package web

import (
	"crypto/sha256"
	"embed"
	"encoding/base64"
	"fmt"
	"html/template"
	"log/slog"
	"net/http"
	"time"

	"github.com/scottyah/fit/internal/config"
	"github.com/scottyah/fit/internal/store"
)

//go:embed templates/*.html
var templateFS embed.FS

//go:embed static/*
var staticFS embed.FS

type Server struct {
	cfg      *config.Config
	store    *store.Store
	tpl      *template.Template
	mux      *http.ServeMux
	assetVer string           // content hash, appended to static URLs
	now      func() time.Time // swapped in tests; every date derives from it
}

func New(cfg *config.Config, st *store.Store) (*Server, error) {
	s := &Server{cfg: cfg, store: st, assetVer: assetVersion(), now: time.Now}

	tpl, err := template.New("").Funcs(s.templateFuncs()).ParseFS(templateFS, "templates/*.html")
	if err != nil {
		return nil, fmt.Errorf("parse templates: %w", err)
	}
	s.tpl = tpl

	s.routes()
	return s, nil
}

func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method == http.MethodPost && !sameSite(r) {
		http.Error(w, "cross-site write refused", http.StatusForbidden)
		return
	}
	s.mux.ServeHTTP(w, r)
}

// sameSite rejects writes a browser reports as coming from somewhere else.
// The only thing guarding this app is basic auth at the ingress, and browsers
// attach those credentials to a cross-origin form post, so without this check
// a page on any other domain could quietly overwrite the log. Requests with no
// Sec-Fetch-Site header are not browsers and are left alone.
func sameSite(r *http.Request) bool {
	switch r.Header.Get("Sec-Fetch-Site") {
	case "", "same-origin", "none":
		return true
	default:
		return false
	}
}

func (s *Server) routes() {
	mux := http.NewServeMux()

	mux.HandleFunc("GET /{$}", s.handleHome)
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("ok"))
	})

	mux.HandleFunc("POST /setup", s.handleSetup)

	mux.HandleFunc("GET /d/{date}", s.handleDay)
	mux.HandleFunc("POST /d/{date}", s.handleSaveDay)

	mux.HandleFunc("GET /settings", s.handleSettings)
	mux.HandleFunc("POST /settings", s.handleSaveSettings)

	mux.HandleFunc("GET /export.json", s.handleExport)
	mux.HandleFunc("POST /import", s.handleImport)

	mux.HandleFunc("GET /manifest.webmanifest", s.handleManifest)

	// Static assets are immutable in the image, so they cache hard.
	static := http.FileServer(http.FS(staticFS))
	mux.Handle("GET /static/", cacheForever(static))

	s.mux = mux
}

func cacheForever(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Safe to cache hard because every reference carries a content hash;
		// changing a file changes its URL.
		w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		h.ServeHTTP(w, r)
	})
}

// assetVersion hashes the embedded static files so a stylesheet edit produces
// a new URL. Without it, a deploy would leave the phone on a week-old CSS.
func assetVersion() string {
	sum := sha256.New()
	entries, err := staticFS.ReadDir("static")
	if err != nil {
		return "dev"
	}
	for _, entry := range entries {
		body, err := staticFS.ReadFile("static/" + entry.Name())
		if err != nil {
			continue
		}
		sum.Write([]byte(entry.Name()))
		sum.Write(body)
	}
	return base64.RawURLEncoding.EncodeToString(sum.Sum(nil))[:10]
}

// ---------------------------------------------------------------- view model

// dayView is one day as the page needs it: the log itself plus everything
// derived from the calendar and the targets.
type dayView struct {
	Date     string
	Time     time.Time
	Number   int // 1-based position in the challenge, 0 outside it
	Marks    store.Marks
	Score    int
	Logged   bool
	IsToday  bool
	IsFuture bool
}

// meter is one of the three numbers, with everything the band needs to draw
// itself. Mode is "floor" for a target to reach and "ceiling" for a budget not
// to exceed, which is the difference between protein and calories.
type meter struct {
	Key    string
	Label  string
	Unit   string
	Value  *int
	Target int
	Mode   string
	Pct    int
	Met    bool
	Over   bool
	Note   string
}

type stats struct {
	Complete  int
	Logged    int
	Elapsed   int // days of the challenge that have started, capped at Length
	Remaining int
	Streak    int
	Marks     [5]int // how many days each of the five was hit
}

type pageData struct {
	Title    string
	Settings store.Settings
	Day      store.Day
	View     dayView
	Meters   []meter
	Card     []dayView
	Stats    stats
	PrevDate string
	NextDate string
	Today    string
	Status   string // "before", "during" or "after" the challenge window
	Flash    string
	Error    string
}

func (s *Server) render(w http.ResponseWriter, status int, name string, data pageData) {
	data.Today = s.today()
	if data.Settings.Length == 0 {
		data.Settings = s.store.Settings()
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := s.tpl.ExecuteTemplate(w, name, data); err != nil {
		slog.Error("render template", "template", name, "err", err)
	}
}

// today is the current date in the configured timezone. Every date in the app
// comes from here, so the day rolls over at local midnight rather than UTC's.
func (s *Server) today() string {
	return s.now().In(s.cfg.TZ).Format(store.DateLayout)
}

// asset stamps a static path with the build's content hash.
func (s *Server) asset(path string) string {
	return path + "?v=" + s.assetVer
}