package api

import (
	"context"
	"errors"
	"io"
	"mime/multipart"
	"net/http"
	"strconv"

	"git.golem15.com/golem15/summercms/modules/lagoon"
	"git.golem15.com/golem15/summercms/modules/lagoon/attach"
	"git.golem15.com/golem15/summercms/modules/surf"
	"git.golem15.com/golem15/summercms/modules/wire"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gocloud.dev/blob"
	"gorm.io/gorm"
)

// MaterialFileMaxBytes is the largest file the management API stores, the
// admin form's maxFilesize (50 MB).
const MaterialFileMaxBytes = 50 << 20

// MaterialFilesBodyLimit is the body cap of POST /materials/{id}/files: one
// file of MaterialFileMaxBytes plus the multipart framing.
const MaterialFilesBodyLimit = MaterialFileMaxBytes + 1<<20

// MaterialFilesMax is the most files a material holds, the admin form's
// maxFiles.
const MaterialFilesMax = 20

// fileLimits are the attach.Store rules of a material file: the default
// document and image extensions, up to MaterialFileMaxBytes.
var fileLimits = attach.Limits{MaxBytes: MaterialFileMaxBytes}

func (h *Handlers) bucket(w http.ResponseWriter) (*blob.Bucket, bool) {
	var b *blob.Bucket
	if h.Bucket != nil {
		b = h.Bucket()
	}
	if b == nil {
		writeOpaque500(w)
		return nil, false
	}
	return b, true
}

func materialFiles(db *gorm.DB, m models.Material) *gorm.DB {
	return db.Where("attachment_type = ? AND attachment_id = ? AND field = ?",
		m.MorphName(), strconv.FormatUint(uint64(m.ID), 10), models.MaterialFilesField)
}

// findMaterial loads the material of the {id} path parameter and answers 404
// itself when there is none.
func findMaterial(w http.ResponseWriter, r *http.Request, db *gorm.DB) (models.Material, bool) {
	var m models.Material
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return m, false
	}
	res := db.Where("id = ?", id).Limit(1).Find(&m)
	if res.Error != nil {
		writeOpaque500(w)
		return m, false
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return m, false
	}
	return m, true
}

// AttachMaterialFiles answers POST /materials/{id}/files: a multipart body
// whose "file" parts are stored as public files of the material, after the
// ones it has. Every part is checked by attach.Store (type, size); one
// refused part refuses the request and stores nothing. The answer is the
// material as GET /materials/{id} shows it, 201.
func (h *Handlers) AttachMaterialFiles(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	bucket, ok := h.bucket(w)
	if !ok {
		return
	}
	m, ok := findMaterial(w, r, db)
	if !ok {
		return
	}
	mr, err := r.MultipartReader()
	if err != nil {
		writeInvalid(w, "Send the files as multipart/form-data in parts named \"file\".")
		return
	}
	var refusal string
	// The blobs written are deleted again when the transaction did not commit.
	stored, err := h.storeParts(r.Context(), db, bucket, m, mr, &refusal)
	if err != nil || refusal != "" {
		if len(stored) > 0 {
			_ = attach.DeleteKeys(context.WithoutCancel(r.Context()), bucket, stored)
		}
		var tooLarge *http.MaxBytesError
		switch {
		case refusal != "":
			writeValidation(w, map[string][]string{"file": {refusal}})
		case errors.As(err, &tooLarge):
			wire.WriteJSON(w, http.StatusRequestEntityTooLarge, map[string]any{"error": true, "message": "Request body too large."})
		default:
			writeOpaque500(w)
		}
		return
	}
	h.writeMaterialDetail(w, r, db, m.ID, http.StatusCreated)
}

// storeParts stores and binds every "file" part in one transaction. A
// refusal (no file, too many, a type or size attach.Store turns down) is
// set in *refusal and rolls back; the returned keys are the blobs written.
func (h *Handlers) storeParts(ctx context.Context, db *gorm.DB, bucket *blob.Bucket, m models.Material, mr *multipart.Reader, refusal *string) ([]string, error) {
	var keys []string
	errRefused := errors.New("refused")
	err := lagoon.Transaction(ctx, db, func(_ context.Context, tx *gorm.DB) error {
		added := 0
		for {
			part, err := mr.NextPart()
			if err == io.EOF {
				break
			}
			if err != nil {
				return err
			}
			if part.FormName() != "file" || part.FileName() == "" {
				part.Close()
				continue
			}
			f, why, err := storeMaterialFile(ctx, tx, bucket, m, part.FileName(), part, fileLimits)
			part.Close()
			if f != nil {
				keys = append(keys, attach.BlobKeys(*f)...)
			}
			if err != nil {
				return err
			}
			if why != "" {
				*refusal = why
				return errRefused
			}
			added++
		}
		if added == 0 {
			*refusal = "No file: send at least one multipart part named \"file\"."
			return errRefused
		}
		return nil
	})
	if errors.Is(err, errRefused) {
		err = nil
	}
	return keys, err
}

// storeMaterialFile stores one file through attach.Store as a public file of
// m and binds it to the material, inside tx. It is the only way the
// management API writes a material file: the multipart route, the inline
// (base64) route and the signed upload all call it. The material's
// MaterialFilesMax cap and attach's extension, MIME and size checks (lim)
// apply. A refusal is returned as a text for the answer, with no error; the
// returned file, when not nil, has blobs the caller deletes when tx does
// not commit.
func storeMaterialFile(ctx context.Context, tx *gorm.DB, bucket *blob.Bucket, m models.Material, name string, body io.Reader, lim attach.Limits) (*attach.File, string, error) {
	var have int64
	if err := materialFiles(tx.Model(&attach.File{}), m).Count(&have).Error; err != nil {
		return nil, "", err
	}
	if have >= MaterialFilesMax {
		return nil, "A material holds at most " + strconv.Itoa(MaterialFilesMax) + " files.", nil
	}
	f, err := attach.Store(ctx, tx, bucket, attach.Upload{FileName: name, Body: body, Public: true}, lim)
	switch {
	case errors.Is(err, attach.ErrTooLarge):
		return nil, name + ": the file is larger than " + sizeMB(lim.MaxBytes) + ".", nil
	case errors.Is(err, attach.ErrFileType), errors.Is(err, attach.ErrMIMEType):
		return nil, name + ": this file type is not allowed.", nil
	case err != nil:
		return nil, "", err
	}
	err = tx.Model(&attach.File{}).Where("id = ?", f.ID).Updates(map[string]any{
		"attachment_type": m.MorphName(),
		"attachment_id":   strconv.FormatUint(uint64(m.ID), 10),
		"field":           models.MaterialFilesField,
	}).Error
	return f, "", err
}

// sizeMB names a byte limit in the refusal texts: 50 MB for 50 MiB, 3 MB
// for 3000000 bytes.
func sizeMB(n int64) string {
	if n%(1<<20) == 0 {
		return strconv.FormatInt(n>>20, 10) + " MB"
	}
	return strconv.FormatInt(n/1_000_000, 10) + " MB"
}

// DetachMaterialFile answers DELETE /materials/{id}/files/{file}: the file
// row goes, then its blob and thumbnails. A file of another material is a
// 404.
func (h *Handlers) DetachMaterialFile(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	bucket, ok := h.bucket(w)
	if !ok {
		return
	}
	m, ok := findMaterial(w, r, db)
	if !ok {
		return
	}
	fileID, ok := surf.IntParam(r, "file")
	if !ok {
		writeNotFound(w)
		return
	}
	var f attach.File
	res := materialFiles(db, m).Where("id = ?", fileID).Limit(1).Find(&f)
	if res.Error != nil {
		writeOpaque500(w)
		return
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return
	}
	if err := db.Where("id = ?", f.ID).Delete(&attach.File{}).Error; err != nil {
		writeOpaque500(w)
		return
	}
	// The row is gone, so the file is no longer served; a blob left behind
	// by a failed delete is only disk space.
	_ = attach.DeleteKeys(r.Context(), bucket, attach.BlobKeys(f))
	w.WriteHeader(http.StatusNoContent)
}