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// Package roman numerals
//
// For fluff, the unicode overbar is recognized as a factor of 1000.
//
// If you see boxes in the code below, those are supposed to be the
// Unicode combining overline (U+0305) and look like I̅V̅X̅L̅C̅D̅M̅. Or, if
// you see overstruck combinations of letters, that's a different font
// rendering problem. (If you need roman numerals > 3999 reliably, it
// might best to stick to chiseling them in stone...)
//
// Source: https://www.rosettacode.org/wiki/Roman_numerals/Encode#Go
package roman

var (
	m0 = []string{"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"}
	m1 = []string{"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"}
	m2 = []string{"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"}
	m3 = []string{"", "M", "MM", "MMM", "I̅V̅", "V̅", "V̅I̅", "V̅I̅I̅", "V̅I̅I̅I̅", "I̅X̅"}
	m4 = []string{"", "X̅", "X̅X̅", "X̅X̅X̅", "X̅L̅", "L̅", "L̅X̅", "L̅X̅X̅", "L̅X̅X̅X̅", "X̅C̅"}
	m5 = []string{"", "C̅", "C̅C̅", "C̅C̅C̅", "C̅D̅", "D̅", "D̅C̅", "D̅C̅C̅", "D̅C̅C̅C̅", "C̅M̅"}
	m6 = []string{"", "M̅", "M̅M̅", "M̅M̅M̅"}
)

// Roman represents a roman numeral in interval 0 < x < 4e6
type Roman int

func (n Roman) String() string {
	if n <= 0 || n >= 4e6 {
		return ""
	}
	// this is efficient in Go.  the seven operands are evaluated,
	// then a single allocation is made of the exact size needed for the result.
	return m6[n/1e6] + m5[n%1e6/1e5] + m4[n%1e5/1e4] + m3[n%1e4/1e3] +
		m2[n%1e3/1e2] + m1[n%1e2/1e1] + m0[n%1e1]
}