package mountain_pass

import (
	"crypto/md5"
	"encoding/hex"
	"net/http"
	"net/http/httptest"
	"os"
	"path/filepath"
	"strings"
	"testing"

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

// osmd5Hex mirrors the production helper in the test so the expected checksum
// served by the fake geofabrik server is derived independently of pbfMD5.
func osmd5Hex(data []byte) string {
	sum := md5.Sum(data)
	return hex.EncodeToString(sum[:])
}

// fakeGeofabrik serves a PBF payload and an optional .md5 sibling.
func fakeGeofabrik(t *testing.T, pbf []byte, md5Body string) *httptest.Server {
	t.Helper()
	mux := http.NewServeMux()
	mux.HandleFunc("/france-latest.osm.pbf", func(w http.ResponseWriter, r *http.Request) {
		w.Write(pbf)
	})
	mux.HandleFunc("/france-latest.osm.pbf.md5", func(w http.ResponseWriter, r *http.Request) {
		if md5Body == "" {
			http.Error(w, "not found", http.StatusNotFound)
			return
		}
		w.Write([]byte(md5Body))
	})
	srv := httptest.NewServer(mux)
	t.Cleanup(srv.Close)
	return srv
}

func TestFetchFrancePBFDownloadsAndVerifies(t *testing.T) {
	pbf := []byte("some-valid-pbf-content-1")
	srv := fakeGeofabrik(t, pbf, osmd5Hex(pbf)+"  france-latest.osm.pbf\n")
	dest := filepath.Join(t.TempDir(), "france-latest.osm.pbf")

	err := fetchFrancePBF(srv.Client(), srv.URL+"/france-latest.osm.pbf", dest)
	require.NoError(t, err)

	got, err := os.ReadFile(dest)
	require.NoError(t, err)
	assert.Equal(t, pbf, got)
}

func TestFetchFrancePBFMismatchRetainsFile(t *testing.T) {
	pbf := []byte("some-valid-pbf-content-2")
	srv := fakeGeofabrik(t, pbf, strings.Repeat("0", 32)+"  france-latest.osm.pbf\n")
	dest := filepath.Join(t.TempDir(), "france-latest.osm.pbf")

	err := fetchFrancePBF(srv.Client(), srv.URL+"/france-latest.osm.pbf", dest)
	require.Error(t, err)
	assert.Contains(t, err.Error(), "checksum mismatch")

	// The corrupt file is kept for inspection, not deleted.
	got, readErr := os.ReadFile(dest)
	require.NoError(t, readErr)
	assert.Equal(t, pbf, got)
}

func TestFetchFrancePBFAlreadyCompleteVerified(t *testing.T) {
	pbf := []byte("some-valid-pbf-content-3")
	srv := fakeGeofabrik(t, pbf, osmd5Hex(pbf)+"  france-latest.osm.pbf\n")
	dest := filepath.Join(t.TempDir(), "france-latest.osm.pbf")
	require.NoError(t, os.WriteFile(dest, pbf, 0o644))

	err := fetchFrancePBF(srv.Client(), srv.URL+"/france-latest.osm.pbf", dest)
	require.NoError(t, err)

	got, _ := os.ReadFile(dest)
	assert.Equal(t, pbf, got)
}

func TestFetchFrancePBFAlreadyCompleteCorrupt(t *testing.T) {
	pbf := []byte("the-real-content")
	corrupt := []byte(strings.Repeat("x", len(pbf)))
	require.Equal(t, len(pbf), len(corrupt), "same length to prove size-only check is not enough")
	srv := fakeGeofabrik(t, pbf, osmd5Hex(pbf)+"  france-latest.osm.pbf\n")
	dest := filepath.Join(t.TempDir(), "france-latest.osm.pbf")
	require.NoError(t, os.WriteFile(dest, corrupt, 0o644))

	err := fetchFrancePBF(srv.Client(), srv.URL+"/france-latest.osm.pbf", dest)
	require.Error(t, err)
	assert.Contains(t, err.Error(), "checksum mismatch")

	got, _ := os.ReadFile(dest)
	assert.Equal(t, corrupt, got, "corrupt file retained for inspection")
}

func TestFetchFrancePBFSkipsVerificationWhenChecksumUnreachable(t *testing.T) {
	pbf := []byte("some-valid-pbf-content-4")
	srv := fakeGeofabrik(t, pbf, "") // md5 endpoint returns 404
	dest := filepath.Join(t.TempDir(), "france-latest.osm.pbf")

	err := fetchFrancePBF(srv.Client(), srv.URL+"/france-latest.osm.pbf", dest)
	require.NoError(t, err)

	got, _ := os.ReadFile(dest)
	assert.Equal(t, pbf, got)
}

func TestPBFMD5(t *testing.T) {
	data := []byte("known-content-for-md5-test")
	expected := osmd5Hex(data)
	path := filepath.Join(t.TempDir(), "sample.bin")
	require.NoError(t, os.WriteFile(path, data, 0o644))

	got, err := pbfMD5(path)
	require.NoError(t, err)
	assert.Equal(t, expected, got)
}