Feat/support multi level association (#39)

* refactor: extract association logic to file

* refactor: extract tag logic to file

* feat: add dag

* feat: support multi level association

* test: correct testing

* test: correct testing at mysqlf

* test: correct testing at postgresf

* test: correct testing at gormf

* refactor: remove unnecessary comment

---------

Co-authored-by: Eyo Chen <[email protected]>

dag.go

@@ -0,0 +1,85 @@
+package gofacto
+
+type dag struct {
+	nodes map[string]assocNode
+	edges map[string][]string
+}
+
+func newDAG() *dag {
+	return &dag{
+		nodes: make(map[string]assocNode),
+		edges: make(map[string][]string),
+	}
+}
+
+func (d *dag) addNode(node assocNode) {
+	d.nodes[node.name] = node
+}
+
+func (d *dag) addEdge(from, to string) {
+	d.edges[from] = append(d.edges[from], to)
+}
+
+// topologicalSort returns the topological sort of the DAG
+func (d *dag) topologicalSort() []assocNode {
+	visited := make(map[string]bool)
+	result := make([]assocNode, len(d.nodes))
+	i := len(result) - 1
+
+	var dfs func(node string)
+	dfs = func(node string) {
+		if visited[node] {
+			return
+		}
+
+		visited[node] = true
+		for _, neighbor := range d.edges[node] {
+			dfs(neighbor)
+		}
+
+		result[i] = d.nodes[node]
+		i--
+	}
+
+	for node := range d.nodes {
+		dfs(node)
+	}
+
+	return result
+}
+
+// hasCycle returns true if the DAG has a cycle
+func (d *dag) hasCycle() bool {
+	visited := make(map[string]bool)
+	recursionStack := make(map[string]bool)
+
+	var dfs func(node string) bool
+	dfs = func(node string) bool {
+		if recursionStack[node] {
+			return true
+		}
+
+		if visited[node] {
+			return false
+		}
+
+		visited[node] = true
+		recursionStack[node] = true
+		for _, neighbor := range d.edges[node] {
+			if dfs(neighbor) {
+				return true
+			}
+		}
+
+		recursionStack[node] = false
+		return false
+	}
+
+	for node := range d.nodes {
+		if dfs(node) {
+			return true
+		}
+	}
+
+	return false
+}