from __future__ import annotations

import json
import re
from dataclasses import dataclass
from pathlib import Path
from typing import Any

from pypdf import PdfReader

from us_cpa.sources import TaxYearCorpus, build_primary_law_authorities


TOPIC_RULES = [
    {
        "issue": "standard_deduction",
        "keywords": ("standard deduction",),
        "authority_slugs": ("i1040gi",),
        "answer_by_status": {
            "single": "$15,750",
            "married_filing_jointly": "$31,500",
            "qualifying_surviving_spouse": "$31,500",
            "head_of_household": "$23,625",
        },
        "summary_template": "{filing_status_label} filers use a {answer} standard deduction for tax year {tax_year}.",
        "confidence": "high",
    },
    {
        "issue": "schedule_c_required",
        "keywords": ("schedule c", "sole proprietor", "self-employment"),
        "authority_slugs": ("f1040sc", "i1040sc"),
        "answer": "Schedule C is generally required when a taxpayer reports sole proprietorship business income or expenses.",
        "summary": "Business income and expenses from a sole proprietorship generally belong on Schedule C.",
        "confidence": "medium",
    },
    {
        "issue": "schedule_d_required",
        "keywords": ("schedule d", "capital gains"),
        "authority_slugs": ("f1040sd", "i1040sd", "f8949", "i8949"),
        "answer": "Schedule D is generally required when a taxpayer reports capital gains or losses, often alongside Form 8949.",
        "summary": "Capital gains and losses generally flow through Schedule D, with Form 8949 supporting detail when required.",
        "confidence": "medium",
    },
    {
        "issue": "schedule_e_required",
        "keywords": ("schedule e", "rental income"),
        "authority_slugs": ("f1040se", "i1040se"),
        "answer": "Schedule E is generally required when a taxpayer reports rental real-estate income or expenses.",
        "summary": "Rental income and expenses generally belong on Schedule E.",
        "confidence": "medium",
    },
]


RISK_BY_CONFIDENCE = {
    "high": "low",
    "medium": "medium",
    "low": "high",
}


QUESTION_STOPWORDS = {
    "a",
    "also",
    "am",
    "an",
    "and",
    "are",
    "as",
    "at",
    "be",
    "before",
    "but",
    "by",
    "can",
    "considered",
    "did",
    "do",
    "does",
    "for",
    "from",
    "had",
    "has",
    "have",
    "her",
    "hers",
    "his",
    "i",
    "if",
    "in",
    "is",
    "it",
    "its",
    "my",
    "of",
    "or",
    "our",
    "she",
    "should",
    "that",
    "the",
    "their",
    "them",
    "they",
    "this",
    "to",
    "was",
    "we",
    "went",
    "what",
    "worked",
    "would",
    "year",
    "you",
    "your",
}


SEARCH_SOURCE_BONUS = {
    "irs_publication": 30,
    "irs_instructions": 20,
    "irs_faq": 10,
    "irs_form": 0,
}


def _normalize_question(question: str) -> str:
    return question.strip().lower()


def _filing_status_label(status: str) -> str:
    return status.replace("_", " ").title()


def _question_terms(normalized_question: str) -> list[str]:
    terms = []
    for token in re.findall(r"[a-z0-9]+", normalized_question):
        if len(token) < 3 or token in QUESTION_STOPWORDS or token.isdigit():
            continue
        terms.append(token)

    expanded = set(terms)
    if any(token in expanded for token in {"dependent", "dependents", "daughter", "son", "child", "children"}):
        expanded.update({"dependent", "qualifying", "child", "support", "residency"})
    if any(token in expanded for token in {"college", "school", "student", "tuition"}):
        expanded.update({"student", "school", "education", "temporary", "absence"})

    return sorted(expanded)


def _load_searchable_pages(path: Path) -> list[str]:
    payload = path.read_bytes()
    if payload.startswith(b"%PDF"):
        try:
            reader = PdfReader(path)
            pages = []
            for page in reader.pages:
                text = page.extract_text() or ""
                if text.strip():
                    pages.append(text)
            if pages:
                return pages
        except Exception:
            pass

    try:
        decoded = payload.decode("utf-8", errors="ignore")
    except Exception:
        return []
    return [decoded] if decoded.strip() else []


def _build_excerpt(text: str, terms: list[str], *, width: int = 420) -> str:
    lowered = text.lower()
    first_index = None
    for term in terms:
        idx = lowered.find(term)
        if idx >= 0 and (first_index is None or idx < first_index):
            first_index = idx
    if first_index is None:
        cleaned = " ".join(text.split())
        return cleaned[:width]

    start = max(0, first_index - 120)
    end = min(len(text), first_index + width)
    cleaned = " ".join(text[start:end].split())
    return cleaned


def _rank_research_hits(manifest: dict[str, Any], normalized_question: str) -> list[dict[str, Any]]:
    terms = _question_terms(normalized_question)
    if not terms:
        return []

    hits: list[dict[str, Any]] = []
    for source in manifest["sources"]:
        path = Path(source["localPath"])
        if not path.exists():
            continue
        pages = _load_searchable_pages(path)
        for page_number, text in enumerate(pages, start=1):
            lowered = text.lower()
            matched_terms = [term for term in terms if term in lowered]
            if not matched_terms:
                continue
            score = (
                len(matched_terms) * 10
                + SEARCH_SOURCE_BONUS.get(source["sourceClass"], 0)
                - int(source["authorityRank"])
            )
            hits.append(
                {
                    "slug": source["slug"],
                    "title": source["title"],
                    "sourceClass": source["sourceClass"],
                    "url": source["url"],
                    "localPath": source["localPath"],
                    "authorityRank": source["authorityRank"],
                    "page": page_number,
                    "score": score,
                    "matchedTerms": matched_terms,
                    "excerpt": _build_excerpt(text, matched_terms),
                }
            )

    hits.sort(key=lambda item: (-item["score"], item["authorityRank"], item["slug"], item["page"]))
    return hits[:5]


FILING_STATUS_PATTERNS = (
    (("qualifying surviving spouse",), "qualifying_surviving_spouse"),
    (("qualifying widow",), "qualifying_surviving_spouse"),
    (("qualifying widower",), "qualifying_surviving_spouse"),
    (("surviving spouse",), "qualifying_surviving_spouse"),
    (("married filing jointly",), "married_filing_jointly"),
    (("mfj",), "married_filing_jointly"),
    (("head of household",), "head_of_household"),
    (("hoh",), "head_of_household"),
    (("married filing separately",), "married_filing_separately"),
    (("mfs",), "married_filing_separately"),
    (("single",), "single"),
)


def _infer_filing_status(normalized_question: str, case_facts: dict[str, Any]) -> str:
    if "filingStatus" in case_facts:
        return case_facts["filingStatus"]

    for patterns, filing_status in FILING_STATUS_PATTERNS:
        if all(pattern in normalized_question for pattern in patterns):
            return filing_status

    return "single"


@dataclass
class QuestionEngine:
    corpus: TaxYearCorpus

    def _manifest(self, tax_year: int) -> dict[str, Any]:
        path = self.corpus.paths_for_year(tax_year).manifest_path
        if not path.exists():
            raise FileNotFoundError(
                f"Tax year {tax_year} corpus not found at {path}. Run fetch-year first."
            )
        return json.loads(path.read_text())

    def _authorities_for(self, manifest: dict[str, Any], slugs: tuple[str, ...]) -> list[dict[str, Any]]:
        found = []
        sources = {item["slug"]: item for item in manifest["sources"]}
        for slug in slugs:
            if slug in sources:
                source = sources[slug]
                found.append(
                    {
                        "slug": source["slug"],
                        "title": source["title"],
                        "sourceClass": source["sourceClass"],
                        "url": source["url"],
                        "localPath": source["localPath"],
                        "authorityRank": source["authorityRank"],
                    }
                )
        return found

    def answer(self, *, question: str, tax_year: int, case_facts: dict[str, Any]) -> dict[str, Any]:
        manifest = self._manifest(tax_year)
        normalized = _normalize_question(question)
        facts_used = [{"field": key, "value": value} for key, value in sorted(case_facts.items())]

        for rule in TOPIC_RULES:
            if all(keyword in normalized for keyword in rule["keywords"]):
                authorities = self._authorities_for(manifest, rule["authority_slugs"])
                if rule["issue"] == "standard_deduction":
                    filing_status = _infer_filing_status(normalized, case_facts)
                    answer = rule["answer_by_status"].get(filing_status, rule["answer_by_status"]["single"])
                    summary = rule["summary_template"].format(
                        filing_status_label=_filing_status_label(filing_status),
                        answer=answer,
                        tax_year=tax_year,
                    )
                else:
                    answer = rule["answer"]
                    summary = rule["summary"]

                return {
                    "issue": rule["issue"],
                    "taxYear": tax_year,
                    "factsUsed": facts_used,
                    "missingFacts": [],
                    "authorities": authorities,
                    "conclusion": {"answer": answer, "summary": summary},
                    "confidence": rule["confidence"],
                    "riskLevel": RISK_BY_CONFIDENCE[rule["confidence"]],
                    "followUpQuestions": [],
                    "primaryLawRequired": False,
                    "excerpts": [],
                }

        research_hits = _rank_research_hits(manifest, normalized)
        if research_hits:
            authorities = []
            seen = set()
            for hit in research_hits:
                if hit["slug"] in seen:
                    continue
                authorities.append(
                    {
                        "slug": hit["slug"],
                        "title": hit["title"],
                        "sourceClass": hit["sourceClass"],
                        "url": hit["url"],
                        "localPath": hit["localPath"],
                        "authorityRank": hit["authorityRank"],
                    }
                )
                seen.add(hit["slug"])

            return {
                "issue": "irs_corpus_research",
                "taxYear": tax_year,
                "factsUsed": facts_used,
                "missingFacts": [],
                "authorities": authorities,
                "excerpts": [
                    {
                        "slug": hit["slug"],
                        "title": hit["title"],
                        "page": hit["page"],
                        "matchedTerms": hit["matchedTerms"],
                        "excerpt": hit["excerpt"],
                    }
                    for hit in research_hits
                ],
                "conclusion": {
                    "answer": "Relevant IRS authorities were found in the downloaded tax-year corpus. Answer from those authorities directly, and only escalate further if the cited passages are still insufficient.",
                    "summary": "Relevant IRS materials in the cached tax-year corpus address this question. Use the cited passages below to answer it directly.",
                },
                "confidence": "medium",
                "riskLevel": "medium",
                "followUpQuestions": [],
                "primaryLawRequired": False,
            }

        return {
            "issue": "requires_primary_law_escalation",
            "taxYear": tax_year,
            "factsUsed": facts_used,
            "missingFacts": [
                "Internal Revenue Code or Treasury regulation analysis is required before answering this question confidently."
            ],
            "authorities": build_primary_law_authorities(question),
            "conclusion": {
                "answer": "Insufficient IRS-form and instruction support for a confident answer.",
                "summary": "This question needs primary-law analysis before a reliable answer can be given.",
            },
            "confidence": "low",
            "riskLevel": "high",
            "followUpQuestions": [
                "What facts drive the section-level issue?",
                "Is there an existing return position or drafted treatment to review?",
            ],
            "primaryLawRequired": True,
            "excerpts": [],
        }


def render_analysis(analysis: dict[str, Any]) -> str:
    lines = [analysis["conclusion"]["summary"]]
    lines.append(
        f"Confidence: {analysis['confidence']}. Risk: {analysis['riskLevel']}."
    )
    if analysis["factsUsed"]:
        facts = ", ".join(f"{item['field']}={item['value']}" for item in analysis["factsUsed"])
        lines.append(f"Facts used: {facts}.")
    if analysis["authorities"]:
        titles = "; ".join(item["title"] for item in analysis["authorities"])
        lines.append(f"Authorities: {titles}.")
    if analysis.get("excerpts"):
        excerpt_lines = []
        for item in analysis["excerpts"][:3]:
            excerpt_lines.append(f"{item['title']} p.{item['page']}: {item['excerpt']}")
        lines.append(f"Excerpts: {' | '.join(excerpt_lines)}")
    if analysis["missingFacts"]:
        lines.append(f"Open items: {' '.join(analysis['missingFacts'])}")
    return " ".join(lines)


def render_memo(analysis: dict[str, Any]) -> str:
    lines = [
        "# Tax Memo",
        "",
        f"## Issue\n{analysis['issue']}",
        "",
        "## Facts",
    ]
    if analysis["factsUsed"]:
        for item in analysis["factsUsed"]:
            lines.append(f"- {item['field']}: {item['value']}")
    else:
        lines.append("- No case-specific facts supplied.")
    lines.extend(["", "## Authorities"])
    if analysis["authorities"]:
        for authority in analysis["authorities"]:
            lines.append(f"- {authority['title']}")
    else:
        lines.append("- Primary-law escalation required.")
    if analysis.get("excerpts"):
        lines.extend(["", "## IRS Excerpts"])
        for item in analysis["excerpts"]:
            lines.append(f"- {item['title']} (page {item['page']}): {item['excerpt']}")
    lines.extend(
        [
            "",
            "## Analysis",
            analysis["conclusion"]["summary"],
            f"Confidence: {analysis['confidence']}",
            f"Risk level: {analysis['riskLevel']}",
            "",
            "## Conclusion",
            analysis["conclusion"]["answer"],
        ]
    )
    if analysis["missingFacts"]:
        lines.extend(["", "## Open Items"])
        for item in analysis["missingFacts"]:
            lines.append(f"- {item}")
    return "\n".join(lines)