from __future__ import annotations

from typing import Any, Optional


def merge_dicts(left: dict[str, Any], *others: dict[str, Any]) -> dict[str, Any]:
    """Merge many dicts, handling specific scenarios where a key exists in both
    dictionaries but has a value of None in 'left'. In such cases, the method uses the
    value from 'right' for that key in the merged dictionary.

    Args:
        left: The first dictionary to merge.
        others: The other dictionaries to merge.

    Returns:
        The merged dictionary.

    Raises:
        TypeError: If the key exists in both dictionaries but has a different type.
        TypeError: If the value has an unsupported type.

    Example:
        If left = {"function_call": {"arguments": None}} and
        right = {"function_call": {"arguments": "{\n"}}
        then, after merging, for the key "function_call",
        the value from 'right' is used,
        resulting in merged = {"function_call": {"arguments": "{\n"}}.
    """
    merged = left.copy()
    for right in others:
        for right_k, right_v in right.items():
            if right_k not in merged or right_v is not None and merged[right_k] is None:
                merged[right_k] = right_v
            elif right_v is None:
                continue
            elif type(merged[right_k]) is not type(right_v):
                msg = (
                    f'additional_kwargs["{right_k}"] already exists in this message,'
                    " but with a different type."
                )
                raise TypeError(msg)
            elif isinstance(merged[right_k], str):
                # TODO: Add below special handling for 'type' key in 0.3 and remove
                # merge_lists 'type' logic.
                #
                # if right_k == "type":
                #     if merged[right_k] == right_v:
                #         continue
                #     else:
                #         raise ValueError(
                #             "Unable to merge. Two different values seen for special "
                #             f"key 'type': {merged[right_k]} and {right_v}. 'type' "
                #             "should either occur once or have the same value across "
                #             "all dicts."
                #         )
                merged[right_k] += right_v
            elif isinstance(merged[right_k], dict):
                merged[right_k] = merge_dicts(merged[right_k], right_v)
            elif isinstance(merged[right_k], list):
                merged[right_k] = merge_lists(merged[right_k], right_v)
            elif merged[right_k] == right_v:
                continue
            else:
                msg = (
                    f"Additional kwargs key {right_k} already exists in left dict and "
                    f"value has unsupported type {type(merged[right_k])}."
                )
                raise TypeError(msg)
    return merged


def merge_lists(left: Optional[list], *others: Optional[list]) -> Optional[list]:
    """Add many lists, handling None.

    Args:
        left: The first list to merge.
        others: The other lists to merge.

    Returns:
        The merged list.
    """
    merged = left.copy() if left is not None else None
    for other in others:
        if other is None:
            continue
        elif merged is None:
            merged = other.copy()
        else:
            for e in other:
                if isinstance(e, dict) and "index" in e and isinstance(e["index"], int):
                    to_merge = [
                        i
                        for i, e_left in enumerate(merged)
                        if e_left["index"] == e["index"]
                    ]
                    if to_merge:
                        # TODO: Remove this once merge_dict is updated with special
                        # handling for 'type'.
                        if "type" in e:
                            e = {k: v for k, v in e.items() if k != "type"}
                        merged[to_merge[0]] = merge_dicts(merged[to_merge[0]], e)
                    else:
                        merged.append(e)
                else:
                    merged.append(e)
    return merged


def merge_obj(left: Any, right: Any) -> Any:
    """Merge two objects.

    It handles specific scenarios where a key exists in both
    dictionaries but has a value of None in 'left'. In such cases, the method uses the
    value from 'right' for that key in the merged dictionary.

    Args:
        left: The first object to merge.
        right: The other object to merge.

    Returns:
        The merged object.

    Raises:
        TypeError: If the key exists in both dictionaries but has a different type.
        ValueError: If the two objects cannot be merged.
    """
    if left is None or right is None:
        return left if left is not None else right
    elif type(left) is not type(right):
        msg = (
            f"left and right are of different types. Left type:  {type(left)}. Right "
            f"type: {type(right)}."
        )
        raise TypeError(msg)
    elif isinstance(left, str):
        return left + right
    elif isinstance(left, dict):
        return merge_dicts(left, right)
    elif isinstance(left, list):
        return merge_lists(left, right)
    elif left == right:
        return left
    else:
        msg = (
            f"Unable to merge {left=} and {right=}. Both must be of type str, dict, or "
            f"list, or else be two equal objects."
        )
        raise ValueError(msg)