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|
//! The retained tree: nodes, props, children, and the event queue jolt polls.
//!
//! This is the same shape `crates/jolt-vidya/src/tree.rs` holds and
//! `crates/jolt-tui` holds again — a tree the caller mutates between frames and
//! a painter walks during one. Nothing here knows what paints it.
const std = @import("std");
const Allocator = std.mem.Allocator;
/// A prop value. The three types jolt's FFI vocabulary can carry.
pub const Value = union(enum) {
str: []u8,
num: f64,
boolean: bool,
};
/// One queued event, drained by `poll`.
pub const Event = struct {
node: u32,
/// Static: `click`, `change`, `toggled`, `activate`.
name: []const u8,
text: []u8,
num: f64,
};
pub const Node = struct {
tag: []u8 = &.{},
props: std.StringHashMapUnmanaged(Value) = .empty,
children: std.ArrayList(u32) = .empty,
parent: u32 = 0,
alive: bool = false,
/// Bumped every time this slot is handed out again. Widget identity is
/// `(generation, index)` rather than the index alone, so a node freed and
/// reallocated in the same frame does not inherit the widget state of the
/// node that used to live here — which is the bug class the reconciler
/// notes in frq's deps.edn describe from the other side.
generation: u32 = 0,
/// Persistent edit buffer for `entry` nodes, kept across frames because a
/// text field owns its contents between the caller's writes.
entry: ?std.ArrayList(u8) = null,
/// Whether `entry` has been seeded from the `text` prop yet.
entry_seeded: bool = false,
};
pub const Tree = struct {
gpa: Allocator,
/// Slot 0 is never handed out — 0 is how this ABI spells "no node", the
/// same way `vidya_node_new` answers 0 on failure.
nodes: std.ArrayList(Node) = .empty,
free: std.ArrayList(u32) = .empty,
events: std.ArrayList(Event) = .empty,
/// Read position in `events`; the queue compacts when it drains.
head: usize = 0,
current: ?Event = null,
pub fn init(gpa: Allocator) !Tree {
var self: Tree = .{ .gpa = gpa };
// Slot 0: the null node. Slot 1: the root, which is never freed.
try self.nodes.append(gpa, .{});
const root_id = try self.alloc("window");
std.debug.assert(root_id == 1);
return self;
}
pub fn deinit(self: *Tree) void {
for (self.nodes.items) |*n| self.release(n);
self.nodes.deinit(self.gpa);
self.free.deinit(self.gpa);
for (self.events.items) |e| self.gpa.free(e.text);
self.events.deinit(self.gpa);
if (self.current) |e| self.gpa.free(e.text);
self.current = null;
}
fn release(self: *Tree, n: *Node) void {
if (n.tag.len != 0) self.gpa.free(n.tag);
n.tag = &.{};
self.clearProps(n);
n.props.deinit(self.gpa);
n.props = .empty;
n.children.deinit(self.gpa);
n.children = .empty;
if (n.entry) |*buf| buf.deinit(self.gpa);
n.entry = null;
n.entry_seeded = false;
}
fn clearProps(self: *Tree, n: *Node) void {
var it = n.props.iterator();
while (it.next()) |kv| {
self.gpa.free(kv.key_ptr.*);
if (kv.value_ptr.* == .str) self.gpa.free(kv.value_ptr.str);
}
n.props.clearRetainingCapacity();
}
pub fn root(self: *Tree) u32 {
_ = self;
return 1;
}
pub fn get(self: *Tree, id: u32) ?*Node {
if (id == 0 or id >= self.nodes.items.len) return null;
const n = &self.nodes.items[id];
return if (n.alive) n else null;
}
fn alloc(self: *Tree, tag: []const u8) !u32 {
const owned = try self.gpa.dupe(u8, tag);
errdefer self.gpa.free(owned);
if (self.free.pop()) |id| {
const n = &self.nodes.items[id];
n.* = .{
.tag = owned,
.alive = true,
// Reuse never repeats an identity.
.generation = n.generation +% 1,
};
return id;
}
const id: u32 = @intCast(self.nodes.items.len);
try self.nodes.append(self.gpa, .{ .tag = owned, .alive = true });
return id;
}
pub fn new(self: *Tree, tag: []const u8) u32 {
return self.alloc(tag) catch 0;
}
/// Free a node and everything under it. Detaches from its parent first, so
/// a caller that frees a subtree still holds a consistent tree.
pub fn free_node(self: *Tree, id: u32) void {
if (id <= 1) return; // never free the null slot or the root
const n = self.get(id) orelse return;
const parent = n.parent;
if (self.get(parent)) |p| {
if (std.mem.indexOfScalar(u32, p.children.items, id)) |i| {
_ = p.children.orderedRemove(i);
}
}
self.freeSubtree(id);
}
fn freeSubtree(self: *Tree, id: u32) void {
const n = self.get(id) orelse return;
// Copy the child list: releasing the node frees the backing array.
const kids = self.gpa.dupe(u32, n.children.items) catch &.{};
defer if (kids.len != 0) self.gpa.free(kids);
for (kids) |c| self.freeSubtree(c);
const node = &self.nodes.items[id];
self.release(node);
node.alive = false;
node.parent = 0;
self.free.append(self.gpa, id) catch {};
}
/// The identity a painter keys widget state by: never repeated after reuse.
pub fn widgetId(self: *Tree, id: u32) usize {
const gen: usize = if (id < self.nodes.items.len) self.nodes.items[id].generation else 0;
return (gen << 32) | @as(usize, id);
}
// ── Props ───────────────────────────────────────────────────────────────
fn put(self: *Tree, n: *Node, key: []const u8, value: Value) !void {
const gop = try n.props.getOrPut(self.gpa, key);
if (gop.found_existing) {
if (gop.value_ptr.* == .str) self.gpa.free(gop.value_ptr.str);
} else {
gop.key_ptr.* = self.gpa.dupe(u8, key) catch |e| {
_ = n.props.remove(key);
return e;
};
}
gop.value_ptr.* = value;
}
pub fn setStr(self: *Tree, id: u32, key: []const u8, value: []const u8) void {
const n = self.get(id) orelse return;
const owned = self.gpa.dupe(u8, value) catch return;
self.put(n, key, .{ .str = owned }) catch self.gpa.free(owned);
// A caller writing `text` is authoritative over an entry's contents.
if (std.mem.eql(u8, key, "text")) n.entry_seeded = false;
}
pub fn setNum(self: *Tree, id: u32, key: []const u8, value: f64) void {
const n = self.get(id) orelse return;
self.put(n, key, .{ .num = value }) catch {};
}
pub fn setBool(self: *Tree, id: u32, key: []const u8, value: bool) void {
const n = self.get(id) orelse return;
self.put(n, key, .{ .boolean = value }) catch {};
}
pub fn clear(self: *Tree, id: u32) void {
const n = self.get(id) orelse return;
self.clearProps(n);
}
pub fn getStr(self: *Tree, id: u32, key: []const u8) []const u8 {
const n = self.get(id) orelse return "";
const v = n.props.get(key) orelse return "";
return switch (v) {
.str => |s| s,
else => "",
};
}
pub fn getNum(self: *Tree, id: u32, key: []const u8) f64 {
const n = self.get(id) orelse return 0;
const v = n.props.get(key) orelse return 0;
return switch (v) {
.num => |x| x,
.boolean => |b| if (b) 1 else 0,
.str => 0,
};
}
pub fn getBool(self: *Tree, id: u32, key: []const u8) bool {
const n = self.get(id) orelse return false;
const v = n.props.get(key) orelse return false;
return switch (v) {
.boolean => |b| b,
.num => |x| x != 0,
.str => |s| s.len != 0,
};
}
// ── Children ────────────────────────────────────────────────────────────
/// Detach `child` from whatever parent currently holds it.
fn detach(self: *Tree, child: u32) void {
const c = self.get(child) orelse return;
if (self.get(c.parent)) |p| {
if (std.mem.indexOfScalar(u32, p.children.items, child)) |i| {
_ = p.children.orderedRemove(i);
}
}
c.parent = 0;
}
/// True when `ancestor` is `node` or is above it — a cycle check, because
/// appending a node into its own subtree makes a walk that never returns.
fn contains(self: *Tree, ancestor: u32, node: u32) bool {
var walk = node;
var guard_count: usize = 0;
while (walk != 0) : (guard_count += 1) {
if (walk == ancestor) return true;
if (guard_count > self.nodes.items.len) return true; // already cyclic
const n = self.get(walk) orelse return false;
walk = n.parent;
}
return false;
}
pub fn append(self: *Tree, parent: u32, child: u32) bool {
if (parent == child) return false;
_ = self.get(child) orelse return false;
const p = self.get(parent) orelse return false;
if (self.contains(child, parent)) return false;
self.detach(child);
const pp = self.get(parent).?;
pp.children.append(self.gpa, child) catch return false;
self.get(child).?.parent = parent;
_ = p;
return true;
}
pub fn remove(self: *Tree, parent: u32, child: u32) void {
const p = self.get(parent) orelse return;
if (std.mem.indexOfScalar(u32, p.children.items, child)) |i| {
_ = p.children.orderedRemove(i);
if (self.get(child)) |c| c.parent = 0;
}
}
pub fn insertAfter(self: *Tree, parent: u32, child: u32, sibling: u32) bool {
if (parent == child) return false;
_ = self.get(child) orelse return false;
_ = self.get(parent) orelse return false;
if (self.contains(child, parent)) return false;
self.detach(child);
const p = self.get(parent).?;
// A sibling of 0, or one that is not here, means the front — which is
// what "insert after nothing" means to a reconciler walking a list.
const at: usize = if (sibling == 0)
0
else if (std.mem.indexOfScalar(u32, p.children.items, sibling)) |i|
i + 1
else
p.children.items.len;
p.children.insert(self.gpa, at, child) catch return false;
self.get(child).?.parent = parent;
return true;
}
pub fn replace(self: *Tree, parent: u32, old_child: u32, new_child: u32) bool {
if (old_child == new_child) return true;
_ = self.get(new_child) orelse return false;
const p = self.get(parent) orelse return false;
const at = std.mem.indexOfScalar(u32, p.children.items, old_child) orelse return false;
if (self.contains(new_child, parent)) return false;
self.detach(new_child);
const pp = self.get(parent).?;
// `detach` may have shifted the list if new_child was a sibling.
const idx = std.mem.indexOfScalar(u32, pp.children.items, old_child) orelse at;
pp.children.items[idx] = new_child;
self.get(new_child).?.parent = parent;
if (self.get(old_child)) |o| o.parent = 0;
return true;
}
pub fn childCount(self: *Tree, id: u32) u32 {
const n = self.get(id) orelse return 0;
return @intCast(n.children.items.len);
}
pub fn childAt(self: *Tree, id: u32, index: u32) u32 {
const n = self.get(id) orelse return 0;
if (index >= n.children.items.len) return 0;
return n.children.items[index];
}
// ── Events ──────────────────────────────────────────────────────────────
pub fn emit(self: *Tree, node: u32, name: []const u8, text: []const u8, num: f64) void {
const owned = self.gpa.dupe(u8, text) catch return;
self.events.append(self.gpa, .{
.node = node,
.name = name,
.text = owned,
.num = num,
}) catch self.gpa.free(owned);
}
/// Dequeue one event. True while there was one; the accessors below then
/// describe it until the next poll.
pub fn poll(self: *Tree) bool {
if (self.current) |e| {
self.gpa.free(e.text);
self.current = null;
}
if (self.head >= self.events.items.len) {
// Drained: reset rather than grow the backing array forever.
self.events.clearRetainingCapacity();
self.head = 0;
return false;
}
self.current = self.events.items[self.head];
self.head += 1;
return true;
}
// ── Debugging ───────────────────────────────────────────────────────────
pub fn dump(self: *Tree, id: u32, out: *std.ArrayList(u8), depth: usize) void {
const n = self.get(id) orelse return;
out.appendNTimes(self.gpa, ' ', depth * 2) catch return;
out.print(self.gpa, "<{s} #{d}", .{ n.tag, id }) catch return;
var it = n.props.iterator();
while (it.next()) |kv| {
switch (kv.value_ptr.*) {
.str => |s| out.print(self.gpa, " {s}=\"{s}\"", .{ kv.key_ptr.*, s }) catch return,
.num => |x| out.print(self.gpa, " {s}={d}", .{ kv.key_ptr.*, x }) catch return,
.boolean => |b| out.print(self.gpa, " {s}={}", .{ kv.key_ptr.*, b }) catch return,
}
}
out.appendSlice(self.gpa, ">\n") catch return;
const kids = self.gpa.dupe(u32, n.children.items) catch return;
defer self.gpa.free(kids);
for (kids) |c| self.dump(c, out, depth + 1);
}
};
// ── Tests ───────────────────────────────────────────────────────────────────
//
// The tree is the half worth testing without a window: everything here is what
// a reconciler does to it between frames.
const testing = std.testing;
fn childrenOf(t: *Tree, id: u32) []const u32 {
return (t.get(id) orelse unreachable).children.items;
}
test "root exists and is not freeable" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
try testing.expectEqual(@as(u32, 1), t.root());
t.free_node(t.root());
try testing.expect(t.get(t.root()) != null);
}
test "props round-trip and coerce" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const n = t.new("label");
t.setStr(n, "text", "hello");
t.setNum(n, "size", 12.5);
t.setBool(n, "active", true);
try testing.expectEqualStrings("hello", t.getStr(n, "text"));
try testing.expectEqual(@as(f64, 12.5), t.getNum(n, "size"));
try testing.expect(t.getBool(n, "active"));
// A bool reads as a number and a number as a bool; a missing prop is zero.
try testing.expectEqual(@as(f64, 1), t.getNum(n, "active"));
try testing.expectEqual(@as(f64, 0), t.getNum(n, "absent"));
try testing.expectEqualStrings("", t.getStr(n, "absent"));
// Overwriting a string frees the old one rather than leaking it.
t.setStr(n, "text", "goodbye");
try testing.expectEqualStrings("goodbye", t.getStr(n, "text"));
t.clear(n);
try testing.expectEqualStrings("", t.getStr(n, "text"));
}
test "append moves a child rather than duplicating it" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const a = t.new("box");
const b = t.new("box");
const c = t.new("label");
try testing.expect(t.append(t.root(), a));
try testing.expect(t.append(t.root(), b));
try testing.expect(t.append(a, c));
try testing.expectEqualSlices(u32, &.{c}, childrenOf(&t, a));
// Re-appending elsewhere detaches from the old parent.
try testing.expect(t.append(b, c));
try testing.expectEqualSlices(u32, &.{}, childrenOf(&t, a));
try testing.expectEqualSlices(u32, &.{c}, childrenOf(&t, b));
try testing.expectEqual(b, t.get(c).?.parent);
}
test "a node cannot be appended into its own subtree" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const a = t.new("box");
const b = t.new("box");
try testing.expect(t.append(t.root(), a));
try testing.expect(t.append(a, b));
// Both the direct cycle and the deeper one are refused; a walk that never
// returns is a hang in the painter, not an error the caller would see.
try testing.expect(!t.append(a, a));
try testing.expect(!t.append(b, a));
try testing.expectEqualSlices(u32, &.{b}, childrenOf(&t, a));
}
test "insert_after places by sibling, and 0 means the front" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const p = t.new("box");
_ = t.append(t.root(), p);
const a = t.new("label");
const b = t.new("label");
const c = t.new("label");
_ = t.append(p, a);
_ = t.append(p, b);
try testing.expect(t.insertAfter(p, c, a));
try testing.expectEqualSlices(u32, &.{ a, c, b }, childrenOf(&t, p));
const d = t.new("label");
try testing.expect(t.insertAfter(p, d, 0));
try testing.expectEqualSlices(u32, &.{ d, a, c, b }, childrenOf(&t, p));
}
test "replace keeps position, including when the new child is a sibling" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const p = t.new("box");
_ = t.append(t.root(), p);
const a = t.new("label");
const b = t.new("label");
const c = t.new("label");
_ = t.append(p, a);
_ = t.append(p, b);
_ = t.append(p, c);
// Replacing with a node already in the list must not leave it twice, and
// must not shift the slot out from under the index it was found at.
try testing.expect(t.replace(p, a, c));
try testing.expectEqualSlices(u32, &.{ c, b }, childrenOf(&t, p));
try testing.expectEqual(@as(u32, 0), t.get(a).?.parent);
}
test "free takes the subtree and detaches from the parent" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const p = t.new("box");
_ = t.append(t.root(), p);
const a = t.new("box");
const b = t.new("label");
_ = t.append(p, a);
_ = t.append(a, b);
t.free_node(a);
try testing.expect(t.get(a) == null);
try testing.expect(t.get(b) == null);
try testing.expectEqualSlices(u32, &.{}, childrenOf(&t, p));
}
test "a reused id is never the same widget identity" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const a = t.new("button");
_ = t.append(t.root(), a);
const first = t.widgetId(a);
t.free_node(a);
const b = t.new("button");
// The id comes back — that is the point of the free list — but the identity
// a painter keys widget state by must not, or the new node inherits the old
// one's cursor, scroll position and animation.
try testing.expectEqual(a, b);
try testing.expect(first != t.widgetId(b));
}
test "events queue in order and drain once" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const a = t.new("button");
t.emit(a, "click", "", 0);
t.emit(a, "change", "typed", 3);
try testing.expect(t.poll());
try testing.expectEqualStrings("click", t.current.?.name);
try testing.expect(t.poll());
try testing.expectEqualStrings("change", t.current.?.name);
try testing.expectEqualStrings("typed", t.current.?.text);
try testing.expectEqual(@as(f64, 3), t.current.?.num);
try testing.expect(!t.poll());
try testing.expect(t.current == null);
}
test "dump shows the shape" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
const l = t.new("label");
t.setStr(l, "text", "hi");
_ = t.append(t.root(), l);
var out: std.ArrayList(u8) = .empty;
defer out.deinit(testing.allocator);
t.dump(t.root(), &out, 0);
try testing.expectEqualStrings(
\\<window #1>
\\ <label #2 text="hi">
\\
, out.items);
}
test "a bad id is a miss, not an index" {
var t = try Tree.init(testing.allocator);
defer t.deinit();
try testing.expect(t.get(0) == null);
try testing.expect(t.get(9999) == null);
try testing.expectEqual(@as(u32, 0), t.childCount(9999));
try testing.expectEqual(@as(u32, 0), t.childAt(9999, 0));
try testing.expect(!t.append(9999, 1));
t.setStr(9999, "text", "ignored");
t.free_node(9999);
}
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