// SPDX-License-Identifier: Apache-2.0
package main

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/http/httputil"
	"os"
	"regexp"
	"strconv"
	"time"

	"github.com/davidbyttow/govips/v2/vips"
)

type Handler struct {
	// Port is the port to serve on.
	Port int `json:"port"`
	// Whether to log debug messages
	Debug bool `json:"debug"`
	// Patterns is an array of image URL patterns to serve.
	Patterns []pattern `json:"patterns"`
	// ProxyTarget is the host that requests for the default image size will be rewritten to.
	ProxyTarget string `json:"proxy_target"`
	proxy       *httputil.ReverseProxy
}

type pattern struct {
	Input       string `json:"input"`
	Output      string `json:"output"`
	CacheKey    string `json:"cache_key"`
	ContentType string `json:"content_type"`
	Sizes       []int  `json:"sizes"`
	regexp      *regexp.Regexp
}

func (p *pattern) acceptsSize(size int) bool {
	for i := range p.Sizes {
		if p.Sizes[i] == size {
			return true
		}
	}
	return false
}

// The proxy handler entrypoint. This handles rewriting the URL to the original image, and
func (hn *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var pattern *pattern
	for i := range hn.Patterns {
		if hn.Patterns[i].regexp.MatchString(r.URL.Path) {
			pattern = &hn.Patterns[i]
			break
		}
	}

	if pattern == nil {
		http.Error(w, "Invalid image URL", http.StatusBadRequest)
		return
	}

	var size int
	if s := r.FormValue("size"); s != "" {
		i, err := strconv.Atoi(s)
		if err != nil {
			http.Error(w, "Invalid image size", http.StatusBadRequest)
			return
		}
		size = i
	} else {
		size = pattern.Sizes[0]
	}

	if !pattern.acceptsSize(size) {
		http.Error(w, "Invalid image size", http.StatusBadRequest)
		return
	}

	// If the requested size is the default, just proxy the request
	if size == pattern.Sizes[0] {
		if hn.Debug {
			log.Printf("[DEBUG] Proxying image %q as it has default size of %v", r.URL.Path, size)
		}
		hn.proxy.ServeHTTP(w, r)
		return
	}

	url := pattern.regexp.ReplaceAllString(r.URL.Path, pattern.Output)
	cacheKey := pattern.regexp.ReplaceAllString(r.URL.Path, pattern.CacheKey)

	if hn.Debug {
		log.Printf("[DEBUG] Resizing image %q to size %v and serving it", r.URL.Path, size)
	}

	hn.proxyImage(r.Context(), w, cacheKey, url, pattern.ContentType, size)
}

func (hn *Handler) proxyImage(ctx context.Context, w http.ResponseWriter, cacheKey, url, contentType string, size int) {
	// Check if we've cached the image
	cacheName := fmt.Sprintf("cache/%v/%v", size, cacheKey)
	cacheFile, err := os.Open(cacheName)
	if err == nil {
		defer func() {
			err := cacheFile.Close()
			if err != nil {
				log.Printf("error closing file %q: %v", cacheName, err)
			}
		}()

		fi, err := cacheFile.Stat()
		if err != nil {
			log.Printf("error getting file info for file %q: %v", cacheName, err)
			return
		}

		// If so, just copy it to the output
		w.Header().Add("Content-Type", contentType)
		w.Header().Add("Content-Length", strconv.FormatInt(fi.Size(), 10))
		_, err = io.Copy(w, cacheFile)
		if err != nil {
			log.Printf("error serving cached file %q: %v", cacheName, err)
		}
		return
	} else {
		if !errors.Is(err, os.ErrNotExist) {
			log.Printf("error opening cache file %q: %v", cacheName, err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
	}

	// Otherwise, fall back to fetching the image + resizing it
	start := time.Now()

	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
	if err != nil {
		log.Printf("creating request: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		log.Printf("executing request: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	switch resp.StatusCode {
	case http.StatusOK:
	case http.StatusNotFound:
		http.Error(w, "Not found", http.StatusNotFound)
		return
	default:
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	defer resp.Body.Close()

	image, err := vips.NewImageFromReader(resp.Body)
	if err != nil {
		log.Printf("creating vips image: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	err = image.ThumbnailWithSize(size, size, vips.InterestingCentre, vips.SizeBoth)
	if err != nil {
		log.Printf("resizing vips image: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	out, _, err := export(image, contentType)
	if err != nil {
		log.Printf("exporting vips image: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	if hn.Debug {
		log.Printf("resized image %q in %v", cacheKey, time.Since(start).Round(time.Microsecond))
	}

	go func(b []byte) {
		err = os.WriteFile(cacheName, b, 0o644)
		if err != nil {
			log.Printf("writing image to cache: %v", err)
			return
		}
	}(out)

	w.Header().Add("Content-Type", contentType)
	w.Header().Add("Content-Length", strconv.Itoa(len(out)))
	_, err = w.Write(out)
	if err != nil {
		log.Printf("error writing resized file to response: %v", err)
	}
}

func export(image *vips.ImageRef, contentType string) ([]byte, *vips.ImageMetadata, error) {
	switch contentType {
	case "image/webp":
		params := vips.NewWebpExportParams()
		params.Quality = 90
		return image.ExportWebp(params)
	case "image/jpeg":
		params := vips.NewJpegExportParams()
		params.Quality = 90
		return image.ExportJpeg(params)
	case "image/png":
		params := vips.NewPngExportParams()
		params.Quality = 90
		return image.ExportPng(params)
	case "image/gif":
		params := vips.NewGifExportParams()
		params.Quality = 90
		return image.ExportGIF(params)
	}

	return nil, nil, errors.New("invalid image content type")
}