# -*- encoding : utf-8 -*-
module MustacheRender
  class Mustache
    # A ContextMiss is raised whenever a tag's target can not be found
    # in the current context if `Mustache#raise_on_context_miss?` is
    # set to true.
    #
    # For example, if your View class does not respond to `music` but
    # your template contains a `{{music}}` tag this exception will be raised.
    #
    # By default it is not raised. See Mustache.raise_on_context_miss.
    class ContextMiss < RuntimeError;  end

    # A Context represents the context which a Mustache template is
    # executed within. All Mustache tags reference keys in the Context.
    class Context
      # Expect to be passed an instance of `Mustache`.
      def initialize(mustache)
        @stack = [mustache]
      end

      # A {{>partial}} tag translates into a call to the context's
      # `partial` method, which would be this sucker right here.
      #
      # If the Mustache view handling the rendering (e.g. the view
      # representing your profile page or some other template) responds
      # to `partial`, we call it and render the result.
      def partial(name, indentation = '')
        # Look for the first Mustache in the stack.
        mustache = mustache_in_stack

        # Indent the partial template by the given indentation.
        part = mustache.partial(name).to_s.gsub(/^/, indentation)

        # Call the Mustache's `partial` method and render the result.
        result = mustache.render(part, self)
      end

      # Find the first Mustache in the stack. If we're being rendered
      # inside a Mustache object as a context, we'll use that one.
      def mustache_in_stack
        @stack.detect { |frame| frame.is_a?(Mustache) }
      end

      # Allows customization of how Mustache escapes things.
      #
      # Returns a String.
      def escapeHTML(str)
        mustache_in_stack.escapeHTML(str)
      end

      # Adds a new object to the context's internal stack.
      #
      # Returns the Context.
      def push(new)
        @stack.unshift(new)
        self
      end
      alias_method :update, :push

      # Removes the most recently added object from the context's
      # internal stack.
      #
      # Returns the Context.
      def pop
        @stack.shift
        self
      end

      # Can be used to add a value to the context in a hash-like way.
      #
      # context[:name] = "Chris"
      def []=(name, value)
        push(name => value)
      end

      # Alias for `fetch`.
      def [](name)
        fetch(name, nil)
      end

      # Do we know about a particular key? In other words, will calling
      # `context[key]` give us a result that was set. Basically.
      def has_key?(key)
        !!fetch(key)
      rescue ContextMiss
        false
      end

      # Similar to Hash#fetch, finds a value by `name` in the context's
      # stack. You may specify the default return value by passing a
      # second parameter.
      #
      # If no second parameter is passed (or raise_on_context_miss is
      # set to true), will raise a ContextMiss exception on miss.
      def fetch(name, default = :__raise)
        @stack.each do |frame|
          # Prevent infinite recursion.
          next if frame == self

          value = find(frame, name, :__missing)
          if value != :__missing
            return value
          end
        end

        if default == :__raise || MustacheRender.config.raise_on_context_miss?
          raise ContextMiss.new("Can't find #{name} in #{@stack.inspect}")
        else
          default
        end
      end

      # Finds a key in an object, using whatever method is most
      # appropriate. If the object is a hash, does a simple hash lookup.
      # If it's an object that responds to the key as a method call,
      # invokes that method. You get the idea.
      #
      #     obj - The object to perform the lookup on.
      #     key - The key whose value you want.
      # default - An optional default value, to return if the
      #           key is not found.
      #
      # Returns the value of key in obj if it is found and default otherwise.
      def find(obj, key, default = nil)
        hash = obj.respond_to?(:has_key?)

        if hash && obj.has_key?(key)
          obj[key]
        elsif hash && obj.has_key?(key.to_s)
          obj[key.to_s]
        elsif !hash && obj.respond_to?(key)
          meth = obj.method(key) rescue proc { obj.send(key) }
          if meth.arity == 1
            meth.to_proc
          else
            meth[]
          end
        else
          default
        end
      end
    end
  end
end