import sys
from pathlib import Path
from typing import Dict, Optional, Union
import clr_loader

__all__ = ["set_runtime", "set_default_runtime", "load"]

_RUNTIME: Optional[clr_loader.Runtime] = None
_LOADER_ASSEMBLY: Optional[clr_loader.wrappers.Assembly] = None
_LOADED: bool = False


def set_runtime(runtime: Union[clr_loader.Runtime, str], **params: str) -> None:
    """Set up a clr_loader runtime without loading it

    :param runtime: Either an already initialised `clr_loader` runtime, or one
    of netfx, coreclr, mono, or default. If a string parameter is given, the
    runtime will be created."""

    global _RUNTIME
    if _LOADED:
        raise RuntimeError(f"The runtime {_RUNTIME} has already been loaded")

    if isinstance(runtime, str):
        runtime = _create_runtime_from_spec(runtime, params)

    _RUNTIME = runtime


def _get_params_from_env(prefix: str) -> Dict[str, str]:
    from os import environ

    full_prefix = f"PYTHONNET_{prefix.upper()}"
    len_ = len(full_prefix)

    env_vars = {
        (k[len_:].lower()): v
        for k, v in environ.items()
        if k.upper().startswith(full_prefix)
    }

    return env_vars


def _create_runtime_from_spec(
    spec: str, params: Optional[Dict[str, str]] = None
) -> clr_loader.Runtime:
    if spec == "default":
        if sys.platform == "win32":
            spec = "netfx"
        else:
            spec = "mono"

    params = params or _get_params_from_env(spec)

    if spec == "netfx":
        return clr_loader.get_netfx(**params)
    elif spec == "mono":
        return clr_loader.get_mono(**params)
    elif spec == "coreclr":
        return clr_loader.get_coreclr(**params)
    else:
        raise RuntimeError(f"Invalid runtime name: '{spec}'")


def set_default_runtime() -> None:
    """Set up the default runtime

    This will use the environment variable PYTHONNET_RUNTIME to decide the
    runtime to use, which may be one of netfx, coreclr or mono. The parameters
    of the respective clr_loader.get_ functions can also be given as
    environment variables, named `PYTHONNET__`. In
    particular, to use `PYTHONNET_RUNTIME=coreclr`, the variable
    `PYTHONNET_CORECLR_RUNTIME_CONFIG` has to be set to a valid
    `.runtimeconfig.json`.

    If no environment variable is specified, a globally installed Mono is used
    for all environments but Windows, on Windows the legacy .NET Framework is
    used.
    """
    from os import environ

    print("Set default RUNTIME")
    raise RuntimeError("Shouldn't be called here")

    spec = environ.get("PYTHONNET_RUNTIME", "default")
    runtime = _create_runtime_from_spec(spec)
    set_runtime(runtime)


def load(
    runtime: Union[clr_loader.Runtime, str] = "default", **params: Dict[str, str]
) -> None:
    """Load Python.NET in the specified runtime

    The same parameters as for `set_runtime` can be used. By default,
    `set_default_runtime` is called if no environment has been set yet and no
    parameters are passed."""
    global _LOADED, _LOADER_ASSEMBLY

    if _LOADED:
        return

    if _RUNTIME is None:
        set_runtime(runtime, **params)

    if _RUNTIME is None:
        raise RuntimeError("No valid runtime selected")

    dll_path = Path(__file__).parent / "runtime" / "Python.Runtime.dll"

    _LOADER_ASSEMBLY = _RUNTIME.get_assembly(str(dll_path))

    func = _LOADER_ASSEMBLY["Python.Runtime.Loader.Initialize"]
    if func(b"") != 0:
        raise RuntimeError("Failed to initialize Python.Runtime.dll")

    import atexit

    atexit.register(unload)


def unload() -> None:
    """Explicitly unload a laoded runtime and shut down Python.NET"""

    global _RUNTIME, _LOADER_ASSEMBLY
    if _LOADER_ASSEMBLY is not None:
        func = _LOADER_ASSEMBLY["Python.Runtime.Loader.Shutdown"]
        if func(b"full_shutdown") != 0:
            raise RuntimeError("Failed to call Python.NET shutdown")

        _LOADER_ASSEMBLY = None

    if _RUNTIME is not None:
        # TODO: Add explicit `close` to clr_loader
        _RUNTIME = None