// ABOUTME: Cycle phase calculation utilities.
// ABOUTME: Determines current cycle day and phase from last period date with variable cycle lengths.
import type { CyclePhase, PhaseConfig } from "@/types";

// Base phase configurations with weekly limits and training guidance.
// Note: The 'days' field is for the default 31-day cycle; actual boundaries
// are calculated dynamically by getPhaseBoundaries() based on cycleLength.
export const PHASE_CONFIGS: PhaseConfig[] = [
  {
    name: "MENSTRUAL",
    days: [1, 3],
    weeklyLimit: 30,
    dailyAvg: 10,
    trainingType: "Gentle rebounding only",
  },
  {
    name: "FOLLICULAR",
    days: [4, 15],
    weeklyLimit: 120,
    dailyAvg: 17,
    trainingType: "Strength + rebounding",
  },
  {
    name: "OVULATION",
    days: [16, 17],
    weeklyLimit: 80,
    dailyAvg: 40,
    trainingType: "Peak performance",
  },
  {
    name: "EARLY_LUTEAL",
    days: [18, 24],
    weeklyLimit: 100,
    dailyAvg: 14,
    trainingType: "Moderate training",
  },
  {
    name: "LATE_LUTEAL",
    days: [25, 31],
    weeklyLimit: 50,
    dailyAvg: 8,
    trainingType: "Gentle rebounding ONLY",
  },
];

// Phase boundaries scale based on cycle length using fixed luteal, variable follicular.
// Per spec: luteal phase is biologically consistent (14 days); follicular expands/contracts.
// Formula from specs/cycle-tracking.md:
//   MENSTRUAL: 1-3 (fixed)
//   FOLLICULAR: 4 to (cycleLength - 16)
//   OVULATION: (cycleLength - 15) to (cycleLength - 14)
//   EARLY_LUTEAL: (cycleLength - 13) to (cycleLength - 7)
//   LATE_LUTEAL: (cycleLength - 6) to cycleLength
function getPhaseBoundaries(
  cycleLength: number,
): Array<{ phase: CyclePhase; start: number; end: number }> {
  return [
    { phase: "MENSTRUAL", start: 1, end: 3 },
    { phase: "FOLLICULAR", start: 4, end: cycleLength - 16 },
    { phase: "OVULATION", start: cycleLength - 15, end: cycleLength - 14 },
    { phase: "EARLY_LUTEAL", start: cycleLength - 13, end: cycleLength - 7 },
    { phase: "LATE_LUTEAL", start: cycleLength - 6, end: cycleLength },
  ];
}

export function getCycleDay(
  lastPeriodDate: Date,
  cycleLength: number,
  currentDate: Date = new Date(),
): number {
  const diffMs = currentDate.getTime() - lastPeriodDate.getTime();
  const diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));
  return (diffDays % cycleLength) + 1;
}

export function getPhase(cycleDay: number, cycleLength = 31): CyclePhase {
  const boundaries = getPhaseBoundaries(cycleLength);

  for (const { phase, start, end } of boundaries) {
    if (cycleDay >= start && cycleDay <= end) {
      return phase;
    }
  }
  // Default to late luteal for any days beyond cycle length
  return "LATE_LUTEAL";
}

export function getPhaseConfig(phase: CyclePhase): PhaseConfig {
  const config = PHASE_CONFIGS.find((c) => c.name === phase);
  if (!config) {
    throw new Error(`Unknown phase: ${phase}`);
  }
  return config;
}

export function getPhaseLimit(phase: CyclePhase): number {
  return getPhaseConfig(phase).weeklyLimit;
}