"""PYQ Pattern Analysis Service.

Analyses extracted PYQ questions for patterns:
- Repeated topics across years
- Marks distribution
- Answer type distribution
- Chapter-wise and topic-wise question counts
- Years seen

Rules:
- Every pattern must be backed by actual question IDs.
- If fewer than 2 years exist, say "not enough data for pattern analysis."
- Do not use words like "sure shot" or fake high-yield.
- Use "seen in uploaded papers" instead.
"""
from __future__ import annotations

from collections import Counter
from dataclasses import dataclass, field
from typing import Any

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.models.previous_question import PreviousQuestion
from app.models.previous_paper import PreviousPaper


@dataclass
class PatternEvidence:
    question_id: str
    question_text: str
    year: int | None
    marks: int | None
    chapter: str
    topic: str
    paper_id: str
    paper_title: str
    source_url: str | None


@dataclass
class TopicPattern:
    topic: str
    chapter: str
    count: int
    years_seen: list[int]
    question_ids: list[str]
    evidence: list[PatternEvidence]


@dataclass
class MarksDistribution:
    marks: int
    count: int
    percentage: float


@dataclass
class AnswerTypeDistribution:
    answer_type: str
    count: int
    percentage: float


@dataclass
class ChapterWiseCount:
    chapter: str
    total_questions: int
    total_marks: int
    topics: list[str]


@dataclass
class PatternAnalysisResult:
    repeated_topics: list[TopicPattern] = field(default_factory=list)
    marks_distribution: list[MarksDistribution] = field(default_factory=list)
    answer_type_distribution: list[AnswerTypeDistribution] = field(default_factory=list)
    chapter_wise_count: list[ChapterWiseCount] = field(default_factory=list)
    topic_wise_count: list[TopicPattern] = field(default_factory=list)
    years_seen: list[int] = field(default_factory=list)
    total_questions: int = 0
    total_papers: int = 0
    evidence_list: list[PatternEvidence] = field(default_factory=list)
    analysis_note: str = ""
    confidence: float = 0.0


_MIN_YEARS_FOR_PATTERN = 2


def analyze_pyq_patterns(
    db: Session,
    user_id: str,
    *,
    subject: str = "",
    board: str = "",
    class_level: str = "",
    chapter: str = "",
    topic: str = "",
    year_range: tuple[int | None, int | None] | None = None,
    paper_ids: list[str] | None = None,
) -> PatternAnalysisResult:
    """Analyze PYQ patterns from uploaded questions in the database.

    All patterns are backed by actual question IDs from the database.
    """
    result = PatternAnalysisResult()

    paper_query = (
        select(PreviousPaper)
        .where(PreviousPaper.user_id == user_id)
        .where(PreviousPaper.verification_status == "verified")
    )
    if paper_ids:
        paper_query = paper_query.where(PreviousPaper.id.in_(paper_ids))
    if subject:
        paper_query = paper_query.where(PreviousPaper.subject == subject)
    if board:
        paper_query = paper_query.where(PreviousPaper.board == board)
    if class_level:
        paper_query = paper_query.where(PreviousPaper.class_level == class_level)

    papers = list(db.scalars(paper_query).all())

    if year_range:
        min_year, max_year = year_range
        papers = [
            paper for paper in papers
            if (not min_year or not paper.year or paper.year >= min_year)
            and (not max_year or not paper.year or paper.year <= max_year)
        ]

    result.total_papers = len(papers)

    questions: list[PreviousQuestion] = []
    for paper in papers:
        paper_questions = list(paper.questions)
        for q in paper_questions:
            # Apply filters
            if chapter and q.chapter and chapter.lower() not in q.chapter.lower():
                continue
            if topic and q.topic and topic.lower() not in q.topic.lower():
                continue
            if year_range:
                min_year, max_year = year_range
                if min_year and q.year and q.year < min_year:
                    continue
                if max_year and q.year and q.year > max_year:
                    continue
            questions.append(q)

    result.total_questions = len(questions)

    if not questions:
        result.analysis_note = (
            "No uploaded PYQ questions found for the given filters. "
            "Upload previous year question papers to unlock pattern analysis."
        )
        return result

    # Build evidence list
    evidence_map: dict[str, PatternEvidence] = {}
    for q in questions:
        evidence = PatternEvidence(
            question_id=q.id,
            question_text=q.question_text[:200],
            year=q.year,
            marks=q.marks,
            chapter=q.chapter or "",
            topic=q.topic or "",
            paper_id=q.previous_paper.id,
            paper_title=q.previous_paper.title,
            source_url=q.previous_paper.source_url,
        )
        evidence_map[q.id] = evidence
        result.evidence_list.append(evidence)

    # Years seen
    all_years = sorted({q.year for q in questions if q.year is not None})
    result.years_seen = all_years

    # Check if enough data for pattern analysis
    if len(all_years) < _MIN_YEARS_FOR_PATTERN:
        result.analysis_note = (
            f"Only {len(all_years)} year(s) of data available. "
            "Upload papers from at least 2 different years for meaningful pattern analysis."
        )
        result.confidence = 0.3
        # Still provide basic stats
        _compute_basic_stats(questions, evidence_map, result)
        return result

    # Sufficient data — compute full patterns
    result.confidence = min(0.5 + len(all_years) * 0.05, 1.0)

    # Repeated topics
    topic_year_map: dict[str, dict[int, list[str]]] = {}
    for q in questions:
        # Unknown-year evidence cannot prove repetition across exam years.
        if q.year is None:
            continue
        topic_key = q.topic or q.chapter or "Unknown"
        if topic_key not in topic_year_map:
            topic_year_map[topic_key] = {}
        year = q.year
        if year not in topic_year_map[topic_key]:
            topic_year_map[topic_key][year] = []
        topic_year_map[topic_key][year].append(q.id)

    for topic_key, year_map in topic_year_map.items():
        if len(year_map) >= 2:
            years = sorted([y for y in year_map if y > 0])
            q_ids = []
            evidence_items = []
            for y, ids in year_map.items():
                q_ids.extend(ids)
                evidence_items.extend([evidence_map[qid] for qid in ids if qid in evidence_map])

            # Find chapter for this topic
            chapter_val = ""
            for q in questions:
                if (q.topic or q.chapter or "") == topic_key:
                    chapter_val = q.chapter or ""
                    break

            result.repeated_topics.append(TopicPattern(
                topic=topic_key,
                chapter=chapter_val,
                count=len(q_ids),
                years_seen=years,
                question_ids=q_ids,
                evidence=evidence_items[:5],
            ))

    # Sort repeated topics by frequency
    result.repeated_topics.sort(key=lambda t: t.count, reverse=True)

    _compute_basic_stats(questions, evidence_map, result)

    if not result.analysis_note:
        result.analysis_note = (
            f"Pattern analysis based on {result.total_questions} questions "
            f"across {len(all_years)} years ({', '.join(str(y) for y in all_years)}). "
            "All patterns are backed by uploaded question paper evidence."
        )

    return result


def _compute_basic_stats(
    questions: list[PreviousQuestion],
    evidence_map: dict[str, PatternEvidence],
    result: PatternAnalysisResult,
) -> None:
    """Compute marks distribution, answer type distribution, and chapter-wise counts."""
    # Marks distribution
    marks_counter: Counter[int] = Counter()
    for q in questions:
        if q.marks is not None:
            marks_counter[q.marks] += 1

    total = len(questions) or 1
    result.marks_distribution = [
        MarksDistribution(
            marks=marks,
            count=count,
            percentage=round(count / total * 100, 1),
        )
        for marks, count in sorted(marks_counter.items())
    ]

    # Answer type distribution
    type_counter: Counter[str] = Counter()
    for q in questions:
        # Standard extraction fills question_type; answer_type is optional.
        at = q.answer_type or q.question_type or "unknown"
        type_counter[at] += 1

    result.answer_type_distribution = [
        AnswerTypeDistribution(
            answer_type=at,
            count=count,
            percentage=round(count / total * 100, 1),
        )
        for at, count in type_counter.most_common()
    ]

    # Chapter-wise count
    chapter_map: dict[str, dict[str, Any]] = {}
    for q in questions:
        ch = q.chapter or "Unknown"
        if ch not in chapter_map:
            chapter_map[ch] = {"count": 0, "marks": 0, "topics": set()}
        chapter_map[ch]["count"] += 1
        chapter_map[ch]["marks"] += q.marks or 0
        if q.topic:
            chapter_map[ch]["topics"].add(q.topic)

    result.chapter_wise_count = [
        ChapterWiseCount(
            chapter=ch,
            total_questions=data["count"],
            total_marks=data["marks"],
            topics=sorted(data["topics"]),
        )
        for ch, data in sorted(chapter_map.items(), key=lambda x: x[1]["count"], reverse=True)
    ]

    # Topic-wise count (all topics, not just repeated)
    topic_map: dict[str, dict[str, Any]] = {}
    for q in questions:
        t = q.topic or q.chapter or "Unknown"
        if t not in topic_map:
            topic_map[t] = {"count": 0, "years": set(), "ids": [], "chapter": q.chapter or ""}
        topic_map[t]["count"] += 1
        if q.year:
            topic_map[t]["years"].add(q.year)
        topic_map[t]["ids"].append(q.id)

    result.topic_wise_count = [
        TopicPattern(
            topic=t,
            chapter=data["chapter"],
            count=data["count"],
            years_seen=sorted(data["years"]),
            question_ids=data["ids"],
            evidence=[evidence_map[qid] for qid in data["ids"][:5] if qid in evidence_map],
        )
        for t, data in sorted(topic_map.items(), key=lambda x: x[1]["count"], reverse=True)
    ]