Extract immutable report preparation

internal/app/prepared_report_test.go

@@ -0,0 +1,64 @@
+package app
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/collect"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+func TestPrepareReportBuildsImmutableDeterministicInputs(t *testing.T) {
+	cfg := generationConfig()
+	bundle := generationBundle(t)
+	resolved, err := ResolveGenerate(GenerateRequest{
+		Config: cfg, Report: ReportDaily,
+		Date: generationTime("2026-05-29T12:00:00-05:00"), Now: generationTime("2026-05-29T08:30:00-05:00"),
+	}, generationTime("2026-05-29T08:30:00-05:00"))
+	if err != nil {
+		t.Fatalf("ResolveGenerate() error = %v", err)
+	}
+
+	request := prepareReportRequest{Config: cfg, Resolved: resolved, Collection: collect.Result{Bundle: &bundle}}
+	prepared, err := prepareReport(request)
+	if err != nil {
+		t.Fatalf("prepareReport() error = %v", err)
+	}
+	repeated, err := prepareReport(request)
+	if err != nil {
+		t.Fatalf("second prepareReport() error = %v", err)
+	}
+	if len(prepared.dataPackage) == 0 || !bytes.Equal(prepared.dataPackage, repeated.dataPackage) || !reflect.DeepEqual(prepared.briefingMetadata, repeated.briefingMetadata) {
+		t.Fatalf("prepared package/metadata are not deterministic: %q/%#v", prepared.dataPackage, prepared.briefingMetadata)
+	}
+
+	originalDataPackage := append([]byte(nil), prepared.dataPackage...)
+	originalMetadata := prepared.briefingMetadata
+	originalWarnings := append([]weatherdata.SourceWarning(nil), prepared.sourceWarnings...)
+	metadata, snapshot, reportFacts, err := prepared.renderInputs()
+	if err != nil {
+		t.Fatalf("renderInputs() error = %v", err)
+	}
+	metadata.SourceWarnings = append(metadata.SourceWarnings, weatherdata.SourceWarning{Source: "test", Message: "consumer mutation"})
+	snapshot.Outputs = nil
+	reportFacts.Collected.Hourly.Periods[0].TextDescription = "consumer mutation"
+	bundle.Hourly.Periods[0].TextDescription = "mutated after preparation"
+	bundle.Warnings = append(bundle.Warnings, weatherdata.SourceWarning{Source: "test", Message: "mutated warning"})
+	if len(bundle.Sources) > 0 {
+		if bundle.Sources[0].Query == nil {
+			bundle.Sources[0].Query = map[string]string{}
+		}
+		bundle.Sources[0].Query["mutated"] = "true"
+	}
+
+	if !bytes.Equal(prepared.dataPackage, originalDataPackage) || !reflect.DeepEqual(prepared.briefingMetadata, originalMetadata) || !reflect.DeepEqual(prepared.sourceWarnings, originalWarnings) {
+		t.Fatalf("prepared values changed after caller mutation: %#v", prepared)
+	}
+	if prepared.reportFacts.Collected.Hourly.Periods[0].TextDescription == "mutated after preparation" {
+		t.Fatal("prepared report facts retain caller-owned weather data")
+	}
+	if prepared.reportFacts.Collected.Hourly.Periods[0].TextDescription == "consumer mutation" || len(prepared.moduleSnapshot.Outputs) == 0 {
+		t.Fatal("prepared report values retain consumer mutation")
+	}
+}