package web

import (
	"bytes"
	"context"
	"errors"
	"image"
	"image/jpeg"
	"image/png"
	"io"
	"log"
	"mime"
	"mime/multipart"
	"net/http"
	"path"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/rwcarlsen/goexif/exif"
	"golang.org/x/image/draw"
	_ "golang.org/x/image/webp"

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

const (
	defaultRequestBodyBytes  = 3 << 20
	postImageMaxFileBytes    = 5 << 20
	postImageMaxRequestBytes = 22 << 20
	postImageMultipartMemory = 2 << 20
	postImageMaxSourceDim    = 6000
	postImageMaxSourcePixels = 16_000_000
	postImageMaxRenderedDim  = 1600
	postImageCleanupTimeout  = 10 * time.Second
)

func requestBodyLimit(r *http.Request) int64 {
	if r.Method != http.MethodPost {
		return defaultRequestBodyBytes
	}
	switch {
	case r.URL.Path == "/submit", r.URL.Path == "/posts":
		return postImageMaxRequestBytes
	case strings.HasPrefix(r.URL.Path, "/posts/") && strings.HasSuffix(r.URL.Path, "/edit"):
		return postImageMaxRequestBytes
	default:
		return defaultRequestBodyBytes
	}
}

type postImageRequestError struct {
	status  int
	message string
	cause   error
}

func (e *postImageRequestError) Error() string {
	if e.cause == nil {
		return e.message
	}
	return e.message + ": " + e.cause.Error()
}

func parsePostMutationForm(w http.ResponseWriter, r *http.Request) (func(), bool) {
	contentType := r.Header.Get("Content-Type")
	mediaType, _, err := mime.ParseMediaType(contentType)
	if err != nil && strings.HasPrefix(strings.ToLower(contentType), "multipart/") {
		http.Error(w, "Could not read image upload.", http.StatusBadRequest)
		return func() {}, false
	}
	if mediaType != "multipart/form-data" {
		if err := r.ParseForm(); err != nil {
			writePostImageRequestError(w, err)
			return func() {}, false
		}
		return func() {}, true
	}
	if err := r.ParseMultipartForm(postImageMultipartMemory); err != nil {
		writePostImageRequestError(w, err)
		return func() {}, false
	}
	cleanup := func() {
		if r.MultipartForm != nil {
			_ = r.MultipartForm.RemoveAll()
		}
	}
	return cleanup, true
}

func writePostImageRequestError(w http.ResponseWriter, err error) {
	var requestErr *postImageRequestError
	if errors.As(err, &requestErr) {
		http.Error(w, requestErr.message, requestErr.status)
		return
	}
	var maxErr *http.MaxBytesError
	if errors.As(err, &maxErr) {
		http.Error(w, "Image upload is too large.", http.StatusRequestEntityTooLarge)
		return
	}
	http.Error(w, "Could not read image upload.", http.StatusBadRequest)
}

func (s *Server) postImagesFromForm(
	ctx context.Context,
	r *http.Request,
	postID string,
	existing []store.PostImage,
) ([]store.PostImage, []string, error) {
	if r.MultipartForm == nil {
		return append([]store.PostImage(nil), existing...), nil, nil
	}
	retained, err := retainedPostImages(r.MultipartForm, existing)
	if err != nil {
		return nil, nil, err
	}
	files := r.MultipartForm.File["images"]
	descriptions := r.MultipartForm.Value["image_description"]
	if len(descriptions) > len(files) {
		return nil, nil, invalidPostImage("Image descriptions do not match selected images.", nil)
	}
	if len(retained)+len(files) > store.MaxPostImages {
		return nil, nil, invalidPostImage("You can attach up to 4 images.", nil)
	}
	if len(files) > 0 && !s.cfg.Blob.Enabled() {
		return nil, nil, &postImageRequestError{
			status:  http.StatusServiceUnavailable,
			message: "Image uploads are not configured on this server.",
		}
	}

	images := append([]store.PostImage(nil), retained...)
	newKeys := make([]string, 0, len(files))
	for i, header := range files {
		description := ""
		if i < len(descriptions) {
			description = strings.TrimSpace(descriptions[i])
		}
		if len([]rune(description)) > store.MaxImageDescriptionRunes {
			s.deletePostImageObjects(newKeys)
			return nil, nil, invalidPostImage("Image descriptions must be 500 characters or fewer.", nil)
		}
		prepared, err := preparePostImage(header)
		if err != nil {
			s.deletePostImageObjects(newKeys)
			return nil, nil, err
		}
		imageID := uuid.NewString()
		objectKey := path.Join("post-images", postID, imageID+prepared.extension)
		publicURL, err := s.cfg.Blob.Upload(ctx, blob.FileUpload{
			Key:         objectKey,
			Body:        bytes.NewReader(prepared.body),
			ContentType: prepared.contentType,
			Size:        int64(len(prepared.body)),
		})
		if err != nil {
			s.deletePostImageObjects(newKeys)
			return nil, nil, &postImageRequestError{
				status:  http.StatusServiceUnavailable,
				message: "Could not upload image. Try again later.",
				cause:   err,
			}
		}
		newKeys = append(newKeys, objectKey)
		images = append(images, store.PostImage{
			ID:          imageID,
			PostID:      postID,
			ObjectKey:   objectKey,
			PublicURL:   publicURL,
			Description: description,
			Width:       prepared.width,
			Height:      prepared.height,
		})
	}
	return images, newKeys, nil
}

func retainedPostImages(form *multipart.Form, existing []store.PostImage) ([]store.PostImage, error) {
	byID := make(map[string]store.PostImage, len(existing))
	for _, image := range existing {
		byID[image.ID] = image
	}
	ids := form.Value["existing_image_id"]
	descriptions := form.Value["existing_image_description"]
	if len(descriptions) > len(ids) {
		return nil, invalidPostImage("Existing image descriptions do not match the images.", nil)
	}
	seen := make(map[string]bool, len(ids))
	retained := make([]store.PostImage, 0, len(ids))
	for i, id := range ids {
		id = strings.TrimSpace(id)
		image, ok := byID[id]
		if !ok || seen[id] {
			return nil, invalidPostImage("An existing image selection is invalid.", nil)
		}
		seen[id] = true
		if i < len(descriptions) {
			image.Description = strings.TrimSpace(descriptions[i])
		}
		if len([]rune(image.Description)) > store.MaxImageDescriptionRunes {
			return nil, invalidPostImage("Image descriptions must be 500 characters or fewer.", nil)
		}
		retained = append(retained, image)
	}
	return retained, nil
}

func invalidPostImage(message string, cause error) error {
	return &postImageRequestError{status: http.StatusBadRequest, message: message, cause: cause}
}

type preparedPostImage struct {
	body        []byte
	extension   string
	contentType string
	width       int
	height      int
}

func preparePostImage(header *multipart.FileHeader) (preparedPostImage, error) {
	if header == nil {
		return preparedPostImage{}, invalidPostImage("Select a valid image.", nil)
	}
	if header.Size > postImageMaxFileBytes {
		return preparedPostImage{}, &postImageRequestError{
			status:  http.StatusRequestEntityTooLarge,
			message: "Each image must be 5 MB or smaller.",
		}
	}
	file, err := header.Open()
	if err != nil {
		return preparedPostImage{}, invalidPostImage("Could not read image.", err)
	}
	defer file.Close()
	raw, err := io.ReadAll(io.LimitReader(file, postImageMaxFileBytes+1))
	if err != nil {
		return preparedPostImage{}, invalidPostImage("Could not read image.", err)
	}
	if len(raw) == 0 {
		return preparedPostImage{}, invalidPostImage("Images cannot be empty.", nil)
	}
	if int64(len(raw)) > postImageMaxFileBytes {
		return preparedPostImage{}, &postImageRequestError{
			status:  http.StatusRequestEntityTooLarge,
			message: "Each image must be 5 MB or smaller.",
		}
	}
	sniffed := http.DetectContentType(raw)
	switch sniffed {
	case "image/jpeg", "image/png", "image/webp":
	default:
		return preparedPostImage{}, invalidPostImage("Images must be JPEG, PNG, or WebP.", nil)
	}
	cfg, format, err := image.DecodeConfig(bytes.NewReader(raw))
	if err != nil {
		return preparedPostImage{}, invalidPostImage("Could not decode image.", err)
	}
	if cfg.Width <= 0 || cfg.Height <= 0 ||
		cfg.Width > postImageMaxSourceDim || cfg.Height > postImageMaxSourceDim ||
		int64(cfg.Width)*int64(cfg.Height) > postImageMaxSourcePixels {
		return preparedPostImage{}, invalidPostImage("Image dimensions are too large.", nil)
	}
	decoded, decodedFormat, err := image.Decode(bytes.NewReader(raw))
	if err != nil {
		return preparedPostImage{}, invalidPostImage("Could not decode image.", err)
	}
	if format != "" {
		decodedFormat = format
	}
	if sniffed == "image/jpeg" {
		decoded = orientPostImage(decoded, jpegOrientation(raw))
	}
	decoded = fitPostImage(decoded, postImageMaxRenderedDim)

	var out bytes.Buffer
	result := preparedPostImage{}
	switch decodedFormat {
	case "jpeg":
		if err := jpeg.Encode(&out, decoded, &jpeg.Options{Quality: 85}); err != nil {
			return preparedPostImage{}, invalidPostImage("Could not encode image.", err)
		}
		result.extension = ".jpg"
		result.contentType = "image/jpeg"
	case "png", "webp":
		if err := png.Encode(&out, decoded); err != nil {
			return preparedPostImage{}, invalidPostImage("Could not encode image.", err)
		}
		result.extension = ".png"
		result.contentType = "image/png"
	default:
		return preparedPostImage{}, invalidPostImage("Images must be JPEG, PNG, or WebP.", nil)
	}
	result.body = out.Bytes()
	result.width = decoded.Bounds().Dx()
	result.height = decoded.Bounds().Dy()
	return result, nil
}

func jpegOrientation(raw []byte) int {
	metadata, err := exif.Decode(bytes.NewReader(raw))
	if err != nil {
		return 1
	}
	tag, err := metadata.Get(exif.Orientation)
	if err != nil {
		return 1
	}
	orientation, err := tag.Int(0)
	if err != nil || orientation < 1 || orientation > 8 {
		return 1
	}
	return orientation
}

func orientPostImage(source image.Image, orientation int) image.Image {
	if orientation <= 1 || orientation > 8 {
		return source
	}
	bounds := source.Bounds()
	width, height := bounds.Dx(), bounds.Dy()
	targetWidth, targetHeight := width, height
	if orientation >= 5 {
		targetWidth, targetHeight = height, width
	}
	target := image.NewNRGBA(image.Rect(0, 0, targetWidth, targetHeight))
	for y := 0; y < targetHeight; y++ {
		for x := 0; x < targetWidth; x++ {
			sourceX, sourceY := x, y
			switch orientation {
			case 2:
				sourceX = width - 1 - x
			case 3:
				sourceX, sourceY = width-1-x, height-1-y
			case 4:
				sourceY = height - 1 - y
			case 5:
				sourceX, sourceY = y, x
			case 6:
				sourceX, sourceY = y, height-1-x
			case 7:
				sourceX, sourceY = width-1-y, height-1-x
			case 8:
				sourceX, sourceY = width-1-y, x
			}
			target.Set(x, y, source.At(bounds.Min.X+sourceX, bounds.Min.Y+sourceY))
		}
	}
	return target
}

func fitPostImage(source image.Image, maxDimension int) image.Image {
	bounds := source.Bounds()
	width, height := bounds.Dx(), bounds.Dy()
	if width <= maxDimension && height <= maxDimension {
		return source
	}
	scale := float64(maxDimension) / float64(width)
	if float64(height)*scale > float64(maxDimension) {
		scale = float64(maxDimension) / float64(height)
	}
	targetWidth := max(1, int(float64(width)*scale))
	targetHeight := max(1, int(float64(height)*scale))
	target := image.NewNRGBA(image.Rect(0, 0, targetWidth, targetHeight))
	draw.CatmullRom.Scale(target, target.Bounds(), source, bounds, draw.Over, nil)
	return target
}

func (s *Server) deletePostImageObjects(keys []string) {
	if len(keys) == 0 {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), postImageCleanupTimeout)
	defer cancel()
	for _, key := range keys {
		if err := s.cfg.Blob.Delete(ctx, key); err != nil {
			log.Printf("delete post image %s: %v", key, err)
		}
	}
}

func removedPostImageKeys(before, after []store.PostImage) []string {
	retained := make(map[string]bool, len(after))
	for _, image := range after {
		retained[image.ObjectKey] = true
	}
	var removed []string
	for _, image := range before {
		if !retained[image.ObjectKey] {
			removed = append(removed, image.ObjectKey)
		}
	}
	return removed
}