use std::collections::HashMap;
use std::env;
use std::error::Error;
use std::fs::File;
use std::io::{BufReader, prelude::*};
use std::str::FromStr;

/// Parse a report into a Vec<T>
fn parse_report<T>(line: &str) -> Result<Vec<T>, <T as FromStr>::Err>
where
    T: FromStr,
{
    let parsed_line = line
        .split(char::is_whitespace)
        .map(|v| v.parse())
        .collect::<Result<Vec<T>, _>>()?;
    Ok(parsed_line)
}

enum ReportDirection {
    Asc,
    Desc,
}

fn is_report_safe(report: &Vec<i64>) -> bool {
    let direction = if report[0] < report[1] {
        ReportDirection::Asc
    } else {
        ReportDirection::Desc
    };

    match direction {
        ReportDirection::Asc => {
            let mut prev_report_level = report[0];
            for report_level in report[1..].iter() {
                if prev_report_level >= *report_level || report_level - prev_report_level > 3 {
                    return false;
                }
                prev_report_level = *report_level;
            }
        }
        ReportDirection::Desc => {
            let mut prev_report_level = report[0];
            for report_level in report[1..].iter() {
                if prev_report_level <= *report_level || prev_report_level - report_level > 3 {
                    return false;
                }
                prev_report_level = *report_level;
            }
        }
    };

    true
}

fn main() -> Result<(), Box<dyn Error>> {
    // Handle command input
    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        panic!(
            "{} must be run with a single argument of files name!",
            &args[0]
        )
    }
    let input_file_string = &args[1];

    let input_file = File::open(input_file_string)?;
    let input_reader = BufReader::new(input_file);

    let mut accumulator = 0;
    for line in input_reader.lines() {
        let line = line?;
        let parsed_report: Vec<i64> = parse_report(&line)?;
        if is_report_safe(&parsed_report) {
            accumulator += 1;
        }
    }

    println!("Number of SAFE reports: {}", accumulator);

    Ok(())
}