package generatedtext

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"strings"
)

func decodeGeneratedText[T any](data []byte, name string) (T, error) {
	var value T
	decoder := json.NewDecoder(bytes.NewReader(data))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&value); err != nil {
		return value, fmt.Errorf("decode %s generated text: %w", name, err)
	}
	var extra any
	if err := decoder.Decode(&extra); err != nil {
		if err != io.EOF {
			return value, fmt.Errorf("decode %s generated text: %w", name, err)
		}
		return value, nil
	}
	return value, fmt.Errorf("decode %s generated text: multiple JSON values", name)
}

func requireGeneratedTextStringField(data []byte, name, field string) error {
	var fields map[string]json.RawMessage
	if err := json.Unmarshal(data, &fields); err != nil {
		return fmt.Errorf("decode %s generated text: %w", name, err)
	}
	raw, ok := fields[field]
	if !ok {
		return fmt.Errorf("%s generated text %s is required", name, strings.ReplaceAll(field, "_", " "))
	}
	if bytes.Equal(bytes.TrimSpace(raw), []byte("null")) {
		return fmt.Errorf("%s generated text %s must be a string", name, strings.ReplaceAll(field, "_", " "))
	}
	return nil
}

func normalizeGeneratedText[T any](value T, name string) ([]byte, error) {
	normalized, err := json.Marshal(value)
	if err != nil {
		return nil, fmt.Errorf("normalize %s generated text: %w", name, err)
	}
	return normalized, nil
}