oikos/oikos/approve.py

#!/usr/bin/env python3
"""oikos/approve.py — the approval engine (escalate route of the OODA loop).

Repo-side half of the Week-3 approval flow. This module owns the request/
grant lifecycle and the HMAC signing; it does NOT talk to Matrix directly.
There is no dedicated Matrix bot in this homelab — alerts already go out
as the operator's own Hermes agent posting to @dtoro:avispero (see
infrastructure/monitoring.md's homelab-health-watchdog). The integration
contract is:

  1. An agent or the Week-3 scheduler calls `request()` (or the CLI
     `request` subcommand) to open an approval. This prints the Matrix-
     ready message text (evidence, options, reply format).
  2. Hermes posts that text to Matrix using its existing send capability
     (the same one homelab-health-watchdog already uses) and later reads
     the operator's reply/reaction.
  3. Hermes calls back `reply()` (or `oikos/approve.py reply <id>
     approve|deny`) with the operator's decision. This module verifies
     `requires_phrase` for destructive actions, then issues a short-TTL
     HMAC-signed grant.
  4. Mutating `homelab` commands call `check_grant()` before executing a
     config_mutation/destructive action.

Storage: approvals/<YYYY-MM>.jsonl, same append-only-JSONL-with-latest-
state-wins convention as oikos/signal.py.

Grant signing key: secrets/oikos-approval-hmac.yaml (SOPS, recipients:
apps + hubris — see .sops.yaml). Decrypted on demand; never cached to
disk in plaintext.
"""

from __future__ import annotations

import hashlib
import hmac
import json
import os
import subprocess
import sys
from datetime import datetime, timedelta, timezone
from functools import lru_cache
from pathlib import Path

import yaml

REPO = Path(__file__).resolve().parent.parent
APPROVALS_DIR = REPO / "approvals"
HMAC_SECRET = REPO / "secrets" / "oikos-approval-hmac.yaml"
AGE_KEY = Path(os.environ.get("SOPS_AGE_KEY_FILE", "/etc/age/key.txt"))

VALID_STATES = ("pending", "approved", "denied", "expired")
REQUEST_TTL_HOURS = 24
GRANT_TTL_MINUTES = 15


def _month_path(dt: datetime | None = None) -> Path:
    dt = dt or datetime.now(timezone.utc)
    return APPROVALS_DIR / f"{dt.strftime('%Y-%m')}.jsonl"


def _all_entries() -> list[dict]:
    if not APPROVALS_DIR.exists():
        return []
    out = []
    for path in sorted(APPROVALS_DIR.glob("*.jsonl")):
        for line in path.read_text().splitlines():
            if not line.strip():
                continue
            try:
                out.append(json.loads(line))
            except json.JSONDecodeError:
                continue
    return out


def _next_id(dt: datetime | None = None) -> str:
    dt = dt or datetime.now(timezone.utc)
    prefix = f"appr-{dt.strftime('%Y-%m-%d')}-"
    existing = [e["id"] for e in _all_entries() if e.get("id", "").startswith(prefix)]
    n = 1
    while f"{prefix}{n:04d}" in existing:
        n += 1
    return f"{prefix}{n:04d}"


def _append(entry: dict) -> dict:
    APPROVALS_DIR.mkdir(exist_ok=True)
    entry = {k: v for k, v in entry.items() if v is not None}
    with _month_path().open("a") as f:
        f.write(json.dumps(entry, sort_keys=False) + "\n")
    return entry


def current(request_id: str) -> dict | None:
    matches = [e for e in _all_entries() if e.get("id") == request_id]
    if not matches:
        return None
    matches.sort(key=lambda e: e.get("ts", ""))
    return matches[-1]


def list_approvals(state: str | None = None) -> list[dict]:
    latest: dict[str, dict] = {}
    for e in sorted(_all_entries(), key=lambda e: e.get("ts", "")):
        rid = e.get("id")
        if rid:
            latest[rid] = e
    now = datetime.now(timezone.utc).isoformat(timespec="seconds")
    out = []
    for e in latest.values():
        if e.get("state") == "pending" and e.get("expires_at") and e["expires_at"] < now:
            e = {**e, "state": "expired"}
        if state and e.get("state") != state:
            continue
        out.append(e)
    out.sort(key=lambda e: e.get("ts", ""), reverse=True)
    return out


def _matrix_message(entry: dict) -> str:
    lines = [
        f"[Oikos approval {entry['id']}] {entry['entity']} — {entry['action']}",
        f"risk: {entry['risk']}",
        f"evidence: {entry['evidence']}",
    ]
    if entry.get("verification"):
        lines.append(f"verification: {entry['verification']}")
    if entry.get("requires_phrase"):
        lines.append(f'reply: "approve {entry["id"]} {entry["confirmation_phrase"]}" or "deny {entry["id"]}"')
    else:
        lines.append(f'reply: ✅ to approve, ❌ to deny (or "approve {entry["id"]}" / "deny {entry["id"]}")')
    return "\n".join(lines)


def request(entity: str, action: str, risk: str, evidence: str, *,
            verification: str | None = None, signal_id: str | None = None,
            requires_phrase: bool = False, requested_by: str | None = None,
            ttl_hours: int = REQUEST_TTL_HOURS) -> dict:
    """Open a new approval request. `requires_phrase=True` (use for
    `destructive`-class actions per oikos/policy.yaml) generates a
    confirmation phrase the operator must echo back — a reaction alone
    can't authorize it."""
    rid = _next_id()
    now = datetime.now(timezone.utc)
    phrase = f"{action} {entity}" if requires_phrase else None
    entry = {
        "id": rid,
        "ts": now.isoformat(timespec="seconds"),
        "entity": entity,
        "action": action,
        "risk": risk,
        "evidence": evidence,
        "verification": verification,
        "signal_id": signal_id,
        "requires_phrase": requires_phrase,
        "confirmation_phrase": phrase,
        "requested_by": requested_by or os.environ.get("HOMELAB_AGENT_ID"),
        "state": "pending",
        "expires_at": (now + timedelta(hours=ttl_hours)).isoformat(timespec="seconds"),
    }
    recorded = _append(entry)
    recorded["matrix_message"] = _matrix_message(recorded)
    return recorded


@lru_cache(maxsize=1)
def _hmac_key() -> str:
    if not HMAC_SECRET.exists():
        raise RuntimeError(f"no secret at {HMAC_SECRET} — has it been provisioned?")
    env = {**os.environ}
    if AGE_KEY.exists():
        env["SOPS_AGE_KEY_FILE"] = str(AGE_KEY)
    proc = subprocess.run(["sops", "-d", str(HMAC_SECRET)],
                          capture_output=True, text=True, env=env)
    if proc.returncode != 0:
        raise RuntimeError(
            f"sops decrypt of oikos-approval-hmac failed (is this host a recipient?): "
            f"{proc.stderr.strip()}")
    return yaml.safe_load(proc.stdout)["hmac_key"]


def _sign(request_id: str, entity: str, action: str, expires_at: str) -> str:
    key = _hmac_key().encode()
    msg = f"{request_id}:{entity}:{action}:{expires_at}".encode()
    return hmac.new(key, msg, hashlib.sha256).hexdigest()


def reply(request_id: str, decision: str, *, phrase: str | None = None,
          decided_by: str | None = None) -> dict:
    """Record the operator's decision. On approval, issues a short-TTL
    HMAC-signed grant token. Raises ValueError if a required confirmation
    phrase is missing or wrong, or if the request already expired."""
    if decision not in ("approve", "deny"):
        raise ValueError("decision must be 'approve' or 'deny'")
    entry = current(request_id)
    if entry is None:
        raise ValueError(f"unknown approval id: {request_id}")
    if entry.get("state") != "pending":
        raise ValueError(f"{request_id} is not pending (state={entry.get('state')})")
    now_s = datetime.now(timezone.utc).isoformat(timespec="seconds")
    if entry.get("expires_at") and entry["expires_at"] < now_s:
        _append({**entry, "ts": now_s, "state": "expired"})
        raise ValueError(f"{request_id} expired at {entry['expires_at']}")

    if decision == "deny":
        return _append({**entry, "ts": now_s, "state": "denied", "decided_by": decided_by})

    if entry.get("requires_phrase"):
        if phrase != entry.get("confirmation_phrase"):
            raise ValueError(
                "confirmation phrase missing or incorrect — a reaction alone "
                "cannot approve a destructive action")

    grant_expires = (datetime.now(timezone.utc) + timedelta(minutes=GRANT_TTL_MINUTES)) \
        .isoformat(timespec="seconds")
    grant_token = _sign(request_id, entry["entity"], entry["action"], grant_expires)
    return _append({**entry, "ts": now_s, "state": "approved", "decided_by": decided_by,
                    "grant_token": grant_token, "grant_expires": grant_expires})


def check_grant(request_id: str, entity: str, action: str) -> tuple[bool, str]:
    """Verify a request carries a valid, unexpired, matching grant. Returns
    (ok, reason). Callers (homelab CLI mutating commands) must call this
    immediately before executing — grants are single-use in spirit (the
    60/90-day backlog adds exact command+target binding + replay
    prevention; today re-checking the same still-valid grant twice is
    possible, so keep grant TTLs short)."""
    entry = current(request_id)
    if entry is None:
        return False, "unknown approval id"
    if entry.get("state") != "approved":
        return False, f"not approved (state={entry.get('state')})"
    if entry.get("entity") != entity or entry.get("action") != action:
        return False, "grant does not match entity/action"
    now_s = datetime.now(timezone.utc).isoformat(timespec="seconds")
    if not entry.get("grant_expires") or entry["grant_expires"] < now_s:
        return False, "grant expired"
    expected = _sign(request_id, entity, action, entry["grant_expires"])
    if not hmac.compare_digest(expected, entry.get("grant_token", "")):
        return False, "grant signature invalid"
    return True, "ok"


def main() -> int:
    import argparse
    p = argparse.ArgumentParser(description="oikos approval engine")
    sub = p.add_subparsers(dest="cmd", required=True)

    r = sub.add_parser("request")
    r.add_argument("entity")
    r.add_argument("action")
    r.add_argument("risk")
    r.add_argument("evidence")
    r.add_argument("--verification")
    r.add_argument("--signal-id")
    r.add_argument("--requires-phrase", action="store_true")
    r.add_argument("--ttl-hours", type=int, default=REQUEST_TTL_HOURS)

    ls = sub.add_parser("list")
    ls.add_argument("--state", choices=VALID_STATES)

    rp = sub.add_parser("reply")
    rp.add_argument("id")
    rp.add_argument("decision", choices=["approve", "deny"])
    rp.add_argument("--phrase")
    rp.add_argument("--decided-by")

    ck = sub.add_parser("check")
    ck.add_argument("id")
    ck.add_argument("entity")
    ck.add_argument("action")

    args = p.parse_args()
    if args.cmd == "request":
        entry = request(args.entity, args.action, args.risk, args.evidence,
                        verification=args.verification, signal_id=args.signal_id,
                        requires_phrase=args.requires_phrase, ttl_hours=args.ttl_hours)
        print(json.dumps({k: v for k, v in entry.items() if k != "matrix_message"}, indent=2))
        print()
        print("--- post this to Matrix ---")
        print(entry["matrix_message"])
    elif args.cmd == "list":
        for e in list_approvals(state=args.state):
            print(json.dumps(e))
    elif args.cmd == "reply":
        try:
            entry = reply(args.id, args.decision, phrase=args.phrase, decided_by=args.decided_by)
        except (ValueError, RuntimeError) as e:
            print(f"error: {e}", file=sys.stderr)
            return 1
        print(json.dumps(entry, indent=2))
    elif args.cmd == "check":
        ok, reason = check_grant(args.id, args.entity, args.action)
        print(f"{'GRANTED' if ok else 'DENIED'}: {reason}")
        return 0 if ok else 1
    return 0


if __name__ == "__main__":
    sys.exit(main())