package main

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

const indent = "  "

// Pretty formats JSON with stable two-space indentation.
func Pretty(src []byte) ([]byte, error) {
	var value any
	dec := json.NewDecoder(bytes.NewReader(src))
	dec.UseNumber()

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

	return json.MarshalIndent(value, "", indent)
}

// PrettyString is a small convenience wrapper around Pretty.
func PrettyString(src string) (string, error) {
	out, err := Pretty([]byte(src))
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func main() {
	in, err := io.ReadAll(os.Stdin)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	out, err := Pretty(in)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	os.Stdout.Write(out)
	os.Stdout.Write([]byte("\n"))
}

func TestPrettyObject(t *testing.T) {
	got, err := PrettyString(`{"name":"Ada","nums":[1,2],"ok":true}`)
	if err != nil {
		t.Fatal(err)
	}

	want := "{\n  \"name\": \"Ada\",\n  \"nums\": [\n    1,\n    2\n  ],\n  \"ok\": true\n}"
	if got != want {
		t.Fatalf("PrettyString() = %q, want %q", got, want)
	}
}

func TestPrettyRejectsTrailingValue(t *testing.T) {
	if _, err := PrettyString(`{"ok":true} {"extra":true}`); err == nil {
		t.Fatal("expected an error for multiple JSON values")
	}
}