[TT-12454] Extract ApplyPolicies into internal/policy scope (#6367)

### **User description**
This extracts a large problematic `ApplyPolicies` function into it's own
package scope. It does this by:

- defining an interface for policy access and deleting inline mutex use
- updated *Gateway to implement storage interface
- implement storage interface in policy.Store as well (used inline)

On top of that:

- Fixes a bug in the Duration/Less() functions on user.APILimit, fixes
tests
- Adds a test particular to ApplyRateLimits (decrease coginitive
complexity)

The duration was calculated as rate/per, however, the correct way was
per/rate;
This fixes it so duration is calculated correctly, fixing the Less
function comparison.

___

### **PR Type**
Enhancement, Bug fix


___

### **Description**
- Refactored `handleGetPolicy` to use the new `PolicyByID` method.
- Introduced a `Repository` interface and added methods `PolicyIDs`,
`PolicyByID`, and `PolicyCount` to the `Gateway` struct.
- Refactored `ApplyPolicies` in `BaseMiddleware` to use the new `policy`
package.
- Updated `buildNodeInfo` to use `PolicyCount` instead of
`policiesByIDLen`.
- Removed redundant methods `getPolicy` and `policiesByIDLen` from
`Gateway`.


___



### **Changes walkthrough** 📝
<table><thead><tr><th></th><th align="left">Relevant
files</th></tr></thead><tbody><tr><td><strong>Enhancement
</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>api.go</strong><dd><code>Refactor policy retrieval in
`handleGetPolicy`.</code>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

gateway/api.go
- Replaced `getPolicy` with `PolicyByID` in `handleGetPolicy`.



</details>
    

  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/6367/files#diff-644cda3aeb4ac7f325359e85fcddb810f100dd5e6fa480b0d9f9363a743c4e05">+1/-1</a>&nbsp;
&nbsp; &nbsp; </td>
</tr>                    

<tr>
  <td>
    <details>
<summary><strong>gateway.go</strong><dd><code>Add policy-related methods
and interface to Gateway.</code>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
</dd></summary>
<hr>

gateway/gateway.go
<li>Introduced <code>Repository</code> interface.<br> <li> Added methods
<code>PolicyIDs</code>, <code>PolicyByID</code>, and
<code>PolicyCount</code>.<br>


</details>
    

  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/6367/files#diff-17cb8b37eda9018fe1c6cdb5f96b3fc948fc8ba49bc516987b8269576db9fcd4">+38/-0</a>&nbsp;
&nbsp; </td>
</tr>                    

<tr>
  <td>
    <details>
<summary><strong>middleware.go</strong><dd><code>Refactor ApplyPolicies
to use new policy store.</code>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

gateway/middleware.go
<li>Removed <code>clearSession</code> method.<br> <li> Refactored
<code>ApplyPolicies</code> to use <code>policy.New</code> and
<code>store.Apply</code>.<br>


</details>
    

  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/6367/files#diff-703054910891a4db633eca0f42ed779d6b4fa75cd9b3aa4c503e681364201c1b">+3/-411</a>&nbsp;
</td>
</tr>                    

<tr>
  <td>
    <details>
<summary><strong>rpc_storage_handler.go</strong><dd><code>Update policy
count retrieval in buildNodeInfo.</code>&nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

gateway/rpc_storage_handler.go
- Replaced `policiesByIDLen` with `PolicyCount` in `buildNodeInfo`.



</details>
    

  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/6367/files#diff-8875f75b602664c44b62b67a4da41d748124ad270573a44db4ec977ee5d68021">+1/-1</a>&nbsp;
&nbsp; &nbsp; </td>
</tr>                    

<tr>
  <td>
    <details>
<summary><strong>server.go</strong><dd><code>Remove redundant policy
methods from Gateway.</code>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

gateway/server.go
- Removed `getPolicy` and `policiesByIDLen` methods.



</details>
    

  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/6367/files#diff-4652d1bf175a0be8f5e61ef7177c9666f23e077d8626b73ac9d13358fa8b525b">+0/-13</a>&nbsp;
&nbsp; </td>
</tr>                    
</table></td></tr></tr></tbody></table>

___

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---------

Co-authored-by: Tit Petric <tit@tyk.io>

gateway/api.go

@@ -892,7 +892,7 @@ func (gw *Gateway) handleRemoveSortedSetRange(keyName, scoreFrom, scoreTo string
 }
 
 func (gw *Gateway) handleGetPolicy(polID string) (interface{}, int) {
-	if pol := gw.getPolicy(polID); pol.ID != "" {
+	if pol, ok := gw.PolicyByID(polID); ok && pol.ID != "" {
 		return pol, http.StatusOK
 	}
 

gateway/gateway.go

@@ -0,0 +1,38 @@
+package gateway
+
+import (
+	"github.com/TykTechnologies/tyk/internal/policy"
+	"github.com/TykTechnologies/tyk/user"
+)
+
+type Repository interface {
+	policy.Repository
+}
+
+var _ Repository = &Gateway{}
+
+func (gw *Gateway) PolicyIDs() []string {
+	gw.policiesMu.RLock()
+	defer gw.policiesMu.RUnlock()
+
+	result := make([]string, 0, len(gw.policiesByID))
+	for id := range gw.policiesByID {
+		result = append(result, id)
+	}
+	return result
+}
+
+func (gw *Gateway) PolicyByID(polID string) (user.Policy, bool) {
+	gw.policiesMu.RLock()
+	defer gw.policiesMu.RUnlock()
+
+	pol, ok := gw.policiesByID[polID]
+	return pol, ok
+}
+
+func (gw *Gateway) PolicyCount() int {
+	gw.policiesMu.RLock()
+	defer gw.policiesMu.RUnlock()
+
+	return len(gw.policiesByID)
+}