package handler

import (
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"

	"github.com/gin-gonic/gin"

	"github.com/dhao2001/mygo/internal/api"
	"github.com/dhao2001/mygo/internal/middleware"
	"github.com/dhao2001/mygo/internal/model"
	"github.com/dhao2001/mygo/internal/service"
)

// FileHandler handles file management endpoints.
type FileHandler struct {
	fileService *service.FileService
}

// NewFileHandler creates a FileHandler.
func NewFileHandler(fileService *service.FileService) *FileHandler {
	return &FileHandler{fileService: fileService}
}

type createDirRequest struct {
	Name     string  `json:"name" binding:"required"`
	ParentID *string `json:"parent_id"`
}

type updateFileRequest struct {
	Name     string  `json:"name"`
	ParentID *string `json:"parent_id"`
}

// Upload handles POST /api/v1/files.
// If the content type is multipart/form-data, it uploads a file.
// If the content type is application/json, it creates a directory.
func (h *FileHandler) Upload(c *gin.Context) {
	userID := middleware.MustGetUserID(c)
	contentType := c.GetHeader("Content-Type")

	// Directory creation via JSON.
	if len(contentType) >= 16 && contentType[:16] == "application/json" {
		var req createDirRequest
		if err := c.ShouldBindJSON(&req); err != nil {
			api.Error(c, http.StatusBadRequest, "invalid request: "+err.Error())
			return
		}

		dir, err := h.fileService.CreateDir(c.Request.Context(), userID, req.ParentID, req.Name)
		if err != nil {
			api.Error(c, mapError(err), err.Error())
			return
		}

		c.JSON(http.StatusCreated, dir)
		return
	}

	// File upload via multipart.
	if err := c.Request.ParseMultipartForm(32 << 20); err != nil {
		api.Error(c, http.StatusBadRequest, "invalid multipart form: "+err.Error())
		return
	}

	parentIDStr := c.PostForm("parent_id")
	var parentID *string
	if parentIDStr != "" {
		parentID = &parentIDStr
	}

	header, err := c.FormFile("file")
	if err != nil {
		api.Error(c, http.StatusBadRequest, "missing file field: "+err.Error())
		return
	}

	file, err := header.Open()
	if err != nil {
		api.Error(c, http.StatusInternalServerError, "open uploaded file: "+err.Error())
		return
	}
	defer file.Close()

	info, err := h.fileService.Upload(c.Request.Context(), userID, parentID, header.Filename, file, header.Header.Get("Content-Type"))
	if err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}

	c.JSON(http.StatusCreated, info)
}

// List handles GET /api/v1/files.
func (h *FileHandler) List(c *gin.Context) {
	userID := middleware.MustGetUserID(c)

	parentIDStr := c.Query("parent_id")
	var parentID *string
	if parentIDStr != "" {
		parentID = &parentIDStr
	}

	offset, err := strconv.Atoi(c.DefaultQuery("offset", "0"))
	if err != nil || offset < 0 {
		api.Error(c, http.StatusBadRequest, "invalid offset")
		return
	}

	limit, err := strconv.Atoi(c.DefaultQuery("limit", "50"))
	if err != nil || limit < 1 {
		api.Error(c, http.StatusBadRequest, "invalid limit")
		return
	}
	if limit > 200 {
		limit = 200
	}

	list, err := h.fileService.List(c.Request.Context(), userID, parentID, offset, limit)
	if err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}

	c.JSON(http.StatusOK, list)
}

// Get handles GET /api/v1/files/:id.
func (h *FileHandler) Get(c *gin.Context) {
	userID := middleware.MustGetUserID(c)
	fileID := c.Param("id")

	info, err := h.fileService.Get(c.Request.Context(), userID, fileID)
	if err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}

	c.JSON(http.StatusOK, info)
}

// Download handles GET /api/v1/files/:id/content.
func (h *FileHandler) Download(c *gin.Context) {
	userID := middleware.MustGetUserID(c)
	fileID := c.Param("id")

	reader, info, err := h.fileService.Download(c.Request.Context(), userID, fileID)
	if err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}
	defer reader.Close()

	mimeType := info.MimeType
	if mimeType == "" {
		mimeType = "application/octet-stream"
	}

	c.Header("Content-Type", mimeType)
	c.Header("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", url.PathEscape(info.Name)))
	c.Header("Content-Length", strconv.FormatInt(info.Size, 10))

	c.Status(http.StatusOK)
	io.Copy(c.Writer, reader)
}

// Update handles PUT /api/v1/files/:id.
func (h *FileHandler) Update(c *gin.Context) {
	userID := middleware.MustGetUserID(c)
	fileID := c.Param("id")

	var req updateFileRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		api.Error(c, http.StatusBadRequest, "invalid request: "+err.Error())
		return
	}

	// Validate at least one field is provided.
	if req.Name == "" && req.ParentID == nil {
		api.Error(c, http.StatusBadRequest, "at least one of name or parent_id must be provided")
		return
	}

	info, err := h.fileService.Update(c.Request.Context(), userID, fileID, req.Name, req.ParentID)
	if err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}

	c.JSON(http.StatusOK, info)
}

// Delete handles DELETE /api/v1/files/:id.
func (h *FileHandler) Delete(c *gin.Context) {
	userID := middleware.MustGetUserID(c)
	fileID := c.Param("id")

	if err := h.fileService.Delete(c.Request.Context(), userID, fileID); err != nil {
		api.Error(c, mapError(err), err.Error())
		return
	}

	c.Status(http.StatusNoContent)
}

// mapError maps sentinel errors to HTTP status codes.
func mapError(err error) int {
	switch {
	case errors.Is(err, model.ErrNotFound):
		return http.StatusNotFound
	case errors.Is(err, model.ErrForbidden):
		return http.StatusForbidden
	case errors.Is(err, model.ErrDuplicate):
		return http.StatusConflict
	default:
		return http.StatusInternalServerError
	}
}