package xds

import (
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"testing"

	"github.com/golang/protobuf/jsonpb"
	"github.com/golang/protobuf/proto"
	"github.com/hashicorp/go-version"
	"github.com/stretchr/testify/require"
)

// update allows golden files to be updated based on the current output.
var update = flag.Bool("update", false, "update golden files")

// goldenSimple is just for read/write access to a golden file that is not
// envoy specific.
func goldenSimple(t *testing.T, name, got string) string {
	return golden(t, name, "", "", got)
}

// goldenEnvoy is a special variant of golden() that silos each named test by
// each supported envoy version
func goldenEnvoy(t *testing.T, name, envoyVersion, latestEnvoyVersion, got string) string {
	t.Helper()

	require.NotEmpty(t, envoyVersion)

	// We'll need both the name of this golden file for the requested version
	// of envoy AND the latest version of envoy due to how the golden file
	// coalescing works below when there is no xDS generated skew across envoy
	// versions.
	subname := goldenEnvoyVersionName(t, envoyVersion)

	latestSubname := "latest"
	if envoyVersion == latestEnvoyVersion {
		subname = "latest"
	}

	return golden(t, name, subname, latestSubname, got)
}

func goldenEnvoyVersionName(t *testing.T, envoyVersion string) string {
	t.Helper()

	require.NotEmpty(t, envoyVersion)

	// We do version sniffing on the complete version, but only generate
	// golden files ignoring the patch portion
	version := version.Must(version.NewVersion(envoyVersion))
	segments := version.Segments()
	require.Len(t, segments, 3)

	return fmt.Sprintf("envoy-%d-%d-x", segments[0], segments[1])
}

// golden reads and optionally writes the expected data to the golden file,
// returning the contents as a string.
//
// The golden file is named with two components the "name" and the "subname".
// In the common case of xDS tests the "name" component is the logical name of
// the test itself, and the "subname" is derived from the envoy major version.
//
// If latestSubname is specified we use that as a fallback source of comparison
// if the specific golden file referred to by subname is absent.
//
// If the -update flag is passed when executing the tests then the contents of
// the "got" argument are written to the golden file on disk. If the
// latestSubname argument is specified in this mode and the generated content
// matches that of the latest generated content then the specific golden file
// referred to by 'subname' is deleted to avoid unnecessary duplication in the
// testdata directory.
func golden(t *testing.T, name, subname, latestSubname, got string) string {
	t.Helper()

	suffix := ".golden"
	if subname != "" {
		suffix = fmt.Sprintf(".%s.golden", subname)
	}

	golden := filepath.Join("testdata", name+suffix)

	// Always load the latest golden file if configured to do so.
	latestExpected := ""
	if latestSubname != "" && subname != latestSubname {
		latestGolden := filepath.Join("testdata", fmt.Sprintf("%s.%s.golden", name, latestSubname))
		raw, err := os.ReadFile(latestGolden)
		require.NoError(t, err, "%q %q %q", name, subname, latestSubname)
		latestExpected = string(raw)
	}

	// Handle easy updates to the golden files in the agent/xds/testdata
	// directory.
	//
	// To trim down PRs, we only create per-version golden files if they differ
	// from the latest version.
	if *update && got != "" {
		if latestExpected == got {
			// In update mode we erase a golden file if it is identical to
			// the golden file corresponding to the latest version of
			// envoy.
			err := os.Remove(golden)
			if err != nil && !os.IsNotExist(err) {
				require.NoError(t, err)
			}
			return got
		}

		require.NoError(t, os.WriteFile(golden, []byte(got), 0644))
		return got
	}

	expected, err := os.ReadFile(golden)
	if latestExpected != "" && os.IsNotExist(err) {
		// In readonly mode if a specific golden file isn't found, we fallback
		// on the latest one.
		return latestExpected
	}
	require.NoError(t, err)
	return string(expected)
}

func loadTestResource(t *testing.T, name string) string {
	t.Helper()

	expected, err := os.ReadFile(filepath.Join("testdata", name+".golden"))
	require.NoError(t, err)
	return string(expected)
}

func protoToJSON(t *testing.T, pb proto.Message) string {
	t.Helper()
	m := jsonpb.Marshaler{
		Indent: "  ",
	}
	gotJSON, err := m.MarshalToString(pb)
	require.NoError(t, err)
	return gotJSON
}