DB service (#132)

db/handler/parse.go

@@ -0,0 +1,134 @@
+package handler
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/crufter/lexer"
+)
+
+var quoteEscape = fmt.Sprint(0x10FFFF)
+
+const (
+	itemIgnore = iota
+
+	// nouns
+	itemAnd
+	itemInt
+	itemFieldName
+	itemString
+	itemBoolTrue
+	itemBoolFalse
+
+	// ops
+	itemEquals
+	itemNotEquals
+	itemLessThan
+	itemGreaterThan
+	itemLessThanEquals
+	itemGreaterThanEquals
+)
+
+var opToString = map[int]string{
+	itemEquals:            "==",
+	itemNotEquals:         "!=",
+	itemLessThan:          "<",
+	itemGreaterThan:       ">",
+	itemLessThanEquals:    "<=",
+	itemGreaterThanEquals: ">=",
+}
+
+var expressions = []lexer.TokenExpr{
+	{`[ ]+`, itemIgnore}, // Whitespace
+	{`==`, itemEquals},
+	{`!=`, itemNotEquals},
+	{`false`, itemBoolFalse},
+	{`true`, itemBoolTrue},
+	{`and`, itemAnd},
+	{`<=`, itemLessThanEquals},
+	{`>=`, itemGreaterThanEquals},
+	{`<`, itemLessThan},
+	{`>`, itemGreaterThan},
+	{`[0-9]+`, itemInt},
+	{`"(?:[^"\\]|\\.)*"`, itemString},
+	{`[\<\>\!\=\+\-\|\&\*\/A-Za-z][A-Za-z0-9_]*`, itemFieldName},
+}
+
+type Query struct {
+	Field string
+	Op    int
+	Value interface{}
+}
+
+func Parse(q string) ([]Query, error) {
+	if strings.Contains(q, quoteEscape) {
+		return nil, errors.New("query contains illegal max rune")
+	}
+	q = strings.Replace(q, `""`, quoteEscape, -1)
+	tokens, err := lexer.Lex(q, expressions)
+	if err != nil {
+		return nil, err
+	}
+	queries := []Query{}
+	current := Query{}
+	for i, token := range tokens {
+		// and tokens should trigger a query
+		// save and reset
+		if token.Typ == itemAnd {
+			queries = append(queries, current)
+			current = Query{}
+			continue
+		}
+
+		// is an op
+		if token.Typ >= itemEquals {
+			current.Op = token.Typ
+			continue
+		}
+
+		// is a value
+		switch token.Typ {
+		case itemFieldName:
+			current.Field = token.Text
+		case itemString:
+			switch current.Op {
+			case itemEquals, itemNotEquals:
+			default:
+				return nil, fmt.Errorf("operator '%v' can't be used with strings", opToString[token.Typ])
+			}
+
+			if len(token.Text) < 2 {
+				return nil, fmt.Errorf("string literal too short: '%v'", token.Text)
+			}
+			current.Value = strings.Replace(token.Text[1:len(token.Text)-1], quoteEscape, `"`, -1)
+		case itemBoolTrue:
+			switch current.Op {
+			case itemEquals, itemNotEquals:
+			default:
+				return nil, fmt.Errorf("operator '%v' can't be used with bools", opToString[token.Typ])
+			}
+			current.Value = true
+		case itemBoolFalse:
+			switch current.Op {
+			case itemEquals, itemNotEquals:
+			default:
+				return nil, fmt.Errorf("operator '%v' can't be used with bools", opToString[token.Typ])
+			}
+			current.Value = false
+		case itemInt:
+			num, err := strconv.ParseInt(token.Text, 10, 64)
+			if err != nil {
+				return nil, err
+			}
+			current.Value = num
+		}
+
+		// if we are at last position, save last query
+		if i == len(tokens)-1 {
+			queries = append(queries, current)
+		}
+	}
+	return queries, nil
+}