"""Backfill embeddings for memories that lack them (T97, Phase 4).

Walks all memories where no row exists in the ``embeddings`` table. For
each, calls :func:`chat.services.embeddings.generate_embedding` and emits
an ``embedding_indexed`` event so the projector lands the vector.

Phase 4 ships the deterministic local pseudo-embedding so this script
runs synchronously without a network round-trip — the LLMClient argument
is not needed on the pseudo path. Phase 4.5+ will need a real client.

T112 (Phase 4.5) adds two flags:

* ``--re-embed-all`` walks **every** memory regardless of whether it
  already has an ``embeddings`` row. Useful when swapping embedding
  models — the projector is INSERT OR REPLACE, so re-emitting an event
  for an existing memory replaces the prior vector. Without this flag,
  the script keeps the Phase 4 behavior of only filling in gaps.
* ``--model M`` overrides ``Settings.embedding_model`` for this run.
  Defaults to the configured model (which itself defaults to
  ``"pseudo-sha256-384"``).

Run from the repo root:
    .venv/bin/python scripts/backfill_embeddings.py [--limit N] [--dry-run]
    .venv/bin/python scripts/backfill_embeddings.py --re-embed-all
    .venv/bin/python scripts/backfill_embeddings.py --re-embed-all --model bge-small-en-v1.5
"""

from __future__ import annotations

import argparse
import asyncio

from chat.config import Settings, load_settings
from chat.db.connection import open_db
from chat.db.migrate import apply_migrations
from chat.eventlog.log import append_and_apply
from chat.services.embeddings import (
    DEFAULT_EMBEDDING_MODEL,
    FALLBACK_EMBEDDING_MODEL,
    generate_embedding,
)

# Trigger projector handler registration so ``append_and_apply`` lands
# the embedding rows correctly.
import chat.state.embeddings  # noqa: F401
import chat.state.entities  # noqa: F401
import chat.state.memory  # noqa: F401
import chat.state.world  # noqa: F401


def _build_client(settings: Settings):
    """Construct an LLMClient for the backfill run.

    Default-model runs (the pseudo path) don't need a client, so we
    return ``None`` and ``generate_embedding`` skips the call. Non-default
    models route through the real client; injectable via monkeypatch in
    tests.
    """
    if settings.embedding_model == DEFAULT_EMBEDDING_MODEL:
        return None
    from chat.llm.featherless import FeatherlessClient

    return FeatherlessClient(
        api_key=settings.featherless_api_key,
        base_url=settings.featherless_base_url,
    )


async def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "--limit",
        type=int,
        default=None,
        help="Cap the number of memories backfilled in this run.",
    )
    parser.add_argument(
        "--dry-run",
        action="store_true",
        help="Print the count of memories needing embeddings, then exit.",
    )
    parser.add_argument(
        "--re-embed-all",
        action="store_true",
        help=(
            "Walk every memory (not just those without an embeddings row) "
            "and re-emit embedding_indexed events. Use this when swapping "
            "embedding models so the existing rows get replaced."
        ),
    )
    parser.add_argument(
        "--model",
        type=str,
        default=None,
        help=(
            "Embedding model identifier. Overrides Settings.embedding_model "
            "for this run; default uses the configured model."
        ),
    )
    args = parser.parse_args()

    settings = load_settings()
    settings.db_path.parent.mkdir(parents=True, exist_ok=True)
    apply_migrations(settings.db_path)

    model = args.model or settings.embedding_model
    # Override the settings instance so ``_build_client`` sees the
    # effective model when deciding whether to construct a real client.
    settings = settings.model_copy(update={"embedding_model": model})
    client = _build_client(settings)

    with open_db(settings.db_path) as conn:
        if args.re_embed_all:
            sql = "SELECT m.id, m.pov_summary FROM memories m ORDER BY m.id"
        else:
            sql = (
                "SELECT m.id, m.pov_summary FROM memories m "
                "LEFT JOIN embeddings e ON e.memory_id = m.id "
                "WHERE e.memory_id IS NULL "
                "ORDER BY m.id"
            )
        if args.limit is not None:
            sql += f" LIMIT {int(args.limit)}"
        rows = conn.execute(sql).fetchall()
        mode = "re-embedding" if args.re_embed_all else "needing embeddings"
        print(f"Found {len(rows)} memories {mode} (model={model}).")
        if args.dry_run:
            return

        indexed = 0
        skipped = 0
        for memory_id, text in rows:
            result = await generate_embedding(
                client=client,
                text=text or "",
                model=model,
            )
            if result.model == FALLBACK_EMBEDDING_MODEL:
                print(f"  Skipping memory_id={memory_id} (empty text or fallback)")
                skipped += 1
                continue
            append_and_apply(
                conn,
                kind="embedding_indexed",
                payload={
                    "memory_id": memory_id,
                    "model": result.model,
                    "dim": result.dim,
                    "vector": result.vector,
                },
            )
            indexed += 1
            print(f"  Indexed memory_id={memory_id}")
        print(f"Done. Indexed {indexed}, skipped {skipped}.")


if __name__ == "__main__":
    asyncio.run(main())