phaseflow/src/lib/ics.ts

// ABOUTME: ICS calendar feed generation for cycle phase events.
// ABOUTME: Creates subscribable calendar with phase blocks and warnings.
import { createEvents, type EventAttributes } from "ics";

import type { PeriodLog } from "@/types";
import { getCycleDay, getPhase, PHASE_CONFIGS } from "./cycle";

// Phase emojis per calendar.md spec
const PHASE_EMOJIS: Record<string, string> = {
  MENSTRUAL: "🩸",
  FOLLICULAR: "🌱",
  OVULATION: "🌸",
  EARLY_LUTEAL: "🌙",
  LATE_LUTEAL: "🌑",
};

// Phase color categories per calendar.md spec for calendar app color coding
const PHASE_CATEGORIES: Record<string, string> = {
  MENSTRUAL: "Red",
  FOLLICULAR: "Green",
  OVULATION: "Pink",
  EARLY_LUTEAL: "Yellow",
  LATE_LUTEAL: "Orange",
};

interface IcsGeneratorOptions {
  lastPeriodDate: Date;
  cycleLength: number;
  monthsAhead?: number;
  periodLogs?: PeriodLog[];
}

export function generateIcsFeed(options: IcsGeneratorOptions): string {
  const {
    lastPeriodDate,
    cycleLength,
    monthsAhead = 3,
    periodLogs = [],
  } = options;
  const events: EventAttributes[] = [];

  const endDate = new Date();
  endDate.setMonth(endDate.getMonth() + monthsAhead);

  const currentDate = new Date(lastPeriodDate);
  let currentPhase = getPhase(
    getCycleDay(lastPeriodDate, cycleLength, currentDate),
    cycleLength,
  );
  let phaseStartDate = new Date(currentDate);

  while (currentDate <= endDate) {
    const cycleDay = getCycleDay(lastPeriodDate, cycleLength, currentDate);
    const phase = getPhase(cycleDay, cycleLength);

    // Add warning events
    if (cycleDay === 22) {
      events.push({
        start: dateToArray(currentDate),
        end: dateToArray(currentDate),
        title: "⚠️ Late Luteal Phase Starts in 3 Days",
        description: "Begin reducing training intensity",
      });
    }

    if (cycleDay === 25) {
      events.push({
        start: dateToArray(currentDate),
        end: dateToArray(currentDate),
        title: "🔴 CRITICAL PHASE - Gentle Rebounding Only!",
        description: "Late luteal phase - protect your cycle",
      });
    }

    // Track phase changes
    if (phase !== currentPhase) {
      // Close previous phase event
      events.push(createPhaseEvent(currentPhase, phaseStartDate, currentDate));
      currentPhase = phase;
      phaseStartDate = new Date(currentDate);
    }

    currentDate.setDate(currentDate.getDate() + 1);
  }

  // Close final phase
  events.push(createPhaseEvent(currentPhase, phaseStartDate, currentDate));

  // Add predicted vs actual events from period logs
  for (const log of periodLogs) {
    if (!log.predictedDate) {
      continue; // Skip logs without prediction (first log)
    }

    const actual = new Date(log.startDate);
    const predicted = new Date(log.predictedDate);

    // Calculate difference in days
    const diffMs = predicted.getTime() - actual.getTime();
    const diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));

    // Only show predicted event if dates differ
    if (diffDays === 0) {
      continue;
    }

    // Generate predicted menstrual event
    const predictedEnd = new Date(predicted);
    predictedEnd.setDate(predicted.getDate() + 3); // Menstrual phase is 3 days

    let description: string;
    if (diffDays > 0) {
      description = `Original prediction - period arrived ${diffDays} days early`;
    } else {
      description = `Original prediction - period arrived ${Math.abs(diffDays)} days late`;
    }

    events.push({
      start: dateToArray(predicted),
      end: dateToArray(predictedEnd),
      title: "🩸 MENSTRUAL (Predicted)",
      description,
    });
  }

  const { value, error } = createEvents(events);
  if (error) {
    throw new Error(`ICS generation error: ${error}`);
  }

  return value || "";
}

function createPhaseEvent(
  phase: string,
  startDate: Date,
  endDate: Date,
): EventAttributes {
  const config = PHASE_CONFIGS.find((c) => c.name === phase);
  const emoji = PHASE_EMOJIS[phase] || "📅";
  const category = PHASE_CATEGORIES[phase];

  return {
    start: dateToArray(startDate),
    end: dateToArray(endDate),
    title: `${emoji} ${phase.replace("_", " ")}`,
    description: config?.trainingType || "",
    categories: category ? [category] : undefined,
  };
}

function dateToArray(date: Date): [number, number, number, number, number] {
  return [date.getFullYear(), date.getMonth() + 1, date.getDate(), 0, 0];
}