Add processing for requirements and constraints

This change adds a Requirements abstraction that can be used to check
an images' NVIDIA_REQUIRE_* envvars against the host properties such
as CUDA version or architecture.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/requirements/constraints/property.go

@@ -0,0 +1,129 @@
+/**
+# Copyright (c) 2022, NVIDIA CORPORATION.  All rights reserved.
+#
+# 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 constraints
+
+import (
+	"fmt"
+	"strings"
+
+	"golang.org/x/mod/semver"
+)
+
+//go:generate moq -stub -out property_mock.go . Property
+// Property represents a property that is used to check requirements
+type Property interface {
+	Name() string
+	Value() (string, error)
+	String() string
+	CompareTo(string) (int, error)
+	Validate(string) error
+}
+
+// NewStringProperty creates a string property based on the name-value pair
+func NewStringProperty(name string, value string) Property {
+	p := stringProperty{
+		name:  name,
+		value: value,
+	}
+
+	return p
+}
+
+// NewVersionProperty creates a property representing a semantic version based on the name-value pair
+func NewVersionProperty(name string, value string) Property {
+	p := versionProperty{
+		stringProperty: stringProperty{
+			name:  name,
+			value: value,
+		},
+	}
+
+	return p
+}
+
+// stringProperty represents a property that is used to check requirements
+type stringProperty struct {
+	name  string
+	value string
+}
+
+type versionProperty struct {
+	stringProperty
+}
+
+// Name returns a stringProperty's name
+func (p stringProperty) Name() string {
+	return p.name
+}
+
+// Value returns a stringProperty's value or an error if this cannot be determined
+func (p stringProperty) Value() (string, error) {
+	return p.value, nil
+}
+
+// CompareTo compares two strings to each other
+func (p stringProperty) CompareTo(other string) (int, error) {
+	value := p.value
+
+	if value < other {
+		return -1, nil
+	}
+
+	if value > other {
+		return 1, nil
+	}
+
+	return 0, nil
+}
+
+// Validate returns nil for all input strings
+func (p stringProperty) Validate(string) error {
+	return nil
+}
+
+// String returns the string representation of the name value combination
+func (p stringProperty) String() string {
+	v, err := p.Value()
+	if err != nil {
+		return fmt.Sprintf("invalid %v: %v", p.name, err)
+	}
+	return fmt.Sprintf("%v=%v", p.name, v)
+}
+
+// CompareTo compares two versions to each other as semantic versions
+func (p versionProperty) CompareTo(other string) (int, error) {
+	if err := p.Validate(other); err != nil {
+		return 0, fmt.Errorf("invailid value for %v: %v", p.name, err)
+	}
+
+	vValue := ensurePrefix(p.value, "v")
+	vOther := ensurePrefix(other, "v")
+	return semver.Compare(vValue, vOther), nil
+}
+
+// Validate checks whether the supplied value is a valid semantic version
+func (p versionProperty) Validate(value string) error {
+	if !semver.IsValid(ensurePrefix(value, "v")) {
+		return fmt.Errorf("invailid value %v; expected a valid version string", value)
+	}
+
+	return nil
+}
+
+func ensurePrefix(s string, prefix string) string {
+	return prefix + strings.TrimPrefix(s, prefix)
+}