// Package theme is glint's single source of color truth. Every styled span in
// every theme gets an explicit foreground — no terminal-default fallbacks — so
// the editor reads cleanly on both light and dark terminals.
package theme

import (
	"math"
	"strconv"
	"strings"

	"github.com/charmbracelet/lipgloss"
)

// Theme holds every color glint paints, plus its name and the glamour style the
// read-preview should use to stay visually in sync.
type Theme struct {
	Name         string
	GlamourStyle string

	// Markdown element colors.
	Text       lipgloss.Color // base prose
	Emphasis   lipgloss.Color // bold/italic — higher contrast than Text
	Heading    lipgloss.Color // heading text (bold)
	Code       lipgloss.Color // inline + fenced code
	Link       lipgloss.Color // links, URLs, and wikilink targets
	Wikilink   lipgloss.Color // retained == Link (kept for the all-colors check)
	ListMarker lipgloss.Color // list bullets / numbers
	Blockquote lipgloss.Color // blockquote marker + border (muted tone)
	Comment    lipgloss.Color // HTML / %% comments — visible, not dimmed
	Accent     lipgloss.Color // frontmatter keys, selection
	Highlight  lipgloss.Color // ==highlight== background tint
	Spell      lipgloss.Color // misspelled-word undercurl (red)
	Grammar    lipgloss.Color // grammar-issue undercurl (green; Harper, TASK-043)
	TK         lipgloss.Color // 'TK'/'tk' placeholder badge background (fill-in marker, TASK-045)

	// Merge-conflict highlighting (git markers <<<<<<< ||||||| ======= >>>>>>>).
	ConflictMarker lipgloss.Color // bold marker lines
	ConflictOurs   lipgloss.Color // background tint for the "ours"/base block
	ConflictTheirs lipgloss.Color // background tint for the "theirs" block

	// UI colors.
	Background lipgloss.Color
	Muted      lipgloss.Color // markup punctuation, dimmed
	StatusFg   lipgloss.Color
	StatusBg   lipgloss.Color
	SelFg      lipgloss.Color
	SelBg      lipgloss.Color
	Pointer    lipgloss.Color
}

// CycleOrder is the order Ctrl+T steps through themes.
var CycleOrder = []string{"flexoki-light", "flexoki-dark", "charm"}

func registry() map[string]Theme {
	return map[string]Theme{
		"flexoki-light": FlexokiLight(),
		"flexoki-dark":  FlexokiDark(),
		"charm":         Charm(),
	}
}

// ByName looks up a registered theme.
func ByName(name string) (Theme, bool) {
	t, ok := registry()[name]
	return t, ok
}

// Next returns the theme after name in CycleOrder, wrapping around. An unknown
// name yields the first theme in the cycle.
func Next(name string) Theme {
	idx := 0
	for i, n := range CycleOrder {
		if n == name {
			idx = (i + 1) % len(CycleOrder)
			break
		}
	}
	t, _ := ByName(CycleOrder[idx])
	return t
}

// Resolve picks a theme from a config value: "auto"/"" → OS detection; a known
// name → that theme; an unknown name → OS detection. It never errors and never
// returns an empty theme.
func Resolve(configValue string) Theme {
	if configValue == "" || configValue == "auto" {
		t, _ := ByName(Detect())
		return t
	}
	if t, ok := ByName(configValue); ok {
		return t
	}
	t, _ := ByName(Detect())
	return t
}

// HexToRGB converts "#RRGGBB" to the "R;G;B" decimal form used in SGR codes.
// A malformed color yields "" so callers can fall back to unstyled output.
func HexToRGB(hex string) string {
	h := strings.TrimPrefix(hex, "#")
	if len(h) != 6 {
		return ""
	}
	r, err1 := strconv.ParseInt(h[0:2], 16, 0)
	g, err2 := strconv.ParseInt(h[2:4], 16, 0)
	b, err3 := strconv.ParseInt(h[4:6], 16, 0)
	if err1 != nil || err2 != nil || err3 != nil {
		return ""
	}
	return strconv.FormatInt(r, 10) + ";" + strconv.FormatInt(g, 10) + ";" + strconv.FormatInt(b, 10)
}

// LegibleText returns a near-black or near-paper text color, whichever
// contrasts better with the background hex, so heading text stays readable on
// any heading color.
func LegibleText(bgHex string) string {
	if RelLuminance(bgHex) > 0.5 {
		return "#100F0F"
	}
	return "#FFFCF0"
}

// RelLuminance is the WCAG relative luminance of an "#RRGGBB" color, 0 for a
// malformed one.
func RelLuminance(hex string) float64 {
	h := strings.TrimPrefix(hex, "#")
	if len(h) != 6 {
		return 0
	}
	chan8 := func(s string) float64 {
		n, _ := strconv.ParseInt(s, 16, 0)
		c := float64(n) / 255
		if c <= 0.03928 {
			return c / 12.92
		}
		return math.Pow((c+0.055)/1.055, 2.4)
	}
	return 0.2126*chan8(h[0:2]) + 0.7152*chan8(h[2:4]) + 0.0722*chan8(h[4:6])
}