require 'sprockets'

module Jax
  class Shader < Sprockets::DirectiveProcessor
    def self.default_mime_type
      "application/javascript"
    end

    def exports
      @exports ||= {}
    end
    
    def process_require_directive(path)
      super

      # FIXME this is kind of a hacky solution to get function bodies included.
      # Should shaders be rewritten entirely, including the JS APIs?
      shader_name, shader_type = shader_type_and_name_for_path(path)
        
      str = "<%= Jax.import_shader_code(#{shader_name.inspect}, #{shader_type.inspect}) %>\n"
      body.insert 0, str unless body[str]
    end
    
    def evaluate(context, locals, &block)
      body = super
      body = process_exports(body)
      
      shader_name, shader_type = shader_type_and_name_for_path
      
      result = "Jax.shader_data(#{shader_name.inspect})[#{shader_type.inspect}] = #{body.inspect};\n"
      unless exports.empty?
        exports_var = "Jax.shader_data(#{shader_name.inspect})[\"exports\"]"
        exports_str   = "#{exports_var} = #{exports_var} || {};\n"
        exports.each do |name, type|
          exports_str+= "#{exports_var}[#{name.inspect}] = #{type.inspect};\n"
        end
        result.insert 0, exports_str
      end
      result
    end
    
    def process_exports(body, rx = nil)
      if rx
        body.scan(rx).uniq.each do |export|
          # scan gets us mostly there, but we still need the arguments.
          export =~ rx
          type  = $~[1]
          name  = $~[2]
          value = $~[3]
          exports[name] = type
          # we may use type later, when we start actively generating the export code.
          # Currently, that's done in JS.
        end
        body
      else
        process_exports_without_assignment(process_exports_with_assignment(body))
      end
    end
    
    def process_exports_without_assignment(body)
      process_exports body, /export\s*\(\s*([^\s]*),\s*([^\s]*)\s*\);?/
    end
    
    def process_exports_with_assignment(body)
      process_exports body, /export\s*\(\s*([^\s]*),\s*([^\s]*),\s*([^\)]*)\);?/
    end
    
    def shader_type_and_name_for_path(path = nil)
      if path.nil?
        logical_path = context.logical_path
      else
        logical_path = context.environment.attributes_for(context.resolve path).logical_path
      end
      shader_name = File.basename(File.dirname(logical_path))
      shader_type = File.basename(logical_path)
      if (shader_type =~ /\.[^\.]+$/)
        shader_type = $`
      end
      
      [shader_name, shader_type]
    end
  end
end