package routes

import (
	"errors"
	"fmt"
	"io/fs"
	"kooltap-updateserver/internal/apk_util"
	"kooltap-updateserver/internal/auth"
	"kooltap-updateserver/internal/models"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strconv"

	"github.com/Masterminds/semver/v3"
	"github.com/gin-gonic/gin"
	"gorm.io/gorm"
)

// Handler serves the release API.
type Handler struct {
	DB        *gorm.DB
	UploadDir string // published APKs, served under /downloads
	TmpDir    string // incoming uploads while they are inspected
	MaxUpload int64  // maximum request body size in bytes for uploads
}

func (h *Handler) Register(r *gin.Engine) {

	api := r.Group("/api")
	{
		api.GET("/update", h.CheckUpdate)
		api.GET("/releases", h.ListReleases)
	}

	r.GET("/download/latest", h.DownloadLatest)

	admin := r.Group("/admin")
	admin.Use(auth.AdminAuth())
	{
		admin.POST("/releases", h.UploadRelease)
		admin.DELETE("/releases/:id", h.DeleteRelease)
	}
}

// CheckUpdate tells a tablet whether a newer release exists. Tablets send their
// versionName as "version" and, optionally, their versionCode as "code"; the
// code is the most reliable comparison, so it wins when present.
func (h *Handler) CheckUpdate(c *gin.Context) {

	latest, err := h.latestRelease()
	if errors.Is(err, gorm.ErrRecordNotFound) {
		c.JSON(http.StatusOK, gin.H{"update": false})
		return
	}
	if err != nil {
		internalError(c, err)
		return
	}

	if !isNewer(latest, c.Query("version"), c.Query("code")) {
		c.JSON(http.StatusOK, gin.H{"update": false})
		return
	}

	c.JSON(http.StatusOK, gin.H{
		"update":    true,
		"version":   latest.Version,
		"code":      latest.VersionCode,
		"notes":     latest.Notes,
		"mandatory": latest.Mandatory,
		"sha256":    latest.SHA256,
		"download":  "/downloads/" + latest.APKFile,
	})
}

func isNewer(latest *models.Release, version, code string) bool {

	if code != "" {
		if cc, err := strconv.ParseInt(code, 10, 64); err == nil {
			return latest.VersionCode > cc
		}
	}

	cv, err1 := semver.NewVersion(version)
	lv, err2 := semver.NewVersion(latest.Version)
	if err1 != nil || err2 != nil {
		return latest.Version != version
	}

	return lv.GreaterThan(cv)
}

// DownloadLatest redirects to the newest APK, for installing on a new tablet from a browser
func (h *Handler) DownloadLatest(c *gin.Context) {

	latest, err := h.latestRelease()
	if errors.Is(err, gorm.ErrRecordNotFound) {
		c.JSON(http.StatusNotFound, gin.H{"error": "No releases yet"})
		return
	}
	if err != nil {
		internalError(c, err)
		return
	}

	c.Redirect(http.StatusFound, "/downloads/"+latest.APKFile)
}

// latestRelease returns the release with the highest Android version code,
// which is the latest build regardless of upload order.
func (h *Handler) latestRelease() (*models.Release, error) {
	var release models.Release
	err := h.DB.Order("version_code desc").First(&release).Error
	if err != nil {
		return nil, err
	}
	return &release, nil
}

func (h *Handler) ListReleases(c *gin.Context) {

	releases := []models.Release{}

	if err := h.DB.Order("created_at desc").Find(&releases).Error; err != nil {
		internalError(c, err)
		return
	}

	c.JSON(http.StatusOK, releases)
}

func (h *Handler) UploadRelease(c *gin.Context) {

	if h.MaxUpload > 0 {
		c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, h.MaxUpload)
	}

	notes := c.PostForm("notes")
	mandatory := c.PostForm("mandatory") == "true"

	file, err := c.FormFile("apk")
	if err != nil {
		var tooLarge *http.MaxBytesError
		if errors.As(err, &tooLarge) {
			c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "APK too large"})
			return
		}
		c.JSON(http.StatusBadRequest, gin.H{"error": "APK required"})
		return
	}

	// Save to a private temp file first because we need to inspect the APK;
	// the hash is computed while copying so the file is only read once.
	tempPath, sum, err := saveTemp(file, h.TmpDir)
	if err != nil {
		internalError(c, err)
		return
	}
	defer os.Remove(tempPath)

	// Extract version information from APK
	info, err := apk_util.Read(tempPath)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid APK: " + err.Error()})
		return
	}

	// Tablets only see the release with the highest version code, so an older or equal one would never be offered
	latest, err := h.latestRelease()
	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
		internalError(c, err)
		return
	}
	if latest != nil && int64(info.VersionCode) <= latest.VersionCode {
		c.JSON(http.StatusConflict, gin.H{
			"error": fmt.Sprintf("version code %d must be higher than the latest release (%s, code %d)",
				info.VersionCode, latest.Version, latest.VersionCode),
		})
		return
	}

	// versionName comes from the uploaded file, so keep it from escaping the upload directory
	filename := "app-" + safeName(info.Version) + ".apk"
	path := filepath.Join(h.UploadDir, filename)

	// Prevent overwriting an existing release
	if _, err := os.Stat(path); err == nil {
		c.JSON(http.StatusConflict, gin.H{"error": "version already exists"})
		return
	}

	if err := moveFile(tempPath, path); err != nil {
		if errors.Is(err, fs.ErrExist) {
			c.JSON(http.StatusConflict, gin.H{"error": "version already exists"})
			return
		}
		internalError(c, err)
		return
	}

	release := models.Release{
		Version:     info.Version,
		VersionCode: int64(info.VersionCode),
		APKFile:     filename,
		Notes:       notes,
		Mandatory:   mandatory,
		SHA256:      sum,
	}

	if err := h.DB.Create(&release).Error; err != nil {

		// cleanup uploaded file if DB fails
		os.Remove(path)

		// A concurrent upload of the same version won the race
		if errors.Is(err, gorm.ErrDuplicatedKey) {
			c.JSON(http.StatusConflict, gin.H{"error": "version already exists"})
			return
		}

		internalError(c, err)
		return
	}

	c.JSON(http.StatusOK, release)
}

func (h *Handler) DeleteRelease(c *gin.Context) {

	id, err := strconv.ParseUint(c.Param("id"), 10, 64)
	if err != nil {
		c.JSON(http.StatusNotFound, gin.H{"error": "Not found"})
		return
	}

	var release models.Release

	if err := h.DB.First(&release, id).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			c.JSON(http.StatusNotFound, gin.H{"error": "Not found"})
			return
		}
		internalError(c, err)
		return
	}

	// Remove the row first: a leftover file is harmless, a row pointing at a missing file is not
	if err := h.DB.Delete(&release).Error; err != nil {
		internalError(c, err)
		return
	}

	if err := os.Remove(filepath.Join(h.UploadDir, release.APKFile)); err != nil && !errors.Is(err, os.ErrNotExist) {
		log.Printf("release %d deleted but removing %s failed: %v", release.ID, release.APKFile, err)
	}

	c.JSON(http.StatusOK, gin.H{"success": true})
}

func internalError(c *gin.Context, err error) {
	log.Printf("%s %s: %v", c.Request.Method, c.Request.URL.Path, err)
	c.JSON(http.StatusInternalServerError, gin.H{"error": "internal server error"})
}

var unsafeChars = regexp.MustCompile(`[^A-Za-z0-9._+-]`)

func safeName(s string) string {
	s = unsafeChars.ReplaceAllString(s, "_")
	if s == "" || s == "." || s == ".." {
		s = "_"
	}
	return s
}