package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

type Set map[int]struct{}

// Provide a filename as input, get the result on stdout
func main() {
	x := 0
	found := false
	seen := Set{0: struct{}{}}

	for {
		x, found = ScanFrequencies(os.Args[1], &seen, x)
		if found {
			break
		}
		fmt.Println("All frequencies scanned, repeating...")
	}

	fmt.Println("Repeat frequency detected, calibration complete: ", x)
}

// ScanFrequencies iterates over a list of frequencies (provided as an open
// file handle), compares against a list of frequencies already seen and a 'current' frequency counter,
// and returns `true` when a duplicate frequency is found. Integer value returned is the new, adjusted frequency
func ScanFrequencies(freqFile string, seen *Set, frequency int) (int, bool) {
	file, err := os.Open(os.Args[1])
	if err != nil {
		panic(err)
	}

	duplicateFound := false
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		y, err := strconv.Atoi(scanner.Text())
		if err != nil {
			panic(err)
		}
		frequency += y
		if _, ok := (*seen)[frequency]; ok {
			duplicateFound = true
			break
		}

		(*seen)[frequency] = struct{}{}
	}

	file.Close()
	return frequency, duplicateFound
}