// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// A package of simple functions to manipulate strings.
package strings

import "utf8"

// explode splits s into an array of UTF-8 sequences, one per Unicode character (still strings) up to a maximum of n (n <= 0 means no limit).
// Invalid UTF-8 sequences become correct encodings of U+FFF8.
func explode(s string, n int) []string {
	if n <= 0 {
		n = len(s);
	}
	a := make([]string, n);
	var size, rune int;
	na := 0;
	for len(s) > 0 {
		if na+1 >= n {
			a[na] = s;
			na++;
			break
		}
		rune, size = utf8.DecodeRuneInString(s);
		s = s[size:len(s)];
		a[na] = string(rune);
		na++;
	}
	return a[0:na]
}

// Count counts the number of non-overlapping instances of sep in s.
func Count(s, sep string) int {
	if sep == "" {
		return utf8.RuneCountInString(s)+1
	}
	c := sep[0];
	n := 0;
	for i := 0; i+len(sep) <= len(s); i++ {
		if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
			n++;
			i += len(sep)-1
		}
	}
	return n
}

// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
func Index(s, sep string) int {
	n := len(sep);
	if n == 0 {
		return 0
	}
	c := sep[0];
	for i := 0; i+n <= len(s); i++ {
		if s[i] == c && (n == 1 || s[i:i+n] == sep) {
			return i
		}
	}
	return -1
}

// Index returns the index of the last instance of sep in s, or -1 if sep is not present in s.
func LastIndex(s, sep string) int {
	n := len(sep);
	if n == 0 {
		return len(s)
	}
	c := sep[0];
	for i := len(s)-n; i >= 0; i-- {
		if s[i] == c && (n == 1 || s[i:i+n] == sep) {
			return i
		}
	}
	return -1
}

// Split splits the string s around each instance of sep, returning an array of substrings of s.
// If sep is empty, Split splits s after each UTF-8 sequence.
// If n > 0, split Splits s into at most n substrings; the last subarray will contain an unsplit remainder string.
func Split(s, sep string, n int) []string {
	if sep == "" {
		return explode(s, n)
	}
	if n <= 0 {
		n = Count(s, sep) + 1;
	}
	c := sep[0];
	start := 0;
	a := make([]string, n);
	na := 0;
	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
		if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
			a[na] = s[start:i];
			na++;
			start = i+len(sep);
			i += len(sep)-1;
		}
	}
	a[na] = s[start:len(s)];
	return a[0:na+1]
}

// Join concatenates the elements of a to create a single string.   The separator string
// sep is placed between elements in the resulting string.
func Join(a []string, sep string) string {
	if len(a) == 0 {
		return ""
	}
	if len(a) == 1 {
		return a[0]
	}
	n := len(sep) * (len(a)-1);
	for i := 0; i < len(a); i++ {
		n += len(a[i])
	}

	b := make([]byte, n);
	bp := 0;
	for i := 0; i < len(a); i++ {
		s := a[i];
		for j := 0; j < len(s); j++ {
			b[bp] = s[j];
			bp++
		}
		if i + 1 < len(a) {
			s = sep;
			for j := 0; j < len(s); j++ {
				b[bp] = s[j];
				bp++
			}
		}
	}
	return string(b)
}

// HasPrefix tests whether the string s begins with prefix.
func HasPrefix(s, prefix string) bool {
	return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
}

// HasSuffix tests whether the string s ends with suffix.
func HasSuffix(s, suffix string) bool {
	return len(s) >= len(suffix) && s[len(s)-len(suffix):len(s)] == suffix
}

// Upper returns a copy of the string s, with all low ASCII lowercase letters
// converted to uppercase.
// TODO: full Unicode support
func UpperASCII(s string) string {
	// Note, we can work byte-by-byte because UTF-8 multibyte characters
	// don't use any low ASCII byte values.
	b := make([]byte, len(s));
	for i := 0; i < len(s); i++ {
		c := s[i];
		if 'a' <= c && c <= 'z' {
			c -= 'a' - 'A';
		}
		b[i] = c;
	}
	return string(b);
}

// Upper returns a copy of the string s, with all low ASCII lowercase letters
// converted to lowercase.
// TODO: full Unicode support
func LowerASCII(s string) string {
	// Note, we can work byte-by-byte because UTF-8 multibyte characters
	// don't use any low ASCII byte values.
	b := make([]byte, len(s));
	for i := 0; i < len(s); i++ {
		c := s[i];
		if 'A' <= c && c <= 'Z' {
			c += 'a' - 'A';
		}
		b[i] = c;
	}
	return string(b);
}

func isWhitespaceASCII(c byte) bool {
	switch int(c) {
	case ' ', '\t', '\r', '\n':
		return true;
	}
 	return false;
}

// Trim returns a slice of the string s, with all leading and trailing whitespace
// removed.  "Whitespace" for now defined as space, tab, CR, or LF.
// TODO: full Unicode whitespace support (need a unicode.IsWhitespace method)
func TrimSpaceASCII(s string) string {
	// Note, we can work byte-by-byte because UTF-8 multibyte characters
	// don't use any low ASCII byte values.
	start, end := 0, len(s);
	for start < end && isWhitespaceASCII(s[start]) {
		start++;
	}
	for start < end && isWhitespaceASCII(s[end-1]) {
		end--;
	}
	return s[start:end];
}