"""Finance assistant: LLM-backed expense parsing and ledger actions."""

import json
import re
import logging
from datetime import datetime
from typing import Generator
from huggingface_hub import InferenceClient

from ledger import Ledger

logger = logging.getLogger(__name__)

MODEL = "openai/gpt-oss-20b"

SYSTEM = """\
You are a personal finance assistant. Help the user log expenses, query spending summaries, and manage their ledger.

When the user describes an expense, extract it and include a JSON action block in your response:
```json
{"action": "add", "date": "YYYY-MM-DD", "description": "...", "category": "Food|Transport|Utilities|Entertainment|Health|Shopping|Rent|Other", "amount": 0.00}
```

When the user wants to undo or delete the last entry:
```json
{"action": "delete_last"}
```

Use today's date if none is given. Keep replies brief and friendly.
If the user asks about their spending, use the ledger context below to answer accurately.
If no ledger action is needed, just respond conversationally — no JSON block."""


# ── context & parsing ─────────────────────────────────────────────────────────

def _ledger_context(ledger: Ledger) -> str:
    if ledger.df.empty:
        return "Ledger is empty."
    total = ledger.total()
    by_cat = ledger.by_category()
    cat_str = " | ".join(
        f"{k} ${v:.2f}" for k, v in sorted(by_cat.items(), key=lambda x: -x[1])
    )
    recent = ledger.recent(5).to_string(index=False)
    return f"Total: ${total:.2f}  |  {cat_str}\nRecent entries:\n{recent}"


def _parse_action(text: str) -> dict | None:
    m = re.search(r"```json\s*(\{.*?\})\s*```", text, re.DOTALL)
    if m:
        try:
            return json.loads(m.group(1))
        except json.JSONDecodeError:
            pass
    return None


def _clean(text: str) -> str:
    """Strip JSON action blocks from visible reply."""
    return re.sub(r"```json.*?```", "", text, flags=re.DOTALL).strip()


def _build_messages(message: str, history: list[dict], ledger: Ledger) -> list[dict]:
    system = SYSTEM + "\n\nCurrent ledger:\n" + _ledger_context(ledger)
    return [{"role": "system", "content": system}] + history + [{"role": "user", "content": message}]


# ── actions ───────────────────────────────────────────────────────────────────

def execute(action: dict, ledger: Ledger, fallback_desc: str = "") -> str:
    """Run a parsed action against the ledger. Returns a confirmation string."""
    if action.get("action") == "add":
        ok = ledger.add(
            date=action.get("date", datetime.now().strftime("%Y-%m-%d")),
            description=action.get("description", fallback_desc),
            category=action.get("category", "Other"),
            amount=float(action.get("amount", 0)),
        )
        if ok:
            return f"✅ Logged **{action.get('category')}** — ${float(action.get('amount', 0)):.2f}"
        return "❌ Failed to save entry."

    if action.get("action") == "delete_last":
        return "🗑️ Last entry removed." if ledger.delete_last() else "Nothing to delete."

    return ""


# ── inference ─────────────────────────────────────────────────────────────────

def stream_response(
    message: str, history: list[dict], ledger: Ledger, token: str
) -> Generator[tuple[str, dict | None], None, None]:
    """
    Yields (partial_reply, action) tuples.
    action is None on all intermediate yields; populated only on the final yield.
    """
    client = InferenceClient(token=token, model=MODEL)
    messages = _build_messages(message, history, ledger)

    accumulated = ""
    for chunk in client.chat_completion(messages, max_tokens=512, stream=True, temperature=0.2):
        if chunk.choices and chunk.choices[0].delta.content:
            accumulated += chunk.choices[0].delta.content
            yield _clean(accumulated), None

    yield _clean(accumulated), _parse_action(accumulated)


def batch_response(
    message: str, history: list[dict], ledger: Ledger, token: str
) -> tuple[str, dict | None]:
    """Synchronous single-call variant used by the Telegram bot."""
    client = InferenceClient(token=token, model=MODEL)
    messages = _build_messages(message, history, ledger)
    raw = client.chat_completion(messages, max_tokens=512, temperature=0.2).choices[0].message.content
    return _clean(raw), _parse_action(raw)