"""
generation.py
-----------------------
Answer generation — ZeroGPU version.
"""
import spaces

from config import MAX_PROMPT_TOKENS, ZEROGPU_DURATION
from model_setup import text_gen_pipeline, tokenizer
from utils import format_prompt, clean_final_answer
from logging_config import get_logger

logger = get_logger(__name__)


# The ONLY GPU-touching function in the codebase

@spaces.GPU(duration=ZEROGPU_DURATION)
def _generate_on_gpu(prompt: str) -> str:
  """
  Run the actual LLM inference. This is the single point in the
  entire application where a real GPU is attached to the process.

  Deliberately minimal: no logging of prompt content here (keep
  the GPU-held window as short as possible), no retries, no
  fallback logic — just the inference call. All the surrounding
  orchestration (prompt building, history handling, streaming)
  happens in generate_answer() below, OUTSIDE the GPU-decorated
  boundary, where a real GPU is not needed and thus not consumed.

  Returns the complete generated text (already stripped).
  """
  output = text_gen_pipeline(prompt)
  return output[0]["generated_text"].strip()


# Prompt building + streaming wrapper (no GPU here)

def generate_answer(state: dict):
  """
  Generator that yields (token_text, prompt_token_count) tuples.

  This function itself is NOT @spaces.GPU-decorated — it does no CUDA work directly.
  It builds the prompt (CPU-side string operations), calls _generate_on_gpu() once to get the complete
  response, then splits it into words and yields them one by one for the streaming UI effect in `app.py`.

  Splitting the concerns this way means the GPU slot is held for the minimum possible time —
  just the actual generation call — while all the prompt-assembly and history-formatting logic runs
  on CPU without competing for the shared GPU resource.
  """
  from ui_helpers import get_history_text, _safe_content

  query = state["query"]
  history = state.get("history", [])
  retrieved_docs = _safe_content(state.get("retrieved_docs", ""))
  web_results = _safe_content(state.get("web_results",    ""))

  # Safety valve: both retrieval phases returned nothing
  if not retrieved_docs and not web_results:
    yield (
        "I could not retrieve relevant information for your question. "
        "Please check that the TAVILY_API_KEY secret is set in the "
        "Space settings, or try rephrasing your question.",
        0,
    )
    return

  # Build context block
  context_parts = []
  if retrieved_docs:
    context_parts.append(f"## Internal Knowledge Base\n\n{retrieved_docs}")
  if web_results:
    context_parts.append(f"## Web Search Results\n\n{web_results}")
  context = "\n\n".join(context_parts)

  # System prompt
  system_msg = (
      "You are a precise, factual research assistant.\n\n"
      "Rules:\n"
      "1. Answer ONLY using the context and conversation history provided.\n"
      "2. If the context is insufficient, say so clearly.\n"
      "3. Cite factual claims with markdown links: [Title](URL).\n"
      "   Use ONLY URLs that appear explicitly in the context.\n"
      "4. Be concise: 2-4 paragraphs.\n"
      "5. Do NOT reproduce context verbatim. Synthesise and summarise.\n"
      "6. For follow-up questions, use the conversation history to\n"
      "   understand what the user is referring to."
  )

  # User message: history (if any) + context + question
  history_text = get_history_text(history, max_turns=3)
  if history_text:
      user_msg = (
          f"Previous conversation:\n{history_text}\n\n"
          f"Context:\n{context}\n\n"
          f"---\n\n"
          f"Current question: {query}\n\nAnswer:"
      )
  else:
      user_msg = f"Context:\n{context}\n\n---\n\nQuestion: {query}\n\nAnswer:"

  # format_prompt() uses tokenizer.apply_chat_template — CPU-side,
  # no CUDA involved, safe to call outside the GPU-decorated function.
  prompt = format_prompt(system=system_msg, user=user_msg)

  # Token budget: trim from the LEFT if over limit (tokenizer.encode
  # is also CPU-side — no GPU needed for this step).
  token_ids  = tokenizer.encode(prompt)
  token_count = len(token_ids)
  if token_count > MAX_PROMPT_TOKENS:
      token_ids = token_ids[-MAX_PROMPT_TOKENS:]
      token_count = len(token_ids) # MAX_PROMPT_TOKENS
      prompt = tokenizer.decode(token_ids, skip_special_tokens=False)

  logger.info(f"Prompt: {token_count} tokens | history turns: {len(history)}")

  # --- The ONLY call into GPU-decorated code -----------------
  # This is where the ZeroGPU backend actually attaches a real GPU
  # to the process, runs inference, and releases the slot when done.
  full_text = _generate_on_gpu(prompt)

  # Post-process: fix Qwen's URL formatting quirks
  full_text = clean_final_answer(full_text)

  # --- Word-by-word yield (CPU-side, instant) -----------------
  # Simulates streaming by splitting the already-complete response.
  # This is identical to the CPU version's approach — the only
  # difference is that _generate_on_gpu() ran on a real GPU instead
  # of the CPU-bound text_gen_pipeline() call.
  words = full_text.split()
  for i, word in enumerate(words):
      yield word + (" " if i < len(words) - 1 else ""), token_count