ui/table: Add small package for writing tables

internal/ui/table/table.go

@@ -0,0 +1,206 @@
+package table
+
+import (
+	"bytes"
+	"io"
+	"strings"
+
+	"text/template"
+)
+
+// Table contains data for a table to be printed.
+type Table struct {
+	columns   []string
+	templates []*template.Template
+	data      []interface{}
+	footer    []string
+
+	CellSeparator  string
+	PrintHeader    func(io.Writer, string) error
+	PrintSeparator func(io.Writer, string) error
+	PrintData      func(io.Writer, int, string) error
+	PrintFooter    func(io.Writer, string) error
+}
+
+var funcmap = template.FuncMap{
+	"join": strings.Join,
+}
+
+// New initializes a new Table
+func New() *Table {
+	p := func(w io.Writer, s string) error {
+		_, err := w.Write(append([]byte(s), '\n'))
+		return err
+	}
+	return &Table{
+		CellSeparator:  "  ",
+		PrintHeader:    p,
+		PrintSeparator: p,
+		PrintData: func(w io.Writer, _ int, s string) error {
+			return p(w, s)
+		},
+		PrintFooter: p,
+	}
+}
+
+// AddColumn adds a new header field with the header and format, which is
+// expected to be template string compatible with text/template. When compiling
+// the format fails, AddColumn panics.
+func (t *Table) AddColumn(header, format string) {
+	t.columns = append(t.columns, header)
+	tmpl, err := template.New("template for " + header).Funcs(funcmap).Parse(format)
+	if err != nil {
+		panic(err)
+	}
+
+	t.templates = append(t.templates, tmpl)
+}
+
+// AddRow adds a new row to the table, which is filled with data.
+func (t *Table) AddRow(data interface{}) {
+	t.data = append(t.data, data)
+}
+
+// AddFooter prints line after the table
+func (t *Table) AddFooter(line string) {
+	t.footer = append(t.footer, line)
+}
+
+func printLine(w io.Writer, print func(io.Writer, string) error, sep string, data []string, widths []int) error {
+	var fields [][]string
+
+	maxLines := 1
+	for _, d := range data {
+		lines := strings.Split(d, "\n")
+		if len(lines) > maxLines {
+			maxLines = len(lines)
+		}
+		fields = append(fields, lines)
+	}
+
+	for i := 0; i < maxLines; i++ {
+		var s string
+
+		for fieldNum, lines := range fields {
+			var v string
+
+			if i < len(lines) {
+				v += lines[i]
+			}
+
+			// apply padding
+			pad := widths[fieldNum] - len(v)
+			if pad > 0 {
+				v += strings.Repeat(" ", pad)
+			}
+
+			if fieldNum > 0 {
+				v = sep + v
+			}
+
+			s += v
+		}
+
+		err := print(w, strings.TrimRight(s, " "))
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Write prints the table to w.
+func (t *Table) Write(w io.Writer) error {
+	columns := len(t.templates)
+	if columns == 0 {
+		return nil
+	}
+
+	// collect all data fields from all columns
+	lines := make([][]string, 0, len(t.data))
+	buf := bytes.NewBuffer(nil)
+
+	for _, data := range t.data {
+		row := make([]string, 0, len(t.templates))
+		for _, tmpl := range t.templates {
+			err := tmpl.Execute(buf, data)
+			if err != nil {
+				return err
+			}
+
+			row = append(row, string(buf.Bytes()))
+			buf.Reset()
+		}
+		lines = append(lines, row)
+	}
+
+	// find max width for each cell
+	columnWidths := make([]int, columns)
+	for i, desc := range t.columns {
+		for _, line := range strings.Split(desc, "\n") {
+			if columnWidths[i] < len(line) {
+				columnWidths[i] = len(desc)
+			}
+		}
+	}
+	for _, line := range lines {
+		for i, content := range line {
+			for _, l := range strings.Split(content, "\n") {
+				if columnWidths[i] < len(l) {
+					columnWidths[i] = len(l)
+				}
+			}
+		}
+	}
+
+	// calculate the total width of the table
+	totalWidth := 0
+	for _, width := range columnWidths {
+		totalWidth += width
+	}
+	totalWidth += (columns - 1) * len(t.CellSeparator)
+
+	// write header
+	if len(t.columns) > 0 {
+		err := printLine(w, t.PrintHeader, t.CellSeparator, t.columns, columnWidths)
+		if err != nil {
+			return err
+		}
+
+		// draw separation line
+		err = t.PrintSeparator(w, strings.Repeat("-", totalWidth))
+		if err != nil {
+			return err
+		}
+	}
+
+	// write all the lines
+	for i, line := range lines {
+		print := func(w io.Writer, s string) error {
+			return t.PrintData(w, i, s)
+		}
+		err := printLine(w, print, t.CellSeparator, line, columnWidths)
+		if err != nil {
+			return err
+		}
+	}
+
+	// draw separation line
+	err := t.PrintSeparator(w, strings.Repeat("-", totalWidth))
+	if err != nil {
+		return err
+	}
+
+	if len(t.footer) > 0 {
+		// write the footer
+		for _, line := range t.footer {
+			err := t.PrintFooter(w, line)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}