package main

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

// prettyJSON formats JSON with two-space indentation.
func prettyJSON(src []byte) ([]byte, error) {
	var out bytes.Buffer
	if err := json.Indent(&out, bytes.TrimSpace(src), "", "  "); err != nil {
		return nil, err
	}
	out.WriteByte('\n')
	return out.Bytes(), nil
}

// runTests provides a couple of lightweight checks in this single-file program.
func runTests() error {
	tests := []struct {
		input string
		want  string
	}{
		{`{"name":"Ada","active":true}`, "{\n  \"name\": \"Ada\",\n  \"active\": true\n}\n"},
		{`[1,{"x":null}]`, "[\n  1,\n  {\n    \"x\": null\n  }\n]\n"},
	}

	for i, test := range tests {
		got, err := prettyJSON([]byte(test.input))
		if err != nil {
			return fmt.Errorf("test %d: %w", i+1, err)
		}
		if string(got) != test.want {
			return fmt.Errorf("test %d: got %q, want %q", i+1, got, test.want)
		}
	}
	return nil
}

func main() {
	if len(os.Args) == 2 && os.Args[1] == "-test" {
		if err := runTests(); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		fmt.Println("tests passed")
		return
	}

	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, "invalid JSON:", err)
		os.Exit(1)
	}
	os.Stdout.Write(output)
}