feat(storage): extend application schema for storage flag

docs/resources/application.md

@@ -78,6 +78,7 @@ resource "juju_application" "placement_example" {
 		  latest revision.
 	    * If the charm revision or channel are not updated, then no changes will take 
 		  place (juju does not have an "un-attach" command for resources).
+- `storage` (Attributes Set) Configure storage constraints for the juju application. (see [below for nested schema](#nestedatt--storage))
 - `trust` (Boolean) Set the trust for the application.
 - `units` (Number) The number of application units to deploy for the charm.
 
@@ -122,6 +123,20 @@ Optional:
 - `endpoints` (String) Expose only the ports that charms have opened for this comma-delimited list of endpoints
 - `spaces` (String) A comma-delimited list of spaces that should be able to access the application ports once exposed.
 
+
+<a id="nestedatt--storage"></a>
+### Nested Schema for `storage`
+
+Required:
+
+- `label` (String) The specific storage option defined in the charm.
+
+Optional:
+
+- `count` (Number) The number of volumes.
+- `pool` (String) Name of the storage pool to use. E.g. ebs on aws.
+- `size` (String) The size of each volume. E.g. 100G.
+
 ## Import
 
 Import is supported using the following syntax:

internal/provider/resource_application.go

@@ -20,13 +20,13 @@ import (
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/int64default"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/int64planmodifier"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/planmodifier"
+	"github.com/hashicorp/terraform-plugin-framework/resource/schema/stringdefault"
 	"github.com/hashicorp/terraform-plugin-framework/resource/schema/stringplanmodifier"
 	"github.com/hashicorp/terraform-plugin-framework/schema/validator"
 	"github.com/hashicorp/terraform-plugin-framework/tfsdk"
 	"github.com/hashicorp/terraform-plugin-framework/types"
 	"github.com/hashicorp/terraform-plugin-log/tflog"
 	"github.com/juju/errors"
-
 	"github.com/juju/juju/core/constraints"
 
 	"github.com/juju/terraform-provider-juju/internal/juju"
@@ -164,6 +164,55 @@ func (r *applicationResource) Schema(_ context.Context, _ resource.SchemaRequest
 					stringplanmodifier.UseStateForUnknown(),
 				},
 			},
+			"storage": schema.SetNestedAttribute{
+				Description: "Configure storage constraints for the juju application.",
+				Optional:    true,
+				NestedObject: schema.NestedAttributeObject{
+					Attributes: map[string]schema.Attribute{
+						"label": schema.StringAttribute{
+							Description: "The specific storage option defined in the charm.",
+							Required:    true,
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"size": schema.StringAttribute{
+							Description: "The size of each volume. E.g. 100G.",
+							Optional:    true,
+							Computed:    true,
+							Default:     stringdefault.StaticString("1G"),
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"pool": schema.StringAttribute{
+							Description: "Name of the storage pool to use. E.g. ebs on aws.",
+							Optional:    true,
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"count": schema.Int64Attribute{
+							Description: "The number of volumes.",
+							Optional:    true,
+							Computed:    true,
+							Default:     int64default.StaticInt64(int64(1)),
+							PlanModifiers: []planmodifier.Int64{
+								int64planmodifier.RequiresReplaceIfConfigured(),
+								int64planmodifier.UseStateForUnknown(),
+							},
+						},
+					},
+				},
+				Validators: []validator.Set{
+					setNestedIsAttributeUniqueValidator{
+						PathExpressions: path.MatchRelative().AtAnySetValue().MergeExpressions(path.MatchRelative().AtName("label")),
+					},
+				},
+			},
 			"trust": schema.BoolAttribute{
 				Description: "Set the trust for the application.",
 				Optional:    true,