package ui

import (
	"bytes"
	"image/color"
	"strconv"
	"strings"
	"sync"
	"time"
)

// terminalInfo is what the terminal said about itself at startup.
type terminalInfo struct {
	graphics bool       // the Kitty graphics protocol is supported
	bg       color.RGBA // its background color, if hasBG
	hasBG    bool
}

var (
	terminalOnce   sync.Once
	terminalResult terminalInfo
)

// terminalAnswers asks the terminal once (see probeTerminal) and remembers the
// answers. The first call must happen before the screen is set up, which owns
// the terminal afterwards; New makes it. It is a variable so tests can replace it.
var terminalAnswers = func() terminalInfo {
	terminalOnce.Do(func() { terminalResult = probeTerminal(300 * time.Millisecond) })
	return terminalResult
}

// parseTerminalAnswers reads the answers to probeTerminal's questions.
func parseTerminalAnswers(got []byte) (info terminalInfo) {
	info.graphics = bytes.Contains(got, []byte("_Gi=31;OK"))
	info.bg, info.hasBG = parseColorAnswer(got, "11")
	return info
}

// parseColorAnswer finds the answer to an OSC color query such as 11
// (background): ESC ] 11 ; rgb:RRRR/GGGG/BBBB, ended by ST or BEL. Each
// component has 1 to 4 hex digits.
func parseColorAnswer(got []byte, osc string) (color.RGBA, bool) {
	prefix := []byte("\x1b]" + osc + ";rgb:")
	i := bytes.Index(got, prefix)
	if i < 0 {
		return color.RGBA{}, false
	}
	rest := got[i+len(prefix):]
	if end := bytes.IndexAny(rest, "\x1b\a"); end >= 0 {
		rest = rest[:end]
	}
	parts := strings.Split(string(rest), "/")
	if len(parts) != 3 {
		return color.RGBA{}, false
	}
	var c [3]uint8
	for j, p := range parts {
		v, err := strconv.ParseUint(p, 16, 16)
		if err != nil || len(p) < 1 || len(p) > 4 {
			return color.RGBA{}, false
		}
		c[j] = uint8(v * 255 / (1<<(4*len(p)) - 1))
	}
	return color.RGBA{c[0], c[1], c[2], 255}, true
}

// luminance is the relative brightness of c, from 0 (black) to 1 (white).
func luminance(c color.RGBA) float64 {
	return (0.2126*float64(c.R) + 0.7152*float64(c.G) + 0.0722*float64(c.B)) / 255
}