package settings

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

var (
	KeyValueDelimiterChars = []byte{':', '='}

	ErrNoValidDelimiter = fmt.Errorf("no valid delimiter found (use %s)", KeyValueDelimiterCharsToString())
)

func KeyValueDelimiterCharsToString() string {
	var builder strings.Builder
	for i, char := range KeyValueDelimiterChars {
		builder.WriteString(fmt.Sprintf("'%c'", char))
		if i < len(KeyValueDelimiterChars)-1 {
			builder.WriteString(" or ")
		}
	}
	return builder.String()
}

func LineIsComment(line string) bool {
	return strings.HasPrefix(line, "//") || strings.HasPrefix(line, "#")
}

type Scanner struct {
	lineNumber int
	scanner    *bufio.Scanner
}

// returns errors without any key/value.
// does not clone the strings it extracted.
func (s *Scanner) ReadNextLine() (key, value string, err error) {
	for s.scanner.Scan() {
		s.lineNumber++
		line := strings.TrimSpace(s.scanner.Text())
		if len(line) == 0 || LineIsComment(line) {
			continue
		}
		splitIndex := strings.IndexAny(line, string(KeyValueDelimiterChars))
		if splitIndex == -1 {
			return "", "", fmt.Errorf("line %d: %w", s.lineNumber, ErrNoValidDelimiter)
		}
		key = strings.TrimSpace(line[:splitIndex])
		value = strings.TrimSpace(line[splitIndex+1:])
		return
	}
	return "", "", io.EOF
}

func NewScanner(r io.Reader) *Scanner {
	return &Scanner{
		lineNumber: 0,
		scanner:    bufio.NewScanner(r),
	}
}