"""Database migration functions.

Each migration is idempotent and safe to run on a database that has already been migrated.
Run via run_migration() called from app startup after init_db().
"""

import sqlite3

from db import DB_PATH


def run_migration() -> None:
    """Apply all pending schema migrations in order.

    Currently applies:
      - v1: Add ai_blocks column to books; clear AI-derived data while preserving user data.
      - v2: Add batch_queue table for persistent batch processing queue.

    Migrations are idempotent — running them on an already-migrated database is a no-op.
    """
    c = sqlite3.connect(DB_PATH)
    c.row_factory = sqlite3.Row
    c.execute("PRAGMA foreign_keys = ON")
    try:
        _migrate_v1(c)
        _migrate_v2(c)
        c.commit()
    except Exception:
        c.rollback()
        raise
    finally:
        c.close()


def _migrate_v1(c: sqlite3.Connection) -> None:
    """Add ai_blocks column and clear stale AI data from all books (first run only).

    - Adds ai_blocks TEXT DEFAULT NULL column if it does not exist.
    - On first run only (when the column is absent): clears raw_text, ai_*, title_confidence,
      analyzed_at, candidates, ai_blocks from all books (these are regenerated by the new pipeline).
    - For user_approved books: copies user fields back to ai_* so that
      compute_status() still returns 'user_approved' after the ai_* clear.

    This migration assumes the database already has the base books schema.
    It is a no-op if ai_blocks already exists.
    """
    cols = {row["name"] for row in c.execute("PRAGMA table_info(books)")}
    if "ai_blocks" not in cols:
        c.execute("ALTER TABLE books ADD COLUMN ai_blocks TEXT DEFAULT NULL")

        # Clear AI-derived fields only when first adding the column.
        c.execute(
            "UPDATE books SET "
            "raw_text='', ai_title='', ai_author='', ai_year='', ai_isbn='', ai_publisher='', "
            "title_confidence=0, analyzed_at=NULL, candidates=NULL, ai_blocks=NULL"
        )

        # For user_approved books, restore ai_* = user fields so status stays user_approved.
        c.execute(
            "UPDATE books SET "
            "ai_title=title, ai_author=author, ai_year=year, ai_isbn=isbn, ai_publisher=publisher "
            "WHERE identification_status='user_approved'"
        )


def _migrate_v2(c: sqlite3.Connection) -> None:
    """Add batch_queue table for persistent batch processing queue.

    Replaces data/batch_pending.json with a DB table so batch state survives
    across restarts alongside all other persistent data.
    """
    c.execute("CREATE TABLE IF NOT EXISTS batch_queue (" "book_id  TEXT PRIMARY KEY," "added_at REAL NOT NULL" ")")