Email tokenizer

email-tokenizer.js

export const STATE_LOCAL_PART = "STATE_LOCAL_PART"
export const STATE_DOMAIN = "STATE_DOMAIN"

export const ALPHANUMERICS = "abcdefghijklmnopqrstuvwxyz1234567890"

export const LOCAL_PARTS_CHARACTERS = [...ALPHANUMERICS, ..."!#$%&'*+-/=?^_`{|}~."]
export const LOCAL_DOMAIN_CHARACTERS = [...ALPHANUMERICS, ..."-."]

export const tokenize = function(input) {
	const characters = [...input]
	let state = STATE_LOCAL_PART
	const tokens = []
	let token = { type: "local_part", buffer: "", bufferIndex: 0 }
	for(const [index, character] of characters.entries()) {
		if(state === STATE_LOCAL_PART && LOCAL_PARTS_CHARACTERS.includes(character.toLowerCase())) {
			if(character === "."  && (index === 0 || characters[index + 1] === "@" || characters[index - 1] === ".")) {
				return false
			} else {
				token.buffer += character
			}
		} else if(state === STATE_DOMAIN && LOCAL_DOMAIN_CHARACTERS.includes(character.toLowerCase())) {
			if(character === "-" && (index === 0 || index === characters.length  -1)
			|| character === "."  && (index === token.bufferIndex || characters[index - 1] === "." || index === characters.length - 1)) {
				return false
			} else {
				token.buffer += character
			}
			if(index === characters.length - 1) {
				tokens.push(token)
			}
		} else if(state === STATE_LOCAL_PART && character === "@") {
			tokens.push(token)
			token = { type: "domain", buffer: "", bufferIndex: index + 1 }
			state = STATE_DOMAIN
		} else {
			return false
		}
	}
	if(tokens.length < 2) {
		return false
	}
	return tokens
}

console.log(tokenize("stackoverflow@."))