package gormlog_test

import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"testing"

	"github.com/stretchr/testify/require"
)

// minNonTestFiles guards the walk below against passing because it
// found nothing to look at. The tree held 60 non-test .go files when
// this was written.
const minNonTestFiles = 40

// isRowProducer reports whether name is a method that returns a
// database/sql row handle. GORM's Row and Rows return *sql.Row and
// *sql.Rows, so Scan on the result of one of them is database/sql's
// Scan and never (*gorm.DB).Scan.
func isRowProducer(name string) bool {
	switch name {
	case "Row", "Rows", "QueryRow", "QueryRowContext":
		return true
	default:
		return false
	}
}

// receiverIsRowHandle reports whether x is syntactically a call to a
// row producer, which is the only receiver form this check accepts for
// a Scan.
func receiverIsRowHandle(x ast.Expr) bool {
	call, ok := x.(*ast.CallExpr)
	if !ok {
		return false
	}

	sel, ok := call.Fun.(*ast.SelectorExpr)
	if !ok {
		return false
	}

	return isRowProducer(sel.Sel.Name)
}

// unguardedScans returns the position of every Scan call in file whose
// receiver is not a row handle. It fails closed: a receiver it cannot
// resolve syntactically — a local variable, a struct field — is
// reported rather than assumed safe.
func unguardedScans(
	fset *token.FileSet, file *ast.File,
) []token.Position {
	var found []token.Position

	ast.Inspect(file, func(n ast.Node) bool {
		call, ok := n.(*ast.CallExpr)
		if !ok {
			return true
		}

		sel, ok := call.Fun.(*ast.SelectorExpr)
		if !ok || sel.Sel.Name != "Scan" {
			return true
		}

		if !receiverIsRowHandle(sel.X) {
			found = append(found, fset.Position(sel.Sel.Pos()))
		}

		return true
	})

	return found
}

// moduleRoot walks up from the working directory to the directory
// holding go.mod.
func moduleRoot(t *testing.T) string {
	t.Helper()

	dir, err := os.Getwd()
	require.NoError(t, err)

	for {
		_, statErr := os.Stat(filepath.Join(dir, "go.mod"))
		if statErr == nil {
			return dir
		}

		parent := filepath.Dir(dir)
		require.NotEqual(t, parent, dir, "no go.mod above %s", dir)

		dir = parent
	}
}

// skipDir reports whether a directory holds no source this check
// governs.
func skipDir(name string) bool {
	switch name {
	case ".git", "bin", "node_modules", "testdata":
		return true
	default:
		return false
	}
}

// walkNonTestGo parses every non-test .go file under root and returns
// how many it parsed along with every unguarded Scan it found.
func walkNonTestGo(t *testing.T, root string) (int, []string) {
	t.Helper()

	var (
		parsed int
		hits   []string
	)

	fset := token.NewFileSet()

	require.NoError(t, filepath.WalkDir(
		root,
		func(path string, d fs.DirEntry, err error) error {
			if err != nil {
				return err
			}

			if d.IsDir() {
				if skipDir(d.Name()) {
					return fs.SkipDir
				}

				return nil
			}

			if !isNonTestGo(d.Name()) {
				return nil
			}

			file, err := parser.ParseFile(fset, path, nil, 0)
			if err != nil {
				return err
			}

			parsed++

			for _, pos := range unguardedScans(fset, file) {
				hits = append(hits, relPosition(root, pos))
			}

			return nil
		},
	))

	return parsed, hits
}

// isNonTestGo reports whether a file name is Go source this check
// governs.
func isNonTestGo(name string) bool {
	return strings.HasSuffix(name, ".go") &&
		!strings.HasSuffix(name, "_test.go")
}

// relPosition renders pos with its path relative to root, so a failure
// names the file the way the repository does.
func relPosition(root string, pos token.Position) string {
	name := pos.Filename

	rel, err := filepath.Rel(root, name)
	if err == nil {
		name = rel
	}

	return fmt.Sprintf("%s:%d:%d", name, pos.Line, pos.Column)
}

// TestGormScanIsNeverCalledOutsideTests keeps (*gorm.DB).Scan out of
// non-test code.
//
// It is the one statement path (*Logger).ParamsFilter does not reach:
// Scan swaps GORM's own trace recorder in for the adapter, and that
// recorder does not implement gorm.ParamsFilter, so the statement is
// logged with its values interpolated. The package comment states the
// limit; this fails when someone adds a call site anyway.
//
// The current tree has one caller, internal/database/database_test.go,
// which this check does not govern: it is test-only and its SELECT 1
// binds nothing.
func TestGormScanIsNeverCalledOutsideTests(t *testing.T) {
	t.Parallel()

	parsed, offenders := walkNonTestGo(t, moduleRoot(t))

	require.GreaterOrEqual(
		t, parsed, minNonTestFiles,
		"parsed %d non-test .go files, so this check found "+
			"nothing to look at", parsed,
	)
	require.Empty(
		t, offenders,
		"Scan called on a receiver this check cannot show is a "+
			"database/sql row handle. (*gorm.DB).Scan logs the "+
			"statement with its bound values interpolated — use "+
			"Find, Pluck, or Raw(...).Row().Scan instead. A "+
			"database/sql Scan reached through a variable is "+
			"reported too; write it as <producer>().Scan rather "+
			"than widening this check.",
	)
}

// scanGuardCase is one planted snippet and whether the check above
// should report it.
type scanGuardCase struct {
	name string
	body string
	want int
}

func scanGuardCases() []scanGuardCase {
	return []scanGuardCase{
		{"gorm chain", `db.DB().Raw("SELECT 1").Scan(&v)`, 1},
		{"gorm receiver", `gdb.Scan(&v)`, 1},
		{"gorm via variable", "q := gdb.Raw(\"x\")\nq.Scan(&v)", 1},
		{"gorm model chain", `gdb.Model(&x).Scan(&v)`, 1},
		{"sql row", `gdb.Raw("SELECT 1").Row().Scan(&v)`, 0},
		{"sql rows", `gdb.Raw("SELECT 1").Rows().Scan(&v)`, 0},
		{"unrelated call", `gdb.Find(&v)`, 0},
	}
}

// TestScanGuard_ReportsPlantedCalls proves the check fires. Without it
// a detector that matched nothing would satisfy the walk above no
// matter what the tree contained.
func TestScanGuard_ReportsPlantedCalls(t *testing.T) {
	t.Parallel()

	for _, tc := range scanGuardCases() {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			fset := token.NewFileSet()
			src := fmt.Sprintf(
				"package p\n\nfunc f() {\n\t%s\n}\n", tc.body,
			)

			file, err := parser.ParseFile(
				fset, tc.name+".go", src, 0,
			)
			require.NoError(t, err)

			require.Len(t, unguardedScans(fset, file), tc.want)
		})
	}
}