package photosapi

import (
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
)

const (
	MaxUploadPartSize = 4 << 20 // 4MB
)

var (
	ErrUploadNotExists               = errors.New("upload id does not exists")
	ErrUploadPartTooLarge            = fmt.Errorf("upload part too large (> %d B)", MaxUploadPartSize)
	ErrUploadPartWrongSha256         = errors.New("upload part sha256 does not match")
	ErrFileAlreadExists              = errors.New("file already exists")
	ErrUploadPartsCombineWrongSha256 = errors.New("upload parts combined sha256 does not match")
)

// Model
type File struct {
	ID        uint32    `gorm:"primary_key" json:"id"`
	Name      string    `gorm:"not null" json:"name"`
	Checksum  string    `gorm:"unique;size:44;not null"`
	Size      uint64    `gorm:"not null"`
	Author    *Account  `gorm:"constraint:OnDelete:SET NULL,OnUpdate:CASCADE" json:"author"`
	AuthorId  *uint32   `json:"-"`
	CreatedAt time.Time `json:"created_at"`
	UpdatedAt time.Time `json:"updated_at"`
}

func (s *Service) UploadCreate(c *gin.Context) {
	sha, err := uuid.NewRandom()
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	upload := &Upload{sha.String()}

	if err := s.StorageTmp.Create(upload.Id); err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	c.JSON(http.StatusCreated, upload)
}

// Service

type Upload struct {
	Id string `json:"upload_id" uri:"upload_id" binding:"required,uuid"`
}

type UploadPartQuery struct {
	Part       uint   `form:"part" binding:"required"`
	PartSha256 string `form:"sha256" binding:"required,sha256"`
}

type UploadCompleteRequest struct {
	Sha256 string `json:"sha256" binding:"required,sha256"`
	Name   string `json:"name" binding:"required"`
	Parts  uint   `json:"parts" binding:"required"`
}

type UploadCompleteFileOptions struct {
	Ext    string
	IsTemp bool
}

func (u *UploadCompleteRequest) Paths() []string {
	return []string{u.Sha256[0:1], u.Sha256[1:2]}
}

func (u *UploadCompleteRequest) File(options *UploadCompleteFileOptions) []string {
	filename := []string{}
	if options == nil {
		options = &UploadCompleteFileOptions{}
	}

	if options.IsTemp {
		filename = append(filename, "._tmp_")
	}
	filename = append(filename, u.Sha256)
	if len(options.Ext) > 0 {
		filename = append(filename, ".", options.Ext)
	}

	return []string{
		u.Sha256[0:1],
		u.Sha256[1:2],
		strings.Join(filename, ""),
	}
}

func (s *Service) UploadPart(c *gin.Context) {
	var (
		upload     Upload
		uploadPart UploadPartQuery
	)

	if c.BindUri(&upload) != nil || c.BindQuery(&uploadPart) != nil {
		return
	}

	if !s.StorageTmp.Exists(upload.Id) {
		c.AbortWithError(http.StatusNotFound, ErrUploadNotExists)
		return
	}

	if c.Request.ContentLength > MaxUploadPartSize {
		c.AbortWithError(http.StatusRequestEntityTooLarge, ErrUploadPartTooLarge)
		return
	}

	tmp_file := s.StorageTmp.Join(upload.Id, fmt.Sprintf("._tmp_%d", uploadPart.Part))
	file := s.StorageTmp.Join(upload.Id, fmt.Sprint(uploadPart.Part))

	f, err := os.Create(tmp_file)
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	sha := NewChecksum()
	t := io.TeeReader(c.Request.Body, sha)
	_, err = io.Copy(f, t)
	if err != nil {
		f.Close()
		os.Remove(tmp_file)
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}
	f.Close()

	if !sha.Match(uploadPart.PartSha256) {
		os.Remove(tmp_file)
		c.AbortWithError(http.StatusBadRequest, ErrUploadPartWrongSha256)
		return
	}

	err = os.Rename(tmp_file, file)
	if err != nil {
		os.Remove(tmp_file)
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	c.Status(http.StatusNoContent)
}

func (s *Service) UploadCancel(c *gin.Context) {
	var upload Upload
	if c.BindUri(&upload) != nil {
		return
	}

	if err := s.StorageTmp.Delete(upload.Id); err != nil {
		c.AbortWithError(http.StatusNotFound, ErrUploadNotExists)
		return
	}

	c.Status(http.StatusNoContent)
}

func (s *Service) UploadComplete(c *gin.Context) {
	var (
		upload                Upload
		uploadCompleteRequest UploadCompleteRequest
	)
	if c.BindUri(&upload) != nil || c.BindJSON(&uploadCompleteRequest) != nil {
		return
	}

	if !s.StorageTmp.Exists(upload.Id) {
		c.AbortWithError(http.StatusNotFound, ErrUploadNotExists)
		return
	}

	if f, err := s.StorageUpload.Stat(uploadCompleteRequest.File(nil)...); err == nil && f.Mode().IsRegular() {
		c.AbortWithError(http.StatusConflict, ErrFileAlreadExists)
		return
	}

	if err := s.StorageUpload.Create(uploadCompleteRequest.Paths()...); err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	f, err := os.Create(s.StorageUpload.Join(uploadCompleteRequest.File(&UploadCompleteFileOptions{IsTemp: true})...))
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}
	fsha := NewChecksum()
	ft := io.MultiWriter(f, fsha)
	size := uint64(0)

	defer f.Close()
	for part := uint(1); part <= uploadCompleteRequest.Parts; part++ {
		p, err := os.Open(s.StorageTmp.Join(upload.Id, fmt.Sprint(part)))
		if err != nil {
			c.AbortWithError(http.StatusNotFound, fmt.Errorf("upload part %d missing", part))
			return
		}
		w, err := io.Copy(ft, p)
		if err != nil {
			c.AbortWithError(http.StatusInternalServerError, err)
			return
		}
		size += uint64(w)
	}

	if !fsha.Match(uploadCompleteRequest.Sha256) {
		c.AbortWithError(http.StatusExpectationFailed, ErrUploadPartsCombineWrongSha256)
		return
	}

	f.Close()
	if err := os.Rename(
		s.StorageUpload.Join(uploadCompleteRequest.File(&UploadCompleteFileOptions{IsTemp: true})...),
		s.StorageUpload.Join(uploadCompleteRequest.File(nil)...),
	); err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	sess := s.CurrentSession(c)
	record := &File{
		Name:     uploadCompleteRequest.Name,
		Checksum: uploadCompleteRequest.Sha256,
		AuthorId: &sess.Account.ID,
		Size:     size,
	}

	if err := s.DB.Create(record).Error; err != nil {
		c.AbortWithError(http.StatusConflict, err)
		return
	}

	c.Status(http.StatusNoContent)
}

func (s *Service) UploadInit() {
	upload := s.Gin.Group("/upload")
	upload.Use(s.RequireSession)

	// start
	upload.POST("", s.UploadCreate)
	// Cancel
	upload.DELETE("/:upload_id", s.UploadCancel)
	// Add part
	upload.PUT("/:upload_id", s.UploadPart)
	// Complete
	upload.POST("/:upload_id", s.UploadComplete)
}