package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"testing"
)

// PrettyJSON validates JSON and returns it with stable two-space indentation.
func PrettyJSON(input []byte) ([]byte, error) {
	var value any
	dec := json.NewDecoder(bytes.NewReader(input))
	dec.UseNumber()

	if err := dec.Decode(&value); err != nil {
		return nil, err
	}
	if dec.Decode(&struct{}{}) != io.EOF {
		return nil, fmt.Errorf("multiple JSON values")
	}

	var out bytes.Buffer
	enc := json.NewEncoder(&out)
	enc.SetIndent("", "  ")
	enc.SetEscapeHTML(false)

	if err := enc.Encode(value); err != nil {
		return nil, err
	}
	return out.Bytes(), nil
}

// main reads JSON from stdin and writes pretty JSON to stdout.
func main() {
	input, err := io.ReadAll(os.Stdin)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	output, err := PrettyJSON(input)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	if _, err := os.Stdout.Write(output); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func TestPrettyJSON(t *testing.T) {
	got, err := PrettyJSON([]byte(`{"name":"Ada","scores":[3,1],"active":true}`))
	if err != nil {
		t.Fatal(err)
	}

	want := "{\n  \"active\": true,\n  \"name\": \"Ada\",\n  \"scores\": [\n    3,\n    1\n  ]\n}\n"
	if string(got) != want {
		t.Fatalf("PrettyJSON() = %q, want %q", got, want)
	}
}

func TestPrettyJSONRejectsInvalidInput(t *testing.T) {
	if _, err := PrettyJSON([]byte(`{"broken":`)); err == nil {
		t.Fatal("PrettyJSON() returned nil error for invalid JSON")
	}
}