Extract generic row printer that adjusts itself for receiving terminal

This makes the approach from `pr list` reusable across other commands
that may benefit from table-based output, e.g. `issue list` or `pr status`

The idea is: instantiate a printer, connect it to stdout, feed it some
data, and it does the rest: colored, truncated column output that fits
into a terminal, or tab-delimited output (no color, no truncation) for
scripts.

command/pr.go

@@ -2,13 +2,11 @@ package command
 
 import (
 	"fmt"
-	"os"
 	"strconv"
 
 	"github.com/github/gh-cli/api"
 	"github.com/github/gh-cli/utils"
 	"github.com/spf13/cobra"
-	"golang.org/x/crypto/ssh/terminal"
 )
 
 func init() {
@@ -158,53 +156,30 @@ func prList(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
-	tty := false
-	ttyWidth := 80
-	out := cmd.OutOrStdout()
-	if outFile, isFile := out.(*os.File); isFile {
-		fd := int(outFile.Fd())
-		tty = terminal.IsTerminal(fd)
-		if w, _, err := terminal.GetSize(fd); err == nil {
-			ttyWidth = w
-		}
-	}
-
-	numWidth := 0
-	maxTitleWidth := 0
+	table := utils.NewTablePrinter(cmd.OutOrStdout())
 	for _, pr := range prs {
-		numLen := len(strconv.Itoa(pr.Number)) + 1
-		if numLen > numWidth {
-			numWidth = numLen
-		}
-		if len(pr.Title) > maxTitleWidth {
-			maxTitleWidth = len(pr.Title)
-		}
+		table.SetContentWidth(0, len(strconv.Itoa(pr.Number))+1)
+		table.SetContentWidth(1, len(pr.Title))
+		table.SetContentWidth(2, len(pr.HeadLabel()))
 	}
 
-	branchWidth := 40
-	titleWidth := ttyWidth - branchWidth - 2 - numWidth - 2
-
-	if maxTitleWidth < titleWidth {
-		branchWidth += titleWidth - maxTitleWidth
-		titleWidth = maxTitleWidth
-	}
+	table.FitColumns()
+	table.SetColorFunc(2, utils.Cyan)
 
 	for _, pr := range prs {
-		if tty {
-			prNum := fmt.Sprintf("% *s", numWidth, fmt.Sprintf("#%d", pr.Number))
-			switch pr.State {
-			case "OPEN":
-				prNum = utils.Green(prNum)
-			case "CLOSED":
-				prNum = utils.Red(prNum)
-			case "MERGED":
-				prNum = utils.Magenta(prNum)
-			}
-			prBranch := utils.Cyan(truncate(branchWidth, pr.HeadLabel()))
-			fmt.Fprintf(out, "%s  %-*s  %s\n", prNum, titleWidth, truncate(titleWidth, pr.Title), prBranch)
-		} else {
-			fmt.Fprintf(out, "%d\t%s\t%s\n", pr.Number, pr.Title, pr.HeadLabel())
+		prNum := strconv.Itoa(pr.Number)
+		if table.IsTTY {
+			prNum = "#" + prNum
 		}
+		switch pr.State {
+		case "OPEN":
+			table.SetColorFunc(0, utils.Green)
+		case "CLOSED":
+			table.SetColorFunc(0, utils.Red)
+		case "MERGED":
+			table.SetColorFunc(0, utils.Magenta)
+		}
+		table.WriteRow(prNum, pr.Title, pr.HeadLabel())
 	}
 	return nil
 }

utils/table_printer.go

@@ -0,0 +1,108 @@
+package utils
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+func NewTablePrinter(w io.Writer) *TTYTablePrinter {
+	tty := false
+	ttyWidth := 80
+	if outFile, isFile := w.(*os.File); isFile {
+		fd := int(outFile.Fd())
+		tty = terminal.IsTerminal(fd)
+		if w, _, err := terminal.GetSize(fd); err == nil {
+			ttyWidth = w
+		}
+	}
+	return &TTYTablePrinter{
+		out:       w,
+		IsTTY:     tty,
+		maxWidth:  ttyWidth,
+		colWidths: []int{},
+		colFuncs:  make(map[int]func(string) string),
+	}
+}
+
+type TTYTablePrinter struct {
+	out       io.Writer
+	IsTTY     bool
+	maxWidth  int
+	colWidths []int
+	colFuncs  map[int]func(string) string
+}
+
+func (t *TTYTablePrinter) SetContentWidth(col, width int) {
+	if col == len(t.colWidths) {
+		t.colWidths = append(t.colWidths, 0)
+	}
+	if width > t.colWidths[col] {
+		t.colWidths[col] = width
+	}
+}
+
+func (t *TTYTablePrinter) SetColorFunc(col int, colorize func(string) string) {
+	t.colFuncs[col] = colorize
+}
+
+// FitColumns caps all but first column to fit available terminal width.
+func (t *TTYTablePrinter) FitColumns() {
+	numCols := len(t.colWidths)
+	delimWidth := 2
+	availWidth := t.maxWidth - t.colWidths[0] - ((numCols - 1) * delimWidth)
+	// TODO: avoid widening columns that already fit
+	// TODO: support weighted instead of even redistribution
+	for col := 1; col < len(t.colWidths); col++ {
+		t.colWidths[col] = availWidth / (numCols - 1)
+	}
+}
+
+func (t *TTYTablePrinter) WriteRow(fields ...string) error {
+	lastCol := len(fields) - 1
+	delim := "\t"
+	if t.IsTTY {
+		delim = "  "
+	}
+
+	for col, val := range fields {
+		if col > 0 {
+			_, err := fmt.Fprint(t.out, delim)
+			if err != nil {
+				return err
+			}
+		}
+		if t.IsTTY {
+			truncVal := truncate(t.colWidths[col], val)
+			if col != lastCol {
+				truncVal = fmt.Sprintf("%-*s", t.colWidths[col], truncVal)
+			}
+			if t.colFuncs[col] != nil {
+				truncVal = t.colFuncs[col](truncVal)
+			}
+			_, err := fmt.Fprint(t.out, truncVal)
+			if err != nil {
+				return err
+			}
+		} else {
+			_, err := fmt.Fprint(t.out, val)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	_, err := fmt.Fprint(t.out, "\n")
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func truncate(maxLength int, title string) string {
+	if len(title) > maxLength {
+		return title[0:maxLength-3] + "..."
+	}
+	return title
+}