layout.go

package progress

const (
	prefix           = "processing (" // prepended to each progress status line rendered to the terminal
	suffix           = "%): "         // appended to each percentage status calculation rendered to the terminal

	minWidth         = 80             // fallback for pipes, redirects, and non-tty outputs
	pctFieldLen      =  3             // the fixed length of the percentage displayed (e.g., "0.0", " 37", "100")
	colorBlockFactor = 23             // 23 bytes per column for 24-bit color gradient blocks
	maxBytesPerCol   =  4             //  4 bytes per column for worst-case UTF-8 status text truncation thresholds
)

// layout encapsulates the terminal-specific rendering layout configuration.
type layout struct {
	staticWidth      int    // the static width reserved for the prefix prepended to each status message, e.g., "processing (7.4%): "
	colorBlockFactor int    // the number of bytes to allocate to the rendering buffer per each terminal column
	prefix           string // prepended to each progress status line rendered to the terminal
	suffix           string // appended to each status percentage calculation rendered to the terminal, e.g., "%): " or "%)"
	clearSeq         string // ANSI escape sequence used to clear the current terminal line
	doneSeq          string // ANSI escape sequence used to restore the terminal cursor
	lineTerminator   string // output line terminator: "" when *Progress.output (nominally os.Stderr) is a terminal; "\n" otherwise
	finalStatus      string // status message to display upon completion (e.g., "done")
}

func defaultLayout() layout {
	layout := layout{
		prefix:           prefix,
		suffix:           suffix,
		colorBlockFactor: 1,    // conditionally overridden in prepareTerminal
		clearSeq:         "",   // conditionally overridden in prepareTerminal
		doneSeq:          "\n", // conditionally overridden in prepareTerminal
		lineTerminator:   "\n", // conditionally overridden in prepareTerminal
		finalStatus:      "done",
	}
	layout.staticWidth = len(layout.prefix) + pctFieldLen + len(layout.suffix)
	return layout
}

func (l layout) bufCap(termWidth int) int {
	return (maxBytesPerCol     * termWidth) +
	       (l.colorBlockFactor * termWidth) +
	       len(l.prefix                   ) +
	       len(l.suffix                   ) +
	       len(l.clearSeq                 ) +
	       len(l.lineTerminator           )
}