"""ProviderDescriptor - the declarative catalogue entry for one model provider (R03-T02).

Today the knowledge of "what a provider is" is scattered across three places
that must be edited together and can silently drift apart:

* ``providers/factory.py::_REGISTRY``  - name -> implementation class
* ``config.py::DEFAULT_CONFIG["providers"]`` - default base_url / model / api_key
* ``config.py::PROVIDER_LABELS``       - the human label shown in Settings

Adding a provider means remembering all three; forgetting one produces a
provider that exists but has no label, or a label with no implementation. This
value object folds those facts into a single immutable description that the
registry (``infrastructure/providers/provider_registry.py``) and the UI can both
read, so a new provider is declared once.

Pure domain code: stdlib only, no Qt, no network, no config access. It describes
a provider; building one is infrastructure's job.
"""
from __future__ import annotations

from dataclasses import dataclass, field
from enum import Enum
from typing import Any, Dict, FrozenSet, List, Mapping, Optional, Tuple


class ProviderCapability(str, Enum):
    """What a provider can do, as advertised by its descriptor.

    Kept as a closed enum rather than free-form strings so a typo
    (``"vison"``) fails at import time instead of silently disabling a feature
    at runtime. Inherits ``str`` so existing dict/JSON code that compares against
    plain strings keeps working during the migration.
    """

    STREAMING = "streaming"      # can stream answer fragments through on_text
    TOOLS = "tools"              # can be given a ToolSpec catalogue and call tools
    VISION = "vision"            # accepts image content blocks (see providers/base.py)
    REASONING = "reasoning"      # emits a separate private "thinking" stream
    MODEL_LISTING = "model_listing"  # list_models() returns a real catalogue


@dataclass(frozen=True)
class ProviderDescriptor:
    """An immutable description of one provider the app can talk to.

    Attributes:
        id: the config key, e.g. ``"openai_compat"``. Also the ``provider`` half
            of a routing candidate key (``provider/model_id``).
        label: human-readable name for Settings and the model picker.
        protocol: which wire format this provider speaks. Several ids share one
            protocol - ``ollama``, ``github_copilot`` and ``codex`` are all
            OpenAI-compatible endpoints - which is exactly why protocol and id
            must be separate fields.
        default_model: the model used when the user has not chosen one.
        capabilities: what the provider supports (see :class:`ProviderCapability`).
        requires_api_key: whether an empty ``api_key`` makes it unusable.
        requires_base_url: whether an empty ``base_url`` makes it unusable.
        local: True when the endpoint runs on the user's own machine. Routing
            treats local models as zero-cost, and the security layer treats them
            as not leaving the machine, so this is a real behavioural flag and
            not just documentation.
        notes: free-form remark shown in Settings (e.g. "paste a Copilot token").
    """

    id: str
    label: str
    protocol: str
    default_model: str = ""
    capabilities: FrozenSet[ProviderCapability] = field(default_factory=frozenset)
    requires_api_key: bool = True
    requires_base_url: bool = True
    local: bool = False
    notes: str = ""

    # -- capability queries ---------------------------------------------- #
    def supports(self, capability: ProviderCapability) -> bool:
        """True when this provider advertises ``capability``."""
        return capability in self.capabilities

    @property
    def supports_vision(self) -> bool:
        """Mirrors ``providers.base.Provider.supports_vision`` so callers can ask
        the descriptor (no instance, no network) before building a provider."""
        return self.supports(ProviderCapability.VISION)

    @property
    def supports_tools(self) -> bool:
        """True when this provider can run an agent turn with tools. A provider
        without it can still chat, but must never be routed a tool-using task."""
        return self.supports(ProviderCapability.TOOLS)

    def capability_names(self) -> List[str]:
        """Capabilities as sorted plain strings - the shape the routing layer's
        ``required_capabilities`` filter and the assessment store both use."""
        return sorted(c.value for c in self.capabilities)

    # -- configuration validation ---------------------------------------- #
    def missing_settings(self, conf: Mapping[str, Any]) -> List[str]:
        """Which required config keys are absent or blank in ``conf``.

        Returned as a list (not a bool) so Settings can tell the user exactly
        what to fill in, instead of a generic "not configured". A provider that
        needs nothing returns an empty list.
        """
        missing: List[str] = []
        if self.requires_api_key and not str(conf.get("api_key", "") or "").strip():
            missing.append("api_key")
        if self.requires_base_url and not str(conf.get("base_url", "") or "").strip():
            missing.append("base_url")
        return missing

    def is_configured(self, conf: Mapping[str, Any]) -> bool:
        """True when ``conf`` carries everything this provider needs to run."""
        return not self.missing_settings(conf)

    def resolve_model(self, conf: Optional[Mapping[str, Any]] = None,
                      requested: str = "") -> str:
        """Pick the model id for a call: explicit request, else configured, else
        this descriptor's default.

        Centralised here because the same three-step fallback is currently
        re-implemented at every call site (chat panel, Co4E, AI-edit, scheduler),
        and each of them gets the precedence subtly different.
        """
        if requested:
            return requested
        configured = str((conf or {}).get("model", "") or "").strip()
        return configured or self.default_model

    def describe(self, conf: Optional[Mapping[str, Any]] = None) -> str:
        """One-line summary for logs and the Settings row, e.g.
        ``"anthropic:claude-sonnet-4-6 (Anthropic Claude)"``."""
        return f"{self.id}:{self.resolve_model(conf)} ({self.label})"

    def candidate_key(self, model_id: str) -> str:
        """The ``provider/model_id`` identity the routing layer keys on.

        Defined here so the domain owns the format; ``core.routing.models`` has
        its own ``candidate_key()`` helper producing the identical string, and
        keeping them equal is what lets the new registry and the existing
        assessment store share one keyspace during the migration.
        """
        return f"{self.id}/{model_id}"

    def to_dict(self) -> Dict[str, Any]:
        """JSON-safe projection, for persisting a catalogue snapshot or sending
        the descriptor to a UI layer that must not import domain types."""
        return {
            "id": self.id,
            "label": self.label,
            "protocol": self.protocol,
            "default_model": self.default_model,
            "capabilities": self.capability_names(),
            "requires_api_key": self.requires_api_key,
            "requires_base_url": self.requires_base_url,
            "local": self.local,
            "notes": self.notes,
        }


def split_candidate_key(key: str) -> Tuple[str, str]:
    """Inverse of :meth:`ProviderDescriptor.candidate_key`.

    Splits on the FIRST ``/`` only: some gateways expose model ids that contain
    a slash (``org/model``), and splitting on the last one would corrupt them.
    """
    provider, _, model_id = key.partition("/")
    return provider, model_id


__all__ = ["ProviderCapability", "ProviderDescriptor", "split_candidate_key"]