import { NextResponse } from "next/server";
import supabase from '@/lib/db';

export async function POST() {
  try {
    // Get current date
    const currentDate = new Date();
    const currentYear = currentDate.getFullYear();
    const currentMonth = currentDate.getMonth() + 1; // getMonth() returns 0-11

    // Get all active students
    const { data: activeStudents, error: fetchError } = await supabase
      .from('mahasiswa')
      .select('nim, tahun_angkatan, semester')
      .eq('status_kuliah', 'Aktif');

    if (fetchError) {
      console.error('Error fetching active students:', fetchError);
      return NextResponse.json(
        { message: "Gagal mengambil data mahasiswa aktif" },
        { status: 500 }
      );
    }

    if (!activeStudents || activeStudents.length === 0) {
      return NextResponse.json({ 
        message: "Tidak ada mahasiswa aktif yang ditemukan",
        affectedRows: 0 
      });
    }

    let updatedCount = 0;
    const errors: string[] = [];

    // Update semester for each active student
    for (const student of activeStudents) {
      try {
        const tahunAngkatan = student.tahun_angkatan;
        if (!tahunAngkatan) {
          errors.push(`Mahasiswa NIM ${student.nim}: Tahun angkatan tidak ditemukan`);
          continue;
        }

        // Calculate current semester based on tahun_angkatan and current date
        const yearsSinceEnrollment = currentYear - tahunAngkatan;
        let currentSemester = yearsSinceEnrollment * 2; // 2 semesters per year

        // Adjust for current month (odd months = odd semesters, even months = even semesters)
        if (currentMonth >= 2 && currentMonth <= 7) {
          // February to July = odd semester (1, 3, 5, etc.)
          currentSemester += 1;
        } else {
          // August to January = even semester (2, 4, 6, etc.)
          currentSemester += 2;
        }

        // Cap at semester 14 (7 years)
        if (currentSemester > 14) {
          currentSemester = 14;
        }

        // Update semester if different
        if (student.semester !== currentSemester) {
          const { error: updateError } = await supabase
            .from('mahasiswa')
            .update({ semester: currentSemester })
            .eq('nim', student.nim);

          if (updateError) {
            errors.push(`Mahasiswa NIM ${student.nim}: Gagal memperbarui semester: ${updateError.message}`);
          } else {
            updatedCount++;
          }
        }
      } catch (error) {
        console.error(`Error updating semester for mahasiswa NIM ${student.nim}:`, error);
        errors.push(`Mahasiswa NIM ${student.nim}: Terjadi kesalahan: ${(error as Error).message}`);
      }
    }

    return NextResponse.json({
      message: `Berhasil memperbarui semester untuk ${updatedCount} mahasiswa`,
      affectedRows: updatedCount,
      errors: errors.length > 0 ? errors : undefined
    });

  } catch (error) {
    console.error('Error in update semester:', error);
    return NextResponse.json(
      { message: "Terjadi kesalahan internal server" },
      { status: 500 }
    );
  }
}