"""Pydantic schemas for structured model responses."""

from pydantic import BaseModel, ConfigDict, Field, model_validator

from gcmd_classifier.models import SupportType


class CandidateDecision(BaseModel):
    """One model-selected application-supplied candidate."""

    model_config = ConfigDict(extra="forbid", frozen=True)

    candidate_id: str = Field(min_length=1)
    confidence: float | None = Field(default=None, ge=0.0, le=1.0)
    evidence: str = Field(min_length=1)
    support_type: SupportType
    reason: str | None = None


class TopicResponse(BaseModel):
    """Structured multi-label Topic routing response."""

    model_config = ConfigDict(extra="forbid", frozen=True)

    selected: list[CandidateDecision] = Field(default_factory=list)
    ambiguous_alternatives: list[str] = Field(default_factory=list)
    no_selection_reason: str | None = None


class _ChildSelectionResponse(BaseModel):
    """Shared response invariants for Term and Variable-level descent decisions."""

    model_config = ConfigDict(extra="forbid", frozen=True)

    selected: list[CandidateDecision] = Field(default_factory=list)
    stop_at_parent: bool
    stop_reason: str | None = None
    ambiguous_alternatives: list[str] = Field(default_factory=list)

    @model_validator(mode="after")
    def validate_stop_and_selection_invariants(self) -> "_ChildSelectionResponse":
        """Reject contradictory child-selection responses before orchestration can use them."""
        if self.stop_at_parent and self.selected:
            raise ValueError("stop_at_parent=true requires selected to be empty")
        if self.selected and self.stop_at_parent:
            raise ValueError("non-empty selected requires stop_at_parent=false")
        if self.stop_at_parent and not self.stop_reason:
            raise ValueError("stop_at_parent=true requires a non-empty stop_reason")
        return self


class TermResponse(_ChildSelectionResponse):
    """Structured Term routing response beneath a selected Topic."""


class VariableResponse(_ChildSelectionResponse):
    """Structured Variable-level descent response beneath a selected parent."""