"""Load the installed Blackmagic module; do not install a similarly named package.

This helper uses standard desktop installation paths or RESOLVE_SCRIPT_API.
It does not enable scripting, start Resolve, open projects or retry API calls.
Validate Python/native-library compatibility against your installed README.txt.
"""
from __future__ import annotations

import importlib.util
import os
from pathlib import Path
import struct
import sys


class ResolveConnectionError(RuntimeError):
    """An explicit environment, module, or application-connection failure."""


def scripting_root() -> Path:
    configured = os.environ.get("RESOLVE_SCRIPT_API")
    if configured is not None:
        if not configured.strip() or configured != configured.strip():
            raise ResolveConnectionError("RESOLVE_SCRIPT_API is empty or has outer whitespace")
        if configured.startswith(('"', "'")) or configured.endswith(('"', "'")):
            raise ResolveConnectionError("Do not store literal outer quotes in RESOLVE_SCRIPT_API")
        root = Path(os.path.expandvars(configured)).expanduser()
    elif sys.platform == "win32":
        root = Path(os.environ.get("PROGRAMDATA", r"C:\ProgramData")) / "Blackmagic Design/DaVinci Resolve/Support/Developer/Scripting"
    elif sys.platform == "darwin":
        root = Path("/Library/Application Support/Blackmagic Design/DaVinci Resolve/Developer/Scripting")
    elif sys.platform.startswith("linux"):
        root = Path("/opt/resolve/Developer/Scripting")
    else:
        raise ResolveConnectionError("Set RESOLVE_SCRIPT_API for this platform/installation")
    if not root.is_absolute():
        raise ResolveConnectionError("RESOLVE_SCRIPT_API must be an absolute Scripting directory")
    return root


def module_file() -> Path:
    # RESOLVE_SCRIPT_API points to Scripting, not its Modules subdirectory.
    return scripting_root() / "Modules" / "DaVinciResolveScript.py"


def load_resolve_module():
    if struct.calcsize("P") * 8 != 64:
        raise ResolveConnectionError("Use a compatible 64-bit Python interpreter")
    source = module_file()
    if not source.is_file():
        raise ResolveConnectionError("Official DaVinciResolveScript.py not found at: " + str(source))
    configured_lib = os.environ.get("RESOLVE_SCRIPT_LIB")
    if configured_lib is not None:
        lib = Path(os.path.expandvars(configured_lib)).expanduser()
        if not lib.is_absolute() or not lib.is_file():
            raise ResolveConnectionError("RESOLVE_SCRIPT_LIB must name the installed native library file")
    name = "DaVinciResolveScript"
    spec = importlib.util.spec_from_file_location(name, source)
    if spec is None or spec.loader is None:
        raise ResolveConnectionError("Cannot create a loader for the official module")
    previous = sys.modules.get(name)
    module = importlib.util.module_from_spec(spec)
    sys.modules[name] = module
    try:
        spec.loader.exec_module(module)
        # Blackmagic's wrapper can replace its sys.modules entry with a native module.
        loaded = sys.modules[name]
        if not callable(getattr(loaded, "scriptapp", None)):
            raise ResolveConnectionError("Loaded module does not expose scriptapp")
        return loaded
    except Exception as exc:
        if previous is None:
            sys.modules.pop(name, None)
        else:
            sys.modules[name] = previous
        raise ResolveConnectionError("Official module was found, but loading it failed") from exc


def connect():
    module = load_resolve_module()
    try:
        resolve = module.scriptapp("Resolve")
    except Exception as exc:
        raise ResolveConnectionError("scriptapp failed; inspect the original exception") from exc
    if not resolve:
        raise ResolveConnectionError("No Resolve object: check running Studio, Local access and Python environment")
    return resolve


def project_manager(resolve):
    manager = resolve.GetProjectManager()
    if not manager:
        raise ResolveConnectionError("Resolve connected, but Project Manager is unavailable")
    return manager