293 lines
14 KiB
Swift
293 lines
14 KiB
Swift
import Foundation
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import SwiftUI
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/// A lightweight Markdown renderer for chat messages — the exact port of the Mac's
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/// `MarkdownText`: fenced code blocks, headings, bullet/numbered lists, GitHub-style tables,
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/// and inline emphasis/links/`code`. Not a full CommonMark implementation — just the
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/// constructs agents actually emit — so a reply renders identically on both devices.
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struct MarkdownText: View {
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let markdown: String
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/// Base prose size; every other size (headings, code, tables) is derived from it so a
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/// response renders on one consistent scale. Scaled with the user's text-size setting
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/// (which drives `.dynamicTypeSize`), anchored to the Mac's transcript prose size.
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@ScaledMetric(relativeTo: .body) private var bodySize: CGFloat = 15
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var body: some View {
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VStack(alignment: .leading, spacing: 8) {
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ForEach(Array(Self.parse(markdown).enumerated()), id: \.offset) { _, block in
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switch block {
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case .code(let code):
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codeBlock(code)
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case .text(let text):
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textBlock(text)
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case .table(let rows):
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tableView(rows)
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}
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}
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}
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// Anchor the whole response to one base size; inline code and body text
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// inherit it, so nothing drifts smaller than the prose around it.
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.font(.system(size: bodySize))
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// Soft off-white (vs. pure white) so chat prose reads calmly at night.
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.foregroundStyle(Palette.primaryText)
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}
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// MARK: - blocks
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private enum Block { case code(String), text(String), table([[String]]) }
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/// Parsed-block cache. The same message string is re-parsed on every body re-evaluation
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/// (scrolling, a sibling row streaming) and on every chat reopen, yet structural parsing
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/// is independent of `bodySize` — so the source string is a complete key. Bounded;
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/// `NSCache` also evicts under memory pressure.
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private final class ParsedBlocks { let blocks: [Block]; init(_ b: [Block]) { self.blocks = b } }
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private static let blockCache: NSCache<NSString, ParsedBlocks> = {
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let cache = NSCache<NSString, ParsedBlocks>()
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cache.countLimit = 2048
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return cache
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}()
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private static func parse(_ markdown: String) -> [Block] {
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let key = markdown as NSString
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if let hit = blockCache.object(forKey: key) { return hit.blocks }
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let blocks = parseUncached(markdown)
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blockCache.setObject(ParsedBlocks(blocks), forKey: key)
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return blocks
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}
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private static func parseUncached(_ markdown: String) -> [Block] {
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var blocks: [Block] = []
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var textBuffer: [String] = []
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func flush() {
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let joined = textBuffer.joined(separator: "\n").trimmingCharacters(in: .whitespacesAndNewlines)
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if !joined.isEmpty { blocks.append(.text(joined)) }
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textBuffer = []
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}
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let lines = markdown.components(separatedBy: "\n")
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var index = 0
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while index < lines.count {
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if lines[index].trimmingCharacters(in: .whitespaces).hasPrefix("```") {
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flush()
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var code: [String] = []
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index += 1
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while index < lines.count,
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!lines[index].trimmingCharacters(in: .whitespaces).hasPrefix("```") {
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code.append(lines[index])
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index += 1
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}
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blocks.append(.code(code.joined(separator: "\n")))
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index += 1 // consume closing fence
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} else if isTableStart(lines, index) {
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flush()
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var rows: [[String]] = [tableCells(lines[index])]
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index += 2 // header row + the |---|--- separator
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while index < lines.count, lines[index].contains("|"),
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!lines[index].trimmingCharacters(in: .whitespaces).isEmpty {
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rows.append(tableCells(lines[index]))
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index += 1
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}
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blocks.append(.table(rows))
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} else {
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textBuffer.append(lines[index])
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index += 1
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}
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}
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flush()
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return blocks
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}
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// MARK: - tables
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/// A GitHub-style table: a `|`-bearing header line immediately followed by a
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/// `|---|:--:|` separator line.
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private static func isTableStart(_ lines: [String], _ index: Int) -> Bool {
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guard lines[index].contains("|"), index + 1 < lines.count else { return false }
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return isSeparatorRow(lines[index + 1])
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}
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private static func isSeparatorRow(_ line: String) -> Bool {
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let cells = tableCells(line)
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guard !cells.isEmpty else { return false }
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return cells.allSatisfy { cell in
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!cell.isEmpty && cell.allSatisfy { $0 == "-" || $0 == ":" } && cell.contains("-")
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}
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}
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/// Split a table row into trimmed cells, dropping the empties created by the
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/// leading/trailing pipes.
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private static func tableCells(_ line: String) -> [String] {
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var trimmed = line.trimmingCharacters(in: .whitespaces)
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if trimmed.hasPrefix("|") { trimmed.removeFirst() }
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if trimmed.hasSuffix("|") { trimmed.removeLast() }
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return trimmed.components(separatedBy: "|").map { $0.trimmingCharacters(in: .whitespaces) }
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}
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private func tableView(_ rows: [[String]]) -> some View {
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let columns = rows.map(\.count).max() ?? 0
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return Grid(alignment: .topLeading, horizontalSpacing: 14, verticalSpacing: 6) {
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ForEach(Array(rows.enumerated()), id: \.offset) { rowIndex, row in
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GridRow {
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ForEach(0..<columns, id: \.self) { col in
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inline(col < row.count ? row[col] : "")
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.font(.system(size: bodySize, weight: rowIndex == 0 ? .semibold : .regular))
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.frame(maxWidth: .infinity, alignment: .leading)
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}
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}
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if rowIndex == 0, columns > 0 {
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Divider().gridCellColumns(columns)
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}
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}
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}
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.padding(10)
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.background(.quaternary.opacity(0.25), in: .rect(cornerRadius: 8))
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.overlay(RoundedRectangle(cornerRadius: 8).strokeBorder(.quaternary, lineWidth: 1))
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}
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private func codeBlock(_ code: String) -> some View {
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ScrollView(.horizontal, showsIndicators: false) {
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Text(code)
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// Same point size as body/inline code, just monospaced — so code
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// doesn't shrink relative to the prose.
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.font(.system(size: bodySize, design: .monospaced))
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.textSelection(.enabled)
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.padding(8)
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.frame(maxWidth: .infinity, alignment: .leading)
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}
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.background(.quaternary.opacity(0.4), in: .rect(cornerRadius: 6))
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}
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private func textBlock(_ text: String) -> some View {
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VStack(alignment: .leading, spacing: 5) {
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ForEach(Array(text.components(separatedBy: "\n").enumerated()), id: \.offset) { _, raw in
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lineView(raw)
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}
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}
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// Breathing room between the visual lines of a single wrapped paragraph,
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// which the per-line VStack spacing above can't reach.
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.lineSpacing(4)
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}
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/// One prose line's classification: the exact string that gets inline-parsed — the cache key
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/// `prewarm` must match — paired with how it's styled. Single source of truth for both the
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/// live `lineView` and the off-main `prewarm`, so a warmed key can never drift from the key
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/// the layout later looks up (any drift and the warm entry would silently miss).
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private enum LineStyle {
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case blank
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case heading(content: String, scale: CGFloat, weight: Font.Weight)
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case bullet(content: String)
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case plain(content: String)
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/// The string handed to `inline(_:)`, or nil for a line that renders without a parse.
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var inlineContent: String? {
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switch self {
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case .blank: return nil
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case .heading(let c, _, _), .bullet(let c), .plain(let c): return c
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}
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}
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}
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/// Classify one raw prose line. Headings are checked before bullets (a heading marker wins),
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/// and the plain case keeps the *raw* line (not the trimmed one) exactly as the old cascade
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/// did — the inline parser preserves leading whitespace under `.inlineOnlyPreservingWhitespace`.
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private static func classify(_ raw: String) -> LineStyle {
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let trimmed = raw.trimmingCharacters(in: .whitespaces)
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if trimmed.isEmpty { return .blank }
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// Headings scale relative to the base prose size so the hierarchy holds at any base and
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// never collapses to the body size.
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if trimmed.hasPrefix("### ") { return .heading(content: String(trimmed.dropFirst(4)), scale: 1.13, weight: .semibold) }
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if trimmed.hasPrefix("## ") { return .heading(content: String(trimmed.dropFirst(3)), scale: 1.28, weight: .bold) }
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if trimmed.hasPrefix("# ") { return .heading(content: String(trimmed.dropFirst(2)), scale: 1.5, weight: .bold) }
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if let bullet = bulletContent(trimmed) { return .bullet(content: bullet) }
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return .plain(content: raw)
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}
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@ViewBuilder
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private func lineView(_ raw: String) -> some View {
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switch Self.classify(raw) {
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case .blank:
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Color.clear.frame(height: 3)
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case .heading(let content, let scale, let weight):
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inline(content).font(.system(size: bodySize * scale, weight: weight))
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case .bullet(let content):
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HStack(alignment: .firstTextBaseline, spacing: 6) {
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Text("•").foregroundStyle(.secondary)
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inline(content)
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}
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case .plain(let content):
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inline(content)
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}
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}
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/// Returns the content after a `- `, `* `, `+ ` or `N. ` list marker, else nil.
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private static func bulletContent(_ trimmed: String) -> String? {
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for marker in ["- ", "* ", "+ "] where trimmed.hasPrefix(marker) {
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return String(trimmed.dropFirst(marker.count))
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}
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// Numbered list: "12. text"
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let parts = trimmed.split(separator: " ", maxSplits: 1)
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if let first = parts.first, parts.count == 2,
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first.hasSuffix("."), Int(first.dropLast()) != nil {
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return String(parts[1])
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}
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return nil
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}
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private func inline(_ string: String) -> Text {
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Text(Self.attributedInline(string))
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}
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/// Inline-Markdown cache. `AttributedString(markdown:)` is the dominant per-row cost
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/// when a transcript first lays out — it runs once per prose line — and the same lines
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/// recur across re-renders and reopens, so memoize the parsed result. Independent of
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/// `bodySize` (callers apply the font), so the source string is a complete key.
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private final class InlineBox { let value: AttributedString; init(_ v: AttributedString) { self.value = v } }
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private static let inlineCache: NSCache<NSString, InlineBox> = {
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let cache = NSCache<NSString, InlineBox>()
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cache.countLimit = 16384
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return cache
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}()
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private static func attributedInline(_ string: String) -> AttributedString {
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let key = string as NSString
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if let hit = inlineCache.object(forKey: key) { return hit.value }
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let options = AttributedString.MarkdownParsingOptions(
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interpretedSyntax: .inlineOnlyPreservingWhitespace)
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// Fall back to the plain string on parse failure — `Text(AttributedString(string))`
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// renders identically to `Text(string)`, so callers see no behavioral change.
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let parsed = (try? AttributedString(markdown: string, options: options)) ?? AttributedString(string)
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inlineCache.setObject(InlineBox(parsed), forKey: key)
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return parsed
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}
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// MARK: - Pre-warming
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/// Populate the block and inline caches for `markdown` ahead of layout. `AttributedString(markdown:)`
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/// is the dominant per-row cost when a long transcript first lays out, and the eager `VStack`
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/// runs it for every prose line synchronously — right as the session is pushed and the tab bar
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/// is sliding away, which is what makes the load-in jitter. Calling this off the main thread
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/// (see `TranscriptList`) does that parsing in the background so the first layout hits ready
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/// results instead.
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///
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/// Safe to call from any thread and redundantly: the caches are `NSCache` (thread-safe) and
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/// keyed only by the source string (independent of `bodySize`), so a warm value equals what
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/// the main thread would compute, and a repeat call is a cheap cache hit. Cooperatively
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/// cancellable — a huge transcript's warm loop bails the moment its owning task is cancelled.
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static func prewarm(_ markdown: String) {
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for block in parse(markdown) { // also warms the block cache
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if Task.isCancelled { return }
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switch block {
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case .code:
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break // a code block renders via `Text(code)` — no inline parse to warm
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case .text(let text):
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for raw in text.components(separatedBy: "\n") {
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if let content = classify(raw).inlineContent { _ = attributedInline(content) }
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}
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case .table(let rows):
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for row in rows where !Task.isCancelled {
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for cell in row { _ = attributedInline(cell) }
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}
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}
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}
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}
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}
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