/*
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 nn: this version has no http(s) support. Even
the unit-tests from the original nn are omitted.

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

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

package main

import (
	"bufio"
	"errors"
	"io"
	"os"
	"strings"
)

// Note: the code is avoiding using the fmt package to save hundreds of
// kilobytes on the resulting executable, which is a noticeable difference.

const info = `
nn [options...] [file...]


Nice Numbers is an app which renders the UTF-8 text it's given to make long
numbers much easier to read. It does so by alternating 3-digit groups which
are colored using ANSI-codes with plain/unstyled 3-digit groups.

Unlike the common practice of inserting commas between 3-digit groups, this
trick doesn't widen the original text, keeping alignments across lines the
same.

Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
feeds.

All (optional) leading options start with either single or double-dash,
and most of them change the style/color used. Some of the options are,
shown in their single-dash form:

    -h          show this help message
    -help       show this help message

    -b          use a blue color
    -blue       use a blue color
    -bold       bold-style digits
    -g          use a green color
    -gray       use a gray color (default)
    -green      use a green color
    -hi         use a highlighting/inverse style
    -m          use a magenta color
    -magenta    use a magenta color
    -o          use an orange color
    -orange     use an orange color
    -r          use a red color
    -red        use a red color
    -u          underline digits
    -underline  underline digits
`

const errorStyle = "\x1b[31m"

// errNoMoreOutput is a dummy error, whose message is ignored, and which
// causes the app to quit 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
		}
	}

	args := os.Args[1:]
	style, _ := lookupStyle(`gray`)

	// if the first argument is 1 or 2 dashes followed by a supported
	// style-name, change the style used
	if len(args) > 0 && strings.HasPrefix(args[0], `-`) {
		name := args[0]
		name = strings.TrimPrefix(name, `-`)
		name = strings.TrimPrefix(name, `-`)

		// check if the `dedashed` argument is a supported style-name
		if s, ok := lookupStyle(name); ok {
			style = s
		} else {
			os.Stderr.WriteString(errorStyle + "invalid style name ")
			os.Stderr.WriteString(name)
			os.Stderr.WriteString("\x1b[0m\n")
			os.Exit(1)
		}
	}

	if len(os.Args) > 2 {
		const msg = `only 1 (optional) named input is supported`
		os.Stderr.WriteString(errorStyle + msg + "\x1b[0m\n")
		os.Exit(1)
	}

	name := `-`
	if len(os.Args) > 1 {
		name = os.Args[1]
	}

	if err := run(os.Stdout, name, style); isActualError(err) {
		os.Stderr.WriteString(errorStyle)
		os.Stderr.WriteString(err.Error())
		os.Stderr.WriteString("\x1b[0m\n")
		os.Exit(1)
	}
}

func run(w io.Writer, name string, style []byte) error {
	if name == `` || name == `-` {
		return restyle(w, os.Stdin, style)
	}

	f, err := os.Open(name)
	if err != nil {
		return errors.New(`can't read from file named "` + name + `"`)
	}
	defer f.Close()

	return restyle(w, f, style)
}

// isActualError is to figure out whether not to ignore an error, and thus
// show it as an error message
func isActualError(err error) bool {
	return err != nil && err != io.EOF && err != errNoMoreOutput
}

func restyle(w io.Writer, r io.Reader, style []byte) error {
	bw := bufio.NewWriter(w)
	defer bw.Flush()

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

	for sc.Scan() {
		restyleLine(bw, sc.Bytes(), style)
		if err := bw.WriteByte('\n'); err != nil {
			// a write error may be the consequence of stdout being closed,
			// perhaps by another app along a pipe
			return errNoMoreOutput
		}
	}
	return sc.Err()
}

func lookupStyle(name string) (style []byte, ok bool) {
	if alias, ok := styleAliases[name]; ok {
		name = alias
	}

	style, ok = styles[name]
	return style, ok
}

var styleAliases = map[string]string{
	`b`: `blue`,
	`g`: `green`,
	`m`: `magenta`,
	`o`: `orange`,
	`p`: `purple`,
	`r`: `red`,
	`u`: `underline`,

	`bolded`:      `bold`,
	`h`:           `inverse`,
	`hi`:          `inverse`,
	`highlight`:   `inverse`,
	`highlighted`: `inverse`,
	`hilite`:      `inverse`,
	`hilited`:     `inverse`,
	`inv`:         `inverse`,
	`invert`:      `inverse`,
	`inverted`:    `inverse`,
	`underlined`:  `underline`,

	`bb`: `blueback`,
	`bg`: `greenback`,
	`bm`: `magentaback`,
	`bo`: `orangeback`,
	`bp`: `purpleback`,
	`br`: `redback`,

	`gb`: `greenback`,
	`mb`: `magentaback`,
	`ob`: `orangeback`,
	`pb`: `purpleback`,
	`rb`: `redback`,

	`bblue`:    `blueback`,
	`bgray`:    `grayback`,
	`bgreen`:   `greenback`,
	`bmagenta`: `magentaback`,
	`borange`:  `orangeback`,
	`bpurple`:  `purpleback`,
	`bred`:     `redback`,

	`backblue`:    `blueback`,
	`backgray`:    `grayback`,
	`backgreen`:   `greenback`,
	`backmagenta`: `magentaback`,
	`backorange`:  `orangeback`,
	`backpurple`:  `purpleback`,
	`backred`:     `redback`,
}

// styles turns style-names into the ANSI-code sequences used for the
// alternate groups of digits
var styles = map[string][]byte{
	`blue`:      []byte("\x1b[38;2;0;95;215m"),
	`bold`:      []byte("\x1b[1m"),
	`gray`:      []byte("\x1b[38;2;168;168;168m"),
	`green`:     []byte("\x1b[38;2;0;135;95m"),
	`inverse`:   []byte("\x1b[7m"),
	`magenta`:   []byte("\x1b[38;2;215;0;255m"),
	`orange`:    []byte("\x1b[38;2;215;95;0m"),
	`plain`:     []byte("\x1b[0m"),
	`red`:       []byte("\x1b[38;2;204;0;0m"),
	`underline`: []byte("\x1b[4m"),

	// `blue`:      []byte("\x1b[38;5;26m"),
	// `bold`:      []byte("\x1b[1m"),
	// `gray`:      []byte("\x1b[38;5;248m"),
	// `green`:     []byte("\x1b[38;5;29m"),
	// `inverse`:   []byte("\x1b[7m"),
	// `magenta`:   []byte("\x1b[38;5;99m"),
	// `orange`:    []byte("\x1b[38;5;166m"),
	// `plain`:     []byte("\x1b[0m"),
	// `red`:       []byte("\x1b[31m"),
	// `underline`: []byte("\x1b[4m"),

	`blueback`:    []byte("\x1b[48;2;0;95;215m\x1b[38;2;238;238;238m"),
	`grayback`:    []byte("\x1b[48;2;168;168;168m\x1b[38;2;238;238;238m"),
	`greenback`:   []byte("\x1b[48;2;0;135;95m\x1b[38;2;238;238;238m"),
	`magentaback`: []byte("\x1b[48;2;215;0;255m\x1b[38;2;238;238;238m"),
	`orangeback`:  []byte("\x1b[48;2;215;95;0m\x1b[38;2;238;238;238m"),
	`purpleback`:  []byte("\x1b[48;2;135;95;255m\x1b[38;2;238;238;238m"),
	`redback`:     []byte("\x1b[48;2;204;0;0m\x1b[38;2;238;238;238m"),
}

// restyleLine renders the line given, using ANSI-styles to make any long
// numbers in it more legible; this func doesn't emit a line-feed, which
// is up to its caller
func restyleLine(w *bufio.Writer, line []byte, style []byte) {
	for len(line) > 0 {
		i := indexDigit(line)
		if i < 0 {
			// no (more) digits to style for sure
			w.Write(line)
			return
		}

		// emit line before current digit-run
		w.Write(line[:i])
		// advance to the start of the current digit-run
		line = line[i:]

		// see where the digit-run ends
		j := indexNonDigit(line)
		if j < 0 {
			// the digit-run goes until the end
			restyleDigits(w, line, style)
			return
		}

		// emit styled digit-run
		restyleDigits(w, line[:j], style)
		// skip right past the end of the digit-run
		line = line[j:]
	}
}

// indexDigit finds the index of the first digit in a string, or -1 when the
// string has no decimal digits
func indexDigit(s []byte) int {
	for i := 0; i < len(s); i++ {
		switch s[i] {
		case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			return i
		}
	}

	// empty slice, or a slice without any digits
	return -1
}

// indexNonDigit finds the index of the first non-digit in a string, or -1
// when the string is all decimal digits
func indexNonDigit(s []byte) int {
	for i := 0; i < len(s); i++ {
		switch s[i] {
		case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			continue
		default:
			return i
		}
	}

	// empty slice, or a slice which only has digits
	return -1
}

// restyleDigits renders a run of digits as alternating styled/unstyled runs
// of 3 digits, which greatly improves readability, and is the only purpose
// of this app; string is assumed to be all decimal digits
func restyleDigits(w *bufio.Writer, digits []byte, altStyle []byte) {
	if len(digits) < 4 {
		// digit sequence is short, so emit it as is
		w.Write(digits)
		return
	}

	// separate leading 0..2 digits which don't align with the 3-digit groups
	i := len(digits) % 3
	// emit leading digits unstyled, if there are any
	w.Write(digits[:i])
	// the rest is guaranteed to have a length which is a multiple of 3
	digits = digits[i:]

	// start by styling, unless there were no leading digits
	style := i != 0

	for len(digits) > 0 {
		if style {
			w.Write(altStyle)
			w.Write(digits[:3])
			w.Write([]byte{'\x1b', '[', '0', 'm'})
		} else {
			w.Write(digits[:3])
		}

		// advance to the next triple: the start of this func is supposed
		// to guarantee this step always works
		digits = digits[3:]

		// alternate between styled and unstyled 3-digit groups
		style = !style
	}
}