62 lines
2.3 KiB
Swift
62 lines
2.3 KiB
Swift
import SwiftUI
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struct NoteTextEditor: View {
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@Binding var text: String
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let remoteText: String?
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@State private var selection: TextSelection? = nil
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var body: some View {
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TextEditor(text: $text, selection: $selection)
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.onChange(of: remoteText) { oldValue, newValue in
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guard let newValue, newValue != text else { return }
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let previousRemote = oldValue ?? text
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// Where the remote edit begins
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let changeStart = commonPrefixUTF16Length(previousRemote, newValue)
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// How many UTF-16 units were inserted (positive) or removed (negative)
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let delta = newValue.utf16.count - previousRemote.utf16.count
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// Apply remote text first
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text = newValue
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// Get current cursor offset
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guard
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let selection,
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case .selection(let range) = selection.indices,
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let cursorPos = range.lowerBound.samePosition(in: text.utf16)
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else { return }
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let cursorUTF16 = text.utf16.distance(
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from: text.utf16.startIndex,
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to: cursorPos
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)
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// Only shift if the change happened strictly before the cursor
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guard changeStart < cursorUTF16 else { return }
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let newCursorUTF16 = max(0, min(cursorUTF16 + delta, newValue.utf16.count))
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let newUTF16 = newValue.utf16
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let newUTF16Index = newUTF16.index(newUTF16.startIndex, offsetBy: newCursorUTF16)
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guard let newIndex = newUTF16Index.samePosition(in: newValue) else { return }
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self.selection = TextSelection(range: newIndex..<newIndex)
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}
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}
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private func commonPrefixUTF16Length(_ a: String, _ b: String) -> Int {
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var count = 0
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let aUTF16 = a.utf16
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let bUTF16 = b.utf16
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let minLen = min(aUTF16.count, bUTF16.count)
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while count < minLen {
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let aIdx = aUTF16.index(aUTF16.startIndex, offsetBy: count)
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let bIdx = bUTF16.index(bUTF16.startIndex, offsetBy: count)
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guard aUTF16[aIdx] == bUTF16[bIdx] else { break }
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count += 1
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}
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return count
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}
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}
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