turnstone/examples/door-game/understone/server.py

"""MCP server for Understone — the only module that imports ``mcp`` (or ``starlette``).

Nine ``door_*`` tools form the entire player interface. Every handler is a
synchronous ``def`` that takes and returns ``str``; no exception is allowed
to cross the MCP boundary (each handler catches, logs server-side, and
returns an in-fiction line). The handlers are thin wrappers over a single
module-level :class:`~understone.game.Game`; all rules live behind that
façade.

Three extra HTTP routes (``/watch`` and its two JSON feeds) serve the
read-only spectator page from :mod:`understone.watch`. They are registered via
FastMCP's ``custom_route`` and ride inside the streamable-http app; the
``starlette`` request/response types appear ONLY here, mirroring the MCP SDK's
own ``custom_route`` examples. The routes are unauthenticated by design and
strictly read-only — they never mutate or persist world state.

Usage::

    understone                 # via entry point (stdio transport)
    python -m understone       # via module
    understone validate PATH   # check a content pack loads cleanly
    understone newpack PATH    # scaffold a new pack + authoring manual

Environment variables
---------------------
UNDERSTONE_DB         SQLite path (default: ./understone.db)
UNDERSTONE_WORLD      Content-pack directory (default: packaged world/data)
UNDERSTONE_TRANSPORT  "stdio" (default) or "streamable-http"
UNDERSTONE_HOST       Bind host for http transport (default: 127.0.0.1)
UNDERSTONE_PORT       Bind port for http transport (default: 8077)
UNDERSTONE_PATH       HTTP path for the MCP endpoint (default: /mcp)
"""

from __future__ import annotations

import argparse
import logging
import os
from pathlib import Path
from typing import TYPE_CHECKING

from mcp.server.fastmcp import FastMCP
from starlette.responses import HTMLResponse, JSONResponse, Response

from understone import cli, watch
from understone.errors import WorldLoadError
from understone.game import Game
from understone.persistence import Store
from understone.world import PACKAGED_WORLD_DIR
from understone.world.loader import load_world

if TYPE_CHECKING:
    from starlette.applications import Starlette
    from starlette.requests import Request

log = logging.getLogger(__name__)

_PREMISE = (
    "Understone is a shared-world BBS door game played through these tools. "
    "Call door_help first to learn how to narrate it."
)

# The DM manual returned by door_help — a module constant so it is stable and
# greppable. It teaches an assistant how to run the game responsibly.
_DM_MANUAL = """\
UNDERSTONE — A GUIDE FOR THE GAME MASTER

WHAT THIS IS
  Understone is a multiplayer, BBS-style ANSI door game — a small text RPG in
  the lineage of the classic BBS door games. Many players share ONE
  persistent world hosted by this server. You are the storyteller at the
  terminal; the server is the rules engine and the single source of truth.

THE GOLDEN RULE
  The server is authoritative. Never invent dice rolls, loot, gold, hit
  points, map tiles, or outcomes. Every number and event comes back from a
  tool call. Narrate AROUND the facts the tools return — never ahead of them.
  If you want something to happen, call the tool and see what the world says.

THE TWO MODES OF PLAY
  1. The overworld (TILE mode). Tools return an ASCII "keyframe": a bordered
     map window centred on the player. '@' is the player, '&' is another
     adventurer, letters are buildings (I inn, $ shop, + healer, > dungeon).
     Movement here is FREE — it costs no daily turns.
  2. Location interiors (MENU mode). Stepping onto a building opens a menu of
     options like (R)est, (B)uy, (H)eal, (D)escend, (L)eave.

PRESENTING FRAMES
  When a tool returns a map or a menu, show it to the player VERBATIM inside a
  fenced code block so the box-drawing lines stay aligned. Then add your prose
  underneath. Do not redraw or paraphrase the frame.

NARRATION
  Be vivid and in-fiction. Turn the terse result lines ("You travel 3 steps.",
  "+8 XP, +3 gold.") into atmosphere. Keep your additions consistent with the
  returned facts and the high-fantasy tone of the Vale of Understone.

THE DAILY RHYTHM
  Each adventurer has a small budget of turns per real-world UTC day. Only
  fighting, descending, and challenging the Wyrm spend a turn; moving,
  resting, shopping and looking do not. When the budget is gone, the day is
  done — encourage the player to return tomorrow. This is a correspondence
  game: a little each day.

WANDERING THE FOREST (the texture of a walk)
  A step through wild country may turn up more than a monster. The server
  rolls a private encounter table as the player walks: most often a foe (which
  stops the walk for a fight or flight), but sometimes a purse of gold, a
  healing spring, a small trap (it can never kill — it floors at 1 HP), or a
  scrap of Vale lore. The non-combat finds are applied at once, narrated in
  the move result, and do NOT stop the walk; at most one such event happens
  per move. These finds are PRIVATE — they are not Herald news — so narrate
  them as the quiet texture of travelling, and watch the lore: it whispers of
  something coiled beneath the dungeon.

THE WYRM BELOW (the endgame, and how to win)
  Deep under the dungeon sleeps the Wyrm Below — a fixed, fearsome boss and
  the ONLY win condition. At the dungeon, a sufficiently seasoned hero may
  'challenge' it (door_action action="challenge"). Under the level threshold,
  the server turns them away in-fiction; once allowed, the challenge spends a
  daily turn and resolves in one call, like a fight.
    * On victory the hero FREES THE VALE. The triumph is heralded to everyone,
      the run is carved into the Hall of Legends (shown by door_rank), and the
      hero is reborn in a classic-door-game-style legacy reset: level, gold, gear and stats
      return to first-day values and they stand again at the town — but they
      keep a permanent ★ for the win, and may set out to do it all again. Their
      remaining turns for the day and their place in the world carry over.
    * On defeat the Wyrm devours them; they wake at the spawn, barely alive.
  Play this beat big: it is the climax of a whole run. Narrate the reset as the
  Vale renewing itself around an undying legend, not as a death.

BESTOWING FORTUNE (use sparingly)
  door_bestow lets you, the storyteller, grant a little gold or healing to
  mark a great story moment — a heroic rescue, a clever solution, a poignant
  death-defiance. It NEVER grants items (gear comes from the shop) and NEVER
  grants turns (the clock does not bend). It is capped by a small daily pool
  per player, and every bestowal is written to the public log for all to see.
  Treat it as seasoning, not a salt-shaker: reserve it for the rare, earned
  beat, and never promise a reward you cannot actually deliver within the cap.

TOOL CHEAT-SHEET
  door_help                      This manual.
  door_join(player)              Sign in (creates or resumes a character).
  door_status(player)            Read the character sheet.
  door_look(player)              Redraw the current view (map or menu).
  door_move(player, ...)         Walk the overworld (free). steps="NNEE" or
                                 heading="east" + distance=3 (max 8 per call).
  door_action(player, action)    Context verb: fight, flee, rest, buy, sell,
                                 heal, descend, challenge (the Wyrm), leave.
  door_log(player)               Read the Understone Herald (the shared feed).
  door_rank(player)              The leaderboard + Hall of Legends (★ = wins).
  door_bestow(player, reason...) Grant a little gold/healing for a story beat.

GETTING STARTED
  Ask the player their adventurer's name, call door_join, present the opening
  keyframe, and set the scene: a small town at the western edge of a wooded
  vale, a road running east toward darker country and a dungeon mouth.
"""

_BLANK_NAME = 'The gatekeeper squints. "I didn\'t catch your name, traveller."'

# Module-level game singleton, built lazily so tests can inject their own.
_GAME: Game | None = None


def _build_game(watch_url: str | None = None) -> Game:
    """Construct the module Game from environment configuration."""
    db_path = os.environ.get("UNDERSTONE_DB", "understone.db")
    world_dir = os.environ.get("UNDERSTONE_WORLD") or str(PACKAGED_WORLD_DIR)
    world = load_world(world_dir)
    store = Store(db_path)
    return Game(world, store, watch_url=watch_url)


def _game() -> Game:
    """Return the module game, building it on first use."""
    global _GAME
    if _GAME is None:
        _GAME = _build_game()
    return _GAME


def _set_game(game: Game) -> None:
    """Install a prebuilt game (used by create_app / tests)."""
    global _GAME
    _GAME = game


def _guard_name(player: str) -> str | None:
    """Return the blank-name refusal when *player* is empty, else None."""
    return None if player.strip() else _BLANK_NAME


mcp: FastMCP = FastMCP(
    "understone",
    instructions=_PREMISE,
)


@mcp.tool()
def door_help() -> str:
    """Read the Understone game-master manual — start here.

    Returns a short guide for running this multiplayer, BBS-style ANSI door
    game (a classic text RPG / dungeon adventure): the two play modes, how
    to present the ASCII map frames, the daily-turn rhythm, and the full tool
    cheat-sheet. Call door_help before your first session to learn how to run
    the game, then call door_join to begin.
    """
    watch_line = _game().watch_line()
    if watch_line:
        return f"{_DM_MANUAL}\nTHE LOBBY TV\n  {watch_line}\n"
    return _DM_MANUAL


@mcp.tool()
def door_join(player: str) -> str:
    """Sign an adventurer into the shared world of Understone — call this first.

    Understone is a multiplayer, BBS-style ANSI door game: a text adventure /
    dungeon RPG in the spirit of the classic BBS door games, played entirely
    through these tools. This creates a new character at the town, or resumes
    an existing one by name, and returns the opening overworld map frame. New
    to running it? Call door_help before your first session.

    Args:
        player: The adventurer's name (their identity in the world).
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().join(player)
    except Exception:
        log.exception("door_join failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_status(player: str) -> str:
    """Show an adventurer's character sheet (level, HP, gear, gold, turns).

    Read-only. Use it to check progress before deciding what to do next.

    Args:
        player: The adventurer's name.
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().status(player)
    except Exception:
        log.exception("door_status failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_look(player: str) -> str:
    """Redraw what the adventurer currently sees (read-only).

    On the overworld this is an ASCII map keyframe centred on the player
    ('@' is you, '&' are other players, letters are buildings). Inside a
    building it is that location's menu. Present the result verbatim in a
    fenced code block, then narrate.

    Args:
        player: The adventurer's name.
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().look(player)
    except Exception:
        log.exception("door_look failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_move(player: str, steps: str = "", heading: str = "", distance: int = 1) -> str:
    """Walk the overworld — movement is free and never costs a daily turn.

    Only valid on the overworld (in a building, use door_action 'leave'
    first). Give EITHER a compact ``steps`` string of cardinal letters such
    as "NNEE", OR a ``heading`` ("north"/"south"/"east"/"west") with a
    ``distance``. At most 8 cells move per call; the walk stops early at
    walls, water, a building door, or a wandering monster.

    Args:
        player: The adventurer's name.
        steps: Cardinal letters, e.g. "NNEE" (takes precedence if given).
        heading: A compass direction used with distance.
        distance: How many cells to travel along heading (1-8).
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().move(player, steps, heading, distance)
    except Exception:
        log.exception("door_move failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_action(player: str, action: str, target: str = "", item: str = "") -> str:
    """Take a context-sensitive action in the world.

    The legal verbs depend on where the adventurer is. On the overworld:
    'fight' or 'flee' a wandering monster (fighting spends one daily turn).
    Inside a building: 'rest' (inn), 'buy'/'sell' (shop), 'heal' (healer),
    or 'leave'. At the dungeon: 'descend' the gauntlet, or 'challenge' the
    Wyrm Below — the endgame boss and the only way to win. The challenge is
    gated by level (under-level heroes are turned away in-fiction) and, once
    allowed, spends a daily turn and resolves in a single call like a fight:
    a victory frees the Vale and begins a new life (see door_help), a defeat
    bounces you home. An illegal verb returns the verbs valid right here.

    Args:
        player: The adventurer's name.
        action: The verb to attempt (fight, flee, rest, buy, sell, heal,
            descend, challenge, leave).
        target: Reserved for future targeted actions.
        item: For shop 'buy', the item id to purchase.
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().action(player, action, target, item)
    except Exception:
        log.exception("door_action failed for %r action=%r", player, action)
        return _unexpected()


@mcp.tool()
def door_log(player: str) -> str:
    """Catch up on what happened in the shared world while the player was away.

    Returns the events since this adventurer last checked (fights, deaths,
    blessings, descents by anyone) and advances their personal marker.

    Args:
        player: The adventurer's name.
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().log(player)
    except Exception:
        log.exception("door_log failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_rank(player: str = "") -> str:
    """Show the Roll of Heroes — the top-ten leaderboard.

    Ordered by level, then experience, then name. If the caller names
    themselves and they place in the top ten, their row is marked. Each ★
    beside a name is one slaying of the Wyrm Below. Below the table, the Hall
    of Legends lists the most recent completed runs (name, level at the kill,
    days the run took, date); it is omitted while no one has yet won.

    Args:
        player: The caller's name (optional; marks their row when present).
    """
    try:
        return _game().rank(player)
    except Exception:
        log.exception("door_rank failed for %r", player)
        return _unexpected()


@mcp.tool()
def door_bestow(player: str, reason: str, gold: int = 0, heal: int = 0) -> str:
    """Grant a small gift of gold or healing to mark a great story moment.

    This is the game master's discretionary channel, to be used SPARINGLY for
    earned, story-driven beats. It grants only gold and/or healing — never
    items (gear comes from the shop) and never turns (the daily clock does not
    bend). Each grant is capped by a small daily pool per adventurer and is
    written to the public log, so spend it on the rare moment that deserves
    it; do not promise more than the cap allows. When a pack sets healing to
    cost nothing, a bestowed heal is free and draws nothing from the pool.

    Args:
        player: The adventurer receiving the gift.
        reason: A short, in-fiction reason (<= 120 characters).
        gold: Gold to grant (>= 0).
        heal: HP to restore (>= 0); only the missing portion is applied and
            charged against the pool.
    """
    blank = _guard_name(player)
    if blank is not None:
        return blank
    try:
        return _game().bestow(player, reason, gold, heal)
    except Exception:
        log.exception("door_bestow failed for %r", player)
        return _unexpected()


# FastMCP.custom_route has no return annotation upstream (mcp 1.27.2), so mypy
# reads the decorator as untyped; the ignore is scoped to that single gap.
@mcp.custom_route("/watch", methods=["GET"])  # type: ignore[untyped-decorator]
async def watch_page(_request: Request) -> Response:
    """Serve the read-only CRT spectator page (static HTML, no world reads)."""
    return HTMLResponse(watch.WATCH_HTML)


@mcp.custom_route("/watch/world.json", methods=["GET"])  # type: ignore[untyped-decorator]
async def watch_world(_request: Request) -> Response:
    """Serve the STATIC map payload (dimensions, coloured rows, locations)."""
    return JSONResponse(watch.build_world_payload(_game().world))


@mcp.custom_route("/watch/state.json", methods=["GET"])  # type: ignore[untyped-decorator]
async def watch_state(_request: Request) -> Response:
    """Serve the DYNAMIC snapshot (players, Herald, Hall) — read-only.

    The builder reads the module Game with no ``await`` in between, so each
    response is a consistent point-in-time snapshot of the shared world.
    """
    return JSONResponse(watch.build_state_payload(_game()))


def _unexpected() -> str:
    """In-fiction line for an unexpected server-side error."""
    return (
        "A strange fog rolls through the Vale and the moment slips away. "
        "(Something went wrong; try again.)"
    )


def create_app(
    db_path: str, world_dir: str | None = None, watch_url: str | None = None
) -> Starlette:
    """Build the streamable-HTTP ASGI app backed by a fresh game.

    Used by both ``main`` (for the http transport) and the integration tests,
    so tests can point at a temp DB without environment juggling. ``watch_url``,
    when given, is the spectator page URL the join banner and help manual
    advertise; ``main`` derives it from the bind host/port.
    """
    world = load_world(world_dir or str(PACKAGED_WORLD_DIR))
    store = Store(db_path)
    _set_game(Game(world, store, watch_url=watch_url))
    return mcp.streamable_http_app()


def _serve() -> None:
    """Serve the Understone MCP world over the configured transport.

    Honours UNDERSTONE_TRANSPORT: "stdio" (default) or "streamable-http".
    For http, host/port/path are read from the environment and applied to the
    FastMCP settings before serving. This is the actual transport launch; it is
    kept separate from argument parsing so the parse step has no side effects.
    """
    logging.basicConfig(level=logging.INFO)
    transport = os.environ.get("UNDERSTONE_TRANSPORT", "stdio")

    if transport == "streamable-http":
        host = os.environ.get("UNDERSTONE_HOST", "127.0.0.1")
        port = int(os.environ.get("UNDERSTONE_PORT", "8077"))
        mcp.settings.host = host
        mcp.settings.port = port
        mcp.settings.streamable_http_path = os.environ.get("UNDERSTONE_PATH", "/mcp")
        mcp.settings.stateless_http = False
        # The spectator page is only reachable over http, so its URL is composed
        # here from the bind address. A 0.0.0.0 bind should advertise a host a
        # browser can actually reach (see the README Watch section).
        watch_url = f"http://{host}:{port}/watch"
        # Build the game eagerly (with the watch URL) so a config error surfaces
        # before serving and the join/help advertisements carry the page link.
        try:
            _set_game(_build_game(watch_url))
        except WorldLoadError as exc:
            raise SystemExit(f"failed to load world: {exc}") from exc
        mcp.run(transport="streamable-http")
        return

    try:
        _game()
    except WorldLoadError as exc:
        raise SystemExit(f"failed to load world: {exc}") from exc
    mcp.run(transport="stdio")


def _build_parser() -> argparse.ArgumentParser:
    """Build the ``understone`` argument parser: serve (default), validate, newpack.

    Parsing is deliberately free of side effects — no world load, no port bind —
    so the resolved subcommand can be inspected without serving anything.
    """
    parser = argparse.ArgumentParser(
        prog="understone",
        description=(
            "Understone — a BBS-style ANSI door game served over MCP, plus the "
            "tools to author its world packs."
        ),
    )
    sub = parser.add_subparsers(dest="cmd")
    sub.add_parser("serve", help="serve the MCP world (the default with no command)")
    validate = sub.add_parser("validate", help="validate a content pack and print a report")
    validate.add_argument("path", type=Path, help="the pack directory to validate")
    newpack = sub.add_parser("newpack", help="scaffold a new content pack from the bundled world")
    newpack.add_argument("path", type=Path, help="the directory to create the pack in")
    return parser


def main(argv: list[str] | None = None) -> None:
    """Run the Understone command line: serve, or author a world pack.

    With no arguments (the entry point and ``python -m understone``) this serves
    the MCP world exactly as before. ``validate PATH`` and ``newpack PATH`` drive
    the pack-authoring loop and exit with the verb's status code.
    """
    args = _build_parser().parse_args(argv)
    if args.cmd == "validate":
        raise SystemExit(cli.cli_validate(args.path))
    if args.cmd == "newpack":
        raise SystemExit(cli.cli_newpack(args.path))
    _serve()