Initial working stage, but not with all tests, because IF NOT EXISTS is not implemented

sql/lexer.go

@@ -0,0 +1,143 @@
+package sql
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"strings"
+	"unicode"
+)
+
+type Token int
+
+const (
+	EOF Token = iota
+	ILLEGAL
+	IDENT
+
+	SEMI
+	LPAREN
+	RPAREN
+	COMMA
+
+	CREATE
+	TABLE
+
+	PRIMARY
+	FOREIGN
+	REFERENCES
+	KEY
+	NOT
+
+	TEXT
+	INTEGER
+	NULL
+)
+
+var keywords map[string]Token = map[string]Token{
+	"CREATE":     CREATE,
+	"TABLE":      TABLE,
+	"PRIMARY":    PRIMARY,
+	"FOREIGN":    FOREIGN,
+	"REFERENCES": REFERENCES,
+	"KEY":        KEY,
+	"NOT":        NOT,
+	"TEXT":       TEXT,
+	"INTEGER":    INTEGER,
+	"NULL":       NULL,
+}
+
+type Position struct {
+	line   int
+	column int
+}
+
+type Lexer struct {
+	pos    Position
+	reader *bufio.Reader
+}
+
+func NewLexer(reader io.Reader) *Lexer {
+	return &Lexer{
+		pos:    Position{line: 1, column: 0},
+		reader: bufio.NewReader(reader),
+	}
+}
+
+func (l *Lexer) Lex() (Position, Token, string) {
+	for {
+		r, _, err := l.reader.ReadRune()
+		if err != nil && errors.Is(err, io.EOF) {
+			return l.pos, EOF, ""
+		} else if err != nil {
+			// Change this
+			panic(err)
+		}
+
+		l.pos.column++
+		switch r {
+		case '\n':
+			l.resetPosition()
+		case ';':
+			return l.pos, SEMI, ";"
+		case ',':
+			return l.pos, COMMA, ","
+		case '(':
+			return l.pos, LPAREN, "("
+		case ')':
+			return l.pos, RPAREN, ")"
+		default:
+			if unicode.IsSpace(r) {
+				continue
+			} else if unicode.IsLetter(r) {
+				startPos := l.pos
+				l.backup()
+				lit := l.lexIdent()
+
+				litUpper := strings.ToUpper(lit)
+				if token, ok := keywords[litUpper]; ok {
+					return startPos, token, litUpper
+				}
+
+				return startPos, IDENT, lit
+			} else {
+				return l.pos, ILLEGAL, string(r)
+			}
+		}
+	}
+}
+
+func (l *Lexer) lexIdent() string {
+	var lit string
+	for {
+		r, _, err := l.reader.ReadRune()
+		if err != nil && errors.Is(err, io.EOF) {
+			return lit
+		} else if err != nil {
+			// Change this
+			panic(err)
+		}
+
+		l.pos.column++
+		if unicode.IsLetter(r) || unicode.IsNumber(r) || r == '_' {
+			// Change this to stringstream or something similar
+			lit = lit + string(r)
+		} else {
+			l.backup()
+			return lit
+		}
+	}
+}
+
+func (l *Lexer) backup() {
+	if err := l.reader.UnreadRune(); err != nil {
+		panic(err)
+	}
+
+	l.pos.column--
+}
+
+func (l *Lexer) resetPosition() {
+	l.pos.line++
+	l.pos.column = 0
+}