1 files changed, 62 insertions, 0 deletions
diff --git a/internal/render/color.go b/internal/render/color.go
new file mode 100644
index 0000000..cf2af89
--- /dev/null
+++ b/internal/render/color.go
@@ -0,0 +1,62 @@
+package render
+
+import "strings"
+
+// Colour uses ANSI slots 0-15 only -- codes 30-37 and 90-97, plus the
+// attributes 1 (bold), 2 (dim) and 4 (underline). Never 256-colour indices:
+// this runs on terminals whose palette remaps the low slots (the phone's is
+// entirely green), where a hardcoded 38;5;196 would be the one off-palette
+// thing on screen.
+const (
+	Reset     = "0"
+	Bold      = "1"
+	Dim       = "2"
+	Underline = "4"
+
+	Blue        = "34"
+	Cyan        = "36"
+	Green       = "32"
+	Yellow      = "33"
+	Red         = "31"
+	BrightBlue  = "94"
+	BrightRed   = "91"
+	BrightWhite = "97"
+)
+
+// Styler returns a function that wraps text in an ANSI code, or returns it
+// unchanged when colour is off.
+func Styler(colour bool) func(code, text string) string {
+	if !colour {
+		return func(_, text string) string { return text }
+	}
+	return func(code, text string) string {
+		if code == "" {
+			return text
+		}
+		return "\033[" + code + "m" + text + "\033[0m"
+	}
+}
+
+// Cell is one character of chart output with the style it should carry.
+type Cell struct {
+	Style string
+	Text  string
+}
+
+// Paint joins cells, emitting one escape sequence per run of identical style
+// rather than one per character. A per-character version makes the chart around
+// ten times larger for output that looks exactly the same.
+func Paint(cells []Cell, c func(string, string) string) string {
+	var b strings.Builder
+	for i := 0; i < len(cells); {
+		j := i
+		var run strings.Builder
+		for j < len(cells) && cells[j].Style == cells[i].Style {
+			run.WriteString(cells[j].Text)
+			j++
+		}
+		b.WriteString(c(cells[i].Style, run.String()))
+		i = j
+	}
+	return b.String()
+}