remove ordinals eg. '21st' -> '21', strict in enforcing rules and supports autocomplete

ordinals.go

package token

import "regexp"

// Ordinals - remove ordinals (such as the 'st' from '21st')
func Ordinals(tokens []string) []string {
	r := []string{}

	var reg = ""
	reg += "(?i)"                                                 // case insensitive
	reg += "((^|\\s)"                                             // start anchor (group $2)
	reg += "((1)st?|(2)nd?|(3)rd?|([4-9])th?)"                    // singles (groups $4$5$6$7)
	reg += "|"                                                    // or
	reg += "(0*([0-9]*)(1[0-9])th?)"                              // teens (groups $9$10), trim leading zeros
	reg += "|"                                                    // or
	reg += "(0*([0-9]*[02-9])((1)st?|(2)nd?|(3)rd?|([04-9])th?))" // the rest (groups $12$14$15$16$17), trim leading zeros
	reg += "($|\\s))"                                             // end anchor (group $18)

	exp := regexp.MustCompile(reg)

	// regex replace all instances
	for _, token := range tokens {
		r = append(r, exp.ReplaceAllString(token, "$2$4$5$6$7$9$10$12$14$15$16$17$18"))
	}
	return r
}

ordinals_test.go

package token

import (
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestOrdinals(t *testing.T) {
	var text, expected []string

	// multiple in same string
	text = []string{"1st 2nd 3rd 4th 5th"}
	expected = []string{"1 2 3 4 5"}
	assert.Equal(t, expected, Ordinals(text))

	// singles
	text = []string{"1st", "2nd", "3rd", "4th", "5th"}
	expected = []string{"1", "2", "3", "4", "5"}
	assert.Equal(t, expected, Ordinals(text))

	// ordindals
	text = []string{"1st", "22nd", "333rd", "4444th", "2500th"}
	expected = []string{"1", "22", "333", "4444", "2500"}
	assert.Equal(t, expected, Ordinals(text))

	// teens
	text = []string{"11th", "12th", "13th", "14th", "15th", "16th", "17th", "18th", "19th", "20th"}
	expected = []string{"11", "12", "13", "14", "15", "16", "17", "18", "19", "20"}
	assert.Equal(t, expected, Ordinals(text))

	// teens (hundreds)
	text = []string{"111th", "112th", "113th", "114th", "115th", "116th", "117th", "118th", "119th", "120th"}
	expected = []string{"111", "112", "113", "114", "115", "116", "117", "118", "119", "120"}
	assert.Equal(t, expected, Ordinals(text))

	// teens (wrong suffix)
	text = []string{"11st", "12nd", "13rd", "111st", "112nd", "113rd"}
	expected = []string{"11st", "12nd", "13rd", "111st", "112nd", "113rd"}
	assert.Equal(t, expected, Ordinals(text))

	// uppercase
	text = []string{"1ST", "22ND", "333RD", "4444TH"}
	expected = []string{"1", "22", "333", "4444"}
	assert.Equal(t, expected, Ordinals(text))

	// autocomplete
	text = []string{"26", "26t", "26th", "3", "3r", "3rd"}
	expected = []string{"26", "26", "26", "3", "3", "3"}
	assert.Equal(t, expected, Ordinals(text))

	// wrong suffix (do nothing)
	text = []string{"0th", "26s", "26st", "31t", "31th", "21r", "21rd", "29n", "29nd"}
	expected = []string{"0th", "26s", "26st", "31t", "31th", "21r", "21rd", "29n", "29nd"}
	assert.Equal(t, expected, Ordinals(text))

	// trim leading zeros
	text = []string{"011th", "0000201st"}
	expected = []string{"11", "201"}
	assert.Equal(t, expected, Ordinals(text))
}