0.0.1

Author: pat

.github/workflows/main.yml

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+name: Ruby
+
+on: [push,pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: 3.0.1
+    - name: Install dependencies
+      run: |
+        gem install bundler
+        bundle install
+    - name: Rubocop
+      run: bundle exec rubocop
+    - name: RSpec
+      env:
+        GOOGLE_CLIENT_ID: ${{ secrets.GOOGLE_CLIENT_ID }}
+        GOOGLE_CLIENT_SECRET: ${{ secrets.GOOGLE_CLIENT_SECRET }}
+        GOOGLE_USERNAME: ${{ secrets.GOOGLE_USERNAME }}
+        GOOGLE_REFRESH_TOKEN: ${{ secrets.GOOGLE_REFRESH_TOKEN }}
+      run: bundle exec rspec

.gitignore

@@ -0,0 +1,11 @@
+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
+
+.env
+Gemfile.lock

.rspec

@@ -0,0 +1,3 @@
+--format documentation
+--color
+--require spec_helper

.rubocop.yml

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+AllCops:
+  TargetRubyVersion: 2.7
+  NewCops: enable
+  SuggestExtensions: false
+
+Layout/LineLength:
+  Max: 80
+
+Metrics/AbcSize:
+  Exclude:
+    - 'lib/calendav/requests/*.rb'
+
+Metrics/BlockLength:
+  Exclude:
+    - 'spec/**/*_spec.rb'
+
+Metrics/MethodLength:
+  Exclude:
+    - 'lib/calendav/requests/*.rb'
+
+Naming/RescuedExceptionsVariableName:
+  PreferredName: error
+
+Style/Documentation:
+  Enabled: false
+
+Style/StringLiterals:
+  EnforcedStyle: double_quotes

CHANGELOG.md

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+## [Unreleased]
+
+## [0.0.1] - 2021-06-13
+
+An initial release with very limited (and likely buggy) support:
+
+* Determining the principal URL.
+* Determining the calendar home path.
+* Listing available calendars.
+* Creating events on a calendar.
+* Listing events on a calendar within a given timespan.
+* Deleting events on a calendar.

CODE_OF_CONDUCT.md

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+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+We as members, contributors, and leaders pledge to make participation in our community a harassment-free experience for everyone, regardless of age, body size, visible or invisible disability, ethnicity, sex characteristics, gender identity and expression, level of experience, education, socio-economic status, nationality, personal appearance, race, religion, or sexual identity and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming, diverse, inclusive, and healthy community.
+
+## Our Standards
+
+Examples of behavior that contributes to a positive environment for our community include:
+
+* Demonstrating empathy and kindness toward other people
+* Being respectful of differing opinions, viewpoints, and experiences
+* Giving and gracefully accepting constructive feedback
+* Accepting responsibility and apologizing to those affected by our mistakes, and learning from the experience
+* Focusing on what is best not just for us as individuals, but for the overall community
+
+Examples of unacceptable behavior include:
+
+* The use of sexualized language or imagery, and sexual attention or
+  advances of any kind
+* Trolling, insulting or derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or email
+  address, without their explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Enforcement Responsibilities
+
+Community leaders are responsible for clarifying and enforcing our standards of acceptable behavior and will take appropriate and fair corrective action in response to any behavior that they deem inappropriate, threatening, offensive, or harmful.
+
+Community leaders have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct, and will communicate reasons for moderation decisions when appropriate.
+
+## Scope
+
+This Code of Conduct applies within all community spaces, and also applies when an individual is officially representing the community in public spaces. Examples of representing our community include using an official e-mail address, posting via an official social media account, or acting as an appointed representative at an online or offline event.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be reported to the community leaders responsible for enforcement at pat@freelancing-gods.com. All complaints will be reviewed and investigated promptly and fairly.
+
+All community leaders are obligated to respect the privacy and security of the reporter of any incident.
+
+## Enforcement Guidelines
+
+Community leaders will follow these Community Impact Guidelines in determining the consequences for any action they deem in violation of this Code of Conduct:
+
+### 1. Correction
+
+**Community Impact**: Use of inappropriate language or other behavior deemed unprofessional or unwelcome in the community.
+
+**Consequence**: A private, written warning from community leaders, providing clarity around the nature of the violation and an explanation of why the behavior was inappropriate. A public apology may be requested.
+
+### 2. Warning
+
+**Community Impact**: A violation through a single incident or series of actions.
+
+**Consequence**: A warning with consequences for continued behavior. No interaction with the people involved, including unsolicited interaction with those enforcing the Code of Conduct, for a specified period of time. This includes avoiding interactions in community spaces as well as external channels like social media. Violating these terms may lead to a temporary or permanent ban.
+
+### 3. Temporary Ban
+
+**Community Impact**: A serious violation of community standards, including sustained inappropriate behavior.
+
+**Consequence**: A temporary ban from any sort of interaction or public communication with the community for a specified period of time. No public or private interaction with the people involved, including unsolicited interaction with those enforcing the Code of Conduct, is allowed during this period. Violating these terms may lead to a permanent ban.
+
+### 4. Permanent Ban
+
+**Community Impact**: Demonstrating a pattern of violation of community standards, including sustained inappropriate behavior,  harassment of an individual, or aggression toward or disparagement of classes of individuals.
+
+**Consequence**: A permanent ban from any sort of public interaction within the community.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 2.0,
+available at https://www.contributor-covenant.org/version/2/0/code_of_conduct.html.
+
+Community Impact Guidelines were inspired by [Mozilla's code of conduct enforcement ladder](https://github.com/mozilla/diversity).
+
+[homepage]: https://www.contributor-covenant.org
+
+For answers to common questions about this code of conduct, see the FAQ at
+https://www.contributor-covenant.org/faq. Translations are available at https://www.contributor-covenant.org/translations.

Gemfile

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+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gemspec

LICENSE.md

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+Calendav Copyright (c) 2021 Pat Allan
+
+Hippocratic License Version Number: 2.1.
+
+Purpose. The purpose of this License is for the Licensor named above to permit the Licensee (as defined below) broad permission, if consistent with Human Rights Laws and Human Rights Principles (as each is defined below), to use and work with the Software (as defined below) within the full scope of Licensor’s copyright and patent rights, if any, in the Software, while ensuring attribution and protecting the Licensor from liability.
+
+Permission and Conditions. The Licensor grants permission by this license (“License”), free of charge, to the extent of Licensor’s rights under applicable copyright and patent law, to any person or entity (the “Licensee”) obtaining a copy of this software and associated documentation files (the “Software”), to do everything with the Software that would otherwise infringe (i) the Licensor’s copyright in the Software or (ii) any patent claims to the Software that the Licensor can license or becomes able to license, subject to all of the following terms and conditions:
+
+* Acceptance. This License is automatically offered to every person and entity subject to its terms and conditions. Licensee accepts this License and agrees to its terms and conditions by taking any action with the Software that, absent this License, would infringe any intellectual property right held by Licensor.
+
+* Notice. Licensee must ensure that everyone who gets a copy of any part of this Software from Licensee, with or without changes, also receives the License and the above copyright notice (and if included by the Licensor, patent, trademark and attribution notice). Licensee must cause any modified versions of the Software to carry prominent notices stating that Licensee changed the Software. For clarity, although Licensee is free to create modifications of the Software and distribute only the modified portion created by Licensee with additional or different terms, the portion of the Software not modified must be distributed pursuant to this License. If anyone notifies Licensee in writing that Licensee has not complied with this Notice section, Licensee can keep this License by taking all practical steps to comply within 30 days after the notice. If Licensee does not do so, Licensee’s License (and all rights licensed hereunder) shall end immediately.
+
+* Compliance with Human Rights Principles and Human Rights Laws.
+
+    1. Human Rights Principles.
+
+        (a) Licensee is advised to consult the articles of the United Nations Universal Declaration of Human Rights and the United Nations Global Compact that define recognized principles of international human rights (the “Human Rights Principles”). Licensee shall use the Software in a manner consistent with Human Rights Principles.
+
+        (b) Unless the Licensor and Licensee agree otherwise, any dispute, controversy, or claim arising out of or relating to (i) Section 1(a) regarding Human Rights Principles, including the breach of Section 1(a), termination of this License for breach of the Human Rights Principles, or invalidity of Section 1(a) or (ii) a determination of whether any Law is consistent or in conflict with Human Rights Principles pursuant to Section 2, below, shall be settled by arbitration in accordance with the Hague Rules on Business and Human Rights Arbitration (the “Rules”); provided, however, that Licensee may elect not to participate in such arbitration, in which event this License (and all rights licensed hereunder) shall end immediately. The number of arbitrators shall be one unless the Rules require otherwise.
+
+        Unless both the Licensor and Licensee agree to the contrary: (1) All documents and information concerning the arbitration shall be public and may be disclosed by any party; (2) The repository referred to under Article 43 of the Rules shall make available to the public in a timely manner all documents concerning the arbitration which are communicated to it, including all submissions of the parties, all evidence admitted into the record of the proceedings, all transcripts or other recordings of hearings and all orders, decisions and awards of the arbitral tribunal, subject only to the arbitral tribunal's powers to take such measures as may be necessary to safeguard the integrity of the arbitral process pursuant to Articles 18, 33, 41 and 42 of the Rules; and (3) Article 26(6) of the Rules shall not apply.
+
+    2. Human Rights Laws. The Software shall not be used by any person or entity for any systems, activities, or other uses that violate any Human Rights Laws.  “Human Rights Laws” means any applicable laws, regulations, or rules (collectively, “Laws”) that protect human, civil, labor, privacy, political, environmental, security, economic, due process, or similar rights; provided, however, that such Laws are consistent and not in conflict with Human Rights Principles (a dispute over the consistency or a conflict between Laws and Human Rights Principles shall be determined by arbitration as stated above).  Where the Human Rights Laws of more than one jurisdiction are applicable or in conflict with respect to the use of the Software, the Human Rights Laws that are most protective of the individuals or groups harmed shall apply.
+
+    3. Indemnity. Licensee shall hold harmless and indemnify Licensor (and any other contributor) against all losses, damages, liabilities, deficiencies, claims, actions, judgments, settlements, interest, awards, penalties, fines, costs, or expenses of whatever kind, including Licensor’s reasonable attorneys’ fees, arising out of or relating to Licensee’s use of the Software in violation of Human Rights Laws or Human Rights Principles.
+
+* Failure to Comply. Any failure of Licensee to act according to the terms and conditions of this License is both a breach of the License and an infringement of the intellectual property rights of the Licensor (subject to exceptions under Laws, e.g., fair use). In the event of a breach or infringement, the terms and conditions of this License may be enforced by Licensor under the Laws of any jurisdiction to which Licensee is subject. Licensee also agrees that the Licensor may enforce the terms and conditions of this License against Licensee through specific performance (or similar remedy under Laws) to the extent permitted by Laws. For clarity, except in the event of a breach of this License, infringement, or as otherwise stated in this License, Licensor may not terminate this License with Licensee.
+
+* Enforceability and Interpretation. If any term or provision of this License is determined to be invalid, illegal, or unenforceable by a court of competent jurisdiction, then such invalidity, illegality, or unenforceability shall not affect any other term or provision of this License or invalidate or render unenforceable such term or provision in any other jurisdiction; provided, however, subject to a court modification pursuant to the immediately following sentence, if any term or provision of this License pertaining to Human Rights Laws or Human Rights Principles is deemed invalid, illegal, or unenforceable against Licensee by a court of competent jurisdiction, all rights in the Software granted to Licensee shall be deemed null and void as between Licensor and Licensee. Upon a determination that any term or provision is invalid, illegal, or unenforceable, to the extent permitted by Laws, the court may modify this License to affect the original purpose that the Software be used in compliance with Human Rights Principles and Human Rights Laws as closely as possible. The language in this License shall be interpreted as to its fair meaning and not strictly for or against any party.
+
+* Disclaimer. TO THE FULL EXTENT ALLOWED BY LAW, THIS SOFTWARE COMES “AS IS,” WITHOUT ANY WARRANTY, EXPRESS OR IMPLIED, AND LICENSOR AND ANY OTHER CONTRIBUTOR SHALL NOT BE LIABLE TO ANYONE FOR ANY DAMAGES OR OTHER LIABILITY ARISING FROM, OUT OF, OR IN CONNECTION WITH THE SOFTWARE OR THIS LICENSE, UNDER ANY KIND OF LEGAL CLAIM.
+
+This Hippocratic License is an Ethical Source license (https://ethicalsource.dev) and is offered for use by licensors and licensees at their own risk, on an “AS IS” basis, and with no warranties express or implied, to the maximum extent permitted by Laws.

README.md

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+# Calendav
+
+A library for interacting with CalDAV servers via Ruby.
+
+At the time of writing, this gem is definitely not ready for production, nor is it anywhere close to supporting a decent set of features. Currently it covers the following:
+
+* Determining the principal URL.
+* Determining the calendar home path.
+* Listing available calendars.
+* Creating events on a calendar.
+* Listing events on a calendar within a given timespan.
+* Deleting events on a calendar.
+
+Other features on the roadmap, in a rough order of priority:
+
+* Consistent access to calendar/event URLs.
+* Updating events.
+* List all events on a calendar.
+* Create new calendars.
+* Update calendars.
+* Delete calendars.
+* Enable etag validation for updates/deletions (If-Match header).
+* Solid exception handling.
+* Use WebDAV-Sync to get changes since last sync.
+* Enable locking/unlocking when making changes.
+* Allow requesting only certain properties for calendars/events.
+
+Also, the plan is to have a test suite that covers multiple CalDAV server implementations.
+
+## Usage
+
+```ruby
+credentials = Calendav.credentials(
+  :google, username: "example@gmail.com", password: "oauth-access-token"
+)
+# Also supported are FastMail and Apple, where the passwords should be
+# app-specific, with authentication via Basic Auth. Google uses a Bearer Token
+# for authentication (supplied as the password).
+#
+# Otherwise, to compose a more custom set of credentials:
+credentials = Calendav::Credentials::Standard.new(
+  host: "https://www.example.com/caldav",
+  username: "example",
+  password: "secret",
+  authentication: :basic_auth # or :bearer_token
+)
+
+client = Calendav.client credentials
+puts client.principal_url
+
+puts client.calendars.home_url
+calendars = client.calendars.list
+calendars.each { |calendar| puts calendar.path, calendar.display_name }
+
+events = client.events.list(
+  calendar.path, from: Time.new(2021, 1, 1), to: Time.new(2022, 1, 1)
+)
+
+# use the icalendar gem to generate ICS strings
+ics = Icalendar::Calendar.new
+ics.event do |event|
+# ...
+end
+ics.publish
+
+# You need to provide the expected filename for the event:
+identifier = "#{SecureRandom.uuid}.ics"
+# … but the server may change it on you, so the new, full URL is returned:
+event_url = client.events.create(calendar.path, identifier, ics.to_ical)
+
+client.events.delete(event_url)
+```
+
+## Installation
+
+Add this line to your application's Gemfile:
+
+```ruby
+gem 'calendav'
+```
+
+And then execute:
+
+    $ bundle install
+
+Or install it yourself as:
+
+    $ gem install calendav
+
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/pat/calendav. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/pat/calendav/blob/main/CODE_OF_CONDUCT.md).
+
+The test suite currently only runs against a Google account I've created especially for this purpose - and the credentials are not public. I realise this makes contributions more difficult, and I'm open to finding better ways to handle this. I did look into running a CalDAV server within the test suite, but couldn't find anything small and easy enough for that purpose. But also: testing against common CalDAV servers does help to ensure this gem is truly useful (and has knowledge of their idiosyncrasies).
+
+## License
+
+The gem is available as open source under the terms of the [Hippocratic License](https://firstdonoharm.dev).
+
+## Code of Conduct
+
+Everyone interacting in the Calendav project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/pat/calendav/blob/main/CODE_OF_CONDUCT.md).

Rakefile

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+# frozen_string_literal: true
+
+require "bundler/gem_tasks"
+require "rspec/core/rake_task"
+
+RSpec::Core::RakeTask.new(:spec)
+
+require "rubocop/rake_task"
+
+RuboCop::RakeTask.new
+
+task default: %i[spec rubocop]

bin/console

@@ -0,0 +1,15 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "calendav"
+
+# You can add fixtures and/or initialization code here to make experimenting
+# with your gem easier. You can also use a different console, if you like.
+
+# (If you use this, don't forget to add pry to your Gemfile!)
+# require "pry"
+# Pry.start
+
+require "irb"
+IRB.start(__FILE__)

bin/setup

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here

calendav.gemspec

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+Gem::Specification.new do |spec|
+  spec.name          = "calendav"
+  spec.version       = "0.0.1"
+  spec.authors       = ["Pat Allan"]
+  spec.email         = ["pat@freelancing-gods.com"]
+
+  spec.summary       = "CalDAV client"
+  spec.homepage      = "https://github.com/pat/calendav"
+  spec.license       = "Hippocratic-2.1"
+
+  spec.required_ruby_version = Gem::Requirement.new(">= 2.7.0")
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = spec.homepage
+  spec.metadata["changelog_uri"] =
+    "https://github.com/pat/calendav/blob/main/CHANGELOG.md"
+
+  spec.files         = Dir["lib/**/*"] + %w[LICENSE.md README.md CHANGELOG.md]
+  spec.test_files    = Dir["spec/**/*"] + %w[.rspec Gemfile Rakefile]
+
+  spec.bindir        = "exe"
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+
+  spec.add_runtime_dependency "http"
+  spec.add_runtime_dependency "nokogiri"
+
+  spec.add_development_dependency "dotenv"
+  spec.add_development_dependency "googleauth"
+  spec.add_development_dependency "icalendar"
+  spec.add_development_dependency "rake"
+  spec.add_development_dependency "rspec"
+  spec.add_development_dependency "rubocop"
+end

lib/calendav.rb

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+# frozen_string_literal: true
+
+require_relative "./calendav/credentials/apple"
+require_relative "./calendav/credentials/fastmail"
+require_relative "./calendav/credentials/google"
+require_relative "./calendav/client"
+
+module Calendav
+  PROVIDERS = {
+    apple: Credentials::Apple,
+    fastmail: Credentials::FastMail,
+    google: Credentials::Google
+  }.freeze
+
+  def self.credentials(provider, username, password)
+    PROVIDERS.fetch(provider).new(username: username, password: password)
+  end
+
+  def self.client(credentials)
+    Client.new(credentials)
+  end
+end

lib/calendav/calendar.rb

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+# frozen_string_literal: true
+
+require_relative "./xml_processor"
+
+module Calendav
+  class Calendar
+    attr_reader :path
+
+    def self.from_xml(node)
+      new(
+        node.xpath("./dav:href").text,
+        node.xpath(".//dav:prop/*").to_xml,
+        node.namespaces
+      )
+    end
+
+    def initialize(path, attribute_nodes, namespaces = {})
+      @path = path
+      @attribute_nodes = attribute_nodes
+      @namespaces = namespaces
+    end
+
+    def display_name
+      attribute_value fragment.xpath("//dav:displayname")
+    end
+
+    def ctag
+      attribute_value fragment.xpath("//cs:getctag")
+    end
+
+    def etag
+      attribute_value fragment.xpath("//dav:getetag")
+    end
+
+    private
+
+    attr_reader :attribute_nodes, :namespaces
+
+    def fragment
+      @fragment ||= XMLProcessor.call(
+        "<nodes>#{attribute_nodes}</nodes>", namespaces
+      )
+    end
+
+    def attribute_value(node)
+      return nil if node.children.empty?
+
+      if node.children.any?(&:element?)
+        node.children.select(&:element?).collect(&:to_xml).join
+      else
+        node.children.text
+      end
+    end
+  end
+end

lib/calendav/client.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require_relative "./contextual_url"
+require_relative "./endpoint"
+require_relative "./clients/calendars_client"
+require_relative "./clients/events_client"
+require_relative "./requests/current_user_principal"
+
+module Calendav
+  class Client
+    def initialize(credentials)
+      @credentials = credentials
+    end
+
+    def calendars
+      @calendars = Clients::CalendarsClient.new(self, endpoint, credentials)
+    end
+
+    def events
+      @events = Clients::EventsClient.new(self, endpoint, credentials)
+    end
+
+    def principal_url
+      @principal_url ||= begin
+        request = Requests::CurrentUserPrincipal.call
+
+        ContextualURL.call(
+          credentials,
+          endpoint
+            .propfind(request.to_xml)
+            .xpath(".//dav:current-user-principal/dav:href")
+            .text
+        )
+      end
+    end
+
+    private
+
+    attr_reader :credentials
+
+    def endpoint
+      @endpoint ||= Endpoint.new(credentials)
+    end
+  end
+end

lib/calendav/clients/calendars_client.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require "securerandom"
+
+require_relative "../calendar"
+require_relative "../requests/calendar_home_set"
+require_relative "../requests/list_calendars"
+require_relative "../requests/make_calendar"
+
+module Calendav
+  module Clients
+    class CalendarsClient
+      def initialize(client, endpoint, credentials)
+        @client = client
+        @endpoint = endpoint
+        @credentials = credentials
+      end
+
+      def home_url
+        @home_url ||= begin
+          request = Requests::CalendarHomeSet.call
+
+          ContextualURL.call(
+            credentials,
+            endpoint
+              .propfind(request.to_xml, url: client.principal_url)
+              .xpath(".//caldav:calendar-home-set/dav:href")
+              .text
+          )
+        end
+      end
+
+      def create(attributes)
+        request = Requests::MakeCalendar.call(attributes)
+
+        id = SecureRandom.uuid
+        id = "/#{id}" unless home_url.end_with?("/")
+        url = home_url + id
+
+        endpoint.mkcalendar(request.to_xml, url: url)
+
+        url
+      end
+
+      def delete(url)
+        endpoint.delete(url: url)
+      end
+
+      def list
+        request = Requests::ListCalendars.call
+        calendar_xpath = ".//dav:resourcetype/caldav:calendar"
+
+        endpoint
+          .propfind(request.to_xml, url: home_url, depth: 1)
+          .xpath(".//dav:response")
+          .select { |node| node.xpath(calendar_xpath).any? }
+          .collect { |node| Calendar.from_xml(node) }
+      end
+
+      private
+
+      attr_reader :client, :endpoint, :credentials
+    end
+  end
+end

lib/calendav/clients/events_client.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require_relative "../event"
+require_relative "../requests/list_events"
+
+module Calendav
+  module Clients
+    class EventsClient
+      def initialize(client, endpoint, credentials)
+        @client = client
+        @endpoint = endpoint
+        @credentials = credentials
+      end
+
+      def create(calendar_url, event_identifier, ics)
+        url = merged_url(calendar_url, event_identifier)
+        result = endpoint.put(ics, url: url, content_type: :ics)
+
+        result.headers["Location"]
+      end
+
+      def delete(event_url)
+        endpoint.delete(url: event_url)
+      end
+
+      def list(calendar_url, from:, to:)
+        request = Requests::ListEvents.call(from: from, to: to)
+
+        endpoint
+          .report(request.to_xml, url: calendar_url, depth: 1)
+          .xpath(".//dav:response")
+          .collect { |node| Event.from_xml(node) }
+      end
+
+      private
+
+      attr_reader :client, :endpoint, :credentials
+
+      def merged_url(calendar_url, event_identifier)
+        if calendar_url.end_with?("/")
+          "#{calendar_url}#{event_identifier}"
+        else
+          "#{calendar_url}/#{event_identifier}"
+        end
+      end
+    end
+  end
+end

lib/calendav/contextual_url.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Calendav
+  class ContextualURL
+    def self.call(credentials, url_or_path)
+      return credentials.host.to_s if url_or_path.nil? || url_or_path.empty?
+
+      if url_or_path.start_with?("/")
+        credentials.host.dup.tap { |new_url| new_url.path = url_or_path }.to_s
+      else
+        URI(url_or_path).to_s
+      end
+    end
+  end
+end

lib/calendav/credentials/apple.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "http"
+require "uri"
+
+require_relative "./standard"
+
+module Calendav
+  module Credentials
+    class Apple < Standard
+      def initialize(username:, password:)
+        super(
+          host: "https://caldav.icloud.com",
+          username: username,
+          password: password
+        )
+      end
+    end
+  end
+end

lib/calendav/credentials/fastmail.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "http"
+require "uri"
+
+require_relative "./standard"
+
+module Calendav
+  module Credentials
+    class FastMail < Standard
+      def initialize(username:, password:)
+        super(
+          host: "https://caldav.fastmail.com/dav/",
+          username: username,
+          password: password
+        )
+      end
+    end
+  end
+end

lib/calendav/credentials/google.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require "http"
+require "uri"
+
+require_relative "./standard"
+
+module Calendav
+  module Credentials
+    class Google < Standard
+      def initialize(username:, password:)
+        super(
+          host: "https://apidata.googleusercontent.com/caldav/v2/",
+          username: username,
+          password: password,
+          authentication: :bearer_token
+        )
+      end
+    end
+  end
+end

lib/calendav/credentials/standard.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require "uri"
+
+module Calendav
+  module Credentials
+    class Standard
+      attr_reader :host, :username, :password, :authentication
+
+      def initialize(host:, username:, password:, authentication: :basic_auth)
+        @host = URI(host)
+        @username = username
+        @password = password
+        @authentication = authentication
+      end
+    end
+  end
+end

lib/calendav/endpoint.rb

@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+
+require_relative "./contextual_url"
+require_relative "./xml_processor"
+
+module Calendav
+  class Endpoint
+    CONTENT_TYPES = {
+      ics: "text/calendar",
+      xml: "application/xml; charset=utf-8"
+    }.freeze
+
+    RequestFailedError = Class.new(StandardError)
+
+    def initialize(credentials)
+      @credentials = credentials
+    end
+
+    def delete(url:)
+      request(:delete, url: url).status.success?
+    end
+
+    def mkcalendar(body, url:)
+      request(
+        :mkcalendar,
+        body,
+        url: url,
+        http: with_headers(content_type: :xml)
+      )
+    end
+
+    def propfind(body, url: nil, depth: 0)
+      request(
+        :propfind,
+        body,
+        url: url,
+        http: with_headers(depth: depth, content_type: :xml)
+      )
+    end
+
+    def put(body, url:, content_type: nil)
+      request(
+        :put,
+        body,
+        url: url,
+        http: with_headers(content_type: content_type)
+      )
+    end
+
+    def report(body, url: nil, depth: 0)
+      request(
+        :report,
+        body,
+        url: url,
+        http: with_headers(depth: depth, content_type: :xml)
+      )
+    end
+
+    private
+
+    attr_reader :credentials
+
+    def authenticated
+      case credentials.authentication
+      when :basic_auth
+        HTTP.basic_auth(user: credentials.username, pass: credentials.password)
+      when :bearer_token
+        HTTP.auth("Bearer #{credentials.password}")
+      else
+        raise "Unexpected authentication approach: " \
+          "#{credentials.authentication}"
+      end
+    end
+
+    def with_headers(content_type: nil, depth: nil)
+      http = authenticated
+
+      http = http.headers(depth: depth) if depth
+      if content_type
+        http = http.headers("Content-Type" => CONTENT_TYPES[content_type])
+      end
+
+      http
+    end
+
+    def request(verb, body = nil, url:, http: with_headers)
+      response = http.request(
+        verb, ContextualURL.call(credentials, url), body: body
+      )
+      unless response.status.success?
+        raise RequestFailedError, response.status.to_s
+      end
+
+      return response if response.content_length&.zero?
+
+      XMLProcessor.call(response.body)
+    end
+  end
+end

lib/calendav/event.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require_relative "./xml_processor"
+
+module Calendav
+  class Event
+    attr_reader :path
+
+    def self.from_xml(node)
+      new(
+        node.xpath("./dav:href").text,
+        node.xpath(".//dav:prop/*").to_xml,
+        node.namespaces
+      )
+    end
+
+    def initialize(path, attribute_nodes, namespaces = {})
+      @path = path
+      @attribute_nodes = attribute_nodes
+      @namespaces = namespaces
+    end
+
+    def calendar_data
+      attribute_value fragment.xpath("//caldav:calendar-data")
+    end
+
+    def etag
+      attribute_value fragment.xpath("//dav:getetag")
+    end
+
+    def summary
+      inner_event.summary
+    end
+
+    private
+
+    attr_reader :attribute_nodes, :namespaces
+
+    def fragment
+      @fragment ||= XMLProcessor.call(
+        "<nodes>#{attribute_nodes}</nodes>", namespaces
+      )
+    end
+
+    def attribute_value(node)
+      return nil if node.children.empty?
+
+      if node.children.any?(&:element?)
+        node.children.select(&:element?).collect(&:to_xml).join
+      else
+        node.children.text
+      end
+    end
+
+    def inner_calendar
+      Icalendar::Calendar.parse(calendar_data).first
+    end
+
+    def inner_event
+      @inner_event = inner_calendar.events.first
+    end
+  end
+end

lib/calendav/requests/calendar_home_set.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
+require_relative "../xml_processor"
+
+module Calendav
+  module Requests
+    class CalendarHomeSet
+      def self.call(...)
+        new(...).call
+      end
+
+      def call
+        Nokogiri::XML::Builder.new do |xml|
+          xml["dav"].propfind(XMLProcessor::NAMESPACES) do
+            xml["dav"].prop do
+              xml["caldav"].public_send(:"calendar-home-set")
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/calendav/requests/current_user_principal.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
+require_relative "../xml_processor"
+
+module Calendav
+  module Requests
+    class CurrentUserPrincipal
+      def self.call(...)
+        new(...).call
+      end
+
+      def call
+        Nokogiri::XML::Builder.new do |xml|
+          xml["dav"].propfind(XMLProcessor::NAMESPACES) do
+            xml["dav"].prop do
+              xml["dav"].public_send(:"current-user-principal")
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/calendav/requests/list_calendars.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
+require_relative "../xml_processor"
+
+module Calendav
+  module Requests
+    class ListCalendars
+      def self.call(...)
+        new(...).call
+      end
+
+      def call
+        Nokogiri::XML::Builder.new do |xml|
+          xml["dav"].propfind(XMLProcessor::NAMESPACES) do
+            xml["dav"].prop do
+              xml["dav"].displayname
+              xml["dav"].resourcetype
+              xml["dav"].getetag
+              xml["cs"].getctag
+              xml["apple"].public_send(:"calendar-color")
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/calendav/requests/list_events.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
+require_relative "../xml_processor"
+
+module Calendav
+  module Requests
+    class ListEvents
+      def self.call(...)
+        new(...).call
+      end
+
+      def initialize(from:, to:)
+        @from = from
+        @to = to
+      end
+
+      def call
+        Nokogiri::XML::Builder.new do |xml|
+          xml["caldav"].public_send(
+            "calendar-query", XMLProcessor::NAMESPACES
+          ) do
+            xml["dav"].prop do
+              xml["dav"].getetag
+              xml["caldav"].public_send(:"calendar-data")
+            end
+            xml["caldav"].filter do
+              xml["caldav"].public_send(:"comp-filter", name: "VCALENDAR") do
+                xml["caldav"].public_send(:"comp-filter", name: "VEVENT") do
+                  xml["caldav"].public_send(
+                    :"time-range",
+                    start: from.utc.iso8601.delete(":-"),
+                    end: to.utc.iso8601.delete(":-")
+                  )
+                end
+              end
+            end
+          end
+        end
+      end
+
+      private
+
+      attr_reader :from, :to
+    end
+  end
+end

lib/calendav/requests/make_calendar.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require "nokogiri"
+
+require_relative "../xml_processor"
+
+module Calendav
+  module Requests
+    class MakeCalendar
+      def self.call(...)
+        new(...).call
+      end
+
+      def initialize(attributes)
+        @attributes = attributes
+      end
+
+      def call
+        Nokogiri::XML::Builder.new do |xml|
+          xml["caldav"].propfind(XMLProcessor::NAMESPACES) do
+            xml["dav"].set do
+              xml["dav"].prop do
+                xml["dav"].displayname display_name
+
+                if description
+                  xml["caldav"].public_send(
+                    :"calendar-description", description
+                  )
+                end
+
+                if time_zone
+                  xml["caldav"].public_send(:"calendar-timezone", time_zone)
+                end
+
+                xml["caldav"].public_send(
+                  :"supported-calendar-component-set"
+                ) do
+                  xml["caldav"].comp name: "VEVENT"
+                end
+              end
+            end
+          end
+        end
+      end
+
+      private
+
+      attr_reader :attributes
+
+      def display_name
+        attributes[:display_name]
+      end
+
+      def description
+        attributes[:description]
+      end
+
+      def time_zone
+        attributes[:time_zone]
+      end
+    end
+  end
+end

lib/calendav/xml_processor.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Calendav
+  class XMLProcessor
+    NAMESPACES = {
+      "xmlns:dav" => "DAV:",
+      "xmlns:caldav" => "urn:ietf:params:xml:ns:caldav",
+      "xmlns:cs" => "http://calendarserver.org/ns/",
+      "xmlns:apple" => "http://apple.com/ns/ical/"
+    }.freeze
+
+    def self.call(...)
+      new(...).call
+    end
+
+    def initialize(raw, namespaces = NAMESPACES)
+      @raw = raw
+      @namespaces = namespaces
+    end
+
+    def call
+      document = parse(raw)
+
+      namespaces.each do |key, value|
+        document.root[key] = value unless document.namespaces[key]
+      end
+
+      parse(document.to_xml)
+    end
+
+    private
+
+    attr_reader :raw, :namespaces
+
+    def parse(string)
+      Nokogiri::XML(string) { |config| config.strict.noblanks }
+    rescue Nokogiri::XML::SyntaxError
+      puts string
+      raise
+    end
+  end
+end

spec/acceptance/google_spec.rb

@@ -0,0 +1,94 @@
+# frozen_string_literal: true
+
+require "googleauth"
+require "icalendar"
+require "uri"
+
+RSpec.describe "Google" do
+  let(:provider) { :google }
+  let(:username) { ENV.fetch("GOOGLE_USERNAME") }
+  let(:access_token) { @access_token }
+  let(:credentials) { Calendav.credentials(provider, username, access_token) }
+
+  subject { Calendav.client(credentials) }
+
+  before :context do
+    @access_token = begin
+      credentials = Google::Auth::UserRefreshCredentials.new(
+        client_id: ENV.fetch("GOOGLE_CLIENT_ID"),
+        scope: [],
+        client_secret: ENV.fetch("GOOGLE_CLIENT_SECRET"),
+        refresh_token: ENV.fetch("GOOGLE_REFRESH_TOKEN"),
+        additional_parameters: { "access_type" => "offline" }
+      )
+      credentials.fetch_access_token!
+      credentials.access_token
+    end
+  end
+
+  it "determines the user's principal URL" do
+    expect(subject.principal_url)
+      .to eq("https://apidata.googleusercontent.com/caldav/v2/#{URI.encode_www_form_component(username)}/user")
+  end
+
+  it "determines the user's calendar URL" do
+    expect(subject.calendars.home_url)
+      .to eq("https://apidata.googleusercontent.com/caldav/v2/#{URI.encode_www_form_component(username)}/")
+  end
+
+  it "can create and delete calendars" do
+    skip "Not supported by Google"
+    url = subject.calendars.create(
+      display_name: "Calendav Test"
+    )
+
+    subject.calendars.delete(url)
+  end
+
+  it "can find calendars" do
+    calendars = subject.calendars.list
+
+    expect(calendars.collect(&:display_name)).to include("Calendav Test")
+  end
+
+  context "with a calendar" do
+    let(:calendars) { subject.calendars.list }
+    let(:calendar_url) do
+      calendars.detect { |cal| cal.display_name == "Calendav Test" }&.path ||
+        subject.calendars.create(display_name: "Calendav Test")
+    end
+    let(:identifier) { "#{SecureRandom.uuid}.ics" }
+    let(:start) { Time.new 2021, 6, 1, 10, 30 }
+    let(:finish) { Time.new 2021, 6, 1, 12, 30 }
+
+    after :each do
+      next if calendars.detect { |cal| cal.display_name == "Calendav Test" }
+
+      subject.calendars.delete(calendar_url)
+    end
+
+    it "can create, find and delete events" do
+      ics = Icalendar::Calendar.new
+      ics.event do |event|
+        event.dtstart = start
+        event.dtend = finish
+        event.summary = "Brunch"
+      end
+      ics.publish
+
+      # Create an event
+      event_url = subject.events.create(calendar_url, identifier, ics.to_ical)
+      expect(event_url).to include(URI.decode_www_form_component(calendar_url))
+
+      # Search for the event
+      events = subject.events.list(
+        calendar_url, from: Time.new(2021, 6, 1), to: Time.new(2021, 6, 2)
+      )
+      expect(events.length).to eq(1)
+      expect(events.first.summary).to eq("Brunch")
+
+      # Delete the event
+      expect(subject.events.delete(event_url)).to eq(true)
+    end
+  end
+end

spec/spec_helper.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "calendav"
+require "dotenv"
+
+Dotenv.load
+
+RSpec.configure do |config|
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end