package artifacts

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path"
	"sort"
	"strings"
	"time"

	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
)

const (
	RemoteLockFormatVersion  = 1
	MaxRemoteLockObjectBytes = 64 << 10
)

const remoteLocksSegment = "locks"

// RemoteLock records an operator lock on one canonical publish source.
type RemoteLock struct {
	FormatVersion int
	Source        string
	Reason        string
	CreatedAt     time.Time
}

// RemoteLockLookup distinguishes an absent lock from a present validated lock.
type RemoteLockLookup struct {
	Lock       RemoteLock
	Present    bool
	Generation string
}

type remoteLockDocument struct {
	FormatVersion int    `json:"format_version"`
	Source        string `json:"source"`
	Reason        string `json:"reason,omitempty"`
	CreatedAt     string `json:"created_at"`
}

// NewRemoteLock constructs and validates one lock payload.
func NewRemoteLock(source, reason string, createdAt time.Time) (RemoteLock, error) {
	lock := RemoteLock{
		FormatVersion: RemoteLockFormatVersion,
		Source:        source,
		Reason:        reason,
		CreatedAt:     createdAt,
	}
	if err := lock.Validate(); err != nil {
		return RemoteLock{}, err
	}
	return lock, nil
}

// Validate checks the complete canonical lock payload contract.
func (l RemoteLock) Validate() error {
	if l.FormatVersion != RemoteLockFormatVersion {
		return fmt.Errorf("unsupported remote lock format version %d", l.FormatVersion)
	}
	if err := validateCanonicalPublishSource(l.Source); err != nil {
		return fmt.Errorf("remote lock source: %w", err)
	}
	if strings.TrimSpace(l.Reason) != l.Reason {
		return fmt.Errorf("remote lock reason must not have surrounding whitespace")
	}
	if l.CreatedAt.IsZero() {
		return fmt.Errorf("remote lock created_at is required")
	}
	_, offset := l.CreatedAt.Zone()
	if offset != 0 {
		return fmt.Errorf("remote lock created_at must be UTC")
	}
	return nil
}

// EncodeRemoteLock returns the canonical bounded JSON representation of a lock.
func EncodeRemoteLock(lock RemoteLock) ([]byte, error) {
	if err := lock.Validate(); err != nil {
		return nil, err
	}
	document := remoteLockDocument{
		FormatVersion: lock.FormatVersion,
		Source:        lock.Source,
		Reason:        lock.Reason,
		CreatedAt:     lock.CreatedAt.UTC().Format(time.RFC3339Nano),
	}
	data, err := json.Marshal(document)
	if err != nil {
		return nil, fmt.Errorf("encode remote lock: %w", err)
	}
	if len(data) > MaxRemoteLockObjectBytes {
		return nil, fmt.Errorf("encode remote lock: payload exceeds %d-byte limit", MaxRemoteLockObjectBytes)
	}
	return data, nil
}

// DecodeRemoteLock strictly decodes and validates one bounded lock payload.
func DecodeRemoteLock(data []byte) (RemoteLock, error) {
	if len(data) > MaxRemoteLockObjectBytes {
		return RemoteLock{}, fmt.Errorf("decode remote lock: payload exceeds %d-byte limit", MaxRemoteLockObjectBytes)
	}
	var document remoteLockDocument
	if err := decodeStrictJSON(data, &document); err != nil {
		return RemoteLock{}, fmt.Errorf("decode remote lock: %w", err)
	}
	createdAt, err := time.Parse(time.RFC3339Nano, document.CreatedAt)
	if err != nil {
		return RemoteLock{}, fmt.Errorf("decode remote lock created_at: %w", err)
	}
	if !strings.HasSuffix(document.CreatedAt, "Z") || createdAt.UTC().Format(time.RFC3339Nano) != document.CreatedAt {
		return RemoteLock{}, fmt.Errorf("decode remote lock created_at: must be canonical RFC 3339 UTC")
	}
	lock := RemoteLock{
		FormatVersion: document.FormatVersion,
		Source:        document.Source,
		Reason:        document.Reason,
		CreatedAt:     createdAt,
	}
	if err := lock.Validate(); err != nil {
		return RemoteLock{}, fmt.Errorf("decode remote lock: %w", err)
	}
	return lock, nil
}

// RemoteLockKey returns the independent lock key for one canonical source.
func RemoteLockKey(sessionPrefix, source string) (string, error) {
	locksPrefix, err := remoteLocksPrefix(sessionPrefix)
	if err != nil {
		return "", err
	}
	if err := validateCanonicalPublishSource(source); err != nil {
		return "", err
	}
	return locksPrefix + remoteLockDigest(source) + ".lock", nil
}

// LookupRemoteLock opens and validates the lock for one source when present.
func LookupRemoteLock(ctx context.Context, store storage.ObjectStore, sessionPrefix, source string) (RemoteLockLookup, error) {
	if store == nil {
		return RemoteLockLookup{}, fmt.Errorf("lookup remote lock: object store is required")
	}
	key, err := RemoteLockKey(sessionPrefix, source)
	if err != nil {
		return RemoteLockLookup{}, fmt.Errorf("lookup remote lock: %w", err)
	}
	return lookupRemoteLockAtKey(ctx, store, key, source)
}

// ListRemoteLocks validates every object in the reserved lock prefix and sorts
// the resulting locks by source.
func ListRemoteLocks(ctx context.Context, store storage.ObjectStore, sessionPrefix string) ([]RemoteLock, error) {
	if store == nil {
		return nil, fmt.Errorf("list remote locks: object store is required")
	}
	locksPrefix, err := remoteLocksPrefix(sessionPrefix)
	if err != nil {
		return nil, fmt.Errorf("list remote locks: %w", err)
	}
	objects, err := store.List(ctx, locksPrefix)
	if err != nil {
		return nil, fmt.Errorf("list remote locks under %q: %w", locksPrefix, err)
	}
	locks := make([]RemoteLock, 0, len(objects))
	seenSources := make(map[string]struct{}, len(objects))
	for _, object := range objects {
		digest, err := remoteLockDigestFromKey(locksPrefix, object.Key)
		if err != nil {
			return nil, fmt.Errorf("list remote locks: %w", err)
		}
		info, data, err := storage.ReadObjectBounded(ctx, store, object.Key, MaxRemoteLockObjectBytes)
		if err != nil {
			return nil, fmt.Errorf("read remote lock %q: %w", object.Key, err)
		}
		if info.Key != "" && info.Key != object.Key {
			return nil, fmt.Errorf("read remote lock %q: store returned key %q", object.Key, info.Key)
		}
		lock, err := DecodeRemoteLock(data)
		if err != nil {
			return nil, fmt.Errorf("read remote lock %q: %w", object.Key, err)
		}
		if actual := remoteLockDigest(lock.Source); actual != digest {
			return nil, fmt.Errorf("remote lock %q source hash mismatch", object.Key)
		}
		if _, duplicate := seenSources[lock.Source]; duplicate {
			return nil, fmt.Errorf("remote lock source %q is duplicated", lock.Source)
		}
		seenSources[lock.Source] = struct{}{}
		locks = append(locks, lock)
	}
	sort.Slice(locks, func(i, j int) bool { return locks[i].Source < locks[j].Source })
	return locks, nil
}

// AddRemoteLock conditionally creates one lock. With force, one observed lock
// generation may be replaced; conflicts are returned for operator retry.
func AddRemoteLock(ctx context.Context, store storage.ObjectStore, sessionPrefix string, lock RemoteLock, force bool) error {
	if store == nil {
		return fmt.Errorf("add remote lock: object store is required")
	}
	data, err := EncodeRemoteLock(lock)
	if err != nil {
		return fmt.Errorf("add remote lock: %w", err)
	}
	key, err := RemoteLockKey(sessionPrefix, lock.Source)
	if err != nil {
		return fmt.Errorf("add remote lock: %w", err)
	}
	condition := storage.WriteCondition{RequireAbsent: true}
	if force {
		current, err := lookupRemoteLockAtKey(ctx, store, key, lock.Source)
		if err != nil {
			return fmt.Errorf("add remote lock %q: %w", lock.Source, err)
		}
		if current.Present {
			if strings.TrimSpace(current.Generation) == "" {
				return fmt.Errorf("add remote lock %q: current generation is required for replacement", lock.Source)
			}
			condition = storage.WriteCondition{MatchETag: current.Generation}
		}
	}
	_, err = store.UploadConditional(ctx, bytes.NewReader(data), key, storage.UploadOptions{ContentType: "application/json"}, condition)
	if err != nil {
		return fmt.Errorf("add remote lock %q: %w", lock.Source, err)
	}
	return nil
}

// RemoveRemoteLock idempotently removes the lock for one canonical source.
func RemoveRemoteLock(ctx context.Context, store storage.ObjectStore, sessionPrefix, source string) error {
	if store == nil {
		return fmt.Errorf("remove remote lock: object store is required")
	}
	key, err := RemoteLockKey(sessionPrefix, source)
	if err != nil {
		return fmt.Errorf("remove remote lock: %w", err)
	}
	if err := store.Delete(ctx, key); err != nil {
		return fmt.Errorf("remove remote lock %q: %w", source, err)
	}
	return nil
}

func lookupRemoteLockAtKey(ctx context.Context, store storage.ObjectStore, key, source string) (RemoteLockLookup, error) {
	info, data, err := storage.ReadObjectBounded(ctx, store, key, MaxRemoteLockObjectBytes)
	if errors.Is(err, os.ErrNotExist) {
		return RemoteLockLookup{}, nil
	}
	if err != nil {
		return RemoteLockLookup{}, fmt.Errorf("read object %q: %w", key, err)
	}
	lock, err := DecodeRemoteLock(data)
	if err != nil {
		return RemoteLockLookup{}, fmt.Errorf("read object %q: %w", key, err)
	}
	if lock.Source != source || remoteLockDigest(lock.Source) != strings.TrimSuffix(path.Base(key), ".lock") {
		return RemoteLockLookup{}, fmt.Errorf("remote lock %q source hash mismatch", key)
	}
	return RemoteLockLookup{Lock: lock, Present: true, Generation: info.ETag}, nil
}

func remoteLocksPrefix(sessionPrefix string) (string, error) {
	if err := validateRemoteLockSessionPrefix(sessionPrefix); err != nil {
		return "", err
	}
	return sessionPrefix + remoteLocksSegment + "/", nil
}

func validateRemoteLockSessionPrefix(sessionPrefix string) error {
	return validateRemoteSessionPrefix(sessionPrefix)
}

func remoteLockDigest(source string) string {
	sum := sha256.Sum256([]byte(source))
	return hex.EncodeToString(sum[:])
}

func remoteLockDigestFromKey(prefix, key string) (string, error) {
	if err := validateRemoteObjectKey(key); err != nil {
		return "", fmt.Errorf("invalid remote lock key %q: %w", key, err)
	}
	if !strings.HasPrefix(key, prefix) {
		return "", fmt.Errorf("unexpected object %q outside remote lock prefix %q", key, prefix)
	}
	name := strings.TrimPrefix(key, prefix)
	if strings.Contains(name, "/") || !strings.HasSuffix(name, ".lock") {
		return "", fmt.Errorf("unexpected object %q in remote lock prefix", key)
	}
	digest := strings.TrimSuffix(name, ".lock")
	if err := validateSHA256(digest); err != nil {
		return "", fmt.Errorf("unexpected remote lock object %q: %w", key, err)
	}
	return digest, nil
}