Sapling/Tests/SaplingEditorTests/EditorLargeDocumentValidationTests.swift

import XCTest
@testable import SaplingEditor

final class EditorLargeDocumentValidationTests: XCTestCase {
    func testLargeDocumentOpenAndDirtyRenderPlanning() {
        for lineCount in [1_000, 5_000, 10_000] {
            let source = Self.prototypeDocument(lineCount: lineCount)
            let activeLineIndex = lineCount / 2

            let openMeasurement = elapsedTime {
                _ = EditorState(
                    document: document(source: source, lineCount: lineCount),
                    activeLineIndex: activeLineIndex
                )
            }

            let updatedSource = Self.replacingLine(
                activeLineIndex,
                in: source,
                with: "Line \(activeLineIndex + 1) edited with **bold** and `inline code`."
            )
            let updateMeasurement = elapsedTime {
                var state = EditorState(
                    document: document(source: source, lineCount: lineCount),
                    activeLineIndex: activeLineIndex
                )
                state.updateSource(updatedSource)
                _ = EditorDirtyLineInvalidator.plan(
                    previousText: source,
                    currentText: updatedSource,
                    previousActiveLineIndex: activeLineIndex,
                    currentActiveLineIndex: activeLineIndex
                )
            }
            let plan = EditorDirtyLineInvalidator.plan(
                previousText: source,
                currentText: updatedSource,
                previousActiveLineIndex: activeLineIndex,
                currentActiveLineIndex: activeLineIndex
            )
            let dirtyRenderMeasurement = elapsedTime {
                let lines = EditorActiveLineTracker.lines(from: updatedSource, activeLineIndex: activeLineIndex)
                let dirty = Set(plan.dirtyLineIndexes)
                let renderer = HybridMarkdownLineRenderer()
                _ = lines
                    .filter { dirty.contains($0.index) }
                    .map(renderer.renderPlan(for:))
            }

            XCTAssertEqual(EditorActiveLineTracker.lines(from: source, activeLineIndex: activeLineIndex).count, lineCount)
            XCTAssertFalse(plan.isFullRender)
            XCTAssertLessThanOrEqual(plan.dirtyLineCount, 3)
            XCTAssertLessThan(openMeasurement, 0.25, "Opening \(lineCount) generated lines should remain interactive.")
            XCTAssertLessThan(updateMeasurement, 0.50, "State update for \(lineCount) lines should remain bounded.")
            XCTAssertLessThan(dirtyRenderMeasurement, 0.05, "Dirty render planning should not scale with the full document.")
        }
    }

    func testLargeDocumentActiveLineNavigationDoesNotScheduleFullRender() {
        let source = Self.prototypeDocument(lineCount: 10_000)

        let plan = EditorDirtyLineInvalidator.plan(
            previousText: source,
            currentText: source,
            previousActiveLineIndex: 250,
            currentActiveLineIndex: 9_750
        )

        XCTAssertEqual(plan.reason, .activeLineChange)
        XCTAssertFalse(plan.isFullRender)
        XCTAssertEqual(plan.dirtyLineIndexes, [250, 9_750])
    }

    private func document(source: String, lineCount: Int) -> EditorDocument {
        EditorDocument(
            url: URL(fileURLWithPath: "/tmp/EditorLargeDocument-\(lineCount).md"),
            title: "EditorLargeDocument-\(lineCount)",
            source: source
        )
    }

    private func elapsedTime(_ operation: () -> Void) -> TimeInterval {
        let start = Date()
        operation()
        return Date().timeIntervalSince(start)
    }

    private static func prototypeDocument(lineCount: Int) -> String {
        (1...lineCount).map { index in
            if index.isMultiple(of: 25) {
                return "## Section \(index / 25)"
            }
            if index.isMultiple(of: 5) {
                return "Line \(index) uses **bold** context and `inline code` for scanning."
            }
            return "Line \(index) is a realistic paragraph with *light emphasis* and enough text to wrap naturally."
        }
        .joined(separator: "\n")
    }

    private static func replacingLine(_ lineIndex: Int, in source: String, with replacement: String) -> String {
        var lines = source.components(separatedBy: "\n")
        lines[lineIndex] = replacement
        return lines.joined(separator: "\n")
    }
}