solve(codewars): Human readable duration format [4 kyu]

Author: jestenough

services/codewars/katas/4_kyu/Human readable duration format/README.md

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+# Human readable duration format
+
+Your task in order to complete this Kata is to write a function which formats a duration, given as a number of seconds, in a human-friendly way.
+
+The function must accept a non-negative integer. If it is zero, it just returns `"now"`. Otherwise, the duration is expressed as a combination of `years`, `days`, `hours`, `minutes` and `seconds`.
+
+It is much easier to understand with an example:
+
+```
+* For seconds = 62, your function should return 
+    "1 minute and 2 seconds"
+* For seconds = 3662, your function should return
+    "1 hour, 1 minute and 2 seconds"
+```
+
+For the purpose of this Kata, a year is 365 days and a day is 24 hours.
+
+Note that spaces are important.
+
+Detailed rules
+
+The resulting expression is made of components like 4 seconds, 1 year, etc. In general, a positive integer and one of the valid units of time, separated by a space. The unit of time is used in plural if the integer is greater than 1.
+
+The components are separated by a comma and a space (", "). Except the last component, which is separated by " and ", just like it would be written in English.
+
+A more significant units of time will occur before than a least significant one. Therefore, 1 second and 1 year is not correct, but 1 year and 1 second is.
+
+Different components have different unit of times. So there is not repeated units like in 5 seconds and 1 second.
+
+A component will not appear at all if its value happens to be zero. Hence, 1 minute and 0 seconds is not valid, but it should be just 1 minute.
+
+A unit of time must be used "as much as possible". It means that the function should not return 61 seconds, but 1 minute and 1 second instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.
+
+[Kata link](https://www.codewars.com/kata/52742f58faf5485cae000b9a)

services/codewars/katas/4_kyu/Human readable duration format/src/go.mod

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+module src
+
+go 1.21

services/codewars/katas/4_kyu/Human readable duration format/src/solution.go

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+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+type timeComponent struct {
+	value        int64
+	verboseName  string
+	pluralSuffix string
+}
+
+func FormatDuration(seconds int64) string {
+	if seconds < 0 {
+		return "now"
+	}
+
+	const (
+		secondsPerYear   = 31536000
+		secondsPerDay    = 86400
+		secondsPerHour   = 3600
+		secondsPerMinute = 60
+	)
+	years, yearsRemainder := seconds/secondsPerYear, seconds%secondsPerYear
+	days, hoursRemainder := yearsRemainder/secondsPerDay, yearsRemainder%secondsPerDay
+	hours, minuteRemainder := hoursRemainder/secondsPerHour, hoursRemainder%secondsPerHour
+	minutes, secondsRemainder := minuteRemainder/secondsPerMinute, minuteRemainder%secondsPerMinute
+
+	timeComponents := []timeComponent{
+		{years, "year", "s"},
+		{days, "day", "s"},
+		{hours, "hour", "s"},
+		{minutes, "minute", "s"},
+		{secondsRemainder, "second", "s"},
+	}
+
+	var formattedComponents []string
+	for _, component := range timeComponents {
+		if formattedValue := formatTimeComponent(component); formattedValue != "" {
+			formattedComponents = append(formattedComponents, formattedValue)
+		}
+	}
+
+	separatedByCommaValues := strings.Join(formattedComponents, ", ")
+	if lastCommaIndex := strings.LastIndex(separatedByCommaValues, ", "); lastCommaIndex != -1 {
+		separatedByCommaValues = separatedByCommaValues[:lastCommaIndex] + " and" + separatedByCommaValues[lastCommaIndex+1:]
+	}
+
+	return separatedByCommaValues
+}
+
+func formatTimeComponent(component timeComponent) string {
+	if component.value == 0 {
+		return ""
+	} else if component.value > 1 {
+		return fmt.Sprintf("%d %s%s", component.value, component.verboseName, component.pluralSuffix)
+	}
+
+	return fmt.Sprintf("%d %s", component.value, component.verboseName)
+}