"""Resolve a step's images from the resource that actually produced them."""

from typing import Any


def step_image_name(step: Any, which: str) -> str | None:
    def field(name):
        return step.get(name) if isinstance(step, dict) else getattr(step, name, None)

    result = field("last_execution_result")
    execution = result.get("execution") if isinstance(result, dict) else None
    actions = execution if isinstance(execution, list) else field("action_taken")
    if isinstance(actions, dict):
        actions = [actions]
    actions = actions if isinstance(actions, list) else []
    plugins = [
        action
        for action in actions
        if isinstance(action, dict)
        and (action.get("plugin_id") or str(action.get("action", "")).startswith("plug_"))
    ]
    if not plugins:
        return field(f"{which}_image_name")
    # A burst may span several resources. Its per-call evidence must not be
    # presented as a before/after pair on one screen.
    if len(actions) != 1:
        return None
    action = plugins[0]
    if isinstance(execution, list) or f"{which}_image_name" in action:
        if which == "pre" and not action.get("pre_image_valid"):
            return None
        return action.get(f"{which}_image_name")
    # Older Flash records already stored source-specific images at step level.
    return field(f"{which}_image_name")