"""
Conversation history management.

Backed by LangChain's InMemoryChatMessageHistory for structured message
storage. The agent state dict still uses plain {"role", "content"} dicts
(so the rest of the app stays unchanged), but summarization now uses
LangChain message types internally.

When the raw character count exceeds SUMMARIZE_THRESHOLD, the oldest
turns (beyond the last KEEP_RECENT pairs) are collapsed into a single
summary message so the context never explodes on long sessions.
"""
from __future__ import annotations

import logging

from langchain_core.chat_history     import InMemoryChatMessageHistory
from langchain_core.messages         import (
    SystemMessage,
    HumanMessage,
    AIMessage,
    BaseMessage,
)

logger = logging.getLogger(__name__)

SUMMARIZE_THRESHOLD = 24_000   # chars — rough proxy for ~8 k tokens
KEEP_RECENT         = 4        # verbatim turn-pairs to keep after summarization



def _to_lc_message(msg: dict) -> BaseMessage:
    """Convert a {"role": ..., "content": ...} dict to a LangChain message."""
    role    = msg.get("role", "user")
    content = msg.get("content", "")
    if role == "system":
        return SystemMessage(content=content)
    if role == "assistant":
        return AIMessage(content=content)
    return HumanMessage(content=content)


def _from_lc_message(msg: BaseMessage) -> dict:
    """Convert a LangChain message back to a plain dict."""
    if isinstance(msg, SystemMessage):
        return {"role": "system",    "content": msg.content}
    if isinstance(msg, AIMessage):
        return {"role": "assistant", "content": msg.content}
    return {"role": "user", "content": msg.content}


def _history_from_messages(messages: list[dict]) -> InMemoryChatMessageHistory:
    """Build a LangChain chat history object from a plain messages list."""
    history = InMemoryChatMessageHistory()
    for m in messages:
        history.add_message(_to_lc_message(m))
    return history



def make_state(system_prompt: str) -> dict:
    """Return a fresh agent state dict."""
    return {
        "messages":      [{"role": "system", "content": system_prompt}],
        "current_spec":  None,
        "current_code":  "",
        "iteration":     0,
        "heal_attempts": 0,
        "last_error":    None,
    }


def append_user(state: dict, content: str) -> dict:
    """Return new state with user message appended."""
    return {**state, "messages": state["messages"] + [{"role": "user", "content": content}]}


def append_assistant(state: dict, content: str) -> dict:
    """Return new state with assistant message appended."""
    return {**state, "messages": state["messages"] + [{"role": "assistant", "content": content}]}


def total_chars(messages: list[dict]) -> int:
    return sum(len(m.get("content", "")) for m in messages)


def get_lc_history(state: dict) -> InMemoryChatMessageHistory:
    """
    Return a LangChain InMemoryChatMessageHistory built from state["messages"].
    Useful for passing to LangChain chains that expect a BaseChatMessageHistory.
    """
    return _history_from_messages(state["messages"])


def maybe_summarize(state: dict, summarize_fn) -> dict:
    """
    If total chars exceed SUMMARIZE_THRESHOLD, summarize the oldest turns
    using summarize_fn, then replace them with a single summary message.

    summarize_fn(messages_to_summarize: list[dict]) -> str
    """
    messages = state["messages"]
    if total_chars(messages) <= SUMMARIZE_THRESHOLD:
        return state

    # Always keep system [0] + last KEEP_RECENT*2 messages verbatim
    cutoff = max(1, len(messages) - KEEP_RECENT * 2)
    old    = messages[1:cutoff]    # skip system message
    keep   = messages[cutoff:]

    if not old:
        return state

    logger.info("Summarizing %d old messages via LangChain history", len(old))

    # Build a temporary LangChain history just for the messages being summarized
    temp_history = _history_from_messages(old)
    summary_text = summarize_fn(
        [_from_lc_message(m) for m in temp_history.messages]
    )

    new_messages = (
        [messages[0]]
        + [{"role": "system", "content": f"[Earlier conversation summary]\n{summary_text}"}]
        + keep
    )
    return {**state, "messages": new_messages}