from contextlib import contextmanager
from sqlalchemy.schema import CreateTable

from db.models import Base

from sqlalchemy.orm import sessionmaker
from sqlalchemy.dialects.mysql import insert
from sqlalchemy import create_engine, text, inspect
from env_provider import DB_HOST, DB_PORT, DB_NAME, DB_USER, DB_PASSWORD, DB_SCHEMA_UPDATED, ENVIRONMENT
engine = create_engine(f"mysql+pymysql://{DB_USER}:{DB_PASSWORD}@{DB_HOST}:{DB_PORT}/{DB_NAME}")
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

@contextmanager
def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

def clear_db():
    with engine.connect() as conn:
        conn.execute(text("SET FOREIGN_KEY_CHECKS = 0;"))
        inspector = inspect(engine)
        for table_name in inspector.get_table_names():
            conn.execute(text(f"DROP TABLE IF EXISTS {table_name}"))
        conn.execute(text("SET FOREIGN_KEY_CHECKS = 1;"))


def create_all():
    with engine.begin() as conn:
        Base.metadata.create_all(bind=conn)

def run_scripts():
    from db.models import table_models
    with get_db() as session:
        for model in table_models:
            if hasattr(model, "__scripts__"):
                scripts = model.__scripts__
                for script in scripts:
                    session.execute(script)
        session.commit()

def init_payload():
    from db.models import table_models
    with get_db() as session:
        session.execute(text("SET FOREIGN_KEY_CHECKS = 0;"))
        for model in table_models:
            print(str(CreateTable(model.__table__)))

            print(f"MODEL -- {model}, {hasattr(model, '__payload__')}")
            if hasattr(model, "__payload__"):
                payload = model.__payload__[ENVIRONMENT]
                print(f"- - [ - ] hasattr, {ENVIRONMENT} - {payload}")
                stmt = insert(model.__table__).values(payload).prefix_with("IGNORE")
                print(f"- - [ - ] {stmt}\n")
                session.execute(stmt)
        session.execute(text("SET FOREIGN_KEY_CHECKS = 1;"))
        session.commit()


def _column_exists(conn, table, column):
    row = conn.execute(text(
        "SELECT 1 FROM information_schema.columns "
        "WHERE table_schema = :db AND table_name = :t AND column_name = :c"
    ), {"db": DB_NAME, "t": table, "c": column}).first()
    return row is not None


def _index_exists(conn, table, index):
    row = conn.execute(text(
        "SELECT 1 FROM information_schema.statistics "
        "WHERE table_schema = :db AND table_name = :t AND index_name = :i"
    ), {"db": DB_NAME, "t": table, "i": index}).first()
    return row is not None


def run_migrations():
    """Idempotent additive schema migrations for already-existing tables.

    create_all() creates missing tables (with the new columns) for a fresh
    DB, but never alters existing ones. This adds the new columns to legacy
    tables and backfills sensible defaults. Safe to run on every startup.
    """
    # (table, column, DDL, backfill SQL or None)
    steps = [
        ("apikey", "alias", "ALTER TABLE apikey ADD COLUMN alias VARCHAR(255) NULL",
         "UPDATE apikey SET alias = `key` WHERE alias IS NULL"),
        ("markdown", "updated_at", "ALTER TABLE markdown ADD COLUMN updated_at DATETIME NULL",
         "UPDATE markdown SET updated_at = created_at WHERE updated_at IS NULL"),
        ("markdown", "author", "ALTER TABLE markdown ADD COLUMN author VARCHAR(255) NULL",
         "UPDATE markdown SET author = 'admin' WHERE author IS NULL"),
        ("markdown", "last_modified_by", "ALTER TABLE markdown ADD COLUMN last_modified_by VARCHAR(255) NULL",
         "UPDATE markdown SET last_modified_by = 'admin' WHERE last_modified_by IS NULL"),
        ("markdown_patch", "author", "ALTER TABLE markdown_patch ADD COLUMN author VARCHAR(255) NULL",
         "UPDATE markdown_patch SET author = 'admin' WHERE author IS NULL"),
        ("markdown_patch", "last_modified_by", "ALTER TABLE markdown_patch ADD COLUMN last_modified_by VARCHAR(255) NULL",
         "UPDATE markdown_patch SET last_modified_by = 'admin' WHERE last_modified_by IS NULL"),
    ]
    try:
        with engine.begin() as conn:
            for table, column, ddl, backfill in steps:
                if not _column_exists(conn, table, column):
                    conn.execute(text(ddl))
                    if backfill:
                        conn.execute(text(backfill))
                    print(f"[ x ] migrated {table}.{column}")
            # Unique constraint on apikey.alias once it is populated.
            if not _index_exists(conn, "apikey", "uq_apikey_alias"):
                conn.execute(text(
                    "ALTER TABLE apikey ADD CONSTRAINT uq_apikey_alias UNIQUE (alias)"
                ))
                print("[ x ] migrated apikey.alias unique constraint")
    except Exception as e:
        # Don't block startup on a migration hiccup; surface loudly.
        print(f"[ ! ] run_migrations error (continuing): {e}")


def setup_db():
    if DB_SCHEMA_UPDATED:
        clear_db()
        print("[ x ] db cleared")
    create_all()
    print("[ x ] db created")
    run_migrations()
    print("[ x ] db migrations applied")
    run_scripts()
    print("[ x ] db scripts executed")
    init_payload()
    print("[ x ] payload loaded")