#!/usr/bin/env python3
"""Generates the sharded order CSVs this module partitions over.

Usage:
  generate-shards.py <output-dir> <total-rows> <num-shards> [--corrupt-shard N] [--seed S]

Each shard is orders-shard-NN.csv with header "orderId,customerId,amountCents,region".
Row counts are split as evenly as possible across shards (the last shard absorbs the remainder).
--corrupt-shard N replaces one row near the middle of shard N (0-indexed) with a non-numeric
amountCents field, so FlatFileItemReader's FieldSetMapper throws NumberFormatException wrapped in
FlatFileParseException when that shard is read -- a real, reproducible parse failure, not a
simulated one.
"""
import argparse
import os
import random
import sys

REGIONS = ["NORTH", "SOUTH", "EAST", "WEST", "CENTRAL"]


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument("output_dir")
    ap.add_argument("total_rows", type=int)
    ap.add_argument("num_shards", type=int)
    ap.add_argument("--corrupt-shard", type=int, default=-1)
    ap.add_argument("--seed", type=int, default=42)
    args = ap.parse_args()

    os.makedirs(args.output_dir, exist_ok=True)
    rnd = random.Random(args.seed)

    base = args.total_rows // args.num_shards
    counts = [base] * args.num_shards
    counts[-1] += args.total_rows - base * args.num_shards

    order_id = 1
    for shard_idx, count in enumerate(counts):
        path = os.path.join(args.output_dir, f"orders-shard-{shard_idx:02d}.csv")
        corrupt_at = -1
        if shard_idx == args.corrupt_shard:
            corrupt_at = count // 2
        with open(path, "w", newline="") as f:
            f.write("orderId,customerId,amountCents,region\n")
            for i in range(count):
                customer_id = rnd.randint(1, 2_000_000)
                amount_cents = rnd.randint(500, 9_999_999)
                region = REGIONS[rnd.randint(0, len(REGIONS) - 1)]
                if i == corrupt_at:
                    f.write(f"{order_id},{customer_id},NOT_A_NUMBER,{region}\n")
                else:
                    f.write(f"{order_id},{customer_id},{amount_cents},{region}\n")
                order_id += 1
        print(f"wrote {path}: {count} rows" + (" (1 corrupt row)" if corrupt_at >= 0 else ""))

    print(f"total: {order_id - 1} rows across {args.num_shards} shards in {args.output_dir}")


if __name__ == "__main__":
    main()