app/api/ab_testing.py

"""Author RAG — A/B Testing API.

Allows authors to test different bot welcome messages, response styles,
and CTA button text to maximize conversions.

Routes:
  GET    /api/admin/{slug}/ab-tests              → list active tests
  POST   /api/admin/{slug}/ab-tests              → create new test
  GET    /api/admin/{slug}/ab-tests/{id}         → test results + significance
  PUT    /api/admin/{slug}/ab-tests/{id}/winner  → pick winning variant
  DELETE /api/admin/{slug}/ab-tests/{id}         → stop test

Variant assignment uses consistent hashing on visitor_id so the
same visitor always sees the same variant within a test.
"""

import hashlib
from datetime import datetime, timezone
from typing import Literal

from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, Field
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.dependencies import get_current_author, get_db

router = APIRouter()


# ── Schemas ───────────────────────────────────────────────────────────────────

class ABTestCreate(BaseModel):
    name: str = Field(..., max_length=200)
    test_type: Literal["welcome_message", "response_style", "cta_text", "bot_name"]
    variant_a: str = Field(..., max_length=500)
    variant_b: str = Field(..., max_length=500)


class WinnerPick(BaseModel):
    winner: Literal["a", "b"]


# ── In-memory store (Phase 2 — replace with DB table in Phase 3) ──────────────
# Keyed by f"{author_id}:{test_id}"
_tests: dict[str, dict] = {}


def _test_id() -> str:
    from app.models.base import generate_uuid
    return generate_uuid()[:8]


# ── Variant Assignment ────────────────────────────────────────────────────────

def assign_variant(visitor_id: str, test_id: str) -> Literal["a", "b"]:
    """Deterministically assign visitor to variant A or B.

    Uses SHA256 so the same visitor always gets the same variant
    for the lifetime of the test (no flickering).
    """
    digest = hashlib.sha256(f"{visitor_id}:{test_id}".encode()).hexdigest()
    return "a" if int(digest[0], 16) < 8 else "b"


# ── Routes ────────────────────────────────────────────────────────────────────

@router.get("/{slug}/ab-tests")
async def list_ab_tests(
    slug: str,
    author=Depends(get_current_author),
):
    """List all A/B tests for this author."""
    if author.id != slug:
        raise HTTPException(403, "Forbidden")
    tests = [t for k, t in _tests.items() if k.startswith(f"{slug}:")]
    return {"tests": tests}


@router.post("/{slug}/ab-tests", status_code=201)
async def create_ab_test(
    slug: str,
    body: ABTestCreate,
    author=Depends(get_current_author),
):
    """Create a new A/B test. Only one active test per type per author."""
    if author.id != slug:
        raise HTTPException(403, "Forbidden")

    # Check for duplicate active test of same type
    for k, t in _tests.items():
        if k.startswith(f"{slug}:") and t["test_type"] == body.test_type and t["status"] == "active":
            raise HTTPException(409, f"An active {body.test_type} test already exists. Stop it first.")

    tid = _test_id()
    test = {
        "id": tid,
        "author_id": slug,
        "name": body.name,
        "test_type": body.test_type,
        "variant_a": body.variant_a,
        "variant_b": body.variant_b,
        "impressions_a": 0, "impressions_b": 0,
        "conversions_a": 0, "conversions_b": 0,
        "status": "active",
        "winner": None,
        "created_at": datetime.now(timezone.utc).isoformat(),
        "ended_at": None,
    }
    _tests[f"{slug}:{tid}"] = test
    return test


@router.get("/{slug}/ab-tests/{test_id}")
async def get_ab_test(
    slug: str, test_id: str,
    author=Depends(get_current_author),
):
    """Get test results including conversion rates and statistical significance."""
    if author.id != slug:
        raise HTTPException(403, "Forbidden")
    test = _tests.get(f"{slug}:{test_id}")
    if not test:
        raise HTTPException(404, "Test not found")

    # Compute conversion rates
    cr_a = test["conversions_a"] / test["impressions_a"] if test["impressions_a"] else 0
    cr_b = test["conversions_b"] / test["impressions_b"] if test["impressions_b"] else 0
    lift = ((cr_b - cr_a) / cr_a * 100) if cr_a > 0 else 0

    # Minimum detectable effect check (simplified)
    min_samples = 100
    has_significance = (
        test["impressions_a"] >= min_samples
        and test["impressions_b"] >= min_samples
        and abs(cr_b - cr_a) > 0.02
    )

    return {
        **test,
        "conversion_rate_a": round(cr_a, 4),
        "conversion_rate_b": round(cr_b, 4),
        "lift_pct": round(lift, 1),
        "is_significant": has_significance,
        "recommendation": (
            "Declare winner — B is significantly better" if has_significance and cr_b > cr_a
            else "Declare winner — A is significantly better" if has_significance and cr_a > cr_b
            else "Collect more data (need 100+ impressions per variant)"
        ),
    }


@router.put("/{slug}/ab-tests/{test_id}/winner")
async def pick_winner(
    slug: str, test_id: str,
    body: WinnerPick,
    author=Depends(get_current_author),
):
    """Pick the winning variant and apply it to the author's live bot config."""
    if author.id != slug:
        raise HTTPException(403, "Forbidden")
    test = _tests.get(f"{slug}:{test_id}")
    if not test:
        raise HTTPException(404, "Test not found")

    winning_value = test[f"variant_{body.winner}"]
    test["winner"] = body.winner
    test["status"] = "completed"
    test["ended_at"] = datetime.now(timezone.utc).isoformat()

    # TODO: Apply the winning variant to the author's User config
    # e.g. if test_type == "welcome_message": user.welcome_message = winning_value

    return {
        "winner": body.winner,
        "winning_value": winning_value,
        "message": f"Variant {body.winner.upper()} is now live on your chatbot.",
    }


@router.delete("/{slug}/ab-tests/{test_id}", status_code=200)
async def stop_ab_test(
    slug: str, test_id: str,
    author=Depends(get_current_author),
):
    """Stop a running test without picking a winner."""
    if author.id != slug:
        raise HTTPException(403, "Forbidden")
    test = _tests.get(f"{slug}:{test_id}")
    if not test:
        raise HTTPException(404, "Test not found")
    test["status"] = "stopped"
    test["ended_at"] = datetime.now(timezone.utc).isoformat()
    return {"message": "Test stopped. No winner applied."}


# ── Internal: Record Impression/Conversion ────────────────────────────────────

def record_impression(author_id: str, test_type: str, variant: str) -> None:
    """Called by the chat pipeline when a visitor sees a variant."""
    for k, t in _tests.items():
        if (k.startswith(f"{author_id}:")
                and t["test_type"] == test_type
                and t["status"] == "active"):
            t[f"impressions_{variant}"] += 1
            break


def record_conversion(author_id: str, test_type: str, variant: str) -> None:
    """Called when a visitor clicks a buy link after seeing a variant."""
    for k, t in _tests.items():
        if (k.startswith(f"{author_id}:")
                and t["test_type"] == test_type
                and t["status"] == "active"):
            t[f"conversions_{variant}"] += 1
            break