package day1

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

func getDistance(x, y int) int {
	// Take the distance between two numbers.
	// The distance is the difference between the two numbers.

	if x > y {
		return (x - y)

	} else {
		return (y - x)

	}
}

func processLine(line string) (int, int, error) {
	// Split the line into fields.
	fields := strings.Fields(line)
	if len(fields) != 2 {
		return 0, 0, fmt.Errorf("Expected 2 fields, got %d", len(fields))
	}
	num1, err := strconv.Atoi(fields[0])
	if err != nil {
		return 0, 0, fmt.Errorf("Failed to parse first number: %w", err)
	}

	num2, err := strconv.Atoi(fields[1])
	if err != nil {
		return 0, 0, fmt.Errorf("Failed to parse the second number: %w", err)
	}

	return num1, num2, nil

}

func readDataSet(filename string) ([]int, []int, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, nil, err
	}
	defer file.Close()

	var firstSet, secondSet []int

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		num1, num2, err := processLine(line)
		if err != nil {
			return nil, nil, err
		}
		firstSet = append(firstSet, num1)
		secondSet = append(secondSet, num2)
	}

	return firstSet, secondSet, nil
}

func numFreq(dataset []int) map[int]int {
	// Take a slice of numbers and return an array of each number and the amount of times it occurs.
	distribution := make(map[int]int)
	for _, num := range dataset {
		elem, ok := distribution[num]
		if ok {
			distribution[num] = elem + 1
		} else {
			distribution[num] = 1
		}
	}
	return distribution
}

func partTwo(filename string) (int, error) {
	//Solve part two.
	var similarities int
	firstSet, secondSet, err := readDataSet(filename)

	if err != nil {
		return 0, err
	}

	secondDistribution := numFreq(secondSet)

	for _, num := range firstSet {
		freq, ok := secondDistribution[num]
		if ok {
			similarity := num * freq
			similarities = similarities + similarity
		}
	}

	return similarities, nil
}

func partOne(filename string) (int, error) {
	// Solve part one.

	firstSet, secondSet, err := readDataSet(filename)

	if err != nil {
		return 0, err
	}
	slices.Sort(firstSet)
	slices.Sort(secondSet)
	if len(firstSet) != len(secondSet) {
		return 0, fmt.Errorf("Error: Datasets are not the same size. %v != %v", len(firstSet), len(secondSet))
	}
	var distances int
	for i := 0; i < len(firstSet); i++ {
		distance := getDistance(firstSet[i], secondSet[i])
		distances = distances + distance
	}

	return distances, nil
}

func Day1(filename string) {
	distances, err := partOne(filename)
	if err != nil {
		fmt.Printf("Error: %v", err)
		os.Exit(1)
	}
	fmt.Println("-------- PART 1 -------")
	fmt.Printf("The total distance is %v\n", distances)
	similarities, err := partTwo(filename)
	if err != nil {
		fmt.Printf("Error: %v", err)
		os.Exit(1)
	}

	fmt.Println("-------- PART 2 -------")
	fmt.Printf("The similarities between the two sets: %v\n", similarities)
}