/*
The MIT License (MIT)

Copyright © 2026 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.
*/

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

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

package main

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

const info = `
dejsonl [filepath...]

Turn JSON Lines (JSONL) into proper-JSON arrays. The JSON Lines format is
simply plain-text lines, where each line is valid JSON on its own.
`

const indent = `  `

// 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.Stdout.WriteString(info[1:])
			return
		}
	}

	if len(os.Args) > 2 {
		os.Stderr.WriteString("multiple inputs not allowed\n")
		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]
	}

	liveLines := true
	if _, err := os.Stdout.Seek(0, io.SeekCurrent); err == nil {
		liveLines = false
	}

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

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

	// 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 dejsonl(w, resp.Body, live)
	// }

	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 dejsonl(w, f, live)
}

// dejsonl simplifies control-flow for func handleInput
func dejsonl(w io.Writer, r io.Reader, live bool) error {
	bw := bufio.NewWriter(w)
	defer bw.Flush()

	const gb = 1024 * 1024 * 1024
	sc := bufio.NewScanner(r)
	sc.Buffer(nil, 8*gb)
	got := 0

	for i := 0; sc.Scan(); i++ {
		s := sc.Text()
		if i == 0 && strings.HasPrefix(s, "\xef\xbb\xbf") {
			s = s[3:]
		}

		// trim spaces at both ends of the current line
		for len(s) > 0 && s[0] == ' ' {
			s = s[1:]
		}
		for len(s) > 0 && s[len(s)-1] == ' ' {
			s = s[:len(s)-1]
		}

		// ignore empty(ish) lines
		if len(s) == 0 {
			continue
		}

		// ignore lines starting with unix-style comments
		if len(s) > 0 && s[0] == '#' {
			continue
		}

		if err := checkJSONL(strings.NewReader(s)); err != nil {
			return err
		}

		if got == 0 {
			bw.WriteByte('[')
		} else {
			bw.WriteByte(',')
		}
		if bw.WriteByte('\n') != nil {
			return errNoMoreOutput
		}
		bw.WriteString(indent)
		bw.WriteString(s)
		got++

		if !live {
			continue
		}

		if err := bw.Flush(); err != nil {
			return errNoMoreOutput
		}
	}

	if got == 0 {
		bw.WriteString("[\n]\n")
	} else {
		bw.WriteString("\n]\n")
	}
	return sc.Err()
}

func checkJSONL(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 := checkToken(dec, t); err != nil {
		return err
	}

	_, 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
}

// checkToken handles recursion for func checkJSONL
func checkToken(dec *json.Decoder, t json.Token) error {
	switch t := t.(type) {
	case json.Delim:
		switch t {
		case json.Delim('['):
			return checkArray(dec)
		case json.Delim('{'):
			return checkObject(dec)
		default:
			return errors.New(`unsupported JSON syntax ` + string(t))
		}

	case nil, bool, float64, json.Number, string:
		return nil

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

// handleArray handles arrays for func checkToken
func checkArray(dec *json.Decoder) error {
	for {
		t, err := dec.Token()
		if err != nil {
			return err
		}

		if t == json.Delim(']') {
			return nil
		}

		if err := checkToken(dec, t); err != nil {
			return err
		}
	}

	// make the compiler happy
	return nil
}

// handleObject handles objects for func checkToken
func checkObject(dec *json.Decoder) error {
	for {
		t, err := dec.Token()
		if err != nil {
			return err
		}

		if t == json.Delim('}') {
			return nil
		}

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

		t, err = dec.Token()
		if err == io.EOF || t == json.Delim('}') {
			return errors.New(`expected a value for a key-value pair`)
		}

		if err := checkToken(dec, t); err != nil {
			return err
		}
	}

	// make the compiler happy
	return nil
}