/*
Cargo.toml contains:

[dependencies]
ordermap = "0.2.10"
smallvec = "0.4.0"

[profile.release]
opt-level = 3
lto = true
panic = "abort"


Compiled with:
cargo rustc --release --bin max_column_sum_by_key -- -C target-cpu=native
*/

extern crate ordermap;
extern crate smallvec;

fn main() {
    use std::cmp::max;
    use std::fs::File;
    use std::io::{BufReader, BufRead};
    use std::str::{from_utf8, from_utf8_unchecked};
    use ordermap::OrderMap;
    use smallvec::SmallVec;

    let args: Vec<_> = std::env::args().collect();
    if args.len() != 4 {
        return eprintln!("synopsis: {} filename keyfield valuefield", args[0]);
    }

    let file_name = &args[1];
    let key_field_index: usize = args[2].parse().unwrap();
    let value_field_index: usize = args[3].parse().unwrap();
    let max_field_index = max(key_field_index, value_field_index);
    let delim = b'\t';
    let mut sum_by_key = OrderMap::<SmallVec<[u8; 8]>, i64>::new();

    let fin = File::open(file_name).unwrap();
    let mut input = BufReader::with_capacity(64 * 1024, fin);
    let mut line = vec![];

    loop {
        match input.read_until(b'\n', &mut line) {
            Ok(n) if n > 0 => {
                let mut key = None;
                let mut field_value = None;

                for (i, field) in line.splitn(max_field_index + 2, |&b| b == delim).enumerate() {
                    if i == key_field_index {
                        key = Some(field.into());
                    } else if i == value_field_index {
                        let field = unsafe { from_utf8_unchecked(&field) };
                        field_value = Some(field.parse().unwrap());
                    }
                }

                if let (Some(key), Some(field_value)) = (key, field_value) {
                    *sum_by_key.entry(key).or_insert(0) += field_value;
                }
            },
            _ => break,
        }
        line.clear();
    }

    if let Some((max_key, max_val)) = sum_by_key.iter().max_by_key(|&(_, v)| v) {
        println!("max_key: {} sum: {}", from_utf8(&max_key).unwrap(), max_val);
    } else {
        println!("No entries");
    }
}