conf/conf.go

// module conf
//
// import "code.uint32.ru/tiny/conf"
//
// Module conf implements a very simple config parser with two types of
// values: key value pairs and single word options. Each of these must be
// put on separate line in a file like this:
//
//	key1 = value
//	key2 = value1, value2, value3
//	key3=v1,v2,v3
//	option1
//	option2
//
// Values can also be read from any io.Reader or io.ReadCloser. Note that
// values in key value pairs mey either be separated with spaces or not.
// Typical use case would look like this:
//
//	config, err := conf.ParseFile("filename")
//	if err != nil {
//		// Means we failed to read from file
//		// config variable is now nil and unusable
//	}
//	value, err := config.Find("mykey")
//	if err != nil {
//		// Means that key has not been found
//	}
//	// value now holds conf.Setting.
//	n, err := value.Float64() // tries to parse float from Setting.Value field.
//	//if err is nil then n holds float64.
//
// There is also a quicker Get() method which returns no errors
// ("i'm feeling lucky" way to lookup values). If it does not find
// requested key, the returned Setting has empty string in Value field.
//
//	value2 := config.Get("otherkey")
//	mybool, err := value2.Bool() // tries to interpret Setting.Value field as bool
//	// mybool now holds boolean if "otherkey" was found and error returned
//	// by Bool() method is nil.
//
// Even shorter syntax would be:
//
//	listnumbers, err := config.Get("numbers").IntSlice()
//	// Note that we'd still like to check for errors even if
//	// we're sure the key exists to make sure all values are converted.
//	// listnumbers holds slice of ints. If err is nil all of found values
//	// have been converted successfully.
//
// To check whether single-word options were found use:
//
//	if config.HasOption("wordoption") {
//		// do something
//	}
//
// See description of module's other methods which are
// quite self-explanatory.
package conf

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"os"
)

var (
	ErrFormat       = errors.New("conf: line does not match \"key = value\" pattern")
	ErrDuplicateKey = errors.New("conf: duplicate key found")
)

// Conf holds key value pairs.
type Conf struct {
	values []*kv // values store key value pairs ("key = value" in config file)
}

type kv struct {
	k string
	v Value
}

// Open reads values from file.
func Open(filename string) (*Conf, error) {
	c := new(Conf)
	if err := c.readFile(filename); err != nil {
		return nil, err
	}

	return c, nil
}

// Read reads from r and returns Conf.
func Read(r io.Reader) (*Conf, error) {
	c := new(Conf)
	if err := c.read(r); err != nil {
		return nil, err
	}

	return c, nil
}

// Find looks up a the key and returns Value associated with it.
// If bool is false then the returned Value would be zero.
func (c *Conf) Find(key string) (Value, bool) {
	return c.get(key, "")
}

// Get returns a Value. If key was not found the returned Value
// will be empty.
func (c *Conf) Get(key string) Value {
	v, _ := c.get(key, "")
	return v
}

// GetDefault looks up a Value for requested key.
// If lookup fails it returns Value set to def.
func (c *Conf) GetDefault(key, def string) Value {
	v, _ := c.get(key, def)
	return v
}

func (c *Conf) Keys() []string {
	list := make([]string, 0, len(c.values))

	for i := range c.values {
		list = append(list, c.values[i].k)
	}

	return list
}

func (c *Conf) Read(r io.Reader) error {
	return c.read(r)
}

func (c *Conf) ReadFile(name string) error {
	return c.readFile(name)
}

func (c *Conf) get(key string, def string) (Value, bool) {
	var (
		v     Value
		found bool
	)
	for i := range c.values {
		if c.values[i].k == key {
			v = c.values[i].v
			found = true
			break
		}
	}

	if def != "" && !found {
		v = Value(def)
	}

	return v, found
}

func (c *Conf) readFile(name string) error {
	file, err := os.Open(name)
	if err != nil {
		return err
	}

	if err := c.read(file); err != nil {
		return err
	}

	return file.Close()
}

func (c *Conf) read(r io.Reader) error {
	uniq := make(map[string]struct{})

	scanner := bufio.NewScanner(r)

	for scanner.Scan() {
		line := scanner.Text()

		line = trim(stripComment(line))
		if line == "" {
			continue
		}

		key, value, ok := toKV(line, separatorKV)
		if !ok {
			return ErrFormat
		}

		if _, ok := uniq[key]; ok {
			return fmt.Errorf("%w: %s", ErrDuplicateKey, key)
		}

		uniq[key] = struct{}{}

		kv := &kv{
			k: key,
			v: Value(value),
		}

		c.values = append(c.values, kv)
	}

	if err := scanner.Err(); err != nil {
		return err
	}

	return nil
}