VictoriaMetrics/vendor/github.com/rivo/uniseg/line.go

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package uniseg
import "unicode/utf8"
// FirstLineSegment returns the prefix of the given byte slice after which a
// decision to break the string over to the next line can or must be made,
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// according to the rules of [Unicode Standard Annex #14]. This is used to
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// implement line breaking.
//
// Line breaking, also known as word wrapping, is the process of breaking a
// section of text into lines such that it will fit in the available width of a
// page, window or other display area.
//
// The returned "segment" may not be broken into smaller parts, unless no other
// breaking opportunities present themselves, in which case you may break by
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// grapheme clusters (using the [FirstGraphemeCluster] function to determine the
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// grapheme clusters).
//
// The "mustBreak" flag indicates whether you MUST break the line after the
// given segment (true), for example after newline characters, or you MAY break
// the line after the given segment (false).
//
// This function can be called continuously to extract all non-breaking sub-sets
// from a byte slice, as illustrated in the example below.
//
// If you don't know the current state, for example when calling the function
// for the first time, you must pass -1. For consecutive calls, pass the state
// and rest slice returned by the previous call.
//
// The "rest" slice is the sub-slice of the original byte slice "b" starting
// after the last byte of the identified line segment. If the length of the
// "rest" slice is 0, the entire byte slice "b" has been processed. The
// "segment" byte slice is the sub-slice of the input slice containing the
// identified line segment.
//
// Given an empty byte slice "b", the function returns nil values.
//
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// Note that in accordance with [UAX #14 LB3], the final segment will end with
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// "mustBreak" set to true. You can choose to ignore this by checking if the
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// length of the "rest" slice is 0 and calling [HasTrailingLineBreak] or
// [HasTrailingLineBreakInString] on the last rune.
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//
// Note also that this algorithm may break within grapheme clusters. This is
// addressed in Section 8.2 Example 6 of UAX #14. To avoid this, you can use
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// the [Step] function instead.
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//
// [Unicode Standard Annex #14]: https://www.unicode.org/reports/tr14/
// [UAX #14 LB3]: https://www.unicode.org/reports/tr14/#Algorithm
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func FirstLineSegment(b []byte, state int) (segment, rest []byte, mustBreak bool, newState int) {
// An empty byte slice returns nothing.
if len(b) == 0 {
return
}
// Extract the first rune.
r, length := utf8.DecodeRune(b)
if len(b) <= length { // If we're already past the end, there is nothing else to parse.
return b, nil, true, lbAny // LB3.
}
// If we don't know the state, determine it now.
if state < 0 {
state, _ = transitionLineBreakState(state, r, b[length:], "")
}
// Transition until we find a boundary.
var boundary int
for {
r, l := utf8.DecodeRune(b[length:])
state, boundary = transitionLineBreakState(state, r, b[length+l:], "")
if boundary != LineDontBreak {
return b[:length], b[length:], boundary == LineMustBreak, state
}
length += l
if len(b) <= length {
return b, nil, true, lbAny // LB3
}
}
}
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// FirstLineSegmentInString is like [FirstLineSegment] but its input and outputs
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// are strings.
func FirstLineSegmentInString(str string, state int) (segment, rest string, mustBreak bool, newState int) {
// An empty byte slice returns nothing.
if len(str) == 0 {
return
}
// Extract the first rune.
r, length := utf8.DecodeRuneInString(str)
if len(str) <= length { // If we're already past the end, there is nothing else to parse.
return str, "", true, lbAny // LB3.
}
// If we don't know the state, determine it now.
if state < 0 {
state, _ = transitionLineBreakState(state, r, nil, str[length:])
}
// Transition until we find a boundary.
var boundary int
for {
r, l := utf8.DecodeRuneInString(str[length:])
state, boundary = transitionLineBreakState(state, r, nil, str[length+l:])
if boundary != LineDontBreak {
return str[:length], str[length:], boundary == LineMustBreak, state
}
length += l
if len(str) <= length {
return str, "", true, lbAny // LB3.
}
}
}
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// HasTrailingLineBreak returns true if the last rune in the given byte slice is
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// one of the hard line break code points defined in LB4 and LB5 of [UAX #14].
//
// [UAX #14]: https://www.unicode.org/reports/tr14/#Algorithm
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func HasTrailingLineBreak(b []byte) bool {
r, _ := utf8.DecodeLastRune(b)
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property, _ := propertyLineBreak(r)
return property == prBK || property == prCR || property == prLF || property == prNL
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}
// HasTrailingLineBreakInString is like [HasTrailingLineBreak] but for a string.
func HasTrailingLineBreakInString(str string) bool {
r, _ := utf8.DecodeLastRuneInString(str)
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property, _ := propertyLineBreak(r)
return property == prBK || property == prCR || property == prLF || property == prNL
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}