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parser.go
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parser.go
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package ical
import (
"bufio"
"io"
"os"
"regexp"
"strings"
"github.com/pkg/errors"
)
var errUnreachable = errors.New(`can't reach here`)
func NewParser() *Parser {
return &Parser{}
}
type container interface {
AddEntry(Entry) error
}
type parseCtx struct {
calendar *Calendar
current []string
parent container
scanner *bufio.Scanner
readbuf []string
}
func (p *Parser) ParseFile(filename string) (*Calendar, error) {
f, err := os.Open(filename)
if err != nil {
return nil, errors.Wrapf(err, `failed to open %s for reading`, filename)
}
defer f.Close()
return p.Parse(f)
}
var childEntries = map[string][]string{
"VCALENDAR": []string{"VTIMEZONE", "VEVENT"},
"VTIMEZONE": []string{"DAYLIGHT", "STANDARD"},
}
func (p *Parser) Parse(src io.Reader) (*Calendar, error) {
var ctx parseCtx
ctx.scanner = bufio.NewScanner(src)
if err := ctx.parse("VCALENDAR"); err != nil {
return nil, errors.Wrap(err, `failed to parse ical`)
}
return ctx.calendar, nil
}
func (ctx *parseCtx) next() (ret string, err error) {
if len(ctx.readbuf) > 0 {
l := ctx.readbuf[len(ctx.readbuf)-1]
ctx.readbuf = ctx.readbuf[:len(ctx.readbuf)-1]
return l, nil
}
if !ctx.scanner.Scan() {
return "", io.EOF
}
return ctx.scanner.Text(), nil
}
func (ctx *parseCtx) pushback(l string) {
ctx.readbuf = append(ctx.readbuf, l)
}
func (ctx *parseCtx) peek() (string, error) {
l, err := ctx.next()
if err != nil {
return "", err
}
ctx.pushback(l)
return l, nil
}
var looksLikePropertyRe = regexp.MustCompile(`^[^:]+:.*$`)
func (ctx *parseCtx) nextProperty() (string, string, Parameters, error) {
l, err := ctx.next()
if err != nil {
return "", "", nil, errors.Wrap(err, `failed to fetch line`)
}
pair := strings.SplitN(l, ":", 2)
n, val := pair[0], pair[1]
for {
l, err = ctx.peek()
if err != nil {
break // EOF? oh well
}
if looksLikePropertyRe.MatchString(l) {
break
}
ctx.next()
// Remove first space
val += l[1:]
}
// name may contain parameters
var params = Parameters{}
paramslist := strings.Split(n, ";")
for i, v := range paramslist {
if i == 0 {
continue
}
ppair := strings.SplitN(v, "=", 2)
params.Add(ppair[0], ppair[1])
}
return paramslist[0], strings.Replace(val, "\\", "", -1), params, nil
}
func (ctx *parseCtx) handlerFor(name string) func() error {
switch name {
case "VTIMEZONE":
return ctx.parseTimezone
case "VEVENT":
return ctx.parseEvent
case "DAYLIGHT":
return ctx.parseDaylight
case "STANDARD":
return ctx.parseStandard
}
return func() error { return nil }
}
func (ctx *parseCtx) entryFor(name string) Entry {
switch name {
case "VCALENDAR":
ctx.calendar = New()
return ctx.calendar
case "VTIMEZONE":
return NewTimezone()
case "VEVENT":
return NewEvent()
case "DAYLIGHT":
return NewDaylight()
case "STANDARD":
return NewStandard()
}
return nil
}
func (ctx *parseCtx) parse(name string) error {
children := childEntries[name]
finalize, check, err := ctx.begin(name)
if err != nil {
return err
}
v := ctx.entryFor(name)
if v == nil {
return errors.Errorf(`could not create entry for %s`, name)
}
OUTER:
for {
l, err := ctx.peek()
if err != nil {
return errors.Wrap(err, `failed to peek`)
}
for _, chld := range children {
if l != "BEGIN:"+chld {
continue
}
h := ctx.handlerFor(chld)
oldp := ctx.parent
ctx.parent = v
if err := h(); err != nil {
return errors.Wrapf(err, `failed to parse %s`, chld)
}
ctx.parent = oldp
continue OUTER
}
if check(l) {
if ctx.parent != nil {
ctx.parent.AddEntry(v)
}
return finalize()
}
n, val, params, err := ctx.nextProperty()
if err != nil {
return errors.Wrap(err, `failed to read next property`)
}
v.AddProperty(n, val, WithParameters(params))
}
return errUnreachable
}
func (ctx *parseCtx) begin(name string) (func() error, func(string) bool, error) {
l, err := ctx.next()
if err != nil {
return nil, nil, errors.Wrap(err, `failed to fetch next line`)
}
if l != "BEGIN:"+name {
return nil, nil, errors.Errorf(`expected BEGIN:%s, got %s`, name, l)
}
end := "END:" + name
finalizer := func() error {
l, err := ctx.next()
if err != nil {
return errors.Wrap(err, `failed to fetch next line`)
}
if l != end {
return errors.Errorf(`expected %s, got %s`, end, l)
}
return nil
}
checker := func(s string) bool {
return end == s
}
return finalizer, checker, nil
}
func (ctx *parseCtx) parseTimezone() error {
return ctx.parse("VTIMEZONE")
}
func (ctx *parseCtx) parseDaylight() error {
return ctx.parse("DAYLIGHT")
}
func (ctx *parseCtx) parseStandard() error {
return ctx.parse("STANDARD")
}
func (ctx *parseCtx) parseEvent() error {
return ctx.parse("VEVENT")
}