sqv-engine/sql/parser.go

package sql

import (
	"errors"
	"fmt"
	"io"
	"slices"
)

type Parser struct {
	s    *Lexer
	last struct {
		pos Position
		tok Token
		lit string
	}
}

func NewParser(r io.Reader) *Parser {
	return &Parser{s: NewLexer(r)}
}

func (p *Parser) Parse() (*CreateTableStatement, error) {
	tok, ok := p.expectOne(CREATE, EOF)
	if !ok {
		return nil, p.unexpectedToken()
	} else if tok == EOF {
		return nil, io.EOF
	}

	if !p.expectNext(TABLE) {
		return nil, errors.New("Expect TABLE token")
	}

	if !p.expectNext(IDENT) {
		return nil, errors.New("Expect IDENT token")
	}

	stmt := CreateTableStatement{
		TableName: p.last.lit,
		Columns:   make([]Column, 0),
	}

	_, tok, _ = p.scan()
	if tok != LPAREN {
		return nil, errors.New("Expect LPAREN token")
	}

	for {
		lastTok := p.last.tok
		_, tok, _ := p.scan()

		switch tok {
		case IDENT:
			column, err := p.parseColumn()
			if err != nil {
				return nil, err
			}
			stmt.Columns = append(stmt.Columns, column)

		case RPAREN:
			if !p.expectNext(SEMI) {
				return nil, p.unexpectedToken()
			}
			return &stmt, nil

		case SEMI:
			if lastTok != RPAREN {
				return nil, p.unexpectedToken()
			}

			return &stmt, nil

		case FOREIGN:
			if !p.expectNext(KEY) {
				return nil, p.unexpectedToken()
			}
			if !p.expectNext(LPAREN) {
				return nil, p.unexpectedToken()
			}

			if !p.expectNext(IDENT) {
				return nil, p.unexpectedToken()
			}
			columnName := p.last.lit

			if !p.expectNext(RPAREN) {
				return nil, p.unexpectedToken()
			}

			if !p.expectNext(REFERENCES) {
				return nil, p.unexpectedToken()
			}

			ref, err := p.references()
			if err != nil {
				return nil, err
			}

			column := slices.IndexFunc(stmt.Columns, func(c Column) bool {
				return c.Name == columnName
			})

			stmt.Columns[column].Extra = append(stmt.Columns[column].Extra, ref)

		default:
			return nil, p.unexpectedToken()
		}
	}
}

func (p *Parser) parseColumn() (Column, error) {
	column := Column{Name: p.last.lit, Extra: make([]string, 0)}

	_, tok, lit := p.scan()
	switch tok {
	case TEXT:
		fallthrough
	case INTEGER:
		column.Type = lit
	default:
		return Column{}, p.unexpectedToken()
	}

	for {
		_, tok, lit := p.scan()
		switch tok {
		case COMMA:
			fallthrough
		case RPAREN:
			return column, nil

		case PRIMARY:
			fallthrough
		case NOT:
			if _, ok := p.expectOne(NULL, KEY); !ok {
				return Column{}, p.unexpectedToken()
			}
			column.Extra = append(column.Extra, fmt.Sprintf("%v_%v", lit, p.last.lit))

		case REFERENCES:
			ref, err := p.references()
			if err != nil {
				return Column{}, err
			}
			column.Extra = append(column.Extra, ref)

		default:
			return Column{}, p.unexpectedToken()
		}
	}
}

func (p *Parser) unexpectedToken() error {
	return fmt.Errorf("Encountered unexpected token: %v lit: '%v' on pos: %v", p.last.tok, p.last.lit, p.last.pos)
}

func (p *Parser) references() (string, error) {
	if !p.expectNext(IDENT) {
		return "", p.unexpectedToken()
	}
	referenceTableName := p.last.lit

	if !p.expectNext(LPAREN) {
		return "", p.unexpectedToken()
	}

	if !p.expectNext(IDENT) {
		return "", p.unexpectedToken()
	}

	referenceColumnName := p.last.lit

	if !p.expectNext(RPAREN) {
		return "", p.unexpectedToken()
	}

	return fmt.Sprintf("ref %v.%v", referenceTableName, referenceColumnName), nil
}

func (p *Parser) expectNext(token Token) bool {
	_, tok, _ := p.scan()
	return tok == token
}

func (p *Parser) expectOne(token ...Token) (Token, bool) {
	_, tok, _ := p.scan()
	ok := slices.ContainsFunc(token, func(t Token) bool {
		return tok == t
	})
	return tok, ok
}

func (p *Parser) scan() (Position, Token, string) {
	pos, tok, lit := p.s.Lex()
	// fmt.Printf("Scanning next Token: %v | pos: %v | lit: %v\n", tok, pos, lit)

	p.last = struct {
		pos Position
		tok Token
		lit string
	}{
		pos,
		tok,
		lit,
	}
	return pos, tok, lit
}