"""Personal Access Token (PAT) credentials for programmatic API access.

Tokens are ``dfp_`` + base62(32 CSPRNG bytes), shown exactly once in the
create response and persisted only as a SHA-256 digest. Validation is a
digest-indexed lookup plus a constant-time re-comparison, with a single
generic failure surface so a 401 never reveals which check failed.

v1 scopes are exactly the route-permission strings owned by
``app.gateway.authz`` — a PAT can only narrow its owning user's
permissions, never widen them.
"""

from __future__ import annotations

import functools
import hashlib
import hmac
import re
import secrets
from typing import Any

PAT_TOKEN_PREFIX = "dfp_"
PAT_RANDOM_BYTES = 32
# Best-effort ``last_used_at`` writes are throttled per token so high-volume
# automation does not turn every request into a database write.
PAT_LAST_USED_WRITE_INTERVAL_SECONDS = 300.0

PAT_ALLOWED_SCOPES: frozenset[str] = frozenset(
    {
        "threads:read",
        "threads:write",
        "threads:delete",
        "runs:create",
        "runs:read",
        "runs:cancel",
        "projects:read",
        "projects:write",
        "projects:delete",
    }
)

PAT_MAX_NAME_LENGTH = 128

# Default-deny route boundary for PAT callers (#5041 review P1-1): scope
# intersection in AuthMiddleware only constrains routes that consult
# ``request.state.auth.permissions`` (``@require_permission``). Authenticated
# mutation routes without that decorator — memory deletion, agent creation,
# credential switching, channel configuration — would otherwise accept a
# PAT holding a single read scope. A route is reachable by PAT only when it
# is explicitly listed here, and only together with the thread/run lifecycle
# the v1 scopes govern; everything else answers 403 regardless of scopes.
_PAT_ROUTE_RULES: tuple[tuple[frozenset[str], re.Pattern[str]], ...] = (
    (frozenset({"POST"}), re.compile(r"^/api/threads$")),
    (frozenset({"POST"}), re.compile(r"^/api/threads/search$")),
    (frozenset({"GET", "PATCH", "DELETE"}), re.compile(r"^/api/threads/[^/]+$")),
    (frozenset({"GET", "PUT", "DELETE"}), re.compile(r"^/api/threads/[^/]+/goal$")),
    (frozenset({"GET", "POST"}), re.compile(r"^/api/threads/[^/]+/state$")),
    (frozenset({"POST"}), re.compile(r"^/api/threads/[^/]+/(compact|history|branches)$")),
    (frozenset({"POST"}), re.compile(r"^/api/threads/[^/]+/move$")),
    # Projects subtree: same enumerated-no-dead-methods precision as the
    # threads/runs rules — only the methods the projects router implements
    # are admitted, so a future projects route is default-denied until
    # explicitly listed. Scope narrowing (projects:read|write|delete and
    # threads:write for move) stays enforced by ``@require_permission``.
    (frozenset({"GET", "POST"}), re.compile(r"^/api/projects$")),
    (frozenset({"GET", "PATCH", "DELETE"}), re.compile(r"^/api/projects/[^/]+$")),
    (frozenset({"POST"}), re.compile(r"^/api/projects/[^/]+/(archive|restore)$")),
    (frozenset({"GET"}), re.compile(r"^/api/projects/[^/]+/threads$")),
    # Runs subtree: enumerated per implemented subroute instead of a
    # ``runs(/.*)?`` wildcard, so a route added under /runs is default-denied
    # until explicitly listed — the same no-dead-methods precision the
    # threads collection rule enforces. The ``{run_id}`` slot necessarily
    # matches any single segment; the POST-only collection endpoints sharing
    # that depth (stream, wait, regenerate, edit-regenerate) are excluded
    # from the GET run-id rule so no unimplemented method is pre-authorized.
    (frozenset({"GET", "POST"}), re.compile(r"^/api/threads/[^/]+/runs$")),
    (
        frozenset({"POST"}),
        re.compile(r"^/api/threads/[^/]+/runs/(stream|wait|regenerate/prepare|edit-regenerate/prepare)$"),
    ),
    (
        frozenset({"GET"}),
        re.compile(r"^/api/threads/[^/]+/runs/(?!stream$|wait$|regenerate$|edit-regenerate$)[^/]+$"),
    ),
    (frozenset({"POST"}), re.compile(r"^/api/threads/[^/]+/runs/[^/]+/cancel$")),
    (
        frozenset({"GET"}),
        re.compile(r"^/api/threads/[^/]+/runs/[^/]+/(join|messages|events|workspace-changes)$"),
    ),
    (frozenset({"GET", "POST"}), re.compile(r"^/api/threads/[^/]+/runs/[^/]+/artifacts/archive$")),
    (frozenset({"GET", "POST"}), re.compile(r"^/api/threads/[^/]+/runs/[^/]+/stream$")),
    (frozenset({"POST"}), re.compile(r"^/api/runs/(stream|wait)$")),
    (frozenset({"GET"}), re.compile(r"^/api/runs/[^/]+/(messages|feedback)$")),
)

_BASE62_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"


def is_pat_allowed_route(method: str, path: str) -> bool:
    """Return whether the PAT route policy admits *method* + *path*.

    Trailing slashes are normalized away so the mounted route and its
    redirect-style twin resolve identically.
    """
    normalized = path.rstrip("/") or "/"
    return any(method in methods and pattern.match(normalized) for methods, pattern in _PAT_ROUTE_RULES)


@functools.cache
def _base62_width(byte_length: int) -> int:
    """Digits sufficient for any *byte_length*-byte value (exact integer math)."""
    width = 1
    limit = 1 << (8 * byte_length)
    while 62**width < limit:
        width += 1
    return width


def _base62(data: bytes) -> str:
    """Fixed-width big-endian base62 of *data*, ``0``-padded on the left.

    ``int.from_bytes`` discards leading zero bytes, so an unpadded encoding
    would be variable-length (and empty for all-zero input) — any draw below
    62**39 would have produced a shorter-than-expected token. The fixed width
    keeps every token body exactly ``_base62_width(len(data))`` characters
    and makes the format test deterministic.
    """
    value = int.from_bytes(data, "big")
    digits: list[str] = []
    while value:
        value, remainder = divmod(value, 62)
        digits.append(_BASE62_ALPHABET[remainder])
    body = "".join(reversed(digits))
    return body.rjust(_base62_width(len(data)), "0")


def generate_pat_token() -> str:
    """Generate a show-once raw token: ``dfp_`` + base62(CSPRNG bytes)."""
    return PAT_TOKEN_PREFIX + _base62(secrets.token_bytes(PAT_RANDOM_BYTES))


def pat_token_digest(token: str) -> str:
    """Return the hex SHA-256 digest persisted for *token*."""
    return hashlib.sha256(token.encode("utf-8")).hexdigest()


def digest_matches(stored_digest: str | None, token: str) -> bool:
    """Constant-time comparison of *token* against a stored digest."""
    if not isinstance(stored_digest, str) or not stored_digest:
        return False
    return hmac.compare_digest(stored_digest, pat_token_digest(token))


def extract_bearer_token(authorization: str | None) -> str | None:
    """Return the Bearer credential from an Authorization header value.

    ``None`` means the request carries no Authorization header at all, so the
    caller should fall through to the session-cookie path. Any other unusable
    value (non-Bearer scheme, empty credential) returns ``""`` so callers
    treat it as an invalid credential rather than an absent one.
    """
    if authorization is None:
        return None
    scheme, _, value = authorization.partition(" ")
    if scheme.lower() != "bearer":
        return ""
    return value.strip()


async def authenticate_pat(app: Any, authorization: str | None) -> tuple[Any, frozenset[str]]:
    """Validate the Bearer credential and resolve its owning user.

    Returns ``(user, scopes)``. Every token-verdict failure mode — malformed
    token, unknown/revoked/expired token, PAT store not configured, missing
    owning user — raises the same generic 401 so responses cannot serve as an
    oracle on which check failed. Infrastructure errors (store I/O failures)
    propagate and fail closed; they are not part of the token verdict.
    """
    from fastapi import HTTPException

    token = extract_bearer_token(authorization)
    if not token or not token.startswith(PAT_TOKEN_PREFIX):
        raise HTTPException(status_code=401, detail="Invalid token")
    pat_repo = getattr(app.state, "pat_repo", None)
    if pat_repo is None:
        raise HTTPException(status_code=401, detail="Invalid token")
    record = await pat_repo.get_active_by_digest(pat_token_digest(token))
    if record is None or not digest_matches(record.get("token_digest"), token):
        raise HTTPException(status_code=401, detail="Invalid token")
    from app.gateway.deps import get_local_provider

    user = await get_local_provider().get_user(str(record["user_id"]))
    if user is None:
        # The owning user was deleted or became unresolvable; the token is
        # dead even though its row survives (deleting a user revokes their
        # PATs, without needing a FK cascade).
        raise HTTPException(status_code=401, detail="Invalid token")
    await pat_repo.touch_last_used(str(record["id"]))
    return user, frozenset(record.get("scopes") or ())


def validate_scopes(scopes: list[str]) -> list[str]:
    """Validate a creation-time scope list; returns the deduplicated order."""
    unknown = sorted(set(scopes) - PAT_ALLOWED_SCOPES)
    if unknown:
        raise ValueError(f"Unknown PAT scopes: {', '.join(unknown)}")
    deduplicated = sorted(set(scopes))
    if not deduplicated:
        raise ValueError("A PAT must request at least one scope")
    return deduplicated