package imageproc

import (
	"bytes"
	"context"
	"crypto/sha1"
	"encoding/hex"
	"fmt"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"io"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"

	_ "golang.org/x/image/bmp"
	_ "golang.org/x/image/tiff"
	_ "golang.org/x/image/webp"
)

type LoadedImage struct {
	Image      image.Image
	Format     string
	SourcePath string
	FromCache  bool
}

func LoadImage(ctx context.Context, source, cacheDir string, client *http.Client) (*LoadedImage, error) {
	if strings.TrimSpace(source) == "" {
		return nil, fmt.Errorf("empty image source")
	}
	if isHTTPURL(source) {
		return loadRemoteImage(ctx, source, cacheDir, client)
	}
	return loadLocalImage(source)
}

func isHTTPURL(raw string) bool {
	u, err := url.Parse(raw)
	return err == nil && (u.Scheme == "http" || u.Scheme == "https")
}

func loadLocalImage(path string) (*LoadedImage, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("open image: %w", err)
	}
	defer file.Close()
	img, format, err := image.Decode(file)
	if err != nil {
		return nil, fmt.Errorf("decode image: %w", err)
	}
	return &LoadedImage{Image: img, Format: format, SourcePath: path}, nil
}

func loadRemoteImage(ctx context.Context, source, cacheDir string, client *http.Client) (*LoadedImage, error) {
	if client == nil {
		client = http.DefaultClient
	}
	if err := os.MkdirAll(cacheDir, 0o755); err != nil {
		return nil, fmt.Errorf("create image cache: %w", err)
	}

	cachePath := filepath.Join(cacheDir, cacheFileName(source))
	if data, err := os.ReadFile(cachePath); err == nil {
		img, format, err := image.Decode(bytes.NewReader(data))
		if err == nil {
			return &LoadedImage{Image: img, Format: format, SourcePath: cachePath, FromCache: true}, nil
		}
		_ = os.Remove(cachePath)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, source, nil)
	if err != nil {
		return nil, fmt.Errorf("create image request: %w", err)
	}
	req.Header.Set("User-Agent", "MaterialAnalyzer/1.0 (+offline preprocessing)")
	req.Header.Set("Accept", "image/webp,image/jpeg,image/png,image/gif,*/*;q=0.1")

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("download image: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("download image returned HTTP %d", resp.StatusCode)
	}

	data, err := io.ReadAll(io.LimitReader(resp.Body, 25<<20))
	if err != nil {
		return nil, fmt.Errorf("read image response: %w", err)
	}
	if len(data) == 0 {
		return nil, fmt.Errorf("downloaded image is empty")
	}
	img, format, err := image.Decode(bytes.NewReader(data))
	if err != nil {
		return nil, fmt.Errorf("decode downloaded image: %w", err)
	}
	if err := os.WriteFile(cachePath, data, 0o644); err != nil {
		return nil, fmt.Errorf("write image cache: %w", err)
	}
	return &LoadedImage{Image: img, Format: format, SourcePath: cachePath}, nil
}

func cacheFileName(source string) string {
	sum := sha1.Sum([]byte(source))
	ext := ".img"
	if u, err := url.Parse(source); err == nil {
		if candidate := strings.ToLower(filepath.Ext(u.Path)); isImageExt(candidate) {
			ext = candidate
		}
	}
	return hex.EncodeToString(sum[:]) + ext
}

func isImageExt(ext string) bool {
	switch ext {
	case ".jpg", ".jpeg", ".png", ".gif", ".webp", ".bmp", ".tif", ".tiff":
		return true
	default:
		return false
	}
}