package bundle

import (
	"context"
	"fmt"

	"gitea.maximumdirect.net/eric/distributor/internal/storage"
)

func ValidateSourcePath(path string) error {
	if err := storage.ValidatePath(path); err != nil {
		return err
	}
	switch path {
	case ManifestName, storage.StateFileName:
		return fmt.Errorf("%q is reserved", path)
	}
	return nil
}

func ValidateManifest(manifest Manifest) error {
	if manifest.SchemaVersion != 1 {
		return fmt.Errorf("schema_version must be 1")
	}
	if manifest.ID == "" {
		return fmt.Errorf("id is required")
	}
	if err := ValidateDigest(manifest.Digest); err != nil {
		return fmt.Errorf("digest: %w", err)
	}
	if manifest.Created.IsZero() {
		return fmt.Errorf("created is required")
	}
	if len(manifest.Files) == 0 {
		return fmt.Errorf("files is required")
	}
	seen := make(map[string]struct{}, len(manifest.Files))
	for index, file := range manifest.Files {
		if err := ValidateSourcePath(file.Path); err != nil {
			return fmt.Errorf("files[%d].path: %w", index, err)
		}
		if err := ValidateDigest(file.SHA256); err != nil {
			return fmt.Errorf("files[%d].sha256: %w", index, err)
		}
		if file.Size < 0 {
			return fmt.Errorf("files[%d].size must be non-negative", index)
		}
		if _, exists := seen[file.Path]; exists {
			return fmt.Errorf("files[%d].path duplicates %q", index, file.Path)
		}
		seen[file.Path] = struct{}{}
	}
	if actual := BundleDigest(manifest.Files); actual != manifest.Digest {
		return fmt.Errorf("digest mismatch: got %s want %s", actual, manifest.Digest)
	}
	return nil
}

func Validate(ctx context.Context, backend storage.Backend, bundleRoot string) (Bundle, error) {
	return validateAt(ctx, backend, bundleRoot, bundleRoot)
}

func validateAt(ctx context.Context, backend storage.Backend, bundleRoot, relativeRoot string) (Bundle, error) {
	if err := storage.ValidatePrefix(bundleRoot); err != nil {
		return Bundle{}, err
	}
	manifestPath, err := storage.Join(bundleRoot, ManifestName)
	if err != nil {
		return Bundle{}, err
	}
	manifestData, err := backend.ReadFile(ctx, manifestPath)
	if err != nil {
		return Bundle{}, fmt.Errorf("read manifest %q: %w", manifestPath, err)
	}
	manifest, err := ParseManifest(manifestData)
	if err != nil {
		return Bundle{}, fmt.Errorf("bundle %q: %w", storage.DisplayPath(relativeRoot), err)
	}

	for index, manifestFile := range manifest.Files {
		filePath, err := storage.Join(bundleRoot, manifestFile.Path)
		if err != nil {
			return Bundle{}, fmt.Errorf("bundle %q file %q: %w", storage.DisplayPath(relativeRoot), manifestFile.Path, err)
		}
		entry, err := backend.Stat(ctx, filePath)
		if err != nil {
			return Bundle{}, fmt.Errorf("bundle %q file %q stat: %w", storage.DisplayPath(relativeRoot), manifestFile.Path, err)
		}
		if entry.Type != storage.EntryTypeFile {
			return Bundle{}, fmt.Errorf("bundle %q file %q must be a regular file", storage.DisplayPath(relativeRoot), manifestFile.Path)
		}
		if entry.Size != manifestFile.Size {
			return Bundle{}, fmt.Errorf("bundle %q file %q size mismatch: got %d want %d", storage.DisplayPath(relativeRoot), manifestFile.Path, entry.Size, manifestFile.Size)
		}
		data, err := backend.ReadFile(ctx, filePath)
		if err != nil {
			return Bundle{}, fmt.Errorf("bundle %q file %q read: %w", storage.DisplayPath(relativeRoot), manifestFile.Path, err)
		}
		actualDigest := FileDigest(data)
		if actualDigest != manifestFile.SHA256 {
			return Bundle{}, fmt.Errorf("bundle %q file %q sha256 mismatch: got %s want %s", storage.DisplayPath(relativeRoot), manifestFile.Path, actualDigest, manifestFile.SHA256)
		}
		manifest.Files[index].SHA256 = actualDigest
		manifest.Files[index].Size = int64(len(data))
	}

	actualBundleDigest := BundleDigest(manifest.Files)
	if actualBundleDigest != manifest.Digest {
		return Bundle{}, fmt.Errorf("bundle %q digest mismatch: got %s want %s", storage.DisplayPath(relativeRoot), actualBundleDigest, manifest.Digest)
	}

	return Bundle{
		RootRelativePath: relativeRoot,
		Manifest:         manifest,
	}, nil
}