import Foundation
import XCTest
@testable import DocsKit

final class CRDTSourceReuseTests: XCTestCase {
    func testAcknowledgedIdenticalSourceReuseBoundsClientsAndPreservesDivergence() async throws {
        let replica = CRDTReplica(guid: "source-reuse-test")
        _ = try await replica.open(update: Data())
        _ = try await replica.command(["op": .string("insert_element"), "at": .number(0), "type": .string("paragraph")])
        let initial = try await replica.presentation(source: 0, selection: NSRange(location: 0, length: 0))
        var source = try XCTUnwrap(initial?.0)
        let original = source
        for index in 0..<100 {
            _ = try await replica.command(["op": .string("display_edit"), "generation": .number(Double(source)), "at": .number(Double(index)), "length": .number(0), "text": .string("a")])
            await replica.retainGenerations([source])
            let next = try await replica.presentation(source: source, selection: NSRange(location: index + 1, length: 0), allowReuse: true)
            source = try XCTUnwrap(next?.0)
        }
        XCTAssertEqual(source, original)
        let (clientData, typed) = try await replica.command(["op": .string("clients")])
        XCTAssertEqual(try JSONDecoder().decode([UInt64].self, from: clientData).count, 2)
        XCTAssertEqual(typed.children.map(\.plainText).joined(), String(repeating: "a", count: 100))

        // A candidate without explicit rendered acknowledgement must remain fresh.
        await replica.retainGenerations([source])
        let unacknowledged = try await replica.presentation(source: source, selection: NSRange(location: 100, length: 0))
        XCTAssertNotEqual(unacknowledged?.0, source)
        await replica.retainGenerations([source])

        // A peer changes authority while displayed source stays at the old state.
        let (snapshot, _) = try await replica.command(["op": .string("snapshot")])
        let peer = CRDTReplica(guid: "source-reuse-test")
        _ = try await peer.open(update: snapshot)
        let (peerUpdate, _) = try await peer.command(["op": .string("display_edit"), "at": .number(0), "length": .number(0), "text": .string("peer ")])
        _ = try await replica.apply(peerUpdate)
        let divergent = try await replica.presentation(source: source, selection: NSRange(location: 100, length: 0), allowReuse: true)
        let changed = try XCTUnwrap(divergent?.0)
        XCTAssertNotEqual(changed, source)
        XCTAssertEqual(divergent?.1.children.map(\.plainText).joined(), "peer " + String(repeating: "a", count: 100))
        XCTAssertEqual(divergent?.2.location, 105)

        // Reusing the newly acknowledged live source does not merge undo ownership.
        await replica.retainGenerations([changed])
        _ = try await replica.command(["op": .string("display_edit"), "generation": .number(Double(changed)), "at": .number(105), "length": .number(0), "text": .string("!")])
        let local = try await replica.presentation(source: changed, selection: NSRange(location: 106, length: 0), allowReuse: true)
        XCTAssertEqual(local?.0, changed)
        _ = try await replica.command(["op": .string("undo")])
        let undone = try await replica.presentation(source: changed, selection: NSRange(location: 106, length: 0), allowReuse: true)
        XCTAssertNotEqual(undone?.0, changed)
        XCTAssertFalse(undone?.1.children.map(\.plainText).joined().hasSuffix("!") ?? true)
        XCTAssertTrue(undone?.1.children.map(\.plainText).joined().hasPrefix("peer ") ?? false)
        await peer.close(); await replica.close()
    }
}