Add Tomorrow generated text contract

internal/generatedtext/tomorrow.go

@@ -0,0 +1,62 @@
+package generatedtext
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"strings"
+)
+
+type Tomorrow struct {
+	Summary             string   `json:"summary"`
+	ForecastDiscussion  []string `json:"forecast_discussion"`
+	PrecipitationTiming string   `json:"precipitation_timing,omitempty"`
+	Confidence          string   `json:"confidence,omitempty"`
+}
+
+func ValidateTomorrow(data []byte) (Tomorrow, []byte, error) {
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+
+	var value Tomorrow
+	if err := decoder.Decode(&value); err != nil {
+		return Tomorrow{}, nil, fmt.Errorf("decode tomorrow generated text: %w", err)
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != nil {
+		if err != io.EOF {
+			return Tomorrow{}, nil, fmt.Errorf("decode tomorrow generated text: %w", err)
+		}
+	} else {
+		return Tomorrow{}, nil, fmt.Errorf("decode tomorrow generated text: multiple JSON values")
+	}
+
+	value.Summary = strings.TrimSpace(value.Summary)
+	value.PrecipitationTiming = strings.TrimSpace(value.PrecipitationTiming)
+	value.Confidence = strings.TrimSpace(value.Confidence)
+	value.ForecastDiscussion = trimNonEmpty(value.ForecastDiscussion)
+	if value.Summary == "" {
+		return Tomorrow{}, nil, fmt.Errorf("tomorrow generated text summary is required")
+	}
+	if len(value.ForecastDiscussion) == 0 {
+		return Tomorrow{}, nil, fmt.Errorf("tomorrow generated text forecast discussion is required")
+	}
+
+	normalized, err := json.Marshal(value)
+	if err != nil {
+		return Tomorrow{}, nil, fmt.Errorf("normalize tomorrow generated text: %w", err)
+	}
+	return value, normalized, nil
+}
+
+func trimNonEmpty(values []string) []string {
+	out := make([]string, 0, len(values))
+	for _, value := range values {
+		trimmed := strings.TrimSpace(value)
+		if trimmed != "" {
+			out = append(out, trimmed)
+		}
+	}
+	return out
+}