"""
Regenerates data/dummy/roll_no/students.csv to match the real batches in
data/dummy/batch_codes/25|26/batches.csv.

Rule: one student {batch_code}-001 per batch. Batches listed in
data/dummy/fixed two sections.txt (batches with two registered sections)
additionally get {batch_code}-002.

Run:
    python data/dummy/generate_student_roster.py
"""

import csv
import os

BASE_DIR = os.path.dirname(os.path.abspath(__file__))
TWO_SECTION_BATCHES_FILE = os.path.join(BASE_DIR, "fixed two sections.txt")
STUDENTS_FILE = os.path.join(BASE_DIR, "roll_no", "students.csv")


def _read_csv(relative_path):
    path = os.path.join(BASE_DIR, relative_path)
    with open(path, newline="", encoding="utf-8") as f:
        return list(csv.DictReader(f))


def _read_two_section_batches():
    with open(TWO_SECTION_BATCHES_FILE, encoding="utf-8") as f:
        return {line.strip() for line in f if line.strip()}


def main():
    batches_25 = _read_csv(os.path.join("batch_codes", "25", "batches.csv"))
    batches_26 = _read_csv(os.path.join("batch_codes", "26", "batches.csv"))
    batches = batches_25 + batches_26

    two_section_batches = _read_two_section_batches()

    students = []
    for batch in batches:
        batch_code = batch["batch_code"]
        seqs = [1, 2] if batch_code in two_section_batches else [1]
        for seq in seqs:
            roll_no = f"{batch_code}-{seq:03d}"
            students.append([roll_no, batch_code, f"Student {roll_no}"])

    os.makedirs(os.path.dirname(STUDENTS_FILE), exist_ok=True)
    with open(STUDENTS_FILE, "w", newline="", encoding="utf-8") as f:
        writer = csv.writer(f)
        writer.writerow(["roll_no", "batch_code", "student_name"])
        writer.writerows(students)

    print(f"wrote {len(students)} rows -> {STUDENTS_FILE}")


if __name__ == "__main__":
    main()