Snapshot System

/**
 * Abstract base class for snapshots representing a consistent view of mutable state
 */
abstract class Snapshot {
    /** Unique identifier for this snapshot */
    abstract val id: Int
    
    /** Whether this snapshot is invalid due to conflicts */
    abstract val invalid: Boolean
    
    /** Set of objects that were read during this snapshot */
    abstract val readSet: Set<Any>
    
    /** Set of objects that were modified during this snapshot */
    abstract val writeSet: Set<Any>
    
    /** Disposes this snapshot and releases resources */
    abstract fun dispose()
    
    companion object {
        /** The global snapshot that all state changes are applied to */
        val global: MutableSnapshot
        
        /** The current snapshot for the current thread */
        val current: Snapshot
        
        /**
         * Takes an immutable snapshot of the current state
         * @param readObserver Optional observer for state reads
         * @return Immutable snapshot
         */
        fun takeSnapshot(readObserver: ((Any) -> Unit)? = null): Snapshot
        
        /**
         * Takes a mutable snapshot for transactional state changes
         * @param readObserver Optional observer for state reads
         * @param writeObserver Optional observer for state writes
         * @return Mutable snapshot for making changes
         */
        fun takeMutableSnapshot(
            readObserver: ((Any) -> Unit)? = null,
            writeObserver: ((Any) -> Unit)? = null
        ): MutableSnapshot
        
        /**
         * Runs a block with the given snapshot as current
         * @param snapshot Snapshot to make current
         * @param block Code to execute with the snapshot
         * @return Result of the block
         */
        fun <T> withSnapshot(snapshot: Snapshot, block: () -> T): T
        
        /**
         * Runs a block with a mutable snapshot
         * @param readObserver Optional observer for state reads
         * @param writeObserver Optional observer for state writes
         * @param block Code to execute in the snapshot
         * @return Result of the block
         */
        fun <T> withMutableSnapshot(
            readObserver: ((Any) -> Unit)? = null,
            writeObserver: ((Any) -> Unit)? = null,
            block: () -> T
        ): T
        
        /**
         * Sends and applies all pending snapshot changes
         */
        fun sendApplyNotifications()
    }
}

/**
 * Mutable snapshot that can be modified and applied
 */
abstract class MutableSnapshot : Snapshot() {
    /** Whether changes have been made to this snapshot */
    abstract val modified: Boolean
    
    /**
     * Applies this snapshot's changes to the global state
     * @return Result indicating success or failure
     */
    abstract fun apply(): SnapshotApplyResult
    
    /**
     * Creates a nested mutable snapshot
     * @param readObserver Optional observer for state reads
     * @param writeObserver Optional observer for state writes
     * @return Nested mutable snapshot
     */
    abstract fun takeNestedMutableSnapshot(
        readObserver: ((Any) -> Unit)? = null,
        writeObserver: ((Any) -> Unit)? = null
    ): MutableSnapshot
    
    /**
     * Creates a nested immutable snapshot
     * @param readObserver Optional observer for state reads
     * @return Nested immutable snapshot
     */
    abstract fun takeNestedSnapshot(readObserver: ((Any) -> Unit)? = null): Snapshot
}

/**
 * Result of applying a snapshot
 */
sealed class SnapshotApplyResult {
    /** Application succeeded */
    object Success : SnapshotApplyResult()
    
    /** Application failed due to conflicts */
    class Failure(val snapshot: Snapshot) : SnapshotApplyResult()
}

// Basic snapshot usage
fun snapshotExample() {
    val snapshot = Snapshot.takeMutableSnapshot()
    
    val result = snapshot.apply {
        // Make changes to state within the snapshot
        someState.value = "new value"
        otherState.value = "other new value"
        
        // Apply all changes atomically
        apply()
    }
    
    when (result) {
        is SnapshotApplyResult.Success -> {
            println("Changes applied successfully")
        }
        is SnapshotApplyResult.Failure -> {
            println("Changes failed to apply due to conflicts")
        }
    }
    
    snapshot.dispose()
}

/**
 * Runs block with global state write observation
 * @param writeObserver Function called when global state is written
 * @param block Code to execute with observation
 * @return Result of the block
 */
fun <T> Snapshot.Companion.withoutReadObservation(block: () -> T): T

/**
 * Registers a global state write observer
 * @param observer Function called when any global state changes
 * @return Handle to remove the observer
 */
fun Snapshot.Companion.registerGlobalWriteObserver(
    observer: (Any) -> Unit
): ObserverHandle

/**
 * Registers a global apply observer
 * @param observer Function called when snapshots are applied
 * @return Handle to remove the observer  
 */
fun Snapshot.Companion.registerApplyObserver(
    observer: (Set<Any>, Snapshot) -> Unit
): ObserverHandle

/**
 * Handle for removing observers
 */
interface ObserverHandle {
    /** Removes the observer */
    fun dispose()
}

/**
 * Creates a Flow that emits the result of block whenever observed state changes
 * The flow emits immediately with the current value, then emits again when any
 * state accessed within block changes
 * @param block Function that reads state and produces values
 * @return Flow that emits when any observed state changes
 */
fun <T> snapshotFlow(block: () -> T): Flow<T>

@Composable
fun SnapshotFlowExample() {
    var name by remember { mutableStateOf("") }
    var age by remember { mutableStateOf(0) }
    
    // Flow that combines multiple state reads
    val userSummary = remember {
        snapshotFlow { 
            if (name.isNotEmpty() && age > 0) {
                "User: $name, Age: $age"
            } else {
                "Incomplete user data"
            }
        }
    }
    
    LaunchedEffect(Unit) {
        userSummary.collect { summary ->
            logger.log("User summary updated: $summary")
        }
    }
    
    // Create a debounced search flow
    val debouncedSearch = remember {
        snapshotFlow { name }
            .debounce(300)
            .filter { it.length >= 2 }
    }
    
    LaunchedEffect(Unit) {
        debouncedSearch.collect { query ->
            performSearch(query)
        }
    }
}

fun nestedSnapshotExample() {
    val outerSnapshot = Snapshot.takeMutableSnapshot()
    
    outerSnapshot.apply {
        someState.value = "outer change"
        
        // Create nested snapshot
        val innerSnapshot = takeNestedMutableSnapshot()
        
        innerSnapshot.apply {
            someState.value = "inner change"
            otherState.value = "another change"
            
            // Apply inner changes first
            apply()
        }
        
        // Apply outer changes (includes inner changes)
        apply()
    }
    
    outerSnapshot.dispose()
}

fun conflictResolutionExample() {
    val state = mutableStateOf("initial")
    
    // First snapshot
    val snapshot1 = Snapshot.takeMutableSnapshot()
    snapshot1.apply {
        state.value = "change 1"
    }
    
    // Second snapshot (concurrent modification)
    val snapshot2 = Snapshot.takeMutableSnapshot()
    snapshot2.apply {
        state.value = "change 2"
    }
    
    // Apply first snapshot
    val result1 = snapshot1.apply()
    
    // Apply second snapshot (may conflict)
    val result2 = snapshot2.apply()
    
    when (result2) {
        is SnapshotApplyResult.Success -> {
            println("Second change applied successfully")
        }
        is SnapshotApplyResult.Failure -> {
            println("Conflict detected, manual resolution required")
            // Handle conflict resolution
        }
    }
    
    snapshot1.dispose()
    snapshot2.dispose()
}

fun stateObservationExample() {
    val readObserver: (Any) -> Unit = { state ->
        println("State read: $state")
    }
    
    val writeObserver: (Any) -> Unit = { state ->
        println("State written: $state")
    }
    
    val snapshot = Snapshot.takeMutableSnapshot(readObserver, writeObserver)
    
    snapshot.apply {
        // These operations will trigger observers
        val value = someState.value // Triggers readObserver
        someState.value = "new value" // Triggers writeObserver
        
        apply()
    }
    
    snapshot.dispose()
}

fun globalStateMonitoringExample() {
    // Monitor all global state writes
    val writeHandle = Snapshot.registerGlobalWriteObserver { state ->
        println("Global state changed: $state")
    }
    
    // Monitor snapshot applications
    val applyHandle = Snapshot.registerApplyObserver { changedObjects, snapshot ->
        println("Snapshot applied with ${changedObjects.size} changes")
    }
    
    // Perform some state changes
    someGlobalState.value = "changed"
    
    // Clean up observers
    writeHandle.dispose()
    applyHandle.dispose()
}

// iOS-specific snapshot handling
fun iosSnapshotExample() {
    // Ensure snapshot operations happen on the main thread
    DispatchQueue.main.async {
        val snapshot = Snapshot.takeMutableSnapshot()
        
        snapshot.apply {
            // Safe to modify state on main thread
            uiState.value = newUIState
            apply()
        }
        
        snapshot.dispose()
    }
}

@Composable
fun UIKitStateIntegration() {
    var composeState by remember { mutableStateOf("") }
    
    // Create flow that watches Compose state
    val stateFlow = remember {
        snapshotFlow { composeState }
    }
    
    LaunchedEffect(Unit) {
        stateFlow.collect { value ->
            // Update UIKit component when Compose state changes
            DispatchQueue.main.async {
                someUIKitView.text = value
            }
        }
    }
}

fun batchStateUpdatesExample() {
    // Batch multiple state changes in a single snapshot
    val snapshot = Snapshot.takeMutableSnapshot()
    
    snapshot.apply {
        // All these changes will be applied atomically
        state1.value = "value1"
        state2.value = "value2"
        state3.value = "value3"
        
        apply() // Single recomposition for all changes
    }
    
    snapshot.dispose()
}

class SnapshotManager {
    private val snapshotPool = mutableListOf<MutableSnapshot>()
    
    fun withPooledSnapshot(block: MutableSnapshot.() -> Unit) {
        val snapshot = snapshotPool.removeFirstOrNull() 
            ?: Snapshot.takeMutableSnapshot()
        
        try {
            snapshot.block()
        } finally {
            if (!snapshot.invalid) {
                snapshotPool.add(snapshot)
            } else {
                snapshot.dispose()
            }
        }
    }
}

fun snapshotErrorHandlingExample() {
    val snapshot = Snapshot.takeMutableSnapshot()
    
    try {
        snapshot.apply {
            // Operations that might fail
            riskyStateOperation()
            apply()
        }
    } catch (e: Exception) {
        // Handle errors - snapshot is automatically invalidated
        println("Snapshot operation failed: ${e.message}")
    } finally {
        snapshot.dispose()
    }
}