import os
import logging
import numpy as np

logger = logging.getLogger(__name__)

OPENROUTER_API_KEY = os.getenv('OPENROUTER_API_KEY')
EMBEDDING_MODEL = 'openai/text-embedding-3-small'
SIMILARITY_THRESHOLD = 0.75


def embed_trip(trip):
    """
    Generates a semantic embedding for a trip using OpenRouter's
    text-embedding-3-small, combining trip name, destination, duration,
    and activities into a single text representation first.

    Data flow:
      trip dict → formatted text string → OpenRouter embeddings API →
      vector list returned for storage in products.embedding /
      client_trips.embedding
    """
    # Imported lazily so this module has no hard dependency on the
    # `openai` package at import time for callers that only need
    # find_comparable_trips() (pure math, no API calls).
    from openai import OpenAI

    text = (
        f"{trip.get('trip_name', '')}\n"
        f"Destination: {trip.get('destination', '')}\n"
        f"Duration: {trip.get('duration_days', '')} days\n"
        f"Activities: {trip.get('activities', '')}\n"
        f"Start: {trip.get('start_location', '')}"
    )

    client = OpenAI(api_key=OPENROUTER_API_KEY, base_url='https://openrouter.ai/api/v1')
    response = client.embeddings.create(model=EMBEDDING_MODEL, input=text)
    return response.data[0].embedding


def _cosine_similarity(a, b):
    """Standard cosine similarity between two equal-length embedding vectors."""
    a, b = np.array(a), np.array(b)
    denom = (np.linalg.norm(a) * np.linalg.norm(b))
    if denom == 0:
        return 0.0
    return float(np.dot(a, b) / denom)


def find_comparable_trips(client_trips, competitor_trips, threshold=SIMILARITY_THRESHOLD):
    """
    Calculates cosine similarity between every client trip and every
    competitor trip, returning matches above threshold sorted by
    similarity score descending.

    Data flow:
      client_trips + competitor_trips (each with .embedding) →
      pairwise cosine similarity → filter by threshold →
      sort by score descending → list of match dicts returned
    """
    matches = []
    for client_trip in client_trips:
        client_embedding = client_trip.get('embedding')
        if not client_embedding:
            continue
        for competitor_trip in competitor_trips:
            competitor_embedding = competitor_trip.get('embedding')
            if not competitor_embedding:
                continue
            score = _cosine_similarity(client_embedding, competitor_embedding)
            if score >= threshold:
                matches.append({
                    'client_product': client_trip.get('trip_name'),
                    'competitor_product': competitor_trip.get('id'),
                    'similarity_score': round(score, 4),
                    'price_difference': _safe_diff(
                        competitor_trip.get('majority_price_usd'), client_trip.get('price_usd')
                    ),
                    'duration_difference': _safe_diff(
                        competitor_trip.get('duration_days'), client_trip.get('duration_days')
                    ),
                })
    matches.sort(key=lambda m: m['similarity_score'], reverse=True)
    return matches


def _safe_diff(a, b):
    """Returns a - b if both are present, else None — keeps the diff fields nullable per schema."""
    if a is None or b is None:
        return None
    return a - b