# frozen_string_literal: true

require 'tsort'

require_relative 'dependency_graph/log'
require_relative 'dependency_graph/vertex'

module Gem::Resolver::Molinillo
  # A directed acyclic graph that is tuned to hold named dependencies
  class DependencyGraph
    include Enumerable

    # Enumerates through the vertices of the graph.
    # @return [Array<Vertex>] The graph's vertices.
    def each
      return vertices.values.each unless block_given?
      vertices.values.each { |v| yield v }
    end

    include TSort

    # @!visibility private
    alias tsort_each_node each

    # @!visibility private
    def tsort_each_child(vertex, &block)
      vertex.successors.each(&block)
    end

    # Topologically sorts the given vertices.
    # @param [Enumerable<Vertex>] vertices the vertices to be sorted, which must
    #   all belong to the same graph.
    # @return [Array<Vertex>] The sorted vertices.
    def self.tsort(vertices)
      TSort.tsort(
        lambda { |b| vertices.each(&b) },
        lambda { |v, &b| (v.successors & vertices).each(&b) }
      )
    end

    # A directed edge of a {DependencyGraph}
    # @attr [Vertex] origin The origin of the directed edge
    # @attr [Vertex] destination The destination of the directed edge
    # @attr [Object] requirement The requirement the directed edge represents
    Edge = Struct.new(:origin, :destination, :requirement)

    # @return [{String => Vertex}] the vertices of the dependency graph, keyed
    #   by {Vertex#name}
    attr_reader :vertices

    # @return [Log] the op log for this graph
    attr_reader :log

    # Initializes an empty dependency graph
    def initialize
      @vertices = {}
      @log = Log.new
    end

    # Tags the current state of the dependency as the given tag
    # @param  [Object] tag an opaque tag for the current state of the graph
    # @return [Void]
    def tag(tag)
      log.tag(self, tag)
    end

    # Rewinds the graph to the state tagged as `tag`
    # @param  [Object] tag the tag to rewind to
    # @return [Void]
    def rewind_to(tag)
      log.rewind_to(self, tag)
    end

    # Initializes a copy of a {DependencyGraph}, ensuring that all {#vertices}
    # are properly copied.
    # @param [DependencyGraph] other the graph to copy.
    def initialize_copy(other)
      super
      @vertices = {}
      @log = other.log.dup
      traverse = lambda do |new_v, old_v|
        return if new_v.outgoing_edges.size == old_v.outgoing_edges.size
        old_v.outgoing_edges.each do |edge|
          destination = add_vertex(edge.destination.name, edge.destination.payload)
          add_edge_no_circular(new_v, destination, edge.requirement)
          traverse.call(destination, edge.destination)
        end
      end
      other.vertices.each do |name, vertex|
        new_vertex = add_vertex(name, vertex.payload, vertex.root?)
        new_vertex.explicit_requirements.replace(vertex.explicit_requirements)
        traverse.call(new_vertex, vertex)
      end
    end

    # @return [String] a string suitable for debugging
    def inspect
      "#{self.class}:#{vertices.values.inspect}"
    end

    # @param [Hash] options options for dot output.
    # @return [String] Returns a dot format representation of the graph
    def to_dot(options = {})
      edge_label = options.delete(:edge_label)
      raise ArgumentError, "Unknown options: #{options.keys}" unless options.empty?

      dot_vertices = []
      dot_edges = []
      vertices.each do |n, v|
        dot_vertices << "  #{n} [label=\"{#{n}|#{v.payload}}\"]"
        v.outgoing_edges.each do |e|
          label = edge_label ? edge_label.call(e) : e.requirement
          dot_edges << "  #{e.origin.name} -> #{e.destination.name} [label=#{label.to_s.dump}]"
        end
      end

      dot_vertices.uniq!
      dot_vertices.sort!
      dot_edges.uniq!
      dot_edges.sort!

      dot = dot_vertices.unshift('digraph G {').push('') + dot_edges.push('}')
      dot.join("\n")
    end

    # @param [DependencyGraph] other
    # @return [Boolean] whether the two dependency graphs are equal, determined
    #   by a recursive traversal of each {#root_vertices} and its
    #   {Vertex#successors}
    def ==(other)
      return false unless other
      return true if equal?(other)
      vertices.each do |name, vertex|
        other_vertex = other.vertex_named(name)
        return false unless other_vertex
        return false unless vertex.payload == other_vertex.payload
        return false unless other_vertex.successors.to_set == vertex.successors.to_set
      end
    end

    # @param [String] name
    # @param [Object] payload
    # @param [Array<String>] parent_names
    # @param [Object] requirement the requirement that is requiring the child
    # @return [void]
    def add_child_vertex(name, payload, parent_names, requirement)
      root = !parent_names.delete(nil) { true }
      vertex = add_vertex(name, payload, root)
      vertex.explicit_requirements << requirement if root
      parent_names.each do |parent_name|
        parent_vertex = vertex_named(parent_name)
        add_edge(parent_vertex, vertex, requirement)
      end
      vertex
    end

    # Adds a vertex with the given name, or updates the existing one.
    # @param [String] name
    # @param [Object] payload
    # @return [Vertex] the vertex that was added to `self`
    def add_vertex(name, payload, root = false)
      log.add_vertex(self, name, payload, root)
    end

    # Detaches the {#vertex_named} `name` {Vertex} from the graph, recursively
    # removing any non-root vertices that were orphaned in the process
    # @param [String] name
    # @return [Array<Vertex>] the vertices which have been detached
    def detach_vertex_named(name)
      log.detach_vertex_named(self, name)
    end

    # @param [String] name
    # @return [Vertex,nil] the vertex with the given name
    def vertex_named(name)
      vertices[name]
    end

    # @param [String] name
    # @return [Vertex,nil] the root vertex with the given name
    def root_vertex_named(name)
      vertex = vertex_named(name)
      vertex if vertex && vertex.root?
    end

    # Adds a new {Edge} to the dependency graph
    # @param [Vertex] origin
    # @param [Vertex] destination
    # @param [Object] requirement the requirement that this edge represents
    # @return [Edge] the added edge
    def add_edge(origin, destination, requirement)
      if destination.path_to?(origin)
        raise CircularDependencyError.new(path(destination, origin))
      end
      add_edge_no_circular(origin, destination, requirement)
    end

    # Deletes an {Edge} from the dependency graph
    # @param [Edge] edge
    # @return [Void]
    def delete_edge(edge)
      log.delete_edge(self, edge.origin.name, edge.destination.name, edge.requirement)
    end

    # Sets the payload of the vertex with the given name
    # @param [String] name the name of the vertex
    # @param [Object] payload the payload
    # @return [Void]
    def set_payload(name, payload)
      log.set_payload(self, name, payload)
    end

    private

    # Adds a new {Edge} to the dependency graph without checking for
    # circularity.
    # @param (see #add_edge)
    # @return (see #add_edge)
    def add_edge_no_circular(origin, destination, requirement)
      log.add_edge_no_circular(self, origin.name, destination.name, requirement)
    end

    # Returns the path between two vertices
    # @raise [ArgumentError] if there is no path between the vertices
    # @param [Vertex] from
    # @param [Vertex] to
    # @return [Array<Vertex>] the shortest path from `from` to `to`
    def path(from, to)
      distances = Hash.new(vertices.size + 1)
      distances[from.name] = 0
      predecessors = {}
      each do |vertex|
        vertex.successors.each do |successor|
          if distances[successor.name] > distances[vertex.name] + 1
            distances[successor.name] = distances[vertex.name] + 1
            predecessors[successor] = vertex
          end
        end
      end

      path = [to]
      while before = predecessors[to]
        path << before
        to = before
        break if to == from
      end

      unless path.last.equal?(from)
        raise ArgumentError, "There is no path from #{from.name} to #{to.name}"
      end

      path.reverse
    end
  end
end
