Merge remote-tracking branch 'rephorm/filter'

2 files changed, 74 insertions, 0 deletions

diff --git a/utils/runes.go b/utils/runes.go
new file mode 100644
index 0000000..76cb5e3
--- /dev/null
+++ b/utils/runes.go
@@ -0,0 +1,24 @@
+package utils
+
+import (
+	rw "github.com/mattn/go-runewidth"
+)
+
+func TruncateFront(s string, w int, prefix string) string {
+	if rw.StringWidth(s) <= w {
+		return s
+	}
+	r := []rune(s)
+	pw := rw.StringWidth(prefix)
+	w -= pw
+	width := 0
+	i := len(r) - 1
+	for ; i >= 0; i-- {
+		cw := rw.RuneWidth(r[i])
+		width += cw
+		if width > w {
+			break
+		}
+	}
+	return prefix + string(r[i+1:len(r)])
+}
diff --git a/utils/runes_test.go b/utils/runes_test.go
new file mode 100644
index 0000000..67ceefc
--- /dev/null
+++ b/utils/runes_test.go
@@ -0,0 +1,50 @@
+package utils
+
+import "testing"
+
+const (
+	ELLIPSIS = "…"
+)
+
+func TestTruncateFront(t *testing.T) {
+	tests := []struct {
+		s      string
+		w      int
+		prefix string
+		want   string
+	}{
+		{"", 0, ELLIPSIS, ""},
+		{"", 1, ELLIPSIS, ""},
+		{"", 10, ELLIPSIS, ""},
+
+		{"abcdef", 0, ELLIPSIS, ELLIPSIS},
+		{"abcdef", 1, ELLIPSIS, ELLIPSIS},
+		{"abcdef", 2, ELLIPSIS, ELLIPSIS + "f"},
+		{"abcdef", 5, ELLIPSIS, ELLIPSIS + "cdef"},
+		{"abcdef", 6, ELLIPSIS, "abcdef"},
+		{"abcdef", 10, ELLIPSIS, "abcdef"},
+
+		{"abcdef", 0, "...", "..."},
+		{"abcdef", 1, "...", "..."},
+		{"abcdef", 3, "...", "..."},
+		{"abcdef", 4, "...", "...f"},
+		{"abcdef", 5, "...", "...ef"},
+		{"abcdef", 6, "...", "abcdef"},
+		{"abcdef", 10, "...", "abcdef"},
+
+		{"｟full～width｠", 15, ".", "｟full～width｠"},
+		{"｟full～width｠", 14, ".", ".full～width｠"},
+		{"｟full～width｠", 13, ".", ".ull～width｠"},
+		{"｟full～width｠", 10, ".", ".～width｠"},
+		{"｟full～width｠", 9, ".", ".width｠"},
+		{"｟full～width｠", 8, ".", ".width｠"},
+		{"｟full～width｠", 3, ".", ".｠"},
+		{"｟full～width｠", 2, ".", "."},
+	}
+
+	for _, test := range tests {
+		if got := TruncateFront(test.s, test.w, test.prefix); got != test.want {
+			t.Errorf("TruncateFront(%q, %d, %q) = %q; want %q", test.s, test.w, test.prefix, got, test.want)
+		}
+	}
+}