// ABOUTME: API route for retrieving period history with calculated cycle lengths.
// ABOUTME: GET /api/period-history returns paginated period logs with cycle statistics.
import type { NextRequest } from "next/server";
import { NextResponse } from "next/server";

import { withAuth } from "@/lib/auth-middleware";
import type { PeriodLog } from "@/types";

// Pagination constants
const MIN_PAGE = 1;
const MIN_LIMIT = 1;
const MAX_LIMIT = 100;
const DEFAULT_LIMIT = 20;

interface PeriodLogWithCycleLength extends PeriodLog {
  cycleLength: number | null;
  daysEarly: number | null;
  daysLate: number | null;
}

interface PeriodHistoryResponse {
  items: PeriodLogWithCycleLength[];
  total: number;
  page: number;
  limit: number;
  totalPages: number;
  hasMore: boolean;
  averageCycleLength: number | null;
}

function calculateDaysBetween(date1: Date, date2: Date): number {
  const d1 = new Date(date1);
  const d2 = new Date(date2);
  const diffTime = Math.abs(d1.getTime() - d2.getTime());
  return Math.round(diffTime / (1000 * 60 * 60 * 24));
}

export const GET = withAuth(async (request: NextRequest, user, pb) => {
  const { searchParams } = new URL(request.url);

  // Parse and validate pagination parameters
  const pageParam = searchParams.get("page");
  const limitParam = searchParams.get("limit");

  let page = MIN_PAGE;
  let limit = DEFAULT_LIMIT;

  // Validate page parameter
  if (pageParam !== null) {
    const parsedPage = Number.parseInt(pageParam, 10);
    if (Number.isNaN(parsedPage) || parsedPage < MIN_PAGE) {
      return NextResponse.json(
        { error: "Invalid page: must be a positive integer" },
        { status: 400 },
      );
    }
    page = parsedPage;
  }

  // Validate limit parameter
  if (limitParam !== null) {
    const parsedLimit = Number.parseInt(limitParam, 10);
    if (
      Number.isNaN(parsedLimit) ||
      parsedLimit < MIN_LIMIT ||
      parsedLimit > MAX_LIMIT
    ) {
      return NextResponse.json(
        {
          error: `Invalid limit: must be between ${MIN_LIMIT} and ${MAX_LIMIT}`,
        },
        { status: 400 },
      );
    }
    limit = parsedLimit;
  }

  // Query period logs for user
  const result = await pb
    .collection("period_logs")
    .getList<PeriodLog>(page, limit, {
      filter: `user="${user.id}"`,
      sort: "-startDate",
    });

  // Calculate cycle lengths between consecutive periods
  // Periods are sorted by startDate descending (most recent first)
  const itemsWithCycleLength: PeriodLogWithCycleLength[] = result.items.map(
    (log, index) => {
      let cycleLength: number | null = null;

      // If there's a next period (earlier period), calculate cycle length
      const nextPeriod = result.items[index + 1];
      if (nextPeriod) {
        cycleLength = calculateDaysBetween(log.startDate, nextPeriod.startDate);
      }

      // Calculate prediction accuracy
      let daysEarly: number | null = null;
      let daysLate: number | null = null;
      if (log.predictedDate) {
        const actualDate = new Date(log.startDate);
        const predictedDate = new Date(log.predictedDate);
        const diffDays = Math.round(
          (actualDate.getTime() - predictedDate.getTime()) /
            (1000 * 60 * 60 * 24),
        );
        if (diffDays < 0) {
          daysEarly = Math.abs(diffDays);
          daysLate = 0;
        } else {
          daysEarly = 0;
          daysLate = diffDays;
        }
      }

      return {
        ...log,
        cycleLength,
        daysEarly,
        daysLate,
      };
    },
  );

  // Calculate average cycle length (only if we have at least 2 periods)
  const cycleLengths = itemsWithCycleLength
    .map((log) => log.cycleLength)
    .filter((length): length is number => length !== null);

  const averageCycleLength =
    cycleLengths.length > 0
      ? Math.round(
          cycleLengths.reduce((sum, len) => sum + len, 0) / cycleLengths.length,
        )
      : null;

  const response: PeriodHistoryResponse = {
    items: itemsWithCycleLength,
    total: result.totalItems,
    page: result.page,
    limit,
    totalPages: result.totalPages,
    hasMore: result.page < result.totalPages,
    averageCycleLength,
  };

  return NextResponse.json(response, { status: 200 });
});