package core

import (
	"bytes"
	"compress/gzip"
	"context"
	"encoding/json"
	"encoding/xml"
	"errors"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	aptclone "github.com/syonad/clonepack/internal/clone/apt"
	rpmclone "github.com/syonad/clonepack/internal/clone/rpm"
	"github.com/syonad/clonepack/internal/store"
)

type SnapshotService struct {
	snapshotStore store.SnapshotStore
	repoStore     store.RepoStore
	dataDir       string
	httpClient    *http.Client
}

func NewSnapshotService(
	snapshotStore store.SnapshotStore,
	repoStore store.RepoStore,
	dataDir string,
) *SnapshotService {
	return &SnapshotService{
		snapshotStore: snapshotStore,
		repoStore:     repoStore,
		dataDir:       dataDir,
		httpClient:    &http.Client{Timeout: 30 * time.Minute},
	}
}

type SnapshotDiff struct {
	From      *store.Snapshot
	To        *store.Snapshot
	Added     []store.SnapshotPackage
	Removed   []store.SnapshotPackage
	Unchanged int
}

func (s *SnapshotService) TakeSnapshot(ctx context.Context, repoID int64, label string) (int64, error) {
	repo, err := s.repoStore.GetRepo(ctx, repoID)
	if err != nil {
		return 0, err
	}

	localDir := filepath.Join(s.dataDir, "repos", fmt.Sprintf("%d", repoID), repo.Type)

	var pkgs []store.SnapshotPackage
	switch repo.Type {
	case "rpm":
		pkgs, err = s.snapshotPackagesRPM(localDir)
	case "apt":
		pkgs, err = s.snapshotPackagesAPT(localDir, repo.Config)
	default:
		return 0, fmt.Errorf("snapshots not supported for repo type %q", repo.Type)
	}
	if err != nil {
		return 0, err
	}

	snapID, err := s.snapshotStore.CreateSnapshot(ctx, repoID, label)
	if err != nil {
		return 0, err
	}
	if len(pkgs) > 0 {
		if err := s.snapshotStore.AddSnapshotPackages(ctx, snapID, pkgs); err != nil {
			return 0, err
		}
	}
	return snapID, nil
}

func (s *SnapshotService) snapshotPackagesRPM(localDir string) ([]store.SnapshotPackage, error) {
	repomdData, err := os.ReadFile(filepath.Join(localDir, "repodata", "repomd.xml"))
	if err != nil {
		return nil, fmt.Errorf("read repomd.xml: %w", err)
	}
	var repomd rpmclone.RepoMD
	if err := xml.Unmarshal(repomdData, &repomd); err != nil {
		return nil, fmt.Errorf("parse repomd.xml: %w", err)
	}
	var primaryHref string
	for _, entry := range repomd.Data {
		if entry.Type == "primary" {
			primaryHref = entry.Location.Href
			break
		}
	}
	if primaryHref == "" {
		return nil, fmt.Errorf("no primary entry in repomd.xml")
	}
	gzData, err := os.ReadFile(filepath.Join(localDir, filepath.FromSlash(primaryHref)))
	if err != nil {
		return nil, fmt.Errorf("read primary.xml.gz: %w", err)
	}
	gz, err := gzip.NewReader(bytes.NewReader(gzData))
	if err != nil {
		return nil, fmt.Errorf("open gzip: %w", err)
	}
	defer gz.Close()
	var primary rpmclone.PrimaryMetadata
	if err := xml.NewDecoder(gz).Decode(&primary); err != nil {
		return nil, fmt.Errorf("parse primary.xml: %w", err)
	}
	pkgs := make([]store.SnapshotPackage, len(primary.Packages))
	for i, p := range primary.Packages {
		pkgs[i] = store.SnapshotPackage{
			Name:         p.Name,
			Version:      p.Version.Ver + "-" + p.Version.Rel,
			Arch:         p.Arch,
			Location:     p.Location.Href,
			Checksum:     p.Checksum.Value,
			ChecksumType: p.Checksum.Type,
			Size:         p.Size.Package,
		}
	}
	return pkgs, nil
}

func (s *SnapshotService) snapshotPackagesAPT(localDir, configJSON string) ([]store.SnapshotPackage, error) {
	var cfg aptclone.Config
	if err := json.Unmarshal([]byte(configJSON), &cfg); err != nil {
		return nil, fmt.Errorf("parse apt config: %w", err)
	}

	seen := make(map[string]struct{})
	var pkgs []store.SnapshotPackage

	for _, component := range cfg.Components {
		for _, arch := range cfg.Architectures {
			pkgsPath := filepath.Join(localDir, "dists", cfg.Suite, component, "binary-"+arch, "Packages")
			data, err := os.ReadFile(pkgsPath)
			if err != nil {
				// Not yet populated — skip silently.
				continue
			}
			debs, err := aptclone.ParsePackages(data)
			if err != nil {
				return nil, fmt.Errorf("parse Packages for %s/%s: %w", component, arch, err)
			}
			for _, d := range debs {
				if _, dup := seen[d.Filename]; dup {
					continue
				}
				seen[d.Filename] = struct{}{}
				pkgs = append(pkgs, store.SnapshotPackage{
					Name:         d.Package,
					Version:      d.Version,
					Arch:         d.Architecture,
					Location:     d.Filename,
					Checksum:     d.SHA256,
					ChecksumType: "sha256",
					Size:         d.Size,
				})
			}
		}
	}
	return pkgs, nil
}

func (s *SnapshotService) List(ctx context.Context, repoID int64) ([]store.Snapshot, error) {
	if _, err := s.repoStore.GetRepo(ctx, repoID); err != nil {
		return nil, err
	}
	return s.snapshotStore.ListSnapshots(ctx, repoID)
}

func (s *SnapshotService) Get(ctx context.Context, repoID, id int64) (*store.Snapshot, []store.SnapshotPackage, error) {
	snap, err := s.snapshotStore.GetSnapshot(ctx, id)
	if err != nil {
		return nil, nil, err
	}
	if snap.RepoID != repoID {
		return nil, nil, store.ErrNotFound
	}
	pkgs, err := s.snapshotStore.GetSnapshotPackages(ctx, id)
	if err != nil {
		return nil, nil, err
	}
	return snap, pkgs, nil
}

func (s *SnapshotService) Delete(ctx context.Context, repoID, id int64) error {
	snap, err := s.snapshotStore.GetSnapshot(ctx, id)
	if err != nil {
		return err
	}
	if snap.RepoID != repoID {
		return store.ErrNotFound
	}
	return s.snapshotStore.DeleteSnapshot(ctx, id)
}

func (s *SnapshotService) Diff(ctx context.Context, repoID, fromID, toID int64) (*SnapshotDiff, error) {
	from, err := s.snapshotStore.GetSnapshot(ctx, fromID)
	if err != nil {
		return nil, err
	}
	to, err := s.snapshotStore.GetSnapshot(ctx, toID)
	if err != nil {
		return nil, err
	}
	if from.RepoID != repoID || to.RepoID != repoID {
		return nil, fmt.Errorf("snapshots do not belong to repo %d", repoID)
	}

	fromPkgs, err := s.snapshotStore.GetSnapshotPackages(ctx, fromID)
	if err != nil {
		return nil, err
	}
	toPkgs, err := s.snapshotStore.GetSnapshotPackages(ctx, toID)
	if err != nil {
		return nil, err
	}

	fromSet := make(map[string]struct{}, len(fromPkgs))
	for _, p := range fromPkgs {
		fromSet[p.Name+"|"+p.Version+"|"+p.Arch] = struct{}{}
	}
	toSet := make(map[string]struct{}, len(toPkgs))
	for _, p := range toPkgs {
		toSet[p.Name+"|"+p.Version+"|"+p.Arch] = struct{}{}
	}

	diff := &SnapshotDiff{From: from, To: to}
	for _, p := range toPkgs {
		if _, ok := fromSet[p.Name+"|"+p.Version+"|"+p.Arch]; ok {
			diff.Unchanged++
		} else {
			diff.Added = append(diff.Added, p)
		}
	}
	for _, p := range fromPkgs {
		if _, ok := toSet[p.Name+"|"+p.Version+"|"+p.Arch]; !ok {
			diff.Removed = append(diff.Removed, p)
		}
	}
	return diff, nil
}

func (s *SnapshotService) Rollback(ctx context.Context, repoID, snapshotID int64) error {
	repo, err := s.repoStore.GetRepo(ctx, repoID)
	if err != nil {
		return err
	}
	snap, err := s.snapshotStore.GetSnapshot(ctx, snapshotID)
	if err != nil {
		return err
	}
	if snap.RepoID != repoID {
		return store.ErrNotFound
	}

	pkgs, err := s.snapshotStore.GetSnapshotPackages(ctx, snapshotID)
	if err != nil {
		return err
	}

	localDir := filepath.Join(s.dataDir, "repos", fmt.Sprintf("%d", repoID), repo.Type)

	snapSet := make(map[string]store.SnapshotPackage, len(pkgs))
	for _, p := range pkgs {
		snapSet[p.Location] = p
	}

	ext := packageExt(repo.Type)
	var errs []error

	if err := filepath.WalkDir(localDir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || filepath.Ext(path) != ext {
			return err
		}
		rel, _ := filepath.Rel(localDir, path)
		rel = filepath.ToSlash(rel)
		if _, ok := snapSet[rel]; !ok {
			if rmErr := os.Remove(path); rmErr != nil {
				errs = append(errs, rmErr)
			}
		}
		return nil
	}); err != nil {
		errs = append(errs, err)
	}

	for _, p := range pkgs {
		dest := filepath.Join(localDir, filepath.FromSlash(p.Location))
		if _, err := os.Stat(dest); err == nil {
			continue
		}
		url := strings.TrimRight(repo.SourceURL, "/") + "/" + p.Location
		if _, dlErr := rpmclone.DownloadAndVerify(ctx, s.httpClient, url, dest, p.ChecksumType, p.Checksum); dlErr != nil {
			errs = append(errs, fmt.Errorf("re-download %s: %w", p.Name, dlErr))
		}
	}

	if err := errors.Join(errs...); err != nil {
		return err
	}

	switch repo.Type {
	case "rpm":
		if err := rpmclone.RegenerateMetadata(localDir); err != nil {
			return fmt.Errorf("regenerate metadata: %w", err)
		}
	case "apt":
		var cfg aptclone.Config
		if err := json.Unmarshal([]byte(repo.Config), &cfg); err != nil {
			return fmt.Errorf("parse apt config: %w", err)
		}
		if err := aptclone.RegenerateMetadata(localDir, cfg); err != nil {
			return fmt.Errorf("regenerate metadata: %w", err)
		}
	}
	return nil
}

func packageExt(repoType string) string {
	switch repoType {
	case "apt":
		return ".deb"
	default:
		return ".rpm"
	}
}