Sources/OrgSwiftUI/OrgLayoutBuilder.swift

  1import OrgSwift
  2import SwiftUI
  3
  4/// Walks an ``OrgDocument`` into an ``OrgLayout``.
  5///
  6/// The third renderer over the shared tree, alongside HTML and `AttributedString`. It
  7/// resolves URLs through the same ``OrgURLResolver`` and numbers footnotes through the same
  8/// ``OrgFootnotes``, so a link that works in the HTML output works here and note 1 is note 1
  9/// in both.
 10@MainActor
 11struct OrgLayoutBuilder {
 12    var options: OrgRenderOptions
 13    var styler: OrgCodeStyler
 14    var keywords: OrgKeywordStyle
 15    var textTransform: ((inout AttributedString) -> Void)? = nil
 16
 17    private var inline: OrgInlineStyler { OrgInlineStyler(options: options) }
 18    private var resolver: OrgURLResolver { OrgURLResolver(options: options) }
 19
 20    func layout(_ document: OrgDocument) -> OrgLayout {
 21        var notes = OrgFootnotes(document: document)
 22        var layout = OrgLayout()
 23        layout.blocks = document.elements.flatMap { block($0, &notes) }
 24        // Numbering is complete only after the whole body is walked, so the notes section is
 25        // built last — exactly as the HTML renderer does it.
 26        layout.footnotes = notes.notes.map {
 27            OrgFootnote(number: $0.number, text: text($0.content, &notes, style: .footnote))
 28        }
 29        return layout
 30    }
 31
 32    private func text(
 33        _ objects: [OrgObject], _ notes: inout OrgFootnotes,
 34        style: Font.TextStyle = .body, bold: Bool = false
 35    ) -> AttributedString {
 36        var string = inline.attributed(objects, &notes, style: style, bold: bold)
 37        textTransform?(&string)
 38        return string
 39    }
 40
 41    /// One element to zero or more blocks. Zero for a footnote definition (it moves to the
 42    /// notes section) and for an export block aimed at another backend.
 43    private func block(_ element: OrgElement, _ notes: inout OrgFootnotes) -> [OrgBlock] {
 44        switch element {
 45        case .heading(let heading):
 46            var title = AttributedString()
 47            if let todo = heading.todo {
 48                var keyword = AttributedString(todo + " ")
 49                keyword.foregroundColor = keywords.color(for: todo)
 50                title += keyword
 51            }
 52            if let priority = heading.priority {
 53                var cookie = AttributedString("[#\(priority)] ")
 54                cookie.foregroundColor = .secondary
 55                title += cookie
 56            }
 57            let level = min(6, max(1, heading.level + options.headingLevelOffset))
 58            title += text(heading.title, &notes, style: Self.headingStyle(level), bold: true)
 59            for tag in heading.tags {
 60                var chip = AttributedString("  \(tag)")
 61                chip.foregroundColor = .secondary
 62                chip.font = .system(.caption, design: .monospaced)
 63                title += chip
 64            }
 65            return [.heading(text: title, level: level)]
 66
 67        case .paragraph(let objects):
 68            if let badges = badgeRow(objects) { return [.badges(badges)] }
 69            return [.paragraph(text(objects, &notes))]
 70
 71        case .list(let list):
 72            return [.list(listLayout(list, &notes))]
 73
 74        case .table(let table):
 75            return [.table(tableLayout(table, &notes))]
 76
 77        case .srcBlock(let language, let code):
 78            return [.code(styled(code: code, language: language))]
 79
 80        case .exampleBlock(let raw):
 81            return [.code(styled(code: raw, language: nil))]
 82
 83        case .quoteBlock(let children):
 84            return [.quote(children.flatMap { block($0, &notes) })]
 85
 86        case .centerBlock(let children):
 87            return [.center(children.flatMap { block($0, &notes) })]
 88
 89        case .verseBlock(let lines):
 90            return [.verse(lines.map { text($0, &notes) })]
 91
 92        case .specialBlock(let name, let children):
 93            return [.special(name: name, blocks: children.flatMap { block($0, &notes) })]
 94
 95        case .exportBlock(let backend, let raw):
 96            // HTML passes through verbatim in the HTML renderer; natively there is nothing to
 97            // pass it to, so it shows as the literal block it is rather than vanishing.
 98            return backend == "html" ? [.code(styled(code: raw, language: nil))] : []
 99
100        case .figure(let figure):
101            return [imageBlock(figure, &notes)]
102
103        case .captioned(_, let caption, let content):
104            return [.captioned(
105                caption: caption.map { text($0, &notes, style: .footnote) },
106                blocks: block(content, &notes)
107            )]
108
109        case .horizontalRule:
110            return [.rule]
111
112        case .footnoteDefinition:
113            return []  // collected into the notes section
114        }
115    }
116
117    /// A paragraph holding nothing but images and image links is the badge row a README
118    /// opens with. It renders as a row of images at their own size rather than as prose —
119    /// the inline styler can only show an image's alt text, and a figure block would blow a
120    /// 95×20 badge up to the column width.
121    ///
122    /// Anything else in the paragraph, a word of prose included, means it is prose.
123    private func badgeRow(_ objects: [OrgObject]) -> [OrgBadge]? {
124        var badges: [OrgBadge] = []
125        for object in objects {
126            switch object {
127            case .text(let string) where string.trimmingCharacters(in: .whitespaces).isEmpty:
128                continue
129            case .image(let figure):
130                guard let badge = badge(figure, link: nil) else { return nil }
131                badges.append(badge)
132            case .link(let link):
133                guard link.description?.count == 1,
134                      case .image(let figure) = link.description?.first
135                else { return nil }
136                // A badge whose link will not resolve is still a badge; it just is not
137                // tappable.
138                let href = resolver.href(for: link.target).flatMap { URL(string: $0) }
139                guard let badge = badge(figure, link: href) else { return nil }
140                badges.append(badge)
141            default:
142                return nil
143            }
144        }
145        return badges.isEmpty ? nil : badges
146    }
147
148    private func badge(_ figure: OrgFigure, link: URL?) -> OrgBadge? {
149        guard let string = resolver.imageSource(figure.source),
150              let url = URL(string: string), url.scheme != nil
151        else { return nil }
152        return OrgBadge(source: url, alt: figure.alt ?? "", link: link)
153    }
154
155    /// An image whose source will not resolve to a safe absolute URL degrades to its alt
156    /// text, the same trade the HTML renderer makes rather than pointing at something unsafe.
157    ///
158    /// The absolute requirement is the one place this diverges from HTML, which may emit a
159    /// relative `src` for a document base URL to resolve. A view has no base, so a relative
160    /// source is unloadable and showing the text beats showing a broken image.
161    private func imageBlock(_ figure: OrgFigure, _ notes: inout OrgFootnotes) -> OrgBlock {
162        let caption = figure.caption.map { text($0, &notes, style: .footnote) }
163        guard let string = resolver.imageSource(figure.source),
164              let url = URL(string: string), url.scheme != nil else {
165            return .paragraph(AttributedString(figure.alt ?? figure.source))
166        }
167        let alt = figure.alt ?? figure.caption.map { OrgParser.plain($0) } ?? ""
168        return .image(source: url, alt: alt, caption: caption)
169    }
170
171    private func styled(code: String, language: String?) -> AttributedString {
172        if let highlighted = styler.highlighted(code: code, language: language) {
173            return highlighted
174        }
175        var plain = AttributedString(code)
176        plain.font = .system(.footnote, design: .monospaced)
177        return plain
178    }
179
180    private func listLayout(_ list: OrgList, _ notes: inout OrgFootnotes) -> OrgListLayout {
181        var items: [OrgListLayout.Item] = []
182        for item in list.items {
183            items.append(OrgListLayout.Item(
184                checkbox: item.checkbox,
185                term: item.term.map { term in
186                    var styled = text(term, &notes)
187                    styled.font = .body.bold()
188                    return styled
189                },
190                blocks: item.content.flatMap { block($0, &notes) }
191            ))
192        }
193        return OrgListLayout(kind: list.kind, items: items)
194    }
195
196    private func tableLayout(_ table: OrgTable, _ notes: inout OrgFootnotes) -> OrgTableLayout {
197        var rows: [OrgTableLayout.Row] = []
198        for row in table.rows {
199            guard case .cells(let cells) = row else { continue }
200            rows.append(OrgTableLayout.Row(cells: cells.map {
201                OrgTableLayout.Cell(text: text($0, &notes, style: .subheadline))
202            }))
203        }
204        return OrgTableLayout(
205            rows: rows,
206            headerRowCount: table.headerRowCount,
207            alignments: table.alignments
208        )
209    }
210
211    private static func headingStyle(_ level: Int) -> Font.TextStyle {
212        switch level {
213        case 1: .title
214        case 2: .title2
215        case 3: .title3
216        case 4: .headline
217        default: .subheadline
218        }
219    }
220}