"""Knowledge Base models.

Mirrors the Project feature's shape (human-friendly *code*, creator FK,
created/updated timestamps). Hierarchy is:

    knowledge_base
      └─ knowledge_topic            (unique per (topic, knowledge_base_id))
           ├─ knowledge_fact        (category_id NULL → fact lives on the topic)
           └─ knowledge_category    (parent NULL → top-level category in topic)
                ├─ knowledge_fact
                └─ knowledge_category (parent → nested)

`project_knowledge_base` is the M2M link between projects and knowledge bases.

Relationships are intentionally kept minimal (no ORM cascade on the
self-referential category tree); deletion ordering is handled explicitly in
the router to stay clear of FK-ordering surprises under MySQL.
"""
from sqlalchemy import Column, Integer, String, Text, DateTime, ForeignKey, UniqueConstraint
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func

from app.core.config import Base


class KnowledgeBase(Base):
    __tablename__ = "knowledge_bases"

    id = Column(Integer, primary_key=True, index=True)
    knowledge_base_code = Column(String(16), unique=True, index=True, nullable=True)
    title = Column(String(200), nullable=False)
    description = Column(Text, nullable=True)
    created_by = Column(Integer, ForeignKey("users.id"), nullable=False)
    created_at = Column(DateTime(timezone=True), server_default=func.now())
    last_updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())

    creator = relationship("User", foreign_keys=[created_by])


class KnowledgeTopic(Base):
    __tablename__ = "knowledge_topics"
    __table_args__ = (
        UniqueConstraint("topic", "knowledge_base_id", name="uq_knowledge_topic_kb"),
    )

    id = Column(Integer, primary_key=True, index=True)
    topic = Column(String(200), nullable=False)
    knowledge_base_id = Column(Integer, ForeignKey("knowledge_bases.id"), nullable=False, index=True)
    description = Column(Text, nullable=True)
    created_by = Column(Integer, ForeignKey("users.id"), nullable=False)
    created_at = Column(DateTime(timezone=True), server_default=func.now())
    last_updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())

    creator = relationship("User", foreign_keys=[created_by])


class KnowledgeCategory(Base):
    __tablename__ = "knowledge_categories"
    __table_args__ = (
        # NOTE: MySQL treats NULLs as distinct in a UNIQUE index, so this only
        # enforces uniqueness for non-NULL `parent`. Top-level categories
        # (parent IS NULL) are de-duped in the router (application-level check).
        UniqueConstraint("topic_id", "parent", "name", name="uq_knowledge_category_triple"),
    )

    id = Column(Integer, primary_key=True, index=True)
    name = Column(String(200), nullable=False)
    parent = Column(Integer, ForeignKey("knowledge_categories.id"), nullable=True, index=True)
    topic_id = Column(Integer, ForeignKey("knowledge_topics.id"), nullable=False, index=True)
    description = Column(Text, nullable=True)
    created_by = Column(Integer, ForeignKey("users.id"), nullable=True)
    last_updated_by = Column(Integer, ForeignKey("users.id"), nullable=True)


class KnowledgeFact(Base):
    __tablename__ = "knowledge_facts"

    id = Column(Integer, primary_key=True, index=True)
    category_id = Column(Integer, ForeignKey("knowledge_categories.id"), nullable=True, index=True)
    topic_id = Column(Integer, ForeignKey("knowledge_topics.id"), nullable=False, index=True)
    fact = Column(Text, nullable=False)
    last_updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())


class ProjectKnowledgeBase(Base):
    __tablename__ = "project_knowledge_bases"
    __table_args__ = (
        UniqueConstraint("project_id", "knowledge_base_id", name="uq_project_knowledge_base"),
    )

    id = Column(Integer, primary_key=True, index=True)
    project_id = Column(Integer, ForeignKey("projects.id"), nullable=False, index=True)
    knowledge_base_id = Column(Integer, ForeignKey("knowledge_bases.id"), nullable=False, index=True)


class KnowledgeBaseCodeCounter(Base):
    __tablename__ = "knowledge_base_code_counters"

    id = Column(Integer, primary_key=True, index=True)
    prefix = Column(String(16), unique=True, index=True, nullable=False)
    next_value = Column(Integer, default=0)