package ui

import (
	"math"
	"math/rand"
	"strconv"
)

// Theme holds color configuration for the UI.
type Theme struct {
	HeaderFG       string
	SelectedFG     string
	SelectedBG     string
	RowFG          string
	RowBG          string
	StatusFG       string
	StatusBG       string
	StartBG        string
	UltraStartedBG string // background for started tasks in ultra mode
	OverdueBG      string
	PrioLowBG      string
	PrioMedBG      string
	PrioHighBG     string
	SearchFG       string
	SearchBG       string
}

// DefaultTheme returns the color theme used by Task Samurai.
func DefaultTheme() Theme {
	return Theme{
		HeaderFG:       "75",  // steel blue — labels in ultra cards
		SelectedFG:     "255", // bright white — text on selected card
		SelectedBG:     "238", // dark grey — clean selection highlight on black background
		RowFG:          "0",
		RowBG:          "57",
		StatusFG:       "229", // light yellow
		StatusBG:       "57",  // dark purple — status bar background
		StartBG:        "6",
		UltraStartedBG: "220", // amber yellow — visually distinct "in progress" indicator
		OverdueBG:      "1",
		PrioLowBG:      "28",  // dark green — subtler than bright 10
		PrioMedBG:      "33",  // medium blue — subtler than bright 12
		PrioHighBG:     "160", // dark red — subtler than bright 9
		SearchFG:       "16",
		SearchBG:       "220", // amber — easier on eyes than pure yellow 226
	}
}

func RandomTheme() Theme {
	th := Theme{
		HeaderFG:       randColor(),
		SelectedBG:     randColor(),
		RowBG:          randColor(),
		StatusBG:       randColor(),
		StartBG:        randColor(),
		UltraStartedBG: randColor(),
		OverdueBG:      randColor(),
		PrioLowBG:      randColor(),
		PrioMedBG:      randColor(),
		PrioHighBG:     randColor(),
		SearchBG:       randColor(),
	}
	th.SelectedFG = contrastColor(th.SelectedBG)
	th.RowFG = contrastColor(th.RowBG)
	th.StatusFG = contrastColor(th.StatusBG)
	th.SearchFG = contrastColor(th.SearchBG)
	return th
}

func randColor() string {
	return strconv.Itoa(rand.Intn(256))
}

func contrastColor(bg string) string {
	i, err := strconv.Atoi(bg)
	if err != nil || i < 0 || i > 255 {
		return "15"
	}
	r, g, b := xtermRGB(i)
	if contrastRatio(r, g, b, 0, 0, 0) >= contrastRatio(r, g, b, 255, 255, 255) {
		return "0"
	}
	return "15"
}

func contrastRatio(r1, g1, b1, r2, g2, b2 int) float64 {
	l1 := relativeLuminance(r1, g1, b1)
	l2 := relativeLuminance(r2, g2, b2)
	if l1 < l2 {
		l1, l2 = l2, l1
	}
	return (l1 + 0.05) / (l2 + 0.05)
}

func relativeLuminance(r, g, b int) float64 {
	return 0.2126*linearizeColorChannel(r) +
		0.7152*linearizeColorChannel(g) +
		0.0722*linearizeColorChannel(b)
}

func linearizeColorChannel(v int) float64 {
	c := float64(v) / 255.0
	if c <= 0.04045 {
		return c / 12.92
	}
	return math.Pow((c+0.055)/1.055, 2.4)
}

func xtermRGB(i int) (int, int, int) {
	if i < 16 {
		var table = [16][3]int{
			{0, 0, 0}, {205, 0, 0}, {0, 205, 0}, {205, 205, 0},
			{0, 0, 238}, {205, 0, 205}, {0, 205, 205}, {229, 229, 229},
			{127, 127, 127}, {255, 0, 0}, {0, 255, 0}, {255, 255, 0},
			{92, 92, 255}, {255, 0, 255}, {0, 255, 255}, {255, 255, 255},
		}
		rgb := table[i]
		return rgb[0], rgb[1], rgb[2]
	}
	if i >= 16 && i <= 231 {
		i -= 16
		r := (i / 36) * 51
		g := (i % 36 / 6) * 51
		b := (i % 6) * 51
		return r, g, b
	}
	v := (i-232)*10 + 8
	return v, v, v
}