parser.js

const _statements = [
  `class_implements 'Foo' and includes 'Bar' then error`,
  `class_extends 'BaseMediator' and import 'component' then error`,
  `method_returns 'Observable' and not name_matches '\\$$' then warn`,
  `class_implements 'Foo' and includes 'Bar' then error`,
];

// noprotect
const f = statements => {
  console.log('===============================');
  Array.from(statements).reduce(
    (acc, v, i, arr) => {
      if (acc.mode === 'then_indicator' && arr.length - 1 === i) {
        if (statements.slice(acc.cursor, i + 1) === 'warn') {
          console.log(v, i, `"${statements.slice(acc.cursor, i + 1)}"`, acc.mode);
          return { mode: 'statement', cursor: arr.length };
        }
        if (statements.slice(acc.cursor, i + 1) === 'error') {
          console.log(v, i, `"${statements.slice(acc.cursor, i + 1)}"`, acc.mode);
          return { mode: 'statement', cursor: arr.length };
        }
      }

      if (acc.mode === 'statement') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === 'c') {
          // class_implements, class_extends
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'indicator', cursor: i };
        }
        if (v === 'm') {
          // method_returns
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'indicator', cursor: i };
        }
        throw new Error('');
      }
      if (acc.mode === 'indicator') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'start_identifier', cursor: i + 1 };
        }
      }
      if (acc.mode === 'start_identifier') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === "'") {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'identifier', cursor: i + 1 };
        }
        throw new Error('');
      }
      if (acc.mode === 'and_then_statement') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === 'a') {
          // and
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_indicator', cursor: i };
        }
        if (v === "'") {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'identifier', cursor: i + 1 };
        }
        if (v === 't') {
          // then
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'then_indicator', cursor: i };
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_then_statement', cursor: i + 1 };
        }
        throw new Error('');
      }
      if (acc.mode === 'and_statement') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === 'i') {
          // includes, import
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_indicator', cursor: i };
        }
        if (v === 'n') {
          // not
          if (statements.slice(acc.cursor, i) === 'not') {
            console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
            return { mode: 'and_indicator', cursor: i };
          }
          if (statements.slice(acc.cursor, i) === 'name_matches') {
            console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
            return { mode: 'and_statement', cursor: i };
          }
        }
        if (v === "'") {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'identifier', cursor: i + 1 };
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_statement', cursor: i + 1 };
        }
      }
      if (acc.mode === 'and_indicator') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_statement', cursor: i + 1 };
        }
      }
      if (acc.mode === 'then_indicator') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'then_statement', cursor: i + 1 };
        }
      }
      if (acc.mode === 'then_statement') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === 'e') {
          // error
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'then_indicator', cursor: i };
        }
        if (v === 'w') {
          // warn
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'then_indicator', cursor: i };
        }
      }
      if (acc.mode === 'identifier') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === "'") {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'end_identifier', cursor: i };
        }
      }
      if (acc.mode === 'end_identifier') {
        if (arr.length - 1 === i) {
          throw new Error('parse error')
        }
        if (v === ' ') {
          console.log(v, i, `"${statements.slice(acc.cursor, i)}"`, acc.mode);
          return { mode: 'and_then_statement', cursor: i + 1 };
        }
      }
      return acc;
    },
    { mode: 'statement', cursor: 0 },
  );
};

f(_statements[0]);