package reportbuf_test

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"sneak.berlin/go/netwatch/internal/config"
	"sneak.berlin/go/netwatch/internal/globals"
	"sneak.berlin/go/netwatch/internal/logger"
	"sneak.berlin/go/netwatch/internal/reportbuf"

	"github.com/klauspost/compress/zstd"
	"go.uber.org/fx"
	"go.uber.org/fx/fxtest"
)

// TestFlushOnShutdown proves the flush-on-shutdown path: a
// report appended after start but before the periodic flush
// window must reach disk when the fx lifecycle stops. This is
// the exact case that silent data loss on restart used to
// destroy.
func TestFlushOnShutdown(t *testing.T) {
	dir := t.TempDir()
	t.Setenv("DATA_DIR", dir)

	var buf *reportbuf.Buffer

	app := fxtest.New(t,
		fx.Provide(
			globals.New,
			logger.New,
			config.New,
			reportbuf.New,
		),
		fx.Populate(&buf),
	)

	app.RequireStart()

	err := buf.Append(map[string]string{"probe": "shutdown"})
	if err != nil {
		t.Fatalf("append report: %v", err)
	}

	// RequireStop runs the reportbuf OnStop hook, which is the
	// only code path that flushes buffered reports on shutdown.
	app.RequireStop()

	if !hasReportFile(t, dir) {
		t.Fatal("no report file on disk after shutdown; " +
			"the buffered report was lost")
	}
}

// TestFailedFinalFlushFailsStop proves a final flush that cannot
// write its file makes the stop fail, which makes the process
// exit non-zero instead of dropping the buffered reports silently.
func TestFailedFinalFlushFailsStop(t *testing.T) {
	dir := t.TempDir()
	t.Setenv("DATA_DIR", dir)

	var buf *reportbuf.Buffer

	app := fxtest.New(t,
		fx.Provide(
			globals.New,
			logger.New,
			config.New,
			reportbuf.New,
		),
		fx.Populate(&buf),
	)

	app.RequireStart()

	err := buf.Append(map[string]string{"probe": "shutdown"})
	if err != nil {
		t.Fatalf("append report: %v", err)
	}

	// Removing the data directory leaves the final flush nowhere to
	// write. A read-only directory would not do: tests run as root
	// in the backend image, and root ignores the read-only bit.
	err = os.RemoveAll(dir)
	if err != nil {
		t.Fatalf("remove data dir: %v", err)
	}

	err = app.Stop(t.Context())
	if !errors.Is(err, fs.ErrNotExist) {
		t.Fatalf("stop error = %v, want the final flush's error", err)
	}
}

// startBuffer starts a Buffer through fx, as main does, with the
// DATA_DIR and DATA_DIR_MAX_BYTES the calling test has set.
func startBuffer(t *testing.T) *reportbuf.Buffer {
	t.Helper()

	var buf *reportbuf.Buffer

	app := fxtest.New(t,
		fx.Provide(
			globals.New,
			logger.New,
			config.New,
			reportbuf.New,
		),
		fx.Populate(&buf),
	)

	app.RequireStart()
	t.Cleanup(app.RequireStop)

	return buf
}

// lineBytes is what one report takes in the buffer: its JSON and a
// newline.
func lineBytes(t *testing.T, report any) int {
	t.Helper()

	line, err := json.Marshal(report)
	if err != nil {
		t.Fatalf("marshal report: %v", err)
	}

	return len(line) + 1
}

func TestAppendPastCapIsRefused(t *testing.T) {
	report := map[string]string{"id": "cap"}

	t.Setenv("DATA_DIR", t.TempDir())
	t.Setenv("DATA_DIR_MAX_BYTES", strconv.Itoa(lineBytes(t, report)))

	buf := startBuffer(t)

	err := buf.Append(report)
	if err != nil {
		t.Fatalf("report that fills the cap exactly: %v", err)
	}

	err = buf.Append(report)
	if !errors.Is(err, reportbuf.ErrFull) {
		t.Fatalf("report past the cap: error = %v, want ErrFull", err)
	}
}

// TestCapCountsReportFilesAlreadyInDataDir starts on a data
// directory holding a report file from an earlier run, and a file
// that is not a report, which must not count.
func TestCapCountsReportFilesAlreadyInDataDir(t *testing.T) {
	const earlierBytes = 100

	report := map[string]string{"id": "cap"}
	dir := t.TempDir()

	writeBytes(t, filepath.Join(dir, "reports-2026-01-01T00-00-00.000Z.jsonl.zst"),
		earlierBytes)
	writeBytes(t, filepath.Join(dir, "notes.txt"), 10*earlierBytes)

	t.Setenv("DATA_DIR", dir)
	t.Setenv("DATA_DIR_MAX_BYTES",
		strconv.Itoa(earlierBytes+lineBytes(t, report)))

	buf := startBuffer(t)

	err := buf.Append(report)
	if err != nil {
		t.Fatalf("report that fills the cap exactly: %v", err)
	}

	err = buf.Append(report)
	if !errors.Is(err, reportbuf.ErrFull) {
		t.Fatalf("report past the cap: error = %v, want ErrFull", err)
	}
}

// TestWrittenReportsCountAtFileSize checks that once reports are
// written, they count as their compressed file, not their
// uncompressed size, which frees room under the cap.
func TestWrittenReportsCountAtFileSize(t *testing.T) {
	// Repetitive, so its file is far smaller than its JSON.
	report := map[string]string{"id": strings.Repeat("a", 1000)}
	size := lineBytes(t, report)

	t.Setenv("DATA_DIR", t.TempDir())
	// Room for the report twice over only if the first one counts
	// at its file's size by the time the second arrives.
	t.Setenv("DATA_DIR_MAX_BYTES", strconv.Itoa(2*size-1))

	buf := startBuffer(t)

	err := buf.Append(report)
	if err != nil {
		t.Fatalf("first report: %v", err)
	}

	err = buf.Flush()
	if err != nil {
		t.Fatalf("flush: %v", err)
	}

	err = buf.Append(report)
	if err != nil {
		t.Fatalf("second report, after the first was written: %v", err)
	}
}

// TestWrittenReportsKeepCounting writes one report file after another
// under a small cap: each report must be taken while the files on disk
// leave room for it, and refused once they do not.
func TestWrittenReportsKeepCounting(t *testing.T) {
	const maxBytes = 200

	report := map[string]string{"id": "written"}
	size := int64(lineBytes(t, report))
	dir := t.TempDir()

	t.Setenv("DATA_DIR", dir)
	t.Setenv("DATA_DIR_MAX_BYTES", strconv.Itoa(maxBytes))

	buf := startBuffer(t)

	// Every file takes at least a byte, so they fill the cap within
	// maxBytes rounds.
	for range maxBytes {
		used := reportFilesBytes(t, dir)

		err := buf.Append(report)
		if used+size > maxBytes {
			if !errors.Is(err, reportbuf.ErrFull) {
				t.Fatalf("with %d bytes of report files: error = %v, "+
					"want ErrFull", used, err)
			}

			return
		}

		if err != nil {
			t.Fatalf("with %d bytes of report files: %v", used, err)
		}

		err = buf.Flush()
		if err != nil {
			t.Fatalf("flush: %v", err)
		}
	}

	t.Fatal("the report files never filled the cap")
}

// TestConcurrentAppendsStopAtCap appends from many goroutines at once
// with room for exactly roomFor reports: exactly that many must be
// taken, which holds only if Append checks and counts each report
// under one lock.
func TestConcurrentAppendsStopAtCap(t *testing.T) {
	const (
		roomFor = 5
		senders = 50
	)

	// Large, so each Append takes long enough for the senders to
	// overlap while the cap is reached.
	report := map[string]string{"id": strings.Repeat("a", 1_000_000)}

	t.Setenv("DATA_DIR", t.TempDir())
	t.Setenv("DATA_DIR_MAX_BYTES",
		strconv.Itoa(roomFor*lineBytes(t, report)))

	buf := startBuffer(t)

	var (
		taken atomic.Int64
		wg    sync.WaitGroup
	)

	start := make(chan struct{})

	for range senders {
		wg.Go(func() {
			<-start

			err := buf.Append(report)
			if err == nil {
				taken.Add(1)
			} else if !errors.Is(err, reportbuf.ErrFull) {
				t.Errorf("append: %v", err)
			}
		})
	}

	close(start)
	wg.Wait()

	if got := taken.Load(); got != roomFor {
		t.Fatalf("%d reports taken, want %d", got, roomFor)
	}
}

// TestTwoFlushesInOneMillisecond flushes twice within one millisecond,
// as a flush for size and the final flush at shutdown can: each flush
// must write a file of its own, and the files must hold every report.
func TestTwoFlushesInOneMillisecond(t *testing.T) {
	// A pair of flushes may straddle a millisecond, which proves
	// nothing, so pairs are flushed until one falls within one.
	const maxPairs = 1000

	dir := t.TempDir()
	t.Setenv("DATA_DIR", dir)

	buf := startBuffer(t)
	flushes := 0

	for pair := 1; ; pair++ {
		start := time.Now().Truncate(time.Millisecond)

		for range 2 {
			flushes++

			err := buf.Append(map[string]int{"id": flushes})
			if err != nil {
				t.Fatalf("append report %d: %v", flushes, err)
			}

			err = buf.Flush()
			if err != nil {
				t.Fatalf("flush %d: %v", flushes, err)
			}
		}

		if time.Now().Truncate(time.Millisecond).Equal(start) {
			break
		}

		if pair == maxPairs {
			t.Fatalf("no pair of flushes fell within one millisecond "+
				"in %d tries", maxPairs)
		}
	}

	files := readReportFiles(t, dir)
	if len(files) != flushes {
		t.Fatalf("%d report files after %d flushes", len(files), flushes)
	}

	for id := 1; id <= flushes; id++ {
		want := fmt.Sprintf(`{"id":%d}`+"\n", id)
		if !slices.Contains(files, want) {
			t.Fatalf("no report file holds report %d alone", id)
		}
	}
}

// reportFilesBytes returns the total size of the report files in dir.
func reportFilesBytes(t *testing.T, dir string) int64 {
	t.Helper()

	paths, err := filepath.Glob(filepath.Join(dir, "reports-*.jsonl.zst"))
	if err != nil {
		t.Fatalf("list report files: %v", err)
	}

	var total int64

	for _, path := range paths {
		info, statErr := os.Stat(path)
		if statErr != nil {
			t.Fatalf("stat %s: %v", path, statErr)
		}

		total += info.Size()
	}

	return total
}

// readReportFiles returns the decompressed contents of each report
// file in dir.
func readReportFiles(t *testing.T, dir string) []string {
	t.Helper()

	paths, err := filepath.Glob(filepath.Join(dir, "reports-*.jsonl.zst"))
	if err != nil {
		t.Fatalf("list report files: %v", err)
	}

	dec, err := zstd.NewReader(nil)
	if err != nil {
		t.Fatalf("create zstd decoder: %v", err)
	}
	defer dec.Close()

	contents := make([]string, 0, len(paths))

	for _, path := range paths {
		compressed, readErr := os.ReadFile(path)
		if readErr != nil {
			t.Fatalf("read %s: %v", path, readErr)
		}

		data, decErr := dec.DecodeAll(compressed, nil)
		if decErr != nil {
			t.Fatalf("decompress %s: %v", path, decErr)
		}

		contents = append(contents, string(data))
	}

	return contents
}

func writeBytes(t *testing.T, path string, n int) {
	t.Helper()

	err := os.WriteFile(path, make([]byte, n), 0o600)
	if err != nil {
		t.Fatalf("write %s: %v", path, err)
	}
}

func hasReportFile(t *testing.T, dir string) bool {
	t.Helper()

	entries, err := os.ReadDir(dir)
	if err != nil {
		t.Fatalf("read data dir: %v", err)
	}

	for _, e := range entries {
		if strings.HasSuffix(e.Name(), ".jsonl.zst") {
			info, statErr := e.Info()
			if statErr != nil {
				t.Fatalf("stat %s: %v", e.Name(), statErr)
			}

			if info.Size() > 0 {
				return true
			}
		}
	}

	return false
}