mirror of
https://github.com/mgrove36/ical-filter-proxy.git
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initial commit
This commit is contained in:
Yung Wood
259
calendar.go
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259
calendar.go
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@@ -0,0 +1,259 @@
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package main
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import (
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"bytes"
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"io"
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"log/slog"
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"net/http"
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"regexp"
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"strings"
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ics "github.com/arran4/golang-ical"
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)
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// All structs defined in this file are used to unmarshall yaml configuration and
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// provide helper functions that are used to fetch and filter events
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// CalendarConfig definition
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type CalendarConfig struct {
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Name string `yaml:"name"`
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Token string `yaml:"token"`
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FeedURL string `yaml:"feed_url"`
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Filters []Filter `yaml:"filters"`
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}
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// Downloads iCal feed from the URL and applies filtering rules
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func (calendarConfig CalendarConfig) fetch() ([]byte, error) {
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// get the iCal feed
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slog.Debug("Fetching iCal feed", "url", calendarConfig.FeedURL)
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resp, err := http.Get(calendarConfig.FeedURL)
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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feedData, err := io.ReadAll(resp.Body)
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if err != nil {
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return nil, err
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}
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// parse calendar
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cal, err := ics.ParseCalendar(strings.NewReader(string(feedData)))
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if err != nil {
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return nil, err
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}
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// process filters
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if len(calendarConfig.Filters) > 0 {
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slog.Debug("Processing filters", "calendar", calendarConfig.Name)
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for _, event := range cal.Events() {
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if !calendarConfig.ProcessEvent(event) {
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cal.RemoveEvent(event.Id())
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}
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}
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slog.Debug("Filter processing completed", "calendar", calendarConfig.Name)
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} else {
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slog.Debug("No filters to evaluate", "calendar", calendarConfig.Name)
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}
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// serialize output
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var buf bytes.Buffer
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err = cal.SerializeTo(&buf)
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if err != nil {
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return nil, err
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}
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// return
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return buf.Bytes(), nil
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}
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// Evaluate the filters for a calendar against a given VEvent and
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// perform any transformations directly to the VEvent (pointer)
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// This function returns false if an event should be deleted
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func (calendarConfig CalendarConfig) ProcessEvent(event *ics.VEvent) bool {
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// Get the Summary (the "title" of the event)
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// In case we cannot parse the event summary it should get dropped
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summary := event.GetProperty(ics.ComponentPropertySummary) // summary only for logging
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if summary == nil {
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return false
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}
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// Iterate through the Filter rules
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for id, filter := range calendarConfig.Filters {
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// Does the filter match the event?
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if filter.matchesEvent(*event) {
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slog.Debug("Filter match found", "rule_id", id, "filter_description", filter.Description, "event_summary", summary.Value)
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// The event should get dropped if RemoveEvent is set
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if filter.RemoveEvent {
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slog.Debug("Event to be removed, no more rules will be processed", "action", "DELETE", "rule_id", id, "filter_description", filter.Description, "event_summary", summary.Value)
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return false
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}
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// Apply transformation rules to event
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filter.transformEvent(event)
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// Check if we should stop processing rules
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if filter.Stop {
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slog.Debug("Stop option is set, no more rules will be processed", "rule_id", id, "filter_description", filter.Description, "event_summary", summary.Value)
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return true
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}
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}
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}
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// Keep event by default if all Filter rules are processed
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slog.Debug("Rule processing complete, event will be kept", "rule_id", nil, "event_summary", summary.Value)
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return true
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}
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// Filter definition
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type Filter struct {
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Description string `yaml:"description"`
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RemoveEvent bool `yaml:"remove"`
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Stop bool `yaml:"stop"`
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Match EventMatchRules `yaml:"match"`
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Transform EventTransformRules `yaml:"transform"`
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}
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// Returns true if a VEvent matches the Filter conditions
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func (filter Filter) matchesEvent(event ics.VEvent) bool {
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// If an event property is not defined golang-ical returns a nil pointer
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// Get event Summary - only used for debug logging
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eventSummary := event.GetProperty(ics.ComponentPropertySummary)
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if eventSummary == nil {
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slog.Warn("Unable to process event summary. Event will be dropped")
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return false // never match if VEvent has no summary
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}
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// Check Summary filters against VEvent
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if filter.Match.Summary.hasConditions() {
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if !filter.Match.Summary.matchesString(eventSummary.Value) {
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return false
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}
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}
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// Check Description filters against VEvent
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if filter.Match.Description.hasConditions() {
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eventDescription := event.GetProperty(ics.ComponentPropertyDescription)
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if eventDescription == nil {
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slog.Debug("Event has no Description so cannot not match filter", "event_summary", eventSummary.Value, "filter", filter.Description)
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return false // if VEvent has no description it cannot match filter
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}
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if !filter.Match.Description.matchesString(eventDescription.Value) {
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slog.Debug("Event Description does not match filter conditions", "event_summary", eventSummary.Value, "filter", filter.Description)
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return false // event doesn't match
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}
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}
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// Check Description filters against VEvent
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if filter.Match.Location.hasConditions() {
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eventLocation := event.GetProperty(ics.ComponentPropertyLocation)
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if eventLocation == nil {
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slog.Warn("Event has no Location so cannot match filter", "event_summary", eventSummary.Value, "filter", filter.Description)
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return false // if VEvent has no location it cannot match filter
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}
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if !filter.Match.Location.matchesString(eventLocation.Value) {
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slog.Debug("Event Location does not match filter conditions", "event_summary", eventSummary.Value, "filter", filter.Description)
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return false // event doesn't match
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}
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}
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// VEvent must match if we get here
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slog.Debug("Event matches filter conditions", "event_summary", eventSummary.Value, "filter", filter.Description)
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return true
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}
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// Applies filter transformations to a VEvent pointer
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func (filter Filter) transformEvent(event *ics.VEvent) {
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// Summary transformations
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if filter.Transform.Summary.Remove {
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event.SetSummary("")
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} else if filter.Transform.Summary.Replace != "" {
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event.SetSummary(filter.Transform.Summary.Replace)
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}
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// Description transformations
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if filter.Transform.Description.Remove {
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event.SetDescription("")
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} else if filter.Transform.Description.Replace != "" {
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event.SetDescription(filter.Transform.Description.Replace)
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}
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}
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// EventMatchRules contains VEvent properties that user can match against
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type EventMatchRules struct {
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Summary StringMatchRule `yaml:"summary"`
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Description StringMatchRule `yaml:"description"`
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Location StringMatchRule `yaml:"location"`
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}
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// StringMatchRule defines match rules for VEvent properties with string values
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type StringMatchRule struct {
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Contains string `yaml:"contains"`
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Prefix string `yaml:"prefix"`
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Suffix string `yaml:"suffix"`
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RegexMatch string `yaml:"regex"`
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}
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// Returns true if StringMatchRule has any conditions
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func (smr StringMatchRule) hasConditions() bool {
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return smr.Contains != "" ||
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smr.Prefix != "" ||
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smr.Suffix != "" ||
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smr.RegexMatch != ""
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}
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// Returns true if a given string (data) matches ALL StringMatchRule conditions
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func (smr StringMatchRule) matchesString(data string) bool {
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// check contains if set
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if smr.Contains != "" {
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if data == "" || !strings.Contains(data, smr.Contains) {
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return false
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}
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}
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// check prefix if set
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if smr.Prefix != "" {
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if data == "" || !strings.HasPrefix(data, smr.Prefix) {
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return false
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}
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}
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// check suffix if set
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if smr.Suffix != "" {
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if data == "" || !strings.HasSuffix(data, smr.Suffix) {
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return false
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}
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}
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// check regex match if set
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if smr.RegexMatch != "" {
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match, err := regexp.MatchString(data, smr.RegexMatch)
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if err != nil {
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slog.Warn("error processing regex rule", "value", smr.RegexMatch)
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return false // regex error is considered a failure to match
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}
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if !match {
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return false // regex didn't match
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}
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}
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return true
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}
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// EventTransformRules contains VEvent properties that user can modify
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type EventTransformRules struct {
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Summary StringTransformRule `yaml:"summary"`
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Description StringTransformRule `yaml:"description"`
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Location StringTransformRule `yaml:"location"`
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}
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// StringTransformRule defines changes for VEvent properties with string values
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type StringTransformRule struct {
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Replace string `yaml:"replace"`
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Remove bool `yaml:"remove"`
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}
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