import json
import os
from typing import Iterable, Sequence


def load_label_mapping(file_path: str) -> list[str]:
    extension = os.path.splitext(file_path)[1].lower()
    if extension == ".txt":
        labels: list[str] = []
        with open(file_path, "r", encoding="utf-8", errors="ignore") as f:
            for raw_line in f:
                line = raw_line.strip()
                if not line or line.startswith("#"):
                    continue
                labels.append(line)
        if not labels:
            raise ValueError("Label mapping file does not contain any labels")
        return labels

    if extension == ".json":
        with open(file_path, "r", encoding="utf-8") as f:
            data = json.load(f)

        if isinstance(data, list):
            labels = [str(item).strip() for item in data]
            if not any(labels):
                raise ValueError("Label mapping JSON list is empty")
            return labels

        if isinstance(data, dict):
            indexed_labels: list[tuple[int, str]] = []
            for key, value in data.items():
                try:
                    index = int(key)
                except (TypeError, ValueError) as exc:
                    raise ValueError("Label mapping JSON object keys must be numeric indices") from exc
                indexed_labels.append((index, str(value).strip()))

            if not indexed_labels:
                raise ValueError("Label mapping JSON object is empty")

            max_index = max(index for index, _ in indexed_labels)
            labels = [""] * (max_index + 1)
            for index, label in indexed_labels:
                labels[index] = label
            return labels

        raise ValueError("Label mapping JSON must be a list or an object")

    raise ValueError("Label mapping file must be .json or .txt")


def apply_label_mapping(base_labels: Sequence[str], mapping: Sequence[str] | None) -> list[str]:
    labels = [str(label) for label in base_labels]
    if not mapping:
        return labels

    mapped = list(labels)
    for index, mapped_label in enumerate(mapping):
        if index >= len(mapped):
            break
        value = str(mapped_label).strip()
        if value:
            mapped[index] = value
    return mapped