import re

from fastapi import APIRouter, Depends, HTTPException, Request, Response, status
from sqlalchemy.ext.asyncio import AsyncSession

from app.auth.deps import get_current_user
from app.database import get_db
from app.middleware.rate_limit import limiter
from app.schemas.experiments import (
    ExperimentConversionCreate,
    ExperimentDefinitionResponse,
    ExperimentDefinitionUpdate,
    ExperimentEventCreate,
    ExperimentImpressionCreate,
    ExperimentIngestResponse,
    ExperimentResult,
)
from app.services.experiments import (
    experiment_exists,
    get_experiment_definition,
    get_experiment_results,
    list_experiment_definitions,
    record_experiment_event,
    upsert_experiment_definition,
)
from app.services.settings import get_feature_settings_snapshot

router = APIRouter(tags=["Experiments"])
BOT_UA_PATTERN = re.compile(r"(bot|crawler|spider|slurp|preview|headless)", re.IGNORECASE)


def _is_bot_request(request: Request) -> bool:
    user_agent = request.headers.get("user-agent", "")
    return bool(BOT_UA_PATTERN.search(user_agent))


def _validate_experiment_assignment(experiment_key: str, variant_key: str) -> None:
    if not experiment_exists(experiment_key, variant_key):
        raise HTTPException(
            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
            detail="unknown experiment or variant",
        )


async def _experiments_enabled(db: AsyncSession) -> bool:
    feature_settings = await get_feature_settings_snapshot(db)
    return feature_settings.experiments_enabled


async def _require_experiments_enabled(db: AsyncSession) -> None:
    if not await _experiments_enabled(db):
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Experiments are currently disabled.")


@router.get("/api/experiments", response_model=list[ExperimentDefinitionResponse])
async def get_experiments(db: AsyncSession = Depends(get_db)):
    if not await _experiments_enabled(db):
        return []
    return await list_experiment_definitions(db)


@router.post("/api/experiments/impression", response_model=ExperimentIngestResponse, status_code=202)
@limiter.limit("30/minute")
async def ingest_experiment_impression(
    request: Request,
    response: Response,
    payload: ExperimentImpressionCreate,
    db: AsyncSession = Depends(get_db),
):
    if not await _experiments_enabled(db):
        return ExperimentIngestResponse(ok=True, accepted=False)

    _validate_experiment_assignment(payload.experiment_key, payload.variant_key)

    if _is_bot_request(request):
        return ExperimentIngestResponse(ok=True, accepted=False)

    await record_experiment_event(db, payload)
    return ExperimentIngestResponse(ok=True, accepted=True)


@router.post("/api/experiments/event", response_model=ExperimentIngestResponse, status_code=202)
@limiter.limit("30/minute")
async def ingest_experiment_event(
    request: Request,
    response: Response,
    payload: ExperimentEventCreate,
    db: AsyncSession = Depends(get_db),
):
    if not await _experiments_enabled(db):
        return ExperimentIngestResponse(ok=True, accepted=False)

    _validate_experiment_assignment(payload.experiment_key, payload.variant_key)

    if _is_bot_request(request):
        return ExperimentIngestResponse(ok=True, accepted=False)

    await record_experiment_event(db, payload)
    return ExperimentIngestResponse(ok=True, accepted=True)


@router.post("/api/experiments/conversion", response_model=ExperimentIngestResponse, status_code=202)
@limiter.limit("30/minute")
async def ingest_experiment_conversion(
    request: Request,
    response: Response,
    payload: ExperimentConversionCreate,
    db: AsyncSession = Depends(get_db),
):
    if not await _experiments_enabled(db):
        return ExperimentIngestResponse(ok=True, accepted=False)

    _validate_experiment_assignment(payload.experiment_key, payload.variant_key)

    if _is_bot_request(request):
        return ExperimentIngestResponse(ok=True, accepted=False)

    await record_experiment_event(db, payload)
    return ExperimentIngestResponse(ok=True, accepted=True)


@router.get("/api/v1/experiments/results", response_model=list[ExperimentResult])
async def experiment_results(
    experiment_key: str | None = None,
    db: AsyncSession = Depends(get_db),
    _=Depends(get_current_user),
):
    await _require_experiments_enabled(db)
    return await get_experiment_results(db, experiment_key)


@router.get("/api/admin/experiments", response_model=list[ExperimentDefinitionResponse])
async def admin_list_experiments(
    db: AsyncSession = Depends(get_db),
    _=Depends(get_current_user),
):
    await _require_experiments_enabled(db)
    return await list_experiment_definitions(db)


@router.get("/api/admin/experiments/{experiment_key}", response_model=ExperimentDefinitionResponse)
async def admin_get_experiment(
    experiment_key: str,
    db: AsyncSession = Depends(get_db),
    _=Depends(get_current_user),
):
    await _require_experiments_enabled(db)
    experiment = await get_experiment_definition(db, experiment_key)
    if experiment is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Experiment not found")

    definitions = await list_experiment_definitions(db)
    match = next((item for item in definitions if item.experiment_key == experiment_key), None)
    assert match is not None
    return match


@router.put("/api/admin/experiments/{experiment_key}", response_model=ExperimentDefinitionResponse)
async def admin_update_experiment(
    experiment_key: str,
    payload: ExperimentDefinitionUpdate,
    db: AsyncSession = Depends(get_db),
    _=Depends(get_current_user),
):
    await _require_experiments_enabled(db)
    try:
        experiment = await upsert_experiment_definition(db, experiment_key, payload)
    except ValueError as exc:
        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc

    return ExperimentDefinitionResponse(
        experiment_key=experiment.experiment_key,
        cookie_name=experiment.cookie_name,
        name=experiment.name,
        description=experiment.description,
        enabled=experiment.enabled,
        eligible_routes=experiment.eligible_routes,
        variants=[
            {
                "variant_key": variant.variant_key,
                "label": variant.label,
                "allocation": variant.allocation,
                "is_control": variant.is_control,
            }
            for variant in experiment.variants
        ],
    )