from __future__ import annotations

from typing import Any


class OpenAIStreamAccumulator:
    """Normalize incremental deltas and provider-specific full-message snapshots."""

    def __init__(self) -> None:
        self.text = ""
        self.saw_delta = False

    def feed(self, choice: dict[str, Any]) -> str:
        delta = choice.get("delta")
        if isinstance(delta, dict) and delta.get("content") is not None:
            chunk = str(delta.get("content") or "")
            if chunk:
                self.saw_delta = True
                self.text += chunk
            return chunk

        message = choice.get("message")
        if not isinstance(message, dict) or message.get("content") is None:
            return ""
        snapshot = str(message.get("content") or "")
        if not snapshot:
            return ""
        if not self.text:
            self.text = snapshot
            return snapshot
        if snapshot == self.text or self.text.startswith(snapshot):
            return ""
        if snapshot.startswith(self.text):
            suffix = snapshot[len(self.text):]
            self.text = snapshot
            return suffix
        if self.saw_delta:
            # A final full snapshot cannot safely replace chunks already delivered.
            return ""
        return ""