[CCV-4035] [datadog_cost_budget] Add Validation for terraform plan Flow

datadog/fwprovider/resource_datadog_cost_budget.go

@@ -2,6 +2,11 @@ package fwprovider
 
 import (
 	"context"
+	"fmt"
+	"regexp"
+	"slices"
+	"sort"
+	"strings"
 
 	"github.com/DataDog/datadog-api-client-go/v2/api/datadogV2"
 	frameworkPath "github.com/hashicorp/terraform-plugin-framework/path"
@@ -12,6 +17,11 @@ import (
 	"github.com/terraform-providers/terraform-provider-datadog/datadog/internal/utils"
 )
 
+var (
+	_                resource.ResourceWithValidateConfig = &costBudgetResource{}
+	metricQueryRegex                                     = regexp.MustCompile(`by\s*\{(.+)\}`)
+)
+
 type costBudgetResource struct {
 	Api  *datadogV2.CloudCostManagementApi
 	Auth context.Context
@@ -198,6 +208,177 @@ func (r *costBudgetResource) ImportState(ctx context.Context, req resource.Impor
 	resource.ImportStatePassthroughID(ctx, frameworkPath.Root("id"), req, resp)
 }
 
+// ValidateConfig performs client-side validation during terraform plan
+// Mirrors BudgetWithEntries.validate() from dd-source: cost-planning-api/budgets/handler.go
+func (r *costBudgetResource) ValidateConfig(ctx context.Context, req resource.ValidateConfigRequest, resp *resource.ValidateConfigResponse) {
+	var data costBudgetModel
+	resp.Diagnostics.Append(req.Config.Get(ctx, &data)...)
+	if resp.Diagnostics.HasError() || data.MetricsQuery.IsUnknown() || data.StartMonth.IsUnknown() || data.EndMonth.IsUnknown() {
+		return
+	}
+
+	// Extract tags from metrics_query
+	tags := extractTagsFromQuery(data.MetricsQuery.ValueString())
+
+	// Validate tags length
+	if len(tags) > 2 {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("metrics_query"),
+			"Invalid metrics_query",
+			"tags must have 0, 1 or 2 elements",
+		)
+	}
+
+	// Validate tags are unique
+	if len(tags) == 2 && tags[0] == tags[1] {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("metrics_query"),
+			"Invalid metrics_query",
+			"tags must be unique",
+		)
+	}
+
+	startMonth := data.StartMonth.ValueInt64()
+	endMonth := data.EndMonth.ValueInt64()
+
+	// Validate start_month
+	if startMonth <= 0 {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("start_month"),
+			"Invalid start_month",
+			"start_month must be greater than 0 and of the format YYYYMM",
+		)
+	}
+
+	// Validate end_month
+	if endMonth <= 0 {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("end_month"),
+			"Invalid end_month",
+			"end_month must be greater than 0 and of the format YYYYMM",
+		)
+	}
+
+	// Validate end_month >= start_month
+	if startMonth > endMonth {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("end_month"),
+			"Invalid end_month",
+			"end_month must be greater than or equal to start_month",
+		)
+	}
+
+	// Track which months exist for each unique tag combination
+	// Example: {"ASE\tstaging": {202501: true, 202502: true}} means team=ASE,account=staging has entries for 202501 & 202502
+	entriesMap := make(map[string]map[int64]bool)
+
+	// Validate entries
+	for i, entry := range data.Entries {
+		month := entry.Month.ValueInt64()
+		amount := entry.Amount.ValueFloat64()
+
+		// Validate entry month in range
+		if month < startMonth || month > endMonth {
+			resp.Diagnostics.AddAttributeError(
+				frameworkPath.Root("entries").AtListIndex(i).AtName("month"),
+				"Invalid month",
+				"entry month must be between start_month and end_month",
+			)
+		}
+
+		// Validate entry amount >= 0
+		if amount < 0 {
+			resp.Diagnostics.AddAttributeError(
+				frameworkPath.Root("entries").AtListIndex(i).AtName("amount"),
+				"Invalid amount",
+				"entry amount must be greater than or equal to 0",
+			)
+		}
+
+		// Validate tag_filters count
+		if len(entry.TagFilters) != len(tags) {
+			resp.Diagnostics.AddAttributeError(
+				frameworkPath.Root("entries").AtListIndex(i).AtName("tag_filters"),
+				"Invalid tag_filters",
+				"entry tag_filters must include all group by tags",
+			)
+			continue
+		}
+
+		// Validate tag_key and collect tag values
+		tagValues := make([]string, len(entry.TagFilters))
+		for j, tf := range entry.TagFilters {
+			tagKey := tf.TagKey.ValueString()
+
+			if !slices.Contains(tags, tagKey) {
+				resp.Diagnostics.AddAttributeError(
+					frameworkPath.Root("entries").AtListIndex(i).AtName("tag_filters").AtListIndex(j).AtName("tag_key"),
+					"Invalid tag_key",
+					"tag_key must be one of the values inside the tags array",
+				)
+			}
+
+			tagValues[j] = tf.TagValue.ValueString()
+		}
+
+		// Build unique key for this tag combination (e.g., "ASE\tstaging")
+		// We sort to ensure same combination regardless of order: {team:ASE,account:staging} = {account:staging,team:ASE}
+		sort.Strings(tagValues)
+		tagCombination := strings.Join(tagValues, "\t")
+		if entriesMap[tagCombination] == nil {
+			entriesMap[tagCombination] = make(map[int64]bool)
+		}
+		entriesMap[tagCombination][month] = true
+	}
+
+	// Validate entries exist
+	if len(entriesMap) == 0 {
+		resp.Diagnostics.AddAttributeError(
+			frameworkPath.Root("entries"),
+			"Missing entries",
+			"entries are required",
+		)
+		return
+	}
+
+	// Validate all tag combinations have entries for all months
+	expectedMonthCount := calculateMonthCount(startMonth, endMonth)
+	for tagCombination, months := range entriesMap {
+		if len(months) != expectedMonthCount {
+			resp.Diagnostics.AddError(
+				"Missing entries for tag combination",
+				fmt.Sprintf("missing entries for tag value pair: %v", tagCombination),
+			)
+		}
+	}
+}
+
+// --- Validation helper functions ---
+
+// extractTagsFromQuery extracts tags from "by {tag1,tag2}" in metrics_query
+// Copied from dd-source: domains/cloud_cost_management/libs/costplanningdb/tables.go
+func extractTagsFromQuery(query string) []string {
+	subGroups := metricQueryRegex.FindStringSubmatch(query)
+	if len(subGroups) != 2 {
+		return []string{}
+	}
+	tags := strings.Split(subGroups[1], ",")
+	for i, tag := range tags {
+		tags[i] = strings.TrimSpace(tag)
+	}
+	return tags
+}
+
+// calculateMonthCount returns the number of months between start and end (inclusive)
+// Copied from dd-source: domains/cloud_cost_management/libs/costplanningdb/tables.go (GetBudgetDuration)
+func calculateMonthCount(start, end int64) int {
+	startYear := start / 100
+	endYear := end / 100
+	startMonth := start % 100
+	endMonth := end % 100
+	return int((endYear-startYear)*12 + endMonth - startMonth + 1)
+}
+
 // --- Helper functions to map between model and API types go here ---
 func buildBudgetWithEntriesFromModel(plan costBudgetModel) datadogV2.BudgetWithEntries {
 	// Convert entries