Sources/OrgDocument/ViewState.swift

 1import OrgCore
 2
 3/// Per-window state for one document: selection and folds, in UTF-16 offsets.
 4public struct ViewState: Sendable, Equatable {
 5    public var selection: [Range<Int>]
 6    /// Start offsets of headings whose whole subtree is folded.
 7    public var folds: Set<Int>
 8    /// Start offsets of headings whose own body is folded; their child headings stay visible.
 9    public var bodyFolds: Set<Int>
10
11    public init(selection: [Range<Int>] = [0..<0], folds: Set<Int> = [], bodyFolds: Set<Int> = []) {
12        self.selection = selection
13        self.folds = folds
14        self.bodyFolds = bodyFolds
15    }
16
17    /// Maps through non-overlapping edits given in old coordinates.
18    public func mapped(through edits: [TextEdit]) -> ViewState {
19        let sorted = edits.sorted { $0.range.lowerBound < $1.range.lowerBound }
20        return ViewState(
21            selection: selection.map { mapOffset($0.lowerBound, sorted)..<mapOffset($0.upperBound, sorted) },
22            folds: Set(folds.map { mapOffset($0, sorted) }),
23            bodyFolds: Set(bodyFolds.map { mapOffset($0, sorted) })
24        )
25    }
26
27    /// Drops folds that no longer sit at the start of a heading.
28    public func pruned(to tree: OrgTree) -> ViewState {
29        guard !folds.isEmpty || !bodyFolds.isEmpty else { return self }
30        return ViewState(
31            selection: selection,
32            folds: folds.filter { isHeadingStart($0, tree.root) },
33            bodyFolds: bodyFolds.filter { isHeadingStart($0, tree.root) }
34        )
35    }
36}
37
38/// Descends only through the sections containing `offset`.
39func isHeadingStart(_ offset: Int, _ root: SyntaxNode) -> Bool {
40    var node = root
41    while let child = node.child(containing: offset) {
42        if child.kind == .heading { return child.range.lowerBound == offset }
43        guard child.kind == .section || child.kind == .zerothSection else { return false }
44        node = child
45    }
46    return false
47}
48
49/// An offset before an edit stays put; one at the start of a replaced range stays at its start;
50/// one inside it, at its end, or at an insertion point moves past the replacement.
51func mapOffset(_ offset: Int, _ sortedEdits: [TextEdit]) -> Int {
52    var shift = 0
53    for edit in sortedEdits {
54        let lower = edit.range.lowerBound, upper = edit.range.upperBound
55        if offset < lower || (offset == lower && upper > lower) { return offset + shift }
56        if offset <= upper { return lower + shift + edit.replacement.utf16.count }
57        shift += edit.replacement.utf16.count - edit.range.count
58    }
59    return offset + shift
60}