from __future__ import annotations

import argparse
import json
import math
import re
from collections import Counter
from dataclasses import dataclass

from tqdm import tqdm

from .config import Settings
from .ollama_client import OllamaClient
from .pdf_processing import ChunkRecord, discover_pdfs, extract_chunks_from_pdf
from .vector_store import ChromaMathStore, RetrievedChunk


PLAIN_FRACTION_RE = re.compile(r"\b(?:[A-Za-z]+|\d+)\s*/\s*(?:[A-Za-z]+|\d+)\b")


@dataclass
class SupplementalChunk:
    record: ChunkRecord
    embedding: list[float]


def build_messages(question: str, chunks: list[RetrievedChunk]) -> list[dict[str, str]]:
    best_chapter = infer_label([chunk.chapter_name for chunk in chunks])
    best_topic = infer_label([chunk.topic for chunk in chunks])

    context_parts = []
    for index, chunk in enumerate(chunks, start=1):
        context_parts.append(
            f"[Source {index}]\n"
            f"Chapter: {chunk.chapter_name}\n"
            f"Topic: {chunk.topic}\n"
            f"Page: {chunk.page_number}\n"
            f"Text:\n{chunk.text}"
        )

    joined_context = "\n\n".join(context_parts)
    system_prompt = (
        "You are an advanced AI Mathematics Tutor and Solver specialized in accurate, verified, step-by-step mathematical reasoning.\n"
        "Your PRIMARY GOAL is MATHEMATICAL CORRECTNESS — not sounding academic or verbose.\n\n"
        "Use only the retrieved context to answer the question. If the context is not enough, say that clearly instead of guessing.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "CORE RULES\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "1. NEVER hallucinate formulas, theorems, chapter names, topic numbers, labels, or references.\n"
        "2. NEVER invent: Formula IDs, “P4”, “Theorem 2”, fake verification statements, or fake derivations.\n"
        "3. ONLY use formulas that are mathematically relevant to the problem.\n"
        "4. EVERY equation must logically follow from the previous equation.\n"
        "5. NEVER generate meaningless expressions such as: nested unnecessary integrals, invalid substitutions, or symbolic nonsense.\n"
        "6. If the mathematical expression is unclear, corrupted, or OCR extraction seems wrong, respond with: 'The mathematical expression is unclear. Please upload a clearer image or rewrite the question.'\n"
        "7. NEVER pretend verification succeeded unless it is actually correct.\n"
        "8. Accuracy is MORE important than speed or style.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "OCR / IMAGE UNDERSTANDING RULES\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "When solving questions extracted from images:\n"
        "1. Carefully identify: powers (², ³), limits of integration, fractions, derivatives, Greek symbols like π, and superscripts/subscripts.\n"
        "2. Distinguish carefully between: sin²x and sin'x, 0 and O, n and π, 1 and l, x² and x.\n"
        "3. Before solving, internally verify that the interpreted equation is mathematically sensible.\n"
        "4. If OCR output appears inconsistent or nonsensical: DO NOT SOLVE. Instead ask for a clearer image.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "MATHEMATICAL SOLVING RULES\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "For EVERY problem:\n"
        "1. Identify the problem type first.\n"
        "2. Choose ONLY the correct mathematical method.\n"
        "3. Show COMPLETE step-by-step derivation.\n"
        "4. Clearly show: Given expression, Formula used, Substitution (if any), Simplification, Computation, Final Answer.\n"
        "5. Use proper LaTeX formatting. Use `$$ ... $$` for standalone equations and `$ ... $` for inline maths.\n"
        "6. Final answers MUST always be enclosed in `\\boxed{...}`.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "INTEGRATION & DEFINITE INTEGRAL RULES\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "1. Check carefully for: substitution, integration by parts, trigonometric identities, partial fractions.\n"
        "2. NEVER confuse: sin²x with sin'(x) or derivative notation with exponents.\n"
        "3. For logarithmic integrals, use correct formulas.\n"
        "4. Verify signs (+/-) carefully.\n"
        "5. Correctly apply limits for definite integrals.\n"
        "6. Check convergence/divergence for improper integrals.\n"
        "7. Never add arbitrary constants to definite integrals.\n"
        "8. DIFFERENTIATE the final answer to verify correctness.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "VERIFICATION LAYER\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "Before giving the final response:\n"
        "1. Recheck every algebraic manipulation, substitutions, and trigonometric identities.\n"
        "2. Recompute the final answer mentally/symbolically.\n"
        "3. Verify the final result: differentiate antiderivatives, substitute solutions back, check arithmetic consistency.\n"
        "4. If any mistake is found: AUTOMATICALLY CORRECT the full solution before responding.\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "STRICTLY FORBIDDEN\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "DO NOT:\n"
        "- hallucinate steps\n"
        "- fabricate verification\n"
        "- invent formulas\n"
        "- generate symbolic nonsense\n"
        "- output contradictory equations\n"
        "- force a solution when OCR is unclear\n"
        "- use irrelevant methods\n"
        "- claim confidence without verification\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "OUTPUT FORMAT\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "Use EXACTLY this structure:\n\n"
        f"Chapter: {best_chapter}\n"
        f"Topic: {best_topic}\n\n"
        "## Given\n\n"
        "## Formula Used\n\n"
        "## Step-by-Step Solution\n\n"
        "## Verification\n\n"
        "## Final Answer\n\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "FINAL PRIORITY\n"
        "━━━━━━━━━━━━━━━━━━\n"
        "Correctness > Clarity > Formatting > Speed\n\n"
        "If uncertain: re-solve carefully, verify again, do NOT guess."
    )
    user_prompt = f"Question:\n{question}\n\nRetrieved context:\n{joined_context}"
    return [
        {"role": "system", "content": system_prompt},
        {"role": "user", "content": user_prompt},
    ]


def build_reformat_messages(
    question: str,
    answer: str,
    chapter: str,
    topic: str,
) -> list[dict[str, str]]:
    system_prompt = (
        "You are an advanced AI Mathematics Tutor cleaning up a Class 12 Mathematics answer.\n"
        "Rewrite the answer into clean Markdown without changing the maths or adding new facts.\n"
        "Convert all mathematics into proper LaTeX.\n"
        "Use `$$ ... $$` for standalone equations and `$ ... $` for short inline maths.\n"
        "Do not leave plain-text fractions like `y/x` or `dy/dx` if they should be proper fractions.\n"
        "Final answers must always be enclosed in a box using `\\boxed{}`.\n"
        "Use EXACTLY this structure:\n"
        f"Chapter: {chapter}\n"
        f"Topic: {topic}\n\n"
        "## Given\n"
        "## Formula Used\n"
        "## Step-by-Step Solution\n"
        "## Verification\n"
        "## Final Answer\n"
        "Put important equations on separate lines and do not use tables.\n"
    )
    user_prompt = (
        f"Original question:\n{question}\n\n"
        f"Answer to clean up:\n{answer}"
    )
    return [
        {"role": "system", "content": system_prompt},
        {"role": "user", "content": user_prompt},
    ]


def needs_reformatting(answer: str) -> bool:
    has_final_answer = "## Final Answer" in answer
    has_structure = any(
        marker in answer
        for marker in ("## Given", "## Step-by-Step Solution", "## Formula Used")
    )
    uses_plain_fractions = bool(PLAIN_FRACTION_RE.search(answer)) and "\\frac{" not in answer
    missing_display_math = "\\frac{" in answer and "$$" not in answer and "\\[" not in answer
    return not (has_final_answer and has_structure) or uses_plain_fractions or missing_display_math


def infer_label(values: list[str]) -> str:
    if not values:
        return "Not identified"
    return Counter(values).most_common(1)[0][0]


def batched(items: list[ChunkRecord], size: int) -> list[list[ChunkRecord]]:
    return [items[index:index + size] for index in range(0, len(items), size)]


def cosine_similarity(left: list[float], right: list[float]) -> float:
    numerator = sum(l * r for l, r in zip(left, right))
    left_norm = math.sqrt(sum(value * value for value in left))
    right_norm = math.sqrt(sum(value * value for value in right))
    if left_norm == 0 or right_norm == 0:
        return 0.0
    return numerator / (left_norm * right_norm)


def build_supplemental_chunks(
    chunks: list[ChunkRecord],
    *,
    ollama: OllamaClient,
    model: str,
) -> list[SupplementalChunk]:
    embeddings: list[list[float]] = []
    for chunk_batch in batched(chunks, 16):
        embeddings.extend(
            ollama.embed_texts(
                [chunk.text for chunk in chunk_batch],
                model=model,
            )
        )

    return [
        SupplementalChunk(record=chunk, embedding=embedding)
        for chunk, embedding in zip(chunks, embeddings)
    ]


def rank_supplemental_chunks(
    *,
    query_embedding: list[float],
    extra_chunks: list[SupplementalChunk],
    top_k: int,
) -> list[RetrievedChunk]:
    ranked = sorted(
        extra_chunks,
        key=lambda chunk: cosine_similarity(query_embedding, chunk.embedding),
        reverse=True,
    )[:top_k]

    return [
        RetrievedChunk(
            chunk_id=chunk.record.chunk_id,
            text=chunk.record.text,
            chapter_number=chunk.record.chapter_number,
            chapter_name=chunk.record.chapter_name,
            topic=chunk.record.topic,
            page_number=chunk.record.page_number,
            source_file=chunk.record.source_file,
            distance=max(0.0, 1.0 - cosine_similarity(query_embedding, chunk.embedding)),
        )
        for chunk in ranked
    ]


def merge_retrieved_chunks(
    store_chunks: list[RetrievedChunk],
    extra_chunks: list[RetrievedChunk],
    *,
    top_k: int,
) -> list[RetrievedChunk]:
    if not store_chunks:
        return extra_chunks[:top_k]
    if not extra_chunks:
        return store_chunks[:top_k]

    store_limit = min(len(store_chunks), max(1, (top_k + 1) // 2))
    extra_limit = min(len(extra_chunks), max(1, top_k - store_limit))

    merged = store_chunks[:store_limit] + extra_chunks[:extra_limit]
    remaining = top_k - len(merged)
    if remaining <= 0:
        return merged[:top_k]

    leftovers = store_chunks[store_limit:] + extra_chunks[extra_limit:]
    return (merged + leftovers[:remaining])[:top_k]


def run_ingestion(settings: Settings, reset: bool = False) -> dict[str, int]:
    settings.chroma_dir.mkdir(parents=True, exist_ok=True)
    settings.processed_dir.mkdir(parents=True, exist_ok=True)

    data_dir = settings.root_dir / "data"
    data_dir.mkdir(parents=True, exist_ok=True)

    pdf_files = discover_pdfs(data_dir)
    if not pdf_files:
        raise FileNotFoundError(f"No PDF files were found in the data directory ({data_dir}).")

    all_chunks: list[ChunkRecord] = []
    for pdf_file in pdf_files:
        all_chunks.extend(
            extract_chunks_from_pdf(
                file_path=pdf_file,
                chunk_size=settings.chunk_size,
                chunk_overlap=settings.chunk_overlap,
            )
        )

    if not all_chunks:
        raise ValueError("No text could be extracted from the PDFs.")

    store = ChromaMathStore(settings)
    if reset:
        store.reset()

    ollama = OllamaClient(settings.ollama_base_url, timeout=settings.request_timeout)

    for chunk_batch in tqdm(batched(all_chunks, 16), desc="Embedding chunks"):
        embeddings = ollama.embed_texts(
            [chunk.text for chunk in chunk_batch],
            model=settings.embed_model,
        )
        store.add_chunks(chunk_batch, embeddings)

    summary = {
        "pdf_count": len(pdf_files),
        "chunks_created": len(all_chunks),
        "vector_count": store.count(),
    }

    summary_path = settings.processed_dir / "ingestion_summary.json"
    summary_path.write_text(json.dumps(summary, indent=2), encoding="utf-8")
    return summary


class MathRAGAssistant:
    def __init__(self, settings: Settings) -> None:
        self.settings = settings
        self.store = ChromaMathStore(settings)
        self.ollama = OllamaClient(settings.ollama_base_url, timeout=settings.request_timeout)

    def answer(
        self,
        question: str,
        extra_chunks: list[SupplementalChunk] | None = None,
    ) -> dict[str, object]:
        store_count = self.store.count()
        if store_count == 0 and not extra_chunks:
            raise ValueError(
                "The ChromaDB collection is empty. Run `python ingest.py --reset` first."
            )

        query_embedding = self.ollama.embed_texts(
            [question],
            model=self.settings.embed_model,
        )[0]
        store_retrieved: list[RetrievedChunk] = []
        if store_count > 0:
            store_retrieved = (
                self.store.query(query_embedding=query_embedding, top_k=self.settings.top_k)
            )
        extra_retrieved: list[RetrievedChunk] = []
        if extra_chunks:
            extra_retrieved = rank_supplemental_chunks(
                query_embedding=query_embedding,
                extra_chunks=extra_chunks,
                top_k=self.settings.top_k,
            )

        retrieved = merge_retrieved_chunks(
            store_retrieved,
            extra_retrieved,
            top_k=self.settings.top_k,
        )
        if not retrieved:
            raise ValueError("No retrievable context is available for this question.")
        answer = self.ollama.chat(
            model=self.settings.llm_model,
            messages=build_messages(question, retrieved),
        )

        best_chapter = infer_label([chunk.chapter_name for chunk in retrieved])
        best_topic = infer_label([chunk.topic for chunk in retrieved])
        if needs_reformatting(answer):
            answer = self.ollama.chat(
                model=self.settings.llm_model,
                messages=build_reformat_messages(
                    question=question,
                    answer=answer,
                    chapter=best_chapter,
                    topic=best_topic,
                ),
            )

        sources = [
            {
                "chapter_number": chunk.chapter_number,
                "chapter_name": chunk.chapter_name,
                "topic": chunk.topic,
                "page_number": chunk.page_number,
                "source_file": chunk.source_file,
            }
            for chunk in retrieved
        ]

        return {"answer": answer, "sources": sources}


def parse_args_and_run_ingestion(settings: Settings) -> None:
    parser = argparse.ArgumentParser(description="Ingest Class 12 Maths PDFs into ChromaDB.")
    parser.add_argument(
        "--reset",
        action="store_true",
        help="Delete the existing collection before re-ingesting the PDFs.",
    )
    args = parser.parse_args()
    summary = run_ingestion(settings=settings, reset=args.reset)
    print(json.dumps(summary, indent=2))