Add CellSet type and related boilerplate functions and tests (#2)

* Add cellset type and related boilerplate functions and tests

* Improve error as suggested

Co-authored-by: Copilot <[email protected]>

* Fix typo introduced by Copilot

---------

Co-authored-by: Copilot <[email protected]>

pkg/h3/cell_set.go

@@ -0,0 +1,57 @@
+package h3
+
+import "fmt"
+
+// CellSet represents a set of H3 cells.
+type CellSet map[Cell]struct{}
+
+// NewCellSetFromStrings creates a new cell set from a list of hex-encoded strings.
+func NewCellSetFromStrings(ss []string) (CellSet, error) {
+	cs := make(CellSet, len(ss))
+	for _, s := range ss {
+		c, err := NewCellFromString(s)
+		if err != nil {
+			return nil, fmt.Errorf("error converting string %s to cell: %w", s, err)
+		}
+		cs[c] = struct{}{}
+	}
+	return cs, nil
+}
+
+// NewCellSetFromCells creates a new cell set from a list of cells.
+func NewCellSetFromCells(cells []Cell) CellSet {
+	cs := make(CellSet, len(cells))
+	for _, c := range cells {
+		cs[c] = struct{}{}
+	}
+	return cs
+}
+
+// Cells returns the cells in the set as a list.
+func (cs CellSet) Cells() []Cell {
+	cells := make([]Cell, 0, len(cs))
+	for c := range cs {
+		cells = append(cells, c)
+	}
+	return cells
+}
+
+// Strings returns the cells in the set as a list of hex-encoded strings.
+func (cs CellSet) Strings() []string {
+	ss := make([]string, 0, len(cs))
+	for c := range cs {
+		ss = append(ss, c.String())
+	}
+	return ss
+}
+
+// Contains returns whether the set contains the given cell.
+func (cs CellSet) Contains(c Cell) bool {
+	_, ok := cs[c]
+	return ok
+}
+
+// Add adds a cell to the set.
+func (cs CellSet) Add(c Cell) {
+	cs[c] = struct{}{}
+}

pkg/h3/cell_set_test.go

@@ -0,0 +1,88 @@
+package h3
+
+import (
+	"testing"
+)
+
+func TestNewCellSetFromStrings(t *testing.T) {
+	strs := []string{"8f283473fffffff", "872830829fffffff"}
+	cs, err := NewCellSetFromStrings(strs)
+	if err != nil {
+		t.Fatalf("NewCellSetFromStrings() error = %v", err)
+	}
+	if len(cs) != len(strs) {
+		t.Errorf("NewCellSetFromStrings() = %v, want %v", len(cs), len(strs))
+	}
+	for _, s := range strs {
+		c, _ := NewCellFromString(s)
+		if !cs.Contains(c) {
+			t.Errorf("NewCellSetFromStrings() missing cell %v", c)
+		}
+	}
+}
+
+func TestNewCellSetFromCells(t *testing.T) {
+	cells := []Cell{0x8f283473fffffff, 0x872830829fffffff}
+	cs := NewCellSetFromCells(cells)
+	if len(cs) != len(cells) {
+		t.Errorf("NewCellSetFromCells() = %v, want %v", len(cs), len(cells))
+	}
+	for _, c := range cells {
+		if !cs.Contains(c) {
+			t.Errorf("NewCellSetFromCells() missing cell %v", c)
+		}
+	}
+}
+
+func TestCellSet_Contains(t *testing.T) {
+	cs := CellSet{0x8f283473fffffff: {}, 0x872830829fffffff: {}}
+	tests := []struct {
+		cell Cell
+		want bool
+	}{
+		{0x8f283473fffffff, true},
+		{0x872830829fffffff, true},
+		{0x8f2834740000000, false},
+	}
+	for _, tt := range tests {
+		if got := cs.Contains(tt.cell); got != tt.want {
+			t.Errorf("Contains() = %v, want %v", got, tt.want)
+		}
+	}
+}
+
+func TestCellSet_Add(t *testing.T) {
+	cs := CellSet{}
+	cell := Cell(0x8f283473fffffff)
+	cs.Add(cell)
+	if !cs.Contains(cell) {
+		t.Errorf("Add() did not add cell %v", cell)
+	}
+}
+
+func TestCellSet_Cells(t *testing.T) {
+	cs := CellSet{0x8f283473fffffff: {}, 0x872830829fffffff: {}}
+	cells := cs.Cells()
+	if len(cells) != len(cs) {
+		t.Errorf("Cells() = %v, want %v", len(cells), len(cs))
+	}
+	for _, c := range cells {
+		if !cs.Contains(c) {
+			t.Errorf("Cells() missing cell %v", c)
+		}
+	}
+}
+
+func TestCellSet_Strings(t *testing.T) {
+	cs := CellSet{0x8f283473fffffff: {}, 0x872830829fffffff: {}}
+	strs := cs.Strings()
+	if len(strs) != len(cs) {
+		t.Errorf("Strings() = %v, want %v", len(strs), len(cs))
+	}
+	for _, s := range strs {
+		c, _ := NewCellFromString(s)
+		if !cs.Contains(c) {
+			t.Errorf("Strings() missing cell %v", c)
+		}
+	}
+}