package atoi

import (
	"math"
	"regexp"
	"strings"
)

var pattern, _ = regexp.Compile(`^\s*([-+]?)(\d+)`)

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func bound(num, low, hi int) int {
	return min(max(low, num), hi)
}

func myAtoi(s string) int {
	groups := pattern.FindStringSubmatch(s)
	if groups == nil {
		return 0
	}

	sign := 1
	if groups[1] == "-" {
		sign = -1
	}

	digits := strings.TrimLeft(groups[2], "0")
	size := len(digits)
	if size > 10 {
		return bound(math.MaxInt64*sign, math.MinInt32, math.MaxInt32)
	}
	result := 0
	for i, d := range digits {
		val := int(d) - 48
		result += int(math.Pow10(size-i-1)) * val
	}

	return bound(result*sign, math.MinInt32, math.MaxInt32)
}

func Convert(s string) int {
	return myAtoi(s)
}