package main

import (
	"fmt"
	"log"
	"os"
	"regexp"
	"strings"
)

var (
	property = regexp.MustCompile(`^\s*--([a-z0-9-]+):\s*#([0-9a-f]{6});\s*$`)
	darkOpen = regexp.MustCompile(`^@media \(prefers-color-scheme: dark\) \{$`)
)

func block(lines []string, start int) (map[string]string, []string) {
	colors := map[string]string{}
	order := []string{}
	for _, line := range lines[start+1:] {
		if strings.TrimSpace(line) == "}" {
			return colors, order
		}
		m := property.FindStringSubmatch(line)
		if m == nil {
			continue
		}
		colors[m[1]] = m[2]
		order = append(order, m[1])
	}
	log.Fatalf("unterminated block at line %d", start+1)
	return nil, nil
}

func swiftName(prop string) string {
	parts := strings.Split(prop, "-")
	for i := 1; i < len(parts); i++ {
		parts[i] = strings.ToUpper(parts[i][:1]) + parts[i][1:]
	}
	return strings.Join(parts, "")
}

func main() {
	css, err := os.ReadFile("../web/style.css")
	if err != nil {
		log.Fatal(err)
	}
	lines := strings.Split(string(css), "\n")
	lightAt, darkAt := -1, -1
	for i, line := range lines {
		if line == ":root {" && lightAt < 0 {
			lightAt = i
		}
		if darkOpen.MatchString(line) && i+1 < len(lines) && strings.TrimSpace(lines[i+1]) == ":root {" {
			darkAt = i + 1
		}
	}
	if lightAt < 0 || darkAt < 0 {
		log.Fatal("web/style.css has no :root block or no prefers-color-scheme: dark :root block")
	}
	light, order := block(lines, lightAt)
	dark, _ := block(lines, darkAt)

	var b strings.Builder
	b.WriteString("// Code generated by go generate ./mac from web/style.css. DO NOT EDIT.\n\n")
	b.WriteString("import AppKit\nimport SwiftUI\n\n")
	b.WriteString("enum Palette {\n")
	for _, prop := range order {
		d, ok := dark[prop]
		if !ok {
			log.Fatalf("--%s has no dark value", prop)
		}
		fmt.Fprintf(&b, "    static let %s = dynamic(0x%s, 0x%s)\n", swiftName(prop), light[prop], d)
	}
	for prop := range dark {
		if _, ok := light[prop]; !ok {
			log.Fatalf("--%s has no light value", prop)
		}
	}
	b.WriteString(`
    private static func rgb(_ hex: UInt32) -> NSColor {
        NSColor(srgbRed: CGFloat(hex >> 16 & 0xff) / 255, green: CGFloat(hex >> 8 & 0xff) / 255, blue: CGFloat(hex & 0xff) / 255, alpha: 1)
    }

    private static func dynamic(_ light: UInt32, _ dark: UInt32) -> Color {
        Color(nsColor: NSColor(name: nil) { appearance in
            appearance.bestMatch(from: [.aqua, .darkAqua]) == .darkAqua ? rgb(dark) : rgb(light)
        })
    }
}
`)
	err = os.WriteFile("Sources/Byre/Palette.swift", []byte(b.String()), 0o644)
	if err != nil {
		log.Fatal(err)
	}
}