package conf

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

const (
	strComment = "#"
	strEqSign  = "="
)

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

// Open reads values from file. It returns nil and error if os.Open(filename) fails.
// It would be wise to always check returned error.
// ParseFile captures two types of values: "key = value" and "option". Either key value pair or
// option must be put in its own line in the file.
// Key or option must be a single word. In example line:
//
//	"option1 option2"
//
// only option1 will be captured. option2 needs to be in a separate line in the file to take effect.
// In line "key = value1,value2,value3" all of value1, value2, and value3 will be
// captured. They can be later accesed separately with Setting's Split() method.
func Open(filename string) (*Conf, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, err
	}

	c, err := parseReader(file)
	if err != nil {
		return nil, err
	}

	return c, file.Close()
}

// Read reads from r and returns Config.
func Read(r io.Reader) (*Conf, error) {
	return parseReader(r)
}

func parseReader(r io.Reader) (*Conf, error) {
	settings := make(map[string]string)

	scanner := bufio.NewScanner(r)

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

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

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

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

		settings[key] = value
	}

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

	return &Conf{
		settings: settings,
	}, nil
}

func toKV(s string) (string, string, bool) {
	k, v, ok := strings.Cut(s, strEqSign)
	if !ok || k == "" || v == "" {
		return "", "", false
	}

	return trim(k), trim(v), true
}

func trim(s string) string {
	s = strings.TrimSpace(s)

	return s
}

func stripComment(s string) string {
	idx := strings.Index(s, strComment)
	if idx > -1 {
		s = s[:idx]
	}

	return s
}