Data commit

Task/Update-a-configuration-file/Go/update-a-configuration-file.go

@@ -0,0 +1,204 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+	"unicode"
+)
+
+// line represents a single line in the configuration file.
+type line struct {
+	kind     lineKind
+	option   string
+	value    string
+	disabled bool
+}
+
+// lineKind represents the different kinds of configuration line.
+type lineKind int
+
+const (
+	_ lineKind = iota
+	ignore
+	parseError
+	comment
+	blank
+	value
+)
+
+func (l line) String() string {
+	switch l.kind {
+	case ignore, parseError, comment, blank:
+		return l.value
+	case value:
+		s := l.option
+		if l.disabled {
+			s = "; " + s
+		}
+		if l.value != "" {
+			s += " " + l.value
+		}
+		return s
+	}
+	panic("unexpected line kind")
+}
+
+func removeDross(s string) string {
+	return strings.Map(func(r rune) rune {
+		if r < 32 || r > 0x7f || unicode.IsControl(r) {
+			return -1
+		}
+		return r
+	}, s)
+}
+
+func parseLine(s string) line {
+	if s == "" {
+		return line{kind: blank}
+	}
+	if s[0] == '#' {
+		return line{kind: comment, value: s}
+	}
+	s = removeDross(s)
+	fields := strings.Fields(s)
+	if len(fields) == 0 {
+		return line{kind: blank}
+	}
+	// Strip leading semicolons (but record that we found them)
+	semi := false
+	for len(fields[0]) > 0 && fields[0][0] == ';' {
+		semi = true
+		fields[0] = fields[0][1:]
+	}
+	// Lose the first field if it was all semicolons
+	if fields[0] == "" {
+		fields = fields[1:]
+	}
+	switch len(fields) {
+	case 0:
+		// This can only happen if the line starts
+		// with a semicolon but has no other information
+		return line{kind: ignore}
+	case 1:
+		return line{
+			kind:     value,
+			option:   strings.ToUpper(fields[0]),
+			disabled: semi,
+		}
+	case 2:
+		return line{
+			kind:     value,
+			option:   strings.ToUpper(fields[0]),
+			value:    fields[1],
+			disabled: semi,
+		}
+	}
+	return line{kind: parseError, value: s}
+}
+
+// Config represents a "standard" configuration file.
+type Config struct {
+	options map[string]int		// index of each option in lines.
+	lines   []line
+}
+
+// index returns the index of the given option in
+// c.lines, or -1 if not found.
+func (c *Config) index(option string) int {
+	if i, ok := c.options[option]; ok {
+		return i
+	}
+	return -1
+}
+
+// addLine adds a line to the config, ignoring
+// duplicate options and "ignore" lines.
+func (c *Config) addLine(l line) {
+	switch l.kind {
+	case ignore:
+		return
+	case value:
+		if c.index(l.option) >= 0 {
+			return
+		}
+		c.options[l.option] = len(c.lines)
+		c.lines = append(c.lines, l)
+	default:
+		c.lines = append(c.lines, l)
+	}
+}
+
+// ReadConfig reads a configuration file from path and returns it.
+func ReadConfig(path string) (*Config, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	r := bufio.NewReader(f)
+	c := &Config{options: make(map[string]int)}
+	for {
+		s, err := r.ReadString('\n')
+		if s != "" {
+			if err == nil {
+				// strip newline unless we encountered an error without finding one.
+				s = s[:len(s)-1]
+			}
+			c.addLine(parseLine(s))
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	return c, nil
+}
+
+// Set sets an option to a value, adding the option if necessary.  If
+// the option was previously disabled, it will be enabled.
+func (c *Config) Set(option string, val string) {
+	if i := c.index(option); i >= 0 {
+		line := &c.lines[i]
+		line.disabled = false
+		line.value = val
+		return
+	}
+	c.addLine(line{
+		kind:   value,
+		option: option,
+		value:  val,
+	})
+}
+
+// Enable sets the enabled status of an option. It is
+// ignored if the option does not already exist.
+func (c *Config) Enable(option string, enabled bool) {
+	if i := c.index(option); i >= 0 {
+		c.lines[i].disabled = !enabled
+	}
+}
+
+// Write writes the configuration file to the writer.
+func (c *Config) Write(w io.Writer) {
+	for _, line := range c.lines {
+		fmt.Println(line)
+	}
+}
+
+func main() {
+	c, err := ReadConfig("/tmp/cfg")
+	if err != nil {
+		log.Fatalln(err)
+	}
+	c.Enable("NEEDSPEELING", false)
+	c.Set("SEEDSREMOVED", "")
+	c.Set("NUMBEROFBANANAS", "1024")
+	c.Set("NUMBEROFSTRAWBERRIES", "62000")
+	c.Write(os.Stdout)
+}