require "json"
require "solve/graph"

module Solve

  Problem = Struct.new(:graph, :demands)

  # Simple struct class that contains a #graph and #demands (in Array form)
  #
  # Can be serialized via Solver::Serializer to create a json representation of
  # a dependency solving problem.
  class Problem

    # Create a Problem from a given Solver.
    #
    # @param [Solve::GecodeSolver,Solve::RubySolver] dependency solver
    # @return [Problem]
    def self.from_solver(solver)
      demands_data = solver.demands.map do |demand|
        [ demand.name, demand.constraint.to_s ]
      end
      new(solver.graph, demands_data)
    end
  end

  class Solver
    class Serializer
      # @param [Solve::Problem] problem struct
      #
      # @return [String]
      def serialize(problem)
        graph = problem.graph
        demands = problem.demands

        graph_hash = format_graph(graph)
        demands_hash = format_demands(demands)

        problem_data = graph_hash.merge(demands_hash)
        problem_data.to_json
      end

      # @param [Hash, #to_s] solver a json string or a hash representing a solver
      #
      # @return [Solve::Problem]
      def deserialize(problem_data)
        unless problem_data.is_a?(Hash)
          problem_data = JSON.parse(problem_data.to_s)
        end

        graph_spec = problem_data["graph"]
        demands_spec = problem_data["demands"]

        graph = load_graph(graph_spec)
        demands = load_demands(demands_spec)

        Solve::Problem.new(graph, demands)
      end

      private

      def format_graph(graph)
        artifacts = graph.artifacts.inject([]) do |list, artifact|
          list << format_artifact(artifact)
        end
        { "graph" => artifacts }
      end

      def format_artifact(artifact)
        dependencies = artifact.dependencies.inject([]) do |list, dependency|
          list << format_dependency(dependency)
        end

        {
          "name" => artifact.name,
          "version" => artifact.version.to_s,
          "dependencies" => dependencies,
        }
      end

      def format_dependency(dependency)
        {
          "name" => dependency.name,
          "constraint" => dependency.constraint.to_s,
        }
      end

      def format_demands(demands)
        demands_list = demands.inject([]) do |list, demand|
          list << format_demand(demand)
        end
        { "demands" => demands_list }
      end

      def format_demand(demand)
        {
          "name" => demand[0],
          "constraint" => demand[1],
        }
      end

      def load_graph(artifacts_list)
        graph = Solve::Graph.new
        artifacts_list.each do |artifact_spec|
          load_artifact(graph, artifact_spec)
        end
        graph
      end

      def load_artifact(graph, artifact_spec)
        artifact = graph.artifact(artifact_spec["name"], artifact_spec["version"])
        artifact_spec["dependencies"].each do |dependency_spec|
          load_dependency(artifact, dependency_spec)
        end
        artifact
      end

      def load_dependency(artifact, dependency_spec)
        artifact.depends(dependency_spec["name"], dependency_spec["constraint"])
      end

      def load_demands(demand_specs)
        demand_specs.inject([]) do |list, demand_spec|
          list << [demand_spec["name"], demand_spec["constraint"]]
        end
      end
    end
  end
end