path: root/query/lexer.go

package query

import (
	"fmt"
	"strings"
	"unicode"
)

type tokenKind int

const (
	_ tokenKind = iota
	tokenKindKV
	tokenKindSearch
)

type token struct {
	kind tokenKind

	// KV
	qualifier string
	value     string

	// Search
	term string
}

func newTokenKV(qualifier, value string) token {
	return token{
		kind:      tokenKindKV,
		qualifier: qualifier,
		value:     value,
	}
}

func newTokenSearch(term string) token {
	return token{
		kind: tokenKindSearch,
		term: term,
	}
}

// tokenize parse and break a input into tokens ready to be
// interpreted later by a parser to get the semantic.
func tokenize(query string) ([]token, error) {
	fields, err := splitQuery(query)
	if err != nil {
		return nil, err
	}

	var tokens []token
	for _, field := range fields {
		split := strings.Split(field, ":")

		// full text search
		if len(split) == 1 {
			tokens = append(tokens, newTokenSearch(removeQuote(field)))
			continue
		}

		if len(split) != 2 {
			return nil, fmt.Errorf("can't tokenize \"%s\"", field)
		}

		if len(split[0]) == 0 {
			return nil, fmt.Errorf("can't tokenize \"%s\": empty qualifier", field)
		}
		if len(split[1]) == 0 {
			return nil, fmt.Errorf("empty value for qualifier \"%s\"", split[0])
		}

		tokens = append(tokens, newTokenKV(split[0], removeQuote(split[1])))
	}
	return tokens, nil
}

// split the query into chunks by splitting on whitespaces but respecting
// quotes
func splitQuery(query string) ([]string, error) {
	lastQuote := rune(0)
	inQuote := false

	isToken := func(r rune) bool {
		switch {
		case !inQuote && isQuote(r):
			lastQuote = r
			inQuote = true
			return true
		case inQuote && r == lastQuote:
			lastQuote = rune(0)
			inQuote = false
			return true
		case inQuote:
			return true
		default:
			return !unicode.IsSpace(r)
		}
	}

	var result []string
	var token strings.Builder
	for _, r := range query {
		if isToken(r) {
			token.WriteRune(r)
		} else {
			if token.Len() > 0 {
				result = append(result, token.String())
				token.Reset()
			}
		}
	}

	if inQuote {
		return nil, fmt.Errorf("unmatched quote")
	}

	if token.Len() > 0 {
		result = append(result, token.String())
	}

	return result, nil
}

func isQuote(r rune) bool {
	return r == '"' || r == '\''
}

func removeQuote(field string) string {
	runes := []rune(field)
	if len(runes) >= 2 {
		r1 := runes[0]
		r2 := runes[len(runes)-1]

		if r1 == r2 && isQuote(r1) {
			return string(runes[1 : len(runes)-1])
		}
	}
	return field
}