// Package gg implements ginger graph creation, traversal, and (de)serialization
package gg

// Value represents a value being stored in a Graph. Exactly one field must be
// non-nil.
type Value struct {
	Name   *string
	Number *int64
	Graph  *Graph

	// TODO coming soon!
	// String *string
}

// Equal returns true if the passed in Value is equivalent.
func (v Value) Equal(v2 Value) bool {
	switch {

	case v.Name != nil && v2.Name != nil && *v.Name == *v2.Name:
		return true

	case v.Number != nil && v2.Number != nil && *v.Number == *v2.Number:
		return true

	case v.Graph != nil && v2.Graph != nil && Equal(v.Graph, v2.Graph):
		return true

	default:
		return false
	}
}

// VertexType enumerates the different possible vertex types.
type VertexType string

const (
	// ValueVertex is a Vertex which contains exactly one value and has at least
	// one edge (either input or output).
	ValueVertex VertexType = "value"

	// TupleVertex is a Vertex which contains two or more in edges and
	// exactly one out edge
	//
	// TODO ^ what about 0 or 1 in edges?
	TupleVertex VertexType = "tuple"
)

////////////////////////////////////////////////////////////////////////////////

// OpenEdge is an un-realized Edge which can't be used for anything except
// constructing graphs. It has no meaning on its own.
type OpenEdge struct {
	fromV vertex
	val   Value
}

// ValueOut creates a OpenEdge which, when used to construct a Graph, represents
// an edge (with edgeVal attached to it) coming from the ValueVertex containing
// val.
//
// When constructing Graphs, Value vertices are de-duplicated on their Value. So
// multiple ValueOut OpenEdges constructed with the same val will be leaving the
// same Vertex instance in the constructed Graph.
func ValueOut(val, edgeVal Value) OpenEdge {
	return OpenEdge{fromV: mkVertex(ValueVertex, val), val: edgeVal}
}

// TupleOut creates an OpenEdge which, when used to construct a Graph,
// represents an edge (with edgeVal attached to it) coming from the
// TupleVertex comprised of the given ordered-set of input edges.
//
// When constructing Graphs Tuple vertices are de-duplicated on their input
// edges. So multiple Tuple OpenEdges constructed with the same set of input
// edges will be leaving the same Tuple instance in the constructed Graph.
func TupleOut(ins []OpenEdge, edgeVal Value) OpenEdge {
	return OpenEdge{
		fromV: mkVertex(TupleVertex, Value{}, ins...),
		val:   edgeVal,
	}
}

func (oe OpenEdge) equal(oe2 OpenEdge) bool {
	return oe.val.Equal(oe2.val) && oe.fromV.equal(oe2.fromV)
}

type vertex struct {
	VertexType
	val Value
	tup []OpenEdge
}

func mkVertex(typ VertexType, val Value, tupIns ...OpenEdge) vertex {
	return vertex{
		VertexType: typ,
		val:        val,
		tup:        tupIns,
	}
}

func (v vertex) equal(v2 vertex) bool {

	if v.VertexType != v2.VertexType {
		return false
	}

	if v.VertexType == ValueVertex {
		return v.val.Equal(v2.val)
	}

	if len(v.tup) != len(v2.tup) {
		return false
	}

	for i := range v.tup {
		if !v.tup[i].equal(v2.tup[i]) {
			return false
		}
	}

	return true
}

type graphValueIn struct {
	val   Value
	edges []OpenEdge
}

func (valIn graphValueIn) cp() graphValueIn {
	cp := valIn
	cp.edges = make([]OpenEdge, len(valIn.edges))
	copy(cp.edges, valIn.edges)
	return valIn
}

func (valIn graphValueIn) equal(valIn2 graphValueIn) bool {
	if !valIn.val.Equal(valIn2.val) {
		return false
	}

	if len(valIn.edges) != len(valIn2.edges) {
		return false
	}

outer:
	for _, edge := range valIn.edges {

		for _, edge2 := range valIn2.edges {

			if edge.equal(edge2) {
				continue outer
			}
		}

		return false
	}

	return true
}

// Graph is an immutable container of a set of vertices. The Graph keeps track
// of all Values which terminate an OpenEdge (which may be a tree of Value/Tuple
// vertices).
//
// NOTE The current implementation of Graph is incredibly inefficient, there's
// lots of O(N) operations, unnecessary copying on changes, and duplicate data
// in memory.
type Graph struct {
	valIns []graphValueIn
}

// ZeroGraph is the root empty graph, and is the base off which all graphs are
// built.
var ZeroGraph = &Graph{}

func (g *Graph) cp() *Graph {
	cp := &Graph{
		valIns: make([]graphValueIn, len(g.valIns)),
	}
	copy(cp.valIns, g.valIns)
	return cp
}

////////////////////////////////////////////////////////////////////////////////
// Graph creation

func (g *Graph) valIn(val Value) graphValueIn {
	for _, valIn := range g.valIns {
		if valIn.val.Equal(val) {
			return valIn
		}
	}

	return graphValueIn{val: val}
}

// AddValueIn takes a OpenEdge and connects it to the Value Vertex containing
// val, returning the new Graph which reflects that connection. Any Vertices
// referenced within toe OpenEdge which do not yet exist in the Graph will also
// be created in this step.
func (g *Graph) AddValueIn(oe OpenEdge, val Value) *Graph {

	valIn := g.valIn(val)

	for _, existingOE := range valIn.edges {
		if existingOE.equal(oe) {
			return g
		}
	}

	valIn = valIn.cp()
	valIn.edges = append(valIn.edges, oe)

	g = g.cp()

	for i, existingValIn := range g.valIns {
		if existingValIn.val.Equal(val) {
			g.valIns[i] = valIn
			return g
		}
	}

	g.valIns = append(g.valIns, valIn)
	return g
}

// Equal returns whether or not the two Graphs are equivalent in value.
func Equal(g1, g2 *Graph) bool {

	if len(g1.valIns) != len(g2.valIns) {
		return false
	}

outer:
	for _, valIn1 := range g1.valIns {

		for _, valIn2 := range g2.valIns {

			if valIn1.equal(valIn2) {
				continue outer
			}
		}

		return false
	}

	return true
}