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// Copyright 2019 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package runewidth is a wrapper over github.com/mattn/go-runewidth which
// gives different treatment to certain runes with ambiguous width.
package runewidth
import runewidth "github.com/mattn/go-runewidth"
// RuneWidth returns the number of cells needed to draw r.
// Background in http://www.unicode.org/reports/tr11/.
//
// Treats runes used internally by termdash as single-cell (half-width) runes
// regardless of the locale. I.e. runes that are used to draw lines, boxes,
// indicate resize or text trimming was needed and runes used by the braille
// canvas.
//
// This should be safe, since even in locales where these runes have ambiguous
// width, we still place all the character content around them so they should
// have be half-width.
func RuneWidth(r rune) int {
if inTable(r, exceptions) {
return 1
}
return runewidth.RuneWidth(r)
}
// StringWidth is like RuneWidth, but returns the number of cells occupied by
// all the runes in the string.
func StringWidth(s string) int {
var width int
for _, r := range []rune(s) {
width += RuneWidth(r)
}
return width
}
// inTable determines if the rune falls within the table.
// Copied from github.com/mattn/go-runewidth/blob/master/runewidth.go.
func inTable(r rune, t table) bool {
// func (t table) IncludesRune(r rune) bool {
if r < t[0].first {
return false
}
bot := 0
top := len(t) - 1
for top >= bot {
mid := (bot + top) >> 1
switch {
case t[mid].last < r:
bot = mid + 1
case t[mid].first > r:
top = mid - 1
default:
return true
}
}
return false
}
type interval struct {
first rune
last rune
}
type table []interval
// exceptions runes defined here are always considered to be half-width even if
// they might be ambiguous in some contexts.
var exceptions = table{
// Characters used by termdash to indicate text trim or scroll.
{0x2026, 0x2026},
{0x21c4, 0x21c4},
{0x21e7, 0x21e7},
{0x21e9, 0x21e9},
// Box drawing, used as line-styles.
// https://en.wikipedia.org/wiki/Box-drawing_character
{0x2500, 0x257F},
// Block elements used as sparks.
// https://en.wikipedia.org/wiki/Box-drawing_character
{0x2580, 0x258F},
}
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