package daemon

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"banger/internal/api"
	"banger/internal/daemon/imagemgr"
	"banger/internal/kernelcat"
	"banger/internal/model"
	"banger/internal/system"
)

// RegisterImage creates or updates an unmanaged image row. Path
// validation + kernel resolution run without imageOpsMu — only the
// lookup-then-upsert atom is held under the lock so concurrent
// registers of the same name don't race.
func (s *ImageService) RegisterImage(ctx context.Context, params api.ImageRegisterParams) (image model.Image, err error) {
	name := strings.TrimSpace(params.Name)
	if name == "" {
		return model.Image{}, fmt.Errorf("image name is required")
	}

	rootfsPath := strings.TrimSpace(params.RootfsPath)
	if rootfsPath == "" {
		return model.Image{}, fmt.Errorf("rootfs path is required")
	}
	workSeedPath := strings.TrimSpace(params.WorkSeedPath)
	if workSeedPath == "" {
		candidate := system.WorkSeedPath(rootfsPath)
		if candidate != "" {
			if _, statErr := os.Stat(candidate); statErr == nil {
				workSeedPath = candidate
			}
		}
	}
	kernelPath, initrdPath, modulesDir, err := s.resolveKernelInputs(ctx, params.KernelRef, params.KernelPath, params.InitrdPath, params.ModulesDir)
	if err != nil {
		return model.Image{}, err
	}

	if err := imagemgr.ValidateRegisterPaths(rootfsPath, workSeedPath, kernelPath, initrdPath, modulesDir); err != nil {
		return model.Image{}, err
	}

	s.imageOpsMu.Lock()
	defer s.imageOpsMu.Unlock()

	now := model.Now()
	existing, lookupErr := s.store.GetImageByName(ctx, name)
	switch {
	case lookupErr == nil:
		if existing.Managed {
			return model.Image{}, fmt.Errorf("managed image %s cannot be updated via register", name)
		}
		image = existing
		image.RootfsPath = rootfsPath
		image.WorkSeedPath = workSeedPath
		image.KernelPath = kernelPath
		image.InitrdPath = initrdPath
		image.ModulesDir = modulesDir
		image.UpdatedAt = now
	case errors.Is(lookupErr, sql.ErrNoRows):
		id, idErr := model.NewID()
		if idErr != nil {
			return model.Image{}, idErr
		}
		image = model.Image{
			ID:           id,
			Name:         name,
			Managed:      false,
			RootfsPath:   rootfsPath,
			WorkSeedPath: workSeedPath,
			KernelPath:   kernelPath,
			InitrdPath:   initrdPath,
			ModulesDir:   modulesDir,
			CreatedAt:    now,
			UpdatedAt:    now,
		}
	default:
		return model.Image{}, lookupErr
	}

	if err := s.store.UpsertImage(ctx, image); err != nil {
		return model.Image{}, err
	}
	return image, nil
}

// PromoteImage copies an unmanaged image's files into the managed
// artifacts dir and flips its managed bit. The expensive file copy,
// SSH-key seeding, and boot-artifact staging all happen outside
// imageOpsMu — only the find/rename/upsert commit atom holds the
// lock.
func (s *ImageService) PromoteImage(ctx context.Context, idOrName string) (image model.Image, err error) {
	op := s.beginOperation(ctx, "image.promote")
	defer func() {
		if err != nil {
			op.fail(err, imageLogAttrs(image)...)
			return
		}
		op.done(imageLogAttrs(image)...)
	}()

	image, err = s.FindImage(ctx, idOrName)
	if err != nil {
		return model.Image{}, err
	}
	if image.Managed {
		return model.Image{}, fmt.Errorf("image %s is already managed", image.Name)
	}
	if err := imagemgr.ValidatePromotePaths(image.RootfsPath, image.KernelPath, image.InitrdPath, image.ModulesDir); err != nil {
		return model.Image{}, err
	}
	if strings.TrimSpace(s.layout.ImagesDir) == "" {
		return model.Image{}, errors.New("images dir is not configured")
	}
	if err := os.MkdirAll(s.layout.ImagesDir, 0o755); err != nil {
		return model.Image{}, err
	}

	artifactDir := filepath.Join(s.layout.ImagesDir, image.ID)
	if _, statErr := os.Stat(artifactDir); statErr == nil {
		return model.Image{}, fmt.Errorf("artifact dir already exists: %s", artifactDir)
	} else if !os.IsNotExist(statErr) {
		return model.Image{}, statErr
	}

	stageDir, err := os.MkdirTemp(s.layout.ImagesDir, image.ID+".promote-")
	if err != nil {
		return model.Image{}, err
	}
	cleanupStage := true
	defer func() {
		if cleanupStage {
			_ = os.RemoveAll(stageDir)
		}
	}()

	rootfsPath := filepath.Join(stageDir, "rootfs.ext4")
	op.stage("copy_rootfs", "source_rootfs_path", image.RootfsPath, "target_rootfs_path", rootfsPath)
	if err := system.CopyFilePreferClone(image.RootfsPath, rootfsPath); err != nil {
		return model.Image{}, err
	}

	workSeedPath := ""
	if image.WorkSeedPath != "" {
		if _, statErr := os.Stat(image.WorkSeedPath); statErr != nil {
			if os.IsNotExist(statErr) {
				op.stage("skip_missing_work_seed", "source_work_seed_path", image.WorkSeedPath)
				image.WorkSeedPath = ""
			} else {
				return model.Image{}, statErr
			}
		}
	}
	if image.WorkSeedPath != "" {
		workSeedPath = filepath.Join(stageDir, "work-seed.ext4")
		op.stage("copy_work_seed", "source_work_seed_path", image.WorkSeedPath, "target_work_seed_path", workSeedPath)
		if err := system.CopyFilePreferClone(image.WorkSeedPath, workSeedPath); err != nil {
			return model.Image{}, err
		}
		image.SeededSSHPublicKeyFingerprint, err = s.seedAuthorizedKeyOnExt4Image(ctx, workSeedPath)
		if err != nil {
			return model.Image{}, err
		}
	} else {
		image.SeededSSHPublicKeyFingerprint = ""
	}
	_, initrdPath, modulesDir, err := imagemgr.StageBootArtifacts(ctx, s.runner, stageDir, image.KernelPath, image.InitrdPath, image.ModulesDir)
	if err != nil {
		return model.Image{}, err
	}

	image.Managed = true
	image.ArtifactDir = artifactDir
	image.RootfsPath = filepath.Join(artifactDir, "rootfs.ext4")
	if workSeedPath != "" {
		image.WorkSeedPath = filepath.Join(artifactDir, "work-seed.ext4")
	}
	image.KernelPath = filepath.Join(artifactDir, "kernel")
	image.InitrdPath = imagemgr.StageOptionalArtifactPath(artifactDir, initrdPath, "initrd.img")
	image.ModulesDir = imagemgr.StageOptionalArtifactPath(artifactDir, modulesDir, "modules")
	image.UpdatedAt = model.Now()

	op.stage("activate_artifacts", "artifact_dir", artifactDir)
	s.imageOpsMu.Lock()
	defer s.imageOpsMu.Unlock()
	if err := os.Rename(stageDir, artifactDir); err != nil {
		return model.Image{}, err
	}
	cleanupStage = false
	if err := s.store.UpsertImage(ctx, image); err != nil {
		_ = os.RemoveAll(artifactDir)
		return model.Image{}, err
	}
	return image, nil
}

// DeleteImage runs the lookup + reference check + store delete under
// imageOpsMu so a concurrent CreateVM can't slip an image_id reference
// in between the check and the delete. File cleanup happens after the
// lock is released — the store row is the authoritative handle.
func (s *ImageService) DeleteImage(ctx context.Context, idOrName string) (model.Image, error) {
	image, err := func() (model.Image, error) {
		s.imageOpsMu.Lock()
		defer s.imageOpsMu.Unlock()
		img, err := s.FindImage(ctx, idOrName)
		if err != nil {
			return model.Image{}, err
		}
		vms, err := s.store.FindVMsUsingImage(ctx, img.ID)
		if err != nil {
			return model.Image{}, err
		}
		if len(vms) > 0 {
			return model.Image{}, fmt.Errorf("image %s is still referenced by %d VM(s)", img.Name, len(vms))
		}
		if err := s.store.DeleteImage(ctx, img.ID); err != nil {
			return model.Image{}, err
		}
		return img, nil
	}()
	if err != nil {
		return model.Image{}, err
	}
	if image.Managed && image.ArtifactDir != "" {
		if err := os.RemoveAll(image.ArtifactDir); err != nil {
			return model.Image{}, err
		}
	}
	return image, nil
}

func firstNonEmpty(values ...string) string {
	for _, value := range values {
		if strings.TrimSpace(value) != "" {
			return value
		}
	}
	return ""
}

// resolveKernelInputs canonicalises user-supplied kernel info: either direct
// paths or a kernel-catalog ref. Shared by RegisterImage and PullImage.
// When kernelRef is given but not yet pulled locally, an auto-pull from the
// embedded kernelcat catalog fires so the caller doesn't have to manage
// kernel/image ordering by hand.
func (s *ImageService) resolveKernelInputs(ctx context.Context, kernelRef, kernelPath, initrdPath, modulesDir string) (string, string, string, error) {
	kernelRef = strings.TrimSpace(kernelRef)
	kernelPath = strings.TrimSpace(kernelPath)
	initrdPath = strings.TrimSpace(initrdPath)
	modulesDir = strings.TrimSpace(modulesDir)

	if kernelRef != "" {
		if kernelPath != "" || initrdPath != "" || modulesDir != "" {
			return "", "", "", fmt.Errorf("--kernel-ref is mutually exclusive with --kernel/--initrd/--modules")
		}
		entry, err := s.readOrAutoPullKernel(ctx, kernelRef)
		if err != nil {
			return "", "", "", err
		}
		return entry.KernelPath, entry.InitrdPath, entry.ModulesDir, nil
	}

	if kernelPath == "" {
		return "", "", "", fmt.Errorf("kernel path is required (pass --kernel <path> or --kernel-ref <name>)")
	}
	return kernelPath, initrdPath, modulesDir, nil
}

// readOrAutoPullKernel tries the local kernelcat first; on miss, checks
// the embedded catalog and auto-pulls the bundle.
//
// Concurrency-safe: takes the same per-name pull lock as KernelPull and
// re-checks ReadLocal after acquiring it. If a peer finished the pull
// while we were waiting, the re-check returns the freshly-pulled entry
// — we explicitly do NOT call s.KernelPull from here because that path
// errors with "already pulled" on a successful peer-pull. Auto-pull's
// contract is "make sure this kernel is local"; "someone beat me to it"
// is success, not failure.
func (s *ImageService) readOrAutoPullKernel(ctx context.Context, kernelRef string) (kernelcat.Entry, error) {
	if entry, err := kernelcat.ReadLocal(s.layout.KernelsDir, kernelRef); err == nil {
		return entry, nil
	} else if !os.IsNotExist(err) {
		return kernelcat.Entry{}, fmt.Errorf("resolve kernel %q: %w", kernelRef, err)
	}
	catalog, loadErr := kernelcat.LoadEmbedded()
	if loadErr != nil {
		return kernelcat.Entry{}, fmt.Errorf("kernel %q not found locally: %w", kernelRef, loadErr)
	}
	catEntry, lookupErr := catalog.Lookup(kernelRef)
	if lookupErr != nil {
		return kernelcat.Entry{}, fmt.Errorf("kernel %q not found in catalog; run 'banger kernel list --available' to browse", kernelRef)
	}

	release, err := s.acquireKernelPullLock(ctx, kernelRef)
	if err != nil {
		return kernelcat.Entry{}, err
	}
	defer release()
	if entry, err := kernelcat.ReadLocal(s.layout.KernelsDir, kernelRef); err == nil {
		return entry, nil
	}

	vmCreateStage(ctx, "auto_pull_kernel", fmt.Sprintf("pulling kernel %s from catalog", kernelRef))
	stored, err := kernelcat.Fetch(ctx, nil, s.layout.KernelsDir, catEntry)
	if err != nil {
		return kernelcat.Entry{}, fmt.Errorf("auto-pull kernel %q: %w", kernelRef, err)
	}
	return stored, nil
}