package artifacts

import (
	"fmt"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/config"
)

// ImmutableRunObjectKey identifies one clean object beneath a session's
// immutable run namespace.
type ImmutableRunObjectKey struct {
	RunID        string
	RelativePath string
}

// ParseImmutableRunObjectKey proves that key belongs to one immutable run in
// the expected campaign/session namespace and returns its run and relative path.
func ParseImmutableRunObjectKey(sessionPrefix, key string) (ImmutableRunObjectKey, error) {
	if err := validateRemoteSessionPrefix(sessionPrefix); err != nil {
		return ImmutableRunObjectKey{}, err
	}
	if err := validateRemoteObjectKey(key); err != nil {
		return ImmutableRunObjectKey{}, fmt.Errorf("immutable object key %q: %w", key, err)
	}
	runsPrefix := sessionPrefix + config.S3RunsSegment + "/"
	remainder, ok := strings.CutPrefix(key, runsPrefix)
	if !ok {
		return ImmutableRunObjectKey{}, fmt.Errorf("immutable object key %q is outside session run prefix %q", key, runsPrefix)
	}
	runID, relativePath, ok := strings.Cut(remainder, "/")
	if !ok || runID == "" {
		return ImmutableRunObjectKey{}, fmt.Errorf("immutable object key %q has an empty run identity", key)
	}
	if err := ValidateRunIdentity(runID); err != nil {
		return ImmutableRunObjectKey{}, fmt.Errorf("immutable object key %q: %w", key, err)
	}
	if err := validateRemoteObjectKey(relativePath); err != nil {
		return ImmutableRunObjectKey{}, fmt.Errorf("immutable object key %q has invalid run-relative path: %w", key, err)
	}
	return ImmutableRunObjectKey{RunID: runID, RelativePath: relativePath}, nil
}

func validateRemoteSessionPrefix(sessionPrefix string) error {
	if sessionPrefix == "" || strings.TrimSpace(sessionPrefix) != sessionPrefix || strings.Contains(sessionPrefix, `\`) || !strings.HasSuffix(sessionPrefix, "/") {
		return fmt.Errorf("session prefix %q must be a canonical relative object prefix", sessionPrefix)
	}
	withoutSlash := strings.TrimSuffix(sessionPrefix, "/")
	if err := validateRemoteObjectKey(withoutSlash); err != nil {
		return fmt.Errorf("session prefix %q: %w", sessionPrefix, err)
	}
	parts := strings.Split(withoutSlash, "/")
	if len(parts) < 4 || parts[len(parts)-4] != config.S3CampaignsSegment || parts[len(parts)-2] != config.S3SessionsSegment {
		return fmt.Errorf("session prefix %q does not identify a campaign session", sessionPrefix)
	}
	if err := ValidateSessionIdentity(parts[len(parts)-3], parts[len(parts)-1]); err != nil {
		return fmt.Errorf("session prefix %q: %w", sessionPrefix, err)
	}
	return nil
}