require 'digest'

require_relative 'artefact_engine.rb'

require_relative 'context.rb'

module Comfpile
    class Core
        attr_reader :processing_stack

        def initialize(build_dir_path: File.join('/tmp/comfpile/', Digest::MD5.hexdigest(Dir.pwd)))
            @build_dir_path = File.expand_path(build_dir_path)

            @artefact_engines = []
            @artefact_prio_counter = 0

            # Artefacts are arranged in a double-hash.
            # First query is stage, second filename.
            @artefacts = {}

            # Stack-style processing queue for item processing
            @processing_stack = []

            @context_key_provider = ContextKeyProvider.new()
        end

        def get_context_key(key)
            return @context_key_provider.provide_context(key)
        end

        def find_artefact(stage, file = :none, context = :default)
            context = get_context_key(context)

            @artefacts.dig(context, stage, file)
        end

        # Create or find a new artefact.
        #
        # This will first see if a given artefact matching
        # the stage and target descriptions already exists, and
        # will return it, if found. Otherwise it will 
        # consult all given artefact crafting engines to
        # see if a new artefact can be created, which will be returned.
        #
        # If no artefact can be made, nil is returned
        #
        # @param [Symbol, String] stage State that shall be created (e.g. :parsed, :compiled, etc.)
        # @param [String] file File or other target that shall be looked at (e.g. "main.cpp")
        #
        # @return [Comfpile::Artefact, nil] Found or created artefact, or nil if nothing could be done
        #
        def craft_artefact(stage, file = :none, context = :default)
            context = get_context_key(context)

            artefact = find_artefact(stage, file, context)

            return artefact unless artefact.nil?

            @artefact_engines.each do |engine|
                artefact = engine.craft stage, file, context
                
                if artefact
                    @artefacts[context] ||= {}
                    @artefacts[context][stage] ||= {}
                    @artefacts[context][stage][file] = artefact
                    
                    @processing_stack.push artefact

                    return artefact
                end
            end

            nil
        end

        def add_artefact(stage, file = :none, context = :default, engine: nil, artefact_class: Comfpile::Artefact)
            context = get_context_key context

            return unless find_artefact(stage, file, context).nil?

            a = Artefact.new(self, engine, stage, file, context);
            
            @artefacts[context] ||= {}
            @artefacts[context][stage] ||= {}
            @artefacts[context][stage][file] = a

            yield(a) if block_given?

            nil
        end

        # @yieldparam [Comfpile::ArtefactEngine] Engine that was newly created
        def add_artefact_engine(engine_class = Comfpile::ArtefactEngine, **options)

            new_engine = if(engine_class.is_a? Comfpile::ArtefactEngine)
                engine_class
            else
                engine = engine_class.new(self,
                    subpriority: @artefact_prio_counter, **options)
                @artefact_prio_counter += 1

                engine
            end

            yield(new_engine) if block_given?

            @artefact_engines << new_engine
            @artefact_engines.sort!

            new_engine
        end

        def processing_stack_prune()
            loop do
                return if @processing_stack.empty?

                if @processing_stack[-1].completed?
                    @processing_stack.pop
                else
                    break
                end
            end

            nil
        end

        def processing_stack_find_next()
            return nil if @processing_stack.empty?

            i = 0
            @processing_stack.reverse_each do |a|
                i += 1
                if a.waiting?
                    # puts "DBG - Found item after #{i} checks"
                    return a 
                end
            end

            # TODO: Fix up later-on for parallel runner capabilities
            raise "Deadlock found, no item was willing to run!"

            nil
        end

        def get_context_build_dir_path(context)
            context = context.context if context.is_a? Artefact

            File.expand_path(File.join(@build_dir_path, context.to_s))
        end

        def execute_step
            return if @processing_stack.empty?
            # puts "Got #{@processing_stack.length} items..."

            processing_stack_prune
            
            artefact = processing_stack_find_next

            return nil if artefact.nil?

            # puts "Processing artefact #{artefact.stage} #{artefact.target}"

            build_path = get_context_build_dir_path(artefact)
            FileUtils.mkpath build_path

            Dir.chdir build_path do
                begin
                    artefact.execute_step
                rescue ArtefactExecSkipError
                end
            end

            nil
        end

        def execute_all
            step_count = 0

            until @processing_stack.empty?
                execute_step()
                step_count += 1
            end

            puts "Done after #{step_count} exec loops..."
        end

        def craft_and_complete(stage, target)
            artefact = craft_artefact(stage, target)

            return nil if artefact.nil?

            while artefact.in_progress?
                execute_step
            end

            artefact
        end
    end
end