// TransactWriteItems and TransactGetItems storage operations
//
// TransactWriteItems: Atomic write of up to 100 items across multiple tables.
//   - Supports Put, Delete, Update, and ConditionCheck actions
//   - ALL actions succeed or ALL fail (all-or-nothing)
//   - ConditionExpressions are evaluated BEFORE any mutations
//   - Uses exclusive locks on all involved tables
//
// TransactGetItems: Atomic read of up to 100 items across multiple tables.
//   - Each item specifies TableName + Key + optional ProjectionExpression
//   - All reads are consistent (snapshot isolation via table locks)
package dynamodb

import "core:strings"
import "core:sync"
import "../rocksdb"

// ============================================================================
// TransactWriteItems Types
// ============================================================================

Transact_Write_Action_Type :: enum {
	Put,
	Delete,
	Update,
	Condition_Check,
}

Transact_Write_Action :: struct {
	type:                Transact_Write_Action_Type,
	table_name:          string,
	// For Put: the full item to write
	item:                Maybe(Item),
	// For Delete/Update/ConditionCheck: the key item
	key:                 Maybe(Item),
	// For Update: the parsed update plan
	update_plan:         Maybe(Update_Plan),
	// ConditionExpression components (shared across all action types)
	condition_expr:      Maybe(string),
	expr_attr_names:     Maybe(map[string]string),
	expr_attr_values:    map[string]Attribute_Value,
	// For Update: ReturnValuesOnConditionCheckFailure (not implemented yet, placeholder)
}

Transact_Write_Result :: struct {
	// For now, either all succeed (no error) or we return a
	// TransactionCanceledException with reasons per action.
	cancellation_reasons: []Cancellation_Reason,
}

Cancellation_Reason :: struct {
	code:    string, // "None", "ConditionalCheckFailed", "ValidationError", etc.
	message: string,
}

transact_write_action_destroy :: proc(action: ^Transact_Write_Action) {
	if item, has := action.item.?; has {
		item_copy := item
		item_destroy(&item_copy)
	}
	if key, has := action.key.?; has {
		key_copy := key
		item_destroy(&key_copy)
	}
	if plan, has := action.update_plan.?; has {
		plan_copy := plan
		update_plan_destroy(&plan_copy)
	}
	if names, has := action.expr_attr_names.?; has {
		for k, v in names {
			delete(k)
			delete(v)
		}
		names_copy := names
		delete(names_copy)
	}
	for k, v in action.expr_attr_values {
		delete(k)
		v_copy := v
		attr_value_destroy(&v_copy)
	}
	delete(action.expr_attr_values)
}

transact_write_result_destroy :: proc(result: ^Transact_Write_Result) {
	if result.cancellation_reasons != nil {
		delete(result.cancellation_reasons)
	}
}

// ============================================================================
// TransactWriteItems — Execute an atomic batch of write operations
//
// DynamoDB semantics:
//   1. Acquire exclusive locks on all involved tables
//   2. Evaluate ALL ConditionExpressions (pre-flight check)
//   3. If any condition fails → cancel entire transaction
//   4. If all pass → apply all mutations
//   5. Release locks
//
// Returns .None on success, Transaction_Cancelled on condition failure.
// ============================================================================

Transaction_Error :: enum {
	None,
	Cancelled,               // One or more conditions failed
	Validation_Error,        // Bad request data
	Internal_Error,          // Storage/serialization failure
}

transact_write_items :: proc(
	engine: ^Storage_Engine,
	actions: []Transact_Write_Action,
) -> (Transact_Write_Result, Transaction_Error) {
	result: Transact_Write_Result

	if len(actions) == 0 {
		return result, .Validation_Error
	}

	// ---- Step 1: Collect unique table names and acquire locks ----
	table_set := make(map[string]bool, allocator = context.temp_allocator)
	for action in actions {
		table_set[action.table_name] = true
	}

	table_names := make([dynamic]string, allocator = context.temp_allocator)
	for name in table_set {
		append(&table_names, name)
	}
	// Sort for deterministic lock ordering
	for i := 0; i < len(table_names); i += 1 {
		for j := i + 1; j < len(table_names); j += 1 {
			if table_names[j] < table_names[i] {
				table_names[i], table_names[j] = table_names[j], table_names[i]
			}
		}
	}

	locks := make([dynamic]^sync.RW_Mutex, allocator = context.temp_allocator)
	for name in table_names {
		lock := get_or_create_table_lock(engine, name)
		sync.rw_mutex_lock(lock)
		append(&locks, lock)
	}
	defer {
		for i := len(locks) - 1; i >= 0; i -= 1 {
			sync.rw_mutex_unlock(locks[i])
		}
	}

	// ---- Step 2: Fetch metadata and evaluate conditions ----
	reasons := make([]Cancellation_Reason, len(actions))
	any_failed := false

	metadata_cache := make(map[string]Table_Metadata, allocator = context.temp_allocator)
	defer {
		for _, meta in metadata_cache {
			meta_copy := meta
			table_metadata_destroy(&meta_copy, engine.allocator)
		}
	}

	for action, idx in actions {
		metadata: ^Table_Metadata
		if cached, found := &metadata_cache[action.table_name]; found {
			metadata = cached
		} else {
			meta, meta_err := get_table_metadata(engine, action.table_name)
			if meta_err != .None {
				reasons[idx] = Cancellation_Reason{
					code    = "ValidationError",
					message = "Table not found",
				}
				any_failed = true
				continue
			}
			metadata_cache[action.table_name] = meta
			metadata = &metadata_cache[action.table_name]
		}

		key_item: Item
		switch action.type {
		case .Put:
			if item, has := action.item.?; has {
				key_item = item
			} else {
				reasons[idx] = Cancellation_Reason{
					code    = "ValidationError",
					message = "Put action missing Item",
				}
				any_failed = true
				continue
			}
		case .Delete, .Update, .Condition_Check:
			if key, has := action.key.?; has {
				key_item = key
			} else {
				reasons[idx] = Cancellation_Reason{
					code    = "ValidationError",
					message = "Action missing Key",
				}
				any_failed = true
				continue
			}
		}

		// Evaluate ConditionExpression
		if cond_str, has_cond := action.condition_expr.?; has_cond {
			existing_item, get_err := get_item_internal(engine, action.table_name, key_item, metadata)
			if get_err != .None && get_err != .Item_Not_Found {
				reasons[idx] = Cancellation_Reason{
					code    = "InternalError",
					message = "Failed to read existing item",
				}
				any_failed = true
				continue
			}
			defer {
				if ex, has_ex := existing_item.?; has_ex {
					ex_copy := ex
					item_destroy(&ex_copy)
				}
			}

			filter_node, parse_ok := parse_filter_expression(
				cond_str, action.expr_attr_names, action.expr_attr_values,
			)
			if !parse_ok || filter_node == nil {
				reasons[idx] = Cancellation_Reason{
					code    = "ValidationError",
					message = "Invalid ConditionExpression",
				}
				any_failed = true
				continue
			}
			defer {
				filter_node_destroy(filter_node)
			}

			eval_item: Item
			if item, has_item := existing_item.?; has_item {
				eval_item = item
			} else {
				eval_item = Item{}
			}

			if !evaluate_filter(eval_item, filter_node) {
				reasons[idx] = Cancellation_Reason{
					code    = "ConditionalCheckFailed",
					message = "The conditional request failed",
				}
				any_failed = true
				continue
			}
		}

		if action.type == .Condition_Check {
			reasons[idx] = Cancellation_Reason{code = "None"}
			continue
		}

		// Validate key/item
		switch action.type {
		case .Put:
			if item, has := action.item.?; has {
				validation_err := validate_item_key_types(
					item, metadata.key_schema, metadata.attribute_definitions,
				)
				if validation_err != .None {
					reasons[idx] = Cancellation_Reason{
						code    = "ValidationError",
						message = "Key attribute type mismatch",
					}
					any_failed = true
					continue
				}
			}
		case .Delete, .Update:
			// Key validation happens during batch building
		case .Condition_Check:
			// Already handled
		}

		reasons[idx] = Cancellation_Reason{code = "None"}
	}

	if any_failed {
		result.cancellation_reasons = reasons
		return result, .Cancelled
	}

	// ---- Step 3: Build atomic WriteBatch with all operations ----
	batch, batch_err := rocksdb.batch_create()
	if batch_err != .None {
		result.cancellation_reasons = reasons
		return result, .Internal_Error
	}
	defer rocksdb.batch_destroy(&batch)

	// Read old items for GSI cleanup (must happen before batch write)
	old_items := make([]Maybe(Item), len(actions), allocator = context.temp_allocator)
	defer {
		for old_item in old_items {
			if old, has := old_item.?; has {
				old_copy := old
				item_destroy(&old_copy)
			}
		}
	}

	for action, idx in actions {
		if action.type == .Condition_Check {
			continue
		}

		metadata := &metadata_cache[action.table_name]

		// Read old item if needed for GSI cleanup
		key_item: Item
		#partial switch action.type {
		case .Put:
			if item, has := action.item.?; has {
				key_item = item
			}
		case .Delete, .Update:
			if key, has := action.key.?; has {
				key_item = key
			}
		}

		existing, _ := get_item_internal(engine, action.table_name, key_item, metadata)
		old_items[idx] = existing
	}

	// Add all operations to batch
	for &action, idx in actions {
		if action.type == .Condition_Check {
			continue
		}

		metadata := &metadata_cache[action.table_name]
		old_item := old_items[idx]

		apply_err := transact_apply_action_batch(&batch, engine, &action, metadata, old_item)
		if apply_err != .None {
			reasons[idx] = Cancellation_Reason{
				code    = "InternalError",
				message = "Failed to build mutation",
			}
			result.cancellation_reasons = reasons
			return result, .Internal_Error
		}
	}

	// ---- Step 4: Write batch atomically (ALL or NOTHING) ----
	write_err := rocksdb.batch_write(&engine.db, &batch)
	if write_err != .None {
		result.cancellation_reasons = reasons
		return result, .Internal_Error
	}

	delete(reasons)
	return result, .None
}

// Apply a single transact write action (called after all conditions have passed)
@(private = "file")
transact_apply_action_batch :: proc(
	batch: ^rocksdb.WriteBatch,
	engine: ^Storage_Engine,
	action: ^Transact_Write_Action,
	metadata: ^Table_Metadata,
	old_item: Maybe(Item),
) -> Storage_Error {
	switch action.type {
	case .Put:
		if item, has := action.item.?; has {
			return put_item_batch(batch, engine, action.table_name, item, metadata, old_item)
		}
		return .Invalid_Key

	case .Delete:
		if key, has := action.key.?; has {
			return delete_item_batch(batch, engine, action.table_name, key, metadata, old_item)
		}
		return .Invalid_Key

	case .Update:
		if key, has := action.key.?; has {
			if plan, has_plan := action.update_plan.?; has_plan {
				plan_copy := plan
				return update_item_batch(batch, engine, action.table_name, key, &plan_copy, metadata, old_item)
			}
			return .Invalid_Key
		}
		return .Invalid_Key

	case .Condition_Check:
		return .None
	}
	return .None
}

@(private = "file")
put_item_batch :: proc(
	batch: ^rocksdb.WriteBatch,
	engine: ^Storage_Engine,
	table_name: string,
	item: Item,
	metadata: ^Table_Metadata,
	old_item: Maybe(Item),
) -> Storage_Error {
	key_struct, key_ok := key_from_item(item, metadata.key_schema)
	if !key_ok {
		return .Missing_Key_Attribute
	}
	defer key_destroy(&key_struct)

	key_values, kv_ok := key_get_values(&key_struct)
	if !kv_ok {
		return .Invalid_Key
	}

	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	encoded_item, encode_ok := encode(item)
	if !encode_ok {
		return .Serialization_Error
	}
	defer delete(encoded_item)

	// Add base item to batch
	rocksdb.batch_put(batch, storage_key, encoded_item)

	// Add old GSI deletions to batch
	if old, has_old := old_item.?; has_old {
		gsi_del_err := gsi_batch_delete_entries(batch, table_name, old, metadata)
		if gsi_del_err != .None {
			return gsi_del_err
		}
	}

	// Add new GSI writes to batch
	gsi_write_err := gsi_batch_write_entries(batch, table_name, item, metadata)
	if gsi_write_err != .None {
		return gsi_write_err
	}

	return .None
}

// Add delete operation to batch (with GSI cleanup)
@(private = "file")
delete_item_batch :: proc(
	batch: ^rocksdb.WriteBatch,
	engine: ^Storage_Engine,
	table_name: string,
	key: Item,
	metadata: ^Table_Metadata,
	old_item: Maybe(Item),
) -> Storage_Error {
	key_struct, key_ok := key_from_item(key, metadata.key_schema)
	if !key_ok {
		return .Missing_Key_Attribute
	}
	defer key_destroy(&key_struct)

	key_values, kv_ok := key_get_values(&key_struct)
	if !kv_ok {
		return .Invalid_Key
	}

	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	// Add base item delete to batch
	rocksdb.batch_delete(batch, storage_key)

	// Add GSI deletions to batch
	if old, has_old := old_item.?; has_old {
		gsi_del_err := gsi_batch_delete_entries(batch, table_name, old, metadata)
		if gsi_del_err != .None {
			return gsi_del_err
		}
	}

	return .None
}

// Add update operation to batch (with GSI maintenance)
@(private = "file")
update_item_batch :: proc(
	batch: ^rocksdb.WriteBatch,
	engine: ^Storage_Engine,
	table_name: string,
	key_item: Item,
	plan: ^Update_Plan,
	metadata: ^Table_Metadata,
	old_item_pre: Maybe(Item),
) -> Storage_Error {
	key_struct, key_ok := key_from_item(key_item, metadata.key_schema)
	if !key_ok {
		return .Missing_Key_Attribute
	}
	defer key_destroy(&key_struct)

	key_values, kv_ok := key_get_values(&key_struct)
	if !kv_ok {
		return .Invalid_Key
	}

	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	// Start with existing item or create new
	existing_item: Item
	if old, has_old := old_item_pre.?; has_old {
		existing_item = item_deep_copy(old)
	} else {
		existing_item = make(Item)
		for ks in metadata.key_schema {
			if val, found := key_item[ks.attribute_name]; found {
				existing_item[strings.clone(ks.attribute_name)] = attr_value_deep_copy(val)
			}
		}
	}
	defer item_destroy(&existing_item)

	// Apply update plan
	if !execute_update_plan(&existing_item, plan) {
		return .Invalid_Key
	}

	// Encode updated item
	encoded_item, encode_ok := encode(existing_item)
	if !encode_ok {
		return .Serialization_Error
	}
	defer delete(encoded_item)

	// Add base item to batch
	rocksdb.batch_put(batch, storage_key, encoded_item)

	// Add old GSI deletions to batch
	if old, has_old := old_item_pre.?; has_old {
		gsi_del_err := gsi_batch_delete_entries(batch, table_name, old, metadata)
		if gsi_del_err != .None {
			return gsi_del_err
		}
	}

	// Add new GSI writes to batch
	gsi_write_err := gsi_batch_write_entries(batch, table_name, existing_item, metadata)
	if gsi_write_err != .None {
		return gsi_write_err
	}

	return .None
}


// ============================================================================
// Internal storage operations that skip lock acquisition
// (Used by transact_write_items which manages its own locking)
// ============================================================================

get_item_internal :: proc(
	engine: ^Storage_Engine,
	table_name: string,
	key: Item,
	metadata: ^Table_Metadata,
) -> (Maybe(Item), Storage_Error) {
	key_struct, key_ok := key_from_item(key, metadata.key_schema)
	if !key_ok {
		return nil, .Missing_Key_Attribute
	}
	defer key_destroy(&key_struct)

	key_values, kv_ok := key_get_values(&key_struct)
	if !kv_ok {
		return nil, .Invalid_Key
	}

	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	value, get_err := rocksdb.db_get(&engine.db, storage_key)
	if get_err == .NotFound {
		return nil, .None
	}
	if get_err != .None {
		return nil, .RocksDB_Error
	}
	defer delete(value)

	item, decode_ok := decode(value)
	if !decode_ok {
		return nil, .Serialization_Error
	}

	return item, .None
}

// ============================================================================
// TransactGetItems Types
// ============================================================================

Transact_Get_Action :: struct {
	table_name: string,
	key:        Item,
	projection: Maybe([]string),  // Optional ProjectionExpression paths
}

Transact_Get_Result :: struct {
	items: []Maybe(Item),  // One per action, nil if item not found
}

transact_get_action_destroy :: proc(action: ^Transact_Get_Action) {
	item_destroy(&action.key)
	if proj, has := action.projection.?; has {
		delete(proj)
	}
}

transact_get_result_destroy :: proc(result: ^Transact_Get_Result) {
	for &maybe_item in result.items {
		if item, has := maybe_item.?; has {
			item_copy := item
			item_destroy(&item_copy)
		}
	}
	delete(result.items)
}

// ============================================================================
// TransactGetItems — Atomically read up to 100 items
//
// DynamoDB semantics:
//   - All reads are performed with a consistent snapshot
//   - Missing items are returned as nil (no error)
//   - ProjectionExpression is applied per-item
// ============================================================================

transact_get_items :: proc(
	engine: ^Storage_Engine,
	actions: []Transact_Get_Action,
) -> (Transact_Get_Result, Transaction_Error) {
	result: Transact_Get_Result

	if len(actions) == 0 {
		return result, .Validation_Error
	}

	// Collect unique tables and acquire shared locks in deterministic order
	table_set := make(map[string]bool, allocator = context.temp_allocator)
	for action in actions {
		table_set[action.table_name] = true
	}

	table_names := make([dynamic]string, allocator = context.temp_allocator)
	for name in table_set {
		append(&table_names, name)
	}
	for i := 0; i < len(table_names); i += 1 {
		for j := i + 1; j < len(table_names); j += 1 {
			if table_names[j] < table_names[i] {
				table_names[i], table_names[j] = table_names[j], table_names[i]
			}
		}
	}

	locks := make([dynamic]^sync.RW_Mutex, allocator = context.temp_allocator)
	for name in table_names {
		lock := get_or_create_table_lock(engine, name)
		sync.rw_mutex_shared_lock(lock)
		append(&locks, lock)
	}
	defer {
		for i := len(locks) - 1; i >= 0; i -= 1 {
			sync.rw_mutex_shared_unlock(locks[i])
		}
	}

	// Cache metadata
	metadata_cache := make(map[string]Table_Metadata, allocator = context.temp_allocator)
	defer {
		for _, meta in metadata_cache {
			meta_copy := meta
			table_metadata_destroy(&meta_copy, engine.allocator)
		}
	}

	items := make([]Maybe(Item), len(actions))

	for action, idx in actions {
		// Get metadata (cached)
		metadata: ^Table_Metadata
		if cached, found := &metadata_cache[action.table_name]; found {
			metadata = cached
		} else {
			meta, meta_err := get_table_metadata(engine, action.table_name)
			if meta_err != .None {
				items[idx] = nil
				continue
			}
			metadata_cache[action.table_name] = meta
			metadata = &metadata_cache[action.table_name]
		}

		// Fetch item
		item_result, get_err := get_item_internal(engine, action.table_name, action.key, metadata)
		if get_err != .None {
			items[idx] = nil
			continue
		}

		// Apply projection if specified
		if item, has_item := item_result.?; has_item {
			if proj, has_proj := action.projection.?; has_proj && len(proj) > 0 {
				projected := apply_projection(item, proj)
				item_copy := item
				item_destroy(&item_copy)
				items[idx] = projected
			} else {
				items[idx] = item
			}
		} else {
			items[idx] = nil
		}
	}

	result.items = items
	return result, .None
}

// ============================================================================
// Helper: Extract modified attribute paths from an Update_Plan
//
// Used for UPDATED_NEW / UPDATED_OLD ReturnValues filtering.
// DynamoDB only returns the attributes that were actually modified
// by the UpdateExpression, not the entire item.
// ============================================================================

get_update_plan_modified_paths :: proc(plan: ^Update_Plan) -> []string {
	paths := make(map[string]bool, allocator = context.temp_allocator)

	for action in plan.sets {
		paths[action.path] = true
	}
	for action in plan.removes {
		paths[action.path] = true
	}
	for action in plan.adds {
		paths[action.path] = true
	}
	for action in plan.deletes {
		paths[action.path] = true
	}

	result := make([]string, len(paths))
	i := 0
	for path in paths {
		result[i] = path
		i += 1
	}
	return result
}

// Filter an item to only include the specified attribute paths.
// Returns a new deep-copied item containing only matching attributes.
filter_item_to_paths :: proc(item: Item, paths: []string) -> Item {
	result := make(Item)
	for path in paths {
		if val, found := item[path]; found {
			result[strings.clone(path)] = attr_value_deep_copy(val)
		}
	}
	return result
}