Update Go version and dependencies; add Angle method to Point type

go.mod

@@ -1,11 +1,11 @@
 module github.com/kelindar/tile
 
-go 1.24
+go 1.25
 
 require (
 	github.com/kelindar/intmap v1.5.0
 	github.com/kelindar/iostream v1.4.0
-	github.com/stretchr/testify v1.9.0
+	github.com/stretchr/testify v1.10.0
 )
 
 require (

go.sum

@@ -6,8 +6,8 @@ github.com/kelindar/iostream v1.4.0 h1:ELKlinnM/K3GbRp9pYhWuZOyBxMMlYAfsOP+gauvZ
 github.com/kelindar/iostream v1.4.0/go.mod h1:MkjMuVb6zGdPQVdwLnFRO0xOTOdDvBWTztFmjRDQkXk=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
-github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

point.go

@@ -5,10 +5,9 @@ package tile
 
 import (
 	"fmt"
+	"math"
 )
 
-const invalid = int16(-1 << 15)
-
 // -----------------------------------------------------------------------------
 
 // Point represents a 2D coordinate.
@@ -121,6 +120,22 @@ func (p Point) DistanceTo(other Point) uint32 {
 	return abs(int32(p.X)-int32(other.X)) + abs(int32(p.Y)-int32(other.Y))
 }
 
+// Angle calculates the angle between two points
+func (p Point) Angle(other Point) Direction {
+	dx := float64(other.X - p.X)
+	dy := float64(other.Y - p.Y)
+
+	// Calculate the angle in radians
+	angle := math.Atan2(dy, dx)
+	alpha := angle + math.Pi/2
+	if alpha < 0 {
+		alpha += 2 * math.Pi
+	}
+
+	// Map to 8 directions (0-7)
+	return Direction(math.Round(alpha/(math.Pi/4))) % 8
+}
+
 func abs(n int32) uint32 {
 	if n < 0 {
 		return uint32(-n)

point_test.go

@@ -73,6 +73,67 @@ func TestDirection_Empty(t *testing.T) {
 	assert.Empty(t, dir.String())
 }
 
+func TestPointAngle(t *testing.T) {
+	tests := []struct {
+		name     string
+		from     Point
+		to       Point
+		expected Direction
+	}{
+		// Cardinal directions from origin
+		{"North", At(0, 0), At(0, -1), North},
+		{"East", At(0, 0), At(1, 0), East},
+		{"South", At(0, 0), At(0, 1), South},
+		{"West", At(0, 0), At(-1, 0), West},
+
+		// Diagonal directions from origin
+		{"NorthEast", At(0, 0), At(1, -1), NorthEast},
+		{"SouthEast", At(0, 0), At(1, 1), SouthEast},
+		{"SouthWest", At(0, 0), At(-1, 1), SouthWest},
+		{"NorthWest", At(0, 0), At(-1, -1), NorthWest},
+
+		// Same point (math.Atan2(0,0) = 0, which maps to East after transformation)
+		{"Same point", At(5, 5), At(5, 5), East},
+
+		// Non-origin starting points
+		{"From 10,10 North", At(10, 10), At(10, 5), North},
+		{"From 10,10 East", At(10, 10), At(15, 10), East},
+		{"From 10,10 South", At(10, 10), At(10, 15), South},
+		{"From 10,10 West", At(10, 10), At(5, 10), West},
+		{"From 10,10 NorthEast", At(10, 10), At(15, 5), NorthEast},
+		{"From 10,10 SouthEast", At(10, 10), At(15, 15), SouthEast},
+		{"From 10,10 SouthWest", At(10, 10), At(5, 15), SouthWest},
+		{"From 10,10 NorthWest", At(10, 10), At(5, 5), NorthWest},
+
+		// Edge cases with larger distances
+		{"Far North", At(0, 0), At(0, -100), North},
+		{"Far East", At(0, 0), At(100, 0), East},
+		{"Far South", At(0, 0), At(0, 100), South},
+		{"Far West", At(0, 0), At(-100, 0), West},
+
+		// Angles close to boundaries (testing rounding)
+		{"Near North boundary", At(0, 0), At(1, -10), North},
+		{"Near NorthEast boundary", At(0, 0), At(10, -10), NorthEast},
+		{"Near East boundary", At(0, 0), At(10, -1), East},
+		{"Near SouthEast boundary", At(0, 0), At(10, 10), SouthEast},
+
+		// Negative coordinates
+		{"Negative coords North", At(-5, -5), At(-5, -10), North},
+		{"Negative coords East", At(-5, -5), At(0, -5), East},
+		{"Negative coords South", At(-5, -5), At(-5, 0), South},
+		{"Negative coords West", At(-5, -5), At(-10, -5), West},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := tc.from.Angle(tc.to)
+			assert.Equal(t, tc.expected, result,
+				"Point %s to %s should be %s, got %s",
+				tc.from.String(), tc.to.String(), tc.expected.String(), result.String())
+		})
+	}
+}
+
 func TestMove(t *testing.T) {
 	tests := []struct {
 		dir Direction