Begin to implement jsonpath

processor/jsonpath/jsonpath.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// JSONStep represents a single step in a JSONPath query
+type JSONStep struct {
+	Type  StepType
+	Key   string // For Child/RecursiveDescent
+	Index int    // For Index (use -1 for wildcard "*")
+}
+
+type StepType int
+
+const (
+	RootStep StepType = iota
+	ChildStep
+	RecursiveDescentStep
+	WildcardStep
+	IndexStep
+)
+
+func ParseJSONPath(path string) ([]JSONStep, error) {
+	if len(path) == 0 || path[0] != '$' {
+		return nil, fmt.Errorf("path must start with $")
+	}
+
+	path = path[1:]
+	steps := []JSONStep{}
+	i := 0
+
+	for i < len(path) {
+		switch path[i] {
+		case '.':
+			i++
+			if i < len(path) && path[i] == '.' {
+				// Recursive descent
+				i++
+				key, nextPos := readKey(path, i)
+				steps = append(steps, JSONStep{Type: RecursiveDescentStep, Key: key})
+				i = nextPos
+			} else {
+				// Child step or wildcard
+				key, nextPos := readKey(path, i)
+				if key == "*" {
+					steps = append(steps, JSONStep{Type: WildcardStep})
+				} else {
+					steps = append(steps, JSONStep{Type: ChildStep, Key: key})
+				}
+				i = nextPos
+			}
+
+		case '[':
+			// Index step
+			i++
+			indexStr, nextPos := readIndex(path, i)
+			if indexStr == "*" {
+				steps = append(steps, JSONStep{Type: IndexStep, Index: -1})
+			} else {
+				index, err := strconv.Atoi(indexStr)
+				if err != nil {
+					return nil, fmt.Errorf("invalid index: %s", indexStr)
+				}
+				steps = append(steps, JSONStep{Type: IndexStep, Index: index})
+			}
+			i = nextPos + 1 // Skip closing ]
+
+		default:
+			return nil, fmt.Errorf("unexpected character: %c", path[i])
+		}
+	}
+
+	return steps, nil
+}
+
+func readKey(path string, start int) (string, int) {
+	i := start
+	for ; i < len(path); i++ {
+		if path[i] == '.' || path[i] == '[' {
+			break
+		}
+	}
+	return path[start:i], i
+}
+
+func readIndex(path string, start int) (string, int) {
+	i := start
+	for ; i < len(path); i++ {
+		if path[i] == ']' {
+			break
+		}
+	}
+	return path[start:i], i
+}
+
+func EvaluateJSONPath(data interface{}, steps []JSONStep) []interface{} {
+	current := []interface{}{data}
+	
+	for _, step := range steps {
+		var next []interface{}
+		for _, node := range current {
+			next = append(next, evalStep(node, step)...)
+		}
+		current = next
+	}
+	
+	return current
+}
+
+func evalStep(node interface{}, step JSONStep) []interface{} {
+	switch step.Type {
+	case ChildStep:
+		return evalChild(node, step.Key)
+	case RecursiveDescentStep:
+		return evalRecursiveDescent(node, step.Key)
+	case WildcardStep:
+		return evalWildcard(node)
+	case IndexStep:
+		return evalIndex(node, step.Index)
+	default:
+		return nil
+	}
+}
+
+func evalChild(node interface{}, key string) []interface{} {
+	if m, ok := node.(map[string]interface{}); ok {
+		if val, exists := m[key]; exists {
+			return []interface{}{val}
+		}
+	}
+	return nil
+}
+
+func evalRecursiveDescent(node interface{}, targetKey string) []interface{} {
+	results := []interface{}{}
+	queue := []interface{}{node}
+
+	for len(queue) > 0 {
+		current := queue[0]
+		queue = queue[1:]
+
+		if m, ok := current.(map[string]interface{}); ok {
+			// Check if current level has target key
+			if val, exists := m[targetKey]; exists {
+				results = append(results, val)
+			}
+			// Add all children to queue
+			for _, v := range m {
+				queue = append(queue, v)
+			}
+		} else if arr, ok := current.([]interface{}); ok {
+			queue = append(queue, arr...)
+		}
+	}
+
+	return results
+}
+
+func evalWildcard(node interface{}) []interface{} {
+	if m, ok := node.(map[string]interface{}); ok {
+		results := make([]interface{}, 0, len(m))
+		for _, v := range m {
+			results = append(results, v)
+		}
+		return results
+	}
+	return nil
+}
+
+func evalIndex(node interface{}, index int) []interface{} {
+	if arr, ok := node.([]interface{}); ok {
+		if index == -1 { // Wildcard [*]
+			return arr
+		}
+		if index >= 0 && index < len(arr) {
+			return []interface{}{arr[index]}
+		}
+	}
+	return nil
+}