"""
data_factory/generator.py
==========================
vLLM-based Natural Language question generator for H100.

This module uses a large LLM (Llama-3-70B or Qwen-72B) served via vLLM
to generate diverse, persona-based natural language paraphrases of the
canonical NL questions in our template library.

KEY DESIGN: The LLM generates ONLY natural language questions.
            SQL is NEVER touched by the LLM.
            This guarantees zero SQL errors in the final dataset.

Persona descriptions:
  ceo          - Direct, short, active voice. Business executive style.
  chatty       - Conversational, verbose, passive voice.
  lazy_typist  - Short, abbreviations, possible informal grammar.
  non_techie   - Plain English, avoids SQL/tech jargon, uses synonyms.
  analyst      - Technical, precise, jargon-heavy.

Usage (on H100 cluster):
  python -m data_factory.generator --templates-per-chunk 20 --n-variants 10
"""

from __future__ import annotations

import json
import logging
import time
from typing import Iterator, Optional

logger = logging.getLogger(__name__)


# ─────────────────────────────────────────────────────────────────────────────
# PERSONA SYSTEM PROMPTS
# ─────────────────────────────────────────────────────────────────────────────

PERSONA_SYSTEM_PROMPTS: dict[str, str] = {

    "ceo": (
        "You are a busy C-level executive who communicates in short, punchy, "
        "direct sentences. You use active voice, skip filler words, and get "
        "straight to the point. You are asking a data analyst for information."
    ),

    "chatty": (
        "You are a friendly, conversational person who likes to be thorough "
        "and explain things fully. You use passive voice sometimes, add context, "
        "and ask questions in a relaxed, detailed way. You are not technical."
    ),

    "lazy_typist": (
        "You type quickly and informally. You use abbreviations (e.g. 'pls', "
        "'lmk', 'asap'), lowercase, minimal punctuation, and sometimes omit "
        "words. You get your meaning across without perfect grammar."
    ),

    "non_techie": (
        "You have no database or SQL knowledge. You use everyday English words "
        "instead of technical terms. For example, you say 'customers' not 'rows', "
        "'most expensive' not 'highest price', 'total money' not 'sum'. "
        "You describe what you want to see, not how to get it."
    ),

    "analyst": (
        "You are a data scientist or BI analyst who is precise and technical. "
        "You use terms like 'aggregate', 'partition', 'granularity', 'distinct', "
        "'filter predicate', 'ranked by metric'. Your questions are precise and unambiguous."
    ),
}


# ─────────────────────────────────────────────────────────────────────────────
# PROMPT BUILDER
# ─────────────────────────────────────────────────────────────────────────────

def build_generation_prompt(
    canonical_nl: str,
    description: str,
    persona: str,
    schema_context: str,
    n_variants: int = 5,
) -> list[dict[str, str]]:
    """
    Build a chat-format prompt asking the LLM to rephrase the canonical NL
    question in the style of the given persona.

    Parameters
    ----------
    canonical_nl   : The base NL question from the template.
    description    : One-line SQL description (gives the LLM additional context).
    persona        : One of the 5 persona keys.
    schema_context : The compact schema string for the domain.
    n_variants     : How many rephrased questions to generate.

    Returns
    -------
    list[dict]  Chat messages in [{"role": ..., "content": ...}] format.
    """
    persona_desc = PERSONA_SYSTEM_PROMPTS[persona]

    system = (
        "You are a data labelling specialist. Your task is to rephrase a database "
        "question in a specific communication style (persona). The rephrased questions "
        "must preserve the EXACT same intent and required information as the original — "
        "do not change what data is being asked for, only how it is expressed.\n\n"
        f"PERSONA: {persona_desc}\n\n"
        "OUTPUT FORMAT: Return ONLY a valid JSON array of strings. "
        "No preamble, no markdown, no extra keys. Example: "
        '["question 1", "question 2", "question 3"]'
    )

    user = (
        f"DATABASE CONTEXT:\n{schema_context}\n\n"
        f"WHAT THE QUERY DOES: {description}\n\n"
        f"CANONICAL QUESTION: {canonical_nl}\n\n"
        f"Generate {n_variants} different ways a person with the persona described "
        f"above would ask this same question. The meaning must stay identical."
    )

    return [
        {"role": "system",    "content": system},
        {"role": "user",      "content": user},
    ]


# ─────────────────────────────────────────────────────────────────────────────
# RESPONSE PARSER
# ─────────────────────────────────────────────────────────────────────────────

def parse_llm_response(raw_text: str) -> list[str]:
    """
    Extract a list of strings from the LLM's JSON response.
    Handles common failures: markdown fences, trailing commas, extra text.

    Returns an empty list if parsing fails completely.
    """
    text = raw_text.strip()

    # Strip markdown fences if present
    if text.startswith("```"):
        lines = text.split("\n")
        text = "\n".join(l for l in lines if not l.strip().startswith("```")).strip()

    # Find the JSON array boundaries
    start = text.find("[")
    end   = text.rfind("]")
    if start == -1 or end == -1 or end <= start:
        logger.warning("LLM response missing JSON array brackets: %s", text[:100])
        return []

    json_str = text[start:end + 1]

    # Fix trailing commas before ] (common LLM mistake)
    json_str = json_str.rstrip()
    json_str = json_str.replace(",]", "]").replace(", ]", "]")

    try:
        parsed = json.loads(json_str)
        if not isinstance(parsed, list):
            return []
        # Filter to only non-empty strings
        return [s.strip() for s in parsed if isinstance(s, str) and s.strip()]
    except json.JSONDecodeError as exc:
        logger.warning("JSON parse error: %s | text: %s", exc, json_str[:200])
        return []


# ─────────────────────────────────────────────────────────────────────────────
# VLLM INTERFACE
# ─────────────────────────────────────────────────────────────────────────────

class VLLMGenerator:
    """
    Wrapper around a running vLLM server for high-throughput NL generation.

    Supports two modes:
      online  : Calls a running vLLM OpenAI-compatible API server.
      offline : Uses vllm.LLM directly (loads model in-process, H100 recommended).

    For H100 cluster usage, prefer 'offline' mode with tensor_parallel_size=4
    to saturate all 4 H100s for maximum throughput.
    """

    def __init__(
        self,
        model_name: str,
        mode: str = "offline",
        tensor_parallel_size: int = 4,
        gpu_memory_utilization: float = 0.90,
        max_model_len: int = 4096,
        # Online mode only
        api_base: str = "http://localhost:8000/v1",
        api_key:  str = "EMPTY",
    ) -> None:
        self.model_name = model_name
        self.mode = mode
        self._llm = None
        self._client = None

        if mode == "offline":
            self._init_offline(tensor_parallel_size, gpu_memory_utilization, max_model_len)
        elif mode == "online":
            self._init_online(api_base, api_key)
        else:
            raise ValueError(f"Unknown mode: {mode!r}. Use 'offline' or 'online'.")

    def _init_offline(
        self,
        tensor_parallel_size: int,
        gpu_memory_utilization: float,
        max_model_len: int,
    ) -> None:
        """Load vLLM engine in-process (best for H100 cluster)."""
        try:
            from vllm import LLM, SamplingParams
            self._LLM = LLM
            self._SamplingParams = SamplingParams
        except ImportError:
            raise ImportError(
                "vLLM not installed. Run: pip install vllm\n"
                "For H100: pip install vllm --extra-index-url https://download.pytorch.org/whl/cu124"
            )

        logger.info("Loading model %s with %d GPUs (offline mode)...", self.model_name, tensor_parallel_size)
        t0 = time.time()
        self._llm = self._LLM(
            model=self.model_name,
            tensor_parallel_size=tensor_parallel_size,
            gpu_memory_utilization=gpu_memory_utilization,
            max_model_len=max_model_len,
            dtype="bfloat16",
            trust_remote_code=True,
        )
        logger.info("Model loaded in %.1f seconds.", time.time() - t0)

    def _init_online(self, api_base: str, api_key: str) -> None:
        """Use OpenAI-compatible vLLM server (for distributed setups)."""
        try:
            from openai import OpenAI
            self._client = OpenAI(base_url=api_base, api_key=api_key)
        except ImportError:
            raise ImportError("pip install openai")
        logger.info("Connected to vLLM server at %s", api_base)

    def generate_batch(
        self,
        prompts: list[list[dict[str, str]]],
        temperature: float = 0.85,
        max_new_tokens: int = 300,
    ) -> list[str]:
        """
        Generate responses for a batch of chat prompts.

        Parameters
        ----------
        prompts        : List of chat message lists (one per item in batch).
        temperature    : Sampling temperature. Higher = more diverse.
        max_new_tokens : Max tokens per response.

        Returns
        -------
        list[str]  Raw text response per prompt (same length as input).
        """
        if self.mode == "offline":
            return self._generate_offline(prompts, temperature, max_new_tokens)
        else:
            return self._generate_online(prompts, temperature, max_new_tokens)

    def _generate_offline(
        self,
        prompts: list[list[dict]],
        temperature: float,
        max_new_tokens: int,
    ) -> list[str]:
        """vLLM offline batched generation — maximises H100 throughput."""
        from vllm import SamplingParams

        sampling = SamplingParams(
            temperature=temperature,
            max_tokens=max_new_tokens,
            stop=["</s>", "<|eot_id|>"],  # Llama-3 stop tokens
        )

        # Convert chat messages to tokenised prompt strings using the model's template
        tokenizer = self._llm.get_tokenizer()
        formatted_prompts: list[str] = []
        for msgs in prompts:
            if hasattr(tokenizer, "apply_chat_template"):
                text = tokenizer.apply_chat_template(
                    msgs, tokenize=False, add_generation_prompt=True
                )
            else:
                # Fallback: simple concatenation
                text = "\n".join(
                    f"<|{m['role']}|>\n{m['content']}" for m in msgs
                )
            formatted_prompts.append(text)

        outputs = self._llm.generate(formatted_prompts, sampling)
        return [o.outputs[0].text for o in outputs]

    def _generate_online(
        self,
        prompts: list[list[dict]],
        temperature: float,
        max_new_tokens: int,
    ) -> list[str]:
        """Sequential generation via OpenAI-compatible API (fallback / debugging)."""
        results = []
        for msgs in prompts:
            try:
                resp = self._client.chat.completions.create(
                    model=self.model_name,
                    messages=msgs,
                    temperature=temperature,
                    max_tokens=max_new_tokens,
                )
                results.append(resp.choices[0].message.content or "")
            except Exception as exc:
                logger.warning("API call failed: %s", exc)
                results.append("")
        return results


# ─────────────────────────────────────────────────────────────────────────────
# HIGH-LEVEL GENERATION LOOP
# ─────────────────────────────────────────────────────────────────────────────

def generate_persona_variants_batch(
    templates_subset: list[dict],
    generator: VLLMGenerator,
    personas: list[str],
    n_variants_per_persona: int = 5,
    batch_size: int = 64,
    temperature: float = 0.85,
    max_new_tokens: int = 300,
) -> Iterator[dict]:
    """
    For each template × persona combination, generate `n_variants_per_persona`
    NL question variants using the LLM.

    Yields dicts:
      {
        "template_idx": int,
        "persona":      str,
        "nl_variants":  list[str],   # successfully parsed NL questions
      }

    Parameters
    ----------
    templates_subset         : List of template dicts (from templates.py).
    generator                : VLLMGenerator instance.
    personas                 : List of persona keys to use.
    n_variants_per_persona   : How many NL variants per (template, persona) pair.
    batch_size               : How many LLM calls to batch together.
    temperature              : Sampling temperature.
    max_new_tokens           : Max tokens for LLM response (should be ~300 for JSON array).
    """
    from data_factory.schemas import SCHEMA_CONTEXT

    # Build all (template_idx, persona) prompt pairs
    all_jobs: list[tuple[int, str, list[dict]]] = []

    for t_idx, template in enumerate(templates_subset):
        schema_ctx = SCHEMA_CONTEXT[template["domain"]]
        for persona in personas:
            prompt = build_generation_prompt(
                canonical_nl=template["base_nl"],
                description=template["description"],
                persona=persona,
                schema_context=schema_ctx,
                n_variants=n_variants_per_persona,
            )
            all_jobs.append((t_idx, persona, prompt))

    total_jobs = len(all_jobs)
    logger.info("Starting LLM generation: %d jobs (templates × personas).", total_jobs)

    # Process in batches
    for batch_start in range(0, total_jobs, batch_size):
        batch = all_jobs[batch_start: batch_start + batch_size]
        prompts = [job[2] for job in batch]

        t0 = time.time()
        raw_responses = generator.generate_batch(
            prompts, temperature=temperature, max_new_tokens=max_new_tokens
        )
        elapsed = time.time() - t0
        logger.info(
            "Batch %d-%d completed in %.1fs (%.1f jobs/s).",
            batch_start, batch_start + len(batch), elapsed, len(batch) / max(elapsed, 0.001)
        )

        for (t_idx, persona, _), raw in zip(batch, raw_responses):
            nl_variants = parse_llm_response(raw)
            if not nl_variants:
                logger.debug(
                    "Empty parse for template_idx=%d persona=%s. raw=%s",
                    t_idx, persona, raw[:100]
                )
                # Fall back to the canonical NL rather than losing this entry
                nl_variants = [templates_subset[t_idx]["base_nl"]]

            yield {
                "template_idx": t_idx,
                "persona":      persona,
                "nl_variants":  nl_variants,
            }