rewrite and simplification

pkg/pagerank/pagerank.go

@@ -0,0 +1,49 @@
+package pagerank
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"github/pippellia-btc/crawler/pkg/graph"
+)
+
+var ErrEmptyWalkStore = errors.New("the walk store is empty")
+
+type VisitCounter interface {
+	// TotalVisits returns the total number of visits, which is the sum of the lengths of all walks.
+	TotalVisits(ctx context.Context) (int, error)
+
+	// Visits returns the number of times each specified node was visited during the walks.
+	// The returned slice contains counts in the same order as the input nodes.
+	Visits(ctx context.Context, nodes ...graph.ID) ([]int, error)
+}
+
+// Global computes the global pagerank score for the specified nodes.
+// If a node is not found, its pagerank is assumed to be 0.
+func Global(ctx context.Context, count VisitCounter, nodes ...graph.ID) ([]float64, error) {
+	if len(nodes) == 0 {
+		return nil, nil
+	}
+
+	total, err := count.TotalVisits(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("Global: failed to get the visits total: %w", err)
+	}
+
+	if total == 0 {
+		return nil, ErrEmptyWalkStore
+	}
+
+	visits, err := count.Visits(ctx, nodes...)
+	if err != nil {
+		return nil, fmt.Errorf("Global: failed to get the nodes visits: %w", err)
+	}
+
+	pageranks := make([]float64, len(visits))
+	for i, v := range visits {
+		pageranks[i] = float64(v) / float64(total)
+
+	}
+
+	return pageranks, nil
+}

pkg/pagerank/utils.go

@@ -0,0 +1,91 @@
+package pagerank
+
+import (
+	"context"
+	"github/pippellia-btc/crawler/pkg/graph"
+	"github/pippellia-btc/crawler/pkg/walks"
+	"math"
+	"strconv"
+)
+
+type WalkStore struct {
+	nextID int
+	Walks  map[walks.ID]walks.Walk
+}
+
+func NewWalkStore() *WalkStore {
+	return &WalkStore{
+		Walks: make(map[walks.ID]walks.Walk, 1000),
+	}
+}
+
+// AddWalks adds walks with sequentials IDs
+func (s *WalkStore) AddWalks(w []walks.Walk) {
+	for _, walk := range w {
+		ID := walks.ID(strconv.Itoa(s.nextID))
+		s.nextID++
+
+		walk.ID = ID
+		s.Walks[ID] = walk
+	}
+}
+
+// ReplaceWalks reassigns the ID --> walk
+func (s *WalkStore) ReplaceWalks(w []walks.Walk) {
+	for _, walk := range w {
+		s.Walks[walk.ID] = walk
+	}
+}
+
+func (s *WalkStore) WalksVisiting(node graph.ID) []walks.Walk {
+	visiting := make([]walks.Walk, 0, walks.N)
+	for _, walk := range s.Walks {
+		if walk.Visits(node) {
+			visiting = append(visiting, walk)
+		}
+	}
+
+	return visiting
+}
+
+func (s *WalkStore) TotalVisits(ctx context.Context) (int, error) {
+	total := 0
+	for _, walk := range s.Walks {
+		total += walk.Len()
+	}
+	return total, nil
+}
+
+func (s *WalkStore) Visits(ctx context.Context, nodes ...graph.ID) ([]int, error) {
+	if len(nodes) == 0 {
+		return nil, nil
+	}
+
+	count := make(map[graph.ID]int, len(nodes))
+	for _, walk := range s.Walks {
+		for _, node := range walk.Path {
+			count[node]++
+		}
+	}
+
+	visits := make([]int, len(nodes))
+	for i, node := range nodes {
+		visits[i] = count[node]
+	}
+
+	return visits, nil
+}
+
+// Distance returns the L1 distance between two lists of ranks.
+func Distance(r1, r2 []float64) float64 {
+	if len(r1) != len(r2) {
+		return math.MaxFloat64
+	}
+
+	var dist float64 = 0
+	for i := range r1 {
+		dist += math.Abs(r1[i] - r2[i])
+	}
+
+	return dist
+}