"""Session branch model — represents a diagnostic hypothesis path within a FlowPilot session."""
import uuid
from datetime import datetime, timezone
from typing import Optional, Any, TYPE_CHECKING

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

from app.core.database import Base

if TYPE_CHECKING:
    from app.models.ai_session import AISession
    from app.models.ai_session_step import AISessionStep
    from app.models.user import User


class SessionBranch(Base):
    """A diagnostic branch within a FlowPilot session."""
    __tablename__ = "session_branches"
    __table_args__ = (
        CheckConstraint(
            "status IN ('active', 'dead_end', 'solved', 'untried', 'revived')",
            name="ck_session_branches_status",
        ),
        CheckConstraint(
            "branch_order > 0",
            name="ck_session_branches_branch_order_positive",
        ),
        Index("ix_session_branches_session_id", "session_id"),
        Index("ix_session_branches_parent_branch_id", "parent_branch_id"),
        Index("ix_session_branches_session_status", "session_id", "status"),
        Index("ix_session_branches_session_order", "session_id", "branch_order"),
    )

    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
    session_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("ai_sessions.id", ondelete="CASCADE"), nullable=False)
    parent_branch_id: Mapped[Optional[uuid.UUID]] = mapped_column(UUID(as_uuid=True), ForeignKey("session_branches.id", ondelete="CASCADE"), nullable=True)
    fork_point_step_id: Mapped[Optional[uuid.UUID]] = mapped_column(UUID(as_uuid=True), ForeignKey("ai_session_steps.id", ondelete="SET NULL"), nullable=True)
    branch_order: Mapped[int] = mapped_column(Integer, nullable=False, default=1)
    label: Mapped[str] = mapped_column(String(200), nullable=False)
    status: Mapped[str] = mapped_column(String(20), nullable=False, default="active")
    status_reason: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
    status_changed_at: Mapped[Optional[datetime]] = mapped_column(DateTime(timezone=True), nullable=True)
    status_changed_by: Mapped[Optional[uuid.UUID]] = mapped_column(UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
    conversation_messages: Mapped[list[dict[str, Any]]] = mapped_column(JSONB, nullable=False, default=list, comment="LLM message history scoped to this branch")
    context_summary: Mapped[Optional[dict[str, Any]]] = mapped_column(JSONB, nullable=True, comment="{tried: [], concluded: str, artifacts: []}")
    evidence_from_branch_id: Mapped[Optional[uuid.UUID]] = mapped_column(UUID(as_uuid=True), ForeignKey("session_branches.id", ondelete="SET NULL"), nullable=True)
    evidence_description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc))
    updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))

    # Relationships
    session: Mapped["AISession"] = relationship("AISession", foreign_keys="[SessionBranch.session_id]", back_populates="branches")
    parent_branch: Mapped[Optional["SessionBranch"]] = relationship("SessionBranch", remote_side="SessionBranch.id", foreign_keys=[parent_branch_id])
    fork_point_step: Mapped[Optional["AISessionStep"]] = relationship("AISessionStep", foreign_keys=[fork_point_step_id])
    status_changed_by_user: Mapped[Optional["User"]] = relationship("User", foreign_keys=[status_changed_by])
    evidence_source: Mapped[Optional["SessionBranch"]] = relationship("SessionBranch", remote_side="SessionBranch.id", foreign_keys=[evidence_from_branch_id])