Collect unused datasources in terraform

main.go

package main

import (
	"fmt"
	"log"
	"os"
	"strings"

	"github.com/awalterschulze/gographviz"
)

func render(graph *gographviz.Graph) error {
	_, err := fmt.Println(graph.String())
	return err
}

func read(path string) (*gographviz.Graph, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	graphAst, err := gographviz.ParseString(string(b))
	if err != nil {
		return nil, err
	}
	graph := gographviz.NewGraph()
	return graph, gographviz.Analyse(graphAst, graph)
}

func collectTransitiveDeps(graph *gographviz.Graph, nodeName string, visited, transitive map[string]bool) {
	if visited[nodeName] {
		return
	}
	_, found := graph.Nodes.Lookup[nodeName]
	if found {
		visited[nodeName] = true
		transitive[nodeName] = true
		edges := graph.Edges.SrcToDsts[nodeName]
		for dst := range edges {
			collectTransitiveDeps(graph, dst, visited, transitive)
		}
	}
}

func collectDeps(graph *gographviz.Graph) {
	transitiveDepsToDatasource := map[string]bool{}
	visited := map[string]bool{}
	edges := graph.Edges.Sorted()
	for _, e := range edges {
		var found bool
		if strings.HasPrefix(e.Dst, "\"[root] data.") {
			found = true
		}
		if found {
			collectTransitiveDeps(graph, e.Src, visited, transitiveDepsToDatasource)
		}
	}
	for _, n := range graph.Nodes.Sorted() {
		_, found := transitiveDepsToDatasource[n.Name]
		if found || !strings.HasPrefix(n.Name, "\"[root] data.") {
			parents := graph.Relations.ChildToParents[n.Name]
			for p := range parents {
				err := graph.RemoveNode(p, n.Name)
				if err != nil {
					fmt.Println(err)
				}
			}
		}
	}
}

func tweak(graph *gographviz.Graph) {
	collectDeps(graph)
}

func mainInternal() error {
	graph, err := read("terraform.dot")
	if err != nil {
		return err
	}
	tweak(graph)
	return render(graph)
}

func main() {
	if err := mainInternal(); err != nil {
		log.Fatal(err)
	}
}