"""Knowledge Gap Detection Service.

Aggregates signals from AI sessions to identify gaps in the knowledge base.
Results are served by the analytics API and cached for 1 hour.

Signals:
1. Frequent free-text escapes — FlowPilot's options didn't cover a common scenario
2. High escalation rate by domain — domains where engineers can't self-resolve
3. Discovery-mode resolutions — novel problems solved without flow guidance
4. Repeated unmatched patterns — keyword-frequency based (Phase 4: embedding clustering)
"""
import logging
from collections import Counter
from datetime import datetime, timezone, timedelta
from typing import Any, Optional
from uuid import UUID

from pydantic import BaseModel
from sqlalchemy import select, func, case, text
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.ai_session import AISession
from app.models.ai_session_step import AISessionStep
from app.models.tree import Tree

logger = logging.getLogger(__name__)

# Cache for expensive gap analysis
_cache: dict[str, Any] = {}
_cache_expiry: dict[str, datetime] = {}
CACHE_TTL = timedelta(hours=1)


class KnowledgeGap(BaseModel):
    gap_type: str  # "weak_options" | "high_escalation" | "uncharted_territory" | "repeated_pattern"
    domain: str | None = None
    severity: str  # "high" | "medium" | "low"
    title: str
    description: str
    evidence: dict[str, Any] = {}
    suggested_action: str


class KnowledgeGapReport(BaseModel):
    generated_at: datetime
    gaps: list[KnowledgeGap]


async def get_knowledge_gaps(
    account_id: UUID,
    db: AsyncSession,
    period_days: int = 30,
) -> KnowledgeGapReport:
    """Generate a knowledge gap report for the account.

    Results are cached for 1 hour per account.
    """
    cache_key = f"gaps:{account_id}:{period_days}"
    now = datetime.now(timezone.utc)

    if cache_key in _cache and _cache_expiry.get(cache_key, now) > now:
        return _cache[cache_key]

    period_start = now - timedelta(days=period_days)

    gaps: list[KnowledgeGap] = []

    # Signal 1: Frequent free-text escapes
    signal1 = await _detect_weak_options(account_id, period_start, db)
    gaps.extend(signal1)

    # Signal 2: High escalation rate by domain
    signal2 = await _detect_high_escalation(account_id, period_start, db)
    gaps.extend(signal2)

    # Signal 3: Discovery-mode resolutions
    signal3 = await _detect_uncharted_territory(account_id, period_start, db)
    gaps.extend(signal3)

    # Signal 4: Repeated unmatched patterns (keyword-based for Phase 3)
    signal4 = await _detect_repeated_patterns(account_id, period_start, db)
    gaps.extend(signal4)

    # Sort by severity (high > medium > low)
    severity_order = {"high": 0, "medium": 1, "low": 2}
    gaps.sort(key=lambda g: severity_order.get(g.severity, 3))

    report = KnowledgeGapReport(generated_at=now, gaps=gaps)

    _cache[cache_key] = report
    _cache_expiry[cache_key] = now + CACHE_TTL

    return report


async def _detect_weak_options(
    account_id: UUID,
    period_start: datetime,
    db: AsyncSession,
) -> list[KnowledgeGap]:
    """Signal 1: Find questions where engineers frequently use free-text escapes."""
    # Count free-text usage per step context_message (the question asked)
    result = await db.execute(
        select(
            AISessionStep.context_message,
            func.count(AISessionStep.id).label("total"),
            func.sum(case((AISessionStep.was_free_text.is_(True), 1), else_=0)).label("free_text_count"),
        )
        .join(AISession, AISessionStep.session_id == AISession.id)
        .where(
            AISession.account_id == account_id,
            AISession.created_at >= period_start,
            AISessionStep.step_type == "question",
            AISessionStep.context_message.isnot(None),
            AISessionStep.responded_at.isnot(None),
        )
        .group_by(AISessionStep.context_message)
        .having(func.count(AISessionStep.id) >= 3)  # Minimum sample size
        .order_by(func.sum(case((AISessionStep.was_free_text.is_(True), 1), else_=0)).desc())
        .limit(5)
    )

    gaps = []
    for row in result.all():
        context_msg, total_raw, free_text_raw = row
        total = int(total_raw or 0)
        free_text_count = int(free_text_raw or 0)
        if total == 0 or not free_text_count:
            continue
        rate = free_text_count / total
        if rate < 0.3:
            continue

        severity = "high" if rate > 0.6 else "medium"
        gaps.append(KnowledgeGap(
            gap_type="weak_options",
            severity=severity,
            title=f"Weak options: {(context_msg or '')[:80]}",
            description=(
                f"Engineers used free-text input {free_text_count}/{total} times "
                f"({rate:.0%}) when asked this question. The predefined options "
                f"may not cover common scenarios."
            ),
            evidence={
                "context_message": context_msg,
                "total_responses": total,
                "free_text_count": free_text_count,
                "free_text_rate": round(rate, 3),
            },
            suggested_action="Review the free-text responses and add common answers as options.",
        ))

    return gaps


async def _detect_high_escalation(
    account_id: UUID,
    period_start: datetime,
    db: AsyncSession,
) -> list[KnowledgeGap]:
    """Signal 2: Find domains with >40% escalation rate."""
    result = await db.execute(
        select(
            AISession.problem_domain,
            func.count(AISession.id).label("total"),
            func.sum(case(
                (AISession.status == "resolved", 1), else_=0
            )).label("resolved"),
            func.sum(case(
                (AISession.status.in_(["escalated", "requesting_escalation"]), 1), else_=0
            )).label("escalated"),
        )
        .where(
            AISession.account_id == account_id,
            AISession.created_at >= period_start,
            AISession.problem_domain.isnot(None),
            AISession.status.in_(["resolved", "escalated", "requesting_escalation"]),
        )
        .group_by(AISession.problem_domain)
        .having(func.count(AISession.id) >= 3)  # Minimum sample
    )

    gaps = []
    for row in result.all():
        domain, total_raw, resolved_raw, escalated_raw = row
        total = int(total_raw or 0)
        resolved = int(resolved_raw or 0)
        escalated = int(escalated_raw or 0)
        if total == 0 or not escalated:
            continue
        escalation_rate = escalated / total
        if escalation_rate < 0.4:
            continue

        severity = "high" if escalation_rate > 0.6 else "medium"
        gaps.append(KnowledgeGap(
            gap_type="high_escalation",
            domain=domain,
            severity=severity,
            title=f"High escalation rate in {domain}",
            description=(
                f"{escalated}/{total} sessions ({escalation_rate:.0%}) in {domain} "
                f"were escalated. Only {resolved} resolved independently."
            ),
            evidence={
                "domain": domain,
                "total": total,
                "resolved": resolved,
                "escalated": escalated,
                "escalation_rate": round(escalation_rate, 3),
            },
            suggested_action=f"Create or improve troubleshooting flows for {domain} issues.",
        ))

    return gaps


async def _detect_uncharted_territory(
    account_id: UUID,
    period_start: datetime,
    db: AsyncSession,
) -> list[KnowledgeGap]:
    """Signal 3: Find discovery-mode resolutions (novel problems solved without flows)."""
    result = await db.execute(
        select(
            AISession.problem_domain,
            func.count(AISession.id).label("count"),
        )
        .where(
            AISession.account_id == account_id,
            AISession.created_at >= period_start,
            AISession.status == "resolved",
            AISession.confidence_tier == "discovery",
        )
        .group_by(AISession.problem_domain)
        .having(func.count(AISession.id) >= 2)
        .order_by(func.count(AISession.id).desc())
        .limit(5)
    )

    gaps = []
    for row in result.all():
        domain, count = row
        severity = "high" if count >= 5 else "medium" if count >= 3 else "low"
        domain_label = domain or "unknown domain"
        gaps.append(KnowledgeGap(
            gap_type="uncharted_territory",
            domain=domain,
            severity=severity,
            title=f"Novel resolutions in {domain_label}",
            description=(
                f"{count} sessions in {domain_label} were resolved in discovery mode "
                f"(no matching flow, low confidence). These represent knowledge capture "
                f"opportunities — check the Review Queue for auto-generated proposals."
            ),
            evidence={
                "domain": domain,
                "discovery_resolution_count": count,
            },
            suggested_action="Review pending flow proposals or create flows from these session patterns.",
        ))

    return gaps


async def _detect_repeated_patterns(
    account_id: UUID,
    period_start: datetime,
    db: AsyncSession,
) -> list[KnowledgeGap]:
    """Signal 4: Find repeated unmatched intake patterns (keyword-frequency based).

    Phase 3 uses keyword frequency on problem_summary. Phase 4 will use
    embedding clustering for deeper semantic analysis.
    """
    # Get problem summaries from unmatched sessions
    result = await db.execute(
        select(AISession.problem_summary, AISession.problem_domain)
        .where(
            AISession.account_id == account_id,
            AISession.created_at >= period_start,
            AISession.problem_summary.isnot(None),
            AISession.matched_flow_id.is_(None),
        )
        .limit(200)
    )
    rows = result.all()

    if len(rows) < 3:
        return []

    # Extract keywords from summaries and count frequency
    word_counts: Counter[str] = Counter()
    domain_for_word: dict[str, str | None] = {}
    for summary, domain in rows:
        if not summary:
            continue
        words = set(summary.lower().split())
        # Filter out common stop words and short words
        stop_words = {"the", "a", "an", "is", "are", "was", "were", "in", "on", "at",
                       "to", "for", "of", "and", "or", "not", "can", "can't", "with",
                       "from", "by", "this", "that", "it", "its", "has", "have", "had",
                       "user", "users", "issue", "error", "problem"}
        keywords = {w for w in words if len(w) > 3 and w not in stop_words}
        for kw in keywords:
            word_counts[kw] += 1
            if kw not in domain_for_word:
                domain_for_word[kw] = domain

    gaps = []
    # Find keywords that appear in many unmatched sessions
    for keyword, count in word_counts.most_common(3):
        if count < 3:
            continue
        severity = "medium" if count >= 5 else "low"
        domain = domain_for_word.get(keyword)
        gaps.append(KnowledgeGap(
            gap_type="repeated_pattern",
            domain=domain,
            severity=severity,
            title=f"Recurring unmatched pattern: '{keyword}'",
            description=(
                f"The keyword '{keyword}' appeared in {count} sessions that had no "
                f"matching flow. This may indicate a systematic knowledge gap."
            ),
            evidence={
                "keyword": keyword,
                "unmatched_session_count": count,
                "domain": domain,
            },
            suggested_action=f"Search for '{keyword}' in recent sessions and consider creating a flow.",
        ))

    return gaps