from __future__ import annotations

from .models import MembershipRecord


def _period_prefix(date: str | None) -> str | None:
    if not date or len(date) < 7:
        return None
    return date[:7]


def build_membership_analytics(
    members: list[MembershipRecord],
    period: str,
    history: list[str],
) -> dict:
    active = sum(1 for member in members if member.status == "active")
    new_members = sum(1 for member in members if _period_prefix(member.joined_at) == period)
    churned = sum(1 for member in members if _period_prefix(member.churned_at) == period)

    prior_period = None
    sorted_periods = sorted(history)
    if period in sorted_periods:
        index = sorted_periods.index(period)
        if index > 0:
            prior_period = sorted_periods[index - 1]

    prior_active = active
    if prior_period:
        prior_active = sum(
            1
            for member in members
            if member.status == "active" and _period_prefix(member.joined_at) <= prior_period
        )

    growth_rate = None
    if prior_active:
        growth_rate = round(((active - prior_active) / prior_active) * 100, 1)

    return {
        "period": period,
        "total_members": len(members),
        "active_members": active,
        "new_members": new_members,
        "churned_members": churned,
        "growth_rate_pct": growth_rate,
        "snapshot_source": "membership.json",
    }