"""Clarifier — single-question elicitation for sparse cold-start personas.

When a user composes a persona with only a thin description ("I like
thrillers, slow pacing annoys me") and clicks Recommend, the agent has
very little to work with. Most multi-turn systems either (a) recommend
on noise and hope, or (b) ask five follow-up questions and feel evasive.

This module sits between those extremes: detect when the cold-start
persona is genuinely too sparse to act on, generate ONE focused,
multiple-choice clarifying question, take the user's answer as an
injected preference signal, then proceed normally.

Triggers only when:
  - persona has no history (n_reviews == 0)
  - explicit signals are sparse (themes + complaints < 3)
  - the description itself is thin (< 20 words)

Never triggers more than once per session — the multi-turn conversation
engine handles further refinement.
"""
from __future__ import annotations

import logging

from pydantic import BaseModel, Field

from core.llm import LLMClient
from core.persona import UserPersona

log = logging.getLogger(__name__)

SPARSE_SIGNAL_THRESHOLD = 3
THIN_DESCRIPTION_WORDS = 20


# ──────────────────────────────────────────────────────────────────────────────
# Schema
# ──────────────────────────────────────────────────────────────────────────────

class ClarifyingQuestion(BaseModel):
    """LLM-generated single clarifying question with quick-pick answers."""
    question: str = Field(
        description="A single focused question that, when answered, would "
                    "meaningfully narrow the recommendations. Conversational, "
                    "not robotic. Maximum 18 words."
    )
    quick_answers: list[str] = Field(
        description="3-4 short, mutually exclusive answer options the user can "
                    "click. Each option max 6 words. Together they should cover "
                    "the realistic answer space."
    )


# ──────────────────────────────────────────────────────────────────────────────
# Trigger heuristic — deterministic, no LLM call
# ──────────────────────────────────────────────────────────────────────────────

def should_clarify(persona: UserPersona) -> bool:
    """Decide whether to ask a clarifying question before recommending.

    Deterministic and cheap. Returns True only when the persona is genuinely
    sparse enough that recommendations without further signal would be noise.
    """
    if persona.n_reviews > 0:
        return False
    signal_count = (len(persona.preferred_themes or [])
                    + len(persona.common_complaints or []))
    desc_length = len((persona.voice_one_liner or "").split())
    return (signal_count < SPARSE_SIGNAL_THRESHOLD
            and desc_length < THIN_DESCRIPTION_WORDS)


# ──────────────────────────────────────────────────────────────────────────────
# Question generation
# ──────────────────────────────────────────────────────────────────────────────

def generate_clarifying_question(persona: UserPersona,
                                 llm: LLMClient | None = None
                                 ) -> ClarifyingQuestion:
    """Generate one focused clarifying question for this sparse persona.

    Uses the bulk model — this is an elicitation task, not deep reasoning.
    Falls back to a safe generic question if the LLM call fails.
    """
    llm = llm or LLMClient()
    themes = ", ".join(persona.preferred_themes) or "(none stated)"
    complaints = ", ".join(persona.common_complaints) or "(none stated)"
    desc = persona.voice_one_liner or "(no description)"

    prompt = (
        f"A user is starting a recommendation session with a thin persona. "
        f"Before recommending, ask ONE focused question whose answer would "
        f"meaningfully narrow the recommendations.\n\n"
        f"PERSONA SO FAR\n"
        f"  Description: {desc}\n"
        f"  Drawn to: {themes}\n"
        f"  Put off by: {complaints}\n\n"
        f"YOUR QUESTION MUST:\n"
        f"  - target the BIGGEST remaining ambiguity (mood, sub-genre, "
        f"length, tone, comfort vs challenge — pick the one most useful)\n"
        f"  - NOT re-ask anything already stated\n"
        f"  - have 3 or 4 distinct, clickable answer options\n"
        f"  - sound like a friend asking, not a customer survey\n\n"
        f"EXAMPLE SHAPE (do not copy verbatim):\n"
        f'  Q: "What mood are you in — light and quick, or something to sink into?"\n'
        f'  Options: ["Light and quick", "Something to sink into", "Either"]'
    )
    try:
        return llm.structured(
            prompt, ClarifyingQuestion, model="bulk",
            system="You ask one well-chosen clarifying question. Brief, "
                   "conversational, helpful — never a survey.",
        )
    except Exception as e:
        log.warning(f"Clarifier LLM call failed ({type(e).__name__}); "
                    f"falling back to generic question")
        return ClarifyingQuestion(
            question="What mood are you in right now?",
            quick_answers=["Something light and quick",
                           "Something to sink into",
                           "Either — surprise me"],
        )


# ──────────────────────────────────────────────────────────────────────────────
# Answer injection
# ──────────────────────────────────────────────────────────────────────────────

def apply_clarification(persona: UserPersona, answer: str) -> UserPersona:
    """Inject the clarification answer into the persona.

    The answer goes to the FRONT of preferred_themes so retrieval picks it
    up as the strongest signal, and is appended to voice_one_liner so the
    HyDE prompt and reranker also see it.
    """
    answer = (answer or "").strip()
    if not answer:
        return persona

    existing = [t for t in (persona.preferred_themes or [])
                if t.lower() != answer.lower()]
    persona.preferred_themes = [answer] + existing
    persona.preferred_themes = persona.preferred_themes[:12]

    voice = (persona.voice_one_liner or "").rstrip(".")
    persona.voice_one_liner = (
        f"{voice}. Specifically asked for: {answer}."
        if voice else f"Specifically asked for: {answer}."
    )
    return persona