import encoding.csv
import flag
import os
import rand

struct CityMean {
    city string
    mean f64
}

fn main() {
    mut fp := flag.new_flag_parser(os.args)
    fp.version('1brc sample generator v1.0.0')
    fp.skip_executable()
    fp.application('Sample generator for 1 billion rows challenge')
    fp.description('The 1 billion rows challenge solved in V.\nFor details, see https://www.morling.dev/blog/one-billion-row-challenge/')
    input_file := fp.string('city-file', `i`, 'cities.txt',
        'Path to input file with cities and means list')
    fp.limit_free_args_to_exactly(1)!
    sample_count := fp.remaining_parameters()[0].u64()

    content := os.read_file(input_file) or { panic(err) }
    mut reader := csv.new_reader(content, csv.ReaderConfig{ delimiter: `,` })
    mut means := []CityMean{}
    for {
        rec := reader.read() or { break }
        means << CityMean{
            city: rec[0]
            mean: rec[1].f64()
        }
    }

    for _ in 0 .. sample_count / 2 {
        mut city := rand.intn(means.len)!
        m1, m2 := rand.normal_pair(mu: means[city].mean, sigma: 10)!
        println('${means[city].city};${m1:.1f}')
        city = rand.intn(means.len)!
        println('${means[city].city};${m2:.1f}')
    }
}