package main

import (
  "log"
  "sync"
  "github.com/google/uuid"
  "time"
)

// Generate a random graphql id
func randid() string{
  uuid_str := uuid.New().String()
  return uuid_str
}

type GraphSignal interface {
  Source() GraphNode
  Type() string
  Description() string
  Time() time.Time
  Last() string
  Trace(id string) GraphSignal
}

type BaseSignal struct {
  source GraphNode
  signal_type string
  description string
  time time.Time
  last_id string
}

func (signal BaseSignal) Time() time.Time {
  return signal.time
}

func (signal BaseSignal) Source() GraphNode {
  return signal.source
}

func (signal BaseSignal) Type() string {
  return signal.signal_type
}

func (signal BaseSignal) Description() string {
  return signal.description
}

func (signal BaseSignal) Trace(id string) GraphSignal {
  new_signal := signal
  new_signal.last_id = id
  return new_signal
}

func (signal BaseSignal) Last() string {
  return signal.last_id
}

func NewSignal(source GraphNode, signal_type string) (BaseSignal) {
  signal := BaseSignal{
    source: source,
    signal_type: signal_type,
  }
  return signal
}

// GraphNode is the interface common to both DAG nodes and Event tree nodes
type GraphNode interface {
  Name() string
  Description() string
  ID() string
  UpdateListeners(update GraphSignal)
  update(update GraphSignal)
  RegisterChannel(listener chan GraphSignal)
  UnregisterChannel(listener chan GraphSignal)
  UpdateChannel() chan GraphSignal
}

// BaseNode is the most basic implementation of the GraphNode interface
// It is used to implement functions common to Events and Resources
type BaseNode struct {
  name string
  description string
  id string
  signal chan GraphSignal
  listeners_lock sync.Mutex
  listeners map[chan GraphSignal]chan GraphSignal
}

func (node * BaseNode) Name() string {
  return node.name
}

func (node * BaseNode) Description() string {
  return node.description
}

func (node * BaseNode) ID() string {
  return node.id
}

// Create a new listener channel for the node, add it to the nodes listener list, and return the new channel
const listener_buffer = 100
func (node * BaseNode) UpdateChannel() chan GraphSignal {
  new_listener := make(chan GraphSignal, listener_buffer)
  node.RegisterChannel(new_listener)
  return new_listener
}

func (node * BaseNode) RegisterChannel(listener chan GraphSignal) {
  node.listeners_lock.Lock()
  _, exists := node.listeners[listener]
  if exists == false {
    node.listeners[listener] = listener
  }
  node.listeners_lock.Unlock()
}

func (node * BaseNode) UnregisterChannel(listener chan GraphSignal) {
  node.listeners_lock.Lock()
  _, exists := node.listeners[listener]
  if exists == false {
    panic("Attempting to unregister non-registered listener")
  } else {
    delete(node.listeners, listener)
  }
  node.listeners_lock.Unlock()
}

// Send the update to listener channels
func (node * BaseNode) UpdateListeners(update GraphSignal) {
  node.listeners_lock.Lock()

  closed := []chan GraphSignal{}

  for _, listener := range node.listeners {
    log.Printf("UPDATE_LISTENER %s: %p", node.Name(), listener)
    select {
    case listener <- update:
    default:
      close(listener)
      closed = append(closed, listener)
    }
  }

  for _, listener := range(closed) {
    delete(node.listeners, listener)
  }

  node.listeners_lock.Unlock()
}

func (node * BaseNode) update(signal GraphSignal) {
}

func SendUpdate(node GraphNode, signal GraphSignal) {
  if signal.Source() != nil {
    log.Printf("UPDATE %s -> %s: %+v", signal.Source().Name(), node.Name(), signal)
  } else {
    log.Printf("UPDATE %s: %+v", node.Name(), signal)

  }
  node.UpdateListeners(signal)
  node.update(signal)
}