package configkit

import (
	"go/ast"
	"go/parser"
	"go/token"
	"io/fs"
	"path/filepath"
	"strconv"
	"strings"
	"testing"
	"unicode"
)

func TestDependencyImportBoundary(t *testing.T) {
	t.Parallel()

	err := filepath.WalkDir(".", func(path string, entry fs.DirEntry, walkErr error) error {
		if walkErr != nil {
			return walkErr
		}
		if entry.IsDir() {
			if path == ".git" {
				return filepath.SkipDir
			}
			return nil
		}
		if filepath.Ext(path) != ".go" {
			return nil
		}
		file, err := parser.ParseFile(token.NewFileSet(), path, nil, parser.ImportsOnly)
		if err != nil {
			return err
		}
		for _, imported := range file.Imports {
			importPath, err := strconv.Unquote(imported.Path.Value)
			if err != nil {
				return err
			}
			if strings.HasPrefix(importPath, "go.yaml.in/yaml/") && !strings.HasPrefix(filepath.ToSlash(path), "internal/yaml/") {
				t.Errorf("%s imports private YAML dependency %s", path, importPath)
			}
			if strings.HasPrefix(importPath, "github.com/google/go-cmp/") && !strings.HasSuffix(path, "_test.go") {
				t.Errorf("%s imports test-only dependency %s", path, importPath)
			}
			production := !strings.HasSuffix(path, "_test.go")
			rootProduction := production && filepath.Dir(path) == "."
			internalProduction := production && strings.HasPrefix(filepath.ToSlash(path), "internal/")
			if rootProduction && strings.HasPrefix(importPath, "gitea.maximumdirect.net/eric/ConfigKit/internal/") && importPath != "gitea.maximumdirect.net/eric/ConfigKit/internal/engine" {
				t.Errorf("%s bypasses the engine boundary through %s", path, importPath)
			}
			if internalProduction && importPath == "gitea.maximumdirect.net/eric/ConfigKit" {
				t.Errorf("%s imports the public root package", path)
			}
		}
		return nil
	})
	if err != nil {
		t.Fatal(err)
	}
}

func TestPublicFacadeBoundary(t *testing.T) {
	t.Parallel()

	entries, err := filepath.Glob("*.go")
	if err != nil {
		t.Fatal(err)
	}
	for _, path := range entries {
		if strings.HasSuffix(path, "_test.go") {
			continue
		}
		file, err := parser.ParseFile(token.NewFileSet(), path, nil, 0)
		if err != nil {
			t.Fatal(err)
		}
		imports := importedPaths(file)
		for _, declaration := range file.Decls {
			switch declaration := declaration.(type) {
			case *ast.FuncDecl:
				if exportedIdentifier(declaration.Name.Name) && usesInternalType(declaration.Type, imports) {
					t.Errorf("%s exposes an internal type in its signature", declaration.Name)
				}
			case *ast.GenDecl:
				for _, specification := range declaration.Specs {
					typeSpec, ok := specification.(*ast.TypeSpec)
					if !ok || !exportedIdentifier(typeSpec.Name.Name) {
						continue
					}
					if typeSpec.Assign.IsValid() {
						t.Errorf("%s is an exported type alias", typeSpec.Name)
					}
					structure, ok := typeSpec.Type.(*ast.StructType)
					if !ok {
						continue
					}
					for _, field := range structure.Fields.List {
						exposed := len(field.Names) == 0
						for _, name := range field.Names {
							exposed = exposed || exportedIdentifier(name.Name)
						}
						if exposed && usesInternalType(field.Type, imports) {
							t.Errorf("%s exposes an internal type through a field", typeSpec.Name)
						}
					}
				}
			}
		}
	}
}

func importedPaths(file *ast.File) map[string]string {
	paths := make(map[string]string, len(file.Imports))
	for _, imported := range file.Imports {
		path, err := strconv.Unquote(imported.Path.Value)
		if err != nil {
			continue
		}
		name := filepath.Base(path)
		if imported.Name != nil {
			name = imported.Name.Name
		}
		paths[name] = path
	}
	return paths
}

func usesInternalType(expression ast.Expr, imports map[string]string) bool {
	internal := false
	ast.Inspect(expression, func(node ast.Node) bool {
		selector, ok := node.(*ast.SelectorExpr)
		if !ok {
			return true
		}
		packageName, ok := selector.X.(*ast.Ident)
		if ok && strings.Contains(imports[packageName.Name], "/internal/") {
			internal = true
		}
		return !internal
	})
	return internal
}

func exportedIdentifier(name string) bool {
	for _, character := range name {
		return unicode.IsUpper(character)
	}
	return false
}