// transact_handlers.odin — HTTP handlers for TransactWriteItems and TransactGetItems
//
// Also contains the UPDATED_NEW / UPDATED_OLD filtering helper for UpdateItem.
package main

import "core:encoding/json"
import "core:fmt"
import "core:strings"
import "dynamodb"

// ============================================================================
// TransactWriteItems Handler
//
// Request format:
// {
//   "TransactItems": [
//     {
//       "Put": {
//         "TableName": "...",
//         "Item": { ... },
//         "ConditionExpression": "...",          // optional
//         "ExpressionAttributeNames": { ... },   // optional
//         "ExpressionAttributeValues": { ... }    // optional
//       }
//     },
//     {
//       "Delete": {
//         "TableName": "...",
//         "Key": { ... },
//         "ConditionExpression": "...",           // optional
//         ...
//       }
//     },
//     {
//       "Update": {
//         "TableName": "...",
//         "Key": { ... },
//         "UpdateExpression": "...",
//         "ConditionExpression": "...",           // optional
//         "ExpressionAttributeNames": { ... },   // optional
//         "ExpressionAttributeValues": { ... }    // optional
//       }
//     },
//     {
//       "ConditionCheck": {
//         "TableName": "...",
//         "Key": { ... },
//         "ConditionExpression": "...",
//         "ExpressionAttributeNames": { ... },   // optional
//         "ExpressionAttributeValues": { ... }    // optional
//       }
//     }
//   ]
// }
// ============================================================================

handle_transact_write_items :: proc(
	engine: ^dynamodb.Storage_Engine,
	request: ^HTTP_Request,
	response: ^HTTP_Response,
) {
	data, parse_err := json.parse(request.body, allocator = context.allocator)
	if parse_err != nil {
		make_error_response(response, .SerializationException, "Invalid JSON")
		return
	}
	defer json.destroy_value(data)

	root, root_ok := data.(json.Object)
	if !root_ok {
		make_error_response(response, .SerializationException, "Request must be an object")
		return
	}

	transact_items_val, found := root["TransactItems"]
	if !found {
		make_error_response(response, .ValidationException, "Missing TransactItems")
		return
	}

	transact_items, ti_ok := transact_items_val.(json.Array)
	if !ti_ok {
		make_error_response(response, .ValidationException, "TransactItems must be an array")
		return
	}

	if len(transact_items) == 0 {
		make_error_response(response, .ValidationException,
			"TransactItems must contain at least one item")
		return
	}

	if len(transact_items) > 100 {
		make_error_response(response, .ValidationException,
			"Member must have length less than or equal to 100")
		return
	}

	// Parse each action
	actions := make([dynamic]dynamodb.Transact_Write_Action)
	defer {
		for &action in actions {
			dynamodb.transact_write_action_destroy(&action)
		}
		delete(actions)
	}

	for elem in transact_items {
		elem_obj, elem_ok := elem.(json.Object)
		if !elem_ok {
			make_error_response(response, .ValidationException,
				"Each TransactItem must be an object")
			return
		}

		action, action_ok := parse_transact_write_action(elem_obj)
		if !action_ok {
			make_error_response(response, .ValidationException,
				"Invalid TransactItem action")
			return
		}
		append(&actions, action)
	}

	// Execute transaction
	result, tx_err := dynamodb.transact_write_items(engine, actions[:])
	defer dynamodb.transact_write_result_destroy(&result)

	switch tx_err {
	case .None:
		response_set_body(response, transmute([]byte)string("{}"))

	case .Cancelled:
		// Build TransactionCanceledException response
		builder := strings.builder_make()
		strings.write_string(&builder, `{"__type":"com.amazonaws.dynamodb.v20120810#TransactionCanceledException","message":"Transaction cancelled, please refer cancellation reasons for specific reasons [`)

		for reason, i in result.cancellation_reasons {
			if i > 0 {
				strings.write_string(&builder, ", ")
			}
			strings.write_string(&builder, reason.code)
		}

		strings.write_string(&builder, `]","CancellationReasons":[`)

		for reason, i in result.cancellation_reasons {
			if i > 0 {
				strings.write_string(&builder, ",")
			}
			fmt.sbprintf(&builder, `{{"Code":"%s","Message":"%s"}}`, reason.code, reason.message)
		}

		strings.write_string(&builder, "]}")

		response_set_status(response, .Bad_Request)
		resp_body := strings.to_string(builder)
		response_set_body(response, transmute([]byte)resp_body)

	case .Validation_Error:
		make_error_response(response, .ValidationException,
			"Transaction validation failed")

	case .Internal_Error:
		make_error_response(response, .InternalServerError,
			"Internal error during transaction")
	}
}

// Parse a single TransactItem action from JSON
@(private = "file")
parse_transact_write_action :: proc(obj: json.Object) -> (dynamodb.Transact_Write_Action, bool) {
	action: dynamodb.Transact_Write_Action
	action.expr_attr_values = make(map[string]dynamodb.Attribute_Value)

	// Try Put
	if put_val, has_put := obj["Put"]; has_put {
		put_obj, put_ok := put_val.(json.Object)
		if !put_ok {
			return {}, false
		}
		action.type = .Put
		return parse_transact_put_action(put_obj, &action)
	}

	// Try Delete
	if del_val, has_del := obj["Delete"]; has_del {
		del_obj, del_ok := del_val.(json.Object)
		if !del_ok {
			return {}, false
		}
		action.type = .Delete
		return parse_transact_key_action(del_obj, &action)
	}

	// Try Update
	if upd_val, has_upd := obj["Update"]; has_upd {
		upd_obj, upd_ok := upd_val.(json.Object)
		if !upd_ok {
			return {}, false
		}
		action.type = .Update
		return parse_transact_update_action(upd_obj, &action)
	}

	// Try ConditionCheck
	if cc_val, has_cc := obj["ConditionCheck"]; has_cc {
		cc_obj, cc_ok := cc_val.(json.Object)
		if !cc_ok {
			return {}, false
		}
		action.type = .Condition_Check
		return parse_transact_key_action(cc_obj, &action)
	}

	return {}, false
}

// Parse common expression fields from a transact action object
@(private = "file")
parse_transact_expression_fields :: proc(obj: json.Object, action: ^dynamodb.Transact_Write_Action) {
	// ConditionExpression
	if ce_val, found := obj["ConditionExpression"]; found {
		if ce_str, str_ok := ce_val.(json.String); str_ok {
			action.condition_expr = strings.clone(string(ce_str))
		}
	}

	// ExpressionAttributeNames
	if ean_val, found := obj["ExpressionAttributeNames"]; found {
		if ean_obj, ean_ok := ean_val.(json.Object); ean_ok {
			names := make(map[string]string)
			for key, val in ean_obj {
				if str, str_ok := val.(json.String); str_ok {
					names[strings.clone(key)] = strings.clone(string(str))
				}
			}
			action.expr_attr_names = names
		}
	}

	// ExpressionAttributeValues
	if eav_val, found := obj["ExpressionAttributeValues"]; found {
		if eav_obj, eav_ok := eav_val.(json.Object); eav_ok {
			for key, val in eav_obj {
				attr, attr_ok := dynamodb.parse_attribute_value(val)
				if attr_ok {
					action.expr_attr_values[strings.clone(key)] = attr
				}
			}
		}
	}
}

// Parse a Put transact action
@(private = "file")
parse_transact_put_action :: proc(
	obj: json.Object,
	action: ^dynamodb.Transact_Write_Action,
) -> (dynamodb.Transact_Write_Action, bool) {
	// TableName
	tn_val, tn_found := obj["TableName"]
	if !tn_found {
		return {}, false
	}
	tn_str, tn_ok := tn_val.(json.String)
	if !tn_ok {
		return {}, false
	}
	action.table_name = strings.clone(string(tn_str))

	// Item
	item_val, item_found := obj["Item"]
	if !item_found {
		return {}, false
	}
	item, item_ok := dynamodb.parse_item_from_value(item_val)
	if !item_ok {
		return {}, false
	}
	action.item = item

	// Expression fields
	parse_transact_expression_fields(obj, action)

	return action^, true
}

// Parse a Delete or ConditionCheck transact action (both use Key)
@(private = "file")
parse_transact_key_action :: proc(
	obj: json.Object,
	action: ^dynamodb.Transact_Write_Action,
) -> (dynamodb.Transact_Write_Action, bool) {
	// TableName
	tn_val, tn_found := obj["TableName"]
	if !tn_found {
		return {}, false
	}
	tn_str, tn_ok := tn_val.(json.String)
	if !tn_ok {
		return {}, false
	}
	action.table_name = strings.clone(string(tn_str))

	// Key
	key_val, key_found := obj["Key"]
	if !key_found {
		return {}, false
	}
	key, key_ok := dynamodb.parse_item_from_value(key_val)
	if !key_ok {
		return {}, false
	}
	action.key = key

	// Expression fields
	parse_transact_expression_fields(obj, action)

	return action^, true
}

// Parse an Update transact action
@(private = "file")
parse_transact_update_action :: proc(
	obj: json.Object,
	action: ^dynamodb.Transact_Write_Action,
) -> (dynamodb.Transact_Write_Action, bool) {
	// TableName
	tn_val, tn_found := obj["TableName"]
	if !tn_found {
		return {}, false
	}
	tn_str, tn_ok := tn_val.(json.String)
	if !tn_ok {
		return {}, false
	}
	action.table_name = strings.clone(string(tn_str))

	// Key
	key_val, key_found := obj["Key"]
	if !key_found {
		return {}, false
	}
	key, key_ok := dynamodb.parse_item_from_value(key_val)
	if !key_ok {
		return {}, false
	}
	action.key = key

	// Expression fields (must be parsed before UpdateExpression so attr values are available)
	parse_transact_expression_fields(obj, action)

	// UpdateExpression
	ue_val, ue_found := obj["UpdateExpression"]
	if !ue_found {
		return {}, false
	}
	ue_str, ue_ok := ue_val.(json.String)
	if !ue_ok {
		return {}, false
	}

	plan, plan_ok := dynamodb.parse_update_expression(
		string(ue_str), action.expr_attr_names, action.expr_attr_values,
	)
	if !plan_ok {
		return {}, false
	}
	action.update_plan = plan

	return action^, true
}

// ============================================================================
// TransactGetItems Handler
//
// Request format:
// {
//   "TransactItems": [
//     {
//       "Get": {
//         "TableName": "...",
//         "Key": { ... },
//         "ProjectionExpression": "...",          // optional
//         "ExpressionAttributeNames": { ... }     // optional
//       }
//     }
//   ]
// }
// ============================================================================

handle_transact_get_items :: proc(
	engine: ^dynamodb.Storage_Engine,
	request: ^HTTP_Request,
	response: ^HTTP_Response,
) {
	data, parse_err := json.parse(request.body, allocator = context.allocator)
	if parse_err != nil {
		make_error_response(response, .SerializationException, "Invalid JSON")
		return
	}
	defer json.destroy_value(data)

	root, root_ok := data.(json.Object)
	if !root_ok {
		make_error_response(response, .SerializationException, "Request must be an object")
		return
	}

	transact_items_val, found := root["TransactItems"]
	if !found {
		make_error_response(response, .ValidationException, "Missing TransactItems")
		return
	}

	transact_items, ti_ok := transact_items_val.(json.Array)
	if !ti_ok {
		make_error_response(response, .ValidationException, "TransactItems must be an array")
		return
	}

	if len(transact_items) == 0 {
		make_error_response(response, .ValidationException,
			"TransactItems must contain at least one item")
		return
	}

	if len(transact_items) > 100 {
		make_error_response(response, .ValidationException,
			"Member must have length less than or equal to 100")
		return
	}

	// Parse each get action
	actions := make([dynamic]dynamodb.Transact_Get_Action)
	defer {
		for &action in actions {
			dynamodb.transact_get_action_destroy(&action)
		}
		delete(actions)
	}

	for elem in transact_items {
		elem_obj, elem_ok := elem.(json.Object)
		if !elem_ok {
			make_error_response(response, .ValidationException,
				"Each TransactItem must be an object")
			return
		}

		get_val, has_get := elem_obj["Get"]
		if !has_get {
			make_error_response(response, .ValidationException,
				"TransactGetItems only supports Get actions")
			return
		}

		get_obj, get_ok := get_val.(json.Object)
		if !get_ok {
			make_error_response(response, .ValidationException,
				"Get action must be an object")
			return
		}

		action, action_ok := parse_transact_get_action(get_obj)
		if !action_ok {
			make_error_response(response, .ValidationException,
				"Invalid Get action")
			return
		}
		append(&actions, action)
	}

	// Execute transaction get
	result, tx_err := dynamodb.transact_get_items(engine, actions[:])
	defer dynamodb.transact_get_result_destroy(&result)

	if tx_err != .None {
		make_error_response(response, .InternalServerError,
			"Transaction get failed")
		return
	}

	// Build response
	builder := strings.builder_make(context.allocator)
	defer strings.builder_destroy(&builder)

	strings.write_string(&builder, `{"Responses":[`)

	for maybe_item, i in result.items {
		if i > 0 {
			strings.write_string(&builder, ",")
		}

		if item, has_item := maybe_item.?; has_item {
			strings.write_string(&builder, `{"Item":`)
			dynamodb.serialize_item_to_builder(&builder, item)
			strings.write_string(&builder, `}`)
		} else {
			strings.write_string(&builder, "{}")
		}
	}

	strings.write_string(&builder, "]}")

	// Clone the string or we gonna have issues again
	resp_body := strings.clone(strings.to_string(builder))
	response_set_body(response, transmute([]byte)resp_body)
}

// Parse a single TransactGetItems Get action
@(private = "file")
parse_transact_get_action :: proc(obj: json.Object) -> (dynamodb.Transact_Get_Action, bool) {
	action: dynamodb.Transact_Get_Action

	// TableName
	tn_val, tn_found := obj["TableName"]
	if !tn_found {
		return {}, false
	}
	tn_str, tn_ok := tn_val.(json.String)
	if !tn_ok {
		return {}, false
	}
	action.table_name = strings.clone(string(tn_str))

	// Key
	key_val, key_found := obj["Key"]
	if !key_found {
		return {}, false
	}
	key, key_ok := dynamodb.parse_item_from_value(key_val)
	if !key_ok {
		return {}, false
	}
	action.key = key

	// ProjectionExpression (optional)
	if pe_val, pe_found := obj["ProjectionExpression"]; pe_found {
		if pe_str, pe_ok := pe_val.(json.String); pe_ok {
			// Parse ExpressionAttributeNames for projection
			attr_names: Maybe(map[string]string) = nil
			if ean_val, ean_found := obj["ExpressionAttributeNames"]; ean_found {
				if ean_obj, ean_ok := ean_val.(json.Object); ean_ok {
					names := make(map[string]string, allocator = context.temp_allocator)
					for key_str, val in ean_obj {
						if str, str_ok := val.(json.String); str_ok {
							names[key_str] = string(str)
						}
					}
					attr_names = names
				}
			}

			parts := strings.split(string(pe_str), ",")
			paths := make([dynamic]string)
			for part in parts {
				trimmed := strings.trim_space(part)
				if len(trimmed) == 0 {
					continue
				}
				resolved, res_ok := dynamodb.resolve_attribute_name(trimmed, attr_names)
				if !res_ok {
					delete(paths)
					dynamodb.item_destroy(&action.key)
					return {}, false
				}
				append(&paths, strings.clone(resolved))
			}
			action.projection = paths[:]
		}
	}

	return action, true
}

// ============================================================================
// UPDATED_NEW / UPDATED_OLD Filtering Helper
//
// DynamoDB ReturnValues semantics:
//   ALL_NEW      → all attributes of the item after the update
//   ALL_OLD      → all attributes of the item before the update
//   UPDATED_NEW  → only the attributes that were modified, with new values
//   UPDATED_OLD  → only the attributes that were modified, with old values
//
// This filters an item to only include the attributes touched by the
// UpdateExpression (the "modified paths").
// ============================================================================

filter_updated_attributes :: proc(
	item: dynamodb.Item,
	plan: ^dynamodb.Update_Plan,
) -> dynamodb.Item {
	modified_paths := dynamodb.get_update_plan_modified_paths(plan)
	defer delete(modified_paths)

	return dynamodb.filter_item_to_paths(item, modified_paths)
}