"""Summarization middleware."""

import uuid
import warnings
from collections.abc import Callable, Iterable, Mapping
from functools import partial
from typing import Any, Literal, cast

from langchain_core.messages import (
    AnyMessage,
    MessageLikeRepresentation,
    RemoveMessage,
    ToolMessage,
)
from langchain_core.messages.human import HumanMessage
from langchain_core.messages.utils import count_tokens_approximately, trim_messages
from langgraph.graph.message import (
    REMOVE_ALL_MESSAGES,
)
from langgraph.runtime import Runtime

from langchain.agents.middleware.types import AgentMiddleware, AgentState
from langchain.chat_models import BaseChatModel, init_chat_model

TokenCounter = Callable[[Iterable[MessageLikeRepresentation]], int]

DEFAULT_SUMMARY_PROMPT = """<role>
Context Extraction Assistant
</role>

<primary_objective>
Your sole objective in this task is to extract the highest quality/most relevant context from the conversation history below.
</primary_objective>

<objective_information>
You're nearing the total number of input tokens you can accept, so you must extract the highest quality/most relevant pieces of information from your conversation history.
This context will then overwrite the conversation history presented below. Because of this, ensure the context you extract is only the most important information to your overall goal.
</objective_information>

<instructions>
The conversation history below will be replaced with the context you extract in this step. Because of this, you must do your very best to extract and record all of the most important context from the conversation history.
You want to ensure that you don't repeat any actions you've already completed, so the context you extract from the conversation history should be focused on the most important information to your overall goal.
</instructions>

The user will message you with the full message history you'll be extracting context from, to then replace. Carefully read over it all, and think deeply about what information is most important to your overall goal that should be saved:

With all of this in mind, please carefully read over the entire conversation history, and extract the most important and relevant context to replace it so that you can free up space in the conversation history.
Respond ONLY with the extracted context. Do not include any additional information, or text before or after the extracted context.

<messages>
Messages to summarize:
{messages}
</messages>"""  # noqa: E501

_DEFAULT_MESSAGES_TO_KEEP = 20
_DEFAULT_TRIM_TOKEN_LIMIT = 4000
_DEFAULT_FALLBACK_MESSAGE_COUNT = 15

ContextFraction = tuple[Literal["fraction"], float]
"""Fraction of model's maximum input tokens.

Example:
    To specify 50% of the model's max input tokens:

    ```python
    ("fraction", 0.5)
    ```
"""

ContextTokens = tuple[Literal["tokens"], int]
"""Absolute number of tokens.

Example:
    To specify 3000 tokens:

    ```python
    ("tokens", 3000)
    ```
"""

ContextMessages = tuple[Literal["messages"], int]
"""Absolute number of messages.

Example:
    To specify 50 messages:

    ```python
    ("messages", 50)
    ```
"""

ContextSize = ContextFraction | ContextTokens | ContextMessages
"""Union type for context size specifications.

Can be either:

- [`ContextFraction`][langchain.agents.middleware.summarization.ContextFraction]: A
    fraction of the model's maximum input tokens.
- [`ContextTokens`][langchain.agents.middleware.summarization.ContextTokens]: An absolute
    number of tokens.
- [`ContextMessages`][langchain.agents.middleware.summarization.ContextMessages]: An
    absolute number of messages.

Depending on use with `trigger` or `keep` parameters, this type indicates either
when to trigger summarization or how much context to retain.

Example:
    ```python
    # ContextFraction
    context_size: ContextSize = ("fraction", 0.5)

    # ContextTokens
    context_size: ContextSize = ("tokens", 3000)

    # ContextMessages
    context_size: ContextSize = ("messages", 50)
    ```
"""


def _get_approximate_token_counter(model: BaseChatModel) -> TokenCounter:
    """Tune parameters of approximate token counter based on model type."""
    if model._llm_type == "anthropic-chat":
        # 3.3 was estimated in an offline experiment, comparing with Claude's token-counting
        # API: https://platform.claude.com/docs/en/build-with-claude/token-counting
        return partial(count_tokens_approximately, chars_per_token=3.3)
    return count_tokens_approximately


class SummarizationMiddleware(AgentMiddleware):
    """Summarizes conversation history when token limits are approached.

    This middleware monitors message token counts and automatically summarizes older
    messages when a threshold is reached, preserving recent messages and maintaining
    context continuity by ensuring AI/Tool message pairs remain together.
    """

    def __init__(
        self,
        model: str | BaseChatModel,
        *,
        trigger: ContextSize | list[ContextSize] | None = None,
        keep: ContextSize = ("messages", _DEFAULT_MESSAGES_TO_KEEP),
        token_counter: TokenCounter = count_tokens_approximately,
        summary_prompt: str = DEFAULT_SUMMARY_PROMPT,
        trim_tokens_to_summarize: int | None = _DEFAULT_TRIM_TOKEN_LIMIT,
        **deprecated_kwargs: Any,
    ) -> None:
        """Initialize summarization middleware.

        Args:
            model: The language model to use for generating summaries.
            trigger: One or more thresholds that trigger summarization.

                Provide a single
                [`ContextSize`][langchain.agents.middleware.summarization.ContextSize]
                tuple or a list of tuples, in which case summarization runs when any
                threshold is met.

                !!! example

                    ```python
                    # Trigger summarization when 50 messages is reached
                    ("messages", 50)

                    # Trigger summarization when 3000 tokens is reached
                    ("tokens", 3000)

                    # Trigger summarization either when 80% of model's max input tokens
                    # is reached or when 100 messages is reached (whichever comes first)
                    [("fraction", 0.8), ("messages", 100)]
                    ```

                    See [`ContextSize`][langchain.agents.middleware.summarization.ContextSize]
                    for more details.
            keep: Context retention policy applied after summarization.

                Provide a [`ContextSize`][langchain.agents.middleware.summarization.ContextSize]
                tuple to specify how much history to preserve.

                Defaults to keeping the most recent `20` messages.

                Does not support multiple values like `trigger`.

                !!! example

                    ```python
                    # Keep the most recent 20 messages
                    ("messages", 20)

                    # Keep the most recent 3000 tokens
                    ("tokens", 3000)

                    # Keep the most recent 30% of the model's max input tokens
                    ("fraction", 0.3)
                    ```
            token_counter: Function to count tokens in messages.
            summary_prompt: Prompt template for generating summaries.
            trim_tokens_to_summarize: Maximum tokens to keep when preparing messages for
                the summarization call.

                Pass `None` to skip trimming entirely.
        """
        # Handle deprecated parameters
        if "max_tokens_before_summary" in deprecated_kwargs:
            value = deprecated_kwargs["max_tokens_before_summary"]
            warnings.warn(
                "max_tokens_before_summary is deprecated. Use trigger=('tokens', value) instead.",
                DeprecationWarning,
                stacklevel=2,
            )
            if trigger is None and value is not None:
                trigger = ("tokens", value)

        if "messages_to_keep" in deprecated_kwargs:
            value = deprecated_kwargs["messages_to_keep"]
            warnings.warn(
                "messages_to_keep is deprecated. Use keep=('messages', value) instead.",
                DeprecationWarning,
                stacklevel=2,
            )
            if keep == ("messages", _DEFAULT_MESSAGES_TO_KEEP):
                keep = ("messages", value)

        super().__init__()

        if isinstance(model, str):
            model = init_chat_model(model)

        self.model = model
        if trigger is None:
            self.trigger: ContextSize | list[ContextSize] | None = None
            trigger_conditions: list[ContextSize] = []
        elif isinstance(trigger, list):
            validated_list = [self._validate_context_size(item, "trigger") for item in trigger]
            self.trigger = validated_list
            trigger_conditions = validated_list
        else:
            validated = self._validate_context_size(trigger, "trigger")
            self.trigger = validated
            trigger_conditions = [validated]
        self._trigger_conditions = trigger_conditions

        self.keep = self._validate_context_size(keep, "keep")
        if token_counter is count_tokens_approximately:
            self.token_counter = _get_approximate_token_counter(self.model)
        else:
            self.token_counter = token_counter
        self.summary_prompt = summary_prompt
        self.trim_tokens_to_summarize = trim_tokens_to_summarize

        requires_profile = any(condition[0] == "fraction" for condition in self._trigger_conditions)
        if self.keep[0] == "fraction":
            requires_profile = True
        if requires_profile and self._get_profile_limits() is None:
            msg = (
                "Model profile information is required to use fractional token limits, "
                "and is unavailable for the specified model. Please use absolute token "
                "counts instead, or pass "
                '`\n\nChatModel(..., profile={"max_input_tokens": ...})`.\n\n'
                "with a desired integer value of the model's maximum input tokens."
            )
            raise ValueError(msg)

    def before_model(self, state: AgentState, runtime: Runtime) -> dict[str, Any] | None:  # noqa: ARG002
        """Process messages before model invocation, potentially triggering summarization."""
        messages = state["messages"]
        self._ensure_message_ids(messages)

        total_tokens = self.token_counter(messages)
        if not self._should_summarize(messages, total_tokens):
            return None

        cutoff_index = self._determine_cutoff_index(messages)

        if cutoff_index <= 0:
            return None

        messages_to_summarize, preserved_messages = self._partition_messages(messages, cutoff_index)

        summary = self._create_summary(messages_to_summarize)
        new_messages = self._build_new_messages(summary)

        return {
            "messages": [
                RemoveMessage(id=REMOVE_ALL_MESSAGES),
                *new_messages,
                *preserved_messages,
            ]
        }

    async def abefore_model(self, state: AgentState, runtime: Runtime) -> dict[str, Any] | None:  # noqa: ARG002
        """Process messages before model invocation, potentially triggering summarization."""
        messages = state["messages"]
        self._ensure_message_ids(messages)

        total_tokens = self.token_counter(messages)
        if not self._should_summarize(messages, total_tokens):
            return None

        cutoff_index = self._determine_cutoff_index(messages)

        if cutoff_index <= 0:
            return None

        messages_to_summarize, preserved_messages = self._partition_messages(messages, cutoff_index)

        summary = await self._acreate_summary(messages_to_summarize)
        new_messages = self._build_new_messages(summary)

        return {
            "messages": [
                RemoveMessage(id=REMOVE_ALL_MESSAGES),
                *new_messages,
                *preserved_messages,
            ]
        }

    def _should_summarize(self, messages: list[AnyMessage], total_tokens: int) -> bool:
        """Determine whether summarization should run for the current token usage."""
        if not self._trigger_conditions:
            return False

        for kind, value in self._trigger_conditions:
            if kind == "messages" and len(messages) >= value:
                return True
            if kind == "tokens" and total_tokens >= value:
                return True
            if kind == "fraction":
                max_input_tokens = self._get_profile_limits()
                if max_input_tokens is None:
                    continue
                threshold = int(max_input_tokens * value)
                if threshold <= 0:
                    threshold = 1
                if total_tokens >= threshold:
                    return True
        return False

    def _determine_cutoff_index(self, messages: list[AnyMessage]) -> int:
        """Choose cutoff index respecting retention configuration."""
        kind, value = self.keep
        if kind in {"tokens", "fraction"}:
            token_based_cutoff = self._find_token_based_cutoff(messages)
            if token_based_cutoff is not None:
                return token_based_cutoff
            # None cutoff -> model profile data not available (caught in __init__ but
            # here for safety), fallback to message count
            return self._find_safe_cutoff(messages, _DEFAULT_MESSAGES_TO_KEEP)
        return self._find_safe_cutoff(messages, cast("int", value))

    def _find_token_based_cutoff(self, messages: list[AnyMessage]) -> int | None:
        """Find cutoff index based on target token retention."""
        if not messages:
            return 0

        kind, value = self.keep
        if kind == "fraction":
            max_input_tokens = self._get_profile_limits()
            if max_input_tokens is None:
                return None
            target_token_count = int(max_input_tokens * value)
        elif kind == "tokens":
            target_token_count = int(value)
        else:
            return None

        if target_token_count <= 0:
            target_token_count = 1

        if self.token_counter(messages) <= target_token_count:
            return 0

        # Use binary search to identify the earliest message index that keeps the
        # suffix within the token budget.
        left, right = 0, len(messages)
        cutoff_candidate = len(messages)
        max_iterations = len(messages).bit_length() + 1
        for _ in range(max_iterations):
            if left >= right:
                break

            mid = (left + right) // 2
            if self.token_counter(messages[mid:]) <= target_token_count:
                cutoff_candidate = mid
                right = mid
            else:
                left = mid + 1

        if cutoff_candidate == len(messages):
            cutoff_candidate = left

        if cutoff_candidate >= len(messages):
            if len(messages) == 1:
                return 0
            cutoff_candidate = len(messages) - 1

        # Advance past any ToolMessages to avoid splitting AI/Tool pairs
        return self._find_safe_cutoff_point(messages, cutoff_candidate)

    def _get_profile_limits(self) -> int | None:
        """Retrieve max input token limit from the model profile."""
        try:
            profile = self.model.profile
        except AttributeError:
            return None

        if not isinstance(profile, Mapping):
            return None

        max_input_tokens = profile.get("max_input_tokens")

        if not isinstance(max_input_tokens, int):
            return None

        return max_input_tokens

    def _validate_context_size(self, context: ContextSize, parameter_name: str) -> ContextSize:
        """Validate context configuration tuples."""
        kind, value = context
        if kind == "fraction":
            if not 0 < value <= 1:
                msg = f"Fractional {parameter_name} values must be between 0 and 1, got {value}."
                raise ValueError(msg)
        elif kind in {"tokens", "messages"}:
            if value <= 0:
                msg = f"{parameter_name} thresholds must be greater than 0, got {value}."
                raise ValueError(msg)
        else:
            msg = f"Unsupported context size type {kind} for {parameter_name}."
            raise ValueError(msg)
        return context

    def _build_new_messages(self, summary: str) -> list[HumanMessage]:
        return [
            HumanMessage(content=f"Here is a summary of the conversation to date:\n\n{summary}")
        ]

    def _ensure_message_ids(self, messages: list[AnyMessage]) -> None:
        """Ensure all messages have unique IDs for the add_messages reducer."""
        for msg in messages:
            if msg.id is None:
                msg.id = str(uuid.uuid4())

    def _partition_messages(
        self,
        conversation_messages: list[AnyMessage],
        cutoff_index: int,
    ) -> tuple[list[AnyMessage], list[AnyMessage]]:
        """Partition messages into those to summarize and those to preserve."""
        messages_to_summarize = conversation_messages[:cutoff_index]
        preserved_messages = conversation_messages[cutoff_index:]

        return messages_to_summarize, preserved_messages

    def _find_safe_cutoff(self, messages: list[AnyMessage], messages_to_keep: int) -> int:
        """Find safe cutoff point that preserves AI/Tool message pairs.

        Returns the index where messages can be safely cut without separating
        related AI and Tool messages. Returns `0` if no safe cutoff is found.

        This is aggressive with summarization - if the target cutoff lands in the
        middle of tool messages, we advance past all of them (summarizing more).
        """
        if len(messages) <= messages_to_keep:
            return 0

        target_cutoff = len(messages) - messages_to_keep
        return self._find_safe_cutoff_point(messages, target_cutoff)

    def _find_safe_cutoff_point(self, messages: list[AnyMessage], cutoff_index: int) -> int:
        """Find a safe cutoff point that doesn't split AI/Tool message pairs.

        If the message at cutoff_index is a ToolMessage, advance until we find
        a non-ToolMessage. This ensures we never cut in the middle of parallel
        tool call responses.
        """
        while cutoff_index < len(messages) and isinstance(messages[cutoff_index], ToolMessage):
            cutoff_index += 1
        return cutoff_index

    def _create_summary(self, messages_to_summarize: list[AnyMessage]) -> str:
        """Generate summary for the given messages."""
        if not messages_to_summarize:
            return "No previous conversation history."

        trimmed_messages = self._trim_messages_for_summary(messages_to_summarize)
        if not trimmed_messages:
            return "Previous conversation was too long to summarize."

        try:
            response = self.model.invoke(self.summary_prompt.format(messages=trimmed_messages))
            return response.text.strip()
        except Exception as e:  # noqa: BLE001
            return f"Error generating summary: {e!s}"

    async def _acreate_summary(self, messages_to_summarize: list[AnyMessage]) -> str:
        """Generate summary for the given messages."""
        if not messages_to_summarize:
            return "No previous conversation history."

        trimmed_messages = self._trim_messages_for_summary(messages_to_summarize)
        if not trimmed_messages:
            return "Previous conversation was too long to summarize."

        try:
            response = await self.model.ainvoke(
                self.summary_prompt.format(messages=trimmed_messages)
            )
            return response.text.strip()
        except Exception as e:  # noqa: BLE001
            return f"Error generating summary: {e!s}"

    def _trim_messages_for_summary(self, messages: list[AnyMessage]) -> list[AnyMessage]:
        """Trim messages to fit within summary generation limits."""
        try:
            if self.trim_tokens_to_summarize is None:
                return messages
            return cast(
                "list[AnyMessage]",
                trim_messages(
                    messages,
                    max_tokens=self.trim_tokens_to_summarize,
                    token_counter=self.token_counter,
                    start_on="human",
                    strategy="last",
                    allow_partial=True,
                    include_system=True,
                ),
            )
        except Exception:  # noqa: BLE001
            return messages[-_DEFAULT_FALLBACK_MESSAGE_COUNT:]