from __future__ import annotations

import ast
import operator
import re
from dataclasses import dataclass
from typing import Callable

from langchain_core.messages import HumanMessage, SystemMessage
from langchain_mistralai import ChatMistralAI

from memory_agent.retrieval import HybridRetriever
from memory_agent.storage import FaissMemoryStore

FALLBACK_MESSAGE = (
    "I don't have enough stored knowledge yet to answer that. "
    "Share a few facts about your domain, and I will learn and help."
)
UNDERSTOOD_MESSAGE = "understood"


@dataclass(slots=True)
class ParsedFact:
    key: str
    value: str


class FactParser:
    _ASSIGNMENT_PATTERNS = (
        re.compile(r"^\s*([A-Za-z][A-Za-z0-9 _-]{0,80})\s*(?:=|:|is)\s*(.+?)\s*$", re.IGNORECASE),
        re.compile(
            r"^\s*(?:set|update|remember)\s+(.+?)\s+(?:to|as|=)\s+(.+?)\s*$",
            re.IGNORECASE,
        ),
    )

    def parse(self, text: str) -> ParsedFact | None:
        for pattern in self._ASSIGNMENT_PATTERNS:
            match = pattern.match(text)
            if not match:
                continue
            key = self._clean_key(match.group(1))
            value = self._clean_value(match.group(2))
            if key and value:
                return ParsedFact(key=key, value=value)
        return None

    @staticmethod
    def _clean_key(raw: str) -> str:
        cleaned = raw.strip().strip(".")
        cleaned = re.sub(r"\b(the|a|an)\b", "", cleaned, flags=re.IGNORECASE)
        cleaned = re.sub(r"\s+", " ", cleaned)
        return cleaned.strip()

    @staticmethod
    def _clean_value(raw: str) -> str:
        cleaned = raw.strip().strip(".").strip()
        if (cleaned.startswith('"') and cleaned.endswith('"')) or (
            cleaned.startswith("'") and cleaned.endswith("'")
        ):
            return cleaned[1:-1].strip()
        return cleaned


class SafeMathEvaluator:
    _BINARY_OPERATORS: dict[type[ast.operator], Callable[[float, float], float]] = {
        ast.Add: operator.add,
        ast.Sub: operator.sub,
        ast.Mult: operator.mul,
        ast.Div: operator.truediv,
        ast.Pow: operator.pow,
        ast.Mod: operator.mod,
        ast.FloorDiv: operator.floordiv,
    }
    _UNARY_OPERATORS: dict[type[ast.unaryop], Callable[[float], float]] = {
        ast.UAdd: operator.pos,
        ast.USub: operator.neg,
    }

    def evaluate(self, expression: str, facts: dict[str, str]) -> float:
        tree = ast.parse(expression, mode="eval")
        return float(self._evaluate_node(tree.body, facts))

    def _evaluate_node(self, node: ast.AST, facts: dict[str, str]) -> float:
        if isinstance(node, ast.Constant) and isinstance(node.value, (int, float)):
            return float(node.value)

        if isinstance(node, ast.Name):
            key = FaissMemoryStore.normalize_key(node.id)
            if key not in facts:
                raise ValueError(f"Unknown variable: {node.id}")
            try:
                return float(facts[key])
            except ValueError as error:
                raise ValueError(f"Variable '{node.id}' is not numeric.") from error

        if isinstance(node, ast.BinOp):
            op_type = type(node.op)
            if op_type not in self._BINARY_OPERATORS:
                raise ValueError("Unsupported operator in expression.")
            left = self._evaluate_node(node.left, facts)
            right = self._evaluate_node(node.right, facts)
            return self._BINARY_OPERATORS[op_type](left, right)

        if isinstance(node, ast.UnaryOp):
            op_type = type(node.op)
            if op_type not in self._UNARY_OPERATORS:
                raise ValueError("Unsupported unary operator in expression.")
            operand = self._evaluate_node(node.operand, facts)
            return self._UNARY_OPERATORS[op_type](operand)

        raise ValueError("Unsupported expression.")


class KnowledgeService:
    def __init__(
        self,
        store: FaissMemoryStore,
        retriever: HybridRetriever,
        llm: ChatMistralAI,
        top_k: int,
        user_prompt_template: str,
    ) -> None:
        self._store = store
        self._retriever = retriever
        self._llm = llm
        self._top_k = top_k
        self._user_prompt_template = user_prompt_template
        self._fact_parser = FactParser()
        self._math_evaluator = SafeMathEvaluator()

    def store_knowledge(
        self,
        namespace: str,
        knowledge_text: str,
        fact_key: str | None = None,
        fact_value: str | None = None,
    ) -> str:
        parsed_fact = self._fact_parser.parse(knowledge_text)
        key = fact_key or (parsed_fact.key if parsed_fact else None)
        value = fact_value or (parsed_fact.value if parsed_fact else None)
        content = knowledge_text
        if key and value:
            content = f"{key} = {value}"

        self._store.upsert_knowledge(
            namespace=namespace,
            content=content,
            fact_key=key,
            fact_value=value,
        )
        return UNDERSTOOD_MESSAGE

    def answer_from_knowledge(self, namespace: str, question: str) -> str:
        facts = self._store.fetch_fact_map(namespace=namespace)
        expression = self._extract_expression(question=question)
        if expression:
            try:
                value = self._math_evaluator.evaluate(expression=expression, facts=facts)
                formatted_value = int(value) if value.is_integer() else round(value, 6)
                substituted = self._substitute_expression(expression=expression, facts=facts)
                return f"Based on stored knowledge: {substituted} = {formatted_value}."
            except ValueError:
                pass

        results = self._retriever.retrieve(namespace=namespace, query=question, k=self._top_k)
        if not results:
            return FALLBACK_MESSAGE

        context = "\n\n".join(
            f"- {doc.page_content}\n  metadata={doc.metadata}"
            for doc, _ in results
        )
        prompt = self._user_prompt_template.format(
            fallback_message=FALLBACK_MESSAGE,
            context=context,
            question=question,
        )
        response = self._llm.invoke(
            [
                SystemMessage(content="You are a memory-only answer tool."),
                HumanMessage(content=prompt),
            ]
        )
        content = str(response.content).strip()
        if not content:
            return FALLBACK_MESSAGE
        return content

    @staticmethod
    def _extract_expression(question: str) -> str | None:
        quoted = re.findall(r'["\']([^"\']+)["\']', question)
        for candidate in quoted:
            if re.search(r"[+\-*/^%()]", candidate):
                return candidate.replace("^", "**")

        inline = re.search(
            r"(?:calculate|equation|expression)\s*[:\-,]?\s*([A-Za-z0-9_+\-*/^%(). ]+)",
            question,
            flags=re.IGNORECASE,
        )
        if inline:
            expression = inline.group(1).strip().rstrip(".")
            fragment = re.search(
                r"((?:[A-Za-z_][A-Za-z0-9_]*|\d+(?:\.\d+)?|\([^)]+\))\s*"
                r"(?:[+\-*/^%]\s*(?:[A-Za-z_][A-Za-z0-9_]*|\d+(?:\.\d+)?|\([^)]+\))\s*)+)",
                expression,
                flags=re.IGNORECASE,
            )
            if fragment:
                return fragment.group(1).strip().replace("^", "**")
            if re.search(r"[+\-*/^%()]", expression):
                return expression.replace("^", "**")

        fragment = re.search(
            r"((?:[A-Za-z_][A-Za-z0-9_]*|\d+(?:\.\d+)?|\([^)]+\))\s*"
            r"(?:[+\-*/^%]\s*(?:[A-Za-z_][A-Za-z0-9_]*|\d+(?:\.\d+)?|\([^)]+\))\s*)+)",
            question,
            flags=re.IGNORECASE,
        )
        if fragment:
            return fragment.group(1).strip().replace("^", "**")
        return None

    @staticmethod
    def _substitute_expression(expression: str, facts: dict[str, str]) -> str:
        substituted = expression
        # Replace longer keys first so short keys do not partially replace longer names.
        for key in sorted(facts.keys(), key=len, reverse=True):
            value = facts[key]
            pattern = re.compile(rf"\b{re.escape(key)}\b", flags=re.IGNORECASE)
            substituted = pattern.sub(value, substituted)
        return substituted