package web

import (
	"bytes"
	"encoding/json"
	"net/url"
	"regexp"
	"strings"
	"text/template"

	"github.com/google/uuid"
)

// Theme is the structured, form-editable look of a blog. Stored as jsonb.
type Theme struct {
	BgColor string `json:"bg_color"`
	BgImage string `json:"bg_image"` // image uuid or ""
	BgMode  string `json:"bg_mode"`  // cover | tile | fixed

	ContentBg    string `json:"content_bg"`
	TextColor    string `json:"text_color"`
	LinkColor    string `json:"link_color"`
	ContentWidth string `json:"content_width"` // narrow | medium | wide
	Font         string `json:"font"`          // sans | serif | mono
	FontSize     string `json:"font_size"`     // small | normal | large

	HeaderShowTitle bool   `json:"header_show_title"`
	HeaderImage     string `json:"header_image"`
	HeaderAlign     string `json:"header_align"` // left | center
	HeaderBg        string `json:"header_bg"`
	HeaderText      string `json:"header_text"`

	NavPosition string `json:"nav_position"` // below-header | top-bar | left-sidebar
	NavBg       string `json:"nav_bg"`
	NavText     string `json:"nav_text"`
	NavShowHome bool   `json:"nav_show_home"`

	FooterText  string `json:"footer_text"`
	FooterBg    string `json:"footer_bg"`
	FooterColor string `json:"footer_color"`
}

func DefaultTheme() Theme {
	return Theme{
		BgColor: "#e9e6df", BgMode: "cover",
		ContentBg: "#ffffff", TextColor: "#222222", LinkColor: "#1a5fb4",
		ContentWidth: "medium", Font: "sans", FontSize: "normal",
		HeaderShowTitle: true, HeaderAlign: "left", HeaderBg: "#2f3a4a", HeaderText: "#ffffff",
		NavPosition: "below-header", NavBg: "#ffffff", NavText: "#222222", NavShowHome: true,
		FooterText: "", FooterBg: "#2f3a4a", FooterColor: "#d0d5dc",
	}
}

// ParseTheme decodes stored JSON on top of the defaults so new fields get sane values.
func ParseTheme(raw json.RawMessage) Theme {
	t := DefaultTheme()
	if len(raw) > 0 {
		_ = json.Unmarshal(raw, &t)
	}
	t.normalize()
	return t
}

var hexColor = regexp.MustCompile(`^#[0-9a-fA-F]{6}$`)

func pick(v string, allowed ...string) string {
	for _, a := range allowed {
		if v == a {
			return v
		}
	}
	return allowed[0]
}

func color(v, def string) string {
	v = strings.TrimSpace(v)
	if hexColor.MatchString(v) {
		return strings.ToLower(v)
	}
	return def
}

func imageID(v string) string {
	if _, err := uuid.Parse(v); err != nil {
		return ""
	}
	return v
}

// normalize clamps every field to an allowed value so the CSS template can trust them.
func (t *Theme) normalize() {
	d := DefaultTheme()
	t.BgColor = color(t.BgColor, d.BgColor)
	t.BgImage = imageID(t.BgImage)
	t.BgMode = pick(t.BgMode, "cover", "tile", "fixed")
	t.ContentBg = color(t.ContentBg, d.ContentBg)
	t.TextColor = color(t.TextColor, d.TextColor)
	t.LinkColor = color(t.LinkColor, d.LinkColor)
	t.ContentWidth = pick(t.ContentWidth, "medium", "narrow", "wide")
	t.Font = pick(t.Font, "sans", "serif", "mono")
	t.FontSize = pick(t.FontSize, "normal", "small", "large")
	t.HeaderImage = imageID(t.HeaderImage)
	t.HeaderAlign = pick(t.HeaderAlign, "left", "center")
	t.HeaderBg = color(t.HeaderBg, d.HeaderBg)
	t.HeaderText = color(t.HeaderText, d.HeaderText)
	t.NavPosition = pick(t.NavPosition, "below-header", "top-bar", "left-sidebar")
	t.NavBg = color(t.NavBg, d.NavBg)
	t.NavText = color(t.NavText, d.NavText)
	t.FooterBg = color(t.FooterBg, d.FooterBg)
	t.FooterColor = color(t.FooterColor, d.FooterColor)
	if len(t.FooterText) > 2000 {
		t.FooterText = t.FooterText[:2000]
	}
}

// ThemeFromForm reads the design form on top of the current theme.
func ThemeFromForm(cur Theme, f url.Values) Theme {
	t := cur
	get := func(k string) string { return strings.TrimSpace(f.Get(k)) }
	t.BgColor = get("bg_color")
	t.BgMode = get("bg_mode")
	t.ContentBg = get("content_bg")
	t.TextColor = get("text_color")
	t.LinkColor = get("link_color")
	t.ContentWidth = get("content_width")
	t.Font = get("font")
	t.FontSize = get("font_size")
	t.HeaderShowTitle = f.Get("header_show_title") == "on"
	t.HeaderAlign = get("header_align")
	t.HeaderBg = get("header_bg")
	t.HeaderText = get("header_text")
	t.NavPosition = get("nav_position")
	t.NavBg = get("nav_bg")
	t.NavText = get("nav_text")
	t.NavShowHome = f.Get("nav_show_home") == "on"
	t.FooterText = get("footer_text")
	t.FooterBg = get("footer_bg")
	t.FooterColor = get("footer_color")
	if f.Get("bg_image_remove") == "on" {
		t.BgImage = ""
	} else if v := get("bg_image"); v != "" {
		t.BgImage = v
	}
	if f.Get("header_image_remove") == "on" {
		t.HeaderImage = ""
	} else if v := get("header_image"); v != "" {
		t.HeaderImage = v
	}
	t.normalize()
	return t
}

func (t Theme) JSON() json.RawMessage {
	b, _ := json.Marshal(t)
	return b
}

// Helpers used by the CSS template.
func (t Theme) FontFamily() string {
	switch t.Font {
	case "serif":
		return `Georgia, "Times New Roman", Times, serif`
	case "mono":
		return `"Courier New", Courier, monospace`
	}
	return `"Helvetica Neue", Helvetica, Arial, sans-serif`
}

func (t Theme) FontSizePx() string {
	switch t.FontSize {
	case "small":
		return "15px"
	case "large":
		return "19px"
	}
	return "17px"
}

func (t Theme) MaxWidth() string {
	switch t.ContentWidth {
	case "narrow":
		return "640px"
	case "wide":
		return "1100px"
	}
	return "840px"
}

var themeCSS = template.Must(template.New("theme").Parse(`
body { margin:0; background-color:{{.BgColor}}; color:{{.TextColor}}; font-family:{{.FontFamily}}; font-size:{{.FontSizePx}}; line-height:1.55;
{{- if .BgImage}} background-image:url(/media/{{.BgImage}});
  {{- if eq .BgMode "cover"}} background-size:cover; background-position:center top; background-repeat:no-repeat;
  {{- else if eq .BgMode "fixed"}} background-size:cover; background-position:center; background-attachment:fixed; background-repeat:no-repeat;
  {{- else}} background-repeat:repeat;{{end}}
{{- end}} }
a { color:{{.LinkColor}}; }
.wrap { max-width:{{.MaxWidth}}; margin:0 auto; }
.site-header { background:{{.HeaderBg}}; color:{{.HeaderText}}; text-align:{{.HeaderAlign}}; }
.site-header a { color:{{.HeaderText}}; }
.site-nav { background:{{.NavBg}}; }
.site-nav a { color:{{.NavText}}; }
.content { background:{{.ContentBg}}; }
.site-footer { background:{{.FooterBg}}; color:{{.FooterColor}}; }
.site-footer a { color:{{.FooterColor}}; }
`))

// CSS renders the per-blog stylesheet; all values were normalized so it is safe to inline.
func (t Theme) CSS() string {
	var b bytes.Buffer
	_ = themeCSS.Execute(&b, t)
	return b.String()
}