grademaxxing/app/utils/gradeSystems.ts

/**
 * German Grading System Utilities
 * German grades: 1 (best) to 6 (worst)
 */

export type GradeSystem = "percentage" | "german" | "us-letter";

export interface GradeSystemConfig {
  type: GradeSystem;
  displayName: string;
  description: string;
}

export const GRADE_SYSTEMS: Record<GradeSystem, GradeSystemConfig> = {
  percentage: {
    type: "percentage",
    displayName: "Percentage (0-100%)",
    description: "Standard percentage-based grading",
  },
  german: {
    type: "german",
    displayName: "German (1-6)",
    description: "1 = sehr gut (very good), 6 = ungenügend (insufficient)",
  },
  "us-letter": {
    type: "us-letter",
    displayName: "US Letter (A-F)",
    description: "A = 90-100%, F = below 60%",
  },
};

/**
 * Convert percentage (0-100) to German grade (1-6)
 * German grading scale:
 * 1 (sehr gut / very good): 92-100%
 * 2 (gut / good): 81-91%
 * 3 (befriedigend / satisfactory): 67-80%
 * 4 (ausreichend / sufficient): 50-66%
 * 5 (mangelhaft / deficient): 30-49%
 * 6 (ungenügend / insufficient): 0-29%
 */
export function percentageToGermanGrade(percentage: number): number {
  if (percentage >= 92) return 1.0;
  if (percentage >= 81) return 2.0;
  if (percentage >= 67) return 3.0;
  if (percentage >= 50) return 4.0;
  if (percentage >= 30) return 5.0;
  return 6.0;
}

/**
 * Convert percentage to German grade with decimal precision
 * Uses linear interpolation within each grade range
 */
export function percentageToGermanGradeDetailed(percentage: number): number {
  if (percentage >= 92) {
    // 1.0 - 1.5 range (92-100%)
    const position = (100 - percentage) / (100 - 92);
    return 1.0 + position * 0.5;
  } else if (percentage >= 81) {
    // 1.5 - 2.5 range (81-91%)
    const position = (92 - percentage) / (92 - 81);
    return 1.5 + position * 1.0;
  } else if (percentage >= 67) {
    // 2.5 - 3.5 range (67-80%)
    const position = (81 - percentage) / (81 - 67);
    return 2.5 + position * 1.0;
  } else if (percentage >= 50) {
    // 3.5 - 4.5 range (50-66%)
    const position = (67 - percentage) / (67 - 50);
    return 3.5 + position * 1.0;
  } else if (percentage >= 30) {
    // 4.5 - 5.5 range (30-49%)
    const position = (50 - percentage) / (50 - 30);
    return 4.5 + position * 1.0;
  } else {
    // 5.5 - 6.0 range (0-29%)
    const position = (30 - percentage) / 30;
    return 5.5 + position * 0.5;
  }
}

/**
 * Convert German grade (1-6) to approximate percentage
 */
export function germanGradeToPercentage(grade: number): number {
  if (grade <= 1.5) return 92 + (1.5 - grade) * 16; // 92-100%
  if (grade <= 2.5) return 81 + (2.5 - grade) * 11; // 81-91%
  if (grade <= 3.5) return 67 + (3.5 - grade) * 14; // 67-80%
  if (grade <= 4.5) return 50 + (4.5 - grade) * 17; // 50-66%
  if (grade <= 5.5) return 30 + (5.5 - grade) * 20; // 30-49%
  return Math.max(0, 30 - (grade - 5.5) * 60); // 0-29%
}

/**
 * Get German grade description
 */
export function getGermanGradeDescription(grade: number): string {
  if (grade <= 1.5) return "sehr gut (very good)";
  if (grade <= 2.5) return "gut (good)";
  if (grade <= 3.5) return "befriedigend (satisfactory)";
  if (grade <= 4.5) return "ausreichend (sufficient)";
  if (grade <= 5.5) return "mangelhaft (deficient)";
  return "ungenügend (insufficient)";
}

/**
 * Get color for German grade
 */
export function getGermanGradeColor(grade: number): string {
  if (grade <= 2.0) return "text-green-600";
  if (grade <= 3.0) return "text-blue-600";
  if (grade <= 4.0) return "text-yellow-600";
  if (grade <= 5.0) return "text-orange-600";
  return "text-red-600";
}

/**
 * Format grade based on system
 */
export function formatGradeBySystem(
  percentage: number,
  system: GradeSystem,
  decimals: number = 2
): string {
  switch (system) {
    case "german": {
      const germanGrade = percentageToGermanGradeDetailed(percentage);
      return germanGrade.toFixed(1);
    }
    case "us-letter": {
      if (percentage >= 90) return "A";
      if (percentage >= 80) return "B";
      if (percentage >= 70) return "C";
      if (percentage >= 60) return "D";
      return "F";
    }
    case "percentage":
    default:
      return `${percentage.toFixed(decimals)}%`;
  }
}

/**
 * Get color for grade based on system
 */
export function getGradeColorBySystem(
  percentage: number,
  system: GradeSystem
): string {
  switch (system) {
    case "german": {
      const germanGrade = percentageToGermanGradeDetailed(percentage);
      return getGermanGradeColor(germanGrade);
    }
    case "percentage":
    case "us-letter":
    default:
      if (percentage >= 90) return "text-green-600";
      if (percentage >= 80) return "text-blue-600";
      if (percentage >= 70) return "text-yellow-600";
      if (percentage >= 60) return "text-orange-600";
      return "text-red-600";
  }
}

/**
 * Get description for grade
 */
export function getGradeDescription(
  percentage: number,
  system: GradeSystem
): string | null {
  if (system === "german") {
    const germanGrade = percentageToGermanGradeDetailed(percentage);
    return getGermanGradeDescription(germanGrade);
  }
  return null;
}