from datetime import datetime, timezone

from pgvector.sqlalchemy import Vector
from sqlalchemy import BigInteger, DateTime, ForeignKey, Integer, Text
from sqlalchemy.orm import Mapped, mapped_column

from scribe.models import Base

# bge-small-en-v1.5 produces 384-dim unit-normalized vectors. The column is a
# native pgvector `vector(384)` (see migration 0067) so similarity search runs
# as an indexed `ORDER BY embedding <=> :q LIMIT k` in Postgres rather than a
# full-table Python cosine scan.
EMBEDDING_DIM = 384


class NoteEmbedding(Base):
    """One embedding vector per CHUNK of a note (#280, migration 0077).

    The model reads at most 512 tokens, so a single whole-document vector
    permanently lost everything past ~400 words. A note now stores one row per
    chunk of `embeddings.chunk_document`, and a query matches the note if it
    matches ANY chunk — retrieval collapses rows to best-chunk-per-note.
    A short note has exactly one row (chunk_index 0) whose text is the
    historical `title\\nbody` shape.
    """

    __tablename__ = "note_embeddings"

    note_id: Mapped[int] = mapped_column(
        Integer,
        ForeignKey("notes.id", ondelete="CASCADE"),
        primary_key=True,
    )
    chunk_index: Mapped[int] = mapped_column(Integer, primary_key=True)
    user_id: Mapped[int] = mapped_column(Integer, nullable=False, index=True)
    embedding: Mapped[list] = mapped_column(Vector(EMBEDDING_DIM), nullable=False)
    # Exactly what this vector encodes — inspectable when a ranking surprises,
    # and the hook for surfacing WHICH section matched, later.
    chunk_text: Mapped[str] = mapped_column(Text, nullable=False)
    # embeddings.CHUNKER_VERSION at write time. The startup backfill re-embeds
    # any note whose rows carry a stale version — shape changes become a
    # version bump instead of a table wipe.
    chunker_version: Mapped[int] = mapped_column(Integer, nullable=False)
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        default=lambda: datetime.now(timezone.utc),
    )


class RuleEmbedding(Base):
    """One embedding vector per CHUNK of a rule (milestone 307, note 3026).

    A SIBLING of NoteEmbedding rather than a generalisation of it, decided
    deliberately. The reasoning below turned out to be the only written
    statement of a rule Scribe applies to every record type, so it is now also
    NOTE 3163 — "When a record type earns its own table" — with the worked
    cases and the cost of leaving `notes`. Read that before splitting a record
    type off; this stays here because it is where the decision was made.

    - The embedding ROW could have been made polymorphic. The SEARCH could not.
      `semantic_search_notes` is a long function of Note-specific scoping —
      the visibility clause, the supersession penalty, note_type/task_kind and
      system filters — and a rule shares none of it. Rules scope by rulebook
      ownership and project applicability instead.
    - Generalising the row while still needing two searches is the worst of
      both: a polymorphic key with referential integrity to neither table, on
      the path every session start runs, to share four columns.
    - What is genuinely common is BEHAVIOUR, not storage — get_embedding,
      chunk_document, embedding_text and CHUNKER_VERSION are already free
      functions and are reused as-is. Sharing those is the DRY win; sharing
      the table would have been the DRY costume.

    No `user_id`: NoteEmbedding carries one and its own search deliberately
    ignores it (scoping on the note instead, or shared records become
    unreachable). Rather than repeat a column that exists to be ignored, a
    rule's reach is resolved by joining the rule.
    """

    __tablename__ = "rule_embeddings"

    rule_id: Mapped[int] = mapped_column(
        BigInteger,
        ForeignKey("rules.id", ondelete="CASCADE"),
        primary_key=True,
    )
    chunk_index: Mapped[int] = mapped_column(Integer, primary_key=True)
    embedding: Mapped[list] = mapped_column(Vector(EMBEDDING_DIM), nullable=False)
    # Exactly what this vector encodes — inspectable when a ranking surprises.
    # For a rule this is the trigger-first document, NOT the rule's `why`:
    # `why` is dated incident narrative and would drag every rule toward one
    # centroid (measured in note 2485).
    chunk_text: Mapped[str] = mapped_column(Text, nullable=False)
    chunker_version: Mapped[int] = mapped_column(Integer, nullable=False)
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        default=lambda: datetime.now(timezone.utc),
    )
