require 'ostruct'
require 'yaml'

# A Rack middleware application that creates a single configuration for Helix Web
# Services.
#
# Most web services are modular Sinatra applications, which does come with it's
# own settings mechanism. We should try to avoid those settings in most cases.
# Perhaps only if those settings are only relevant to the logic directly
# within the Sinatra app.
#
# Many other settings, like the port setting of the associated Helix Versioning
# Engine, should be exposed and overridable by the client application. These
# settings should be defined here.
#
# This class provides middleware that will inject an `hws_settings` object into
# each request. This `hws_settings` object is seeded by values declared on this
# class. When the system starts, our system config file is read in, and default
# system values are overridden. On any request, these settings can be
# overridden by the user.
#
# Additionally, there are "system" settings that are only overridable from the
# system config file. Client classes should reference this class directly:
# HWSSettings.system.
#
# ## Naming Conventions
#
# Use uppercase letters, numbers, or underscores only.
#
# ## HTTP Header Override Syntax
#
# We allow per-request overrides of settings via HTTP headers.
#
# The key format of the custom setting is:
#
# `X-PERFORCE-HELIX_WEB_SERVICES-{key}`
#
# For example:
#
#     X-PERFORCE-HELIX_WEB_SERVICES-P4HOST: perforce.mycompany.com
#     X-PERFORCE-HELIX_WEB_SERVICES-P4CHARSET: auto
#
# Please note that headers will be converted by Rack to all uppercase, hence
# our naming conventions.
#
# ## System Config File
#
# The system configuration is stored in the
# `/etc/perforce/helix_web_services.conf` file. This is a YAML
# file, and we override any locally defined variables with values found in
# this file. ()If you specify a value in this file we do not locally define,
# we ignore it.)
#
# Example values in /etc/perforce/helix_web_services.conf:
#
#     P4HOST: 'perforce.mycompany.com'
#     P4PORT: '9991'
#
#
class HWSSettings
  SYSTEM_CONFIG_PATH = '/etc/perforce/helix_web_services.conf'

  @settings = OpenStruct.new(
      # The .git-fusion depot name
      :GIT_FUSION_DEPOT => '.git-fusion',
      # If set, the HVEProjects class will use this path to locate projects
      # in the system.
      :HVE_PROJECTS_PATH => nil,
      # The current API level used to interact with the Perforce server
      :P4APILEVEL => '78',
      # The hostname of the p4d (Helix Versioning Engine) instance
      :P4HOST => nil,
      # The port of the p4d (Helix Versioning Engine) instance
      :P4PORT => '1666',
      # The charset setting to use when connecting to the p4d instance
      :P4CHARSET => 'auto'
  )

  @system = OpenStruct.new(
      # Allow the indicated commands to be used in the
      # /helix_verdsioning_engine/v1/commands methods
      # Each entry is either a string (the command name) or an Array of command
      # and required arguments.
      :COMMAND_WHITELIST => ['info', ['files', '-m']],
      # Set this to true to use helix cloud as the authentication source.
      :ENABLE_HELIX_CLOUD_AUTH => false,
      # Enable Helix Cloud project helpers.
      :ENABLE_HELIX_CLOUD_PROJECTS => false,
      # The local file location that defines where services are located
      :SERVICE_CONFIGURATION => '/etc/perforce/services.json',
      # Use this working directory for temporary workspaces (typically for making submits)
      :WORKSPACE_DIR => '/var/lib/perforce/helix_web_services/workspaces'
  )

  class << self

    # Returns baseline settings with system overrides applied.
    #
    # This is a copy of state. If you want to alter the default settings in
    # code instead of via config files, use the `settings_handle`
    def settings
      s = OpenStruct.new(@settings)
      s.each_pair do |key, _|
        if overrides.respond_to?(key)
          s[key] = overrides[key]
        end
      end
      s
    end

    # You can tweak the default settings directly here in code.
    def settings_handle
      @settings
    end

    # Returns our system settings overridden by local configuration in overrides.
    #
    # This is a *copy* of the class system settings, suitable for editing and
    # passing on.
    #
    # See the official guide for declared options.
    def system
      s = OpenStruct.new(@system)
      s.each_pair do |key, _|
        if overrides.respond_to?(key)
          s[key] = overrides[key]
        end
      end
      s
    end

    # In case your code wants to edit the system classes directly. Typically
    # used for test initialization.
    def system_handle
      @system
    end

    # Return the system overrides in our system configuration file.
    def overrides
      return @overrides ||= init_overrides
    end

    private

    def init_overrides
      if File.exists?(SYSTEM_CONFIG_PATH)
        OpenStruct.new(YAML.load_file(SYSTEM_CONFIG_PATH))
      end
    end
  end

  def initialize(app)
    @app = app
  end

  def call(env)
    hws_settings = self.class.settings

    env.each do |key, value|
      match = /^HTTP_X_PERFORCE_HELIX_WEB_SERVICES_(.*)$/.match(key)
      if match
        hws_settings[match[1]] = value
      end
    end

    env['hws_settings'] = hws_settings

    @app.call(env)
  end
end