internal/priorityqueue: Actually just make our own priority queue

11 files changed, 118 insertions, 157 deletions

diff --git a/internal/heap/heap.go b/internal/heap/heap.go
deleted file mode 100644
index 7ad551ab..00000000
--- a/internal/heap/heap.go
+++ /dev/null
@@ -1,93 +0,0 @@
-package heap
-
-// Heap is one slice-backed binary heap.
-type Heap[T any] struct {
-	items []T
-	less  func(left, right T) bool
-}
-
-// New builds one empty heap ordered by less.
-func New[T any](less func(left, right T) bool) *Heap[T] {
-	return &Heap[T]{less: less}
-}
-
-// Len reports the number of queued items.
-func (heap *Heap[T]) Len() int {
-	return len(heap.items)
-}
-
-// Empty reports whether the heap is empty.
-func (heap *Heap[T]) Empty() bool {
-	return len(heap.items) == 0
-}
-
-// Peek returns the top item without removing it.
-func (heap *Heap[T]) Peek() (T, bool) {
-	if len(heap.items) == 0 {
-		var zero T
-
-		return zero, false
-	}
-
-	return heap.items[0], true
-}
-
-// Push inserts one item.
-func (heap *Heap[T]) Push(item T) {
-	heap.items = append(heap.items, item)
-	heap.siftUp(len(heap.items) - 1)
-}
-
-// Pop removes one top item.
-func (heap *Heap[T]) Pop() (T, bool) {
-	if len(heap.items) == 0 {
-		var zero T
-
-		return zero, false
-	}
-
-	last := len(heap.items) - 1
-	top := heap.items[0]
-	heap.items[0] = heap.items[last]
-	heap.items = heap.items[:last]
-
-	if len(heap.items) > 0 {
-		heap.siftDown(0)
-	}
-
-	return top, true
-}
-
-func (heap *Heap[T]) siftUp(idx int) {
-	for idx > 0 {
-		parent := (idx - 1) / 2
-		if !heap.less(heap.items[idx], heap.items[parent]) {
-			return
-		}
-
-		heap.items[idx], heap.items[parent] = heap.items[parent], heap.items[idx]
-		idx = parent
-	}
-}
-
-func (heap *Heap[T]) siftDown(idx int) {
-	for {
-		left := idx*2 + 1
-		if left >= len(heap.items) {
-			return
-		}
-
-		best := left
-		right := left + 1
-		if right < len(heap.items) && heap.less(heap.items[right], heap.items[left]) {
-			best = right
-		}
-
-		if !heap.less(heap.items[best], heap.items[idx]) {
-			return
-		}
-
-		heap.items[idx], heap.items[best] = heap.items[best], heap.items[idx]
-		idx = best
-	}
-}
diff --git a/internal/heap/heap_test.go b/internal/heap/heap_test.go
deleted file mode 100644
index 46795702..00000000
--- a/internal/heap/heap_test.go
+++ /dev/null
@@ -1,64 +0,0 @@
-package heap_test
-
-import (
-	"slices"
-	"testing"
-
-	internalheap "codeberg.org/lindenii/furgit/internal/heap"
-)
-
-func TestHeapAscending(t *testing.T) {
-	t.Parallel()
-
-	heap := internalheap.New(func(left, right int) bool {
-		return left < right
-	})
-
-	for _, value := range []int{5, 1, 4, 3, 2} {
-		heap.Push(value)
-	}
-
-	var got []int
-	for !heap.Empty() {
-		value, ok := heap.Pop()
-		if !ok {
-			t.Fatal("Pop should succeed")
-		}
-
-		got = append(got, value)
-	}
-
-	want := []int{1, 2, 3, 4, 5}
-	if !slices.Equal(got, want) {
-		t.Fatalf("pop order = %v, want %v", got, want)
-	}
-}
-
-func TestHeapPeek(t *testing.T) {
-	t.Parallel()
-
-	heap := internalheap.New(func(left, right int) bool {
-		return left > right
-	})
-
-	if _, ok := heap.Peek(); ok {
-		t.Fatal("Peek on empty heap should miss")
-	}
-
-	heap.Push(1)
-	heap.Push(3)
-	heap.Push(2)
-
-	value, ok := heap.Peek()
-	if !ok {
-		t.Fatal("Peek should succeed")
-	}
-
-	if value != 3 {
-		t.Fatalf("Peek = %d, want 3", value)
-	}
-
-	if heap.Len() != 3 {
-		t.Fatalf("Len after Peek = %d, want 3", heap.Len())
-	}
-}
diff --git a/internal/priorityqueue/len.go b/internal/priorityqueue/len.go
new file mode 100644
index 00000000..aca8e0ce
--- /dev/null
+++ b/internal/priorityqueue/len.go
@@ -0,0 +1,6 @@
+package priorityqueue
+
+// Len reports the number of queued items.
+func (queue *Queue[T]) Len() int {
+	return len(queue.items)
+}
diff --git a/internal/priorityqueue/new.go b/internal/priorityqueue/new.go
new file mode 100644
index 00000000..bf1c1819
--- /dev/null
+++ b/internal/priorityqueue/new.go
@@ -0,0 +1,6 @@
+package priorityqueue
+
+// New builds one empty priority queue ordered by less.
+func New[T any](less func(left, right T) bool) *Queue[T] {
+	return &Queue[T]{less: less}
+}
diff --git a/internal/priorityqueue/pop.go b/internal/priorityqueue/pop.go
new file mode 100644
index 00000000..2190b065
--- /dev/null
+++ b/internal/priorityqueue/pop.go
@@ -0,0 +1,21 @@
+package priorityqueue
+
+// Pop removes one highest-priority item.
+func (queue *Queue[T]) Pop() (T, bool) {
+	if len(queue.items) == 0 {
+		var zero T
+
+		return zero, false
+	}
+
+	last := len(queue.items) - 1
+	top := queue.items[0]
+	queue.items[0] = queue.items[last]
+	queue.items = queue.items[:last]
+
+	if len(queue.items) > 0 {
+		queue.siftDown(0)
+	}
+
+	return top, true
+}
diff --git a/internal/priorityqueue/push.go b/internal/priorityqueue/push.go
new file mode 100644
index 00000000..d0c6cadd
--- /dev/null
+++ b/internal/priorityqueue/push.go
@@ -0,0 +1,7 @@
+package priorityqueue
+
+// Push inserts one item.
+func (queue *Queue[T]) Push(item T) {
+	queue.items = append(queue.items, item)
+	queue.siftUp(len(queue.items) - 1)
+}
diff --git a/internal/priorityqueue/queue b/internal/priorityqueue/queue
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/internal/priorityqueue/queue
diff --git a/internal/priorityqueue/queue.go b/internal/priorityqueue/queue.go
new file mode 100644
index 00000000..279a400f
--- /dev/null
+++ b/internal/priorityqueue/queue.go
@@ -0,0 +1,7 @@
+package priorityqueue
+
+// Queue is one slice-backed priority queue.
+type Queue[T any] struct {
+	items []T
+	less  func(left, right T) bool
+}
diff --git a/internal/priorityqueue/queue_test.go b/internal/priorityqueue/queue_test.go
new file mode 100644
index 00000000..acb4f3e8
--- /dev/null
+++ b/internal/priorityqueue/queue_test.go
@@ -0,0 +1,35 @@
+package priorityqueue_test
+
+import (
+	"slices"
+	"testing"
+
+	"codeberg.org/lindenii/furgit/internal/priorityqueue"
+)
+
+func TestQueueAscending(t *testing.T) {
+	t.Parallel()
+
+	queue := priorityqueue.New(func(left, right int) bool {
+		return left < right
+	})
+
+	for _, value := range []int{5, 1, 4, 3, 2} {
+		queue.Push(value)
+	}
+
+	var got []int
+	for queue.Len() > 0 {
+		value, ok := queue.Pop()
+		if !ok {
+			t.Fatal("Pop should succeed")
+		}
+
+		got = append(got, value)
+	}
+
+	want := []int{1, 2, 3, 4, 5}
+	if !slices.Equal(got, want) {
+		t.Fatalf("pop order = %v, want %v", got, want)
+	}
+}
diff --git a/internal/priorityqueue/sift_down.go b/internal/priorityqueue/sift_down.go
new file mode 100644
index 00000000..83e3fd40
--- /dev/null
+++ b/internal/priorityqueue/sift_down.go
@@ -0,0 +1,23 @@
+package priorityqueue
+
+func (queue *Queue[T]) siftDown(idx int) {
+	for {
+		left := idx*2 + 1
+		if left >= len(queue.items) {
+			return
+		}
+
+		best := left
+		right := left + 1
+		if right < len(queue.items) && queue.less(queue.items[right], queue.items[left]) {
+			best = right
+		}
+
+		if !queue.less(queue.items[best], queue.items[idx]) {
+			return
+		}
+
+		queue.items[idx], queue.items[best] = queue.items[best], queue.items[idx]
+		idx = best
+	}
+}
diff --git a/internal/priorityqueue/sift_up.go b/internal/priorityqueue/sift_up.go
new file mode 100644
index 00000000..7ff4453f
--- /dev/null
+++ b/internal/priorityqueue/sift_up.go
@@ -0,0 +1,13 @@
+package priorityqueue
+
+func (queue *Queue[T]) siftUp(idx int) {
+	for idx > 0 {
+		parent := (idx - 1) / 2
+		if !queue.less(queue.items[idx], queue.items[parent]) {
+			return
+		}
+
+		queue.items[idx], queue.items[parent] = queue.items[parent], queue.items[idx]
+		idx = parent
+	}
+}