package ui

import (
	"image/color"

	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
)

// theme is a complete set of colors, so the program looks the same whatever
// palette the terminal's color theme has (themes often make "black" a grey
// that is not their background, and light themes put dark grey slabs under
// white text). Every color is one of the fixed entries 16-255 of the
// 256-color table, so terminals without 24-bit color show exactly these too
// (the nearest match of an exact color is itself, and the first 16 entries,
// which themes change, never equal them).
type theme struct {
	name string

	bg, text, border  tcell.Color
	field, fieldMuted tcell.Color // input fields and buttons; placeholders on them
	list              tcell.Color // open dropdown lists (drawn with bg-colored text)
	pressed           tcell.Color // text of a pressed button (on the text color)
	toast             tcell.Color // background of the popups

	// The accent colors, used by name in the texts ("[yellow]...").
	gray, yellow, green, red, blue, purple tcell.Color
}

func c256(i int) tcell.Color { return tcell.PaletteColor(i).TrueColor() }

var (
	darkTheme = theme{
		name: "dark",
		bg:   c256(232), text: c256(253), border: c256(246),
		field: c256(236), fieldMuted: c256(245),
		list: c256(110), pressed: c256(25), toast: c256(236),
		gray: c256(245), yellow: c256(221), green: c256(113), red: c256(203), blue: c256(75), purple: c256(141),
	}
	lightTheme = theme{
		name: "light",
		bg:   c256(255), text: c256(234), border: c256(243),
		field: c256(252), fieldMuted: c256(245),
		list: c256(67), pressed: c256(255), toast: c256(252),
		gray: c256(243), yellow: c256(130), green: c256(28), red: c256(160), blue: c256(26), purple: c256(91),
	}
)

// current is the theme in use.
var current = darkTheme

// chooseTheme resolves the ui.theme setting: "dark", "light", or "auto" (the
// default), which follows the background color the terminal reported and is
// dark when it did not say. The second value explains the choice for the log.
func chooseTheme(setting string, info terminalInfo) (theme, string) {
	switch setting {
	case "dark":
		return darkTheme, "Theme: dark"
	case "light":
		return lightTheme, "Theme: light"
	}
	if !info.hasBG {
		return darkTheme, "Theme: dark (auto: the terminal did not report its background color)"
	}
	hex := hexColor(info.bg)
	if luminance(info.bg) > 0.5 {
		return lightTheme, "Theme: light (auto: the terminal's background " + hex + " is light)"
	}
	return darkTheme, "Theme: dark (auto: the terminal's background " + hex + " is dark)"
}

// apply makes t the colors of everything created afterwards: tview's default
// styles (widgets copy them when they are created, so this must run before any
// is) and the color names used in the texts, which tview looks up in tcell's
// table: "[yellow]" means this theme's yellow, "white" its text color and
// "black" its background (the active tab is "[black:white]").
func (t theme) apply() {
	current = t
	st := &tview.Styles
	st.PrimitiveBackgroundColor = t.bg
	st.ContrastBackgroundColor = t.field
	st.MoreContrastBackgroundColor = t.list
	st.BorderColor, st.TitleColor, st.GraphicsColor = t.border, t.text, t.border
	st.PrimaryTextColor = t.text
	st.SecondaryTextColor = t.yellow
	st.TertiaryTextColor = t.green
	st.InverseTextColor = t.pressed
	st.ContrastSecondaryTextColor = t.fieldMuted

	for name, c := range map[string]tcell.Color{
		"white": t.text, "black": t.bg,
		"gray": t.gray, "grey": t.gray,
		"yellow": t.yellow, "green": t.green, "red": t.red,
		"blue": t.blue, "purple": t.purple,
	} {
		tcell.ColorNames[name] = c
	}
}

// named returns the theme's color for a name used in the texts.
func named(name string) tcell.Color { return tcell.GetColor(name) }

func hexColor(c color.RGBA) string {
	const digits = "0123456789abcdef"
	b := []byte{'#', 0, 0, 0, 0, 0, 0}
	for i, v := range []uint8{c.R, c.G, c.B} {
		b[1+2*i], b[2+2*i] = digits[v>>4], digits[v&15]
	}
	return string(b)
}