package nwsync

import (
	"context"
	"crypto/sha1"
	"fmt"
	"io"
	"os"
	"path"
	"path/filepath"
	"slices"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/buildinfo"
	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/erf"
)

// fileSizeLimit matches upstream's --limit-file-size default of 15 MB. A
// resource over it is a hard failure, not a skip: upstream quit(1)s and so do
// we. Our largest resource today is 13.66 MiB, so the headroom is thin.
const fileSizeLimit = 15 * 1024 * 1024

// skippedTypes are never published, matching upstream's GobalResTypeSkipList.
var skippedTypes = resTypes("nss", "ndb", "gic")

// emitterVersion identifies the blob/manifest byte format this package
// produces. assemble refuses to merge indexes that disagree on it, because two
// producers of blobs mean a skewed emitter can otherwise write blobs the merged
// manifest quietly disagrees with. Bump it only when emitted bytes change — it
// is deliberately not the build revision, which would invalidate every
// published index on every unrelated commit.
// Version 2 declares Frame_Content_Size on every blob (#86); version 1 omitted
// it below 256 bytes and no client could sync past such a blob.
const emitterVersion = "2"

// serverTypes are loaded only server-side; a manifest holding nothing else
// has no client contents. Mirrors upstream's GlobalResTypeServerList, whose
// trailing 0 is RESTYPE_INVALID.
var serverTypes = append(resTypes(
	"are", "dlg", "fac", "gic", "git", "ifo", "itp", "jrl", "ncs", "ndb",
	"nss", "ptm", "utc", "utd", "ute", "uti", "utm", "utp", "uts", "utt", "utw",
), 0)

func resTypes(extensions ...string) []uint16 {
	types := make([]uint16, 0, len(extensions))
	for _, extension := range extensions {
		restype, ok := erf.ResourceTypeForExtension(extension)
		if !ok {
			panic("nwsync: unknown restype " + extension)
		}
		types = append(types, restype)
	}
	return types
}

// EmitResult reports what one emit run produced.
type EmitResult struct {
	Name         string // artifact name, without extension
	ManifestPath string
	Entries      int
	BlobsWritten int
}

// defaultEmitJobs is how many resources are hashed, compressed and stored at
// once. Emit is latency-bound, not CPU-bound: a blob costs a probe round-trip
// plus an upload round-trip, and a measured backfill spent 26 s of CPU across
// 9.5 minutes of wall clock. The figure matches depot's DEPOT_JOBS default and
// the transport's MaxIdleConnsPerHost, so a worker per connection needs no new
// TLS handshake.
const defaultEmitJobs = 16

// EmitOptions describes one emit run.
type EmitOptions struct {
	ArtifactKey  string // depot key of the artifact; the NSYM key is derived from it
	ArtifactPath string // the file on disk
	As           string // name override, for a TLK whose filename is not its published name
	OutDir       string // write locally instead of uploading — the conformance path
	Jobs         int    // resources in flight at once; 0 means defaultEmitJobs
	Verify       bool   // hash what would be skipped instead of trusting presence
	Sink         sink   // test seam; nil means OutDir or the zone
}

// Emit explodes one artifact — a .hak/.erf or a loose file such as the TLK —
// into NWSync blobs plus a NSYM manifest describing only that artifact.
//
// Blobs go up as they are produced and the index lands last, so the presence of
// an index is the publication marker: an artifact whose emit died halfway has
// real blobs in the zone and no index, which is unambiguous. Blob names are
// content hashes, so re-running skips whatever already landed.
func Emit(options EmitOptions) (EmitResult, error) {
	artifact, err := os.Open(options.ArtifactPath)
	if err != nil {
		return EmitResult{}, fmt.Errorf("read artifact: %w", err)
	}
	defer artifact.Close()
	info, err := artifact.Stat()
	if err != nil {
		return EmitResult{}, fmt.Errorf("read artifact: %w", err)
	}
	// A section reader, not the file itself: hashing must not move the file
	// offset out from under everything that reads the artifact afterwards.
	if err := checkArtifactKey(options.ArtifactKey, io.NewSectionReader(artifact, 0, info.Size())); err != nil {
		return EmitResult{}, err
	}
	name := options.As
	if name == "" {
		name = path.Base(options.ArtifactKey)
	}
	extension := path.Ext(name)
	name = strings.TrimSuffix(name, extension)

	key, err := resolveIndexKey(options.ArtifactKey, options.OutDir)
	if err != nil {
		return EmitResult{}, err
	}

	index, err := readArtifactIndex(options.ArtifactPath, artifact, info.Size(), name)
	if err != nil {
		return EmitResult{}, err
	}

	target, err := openSink(options.OutDir, options.Sink)
	if err != nil {
		return EmitResult{}, err
	}

	jobs := options.Jobs
	if jobs < 1 {
		jobs = defaultEmitJobs
	}
	entries, blobs, onDiskBytes, err := emitResources(artifact, index, target, jobs, options.Verify)
	if err != nil {
		return EmitResult{}, err
	}
	if len(entries) == 0 {
		return EmitResult{}, fmt.Errorf("%s: nothing to index (no publishable resources)", options.ArtifactPath)
	}

	data, err := writeManifest(entries)
	if err != nil {
		return EmitResult{}, err
	}
	if err := putManifestPair(target, key, data, entries, onDiskBytes, Sidecar{ModuleName: name}); err != nil {
		return EmitResult{}, err
	}
	return EmitResult{Name: name, ManifestPath: target.describe(key), Entries: len(entries), BlobsWritten: blobs}, nil
}

// openSink returns the zone sink, or a local directory when outDir is set.
func openSink(outDir string, injected sink) (sink, error) {
	if injected != nil {
		return injected, nil
	}
	if outDir != "" {
		return dirSink{root: outDir}, nil
	}
	return newZoneSink(context.Background(), os.Getenv)
}

// readArtifactIndex locates the resources of an ERF/HAK/MOD, or the single
// resource a loose file represents, without reading any payload. Upstream's
// resman does the same dispatch on the file's first three bytes. name is the
// artifact's published name, which for a loose file is also its resref.
func readArtifactIndex(path string, artifact io.ReaderAt, size int64, name string) ([]erf.IndexEntry, error) {
	magic := make([]byte, 3)
	if size >= 3 {
		if _, err := artifact.ReadAt(magic, 0); err != nil {
			return nil, fmt.Errorf("%s: %w", path, err)
		}
	}
	switch string(magic) {
	case "ERF", "HAK":
		index, err := erf.ReadIndex(artifact, size)
		if err != nil {
			return nil, fmt.Errorf("%s: %w", path, err)
		}
		return index.Entries, nil
	case "MOD":
		// A persistent world never publishes module contents, so the .mod
		// contributes no bytes to a manifest — it only says which haks and
		// which TLK the manifest covers.
		return nil, fmt.Errorf("%s: a module is never emitted; a manifest is haks plus the TLK", path)
	}
	extension := filepath.Ext(filepath.Base(path))
	restype, ok := erf.ResourceTypeForExtension(extension)
	if !ok {
		return nil, fmt.Errorf("%s: unknown resource type %q", path, extension)
	}
	return []erf.IndexEntry{{Name: name, Type: restype, Offset: 0, Size: size}}, nil
}

// emitResources hashes, compresses and stores resources, reading each payload
// from the artifact only when its turn comes. Peak memory tracks the resources
// in flight, not the archive: a 2 GB hak must emit inside a runner's few spare
// GB. jobs of them are in flight at once, so the ceiling is jobs multiplied by
// fileSizeLimit and its compressed copy — bounded, and bounded by a constant
// this package enforces itself.
//
// The returned entries are in artifact order whatever order the workers finish
// in, because a manifest's bytes are promised deterministic by emitterVersion.
func emitResources(artifact io.ReaderAt, index []erf.IndexEntry, target sink, jobs int, verify bool) ([]Entry, int, int64, error) {
	// A resref appearing twice inside one artifact resolves to the last one,
	// the way resman lets the last container added win.
	order := make([]Identity, 0, len(index))
	latest := make(map[Identity]erf.IndexEntry, len(index))
	var tooBig []string
	for _, entry := range index {
		if _, ok := erf.ExtensionForResourceType(entry.Type); !ok {
			return nil, 0, 0, fmt.Errorf("resref %s is not resolvable (unknown restype %d)", entry.Name, entry.Type)
		}
		if slices.Contains(skippedTypes, entry.Type) {
			continue
		}
		if entry.Size > fileSizeLimit {
			tooBig = append(tooBig, fmt.Sprintf("%s: %d bytes > %d", entry.Name, entry.Size, fileSizeLimit))
			continue
		}
		identity := Identity{ResRef: strings.ToLower(entry.Name), ResType: entry.Type}
		if _, seen := latest[identity]; !seen {
			order = append(order, identity)
		}
		latest[identity] = entry
	}
	if len(tooBig) > 0 {
		sort.Strings(tooBig)
		return nil, 0, 0, fmt.Errorf("resources exceed the file size limit:\n  %s", strings.Join(tooBig, "\n  "))
	}

	// Index-addressed, never appended to: a worker owns entries[i] alone, so
	// the slice comes back in artifact order and needs no lock.
	entries := make([]Entry, len(order))
	var blobs int
	var onDiskBytes int64
	var mu sync.Mutex
	var firstErr error
	// Two resrefs in one artifact can hold identical bytes, and therefore one
	// blob. Serially the sink's existence check absorbed that; in parallel both
	// workers would probe, both miss, and both upload. Claiming the sha1 here
	// restores the dedupe and skips the probe round-trip as well.
	claimed := make(map[[20]byte]bool, len(order))

	failed := func() bool {
		mu.Lock()
		defer mu.Unlock()
		return firstErr != nil
	}

	store := func(i int) {
		identity := order[i]
		payload, err := erf.ReadPayload(artifact, latest[identity])
		if err != nil {
			mu.Lock()
			if firstErr == nil {
				firstErr = err
			}
			mu.Unlock()
			return
		}
		sum := sha1.Sum(payload)
		entries[i] = Entry{
			SHA1:    sum,
			Size:    uint32(len(payload)),
			ResRef:  identity.ResRef,
			ResType: identity.ResType,
		}
		mu.Lock()
		duplicate := claimed[sum]
		claimed[sum] = true
		mu.Unlock()
		if duplicate {
			return
		}
		written, err := target.putBlob(fmt.Sprintf("%x", sum), verify, func() []byte { return compressBlob(payload) })
		mu.Lock()
		defer mu.Unlock()
		if err != nil {
			if firstErr == nil {
				firstErr = err
			}
			return
		}
		if written > 0 {
			blobs++
			onDiskBytes += written
		}
	}

	if jobs < 1 {
		jobs = 1
	}
	work := make(chan int)
	var wg sync.WaitGroup
	for range jobs {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for i := range work {
				// After a failure the run is over — the caller discards
				// everything and no index is written. Draining the rest of the
				// channel cheaply, rather than returning, keeps the feeder from
				// blocking on workers that have gone away.
				if failed() {
					continue
				}
				store(i)
			}
		}()
	}
	for i := range order {
		work <- i
	}
	close(work)
	wg.Wait()

	if firstErr != nil {
		return nil, 0, 0, firstErr
	}
	return entries, blobs, onDiskBytes, nil
}

// created is the sidecar timestamp. SOURCE_DATE_EPOCH pins it so a build can
// be reproduced byte for byte; the manifest itself is deterministic already.
func created() int64 {
	if raw := os.Getenv("SOURCE_DATE_EPOCH"); raw != "" {
		if seconds, err := strconv.ParseInt(raw, 10, 64); err == nil {
			return seconds
		}
	}
	return time.Now().Unix()
}

// putManifestPair stores a NSYM manifest and its .json sidecar at key. The
// caller supplies the sidecar fields it knows; the rest are derived from the
// entries. data must be the serialised form of entries.
func putManifestPair(target sink, key string, data []byte, entries []Entry, onDiskBytes int64, sidecar Sidecar) error {
	var totalBytes int64
	clientContents := false
	for _, entry := range entries {
		totalBytes += int64(entry.Size)
		if !slices.Contains(serverTypes, entry.ResType) {
			clientContents = true
		}
	}
	sidecar.Version = manifestVersion
	sidecar.SHA1 = fmt.Sprintf("%x", sha1.Sum(data))
	sidecar.HashTreeDepth = hashTreeDepth
	sidecar.IncludesModuleContents = false
	sidecar.IncludesClientContents = clientContents
	sidecar.TotalFiles = len(entries)
	sidecar.TotalBytes = totalBytes
	sidecar.OnDiskBytes = onDiskBytes
	sidecar.Created = created()
	sidecar.CreatedWith = buildinfo.String()
	sidecar.EmitterVersion = emitterVersion

	body, err := marshalSidecar(sidecar)
	if err != nil {
		return err
	}
	return target.putIndex(key, data, body)
}