package vaultik

import (
	"bytes"
	"context"
	"crypto/rand"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"sync"
	"testing"

	"github.com/spf13/afero"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/vaultik/internal/config"
	"sneak.berlin/go/vaultik/internal/database"
	"sneak.berlin/go/vaultik/internal/log"
	"sneak.berlin/go/vaultik/internal/snapshot"
	"sneak.berlin/go/vaultik/internal/storage"
	"sneak.berlin/go/vaultik/internal/ui"
)

// TestRestoreLocalityAndReadAt asserts three properties of the restore
// hot path that together produce acceptable throughput on real-world
// snapshots. All three currently fail on main:
//
//  1. Peak blob cache occupancy ≤ 1.
//     Restore order must respect blob locality: every file fully
//     contained within the currently cached blob should be restored
//     before any other blob is downloaded. The sweeper then frees
//     each blob as soon as its file set is exhausted. Without smart
//     ordering, path-order interleaves blobs and the cache holds
//     every touched blob until the last file referencing it lands.
//
//  2. Each remote blob is fetched exactly once.
//     Counted via wrapping the Storer.
//
//  3. blobDiskCache.Get is never called during restore.
//     Chunk extraction from a cached blob must go through ReadAt,
//     which reads only the chunk's bytes from disk. Get reads the
//     entire blob (up to 50 GB in production) into memory just to
//     slice out a few KB — currently the dominant cost in restore.
//
// The test deliberately constructs an adversarial scenario: three
// blobs A/B/C of ~6 MB each, nine files distributed across them, and
// path-ordered names that interleave the blobs (a1, b1, c1, a2, b2,
// c2, …) so naive path-order processing would touch every blob before
// finishing any of them.
func TestRestoreLocalityAndReadAt(t *testing.T) {
	log.Initialize(log.Config{})

	fs := afero.NewOsFs()
	tempDir, err := os.MkdirTemp("", "vaultik-locality-")
	require.NoError(t, err)
	defer func() { _ = os.RemoveAll(tempDir) }()

	dataDir := filepath.Join(tempDir, "source")
	storeDir := filepath.Join(tempDir, "remote")
	restoreDir := filepath.Join(tempDir, "restored")
	dbPath := filepath.Join(tempDir, "index.sqlite")

	require.NoError(t, fs.MkdirAll(dataDir, 0o755))

	// Layout: 15 source files of exactly 1 MiB each. With
	// chunkSize (avg) = 4 MiB the chunker's minSize is 1 MiB, so any
	// file of 1 MiB becomes a single chunk. With a 5 MiB blob limit
	// the packer fits exactly 5 chunks per blob, producing 3 blobs
	// containing src-001..005, src-006..010, src-011..015.
	//
	// Then add 9 "copy" files — byte-for-byte clones of three of the
	// sources (one from each blob group) — with interleaved names
	// (cp-001-A, cp-002-B, cp-003-C, cp-004-A, …) so a naive
	// path-ordered restore would touch all three blobs before
	// finishing any of them.
	const (
		srcBytes   = 1024 * 1024
		srcCount   = 15
		blobsCount = 3
		perBlob    = srcCount / blobsCount
	)

	type source struct {
		path string
		data []byte
	}
	sources := make([]*source, srcCount)
	for i := 0; i < srcCount; i++ {
		s := &source{
			path: fmt.Sprintf("src-%03d.bin", i+1),
			data: randomBytes(t, srcBytes),
		}
		sources[i] = s
		require.NoError(t, afero.WriteFile(fs, filepath.Join(dataDir, s.path), s.data, 0o644))
	}

	// Pick one representative source per blob group (src-001 → blob
	// 1, src-006 → blob 2, src-011 → blob 3) and create 3 copies of
	// each with interleaved alphabetical names.
	type copyFile struct {
		path        string
		data        []byte
		sourceBlob  int // 0, 1, or 2
		sourceIndex int // index into sources slice
	}
	groupReps := []int{0, perBlob, 2 * perBlob} // 0, 5, 10
	letters := []byte{'A', 'B', 'C'}
	var copies []copyFile
	for i := 0; i < 3; i++ {
		for j := 0; j < blobsCount; j++ {
			seq := i*blobsCount + j + 1
			name := fmt.Sprintf("cp-%03d-%c.bin", seq, letters[j])
			path := filepath.Join(dataDir, name)
			src := sources[groupReps[j]]
			require.NoError(t, afero.WriteFile(fs, path, src.data, 0o644))
			copies = append(copies, copyFile{path: path, data: src.data, sourceBlob: j, sourceIndex: groupReps[j]})
		}
	}

	// chunkSize avg = 4 MiB makes minSize = 1 MiB, so a 1 MiB file
	// becomes one chunk. maxBlobSize = 5 MiB packs exactly 5 chunks
	// per blob, yielding 3 blobs from 15 source files.
	chunkSize := int64(4 * 1024 * 1024)
	maxBlobSize := int64(5 * 1024 * 1024)

	storer, err := storage.NewFileStorer(storeDir)
	require.NoError(t, err)

	agePublicKey := "age1ezrjmfpwsc95svdg0y54mums3zevgzu0x0ecq2f7tp8a05gl0sjq9q9wjg"
	ageSecretKey := "AGE-SECRET-KEY-19CR5YSFW59HM4TLD6GXVEDMZFTVVF7PPHKUT68TXSFPK7APHXA2QS2NJA5"

	cfg := &config.Config{
		AgeRecipients:    []string{agePublicKey},
		AgeSecretKey:     ageSecretKey,
		CompressionLevel: 3,
		Hostname:         "test-host",
		BlobSizeLimit:    config.Size(maxBlobSize),
	}

	ctx := context.Background()

	db, err := database.New(ctx, dbPath)
	require.NoError(t, err)
	defer func() { _ = db.Close() }()

	repos := database.NewRepositories(db)

	sm := snapshot.NewSnapshotManager(snapshot.SnapshotManagerParams{
		Repos:   repos,
		Storage: storer,
		Config:  cfg,
	})
	sm.SetFilesystem(fs)

	scanner := snapshot.NewScanner(snapshot.ScannerConfig{
		FS:               fs,
		Storage:          storer,
		ChunkSize:        chunkSize,
		MaxBlobSize:      maxBlobSize,
		CompressionLevel: cfg.CompressionLevel,
		AgeRecipients:    cfg.AgeRecipients,
		Repositories:     repos,
	})

	snapshotID, err := sm.CreateSnapshotWithName(ctx, cfg.Hostname, "locality", "test-version", "test-git")
	require.NoError(t, err)

	_, err = scanner.Scan(ctx, dataDir, snapshotID)
	require.NoError(t, err)

	require.NoError(t, sm.CompleteSnapshot(ctx, snapshotID))
	require.NoError(t, sm.ExportSnapshotMetadata(ctx, dbPath, snapshotID))

	blobsOnDisk := listBlobKeys(t, storeDir)
	t.Logf("backup produced %d blobs", len(blobsOnDisk))
	require.GreaterOrEqual(t, len(blobsOnDisk), 3, "expected at least 3 blobs from 3 filler groups")

	require.NoError(t, db.Close())

	// Wrap the storer so we can count downloads per blob key.
	counter := newCountingStorer(storer)

	// Capture the restore-side cache for instrumentation inspection.
	// The observer fires twice (immediately after creation and
	// immediately before close) so we read PeakLen and call counters
	// from the same instance the production code used.
	var cacheRef *blobDiskCache
	v := &Vaultik{
		Config:  cfg,
		Storage: counter,
		Fs:      fs,
		Stdout:  io.Discard,
		Stderr:  io.Discard,
		UI:      ui.NewWithColor(io.Discard, false),
		restoreCacheObserver: func(c *blobDiskCache) {
			cacheRef = c
		},
	}
	v.SetContext(ctx)

	require.NoError(t, v.Restore(&RestoreOptions{
		SnapshotID: snapshotID,
		TargetDir:  restoreDir,
	}))

	require.NotNil(t, cacheRef, "restoreCacheObserver must fire during restore")

	// Verify restored content matches.
	for _, s := range sources {
		restored := filepath.Join(restoreDir, dataDir, s.path)
		got, err := afero.ReadFile(fs, restored)
		require.NoErrorf(t, err, "source missing after restore: %s", s.path)
		require.Truef(t, bytes.Equal(got, s.data), "byte mismatch for source %s", s.path)
	}
	for _, c := range copies {
		restored := filepath.Join(restoreDir, c.path)
		got, err := afero.ReadFile(fs, restored)
		require.NoErrorf(t, err, "copy missing after restore: %s", c.path)
		require.Truef(t, bytes.Equal(got, c.data), "byte mismatch for copy %s", c.path)
	}

	// (1) Each blob fetched exactly once.
	for key, n := range counter.snapshot() {
		if !filterBlobKey(key) {
			continue
		}
		assert.Equalf(t, 1, n, "blob %s fetched %d times, want exactly 1", key, n)
	}

	// (2) Peak cache size ≤ 1. The sweeper plus locality-aware
	// ordering should free each blob before the next one downloads.
	assert.LessOrEqualf(t, cacheRef.PeakLen(), 1,
		"peak cached blobs was %d; expected ≤ 1 with locality-ordered restore", cacheRef.PeakLen())

	// (3) Cache.Get must never be called during restore — chunk
	// extraction has to go through ReadAt so we never read the whole
	// blob from disk to grab a few KB slice.
	assert.Equalf(t, 0, cacheRef.GetCalls(),
		"blobDiskCache.Get was called %d times during restore; restore must use ReadAt exclusively", cacheRef.GetCalls())

	t.Logf("blob cache stats: peak_len=%d get_calls=%d readat_calls=%d",
		cacheRef.PeakLen(), cacheRef.GetCalls(), cacheRef.ReadAtCalls())
}

// randomBytes returns n bytes of random data. Used to make sure the
// chunker picks non-degenerate FastCDC boundaries.
func randomBytes(t *testing.T, n int) []byte {
	t.Helper()
	b := make([]byte, n)
	_, err := rand.Read(b)
	require.NoError(t, err)
	return b
}

// listBlobKeys walks the FileStorer blobs/ tree and returns the
// relative keys for every blob file present.
func listBlobKeys(t *testing.T, storeDir string) []string {
	t.Helper()
	var keys []string
	root := filepath.Join(storeDir, "blobs")
	err := filepath.Walk(root, func(p string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsDir() {
			return nil
		}
		rel, _ := filepath.Rel(storeDir, p)
		keys = append(keys, rel)
		return nil
	})
	require.NoError(t, err)
	sort.Strings(keys)
	return keys
}

// filterBlobKey returns true when key looks like a blob storage path
// (rather than a snapshot metadata path).
func filterBlobKey(key string) bool {
	return len(key) > 6 && key[:6] == "blobs/"
}

// countingStorerInternal wraps a storage.Storer and records the number
// of Get calls per key, so the locality test can assert each blob is
// fetched exactly once. Defined here (rather than reusing the one in
// the integration_test package) because this test lives in package
// vaultik for access to unexported cache internals.
type countingStorerInternal struct {
	storage.Storer
	mu     sync.Mutex
	counts map[string]int
}

func newCountingStorer(inner storage.Storer) *countingStorerInternal {
	return &countingStorerInternal{Storer: inner, counts: make(map[string]int)}
}

func (c *countingStorerInternal) Get(ctx context.Context, key string) (io.ReadCloser, error) {
	c.mu.Lock()
	c.counts[key]++
	c.mu.Unlock()
	return c.Storer.Get(ctx, key)
}

func (c *countingStorerInternal) snapshot() map[string]int {
	c.mu.Lock()
	defer c.mu.Unlock()
	out := make(map[string]int, len(c.counts))
	for k, v := range c.counts {
		out[k] = v
	}
	return out
}