Validator for custom data

Validator.js

/**
 * @file Validator for custom data
 * @author treelite(c.xinle@gmail.com)
 */

const STATE_IDLE = 0;
const STATE_SPLIT = 1;
const STATE_TOKEN = 2;
const STATE_NEWLINE = 3;

class Validator {

    constructor(str) {
        this.str = str;
        // current token
        this.token = '';
        // defined fields
        this.fields = [];
        // extraf fiels
        this.extraFields = [];
        // line count
        this.lines = 0;
        this.error = false;
        // count of empty data
        this.emptyValues = 0;
        this.state = STATE_IDLE;
        // all names
        this.names = [];
        // data for current line
        this.values = [];

        this.validate();
    }

    get fieldCount() {
        return this.fields.length + this.extraFields.length;
    }

    getResult() {
        if (this.error) {
            return '0:0:0:format_error';
        }
        let lastFieldName = this.extraFields.length
            ? this.extraFields[this.extraFields.length - 1]
            : this.fields[this.fields.length - 1];
        return (this.lines - 1) + ':' + this.fieldCount + ':' + this.emptyValues + ':' + lastFieldName;
    }

    validate() {
        let str = this.str;
        let len = str.length;
        let c;
        let steps;
        let i = 0;
        while (i < len) {
            steps = 1;
            c = str.charAt(i);
            if (c === '|') {
                steps = this.split();
            }
            else if (c === '~') {
                steps = this.escape(c + str.charAt(i + 1));
            }
            else {
                steps = this.eatToken(c);
            }
            if (this.error) {
                break;
            }
            i += steps;
        }
    }

    eatToken(c) {
        if (this.state === STATE_TOKEN || this.state === STATE_SPLIT) {
            this.state = STATE_TOKEN;
            this.token += c;
        }
        else {
            this.error = true;
        }
        return 1;
    }

    checkName(name) {
        return name && (this.names.indexOf(name) < 0);
    }

    split() {
        if (this.state === STATE_TOKEN || this.state === STATE_SPLIT) {
            // collect name
            if (this.values.length === 0 && !this.lines) {
                if (this.checkName(this.token)) {
                    this.names.push(this.token);
                }
                else {
                    // name is empty
                    // or not unique
                    this.error = true;
                }
            }
            this.values.push(this.token);
            // handle empty value
            if (!this.token) {
                if (!this.lines) {
                    // field name can't be empty;
                    this.error = true;
                }
                else {
                    this.emptyValues++;
                }
            }
            // handle extra fields
            if (this.lines && this.values.length > this.fieldCount) {
                this.extendField();
            }
            this.token = '';
        }
        this.state = STATE_SPLIT;
        return 1;
    }

    extendField() {
        let count = this.extraFields.length + 1;
        let text = this.fields[this.fields.length - 1];
        this.extraFields.push(text + '_' + count);
    }

    newLine() {
        if (this.state !== STATE_SPLIT) {
            this.error = true;
        }
        else {
            this.state = STATE_NEWLINE;
            if (!this.lines) {
                this.fields = this.values;
            }
            this.values = [];
            this.lines++;
        }
    }

    escape(token) {
        let steps = 1;
        if (token === '~n') {
            this.newLine();
            steps++;
        }
        else if (token === '~|' || token === '~~') {
            this.eatToken(token.charAt(1));
            steps++;
        }
        else {
            this.eatToken(token.charAt(0));
        }
        return steps;
    }
}

function validate(str) {
    let validator = new Validator(str);
    return validator.getResult();
}

console.log(validate('~~~'));
console.log(validate('|name|addr~~ness|~n|Patrick|partick@test.com|pat@test.com|~n|Annie||annie@test.com|~n'));