".", ".."} or "/" in normalized or "\\" in normalized:
            raise AppError(
                code="invalid_request",
                message="Invalid name",
                status_code=400,
                details={field: name},
            )
        return normalized

    def entry_relative_path(self, alias: str, absolute: Path) -> str:
        root = self._roots[alias]
        resolved_absolute = absolute.resolve(strict=False)
        if not self._is_under_root(resolved_absolute, root):
            raise AppError(
                code="symlink_escape_detected",
                message="Entry resolves outside allowed root",
                status_code=403,
                details={"path": f"{alias}"},
            )
        rel = resolved_absolute.relative_to(root).as_posix()
        return self._format_relative(alias, [p for p in rel.split("/") if p])

    @staticmethod
    def _is_under_root(path: Path, root: Path) -> bool:
        try:
            path.relative_to(root)
            return True
        except ValueError:
            return False

    @staticmethod
    def _format_relative(alias: str, rel_segments: list[str]) -> str:
        return alias if not rel_segments else f"{alias}/{'/'.join(rel_segments)}"