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parser.go
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parser.go
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package syntax
import (
"fmt"
"io"
"math"
"strconv"
"strings"
"time"
)
// Parse parses the specified query string. It is shorthand for constructing a
// parser for s and calling its Parse method.
func Parse(s string) (Query, error) {
return NewParser(strings.NewReader(s)).Parse()
}
// Query is the root of the parse tree for a query. A query is the conjunction
// of one or more conditions.
type Query []Condition
func (q Query) String() string {
ss := make([]string, len(q))
for i, cond := range q {
ss[i] = cond.String()
}
return strings.Join(ss, " AND ")
}
// A Condition is a single conditional expression, consisting of a tag, a
// comparison operator, and an optional argument. The type of the argument
// depends on the operator.
type Condition struct {
Tag string
Op Token
Arg *Arg
opText string
}
func (c Condition) String() string {
s := c.Tag + " " + c.opText
if c.Arg != nil {
return s + " " + c.Arg.String()
}
return s
}
// An Arg is the argument of a comparison operator.
type Arg struct {
Type Token
text string
}
func (a *Arg) String() string {
if a == nil {
return ""
}
switch a.Type {
case TString:
return "'" + a.text + "'"
case TTime:
return "TIME " + a.text
case TDate:
return "DATE " + a.text
default:
return a.text
}
}
// Number returns the value of the argument text as a number, or a NaN if the
// text does not encode a valid number value.
func (a *Arg) Number() float64 {
if a == nil {
return -1
}
v, err := strconv.ParseFloat(a.text, 64)
if err == nil && v >= 0 {
return v
}
return math.NaN()
}
// Time returns the value of the argument text as a time, or the zero value if
// the text does not encode a timestamp or datestamp.
func (a *Arg) Time() time.Time {
var ts time.Time
if a == nil {
return ts
}
var err error
switch a.Type {
case TDate:
ts, err = ParseDate(a.text)
case TTime:
ts, err = ParseTime(a.text)
}
if err == nil {
return ts
}
return time.Time{}
}
// Value returns the value of the argument text as a string, or "".
func (a *Arg) Value() string {
if a == nil {
return ""
}
return a.text
}
// Parser is a query expression parser. The grammar for query expressions is
// defined in the syntax package documentation.
type Parser struct {
scanner *Scanner
}
// NewParser constructs a new parser that reads the input from r.
func NewParser(r io.Reader) *Parser {
return &Parser{scanner: NewScanner(r)}
}
// Parse parses the complete input and returns the resulting query.
func (p *Parser) Parse() (Query, error) {
cond, err := p.parseCond()
if err != nil {
return nil, err
}
conds := []Condition{cond}
for p.scanner.Next() != io.EOF {
if tok := p.scanner.Token(); tok != TAnd {
return nil, fmt.Errorf("offset %d: got %v, want %v", p.scanner.Pos(), tok, TAnd)
}
cond, err := p.parseCond()
if err != nil {
return nil, err
}
conds = append(conds, cond)
}
return conds, nil
}
// parseCond parses a conditional expression: tag OP value.
func (p *Parser) parseCond() (Condition, error) {
var cond Condition
if err := p.require(TTag); err != nil {
return cond, err
}
cond.Tag = p.scanner.Text()
if err := p.require(TLeq, TGeq, TLt, TGt, TEq, TContains, TExists); err != nil {
return cond, err
}
cond.Op = p.scanner.Token()
cond.opText = p.scanner.Text()
var err error
switch cond.Op {
case TLeq, TGeq, TLt, TGt:
err = p.require(TNumber, TTime, TDate)
case TEq:
err = p.require(TNumber, TTime, TDate, TString)
case TContains:
err = p.require(TString)
case TExists:
// no argument
return cond, nil
default:
return cond, fmt.Errorf("offset %d: unexpected operator %v", p.scanner.Pos(), cond.Op)
}
if err != nil {
return cond, err
}
cond.Arg = &Arg{Type: p.scanner.Token(), text: p.scanner.Text()}
return cond, nil
}
// require advances the scanner and requires that the resulting token is one of
// the specified token types.
func (p *Parser) require(tokens ...Token) error {
if err := p.scanner.Next(); err != nil {
return fmt.Errorf("offset %d: %w", p.scanner.Pos(), err)
}
got := p.scanner.Token()
for _, tok := range tokens {
if tok == got {
return nil
}
}
return fmt.Errorf("offset %d: got %v, wanted %s", p.scanner.Pos(), got, tokLabel(tokens))
}
// tokLabel makes a human-readable summary string for the given token types.
func tokLabel(tokens []Token) string {
if len(tokens) == 1 {
return tokens[0].String()
}
last := len(tokens) - 1
ss := make([]string, len(tokens)-1)
for i, tok := range tokens[:last] {
ss[i] = tok.String()
}
return strings.Join(ss, ", ") + " or " + tokens[last].String()
}
// ParseDate parses s as a date string in the format used by DATE values.
func ParseDate(s string) (time.Time, error) {
return time.Parse("2006-01-02", s)
}
// ParseTime parses s as a timestamp in the format used by TIME values.
func ParseTime(s string) (time.Time, error) {
return time.Parse(time.RFC3339, s)
}