from datetime import datetime, timezone
from decimal import Decimal

from sqlalchemy import case, func, select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.experiments.registry import EXPERIMENT_REGISTRY
from app.models.experiment import Experiment, ExperimentEvent, ExperimentVariant
from app.schemas.experiments import (
    ExperimentConversionCreate,
    ExperimentDefinitionResponse,
    ExperimentDefinitionUpdate,
    ExperimentEventCreate,
    ExperimentImpressionCreate,
    ExperimentResult,
    ExperimentVariantResult,
)


def experiment_exists(experiment_key: str, variant_key: str) -> bool:
    definition = EXPERIMENT_REGISTRY.get(experiment_key)
    if not definition:
        return False
    return any(variant["variant_key"] == variant_key for variant in definition["variants"])


async def sync_experiment_registry(db: AsyncSession) -> None:
    result = await db.execute(
        select(Experiment).options(selectinload(Experiment.variants))
    )
    existing = {experiment.experiment_key: experiment for experiment in result.scalars().all()}

    for definition in EXPERIMENT_REGISTRY.values():
        experiment = existing.get(definition["experiment_key"])
        existing_variants: dict[str, ExperimentVariant] = {}

        if experiment is None:
            experiment = Experiment(
                experiment_key=definition["experiment_key"],
                cookie_name=definition["cookie_name"],
                name=definition["name"],
                description=definition.get("description"),
                enabled=definition["enabled"],
                eligible_routes=definition["eligible_routes"],
            )
            db.add(experiment)
            await db.flush()
        else:
            existing_variants = {variant.variant_key: variant for variant in experiment.variants}

        for variant_definition in definition["variants"]:
            variant = existing_variants.get(variant_definition["variant_key"])
            if variant is None:
                db.add(
                    ExperimentVariant(
                        experiment_id=experiment.id,
                        variant_key=variant_definition["variant_key"],
                        label=variant_definition["label"],
                        allocation=variant_definition["allocation"],
                        is_control=variant_definition["is_control"],
                    )
                )
                continue

            variant.label = variant_definition["label"]
            variant.allocation = variant_definition["allocation"]
            variant.is_control = variant_definition["is_control"]

    await db.flush()


async def list_experiment_definitions(db: AsyncSession) -> list[ExperimentDefinitionResponse]:
    result = await db.execute(
        select(Experiment).options(selectinload(Experiment.variants)).order_by(Experiment.experiment_key)
    )
    experiments = result.scalars().all()

    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
            ],
        )
        for experiment in experiments
    ]


async def record_experiment_event(
    db: AsyncSession,
    payload: ExperimentImpressionCreate | ExperimentEventCreate | ExperimentConversionCreate,
) -> ExperimentEvent:
    conversion_value = getattr(payload, "conversion_value", None)
    timestamp = payload.timestamp
    if timestamp.tzinfo is None:
        timestamp = timestamp.replace(tzinfo=timezone.utc)

    event = ExperimentEvent(
        experiment_key=payload.experiment_key,
        variant_key=payload.variant_key,
        session_id=payload.session_id,
        user_id=payload.user_id,
        path=payload.path,
        event_type=payload.event_name,
        conversion_value=conversion_value,
        metadata_=payload.metadata,
        created_at=timestamp.astimezone(timezone.utc).replace(tzinfo=None),
    )
    db.add(event)
    await db.flush()
    await db.refresh(event)
    return event


async def get_experiment_results(db: AsyncSession, experiment_key: str | None = None) -> list[ExperimentResult]:
    stmt = select(
        ExperimentEvent.experiment_key,
        ExperimentEvent.variant_key,
        func.sum(case((ExperimentEvent.event_type == "impression", 1), else_=0)).label("impressions"),
        func.sum(case((ExperimentEvent.event_type == "cta_click", 1), else_=0)).label("cta_clicks"),
        func.sum(case((ExperimentEvent.event_type == "form_start", 1), else_=0)).label("form_starts"),
        func.sum(case((ExperimentEvent.event_type == "form_submit", 1), else_=0)).label("form_submits"),
        func.sum(case((ExperimentEvent.event_type == "conversion", 1), else_=0)).label("conversions"),
        func.count(func.distinct(ExperimentEvent.session_id)).label("unique_sessions"),
        func.coalesce(func.sum(ExperimentEvent.conversion_value), Decimal("0")).label("conversion_value_total"),
    ).group_by(ExperimentEvent.experiment_key, ExperimentEvent.variant_key).order_by(
        ExperimentEvent.experiment_key,
        ExperimentEvent.variant_key,
    )

    if experiment_key:
        stmt = stmt.where(ExperimentEvent.experiment_key == experiment_key)

    result = await db.execute(stmt)
    rows = result.all()

    grouped: dict[str, list[ExperimentVariantResult]] = {}
    for row in rows:
        impressions = int(row.impressions or 0)
        conversions = int(row.conversions or 0)
        conversion_rate = conversions / impressions if impressions else 0.0

        grouped.setdefault(row.experiment_key, []).append(
            ExperimentVariantResult(
                variant_key=row.variant_key,
                impressions=impressions,
                cta_clicks=int(row.cta_clicks or 0),
                form_starts=int(row.form_starts or 0),
                form_submits=int(row.form_submits or 0),
                conversions=conversions,
                unique_sessions=int(row.unique_sessions or 0),
                conversion_rate=round(conversion_rate, 4),
                conversion_value_total=float(row.conversion_value_total or 0),
            )
        )

    generated_at = datetime.now(timezone.utc)
    return [
        ExperimentResult(
            experiment_key=key,
            generated_at=generated_at,
            variants=variants,
        )
        for key, variants in grouped.items()
    ]


async def get_experiment_definition(db: AsyncSession, experiment_key: str) -> Experiment | None:
    result = await db.execute(
        select(Experiment)
        .options(selectinload(Experiment.variants))
        .where(Experiment.experiment_key == experiment_key)
    )
    return result.scalars().first()


async def upsert_experiment_definition(
    db: AsyncSession,
    experiment_key: str,
    payload: ExperimentDefinitionUpdate,
) -> Experiment:
    experiment = await get_experiment_definition(db, experiment_key)

    duplicate_cookie = await db.execute(
        select(Experiment).where(
            Experiment.cookie_name == payload.cookie_name,
            Experiment.experiment_key != experiment_key,
        )
    )
    if duplicate_cookie.scalars().first():
        raise ValueError("cookie_name is already used by another experiment")

    if experiment is None:
        experiment = Experiment(
            experiment_key=experiment_key,
            cookie_name=payload.cookie_name,
            name=payload.name,
            description=payload.description,
            enabled=payload.enabled,
            eligible_routes=payload.eligible_routes,
        )
        db.add(experiment)
        await db.flush()
        existing_variants: dict[str, ExperimentVariant] = {}
    else:
        experiment.cookie_name = payload.cookie_name
        experiment.name = payload.name
        experiment.description = payload.description
        experiment.enabled = payload.enabled
        experiment.eligible_routes = payload.eligible_routes
        existing_variants = {variant.variant_key: variant for variant in experiment.variants}

    incoming_keys = {variant.variant_key for variant in payload.variants}
    for variant in list(existing_variants.values()):
        if variant.variant_key not in incoming_keys:
            await db.delete(variant)

    for variant_payload in payload.variants:
        variant = existing_variants.get(variant_payload.variant_key)
        if variant is None:
            db.add(
                ExperimentVariant(
                    experiment_id=experiment.id,
                    variant_key=variant_payload.variant_key,
                    label=variant_payload.label,
                    allocation=variant_payload.allocation,
                    is_control=variant_payload.is_control,
                )
            )
            continue

        variant.label = variant_payload.label
        variant.allocation = variant_payload.allocation
        variant.is_control = variant_payload.is_control

    await db.flush()
    refreshed = await get_experiment_definition(db, experiment_key)
    assert refreshed is not None
    return refreshed