1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48
49. 49
50. 50
51. 51
52. 52
53. 53
54. 54
55. 55
56. 56
57. 57
58. 58
59. 59
60. 60
61. 61
62. 62
63. 63
64. 64
65. 65
66. 66
67. 67
68. 68
69. 69
70. 70
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. 79
80. 80
81. 81
82. 82
83. 83
84. 84
85. 85
86. 86
87. 87
88. 88
89. 89
90. 90
91. 91
92. 92
93. 93
94. 94
95. 95
96. 96
97. 97
98. 98
99. 99
100. 100
101. 101
102. 102

// SPDX-FileCopyrightText: 2024 Shota FUJI <pockawoooh@gmail.com>
//
// SPDX-License-Identifier: Apache-2.0

import type * as Hast from "../../../deps/esm.sh/hast/types.ts";
import { SKIP, visit } from "../../../deps/esm.sh/unist-util-visit/mod.ts";
import { fastUslug } from "../../../deps/esm.sh/@shelf/fast-uslug/mod.ts";
import { isElement } from "../../../deps/esm.sh/hast-util-is-element/mod.ts";
import { toString } from "../../../deps/esm.sh/hast-util-to-string/mod.ts";

export interface TocItem<Node = Hast.ElementContent[]> {
	id: string;
	text: Node;
	level: number;

	children: TocItem<Node>[];
}

export function mapTocItem<A, B>(item: TocItem<A>, f: (a: A) => B): TocItem<B> {
	return {
		id: item.id,
		level: item.level,
		text: f(item.text),
		children: item.children.map((child) => mapTocItem(child, f)),
	};
}

function getParent(level: number, items: readonly TocItem[]): TocItem | null {
	if (!items.length) {
		return null;
	}

	const [head] = items;
	if (head.level >= level) {
		return null;
	}

	if (head.level === level + 1) {
		return items[items.length - 1];
	}

	return getParent(level, items[items.length - 1].children);
}

/**
 * Mutates given Hast by adding ID to headings and Returns table of contents.
 */
export function tocMut<Node extends Hast.Node>(
	hast: Node,
): readonly TocItem<Hast.ElementContent[]>[] {
	const items: TocItem[] = [];

	visit(hast, (node) => {
		if (!isElement(node)) {
			return false;
		}

		switch (node.tagName) {
			case "h1":
			case "h2":
			case "h3":
			case "h4":
			case "h5":
			case "h6":
				return true;
			default:
				return false;
		}
	}, (node) => {
		if (!isElement(node)) {
			return SKIP;
		}

		const levelMatch = node.tagName.match(/^h(\d)$/);
		if (!levelMatch) {
			return SKIP;
		}

		const level = parseInt(levelMatch[1]);
		if (!Number.isFinite(level)) {
			return SKIP;
		}

		let id = node.properties.id;
		if (typeof id !== "string") {
			id = fastUslug(toString(node), {
				lower: false,
			});
			node.properties.id = id;
		}

		const parent = getParent(level, items)?.children || items;
		parent.push({
			id,
			level,
			text: node.children,
			children: [],
		});
	});

	return items;
}