// Package handlers
package handlers

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
)

const maxUploadSize = 10 << 20 // 10 MB

type UploadHandler struct {
	minioClient    *minio.Client
	bucket         string
	endpoint       string
	publicEndpoint string
}

func NewUploadHandler(endpoint, publicEndpoint, accessKey, secretKey, bucket string, useSSL bool) (*UploadHandler, error) {
	client, err := minio.New(endpoint, &minio.Options{
		Creds:  credentials.NewStaticV4(accessKey, secretKey, ""),
		Secure: useSSL,
	})
	if err != nil {
		return nil, err
	}

	return &UploadHandler{
		minioClient:    client,
		bucket:         bucket,
		endpoint:       endpoint,
		publicEndpoint: publicEndpoint,
	}, nil
}

type presignedURLRequest struct {
	ContentType string `json:"content_type"`
	MaxSizeMB   int    `json:"max_size_mb"`
}

type presignedURLResponse struct {
	UploadURL string            `json:"upload_url"`
	FileURL   string            `json:"file_url"`
	Fields    map[string]string `json:"fields"`
}

func (h *UploadHandler) UploadFile(w http.ResponseWriter, r *http.Request) {
	r.Body = http.MaxBytesReader(w, r.Body, maxUploadSize)
	if err := r.ParseMultipartForm(maxUploadSize); err != nil {
		writeError(w, http.StatusBadRequest, "file too large or invalid multipart", err)
		return
	}

	file, header, err := r.FormFile("file")
	if err != nil {
		writeError(w, http.StatusBadRequest, "file is required", err)
		return
	}
	defer file.Close()

	contentType := header.Header.Get("Content-Type")
	validContentTypes := map[string]bool{
		"image/jpeg": true, "image/png": true, "image/webp": true, "image/heic": true,
	}
	if !validContentTypes[contentType] {
		writeError(w, http.StatusBadRequest, "unsupported content type", nil)
		return
	}

	// Заголовок Content-Type подделывается клиентом — проверяем реальную
	// сигнатуру файла по первым байтам, чтобы нельзя было залить произвольный
	// контент под видом изображения.
	if err := verifyImageSignature(file, contentType); err != nil {
		writeError(w, http.StatusBadRequest, "file content does not match declared image type", err)
		return
	}

	ext := ".jpg"
	switch contentType {
	case "image/png":
		ext = ".png"
	case "image/webp":
		ext = ".webp"
	case "image/heic":
		ext = ".heic"
	}
	objectName := "uploads/" + uuid.New().String() + ext

	_, err = h.minioClient.PutObject(r.Context(), h.bucket, objectName, file, header.Size,
		minio.PutObjectOptions{ContentType: contentType},
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to upload file", err)
		return
	}

	fileURL := fmt.Sprintf("%s/%s/%s", h.publicEndpoint, h.bucket, objectName)

	writeJSON(w, http.StatusOK, map[string]string{
		"file_url": fileURL,
	})
}

func (h *UploadHandler) PresignedURL(w http.ResponseWriter, r *http.Request) {
	var req presignedURLRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid request body", err)
		return
	}

	if req.MaxSizeMB <= 0 || req.MaxSizeMB > 50 {
		req.MaxSizeMB = 10
	}

	validContentTypes := map[string]bool{
		"image/jpeg": true, "image/png": true, "image/webp": true, "image/heic": true,
	}
	if !validContentTypes[req.ContentType] {
		writeError(w, http.StatusBadRequest, "unsupported content type", nil)
		return
	}

	fileID := uuid.New().String()
	ext := ".jpg"
	switch req.ContentType {
	case "image/png":
		ext = ".png"
	case "image/webp":
		ext = ".webp"
	case "image/heic":
		ext = ".heic"
	}
	objectName := "uploads/" + fileID + ext

	policy := minio.NewPostPolicy()
	policy.SetBucket(h.bucket)
	policy.SetKey(objectName)
	policy.SetExpires(time.Now().Add(15 * time.Minute))
	policy.SetContentType(req.ContentType)
	policy.SetContentLengthRange(1, int64(req.MaxSizeMB)*1024*1024)

	uploadURL, formData, err := h.minioClient.PresignedPostPolicy(r.Context(), policy)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to generate upload URL", err)
		return
	}

	uploadURLStr := h.publicEndpoint + uploadURL.Path + "?" + uploadURL.RawQuery
	publicUploadURL, err := url.Parse(uploadURLStr)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to build public upload URL", err)
		return
	}

	fileURL := h.publicEndpoint + "/" + h.bucket + "/" + objectName

	writeJSON(w, http.StatusOK, presignedURLResponse{
		UploadURL: publicUploadURL.String(),
		FileURL:   fileURL,
		Fields:    formData,
	})
}

// verifyImageSignature читает первые байты файла и проверяет, что реальная
// сигнатура соответствует заявленному content-type. После проверки возвращает
// курсор файла в начало, чтобы последующая загрузка читала его целиком.
func verifyImageSignature(file io.ReadSeeker, declaredType string) error {
	head := make([]byte, 512)
	n, err := io.ReadFull(file, head)
	if err != nil && err != io.ErrUnexpectedEOF && err != io.EOF {
		return fmt.Errorf("read file header: %w", err)
	}
	head = head[:n]
	if _, err := file.Seek(0, io.SeekStart); err != nil {
		return fmt.Errorf("seek file start: %w", err)
	}

	if !matchesImageType(head, declaredType) {
		return errors.New("file signature mismatch")
	}
	return nil
}

// matchesImageType сверяет байтовую сигнатуру с заявленным типом.
// net/http.DetectContentType умеет распознавать jpeg/png/webp, но не heic,
// поэтому для heic проверяем ISO-BMFF бокс ftyp вручную.
func matchesImageType(head []byte, declaredType string) bool {
	if declaredType == "image/heic" {
		return isHEIC(head)
	}
	return http.DetectContentType(head) == declaredType
}

// isHEIC проверяет, что файл — ISO Base Media File Format с HEIF-брендом.
func isHEIC(head []byte) bool {
	if len(head) < 12 || !bytes.Equal(head[4:8], []byte("ftyp")) {
		return false
	}
	brand := string(head[8:12])
	switch brand {
	case "heic", "heix", "hevc", "heim", "heis", "mif1", "msf1":
		return true
	}
	return false
}

func (h *UploadHandler) DeleteObjects(ctx context.Context, urls []string) error {
	prefix := h.publicEndpoint + "/" + h.bucket + "/"
	for _, fileURL := range urls {
		if !strings.HasPrefix(fileURL, prefix) {
			continue
		}
		objectKey := strings.TrimPrefix(fileURL, prefix)
		if err := h.minioClient.RemoveObject(ctx, h.bucket, objectKey, minio.RemoveObjectOptions{}); err != nil {
			return fmt.Errorf("delete object %s: %w", objectKey, err)
		}
	}
	return nil
}