package main

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

// PrettyJSON formats compact or minified JSON using the requested indentation.
func PrettyJSON(src []byte, indent string) ([]byte, error) {
	var out bytes.Buffer
	if err := json.Indent(&out, bytes.TrimSpace(src), "", indent); err != nil {
		return nil, err
	}
	out.WriteByte('\n')
	return out.Bytes(), nil
}

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

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

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

func TestPrettyJSONObject(t *testing.T) {
	got, err := PrettyJSON([]byte(`{"name":"Ada","skills":["math","code"]}`), "  ")
	if err != nil {
		t.Fatal(err)
	}

	want := "{\n  \"name\": \"Ada\",\n  \"skills\": [\n    \"math\",\n    \"code\"\n  ]\n}\n"
	if string(got) != want {
		t.Fatalf("PrettyJSON() = %q, want %q", got, want)
	}
}

func TestPrettyRejectsInvalidJSON(t *testing.T) {
	if _, err := PrettyJSON([]byte(`{"missing":]`), "  "); err == nil {
		t.Fatal("PrettyJSON() error = nil, want non-nil")
	}
}