package main

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

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

func main() {
	if len(os.Args) == 2 && os.Args[1] == "--self-test" {
		runTests()
		return
	}

	src, err := io.ReadAll(os.Stdin)
	if err != nil {
		exitErr(err)
	}

	out, err := pretty(src)
	if err != nil {
		exitErr(fmt.Errorf("invalid JSON: %w", err))
	}

	if _, err := os.Stdout.Write(out); err != nil {
		exitErr(err)
	}
}

// runTests provides two small checks without requiring a separate test file.
func runTests() {
	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 := pretty([]byte(test.input))
		if err != nil || string(got) != test.want {
			exitErr(fmt.Errorf("test %d failed: got %q, error %v", i+1, got, err))
		}
	}

	fmt.Fprintln(os.Stderr, "tests passed")
}

func exitErr(err error) {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
}