make batch operations work

dynamodb/condition.odin

@@ -0,0 +1,118 @@
+// ConditionExpression support for PutItem, DeleteItem, and UpdateItem
+//
+// ConditionExpression uses the same grammar as FilterExpression but is evaluated
+// against the *existing* item (before the mutation). If the condition evaluates
+// to false, the operation is rejected with ConditionalCheckFailedException.
+//
+// When there is no existing item:
+//   - attribute_not_exists(path) → true  (attribute doesn't exist on a non-existent item)
+//   - attribute_exists(path)     → false
+//   - All comparisons            → false (no attribute to compare)
+//
+// This file provides:
+//   1. parse_condition_expression_string  — extract ConditionExpression from JSON body
+//   2. evaluate_condition                 — evaluate parsed condition against an item
+//   3. Condition_Result                   — result enum for condition evaluation
+package dynamodb
+
+import "core:encoding/json"
+
+// ============================================================================
+// Condition Evaluation Result
+// ============================================================================
+
+Condition_Result :: enum {
+	Passed,              // Condition met (or no condition specified)
+	Failed,              // Condition not met → ConditionalCheckFailedException
+	Parse_Error,         // Malformed ConditionExpression → ValidationException
+}
+
+// ============================================================================
+// Request Parsing
+// ============================================================================
+
+// Extract the raw ConditionExpression string from the request body.
+parse_condition_expression_string :: proc(request_body: []byte) -> (expr: string, ok: bool) {
+	data, parse_err := json.parse(request_body, allocator = context.temp_allocator)
+	if parse_err != nil {
+		return
+	}
+	defer json.destroy_value(data)
+
+	root, root_ok := data.(json.Object)
+	if !root_ok {
+		return
+	}
+
+	ce_val, found := root["ConditionExpression"]
+	if !found {
+		return
+	}
+
+	ce_str, str_ok := ce_val.(json.String)
+	if !str_ok {
+		return
+	}
+
+	expr = string(ce_str)
+	ok = true
+	return
+}
+
+// ============================================================================
+// Full Condition Evaluation Pipeline
+//
+// Parses ConditionExpression + ExpressionAttributeNames/Values from the
+// request body, then evaluates against the existing item.
+//
+// Parameters:
+//   request_body  — full JSON request body
+//   existing_item — the item currently in the database (nil if no item exists)
+//   attr_names    — pre-parsed ExpressionAttributeNames (caller may already have these)
+//   attr_values   — pre-parsed ExpressionAttributeValues
+//
+// Returns Condition_Result:
+//   .Passed      — no ConditionExpression, or condition evaluated to true
+//   .Failed      — condition evaluated to false
+//   .Parse_Error — ConditionExpression is malformed
+// ============================================================================
+
+evaluate_condition_expression :: proc(
+	request_body: []byte,
+	existing_item: Maybe(Item),
+	attr_names: Maybe(map[string]string),
+	attr_values: map[string]Attribute_Value,
+) -> Condition_Result {
+	// Extract ConditionExpression string
+	condition_str, has_condition := parse_condition_expression_string(request_body)
+	if !has_condition {
+		return .Passed // No condition → always pass
+	}
+
+	// Parse the condition into a filter tree (same grammar as FilterExpression)
+	filter_node, parse_ok := parse_filter_expression(condition_str, attr_names, attr_values)
+	if !parse_ok || filter_node == nil {
+		return .Parse_Error
+	}
+	defer {
+		filter_node_destroy(filter_node)
+		free(filter_node)
+	}
+
+	// If there is no existing item, build an empty item for evaluation.
+	// This means attribute_not_exists → true, attribute_exists → false,
+	// all comparisons → false (attribute not found).
+	eval_item: Item
+	if item, has_item := existing_item.?; has_item {
+		eval_item = item
+	} else {
+		// Empty item — no attributes exist
+		eval_item = Item{}
+	}
+
+	if evaluate_filter(eval_item, filter_node) {
+		return .Passed
+	}
+
+	return .Failed
+}