Implement numerical ordering policy

Converts the given list of tags to floats and compares them based on the
ordering rule.
If a tag is not convertible, it will err and fail to compute the latest
version.

Fixes #102

Signed-off-by: Aurel Canciu <aurelcanciu@gmail.com>

api/v1alpha1/imagepolicy_types.go

@@ -52,6 +52,9 @@ type ImagePolicyChoice struct {
 	// Alphabetical set of rules to use for alphabetical ordering of the tags.
 	// +optional
 	Alphabetical *AlphabeticalPolicy `json:"alphabetical,omitempty"`
+	// Numerical set of rules to use for numerical ordering of the tags.
+	// +optional
+	Numerical *NumericalPolicy `json:"numerical,omitempty"`
 }
 
 // SemVerPolicy specifices a semantic version policy.
@@ -73,6 +76,17 @@ type AlphabeticalPolicy struct {
 	Order string `json:"order,omitempty"`
 }
 
+// NumericalPolicy specifices a numerical ordering policy.
+type NumericalPolicy struct {
+	// Order specifies the sorting order of the tags. Given the integer values
+	// from 0 to 9 as tags, ascending order would select 9, and descending order
+	// would select 0.
+	// +kubebuilder:default:="asc"
+	// +kubebuilder:validation:Enum=asc;desc
+	// +optional
+	Order string `json:"order,omitempty"`
+}
+
 // TagFilter enables filtering tags based on a set of defined rules
 type TagFilter struct {
 	// Pattern specifies a regular expression pattern used to filter for image

config/crd/bases/image.toolkit.fluxcd.io_imagepolicies.yaml

@@ -4,7 +4,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    controller-gen.kubebuilder.io/version: v0.4.1
+    controller-gen.kubebuilder.io/version: v0.3.0
   creationTimestamp: null
   name: imagepolicies.image.toolkit.fluxcd.io
 spec:
@@ -84,6 +84,21 @@ spec:
                         - desc
                         type: string
                     type: object
+                  numerical:
+                    description: Numerical set of rules to use for numerical ordering
+                      of the tags.
+                    properties:
+                      order:
+                        default: asc
+                        description: Order specifies the sorting order of the tags.
+                          Given the integer values from 0 to 9 as tags, ascending
+                          order would select 9, and descending order would select
+                          0.
+                        enum:
+                        - asc
+                        - desc
+                        type: string
+                    type: object
                   semver:
                     description: SemVer gives a semantic version range to check against
                       the tags available.

config/crd/bases/image.toolkit.fluxcd.io_imagerepositories.yaml

@@ -4,7 +4,7 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    controller-gen.kubebuilder.io/version: v0.4.1
+    controller-gen.kubebuilder.io/version: v0.3.0
   creationTimestamp: null
   name: imagerepositories.image.toolkit.fluxcd.io
 spec:

internal/policy/alphabetical.go

@@ -33,7 +33,8 @@ type Alphabetical struct {
 	Order string
 }
 
-// NewAlphabetical constructs a Alphabetical object validating the provided semver constraint
+// NewAlphabetical constructs a Alphabetical object validating the provided
+// order argument
 func NewAlphabetical(order string) (*Alphabetical, error) {
 	switch order {
 	case "":

internal/policy/factory.go

@@ -32,6 +32,8 @@ func PolicerFromSpec(choice imagev1.ImagePolicyChoice) (Policer, error) {
 		p, err = NewSemVer(choice.SemVer.Range)
 	case choice.Alphabetical != nil:
 		p, err = NewAlphabetical(strings.ToUpper(choice.Alphabetical.Order))
+	case choice.Numerical != nil:
+		p, err = NewNumerical(strings.ToUpper(choice.Numerical.Order))
 	default:
 		return nil, fmt.Errorf("given ImagePolicyChoice object is invalid")
 	}

internal/policy/numerical.go

@@ -0,0 +1,79 @@
+/*
+Copyright 2021 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package policy
+
+import (
+	"fmt"
+	"strconv"
+)
+
+const (
+	// NumericalOrderAsc ascending order
+	NumericalOrderAsc = "ASC"
+	// NumericalOrderDesc descending order
+	NumericalOrderDesc = "DESC"
+)
+
+// Numerical representes a Numerical ordering policy
+type Numerical struct {
+	Order string
+}
+
+// NewNumerical constructs a Numerical object validating the provided
+// order argument
+func NewNumerical(order string) (*Numerical, error) {
+	switch order {
+	case "":
+		order = NumericalOrderAsc
+	case NumericalOrderAsc, NumericalOrderDesc:
+		break
+	default:
+		return nil, fmt.Errorf("invalid order argument provided: '%s', must be one of: %s, %s", order, NumericalOrderAsc, NumericalOrderDesc)
+	}
+
+	return &Numerical{
+		Order: order,
+	}, nil
+}
+
+// Latest returns latest version from a provided list of strings
+func (p *Numerical) Latest(versions []string) (string, error) {
+	if len(versions) == 0 {
+		return "", fmt.Errorf("version list argument cannot be empty")
+	}
+
+	var latest string
+	var pv float64
+	for i, version := range versions {
+		cv, err := strconv.ParseFloat(version, 64)
+		if err != nil {
+			return "", fmt.Errorf("failed to parse invalid numeric value '%s'", version)
+		}
+
+		switch {
+		case i == 0:
+			break // First iteration, nothing to compare
+		case p.Order == NumericalOrderAsc && cv < pv, p.Order == NumericalOrderDesc && cv > pv:
+			continue
+		}
+
+		latest = version
+		pv = cv
+	}
+
+	return latest, nil
+}