package artifacts

import (
	"os"
	"path/filepath"
	"strings"
)

// ResolveSessionLocalPathForRead resolves manifest/local artifact paths for read use-cases.
// Invariants for stage consumers:
//   - local paths may be absolute, workspace-root qualified, or session-workdir relative.
//   - callers should resolve through this helper instead of manually joining session/workdir roots.
func ResolveSessionLocalPathForRead(paths SessionPaths, localPath string) string {
	p := filepath.Clean(strings.TrimSpace(localPath))
	if p == "" {
		return ""
	}
	if filepath.IsAbs(p) {
		return p
	}

	// Already qualified against known roots.
	if underRoot(p, paths.WorkspaceRoot) || underRoot(p, paths.Root) {
		return p
	}

	candidates := []string{
		p,
		filepath.Clean(filepath.Join(paths.WorkspaceRoot, p)),
		filepath.Clean(filepath.Join(paths.Root, p)),
	}
	for _, c := range candidates {
		if c == "" {
			continue
		}
		if _, err := os.Stat(c); err == nil {
			return c
		}
	}

	// Deterministic fallback for ambiguous relative values.
	if strings.TrimSpace(paths.WorkspaceRoot) != "" {
		return candidates[1]
	}
	return candidates[2]
}

func underRoot(path, root string) bool {
	p := filepath.Clean(strings.TrimSpace(path))
	r := filepath.Clean(strings.TrimSpace(root))
	if p == "" || r == "" {
		return false
	}
	if p == r {
		return true
	}
	return strings.HasPrefix(p, r+string(filepath.Separator))
}