package main

import (
	"bufio"
	"flag"
	"fmt"
	"os"
	"regexp"
	"strings"
)

func init() {
	highlightColor = red
	flag.Var((*colorFlag)(&highlightColor), "c", fmt.Sprintf("highlight `color` %s", colorsChoices))
	background = defaultColor
	flag.Var((*colorFlag)(&background), "bg", fmt.Sprintf("background `color` default|%s", colorsChoices))
}

var (
	highlightColor ansiColor
	background     ansiColor
)

//go:generate stringer -type=ansiColor -linecomment
type ansiColor int

const (
	black ansiColor = iota
	red
	green
	yellow
	blue
	magenta
	cyan
	white
	defaultColor ansiColor = 9 // default
)

var colorsChoices = func() string {
	nColors := white - black + 1
	colors := make([]string, nColors)
	for i := range nColors {
		colors[i] = (black + i).String()
	}
	return strings.Join(colors, "|")
}()

func (c ansiColor) Foreground() int {
	return 30 + int(c)
}

func (c ansiColor) Background() int {
	return 40 + int(c)
}

type colorFlag int

func (c *colorFlag) Set(val string) error {
	var ac ansiColor
	switch strings.ToLower(val) {
	case "default":
		ac = defaultColor
	case "black":
		ac = black
	case "red":
		ac = red
	case "green":
		ac = green
	case "yellow":
		ac = yellow
	case "blue":
		ac = blue
	case "magenta":
		ac = magenta
	case "cyan":
		ac = cyan
	case "white":
		ac = white
	default:
		return fmt.Errorf("unknown color %q (valid choices: %s)", val, colorsChoices)
	}
	*c = colorFlag(ac)
	return nil
}

func (c *colorFlag) String() string {
	return ansiColor(*c).String()
}

func run() error {
	args := flag.Args()
	if len(args) == 0 {
		fmt.Fprintf(os.Stderr, "missing regexp to highlight\n")
		flag.Usage()
	}
	if len(args) > 2 {
		fmt.Fprintf(os.Stderr, "too many positional arguments\n")
		flag.Usage()
	}
	highlightRE, err := regexp.CompilePOSIX(args[0])
	if err != nil {
		return fmt.Errorf("invalid highlight regexp: %s", err)
	}
	foregroundColor := highlightColor.Foreground()
	backgroundColor := background.Background()
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		line := scanner.Text()
		loc := highlightRE.FindStringIndex(line)
		if loc == nil {
			fmt.Printf("%s\n", line)
			continue
		}
		startIdx, endIdx := loc[0], loc[1]
		fmt.Printf("%s\033[%d;%dm%s\033[39;49m%s\n", line[:startIdx], foregroundColor, backgroundColor, line[startIdx:endIdx], line[endIdx:])
	}
	return scanner.Err()
}

func main() {
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: hi [OPTIONS] REGEXP\n")
		flag.PrintDefaults()
		os.Exit(2)
	}
	flag.Parse()
	if err := run(); err != nil {
		fmt.Fprintf(os.Stderr, "hi: %s\n", err)
		os.Exit(1)
	}
}