import enum
import uuid
from datetime import datetime

from sqlalchemy import CheckConstraint, DateTime, Enum, ForeignKey, Index, String, Text, text
from sqlalchemy.dialects.postgresql import JSONB, UUID
from sqlalchemy.orm import Mapped, mapped_column, relationship

from api.models.base import Base, TimestampMixin, new_uuid


class DecisionType(str, enum.Enum):
    made = "made"
    pending = "pending"


class DecisionStatus(str, enum.Enum):
    open = "open"
    resolved = "resolved"
    escalated = "escalated"
    superseded = "superseded"


class DecisionClass(str, enum.Enum):
    """Gate-house decision classes (GH-DEC-2026-026). NULL on a row means legacy (as C0)."""

    C0 = "C0"
    C1 = "C1"
    C2 = "C2"
    C3 = "C3"  # reserved by GH-DEC-2026-026; stored values allowed, the API refuses it


class ResolutionSource(str, enum.Enum):
    text = "text"
    informed_decision = "informed_decision"


# Classes whose resolution needs informed-decision evidence (STATE-WP-0101, design section 3.1).
# C3 is reserved and refused by the API; the database treats it fail-closed like C2.
EVIDENCE_CLASSES = frozenset({DecisionClass.C1, DecisionClass.C2, DecisionClass.C3})
APPROVAL_CLASSES = frozenset({DecisionClass.C2, DecisionClass.C3})
CLASS_RANK = {None: 0, DecisionClass.C0: 0, DecisionClass.C1: 1, DecisionClass.C2: 2, DecisionClass.C3: 3}

# Shared with the Alembic migration (STATE-WP-0101-T02); keep the two in step.
CK_DECISION_CLASS = "decision_class IS NULL OR decision_class IN ('C0','C1','C2','C3')"
CK_RESOLUTION_SOURCE = (
    "resolution_source IS NULL OR resolution_source IN ('text','informed_decision')"
)
CK_CLASS_EVIDENCE = (
    "NOT (status = 'resolved' AND decision_class IN ('C1','C2','C3')) OR "
    "(resolution_source = 'informed_decision' AND memo_id IS NOT NULL "
    "AND resolution_evidence IS NOT NULL)"
)
CK_CLASS_APPROVAL = (
    "NOT (status = 'resolved' AND decision_class IN ('C2','C3')) OR approval_id IS NOT NULL"
)


class Decision(Base, TimestampMixin):
    __tablename__ = "decisions"
    __table_args__ = (
        CheckConstraint(
            "topic_id IS NOT NULL OR workplan_id IS NOT NULL",
            name="ck_decisions_topic_or_workplan",
        ),
        CheckConstraint(CK_DECISION_CLASS, name="ck_decisions_decision_class"),
        CheckConstraint(CK_RESOLUTION_SOURCE, name="ck_decisions_resolution_source"),
        CheckConstraint(CK_CLASS_EVIDENCE, name="ck_decisions_class_evidence"),
        CheckConstraint(CK_CLASS_APPROVAL, name="ck_decisions_class_approval"),
        Index(
            "uq_decisions_memo_id",
            "memo_id",
            unique=True,
            postgresql_where=text("memo_id IS NOT NULL"),
        ),
    )

    id: Mapped[uuid.UUID] = mapped_column(
        UUID(as_uuid=True), primary_key=True, default=new_uuid
    )
    topic_id: Mapped[uuid.UUID | None] = mapped_column(
        UUID(as_uuid=True), ForeignKey("topics.id", ondelete="RESTRICT"), nullable=True, index=True
    )
    workplan_id: Mapped[uuid.UUID | None] = mapped_column(
        UUID(as_uuid=True),
        ForeignKey("workplans.id", ondelete="RESTRICT", onupdate="CASCADE"),
        nullable=True,
        index=True,
    )
    title: Mapped[str] = mapped_column(String(255), nullable=False)
    description: Mapped[str | None] = mapped_column(Text, nullable=True)
    decision_type: Mapped[DecisionType] = mapped_column(
        Enum(DecisionType), nullable=False, default=DecisionType.pending
    )
    status: Mapped[DecisionStatus] = mapped_column(
        Enum(DecisionStatus), nullable=False, default=DecisionStatus.open
    )
    rationale: Mapped[str | None] = mapped_column(Text, nullable=True)
    decided_by: Mapped[str | None] = mapped_column(String(100), nullable=True)
    decided_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
    deadline: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
    escalation_note: Mapped[str | None] = mapped_column(Text, nullable=True)
    superseded_by: Mapped[uuid.UUID | None] = mapped_column(
        UUID(as_uuid=True), ForeignKey("decisions.id", ondelete="SET NULL"), nullable=True
    )
    # STATE-WP-0101: decision class and informed-decision evidence links.
    decision_class: Mapped[str | None] = mapped_column(String(2), nullable=True, index=True)
    memo_id: Mapped[str | None] = mapped_column(Text, nullable=True)
    approval_id: Mapped[uuid.UUID | None] = mapped_column(UUID(as_uuid=True), nullable=True)
    resolution_source: Mapped[str | None] = mapped_column(String(32), nullable=True)
    resolution_evidence: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
    evidence_refs: Mapped[list] = mapped_column(
        JSONB, nullable=False, default=list, server_default=text("'[]'::jsonb")
    )

    topic: Mapped["Topic | None"] = relationship("Topic", back_populates="decisions")  # noqa: F821
    workplan: Mapped["Workplan | None"] = relationship("Workplan", back_populates="decisions")  # noqa: F821
    progress_events: Mapped[list["ProgressEvent"]] = relationship(  # noqa: F821
        "ProgressEvent", back_populates="decision", lazy="selectin"
    )