"""Streaming response handler — accumulates SSE chunks into a complete Message."""

import time
from collections.abc import AsyncIterator, Callable

from app.models.config import DisplayConfig
from app.models.message import Message
from app.models.tool_call import ToolCall, ToolCallFunction
from app.utils.logging import get_logger
from app.utils.token_counter import TokenUsage

logger = get_logger(__name__)

# Minimum interval between content update callbacks (seconds)
_UPDATE_THROTTLE_INTERVAL = 0.1


class StreamHandler:
    """Processes an SSE chunk stream and produces a complete assistant Message.

    Accumulates content deltas and tool call fragments. Notifies the UI via
    optional callbacks during streaming.
    """

    def __init__(self, display_config: DisplayConfig) -> None:
        self._display_config = display_config
        self._accumulated_content: str = ""
        self._accumulated_reasoning: str = ""
        self._tool_calls: dict[int, dict[str, str]] = {}
        self._usage: TokenUsage | None = None
        self._on_content: Callable[[str], None] | None = None
        self._on_thinking: Callable[[], None] | None = None
        self._on_done: Callable[[], None] | None = None

    def set_callbacks(
        self,
        on_content: Callable[[str], None] | None = None,
        on_thinking: Callable[[], None] | None = None,
        on_done: Callable[[], None] | None = None,
    ) -> None:
        """Set UI callbacks for streaming updates.

        Args:
            on_content: Called with accumulated content string (throttled to ~100ms).
            on_thinking: Called once when first reasoning token arrives.
            on_done: Called when streaming is complete.
        """
        self._on_content = on_content
        self._on_thinking = on_thinking
        self._on_done = on_done

    async def process_stream(self, chunk_iter: AsyncIterator[dict]) -> Message:
        """Consume a chunk iterator and return the final Message.

        Args:
            chunk_iter: Async iterator of parsed SSE chunk dicts.

        Returns:
            Complete assistant Message with accumulated content and tool calls.
        """
        thinking_notified = False
        last_update_time = 0.0

        async for chunk in chunk_iter:
            self._process_chunk(chunk)

            if not self._display_config.stream_output:
                continue

            # Notify thinking once
            if (
                not thinking_notified
                and not self._accumulated_content
                and self._accumulated_reasoning
                and self._on_thinking is not None
            ):
                self._on_thinking()
                thinking_notified = True

            # Throttled content updates
            if self._accumulated_content and self._on_content is not None:
                now = time.monotonic()
                if now - last_update_time >= _UPDATE_THROTTLE_INTERVAL:
                    self._on_content(self._accumulated_content)
                    last_update_time = now

        # Final content update (ensures last chunk is shown)
        if (
            self._display_config.stream_output
            and self._accumulated_content
            and self._on_content is not None
        ):
            self._on_content(self._accumulated_content)

        if self._on_done is not None:
            self._on_done()

        tool_calls = self._build_tool_calls() or None
        return Message(
            role="assistant",
            content=self._accumulated_content or None,
            tool_calls=tool_calls,
        )

    def _process_chunk(self, chunk: dict) -> None:
        """Extract content, tool calls, and usage from a single SSE chunk."""
        choices = chunk.get("choices", [])
        if choices:
            delta = choices[0].get("delta", {})

            content_piece = delta.get("content")
            if content_piece:
                self._accumulated_content += content_piece

            reasoning_piece = delta.get("reasoning")
            if reasoning_piece:
                self._accumulated_reasoning += reasoning_piece

            for tc_delta in delta.get("tool_calls", []):
                idx = tc_delta.get("index", 0)
                if idx not in self._tool_calls:
                    self._tool_calls[idx] = {
                        "id": tc_delta.get("id", ""),
                        "name": "",
                        "arguments": "",
                    }
                entry = self._tool_calls[idx]
                if tc_delta.get("id"):
                    entry["id"] = tc_delta["id"]
                func = tc_delta.get("function", {})
                if func.get("name"):
                    entry["name"] += func["name"]
                if func.get("arguments"):
                    entry["arguments"] += func["arguments"]

        usage_data = chunk.get("usage")
        if usage_data:
            self._usage = TokenUsage(
                prompt_tokens=usage_data.get("prompt_tokens", 0),
                completion_tokens=usage_data.get("completion_tokens", 0),
                total_tokens=usage_data.get("total_tokens", 0),
            )

    def _build_tool_calls(self) -> list[ToolCall]:
        """Convert accumulated tool call fragments into sorted ToolCall list."""
        if not self._tool_calls:
            return []

        result: list[ToolCall] = []
        for idx in sorted(self._tool_calls):
            entry = self._tool_calls[idx]
            result.append(
                ToolCall(
                    id=entry["id"],
                    type="function",
                    function=ToolCallFunction(
                        name=entry["name"],
                        arguments=entry["arguments"],
                    ),
                )
            )
        return result

    def get_partial_message(self) -> Message | None:
        """Return whatever content/tool_calls have been accumulated so far."""
        tool_calls = self._build_tool_calls() or None
        if not self._accumulated_content and not tool_calls:
            return None
        return Message(
            role="assistant",
            content=self._accumulated_content or None,
            tool_calls=tool_calls,
        )

    @property
    def usage(self) -> TokenUsage | None:
        """Token usage reported by the API, if available."""
        return self._usage

    @property
    def had_reasoning_only(self) -> bool:
        """True if the model produced reasoning tokens but no content or tool calls."""
        return bool(self._accumulated_reasoning) and not self._accumulated_content and not self._tool_calls

    def reset(self) -> None:
        """Clear all accumulators for the next turn."""
        self._accumulated_content = ""
        self._accumulated_reasoning = ""
        self._tool_calls.clear()
        self._usage = None
        self._on_content = None
        self._on_thinking = None
        self._on_done = None