package longestcommon

import "strings"

//TrimPrefix removes the longest common prefix from all provided strings
func TrimPrefix(strs []string) {
	p := Prefix(strs)
	if p == "" {
		return
	}
	for i, s := range strs {
		strs[i] = strings.TrimPrefix(s, p)
	}
}

//TrimSuffix removes the longest common suffix from all provided strings
func TrimSuffix(strs []string) {
	p := Suffix(strs)
	if p == "" {
		return
	}
	for i, s := range strs {
		strs[i] = strings.TrimSuffix(s, p)
	}
}

//Prefix returns the longest common prefix of the provided strings
func Prefix(strs []string) string {
	return longestCommonXfix(strs, true)
}

//Suffix returns the longest common suffix of the provided strings
func Suffix(strs []string) string {
	return longestCommonXfix(strs, false)
}

func longestCommonXfix(strs []string, pre bool) string {
	//short-circuit empty list
	if len(strs) == 0 {
		return ""
	}
	xfix := strs[0]
	//short-circuit single-element list
	if len(strs) == 1 {
		return xfix
	}
	//compare first to rest
	for _, str := range strs[1:] {
		xfixl := len(xfix)
		strl := len(str)
		//short-circuit empty strings
		if xfixl == 0 || strl == 0 {
			return ""
		}
		//maximum possible length
		maxl := xfixl
		if strl < maxl {
			maxl = strl
		}
		//compare letters
		if pre {
			//prefix, iterate left to right
			for i := 0; i < maxl; i++ {
				if xfix[i] != str[i] {
					xfix = xfix[:i]
					break
				}
			}
		} else {
			//suffix, iternate right to left
			for i := 0; i < maxl; i++ {
				xi := xfixl - i - 1
				si := strl - i - 1
				if xfix[xi] != str[si] {
					xfix = xfix[xi+1:]
					break
				}
			}
		}
	}
	return xfix
}