"""The extension point.

A *feature* is a self-contained bundle of bot behaviour: some commands, and
optionally an interest in plain messages or uploaded files. Adding one means
subclassing :class:`Feature` and registering it -- no edits to the router, the
webhook, or any other feature.

Expense tracking is simply the first feature registered. Anything else a bot
needs to do (reminders, notes, standups, ops alerts) drops in beside it on
equal terms.
"""

from __future__ import annotations

from abc import ABC, abstractmethod
from dataclasses import dataclass, field
from datetime import date
from typing import TYPE_CHECKING, Optional, Sequence

if TYPE_CHECKING:  # pragma: no cover - typing only
    from ..advice import Advisor
    from ..config import Settings
    from ..ingest import Ingestor
    from ..llm import LLMClient
    from ..models import PendingImport
    from ..store import Store
    from ..registry import FeatureRegistry


@dataclass(frozen=True)
class CommandSpec:
    """One slash command, and enough metadata to build /help and setMyCommands."""

    name: str
    help: str
    args: str = ""
    aliases: tuple[str, ...] = ()
    #: Hidden commands still work but stay out of the menu (e.g. /confirm).
    hidden: bool = False

    @property
    def usage(self) -> str:
        return f"/{self.name} {self.args}".strip()


@dataclass
class Attachment:
    """A file the user sent, already downloaded."""

    data: bytes
    filename: str = ""
    mime_type: str = ""
    kind: str = "document"  # "photo" | "document"
    caption: str = ""

    @property
    def is_image(self) -> bool:
        return self.kind == "photo" or self.mime_type.startswith("image/")


@dataclass
class Services:
    """Shared dependencies handed to every feature."""

    settings: "Settings"
    store: "Store"
    llm: "LLMClient"
    ingestor: "Ingestor"
    advisor: "Advisor"
    registry: "FeatureRegistry"
    #: Imports awaiting /confirm, keyed by user id. Held in memory only -- a
    #: Space restart drops them, which is acceptable because the user simply
    #: re-sends the file, and it keeps unconfirmed model output out of storage.
    pending: dict[int, "PendingImport"] = field(default_factory=dict)
    #: Recent coach conversation per user, so follow-ups make sense. In memory
    #: only and shared across surfaces, so a thread started on Telegram
    #: continues in the web chat. Deliberately not persisted: it is chat
    #: scratch, not ledger data, and keeping it out of the mirrored database
    #: avoids storing conversation content alongside the finances.
    conversations: dict[int, list[dict]] = field(default_factory=dict)


@dataclass
class BotContext:
    """Everything a feature needs to answer one update."""

    user_id: int
    chat_id: int
    services: Services
    today: date
    #: Current @handle without the @, empty if unset. Display and access only --
    #: everything stored is keyed on the immutable user_id.
    username: str = ""
    text: str = ""
    command: str = ""
    args: str = ""
    attachment: Optional[Attachment] = None

    @property
    def settings(self) -> "Settings":
        return self.services.settings

    @property
    def store(self) -> "Store":
        return self.services.store


@dataclass
class Reply:
    """What to send back. HTML parse mode -- see finbot.render for why."""

    text: str
    parse_mode: Optional[str] = "HTML"
    disable_preview: bool = True
    #: Optional file to send alongside the text, as (filename, bytes).
    document: Optional[tuple[str, bytes]] = None


class Feature(ABC):
    #: Stable identifier, used in logs and /help grouping.
    name: str = "feature"
    #: One line shown in /help.
    description: str = ""

    def commands(self) -> Sequence[CommandSpec]:
        """Slash commands this feature owns."""
        return ()

    def handle_command(self, ctx: BotContext) -> Optional[Reply]:
        """Handle one of this feature's commands. Return None to decline."""
        return None

    def handle_message(self, ctx: BotContext) -> Optional[Reply]:
        """Handle plain (non-command) text. Return None to let others try."""
        return None

    def handle_attachment(self, ctx: BotContext) -> Optional[Reply]:
        """Handle an uploaded file. Return None to let others try."""
        return None

    #: Lower runs first when several features want the same plain message.
    priority: int = 100


class SimpleFeature(Feature):
    """Convenience base that routes commands to ``cmd_<name>`` methods."""

    @abstractmethod
    def commands(self) -> Sequence[CommandSpec]:  # pragma: no cover - abstract
        ...

    def handle_command(self, ctx: BotContext) -> Optional[Reply]:
        for spec in self.commands():
            if ctx.command == spec.name or ctx.command in spec.aliases:
                handler = getattr(self, f"cmd_{spec.name}", None)
                if handler is None:
                    return None
                return handler(ctx)
        return None