// Storage engine mapping DynamoDB operations to RocksDB
package dynamodb

import "core:c"
import "core:encoding/json"
import "core:fmt"
import "core:mem"
import "core:slice"
import "core:strconv"
import "core:strings"
import "core:sync"
import "core:time"
import "../rocksdb"

Storage_Error :: enum {
	None,
	Table_Not_Found,
	Table_Already_Exists,
	Item_Not_Found,
	Invalid_Key,
	Missing_Key_Attribute,
	Serialization_Error,
	RocksDB_Error,
	Out_Of_Memory,
}

// Result type for Scan operations with pagination
Scan_Result :: struct {
	items:              []Item,
	last_evaluated_key: Maybe([]byte),
}

scan_result_destroy :: proc(result: ^Scan_Result) {
	for item in result.items {
		item_copy := item
		item_destroy(&item_copy)
	}
	delete(result.items)

	if last_key, ok := result.last_evaluated_key.?; ok {
		delete(last_key)
	}
}

// Result type for Query operations with pagination
Query_Result :: struct {
	items:              []Item,
	last_evaluated_key: Maybe([]byte),
}

query_result_destroy :: proc(result: ^Query_Result) {
	for item in result.items {
		item_copy := item
		item_destroy(&item_copy)
	}
	delete(result.items)

	if last_key, ok := result.last_evaluated_key.?; ok {
		delete(last_key)
	}
}

// In-memory representation of table metadata
Table_Metadata :: struct {
	table_name:                string,
	key_schema:                []Key_Schema_Element,
	attribute_definitions:     []Attribute_Definition,
	table_status:              Table_Status,
	creation_date_time:        i64,
	global_secondary_indexes:  Maybe([]Global_Secondary_Index),
	local_secondary_indexes:   Maybe([]Local_Secondary_Index),
}

table_metadata_destroy :: proc(metadata: ^Table_Metadata, allocator: mem.Allocator) {
	delete(metadata.table_name, allocator)

	for ks in metadata.key_schema {
		delete(ks.attribute_name, allocator)
	}
	delete(metadata.key_schema, allocator)

	for ad in metadata.attribute_definitions {
		delete(ad.attribute_name, allocator)
	}
	delete(metadata.attribute_definitions, allocator)

	// TODO: Free GSI/LSI if we implement them
}

// Get the partition key attribute name
table_metadata_get_partition_key_name :: proc(metadata: ^Table_Metadata) -> Maybe(string) {
	for ks in metadata.key_schema {
		if ks.key_type == .HASH {
			return ks.attribute_name
		}
	}
	return nil
}

// Get the attribute type for a given attribute name
table_metadata_get_attribute_type :: proc(metadata: ^Table_Metadata, attr_name: string) -> Maybe(Scalar_Attribute_Type) {
	for ad in metadata.attribute_definitions {
		if ad.attribute_name == attr_name {
			return ad.attribute_type
		}
	}
	return nil
}

// Get the sort key attribute name (if any)
table_metadata_get_sort_key_name :: proc(metadata: ^Table_Metadata) -> Maybe(string) {
	for ks in metadata.key_schema {
		if ks.key_type == .RANGE {
			return ks.attribute_name
		}
	}
	return nil
}

// Storage engine
Storage_Engine :: struct {
	db:                 rocksdb.DB,
	allocator:          mem.Allocator,
	table_locks:        map[string]^sync.RW_Mutex,
	table_locks_mutex:  sync.Mutex,
}

storage_engine_init :: proc(allocator: mem.Allocator, data_dir: string) -> (^Storage_Engine, Storage_Error) {
	db, db_err := rocksdb.db_open(data_dir, true)
	if db_err != .None {
		return nil, .RocksDB_Error
	}

	engine := new(Storage_Engine, allocator)
	engine.db = db
	engine.allocator = allocator
	engine.table_locks = make(map[string]^sync.RW_Mutex, allocator = allocator)

	return engine, .None
}

storage_engine_destroy :: proc(engine: ^Storage_Engine) {
	// Free all table locks
	for key, lock in engine.table_locks {
		delete(key, engine.allocator)
		free(lock, engine.allocator)
	}
	delete(engine.table_locks)

	// Close database
	rocksdb.db_close(&engine.db)

	// Free engine
	free(engine, engine.allocator)
}

// Get or create a table lock
get_or_create_table_lock :: proc(engine: ^Storage_Engine, table_name: string) -> ^sync.RW_Mutex {
	sync.mutex_lock(&engine.table_locks_mutex)
	defer sync.mutex_unlock(&engine.table_locks_mutex)

	if lock, found := engine.table_locks[table_name]; found {
		return lock
	}

	lock := new(sync.RW_Mutex, engine.allocator)
	owned_name := strings.clone(table_name, engine.allocator)
	engine.table_locks[owned_name] = lock
	return lock
}

// Remove a table lock
remove_table_lock :: proc(engine: ^Storage_Engine, table_name: string) {
	sync.mutex_lock(&engine.table_locks_mutex)
	defer sync.mutex_unlock(&engine.table_locks_mutex)

	if lock, found := engine.table_locks[table_name]; found {
		delete(table_name, engine.allocator)
		free(lock, engine.allocator)
		delete_key(&engine.table_locks, table_name)
	}
}

// ============================================================================
// Table Metadata Operations
// ============================================================================

// Serialize table metadata to binary format
serialize_table_metadata :: proc(metadata: ^Table_Metadata) -> ([]byte, bool) {
	// Create a temporary item to hold metadata
	meta_item := make(Item, context.temp_allocator)
	defer delete(meta_item)

	// Encode key schema as JSON string
	ks_builder := strings.builder_make(context.temp_allocator)
	defer strings.builder_destroy(&ks_builder)

	strings.write_string(&ks_builder, "[")
	for ks, i in metadata.key_schema {
		if i > 0 {
			strings.write_string(&ks_builder, ",")
		}
		fmt.sbprintf(&ks_builder, `{"AttributeName":"%s","KeyType":"%s"}`,
			ks.attribute_name, key_type_to_string(ks.key_type))
	}
	strings.write_string(&ks_builder, "]")

	meta_item["KeySchema"] = String(strings.clone(strings.to_string(ks_builder)))

	// Encode attribute definitions as JSON string
	ad_builder := strings.builder_make(context.temp_allocator)
	defer strings.builder_destroy(&ad_builder)

	strings.write_string(&ad_builder, "[")
	for ad, i in metadata.attribute_definitions {
		if i > 0 {
			strings.write_string(&ad_builder, ",")
		}
		fmt.sbprintf(&ad_builder, `{"AttributeName":"%s","AttributeType":"%s"}`,
			ad.attribute_name, scalar_type_to_string(ad.attribute_type))
	}
	strings.write_string(&ad_builder, "]")

	meta_item["AttributeDefinitions"] = String(strings.clone(strings.to_string(ad_builder)))

	// Add other metadata
	meta_item["TableStatus"] = String(strings.clone(table_status_to_string(metadata.table_status)))
	meta_item["CreationDateTime"] = Number(fmt.aprint(metadata.creation_date_time))

	// Encode to binary
	return encode(meta_item)
}

// Deserialize table metadata from binary format
deserialize_table_metadata :: proc(data: []byte, allocator: mem.Allocator) -> (Table_Metadata, bool) {
	meta_item, ok := decode(data)
	if !ok {
		return {}, false
	}
	defer item_destroy(&meta_item)

	metadata: Table_Metadata

	// Parse table status
	if status_val, found := meta_item["TableStatus"]; found {
		#partial switch v in status_val {
		case String:
			metadata.table_status = table_status_from_string(string(v))
		}
	} else {
		metadata.table_status = .ACTIVE
	}

	// Parse creation date time
	if time_val, found := meta_item["CreationDateTime"]; found {
		#partial switch v in time_val {
		case Number:
			val, parse_ok := strconv.parse_i64(string(v))
			metadata.creation_date_time = val if parse_ok else 0
		}
	}

	// Parse KeySchema from embedded JSON string
	if ks_val, found := meta_item["KeySchema"]; found {
		#partial switch v in ks_val {
		case String:
			ks, ks_ok := parse_key_schema_json(string(v), allocator)
			if ks_ok {
				metadata.key_schema = ks
			}
		}
	}

	// Parse AttributeDefinitions from embedded JSON string
	if ad_val, found := meta_item["AttributeDefinitions"]; found {
		#partial switch v in ad_val {
		case String:
			ad, ad_ok := parse_attr_defs_json(string(v), allocator)
			if ad_ok {
				metadata.attribute_definitions = ad
			}
		}
	}

	return metadata, true
}

// Parse key schema from JSON string like [{"AttributeName":"id","KeyType":"HASH"}]
parse_key_schema_json :: proc(json_str: string, allocator: mem.Allocator) -> ([]Key_Schema_Element, bool) {
	data, parse_err := json.parse(transmute([]byte)json_str, allocator = context.temp_allocator)
	if parse_err != nil {
		return nil, false
	}
	defer json.destroy_value(data)

	arr, ok := data.(json.Array)
	if !ok {
		return nil, false
	}

	result := make([]Key_Schema_Element, len(arr), allocator)

	for elem, i in arr {
		obj, obj_ok := elem.(json.Object)
		if !obj_ok {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_name_val, name_found := obj["AttributeName"]
		if !name_found {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_name, name_ok := attr_name_val.(json.String)
		if !name_ok {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		key_type_val, type_found := obj["KeyType"]
		if !type_found {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		key_type_str, type_ok := key_type_val.(json.String)
		if !type_ok {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		kt, kt_ok := key_type_from_string(string(key_type_str))
		if !kt_ok {
			cleanup_key_schema(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		result[i] = Key_Schema_Element{
			attribute_name = strings.clone(string(attr_name), allocator),
			key_type       = kt,
		}
	}

	return result, true
}

cleanup_key_schema :: proc(elems: []Key_Schema_Element, allocator: mem.Allocator) {
	for ks in elems {
		delete(ks.attribute_name, allocator)
	}
}

// Parse attribute definitions from JSON string
parse_attr_defs_json :: proc(json_str: string, allocator: mem.Allocator) -> ([]Attribute_Definition, bool) {
	data, parse_err := json.parse(transmute([]byte)json_str, allocator = context.temp_allocator)
	if parse_err != nil {
		return nil, false
	}
	defer json.destroy_value(data)

	arr, ok := data.(json.Array)
	if !ok {
		return nil, false
	}

	result := make([]Attribute_Definition, len(arr), allocator)

	for elem, i in arr {
		obj, obj_ok := elem.(json.Object)
		if !obj_ok {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_name_val, name_found := obj["AttributeName"]
		if !name_found {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_name, name_ok := attr_name_val.(json.String)
		if !name_ok {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_type_val, type_found := obj["AttributeType"]
		if !type_found {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		attr_type_str, type_ok := attr_type_val.(json.String)
		if !type_ok {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		at, at_ok := scalar_type_from_string(string(attr_type_str))
		if !at_ok {
			cleanup_attr_defs(result[:i], allocator)
			delete(result, allocator)
			return nil, false
		}

		result[i] = Attribute_Definition{
			attribute_name = strings.clone(string(attr_name), allocator),
			attribute_type = at,
		}
	}

	return result, true
}

cleanup_attr_defs :: proc(elems: []Attribute_Definition, allocator: mem.Allocator) {
	for ad in elems {
		delete(ad.attribute_name, allocator)
	}
}

// Get table metadata
get_table_metadata :: proc(engine: ^Storage_Engine, table_name: string) -> (Table_Metadata, Storage_Error) {
	meta_key := build_meta_key(table_name)
	defer delete(meta_key)

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

	metadata, ok := deserialize_table_metadata(value, engine.allocator)
	if !ok {
		return {}, .Serialization_Error
	}

	return metadata, .None
}

// ============================================================================
// Table Operations
// ============================================================================

// Create table
create_table :: proc(
	engine: ^Storage_Engine,
	table_name: string,
	key_schema: []Key_Schema_Element,
	attribute_definitions: []Attribute_Definition,
) -> (Table_Description, Storage_Error) {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_lock(table_lock)
	defer sync.rw_mutex_unlock(table_lock)

	// Check if table already exists
	meta_key := build_meta_key(table_name)
	defer delete(meta_key)

	existing, get_err := rocksdb.db_get(&engine.db, meta_key)
	if get_err == .None && len(existing) > 0 {
		delete(existing)
		return {}, .Table_Already_Exists
	}
	if get_err == .None {
		delete(existing)
	}

	// Create metadata
	now := time.now()._nsec / 1_000_000_000

	metadata := Table_Metadata{
		table_name = strings.clone(table_name, engine.allocator),
		key_schema = slice.clone(key_schema, engine.allocator),
		attribute_definitions = slice.clone(attribute_definitions, engine.allocator),
		table_status = .ACTIVE,
		creation_date_time = now,
	}

	// Deep copy key schema and attr defs
	for &ks in metadata.key_schema {
		ks.attribute_name = strings.clone(ks.attribute_name, engine.allocator)
	}
	for &ad in metadata.attribute_definitions {
		ad.attribute_name = strings.clone(ad.attribute_name, engine.allocator)
	}

	// Serialize and store
	meta_value, serialize_ok := serialize_table_metadata(&metadata)
	if !serialize_ok {
		table_metadata_destroy(&metadata, engine.allocator)
		return {}, .Serialization_Error
	}
	defer delete(meta_value)

	put_err := rocksdb.db_put(&engine.db, meta_key, meta_value)
	if put_err != .None {
		return {}, .RocksDB_Error
	}

	// Return description
	desc := Table_Description{
		table_name = table_name,
		key_schema = key_schema,
		attribute_definitions = attribute_definitions,
		table_status = .ACTIVE,
		creation_date_time = now,
		item_count = 0,
		table_size_bytes = 0,
	}

	return desc, .None
}

// Delete table — removes metadata AND all items with the table's data prefix
delete_table :: proc(engine: ^Storage_Engine, table_name: string) -> Storage_Error {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_lock(table_lock)
	defer sync.rw_mutex_unlock(table_lock)

	// Check table exists
	meta_key := build_meta_key(table_name)
	defer delete(meta_key)

	existing, get_err := rocksdb.db_get(&engine.db, meta_key)
	if get_err == .NotFound {
		return .Table_Not_Found
	}
	if get_err != .None {
		return .RocksDB_Error
	}
	delete(existing)

	// Delete all data items using a prefix scan
	table_prefix := build_table_prefix(table_name)
	defer delete(table_prefix)

	iter := rocksdb.rocksdb_create_iterator(engine.db.handle, engine.db.read_options)
	if iter != nil {
		defer rocksdb.rocksdb_iter_destroy(iter)

		rocksdb.rocksdb_iter_seek(iter, raw_data(table_prefix), c.size_t(len(table_prefix)))

		for rocksdb.rocksdb_iter_valid(iter) != 0 {
			key_len: c.size_t
			key_ptr := rocksdb.rocksdb_iter_key(iter, &key_len)
			key_bytes := key_ptr[:key_len]

			if !has_prefix(key_bytes, table_prefix) {
				break
			}

			// Delete this item
			err: cstring
			rocksdb.rocksdb_delete(
				engine.db.handle,
				engine.db.write_options,
				raw_data(key_bytes),
				c.size_t(len(key_bytes)),
				&err,
			)
			if err != nil {
				rocksdb.rocksdb_free(rawptr(err))
			}

			rocksdb.rocksdb_iter_next(iter)
		}
	}

	// Delete metadata
	del_err := rocksdb.db_delete(&engine.db, meta_key)
	if del_err != .None {
		return .RocksDB_Error
	}

	remove_table_lock(engine, table_name)
	return .None
}

// ============================================================================
// Item Operations
// ============================================================================

// Put item — uses EXCLUSIVE lock (write operation)
put_item :: proc(engine: ^Storage_Engine, table_name: string, item: Item) -> Storage_Error {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_lock(table_lock)
	defer sync.rw_mutex_unlock(table_lock)

	// Get table metadata
	metadata, meta_err := get_table_metadata(engine, table_name)
	if meta_err != .None {
		return meta_err
	}
	defer table_metadata_destroy(&metadata, engine.allocator)

	// Validate key attribute types match schema
	validation_err := validate_item_key_types(item, metadata.key_schema, metadata.attribute_definitions)
	if validation_err != .None {
		return validation_err
	}

	// Extract key from item
	key, key_ok := key_from_item(item, metadata.key_schema)
	if !key_ok {
		return .Missing_Key_Attribute
	}
	defer {
		pk := key.pk
		attr_value_destroy(&pk)
		if sk, ok := key.sk.?; ok {
			sk_copy := sk
			attr_value_destroy(&sk_copy)
		}
	}

	// Get key values
	key_values, kv_ok := key_get_values(&key)
	if !kv_ok {
		return .Invalid_Key
	}

	// Build storage key
	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

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

	// Store in RocksDB
	put_err := rocksdb.db_put(&engine.db, storage_key, encoded_item)
	if put_err != .None {
		return .RocksDB_Error
	}

	return .None
}

// Get item — uses SHARED lock (read operation)
get_item :: proc(engine: ^Storage_Engine, table_name: string, key: Item) -> (Maybe(Item), Storage_Error) {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_shared_lock(table_lock)
	defer sync.rw_mutex_shared_unlock(table_lock)

	// Get table metadata
	metadata, meta_err := get_table_metadata(engine, table_name)
	if meta_err != .None {
		return nil, meta_err
	}
	defer table_metadata_destroy(&metadata, engine.allocator)

	// Extract key
	key_struct, key_ok := key_from_item(key, metadata.key_schema)
	if !key_ok {
		return nil, .Missing_Key_Attribute
	}
	defer {
		pk := key_struct.pk
		attr_value_destroy(&pk)
		if sk, ok := key_struct.sk.?; ok {
			sk_copy := sk
			attr_value_destroy(&sk_copy)
		}
	}

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

	// Build storage key
	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	// Get from RocksDB
	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)

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

	return item, .None
}

// Delete item — uses EXCLUSIVE lock (write operation)
delete_item :: proc(engine: ^Storage_Engine, table_name: string, key: Item) -> Storage_Error {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_lock(table_lock)
	defer sync.rw_mutex_unlock(table_lock)

	// Get table metadata
	metadata, meta_err := get_table_metadata(engine, table_name)
	if meta_err != .None {
		return meta_err
	}
	defer table_metadata_destroy(&metadata, engine.allocator)

	// Extract key
	key_struct, key_ok := key_from_item(key, metadata.key_schema)
	if !key_ok {
		return .Missing_Key_Attribute
	}
	defer {
		pk := key_struct.pk
		attr_value_destroy(&pk)
		if sk, ok := key_struct.sk.?; ok {
			sk_copy := sk
			attr_value_destroy(&sk_copy)
		}
	}

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

	// Build storage key
	storage_key := build_data_key(table_name, key_values.pk, key_values.sk)
	defer delete(storage_key)

	// Delete from RocksDB
	del_err := rocksdb.db_delete(&engine.db, storage_key)
	if del_err != .None {
		return .RocksDB_Error
	}

	return .None
}

// ============================================================================
// Scan — with FIXED pagination
//
// FIX: LastEvaluatedKey must be the key of the LAST RETURNED item, not the
//      next unread item. DynamoDB semantics: ExclusiveStartKey resumes
//      *after* the given key, so we save the last key we actually returned.
// ============================================================================

scan :: proc(
	engine: ^Storage_Engine,
	table_name: string,
	exclusive_start_key: Maybe([]byte),
	limit: int,
) -> (Scan_Result, Storage_Error) {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_shared_lock(table_lock)
	defer sync.rw_mutex_shared_unlock(table_lock)

	// Verify table exists
	metadata, meta_err := get_table_metadata(engine, table_name)
	if meta_err != .None {
		return {}, meta_err
	}
	defer table_metadata_destroy(&metadata, engine.allocator)

	// Create iterator
	iter := rocksdb.rocksdb_create_iterator(engine.db.handle, engine.db.read_options)
	if iter == nil {
		return {}, .RocksDB_Error
	}
	defer rocksdb.rocksdb_iter_destroy(iter)

	// Build table prefix to scan
	table_prefix := build_table_prefix(table_name)
	defer delete(table_prefix)

	// Seek to start position
	if start_key, has_start := exclusive_start_key.?; has_start {
		// Resume from pagination token — seek to the key then skip it (exclusive)
		rocksdb.rocksdb_iter_seek(iter, raw_data(start_key), c.size_t(len(start_key)))
		if rocksdb.rocksdb_iter_valid(iter) != 0 {
			rocksdb.rocksdb_iter_next(iter)
		}
	} else {
		// Start from beginning of table
		rocksdb.rocksdb_iter_seek(iter, raw_data(table_prefix), c.size_t(len(table_prefix)))
	}

	max_items := limit if limit > 0 else 1_000_000

	// Collect items
	items := make([dynamic]Item, context.temp_allocator)
	count := 0
	last_key: Maybe([]byte) = nil
	has_more := false

	for rocksdb.rocksdb_iter_valid(iter) != 0 {
		// Get current key
		key_len: c.size_t
		key_ptr := rocksdb.rocksdb_iter_key(iter, &key_len)
		key_bytes := key_ptr[:key_len]

		// Check if key still has table prefix
		if !has_prefix(key_bytes, table_prefix) {
			break
		}

		// Check limit — if we already have enough items, note there's more and stop
		if count >= max_items {
			has_more = true
			break
		}

		// Get value
		value_len: c.size_t
		value_ptr := rocksdb.rocksdb_iter_value(iter, &value_len)
		value_bytes := value_ptr[:value_len]

		// Decode item
		item, decode_ok := decode(value_bytes)
		if !decode_ok {
			// Skip corrupted items
			rocksdb.rocksdb_iter_next(iter)
			continue
		}

		append(&items, item)
		count += 1

		// Track the key of the last successfully returned item
		if prev_key, had_prev := last_key.?; had_prev {
			delete(prev_key)
		}
		last_key = slice.clone(key_bytes)

		// Move to next
		rocksdb.rocksdb_iter_next(iter)
	}

	// Only emit LastEvaluatedKey if there are more items beyond what we returned
	if !has_more {
		if lk, had_lk := last_key.?; had_lk {
			delete(lk)
		}
		last_key = nil
	}

	// Convert to slice
	result_items := make([]Item, len(items))
	copy(result_items, items[:])

	return Scan_Result{
		items = result_items,
		last_evaluated_key = last_key,
	}, .None
}

// ============================================================================
// Query — with sort key condition filtering and FIXED pagination
// ============================================================================

query :: proc(
	engine: ^Storage_Engine,
	table_name: string,
	partition_key_value: []byte,
	exclusive_start_key: Maybe([]byte),
	limit: int,
	sk_condition: Maybe(Sort_Key_Condition) = nil,
) -> (Query_Result, Storage_Error) {
	table_lock := get_or_create_table_lock(engine, table_name)
	sync.rw_mutex_shared_lock(table_lock)
	defer sync.rw_mutex_shared_unlock(table_lock)

	// Verify table exists
	metadata, meta_err := get_table_metadata(engine, table_name)
	if meta_err != .None {
		return {}, meta_err
	}
	defer table_metadata_destroy(&metadata, engine.allocator)

	// Build partition prefix
	prefix := build_partition_prefix(table_name, partition_key_value)
	defer delete(prefix)

	iter, iter_err := rocksdb.iter_create(&engine.db)
	if iter_err != .None {
		return {}, .RocksDB_Error
	}
	defer rocksdb.iter_destroy(&iter)

	max_items := limit if limit > 0 else 1_000_000

	// Seek to start position
	if start_key, has_start := exclusive_start_key.?; has_start {
		if has_prefix(start_key, prefix) {
			rocksdb.iter_seek(&iter, start_key)
			if rocksdb.iter_valid(&iter) {
				rocksdb.iter_next(&iter)
			}
		} else {
			rocksdb.iter_seek(&iter, prefix)
		}
	} else {
		rocksdb.iter_seek(&iter, prefix)
	}

	items := make([dynamic]Item)
	count := 0
	last_key: Maybe([]byte) = nil
	has_more := false

	for rocksdb.iter_valid(&iter) {
		key := rocksdb.iter_key(&iter)
		if key == nil || !has_prefix(key, prefix) {
			break
		}

		// Hit limit — note there's more and stop
		if count >= max_items {
			has_more = true
			break
		}

		value := rocksdb.iter_value(&iter)
		if value == nil {
			rocksdb.iter_next(&iter)
			continue
		}

		item, decode_ok := decode(value)
		if !decode_ok {
			rocksdb.iter_next(&iter)
			continue
		}

		// ---- Sort key condition filtering ----
		if skc, has_skc := sk_condition.?; has_skc {
			if !evaluate_sort_key_condition(item, &skc) {
				// Item doesn't match SK condition — skip it
				item_copy := item
				item_destroy(&item_copy)
				rocksdb.iter_next(&iter)
				continue
			}
		}

		append(&items, item)
		count += 1

		// Track key of last returned item
		if prev_key, had_prev := last_key.?; had_prev {
			delete(prev_key)
		}
		last_key = slice.clone(key)

		rocksdb.iter_next(&iter)
	}

	// Only emit LastEvaluatedKey if there are more items
	if !has_more {
		if lk, had_lk := last_key.?; had_lk {
			delete(lk)
		}
		last_key = nil
	}

	result_items := make([]Item, len(items))
	copy(result_items, items[:])

	return Query_Result{
		items              = result_items,
		last_evaluated_key = last_key,
	}, .None
}

// ============================================================================
// Sort Key Condition Evaluation
//
// Extracts the sort key attribute from a decoded item and compares it against
// the parsed Sort_Key_Condition using string comparison (matching DynamoDB's
// byte-level comparison semantics for S/N/B types).
// ============================================================================

evaluate_sort_key_condition :: proc(item: Item, skc: ^Sort_Key_Condition) -> bool {
	attr, found := item[skc.sk_name]
	if !found {
		return false
	}

	item_sk_str, ok1 := attr_value_to_string_for_compare(attr)
	if !ok1 {
		return false
	}

	cond_val_str, ok2 := attr_value_to_string_for_compare(skc.value)
	if !ok2 {
		return false
	}

	cmp := strings.compare(item_sk_str, cond_val_str)

	switch skc.operator {
	case .EQ:
		return cmp == 0
	case .LT:
		return cmp < 0
	case .LE:
		return cmp <= 0
	case .GT:
		return cmp > 0
	case .GE:
		return cmp >= 0
	case .BETWEEN:
		if v2, has_v2 := skc.value2.?; has_v2 {
			upper_str, ok3 := attr_value_to_string_for_compare(v2)
			if !ok3 {
				return false
			}
			cmp2 := strings.compare(item_sk_str, upper_str)
			return cmp >= 0 && cmp2 <= 0
		}
		return false
	case .BEGINS_WITH:
		return strings.has_prefix(item_sk_str, cond_val_str)
	}

	return false
}

// Extract a comparable string from a scalar AttributeValue
@(private = "file")
attr_value_to_string_for_compare :: proc(attr: Attribute_Value) -> (string, bool) {
	#partial switch v in attr {
	case String:
		return string(v), true
	case Number:
		return string(v), true
	case Binary:
		return string(v), true
	}
	return "", false
}

// ============================================================================
// Item Key Validation
//
// Validates that an item's key attributes match the types declared in
// AttributeDefinitions. E.g., if PK is declared as "S", the item must
// have a String value for that attribute.
// ============================================================================

validate_item_key_types :: proc(
	item: Item,
	key_schema: []Key_Schema_Element,
	attr_defs: []Attribute_Definition,
) -> Storage_Error {
	for ks in key_schema {
		attr, found := item[ks.attribute_name]
		if !found {
			return .Missing_Key_Attribute
		}

		// Find the expected type from attribute definitions
		expected_type: Maybe(Scalar_Attribute_Type) = nil
		for ad in attr_defs {
			if ad.attribute_name == ks.attribute_name {
				expected_type = ad.attribute_type
				break
			}
		}

		et, has_et := expected_type.?
		if !has_et {
			continue // No definition found — skip validation (shouldn't happen)
		}

		// Check actual type matches expected
		match := false
		#partial switch _ in attr {
		case String:
			match = (et == .S)
		case Number:
			match = (et == .N)
		case Binary:
			match = (et == .B)
		}

		if !match {
			return .Invalid_Key
		}
	}

	return .None
}

// Helper to check if a byte slice has a prefix
has_prefix :: proc(data: []byte, prefix: []byte) -> bool {
	if len(data) < len(prefix) {
		return false
	}
	for i in 0..<len(prefix) {
		if data[i] != prefix[i] {
			return false
		}
	}
	return true
}

// List tables by iterating over meta keys in RocksDB
list_tables :: proc(engine: ^Storage_Engine) -> ([]string, Storage_Error) {
	iter, iter_err := rocksdb.iter_create(&engine.db)
	if iter_err != .None {
		return nil, .RocksDB_Error
	}
	defer rocksdb.iter_destroy(&iter)

	meta_prefix := []byte{u8(Entity_Type.Meta)}
	rocksdb.iter_seek(&iter, meta_prefix)

	tables := make([dynamic]string)

	for rocksdb.iter_valid(&iter) {
		key := rocksdb.iter_key(&iter)
		if key == nil || len(key) == 0 || key[0] != u8(Entity_Type.Meta) {
			break
		}

		decoder := Key_Decoder{data = key, pos = 0}
		_, et_ok := decoder_read_entity_type(&decoder)
		if !et_ok {
			break
		}

		tbl_name_bytes, seg_ok := decoder_read_segment_borrowed(&decoder)
		if !seg_ok {
			break
		}

		append(&tables, strings.clone(string(tbl_name_bytes)))
		rocksdb.iter_next(&iter)
	}

	return tables[:], .None
}