From 4aedc4de39cd74ad09b16071453131d648c67ba3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20Mur=C3=A9?= <michael.mure@consensys.net>
Date: Tue, 18 Mar 2025 18:03:00 +0100
Subject: [PATCH] client: add a convenient PrepareDelegation function

---
 toolkit/client/client.go | 78 ++++++++++++++++++++++++++++++----------
 1 file changed, 59 insertions(+), 19 deletions(-)

diff --git a/toolkit/client/client.go b/toolkit/client/client.go
index f9cca09..346c9fe 100644
--- a/toolkit/client/client.go
+++ b/toolkit/client/client.go
@@ -9,6 +9,8 @@ import (
 	"github.com/ucan-wg/go-ucan/did"
 	"github.com/ucan-wg/go-ucan/pkg/command"
 	"github.com/ucan-wg/go-ucan/pkg/container"
+	"github.com/ucan-wg/go-ucan/pkg/policy"
+	"github.com/ucan-wg/go-ucan/token/delegation"
 	"github.com/ucan-wg/go-ucan/token/invocation"
 )
 
@@ -33,26 +35,11 @@ func NewClient(privKey crypto.PrivKey, requester DelegationRequester) (*Client,
 	}, nil
 }
 
-// PrepareInvoke returns an invocation and the proof delegation, bundled in a container.Writer.
+// PrepareInvoke returns an invocation, bundled in a container.Writer with the necessary proofs.
 func (c *Client) PrepareInvoke(ctx context.Context, cmd command.Command, subject did.DID, opts ...invocation.Option) (container.Writer, error) {
-	var proof []cid.Cid
-
-	// do we already have a valid proof?
-	if proof = c.pool.FindProof(c.did, cmd, subject); len(proof) == 0 {
-		// we need to request a new proof
-		proofBundles, err := c.requester.RequestDelegation(ctx, c.did, cmd, subject)
-		if err != nil {
-			return nil, fmt.Errorf("requesting delegation: %w", err)
-		}
-
-		// cache the new proofs
-		for bundle, err := range proofBundles {
-			if err != nil {
-				return nil, err
-			}
-			proof = append(proof, bundle.Cid)
-			c.pool.AddBundle(bundle)
-		}
+	proof, err := c.findProof(ctx, cmd, subject)
+	if err != nil {
+		return nil, err
 	}
 
 	inv, err := invocation.New(c.did, cmd, subject, proof, opts...)
@@ -76,3 +63,56 @@ func (c *Client) PrepareInvoke(ctx context.Context, cmd command.Command, subject
 
 	return cont, nil
 }
+
+// PrepareDelegation returns a new delegation for a third party DID, bundled in a container.Writer with the necessary proofs.
+func (c *Client) PrepareDelegation(ctx context.Context, aud did.DID, cmd command.Command, subject did.DID, policies policy.Policy, opts ...delegation.Option) (container.Writer, error) {
+	proof, err := c.findProof(ctx, cmd, subject)
+	if err != nil {
+		return nil, err
+	}
+
+	dlg, err := delegation.New(c.did, aud, cmd, policies, subject, opts...)
+	if err != nil {
+		return nil, err
+	}
+
+	dlgSealed, _, err := dlg.ToSealed(c.privKey)
+	if err != nil {
+		return nil, err
+	}
+
+	cont := container.NewWriter()
+	cont.AddSealed(dlgSealed)
+	for bundle, err := range c.pool.GetBundles(proof) {
+		if err != nil {
+			return nil, err
+		}
+		cont.AddSealed(bundle.Sealed)
+	}
+
+	return cont, nil
+}
+
+func (c *Client) findProof(ctx context.Context, cmd command.Command, subject did.DID) ([]cid.Cid, error) {
+	var proof []cid.Cid
+
+	// do we already have a valid proof?
+	if proof = c.pool.FindProof(c.did, cmd, subject); len(proof) == 0 {
+		// we need to request a new proof
+		proofBundles, err := c.requester.RequestDelegation(ctx, c.did, cmd, subject)
+		if err != nil {
+			return nil, fmt.Errorf("requesting delegation: %w", err)
+		}
+
+		// cache the new proofs
+		for bundle, err := range proofBundles {
+			if err != nil {
+				return nil, err
+			}
+			proof = append(proof, bundle.Cid)
+			c.pool.AddBundle(bundle)
+		}
+	}
+
+	return proof, nil
+}