/*
The MIT License (MIT)

Copyright © 2024 pacman64

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the “Software”), to deal
in the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/*
Single-file source-code for j2: this version has no http(s) support. Even
the unit-tests from the original j2 are omitted.

To compile a smaller-sized command-line app, you can use the `go` command as
follows:

go build -ldflags "-s -w" -trimpath j2.go
*/

package main

import (
	"bufio"
	"encoding/json"
	"errors"
	"io"
	"os"
)

const info = `
j2 [filepath...]

Json-2 indents valid JSON input into multi-line JSON which uses 2 spaces for
each indentation level.
`

// errNoMoreOutput is a generic dummy output-error, which is meant to be
// ultimately ignored, being just an excuse to quit the app immediately
// and successfully
var errNoMoreOutput = errors.New(`no more output`)

func main() {
	if len(os.Args) > 1 {
		switch os.Args[1] {
		case `-h`, `--h`, `-help`, `--help`:
			os.Stderr.WriteString(info[1:])
			return
		}
	}

	if len(os.Args) > 2 {
		const msg = "\x1b[31mmultiple inputs not allowed\x1b[0m\n"
		os.Stderr.WriteString(msg)
		os.Exit(1)
	}

	// figure out whether input should come from a named file or from stdin
	path := `-`
	if len(os.Args) > 1 {
		path = os.Args[1]
	}

	err := handleInput(os.Stdout, path)
	if err != nil && err != io.EOF && err != errNoMoreOutput {
		os.Stderr.WriteString("\x1b[31m")
		os.Stderr.WriteString(err.Error())
		os.Stderr.WriteString("\x1b[0m\n")
		os.Exit(1)
	}
}

// handleInput simplifies control-flow for func main
func handleInput(w io.Writer, path string) error {
	if path == `-` {
		return convert(w, os.Stdin)
	}

	// if f := strings.HasPrefix; f(path, `https://`) || f(path, `http://`) {
	// 	resp, err := http.Get(path)
	// 	if err != nil {
	// 		return err
	// 	}
	// 	defer resp.Body.Close()
	// 	return convert(w, resp.Body)
	// }

	f, err := os.Open(path)
	if err != nil {
		// on windows, file-not-found error messages may mention `CreateFile`,
		// even when trying to open files in read-only mode
		return errors.New(`can't open file named ` + path)
	}
	defer f.Close()
	return convert(w, f)
}

// convert simplifies control-flow for func handleInput
func convert(w io.Writer, r io.Reader) error {
	bw := bufio.NewWriter(w)
	defer bw.Flush()
	return json2(bw, r)
}

// escapedStringBytes helps func handleString treat all string bytes quickly
// and correctly, using their officially-supported JSON escape sequences
//
// https://www.rfc-editor.org/rfc/rfc8259#section-7
var escapedStringBytes = [256][]byte{
	{'\\', 'u', '0', '0', '0', '0'}, {'\\', 'u', '0', '0', '0', '1'},
	{'\\', 'u', '0', '0', '0', '2'}, {'\\', 'u', '0', '0', '0', '3'},
	{'\\', 'u', '0', '0', '0', '4'}, {'\\', 'u', '0', '0', '0', '5'},
	{'\\', 'u', '0', '0', '0', '6'}, {'\\', 'u', '0', '0', '0', '7'},
	{'\\', 'b'}, {'\\', 't'},
	{'\\', 'n'}, {'\\', 'u', '0', '0', '0', 'b'},
	{'\\', 'f'}, {'\\', 'r'},
	{'\\', 'u', '0', '0', '0', 'e'}, {'\\', 'u', '0', '0', '0', 'f'},
	{'\\', 'u', '0', '0', '1', '0'}, {'\\', 'u', '0', '0', '1', '1'},
	{'\\', 'u', '0', '0', '1', '2'}, {'\\', 'u', '0', '0', '1', '3'},
	{'\\', 'u', '0', '0', '1', '4'}, {'\\', 'u', '0', '0', '1', '5'},
	{'\\', 'u', '0', '0', '1', '6'}, {'\\', 'u', '0', '0', '1', '7'},
	{'\\', 'u', '0', '0', '1', '8'}, {'\\', 'u', '0', '0', '1', '9'},
	{'\\', 'u', '0', '0', '1', 'a'}, {'\\', 'u', '0', '0', '1', 'b'},
	{'\\', 'u', '0', '0', '1', 'c'}, {'\\', 'u', '0', '0', '1', 'd'},
	{'\\', 'u', '0', '0', '1', 'e'}, {'\\', 'u', '0', '0', '1', 'f'},
	{32}, {33}, {'\\', '"'}, {35}, {36}, {37}, {38}, {39},
	{40}, {41}, {42}, {43}, {44}, {45}, {46}, {47},
	{48}, {49}, {50}, {51}, {52}, {53}, {54}, {55},
	{56}, {57}, {58}, {59}, {60}, {61}, {62}, {63},
	{64}, {65}, {66}, {67}, {68}, {69}, {70}, {71},
	{72}, {73}, {74}, {75}, {76}, {77}, {78}, {79},
	{80}, {81}, {82}, {83}, {84}, {85}, {86}, {87},
	{88}, {89}, {90}, {91}, {'\\', '\\'}, {93}, {94}, {95},
	{96}, {97}, {98}, {99}, {100}, {101}, {102}, {103},
	{104}, {105}, {106}, {107}, {108}, {109}, {110}, {111},
	{112}, {113}, {114}, {115}, {116}, {117}, {118}, {119},
	{120}, {121}, {122}, {123}, {124}, {125}, {126}, {127},
	{128}, {129}, {130}, {131}, {132}, {133}, {134}, {135},
	{136}, {137}, {138}, {139}, {140}, {141}, {142}, {143},
	{144}, {145}, {146}, {147}, {148}, {149}, {150}, {151},
	{152}, {153}, {154}, {155}, {156}, {157}, {158}, {159},
	{160}, {161}, {162}, {163}, {164}, {165}, {166}, {167},
	{168}, {169}, {170}, {171}, {172}, {173}, {174}, {175},
	{176}, {177}, {178}, {179}, {180}, {181}, {182}, {183},
	{184}, {185}, {186}, {187}, {188}, {189}, {190}, {191},
	{192}, {193}, {194}, {195}, {196}, {197}, {198}, {199},
	{200}, {201}, {202}, {203}, {204}, {205}, {206}, {207},
	{208}, {209}, {210}, {211}, {212}, {213}, {214}, {215},
	{216}, {217}, {218}, {219}, {220}, {221}, {222}, {223},
	{224}, {225}, {226}, {227}, {228}, {229}, {230}, {231},
	{232}, {233}, {234}, {235}, {236}, {237}, {238}, {239},
	{240}, {241}, {242}, {243}, {244}, {245}, {246}, {247},
	{248}, {249}, {250}, {251}, {252}, {253}, {254}, {255},
}

// writeSpaces does what it says, minimizing calls to write-like funcs
func writeSpaces(w *bufio.Writer, n int) {
	const spaces = `                                `
	if n < 1 {
		return
	}

	for n >= len(spaces) {
		w.WriteString(spaces)
		n -= len(spaces)
	}
	w.WriteString(spaces[:n])
}

// json2 does it all, given a reader and a writer
func json2(w *bufio.Writer, r io.Reader) error {
	dec := json.NewDecoder(r)
	// avoid parsing numbers, so unusually-long numbers are kept verbatim,
	// even if JSON parsers aren't required to guarantee such input-fidelity
	// for numbers
	dec.UseNumber()

	t, err := dec.Token()
	if err == io.EOF {
		return errors.New(`input has no JSON values`)
	}

	if err = handleToken(w, dec, t, 0, 0); err != nil {
		return err
	}
	// don't forget ending the last line for the last value
	w.WriteByte('\n')

	_, err = dec.Token()
	if err == io.EOF {
		// input is over, so it's a success
		return nil
	}

	if err == nil {
		// a successful `read` is a failure, as it means there are
		// trailing JSON tokens
		return errors.New(`unexpected trailing data`)
	}

	// any other error, perhaps some invalid-JSON-syntax-type error
	return err
}

// handleToken handles recursion for func json2
func handleToken(w *bufio.Writer, dec *json.Decoder, t json.Token, pre, level int) error {
	switch t := t.(type) {
	case json.Delim:
		switch t {
		case json.Delim('['):
			return handleArray(w, dec, pre, level+1)
		case json.Delim('{'):
			return handleObject(w, dec, pre, level+1)
		default:
			return errors.New(`unsupported JSON syntax ` + string(t))
		}

	case nil:
		w.WriteString(`null`)
		return nil

	case bool:
		if t {
			w.WriteString(`true`)
		} else {
			w.WriteString(`false`)
		}
		return nil

	case json.Number:
		writeSpaces(w, 2*pre)
		w.WriteString(t.String())
		return nil

	case string:
		return handleString(w, t, pre)

	default:
		// return fmt.Errorf(`unsupported token type %T`, t)
		return errors.New(`invalid JSON token`)
	}
}

// handleArray handles arrays for func handleToken
func handleArray(w *bufio.Writer, dec *json.Decoder, pre, level int) error {
	writeSpaces(w, 2*pre)
	w.WriteByte('[')

	for i := 0; true; i++ {
		t, err := dec.Token()
		if err == io.EOF {
			endComposite(i, w, level-1, ']')
			return nil
		}

		if err != nil {
			return err
		}

		if t == json.Delim(']') {
			endComposite(i, w, level-1, ']')
			return nil
		}

		if i > 0 {
			_, err := w.WriteString(",\n")
			if err != nil {
				return errNoMoreOutput
			}
		} else {
			w.WriteByte('\n')
		}

		err = handleToken(w, dec, t, level, level)
		if err != nil {
			return err
		}
	}

	// make the compiler happy
	return nil
}

// handleObject handles objects for func handleToken
func handleObject(w *bufio.Writer, dec *json.Decoder, pre, level int) error {
	writeSpaces(w, 2*pre)
	w.WriteByte('{')

	for i := 0; true; i++ {
		t, err := dec.Token()
		if err == io.EOF {
			endComposite(i, w, pre, '}')
			return nil
		}

		if err != nil {
			return err
		}

		if t == json.Delim('}') {
			endComposite(i, w, pre, '}')
			return nil
		}

		if i > 0 {
			_, err := w.WriteString(",\n")
			if err != nil {
				return errNoMoreOutput
			}
		} else {
			w.WriteByte('\n')
		}

		k, ok := t.(string)
		if !ok {
			return errors.New(`expected a string for a key-value pair`)
		}

		err = handleString(w, k, level)
		if err != nil {
			return err
		}

		w.WriteString(": ")

		t, err = dec.Token()
		if err == io.EOF {
			return errors.New(`expected a value for a key-value pair`)
		}

		err = handleToken(w, dec, t, 0, level)
		if err != nil {
			return err
		}
	}

	// make the compiler happy
	return nil
}

// handleString handles strings for func handleToken, and keys for func
// handleObject
func handleString(w *bufio.Writer, s string, level int) error {
	writeSpaces(w, 2*level)
	w.WriteByte('"')
	for i := range s {
		w.Write(escapedStringBytes[s[i]])
	}
	w.WriteByte('"')
	return nil
}

// endComposite handles common closing logic which is used twice both in each
// of func handleArray and func handleObject
func endComposite(i int, w *bufio.Writer, pre int, end byte) {
	if i > 0 {
		w.WriteByte('\n')
		writeSpaces(w, 2*pre)
	}
	w.WriteByte(end)
}