package cid

import (
	"context"
)

// Set is a implementation of a set of Cids, that is, a structure
// to which holds a single copy of every Cids that is added to it.
type Set struct {
	set map[string]struct{}
}

// NewSet initializes and returns a new Set.
func NewSet() *Set {
	return &Set{set: make(map[string]struct{})}
}

// Add puts a Cid in the Set.
func (s *Set) Add(c *Cid) {
	s.set[string(c.Bytes())] = struct{}{}
}

// Has returns if the Set contains a given Cid.
func (s *Set) Has(c *Cid) bool {
	_, ok := s.set[string(c.Bytes())]
	return ok
}

// Remove deletes a Cid from the Set.
func (s *Set) Remove(c *Cid) {
	delete(s.set, string(c.Bytes()))
}

// Len returns how many elements the Set has.
func (s *Set) Len() int {
	return len(s.set)
}

// Keys returns the Cids in the set.
func (s *Set) Keys() []*Cid {
	out := make([]*Cid, 0, len(s.set))
	for k := range s.set {
		c, _ := Cast([]byte(k))
		out = append(out, c)
	}
	return out
}

// Visit adds a Cid to the set only if it is
// not in it already.
func (s *Set) Visit(c *Cid) bool {
	if !s.Has(c) {
		s.Add(c)
		return true
	}

	return false
}

// ForEach allows to run a custom function on each
// Cid in the set.
func (s *Set) ForEach(f func(c *Cid) error) error {
	for cs := range s.set {
		c, _ := Cast([]byte(cs))
		err := f(c)
		if err != nil {
			return err
		}
	}
	return nil
}

// StreamingSet is an extension of Set which allows to implement back-pressure
// for the Visit function
type StreamingSet struct {
	Set *Set
	New chan *Cid
}

// NewStreamingSet initializes and returns new Set.
func NewStreamingSet() *StreamingSet {
	return &StreamingSet{
		Set: NewSet(),
		New: make(chan *Cid),
	}
}

// Visitor creates new visitor which adds a Cids to the set and emits them to
// the set.New channel
func (s *StreamingSet) Visitor(ctx context.Context) func(c *Cid) bool {
	return func(c *Cid) bool {
		if s.Set.Visit(c) {
			select {
			case s.New <- c:
			case <-ctx.Done():
			}
			return true
		}

		return false
	}
}