"""Direct API backend — the first real execution backend.

WHAT THIS IS
------------
This is a **mock of a SOC tool's REST API** (think: a ticketing system / CMDB).
It is one of the four execution backends the dispatcher can route an authorized
action to. It does the *actual work* of a Direct-API action:

    * READS      — get_asset, get_ticket, get_alert        (return mock records)
    * WRITES     — create_low_risk_ticket, add_comment,     (low-risk, reversible
                   update_status                              changes to a store)

It reads and writes the static fixtures from :mod:`data`. There are
**no real network calls** — everything happens against an in-memory copy of the
mock data, so the demo is safe and repeatable.

WHERE IT SITS IN THE TRUST MODEL
--------------------------------
This backend never decides *whether* an action is allowed — that already happened
upstream. By the time ``run`` is called, the gate has said ``ALLOW`` and the
dispatcher has verified the gate's signed grant. So this file can focus purely on *doing*.

    gate decides ─► dispatcher verifies grant ─► THIS backend executes

TWO SAFETY PROPERTIES, EVEN THOUGH IT ONLY RUNS AFTER ALLOW
-----------------------------------------------------------
1. **Allow-list of handlers (defense in depth).** This backend only knows how to
   perform a fixed set of safe actions. A high-risk action (e.g. ``block_ip``)
   has *no handler here at all*, so even if one somehow reached this backend it
   would be refused, not executed. High-risk actions are approval-gated by the
   policy and only ever reach the Safe-CLI/MCP backends after approval — never
   this one without it.
2. **Writes only touch a private copy.** The ticket store is seeded with its own
   deep copy of the fixtures, so creating or editing a ticket here can never
   corrupt the shared seed data other components read.
"""

from __future__ import annotations

from typing import Any, Callable

import data
from control_plane.schema import ProposedAction


class DirectApiError(Exception):
    """Base error for anything this backend refuses or cannot do."""


class DirectApiUnsupportedActionError(DirectApiError):
    """The requested action is not in this backend's allow-list of handlers.

    This is the defense-in-depth guard: anything that isn't one of the safe
    reads/writes below (notably high-risk actions like ``block_ip``) lands here
    and is refused rather than executed.
    """


class RecordNotFoundError(DirectApiError):
    """A read/write referenced an ID that does not exist in the mock data."""


class MissingArgumentError(DirectApiError):
    """A required argument was absent from the action's ``arguments`` map."""


class DirectApiBackend:
    """Mock Direct-API adapter satisfying the dispatcher's ``BackendAdapter`` contract.

    Construct it once and let the dispatcher call :meth:`run` per authorized
    action. Each instance owns its own mutable ticket store, so tests (and
    separate runs) stay isolated from one another.
    """

    def __init__(self) -> None:
        # Read-only reference data: looked up by ID, never modified here.
        self._assets = data.index_by_id("assets")
        self._alerts = data.index_by_id("alerts")

        # The one *writable* store. We take a private deep copy (``load_records``)
        # so create/comment/update operations mutate only this instance, never the
        # shared on-disk seed. Keyed by ticket_id for O(1) reads and updates.
        self._tickets: dict[str, dict[str, Any]] = {
            t["ticket_id"]: t for t in data.load_records("tickets")
        }

        # The allow-list: action_name -> handler. Membership in this table is what
        # makes an action executable by this backend. Anything not here is refused
        # by :meth:`run` (see DirectApiUnsupportedActionError).
        self._handlers: dict[str, Callable[[dict[str, Any]], Any]] = {
            # reads
            "get_asset": self._get_asset,
            "get_ticket": self._get_ticket,
            "get_alert": self._get_alert,
            # bounded, reversible writes
            "create_low_risk_ticket": self._create_low_risk_ticket,
            "add_comment": self._add_comment,
            "update_status": self._update_status,
        }

    # -- dispatcher entry point ------------------------------------------------

    def run(self, action: ProposedAction) -> Any:
        """Execute *action* and return its result (the affected mock record).

        Routes on ``action.action_name`` to a handler in the allow-list. An action
        this backend doesn't handle raises :class:`DirectApiUnsupportedActionError` — it is
        never silently ignored or guessed at.
        """
        handler = self._handlers.get(action.action_name)
        if handler is None:
            raise DirectApiUnsupportedActionError(
                f"direct_api backend cannot perform {action.action_name!r} "
                f"(not in its allow-list of safe actions)"
            )
        # Handlers read everything they need from the action's arguments map.
        return handler(action.arguments)

    # -- read handlers ---------------------------------------------------------

    def _get_asset(self, args: dict[str, Any]) -> dict[str, Any]:
        asset_id = _require(args, "asset_id")
        return _found(self._assets.get(asset_id), "asset", asset_id)

    def _get_alert(self, args: dict[str, Any]) -> dict[str, Any]:
        alert_id = _require(args, "alert_id")
        return _found(self._alerts.get(alert_id), "alert", alert_id)

    def _get_ticket(self, args: dict[str, Any]) -> dict[str, Any]:
        # Tickets are read from the writable store, so a ticket created earlier in
        # the same run can be read back.
        ticket_id = _require(args, "ticket_id")
        return _found(self._tickets.get(ticket_id), "ticket", ticket_id)

    # -- write handlers (low-risk, reversible) ---------------------------------

    def _create_low_risk_ticket(self, args: dict[str, Any]) -> dict[str, Any]:
        """Create a new ticket in the mock store and return it.

        This is the "L2 low-risk ticket" action. It only adds a record;
        it changes nothing on a real host or user, which is what makes it a
        *bounded, reversible* action the policy allows at L2.
        """
        ticket = {
            "ticket_id": self._next_ticket_id(),
            "incident_id": args.get("incident_id"),
            "title": _require(args, "title"),
            "status": "open",
            "priority": args.get("priority", "low"),
            "risk": "low",  # this handler only ever creates low-risk tickets
            "asset_id": args.get("asset_id"),
            "assignee_user_id": args.get("assignee_user_id"),
            "comments": [],
        }
        self._tickets[ticket["ticket_id"]] = ticket
        return ticket

    def _add_comment(self, args: dict[str, Any]) -> dict[str, Any]:
        """Append a comment to an existing ticket (a reversible annotation)."""
        ticket = self._get_ticket_for_write(args)
        ticket["comments"].append(
            {
                "author_user_id": args.get("author_user_id"),
                "body": _require(args, "body"),
            }
        )
        return ticket

    def _update_status(self, args: dict[str, Any]) -> dict[str, Any]:
        """Update a ticket's status field (e.g. open -> in_progress)."""
        ticket = self._get_ticket_for_write(args)
        ticket["status"] = _require(args, "status")
        return ticket

    # -- helpers ---------------------------------------------------------------

    def _get_ticket_for_write(self, args: dict[str, Any]) -> dict[str, Any]:
        """Resolve the ticket a write targets, or refuse if the ID is unknown."""
        ticket_id = _require(args, "ticket_id")
        return _found(self._tickets.get(ticket_id), "ticket", ticket_id)

    def _next_ticket_id(self) -> str:
        """Mint the next ``TKT-####`` id, one past the highest currently stored."""
        numbers = [
            int(tid.split("-")[1])
            for tid in self._tickets
            if tid.startswith("TKT-") and tid.split("-")[1].isdigit()
        ]
        return f"TKT-{(max(numbers, default=5000) + 1):04d}"


# Module-level helpers keep the handlers above short and uniform.


def _require(args: dict[str, Any], key: str) -> Any:
    """Return ``args[key]`` or raise a clear error naming the missing argument."""
    if key not in args or args[key] in (None, ""):
        raise MissingArgumentError(f"missing required argument {key!r}")
    return args[key]


def _found(record: dict[str, Any] | None, kind: str, record_id: str) -> dict[str, Any]:
    """Return *record* if present, else raise a clear not-found error."""
    if record is None:
        raise RecordNotFoundError(f"no {kind} with id {record_id!r}")
    return record