package web

import (
	"bytes"
	"errors"
	"fmt"
	"image"
	"image/jpeg"
	"image/png"
	"io"
	"net/http"
	"path"
	"strings"

	"golang.org/x/image/draw"
	_ "golang.org/x/image/webp"

	"plumber/internal/blob"
	"plumber/internal/geo"
	"plumber/internal/store"
)

type profilePage struct {
	page
	States         []struct{ Code, Name string }
	Questions      []store.RankedQuestion
	QuestionsLabel string
	UploadsEnabled bool
	Error          string
	StateVal       string
	EmailVal       string
}

func (s *Server) handleProfileForm(w http.ResponseWriter, r *http.Request) {
	u := currentUser(r)
	if u == nil {
		http.Redirect(w, r, "/login?next=/profile", http.StatusSeeOther)
		return
	}
	s.renderProfile(w, r, u, "", u.State, u.Email)
}

func (s *Server) handleProfile(w http.ResponseWriter, r *http.Request) {
	u := currentUser(r)
	if u == nil {
		http.Redirect(w, r, "/login?next=/profile", http.StatusSeeOther)
		return
	}
	if err := r.ParseMultipartForm(3 << 20); err != nil {
		s.renderProfile(w, r, u, "Could not read form (max 2MB for images).", u.State, u.Email)
		return
	}
	want := s.sessions.GetString(r.Context(), "csrf")
	got := r.FormValue("_csrf")
	if want == "" || got != want {
		http.Error(w, "invalid csrf token", http.StatusForbidden)
		return
	}

	state := geo.NormalizeState(r.FormValue("state"))
	if !geo.ValidState(state) {
		s.renderProfile(w, r, u, "Choose a valid US state or leave it blank.", state, r.FormValue("email"))
		return
	}
	email, emailErr := store.ValidateEmail(r.FormValue("email"))
	if emailErr != "" {
		s.renderProfile(w, r, u, emailErr, state, r.FormValue("email"))
		return
	}

	avatarURL := ""
	avatarKey := ""
	file, hdr, err := r.FormFile("avatar")
	if err == nil {
		defer file.Close()
		if !s.cfg.Blob.Enabled() {
			s.renderProfile(w, r, u, "Avatar uploads are not configured on this server.", state, email)
			return
		}
		if hdr.Size > 2<<20 {
			s.renderProfile(w, r, u, "Avatar must be 2MB or smaller.", state, email)
			return
		}
		body, ext, contentType, prepErr := prepareAvatar(file, 2<<20)
		if prepErr != nil {
			s.renderProfile(w, r, u, "Avatar must be a JPEG, PNG, or WebP image.", state, email)
			return
		}
		prevURL := u.AvatarURL
		avatarKey = path.Join("avatars", u.ID, "avatar"+ext)
		url, upErr := s.cfg.Blob.Upload(r.Context(), blob.FileUpload{
			Key:         avatarKey,
			Body:        bytes.NewReader(body),
			ContentType: contentType,
			Size:        int64(len(body)),
		})
		if upErr != nil {
			s.renderProfile(w, r, u, "Could not upload avatar. Try again later.", state, email)
			return
		}
		avatarURL = url
		u.State = state
		u.Email = email
		u.AvatarURL = avatarURL
		if err := s.store.SaveUserProfile(r.Context(), u); err != nil {
			_ = s.cfg.Blob.Delete(r.Context(), avatarKey)
			if errors.Is(err, store.ErrDuplicateEmail) {
				s.renderProfile(w, r, u, "That email is already registered.", state, email)
				return
			}
			http.Error(w, "could not save profile", http.StatusInternalServerError)
			return
		}
		if oldKey := avatarObjectKey(prevURL, u.ID); oldKey != "" && oldKey != avatarKey {
			_ = s.cfg.Blob.Delete(r.Context(), oldKey)
		}
		s.sessions.Put(r.Context(), "flash", "Profile saved.")
		http.Redirect(w, r, "/profile", http.StatusSeeOther)
		return
	} else if err != http.ErrMissingFile {
		s.renderProfile(w, r, u, "Could not read avatar file.", state, email)
		return
	}

	u.State = state
	u.Email = email
	if err := s.store.SaveUserProfile(r.Context(), u); err != nil {
		if errors.Is(err, store.ErrDuplicateEmail) {
			s.renderProfile(w, r, u, "That email is already registered.", state, email)
			return
		}
		http.Error(w, "could not save profile", http.StatusInternalServerError)
		return
	}
	s.sessions.Put(r.Context(), "flash", "Profile saved.")
	http.Redirect(w, r, "/profile", http.StatusSeeOther)
}

func avatarObjectKey(publicURL, userID string) string {
	marker := "/avatars/" + userID + "/"
	i := strings.Index(publicURL, marker)
	if i < 0 {
		return ""
	}
	rest := publicURL[i+1:] // avatars/...
	if q := strings.IndexAny(rest, "?#"); q >= 0 {
		rest = rest[:q]
	}
	return rest
}

// prepareAvatar reads at most maxBytes, sniffs/decodes the image, resizes to a
// small avatar, and re-encodes so only bounded valid image bytes are stored.
func prepareAvatar(r io.Reader, maxBytes int64) (body []byte, ext, contentType string, err error) {
	limited := io.LimitReader(r, maxBytes+1)
	raw, err := io.ReadAll(limited)
	if err != nil {
		return nil, "", "", err
	}
	if int64(len(raw)) > maxBytes {
		return nil, "", "", fmt.Errorf("avatar too large")
	}
	if len(raw) == 0 {
		return nil, "", "", fmt.Errorf("empty avatar")
	}

	sniff := http.DetectContentType(raw)
	switch {
	case strings.HasPrefix(sniff, "image/jpeg"),
		strings.HasPrefix(sniff, "image/png"),
		strings.HasPrefix(sniff, "image/webp"):
	default:
		return nil, "", "", fmt.Errorf("unsupported type %s", sniff)
	}

	cfg, format, err := image.DecodeConfig(bytes.NewReader(raw))
	if err != nil {
		return nil, "", "", err
	}
	// Cap decoded size before allocating pixel buffers (~4 MiB RGBA at 1024²).
	const maxDecodeDim = 1024
	const maxPixels = maxDecodeDim * maxDecodeDim
	if cfg.Width <= 0 || cfg.Height <= 0 || cfg.Width > maxDecodeDim || cfg.Height > maxDecodeDim {
		return nil, "", "", fmt.Errorf("image dimensions out of range")
	}
	if int64(cfg.Width)*int64(cfg.Height) > maxPixels {
		return nil, "", "", fmt.Errorf("image too many pixels")
	}

	img, decodedFormat, err := image.Decode(bytes.NewReader(raw))
	if err != nil {
		return nil, "", "", err
	}
	if format != "" {
		decodedFormat = format
	}

	const maxAvatarDim = 512
	img = fitAvatar(img, maxAvatarDim)

	var out bytes.Buffer
	switch decodedFormat {
	case "jpeg":
		if err := jpeg.Encode(&out, img, &jpeg.Options{Quality: 85}); err != nil {
			return nil, "", "", err
		}
		if int64(out.Len()) > maxBytes {
			return nil, "", "", fmt.Errorf("encoded avatar too large")
		}
		return out.Bytes(), ".jpg", "image/jpeg", nil
	case "png", "webp":
		if err := png.Encode(&out, img); err != nil {
			return nil, "", "", err
		}
		if int64(out.Len()) > maxBytes {
			// Fall back to JPEG when PNG balloons past the upload cap.
			out.Reset()
			if err := jpeg.Encode(&out, img, &jpeg.Options{Quality: 85}); err != nil {
				return nil, "", "", err
			}
			if int64(out.Len()) > maxBytes {
				return nil, "", "", fmt.Errorf("encoded avatar too large")
			}
			return out.Bytes(), ".jpg", "image/jpeg", nil
		}
		return out.Bytes(), ".png", "image/png", nil
	default:
		return nil, "", "", fmt.Errorf("unsupported format %s", decodedFormat)
	}
}

// fitAvatar scales img down so both sides are at most maxDim.
func fitAvatar(img image.Image, maxDim int) image.Image {
	b := img.Bounds()
	w, h := b.Dx(), b.Dy()
	if w <= maxDim && h <= maxDim {
		return img
	}
	scale := float64(maxDim) / float64(w)
	if float64(h)*scale > float64(maxDim) {
		scale = float64(maxDim) / float64(h)
	}
	nw := int(float64(w) * scale)
	nh := int(float64(h) * scale)
	if nw < 1 {
		nw = 1
	}
	if nh < 1 {
		nh = 1
	}
	dst := image.NewRGBA(image.Rect(0, 0, nw, nh))
	draw.ApproxBiLinear.Scale(dst, dst.Bounds(), img, b, draw.Over, nil)
	return dst
}

func (s *Server) renderProfile(w http.ResponseWriter, r *http.Request, u *store.User, errMsg, stateVal, emailVal string) {
	var (
		questions []store.RankedQuestion
		label     string
		err       error
	)
	if u.Admin() {
		label = "Questions you answered"
		questions, err = s.store.ListQuestionsAnsweredBy(r.Context(), u.ID)
	} else {
		label = "Your questions"
		questions, err = s.store.ListQuestionsByAuthor(r.Context(), u.ID)
	}
	if err != nil {
		http.Error(w, "could not load questions", http.StatusInternalServerError)
		return
	}
	p := s.basePage(r, "Profile")
	p.User = u
	s.exec(w, "profile", profilePage{
		page:           p,
		States:         geo.States,
		Questions:      questions,
		QuestionsLabel: label,
		UploadsEnabled: s.cfg.Blob.Enabled(),
		Error:          errMsg,
		StateVal:       stateVal,
		EmailVal:       emailVal,
	})
}