package web

import (
	"bytes"
	"fmt"
	"html/template"
	"io/fs"
	"math"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"strings"
	"time"

	"github.com/owen/vibedns/internal/auth"
	"github.com/owen/vibedns/internal/validate"
	"github.com/owen/vibedns/internal/version"
	webui "github.com/owen/vibedns/web"
)

// PageData is the envelope every template receives. Page-specific values live
// under .Data; everything else is chrome the layout needs.
type PageData struct {
	Title    string
	Nav      string
	Subnav   string
	User     auth.Principal
	CSRF     string
	Flashes  []Flash
	Alerts   []Alert
	Version  string
	Asset    string // cache-busting suffix for /static URLs; changes every build
	Now      time.Time
	Data     any
	Query    url.Values
	BasePath string
}

// assetVersion busts the browser cache for /static assets on every new
// build, so a redeploy is never masked by a day-old cached app.js. It falls
// back to the semantic version when no VCS commit was embedded (e.g. a build
// outside a git checkout), which is still stable within one running process.
var assetVersion = func() string {
	if version.Commit != "" {
		return version.Commit
	}
	return version.Version
}()

// Alert is a persistent banner such as "a restart is required".
type Alert struct {
	Level    string // warning, danger, info
	Title    string
	Message  string
	Link     string
	LinkText string
}

// templates holds one parsed template set per page.
type templates struct {
	sets map[string]*template.Template
}

// layoutFiles are parsed into every page set.
var layoutFiles = []string{"layout.html", "partials.html"}

// loadTemplates parses each page against the shared layout.
//
// Each page gets its own template set rather than one global set, because Go
// templates are keyed by name: two pages both defining "content" in a single
// set would silently overwrite each other.
func loadTemplates(funcs template.FuncMap) (*templates, error) {
	src := webui.Templates()

	pages, err := fs.Glob(src, "pages/*.html")
	if err != nil {
		return nil, fmt.Errorf("list page templates: %w", err)
	}
	if len(pages) == 0 {
		return nil, fmt.Errorf("no page templates were found in the binary")
	}

	t := &templates{sets: make(map[string]*template.Template, len(pages))}
	for _, page := range pages {
		name := strings.TrimSuffix(path.Base(page), ".html")
		files := append(append([]string{}, layoutFiles...), page)

		set, err := template.New("layout.html").Funcs(funcs).ParseFS(src, files...)
		if err != nil {
			return nil, fmt.Errorf("parse template %s: %w", page, err)
		}
		t.sets[name] = set
	}
	return t, nil
}

// render executes a page template into a buffer first, so a template error
// produces a proper error page instead of a half-written response.
func (s *Server) render(w http.ResponseWriter, r *http.Request, page string, data PageData) {
	set, ok := s.tmpl.sets[page]
	if !ok {
		s.log.Error("template not found", "page", page)
		s.renderError(w, r, http.StatusInternalServerError, "This page could not be rendered.")
		return
	}

	data.Version = version.Version
	data.Asset = assetVersion
	data.Now = time.Now()
	if data.Query == nil {
		data.Query = r.URL.Query()
	}
	data.Flashes = append(data.Flashes, takeFlashes(w, r)...)
	data.Alerts = append(data.Alerts, s.systemAlerts(r)...)

	var buf bytes.Buffer
	if err := set.ExecuteTemplate(&buf, "layout.html", data); err != nil {
		s.log.Error("could not render page", "page", page, "error", err)
		s.renderError(w, r, http.StatusInternalServerError, "This page could not be rendered.")
		return
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	if _, err := buf.WriteTo(w); err != nil {
		s.log.Debug("could not write response", "error", err)
	}
}

// renderError shows a friendly error page. Stack traces and internal error
// text never reach the browser.
func (s *Server) renderError(w http.ResponseWriter, r *http.Request, status int, message string) {
	set, ok := s.tmpl.sets["error"]
	if !ok {
		http.Error(w, message, status)
		return
	}
	data := PageData{
		Title:   http.StatusText(status),
		Version: version.Version,
		Asset:   assetVersion,
		Now:     time.Now(),
		Data: map[string]any{
			"Status":  status,
			"Text":    http.StatusText(status),
			"Message": message,
		},
	}
	if p, ok := auth.PrincipalFrom(r.Context()); ok {
		data.User = p
		data.CSRF = s.app.Auth.IssueCSRFToken(p.Name)
	}

	var buf bytes.Buffer
	if err := set.ExecuteTemplate(&buf, "layout.html", data); err != nil {
		http.Error(w, message, status)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	_, _ = buf.WriteTo(w)
}

// systemAlerts assembles the banners shown across every page.
func (s *Server) systemAlerts(r *http.Request) []Alert {
	var out []Alert

	if admin, err := s.app.Admin(r.Context()); err == nil && admin.MustChangePassword {
		out = append(out, Alert{
			Level:    "warning",
			Title:    "Change the generated password",
			Message:  "This account still uses the password printed at first startup. Set your own before exposing the interface.",
			Link:     "/account",
			LinkText: "Change it now",
		})
	}
	if pending := s.app.PendingRestart(r.Context()); len(pending) > 0 {
		out = append(out, Alert{
			Level:   "info",
			Title:   "Restart required",
			Message: "These settings are saved but will not take effect until the server restarts: " + strings.Join(pending, "; ") + ".",
		})
	}
	if s.app.PendingRestore() {
		out = append(out, Alert{
			Level:    "danger",
			Title:    "Database restore staged",
			Message:  "A backup will replace the live database the next time this server starts.",
			Link:     "/settings/database",
			LinkText: "Review",
		})
	}
	if problems := s.app.Snapshot().Problems; len(problems) > 0 {
		out = append(out, Alert{
			Level: "warning",
			Title: fmt.Sprintf("%d record(s) could not be loaded", len(problems)),
			Message: "Some records are invalid and are not being served. " +
				"Open the affected zone to see which ones.",
			Link:     "/zones",
			LinkText: "Review zones",
		})
	}
	return out
}

// templateFuncs are the helpers available to every template.
func templateFuncs() template.FuncMap {
	return template.FuncMap{
		"num":       humanNumber,
		"bytes":     humanBytes,
		"pct":       formatPercent,
		"ms":        formatMillis,
		"duration":  formatDuration,
		"timeAgo":   timeAgo,
		"datetime":  formatDateTime,
		"dateOnly":  func(t time.Time) string { return t.Local().Format("2006-01-02") },
		"timeOnly":  func(t time.Time) string { return t.Local().Format("15:04:05") },
		"rfc3339":   func(t time.Time) string { return t.UTC().Format(time.RFC3339) },
		"zeroTime":  func(t time.Time) bool { return t.IsZero() },
		"dict":      dict,
		"list":      func(v ...any) []any { return v },
		"add":       func(a, b int) int { return a + b },
		"sub":       func(a, b int) int { return a - b },
		"mul":       func(a, b int) int { return a * b },
		"seq":       seq,
		"join":      strings.Join,
		"hasPrefix": strings.HasPrefix,
		"hasSuffix": strings.HasSuffix,
		"contains":  strings.Contains,
		"lower":     strings.ToLower,
		"upper":     strings.ToUpper,
		"title":     titleCase,
		"trimDot":   func(s string) string { return strings.TrimSuffix(s, ".") },
		"truncate":  truncate,
		"default":   defaultValue,
		"yesno": func(b bool) string {
			if b {
				return "Yes"
			}
			return "No"
		},
		"badgeFor":    badgeFor,
		"rcodeBadge":  rcodeBadge,
		"sourceBadge": sourceBadge,
		"typeBadge":   typeBadge,
		"withQuery":   withQuery,
		"pages":       paginationRange,
		"json":        toJSON,
		"rdataFields": validate.SplitRData,
		"boolstr":     boolString,
		"toggleIcon":  toggleIcon,
		"toggleVerb":  toggleVerb,
		"statusWord":  statusWord,
		"pick":        ternary,
		"nl2br":       nl2br,
		"lines":       func(s string) []string { return strings.Split(strings.TrimSpace(s), "\n") },
		"joinLines":   func(v []string) string { return strings.Join(v, "\n") },
	}
}

func humanNumber(v any) string {
	var n int64
	switch t := v.(type) {
	case int:
		n = int64(t)
	case int32:
		n = int64(t)
	case int64:
		n = t
	case uint32:
		n = int64(t)
	case float64:
		n = int64(t)
	default:
		return fmt.Sprint(v)
	}
	s := strconv.FormatInt(n, 10)
	neg := strings.HasPrefix(s, "-")
	s = strings.TrimPrefix(s, "-")

	var out []string
	for len(s) > 3 {
		out = append([]string{s[len(s)-3:]}, out...)
		s = s[:len(s)-3]
	}
	out = append([]string{s}, out...)
	res := strings.Join(out, ",")
	if neg {
		return "-" + res
	}
	return res
}

func humanBytes(v any) string {
	var n float64
	switch t := v.(type) {
	case int:
		n = float64(t)
	case int64:
		n = float64(t)
	case float64:
		n = t
	default:
		return fmt.Sprint(v)
	}
	const unit = 1024.0
	if n < unit {
		return fmt.Sprintf("%.0f B", n)
	}
	units := []string{"KB", "MB", "GB", "TB"}
	for _, u := range units {
		n /= unit
		if n < unit {
			return fmt.Sprintf("%.1f %s", n, u)
		}
	}
	return fmt.Sprintf("%.1f PB", n)
}

func formatPercent(v float64) string {
	if math.IsNaN(v) || math.IsInf(v, 0) {
		return "0.0%"
	}
	return fmt.Sprintf("%.1f%%", v)
}

func formatMillis(v float64) string {
	if v < 1 {
		return fmt.Sprintf("%.2f ms", v)
	}
	return fmt.Sprintf("%.1f ms", v)
}

func formatDuration(d time.Duration) string {
	if d < time.Millisecond {
		return fmt.Sprintf("%.0f µs", float64(d.Microseconds()))
	}
	if d < time.Second {
		return fmt.Sprintf("%.1f ms", float64(d.Microseconds())/1000)
	}
	return d.Round(time.Millisecond).String()
}

func formatDateTime(t time.Time) string {
	if t.IsZero() {
		return "never"
	}
	return t.Local().Format("2006-01-02 15:04:05")
}

func timeAgo(t time.Time) string {
	if t.IsZero() {
		return "never"
	}
	d := time.Since(t)
	switch {
	case d < 0:
		return "just now"
	case d < time.Minute:
		return fmt.Sprintf("%d seconds ago", int(d.Seconds()))
	case d < time.Hour:
		m := int(d.Minutes())
		if m == 1 {
			return "a minute ago"
		}
		return fmt.Sprintf("%d minutes ago", m)
	case d < 24*time.Hour:
		h := int(d.Hours())
		if h == 1 {
			return "an hour ago"
		}
		return fmt.Sprintf("%d hours ago", h)
	case d < 30*24*time.Hour:
		days := int(d.Hours() / 24)
		if days == 1 {
			return "yesterday"
		}
		return fmt.Sprintf("%d days ago", days)
	default:
		return t.Local().Format("2006-01-02")
	}
}

func dict(values ...any) (map[string]any, error) {
	if len(values)%2 != 0 {
		return nil, fmt.Errorf("dict needs an even number of arguments")
	}
	m := make(map[string]any, len(values)/2)
	for i := 0; i < len(values); i += 2 {
		key, ok := values[i].(string)
		if !ok {
			return nil, fmt.Errorf("dict keys must be strings")
		}
		m[key] = values[i+1]
	}
	return m, nil
}

func seq(from, to int) []int {
	if to < from {
		return nil
	}
	out := make([]int, 0, to-from+1)
	for i := from; i <= to; i++ {
		out = append(out, i)
	}
	return out
}

func titleCase(s string) string {
	if s == "" {
		return s
	}
	return strings.ToUpper(s[:1]) + s[1:]
}

func truncate(n int, s string) string {
	if len(s) <= n {
		return s
	}
	if n <= 1 {
		return s[:n]
	}
	return s[:n-1] + "…"
}

func defaultValue(def, v any) any {
	switch t := v.(type) {
	case string:
		if strings.TrimSpace(t) == "" {
			return def
		}
	case nil:
		return def
	case int:
		if t == 0 {
			return def
		}
	}
	return v
}

// badgeFor maps an enabled flag to a Bootstrap badge class.
func badgeFor(enabled bool) string {
	if enabled {
		return "text-bg-success"
	}
	return "text-bg-secondary"
}

func rcodeBadge(rcode string) string {
	switch strings.ToUpper(rcode) {
	case "NOERROR":
		return "text-bg-success"
	case "NXDOMAIN":
		return "text-bg-warning"
	case "REFUSED", "SERVFAIL", "DROPPED":
		return "text-bg-danger"
	default:
		return "text-bg-secondary"
	}
}

func sourceBadge(source string) string {
	switch source {
	case "authoritative":
		return "text-bg-primary"
	case "cache":
		return "text-bg-info"
	case "stale":
		return "text-bg-warning"
	case "recursive":
		return "text-bg-secondary"
	case "blocked":
		return "text-bg-danger"
	case "refused", "ratelimited":
		return "text-bg-dark"
	case "error":
		return "text-bg-danger"
	default:
		return "text-bg-light text-dark"
	}
}

// typeBadge colours a record type so the record table scans quickly.
func typeBadge(t string) string {
	switch strings.ToUpper(t) {
	case "A", "AAAA":
		return "type-addr"
	case "CNAME", "DNAME":
		return "type-alias"
	case "MX", "SRV", "NAPTR", "SVCB", "HTTPS":
		return "type-service"
	case "NS", "SOA":
		return "type-auth"
	case "TXT", "SPF", "CAA":
		return "type-text"
	case "DS", "DNSKEY", "RRSIG", "NSEC", "NSEC3", "TLSA", "SSHFP":
		return "type-sec"
	case "PTR":
		return "type-ptr"
	default:
		return "type-other"
	}
}

// withQuery rebuilds the current query string with one key replaced, which is
// what pagination and sort links need.
func withQuery(q url.Values, pairs ...any) template.URL {
	next := url.Values{}
	for k, v := range q {
		next[k] = append([]string{}, v...)
	}
	for i := 0; i+1 < len(pairs); i += 2 {
		key := fmt.Sprint(pairs[i])
		val := fmt.Sprint(pairs[i+1])
		if val == "" {
			next.Del(key)
		} else {
			next.Set(key, val)
		}
	}
	if len(next) == 0 {
		return template.URL("?")
	}
	return template.URL("?" + next.Encode())
}

// paginationRange returns the page numbers to show around the current page.
func paginationRange(current, total int) []int {
	if total <= 1 {
		return nil
	}
	const window = 2
	start := current - window
	if start < 1 {
		start = 1
	}
	end := current + window
	if end > total {
		end = total
	}
	return seq(start, end)
}

// toJSON renders a value as JSON for a data- attribute.
//
// It deliberately returns a plain string rather than template.JS: the value is
// always placed in an HTML attribute, where html/template escapes it, and the
// page reads it back with JSON.parse. That keeps every byte of page data out
// of inline <script> blocks, which the Content-Security-Policy forbids.
func toJSON(v any) (string, error) {
	b, err := jsonMarshal(v)
	if err != nil {
		return "", err
	}
	return string(b), nil
}

// ternary picks between two values, for the small either/or choices templates
// make inline (an icon name, a CSS class) where a full if/else is noise.
// It is registered as "pick" because "if" is a template keyword.
func ternary(cond bool, whenTrue, whenFalse any) any {
	if cond {
		return whenTrue
	}
	return whenFalse
}

// boolString renders a bool as a form value the server will parse back.
func boolString(b bool) string {
	if b {
		return "true"
	}
	return "false"
}

// toggleIcon picks the switch icon showing the current state.
func toggleIcon(enabled bool) string {
	if enabled {
		return "bi-toggle-on"
	}
	return "bi-toggle-off"
}

// toggleVerb names the action a toggle button performs.
func toggleVerb(currentlyEnabled bool) string {
	if currentlyEnabled {
		return "Disable"
	}
	return "Enable"
}

// statusWord labels the current state.
func statusWord(enabled bool) string {
	if enabled {
		return "Enabled"
	}
	return "Disabled"
}

func nl2br(s string) template.HTML {
	escaped := template.HTMLEscapeString(s)
	return template.HTML(strings.ReplaceAll(escaped, "\n", "<br>"))
}