module Rscons
  class Environment
    # Values:
    #  :none - do not print anything
    #  :short - rscons will print a short representation of the step
    #           being performed
    #  :command (default) - print the full command being executed
    attr_accessor :echo

    # Hash of Builder Name => Builder Class
    attr_reader :builders

    def initialize(options = {})
      @echo = :command
      @variables = options.reject { |key, val| not key[0] =~ /[A-Z]/ }
      @builders = {}
      @build_dirs = {}
      unless @variables[:omit_default_builders]
        DEFAULT_BUILDERS.each do |builder_class|
          add_builder(builder_class)
        end
      end
      @echo = options[:echo] if options[:echo]
    end

    def add_builder(builder_class)
      @builders[builder_class.to_s.split(':').last] = builder_class
      var_defs = builder_class.default_variables(self)
      if var_defs
        var_defs.each_pair do |var, val|
          unless @variables.has_key?(var)
            @variables[var] = val
          end
        end
      end
    end

    def [](key)
      @variables[key]
    end

    def []=(key, val)
      @variables[key] = val
    end

    def build_dir(src_dir, build_dir)
      @build_dirs[src_dir] = build_dir
    end

    def execute(short_desc, command, extra_vars)
      merged_variables = @variables.merge(extra_vars)
      expand_varref = proc do |varref|
        if varref.is_a?(Array)
          varref.map do |ent|
            expand_varref.call(ent)
          end
        else
          if varref =~ /^(.*)\$\[(\w+)\](.*)$/
            # expand array with given prefix, suffix
            prefix, varname, suffix = $1, $2, $3
            varval = merged_variables[varname]
            unless varval.is_a?(Array)
              raise "Array expected for $#{varname}"
            end
            varval.map {|e| "#{prefix}#{e}#{suffix}"}
          elsif varref[0] == '$'
            # expand a single variable reference
            varname = varref[1, varref.size]
            varval = merged_variables[varname]
            if varval
              expand_varref.call(varval)
            else
              raise "Could not find variable #{varname.inspect}"
            end
          else
            varref
          end
        end
      end
      command = expand_varref.call(command.flatten).flatten
      if @echo == :command
        puts command.join(' ')
      elsif @echo == :short
        puts short_desc
      end
      system(*command)
    end

    def stem(fname)
      fname.sub(/\.[^.]*$/, '')
    end

    alias_method :orig_method_missing, :method_missing

    def method_missing(method, *args)
      if @builders.has_key?(method.to_s)
        # TODO: build sources if necessary
        builder = @builders[method.to_s].new
        builder.run(self, *args)
      else
        orig_method_missing(method, *args)
      end
    end
  end
end