// Package diamond outputs input in diamond shape.
package diamond
import (
	"fmt"
	"strings"
)
func Gen(in byte) (string, error) {
	if in > 'Z' || in < 'A' {
		return "", fmt.Errorf("out of range")
	}
	var ret strings.Builder
	pivot := int(in - 'A')
	for i := 0; i <= pivot; i++ {
		ret.WriteString(writeLine(pivot, i))
	}
	for i := pivot - 1; i >= 0; i-- {
		// start at pivot-1 as we do not want to dupe middle line
		ret.WriteString(writeLine(pivot, i))
	}
	// fmt.Println(ret.String())
	return ret.String(), nil
}
func writeLine(pivot, i int) string {
	const mark = " " // set to "." for testing
	var ret strings.Builder
	ret.WriteString(strings.Repeat(mark, pivot-i))
	ret.WriteByte(byte(i) + 'A')
	if i != 0 {
		ret.WriteString(strings.Repeat(mark, i*2-1))
		ret.WriteByte(byte(i) + 'A')
	}
	ret.WriteString(strings.Repeat(mark, pivot-i))
	ret.WriteByte('\n')
	return ret.String()
}