ona/src/coral/tree.zig

const coral = @import("./coral.zig");

const std = @import("std");

pub fn Binary(comptime Key: type, comptime Value: type, comptime traits: Traits(Key)) type {
    return struct {
        free_nodes: ?*Node = null,
        active_nodes: ?*Node = null,

        const Node = struct {
            key: Key,
            value: Value,
            has_left: ?*Node = null,
            has_right: ?*Node = null,
            has_parent: ?*Node = null,

            fn deinit(self: *Node, allocator: std.mem.Allocator) void {
                self.has_parent = undefined;

                if (self.has_left) |left| {
                    left.deinit(allocator);
                    allocator.destroy(left);
                }

                self.has_left = undefined;

                if (self.has_right) |right| {
                    right.deinit(allocator);
                    allocator.destroy(right);
                }

                self.has_right = undefined;
            }
        };

        pub const KeyValues = struct {
            nodes: ?*Node,

            pub fn next(self: *KeyValues) ?coral.KeyValuePair(Key, *Value) {
                var nodes = self.nodes;

                while (nodes) |node| {
                    const left = node.has_left orelse {
                        self.nodes = node.has_right;

                        return .{
                            .key = node.key,
                            .value = &node.value,
                        };
                    };

                    // Find the rightmost node in left subtree or link back to current
                    var pred = left;
                    while (pred.has_right != null and pred.has_right != node) {
                        pred = pred.has_right.?;
                    }

                    if (pred.has_right != null) {
                        pred.has_right = null;
                        self.nodes = node.has_right;

                        return .{
                            .key = node.key,
                            .value = &node.value,
                        };
                    }

                    pred.has_right = node;
                    self.nodes = node.has_left;
                    nodes = self.nodes;
                }

                return null;
            }

            pub fn nextKey(self: *KeyValues) ?Key {
                return if (self.next()) |key_value| key_value.key else null;
            }

            pub fn nextValue(self: *KeyValues) ?*Value {
                return if (self.next()) |key_value| key_value.value else null;
            }
        };

        const Self = @This();

        pub fn clear(self: *Self) void {
            var free_nodes: ?*Node = null;

            if (self.active_nodes) |root| {
                // Push root onto stack
                root.has_parent = free_nodes;
                free_nodes = root;
                self.active_nodes = null;
            }

            while (free_nodes) |node| {
                // Pop node from stack
                free_nodes = node.has_parent;

                // Push children onto stack
                if (node.has_left) |left| {
                    left.has_parent = free_nodes;
                    free_nodes = left;
                }

                if (node.has_right) |right| {
                    right.has_parent = free_nodes;
                    free_nodes = right;
                }

                // Add node to free list
                node.has_left = null;
                node.has_right = null;
                node.has_parent = null;
                node.key = undefined;
                node.value = undefined;
                node.has_right = self.free_nodes;
                self.free_nodes = node;
            }
        }

        pub fn createNode(self: *Self, allocator: std.mem.Allocator, node: Node) std.mem.Allocator.Error!*Node {
            if (self.free_nodes) |free_node| {
                self.free_nodes = free_node.has_parent;

                free_node.* = node;

                return free_node;
            }

            const created_node = try allocator.create(Node);

            created_node.* = node;

            return created_node;
        }

        pub fn deinit(self: *Self, allocator: std.mem.Allocator) void {
            if (self.active_nodes) |node| {
                node.deinit(allocator);
                allocator.destroy(node);
            }

            self.active_nodes = undefined;
        }

        pub fn insert(self: *Self, allocator: std.mem.Allocator, key: Key, value: Value) std.mem.Allocator.Error!?*Value {
            var node = self.active_nodes orelse {
                self.active_nodes = try self.createNode(allocator, .{
                    .key = key,
                    .value = value,
                });

                return &self.active_nodes.?.value;
            };

            while (true) {
                switch (traits.compare(key, node.key)) {
                    .equal => {
                        return null;
                    },

                    .lesser => {
                        node = node.has_left orelse {
                            node.has_left = try self.createNode(allocator, .{
                                .key = key,
                                .value = value,
                                .has_parent = node,
                            });

                            return &node.has_left.?.value;
                        };
                    },

                    .greater => {
                        node = node.has_right orelse {
                            node.has_right = try self.createNode(allocator, .{
                                .key = key,
                                .value = value,
                                .has_parent = node,
                            });

                            return &node.has_right.?.value;
                        };
                    },
                }
            }
        }

        pub const empty = Self{
            .active_nodes = null,
        };

        pub fn get(self: Self, key: Key) ?*Value {
            var nodes = self.active_nodes;

            while (nodes) |node| {
                nodes = switch (traits.compare(key, node.key)) {
                    .lesser => node.has_left,
                    .greater => node.has_right,

                    .equal => {
                        return &node.value;
                    },
                };
            }

            return null;
        }

        pub fn getKey(self: Self, key: Key) ?Key {
            var nodes = self.active_nodes;

            while (nodes) |node| {
                nodes = switch (traits.compare(key, node.key)) {
                    .lesser => node.has_left,
                    .greater => node.has_right,

                    .equal => {
                        return node.key;
                    },
                };
            }

            return null;
        }

        pub fn isEmpty(self: *Self) bool {
            return self.active_nodes == null;
        }

        pub fn keyValues(self: *const Self) KeyValues {
            return .{ .nodes = self.active_nodes };
        }
    };
}

pub const Comparison = enum(i2) {
    lesser = -1,
    equal = 0,
    greater = 1,
};

pub fn Traits(comptime Key: type) type {
    return struct {
        compare: fn (Key, Key) Comparison,
    };
}

pub fn scalarTraits(comptime Scalar: type) Traits(Scalar) {
    const traits = switch (@typeInfo(Scalar)) {
        .@"enum" => struct {
            fn compare(a: Scalar, b: Scalar) Comparison {
                const a_int = @intFromEnum(a);
                const b_int = @intFromEnum(b);

                if (a_int < b_int) {
                    return .lesser;
                }

                if (a_int > b_int) {
                    return .greater;
                }

                return .equal;
            }
        },

        .pointer => struct {
            fn compare(a: Scalar, b: Scalar) Comparison {
                const a_int = @intFromPtr(a);
                const b_int = @intFromPtr(b);

                if (a_int < b_int) {
                    return .lesser;
                }

                if (a_int > b_int) {
                    return .greater;
                }

                return .equal;
            }
        },

        .int => struct {
            fn compare(a: Scalar, b: Scalar) Comparison {
                if (a < b) {
                    return .lesser;
                }

                if (a > b) {
                    return .greater;
                }

                return .equal;
            }
        },

        else => {
            @compileError(std.fmt.comptimePrint("parameter `Scalar` must be a scalar type, not {s}", .{
                @typeName(Scalar),
            }));
        },
    };

    return .{
        .compare = traits.compare,
    };
}

pub fn sliceTraits(comptime Slice: type) Traits(Slice) {
    const slice_pointer = switch (@typeInfo(Slice)) {
        .pointer => |pointer| pointer,

        else => {
            @compileError(std.fmt.comptimePrint("parameter `Slice` must be a slice type, not {s}", .{
                @typeName(Slice),
            }));
        },
    };

    const traits = struct {
        fn compare(a: Slice, b: Slice) Comparison {
            return switch (std.mem.order(slice_pointer.child, a, b)) {
                .lt => .lesser,
                .gt => .greater,
                .eq => .equal,
            };
        }
    };

    return .{
        .compare = traits.compare,
    };
}