import re
from pathlib import Path


def ensure_dir(path: Path):
    path.mkdir(parents=True, exist_ok=True)


def _add_to_installed_apps(content: str, app_name: str) -> str:
    """
    Safely add an app to INSTALLED_APPS if not already present.
    """
    pattern = re.compile(r"INSTALLED_APPS\s*=\s*\[(.*?)\]", re.DOTALL)
    match = pattern.search(content)

    if not match:
        return content

    apps_block = match.group(1)

    if f"'{app_name}'" in apps_block or f'"{app_name}"' in apps_block:
        return content

    updated_apps = apps_block.rstrip() + f"\n    '{app_name}',"
    return content[:match.start(1)] + updated_apps + content[match.end(1):]


def update_settings_py(settings_path, db_spec, app_names=None):
    settings_path = Path(settings_path)
    content = settings_path.read_text(encoding="utf-8")

    # --------------------------------------------------
    # 1. Ensure BASE_DIR
    # --------------------------------------------------
    if "BASE_DIR" not in content:
        content = (
            "from pathlib import Path\n\n"
            "BASE_DIR = Path(__file__).resolve().parent.parent\n\n"
            + content
        )

    # --------------------------------------------------
    # 2. Ensure rest_framework + project apps
    # --------------------------------------------------
    content = _add_to_installed_apps(content, "rest_framework")

    if app_names:
        for app in app_names:
            content = _add_to_installed_apps(content, app)

    # --------------------------------------------------
    # 3. Database config (ONLY if NOT sqlite)
    # --------------------------------------------------
    engine = (db_spec or {}).get("engine", "").lower()

    if engine and engine != "sqlite":
        engine_map = {
            "postgresql": "django.db.backends.postgresql",
            "postgres": "django.db.backends.postgresql",
            "mysql": "django.db.backends.mysql",
            "mariadb": "django.db.backends.mysql",
        }

        django_engine = engine_map.get(engine)
        if not django_engine:
            raise ValueError(f"Unsupported DB engine: {engine}")

        database_block = f"""
DATABASES = {{
    'default': {{
        'ENGINE': '{django_engine}',
        'NAME': '{db_spec.get("name")}',
        'USER': '{db_spec.get("user", "")}',
        'PASSWORD': '{db_spec.get("password", "")}',
        'HOST': '{db_spec.get("host", "")}',
        'PORT': '{db_spec.get("port", "")}',
    }}
}}
""".strip()

        content = re.sub(
            r"DATABASES\s*=\s*\{.*?\}\s*\}\s*",
            database_block + "\n\n",
            content,
            flags=re.DOTALL
        )

    # --------------------------------------------------
    # 4. Static & Media (idempotent)
    # --------------------------------------------------
    if "STATIC_ROOT" not in content:
        content += """

# Static files
STATIC_URL = "/static/"
STATIC_ROOT = BASE_DIR / "staticfiles"
STATICFILES_DIRS = [BASE_DIR / "static"]

# Media files
MEDIA_URL = "/media/"
MEDIA_ROOT = BASE_DIR / "media"
"""

    # --------------------------------------------------
    # 5. Write file
    # --------------------------------------------------
    settings_path.write_text(content, encoding="utf-8")

    # --------------------------------------------------
    # 6. Create folders
    # --------------------------------------------------
    project_root = settings_path.parents[2]

    ensure_dir(project_root / "static")
    ensure_dir(project_root / "media")
    ensure_dir(project_root / "staticfiles")


    #print("✅ settings.py updated correctly")