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