package media

import (
	"bytes"
	"encoding/base64"
	"fmt"
	"image/png"

	"github.com/davidbyttow/govips/v2/vips"
	thumbhash "go.n16f.net/thumbhash"
)

// ImageInfo returns the pixel dimensions and a base64-encoded thumbhash for
// the image at path. The thumbhash is generated from a ≤100px thumbnail so
// it is fast regardless of the original size.
func ImageInfo(path string) (width, height int, thumbhashB64 string, err error) {
	img, err := vips.NewImageFromFile(path)
	if err != nil {
		return 0, 0, "", fmt.Errorf("load %s: %w", path, err)
	}
	defer img.Close()

	width = img.Width()
	height = img.Height()

	const maxThumbDim = 100
	if width > maxThumbDim || height > maxThumbDim {
		scale := float64(maxThumbDim) / float64(max(width, height))
		if err := img.Resize(scale, vips.KernelLanczos3); err != nil {
			return width, height, "", fmt.Errorf("resize for thumbhash: %w", err)
		}
	}

	pngBytes, _, err := img.ExportPng(vips.NewPngExportParams())
	if err != nil {
		return width, height, "", fmt.Errorf("export png for thumbhash: %w", err)
	}

	goImg, err := png.Decode(bytes.NewReader(pngBytes))
	if err != nil {
		return width, height, "", fmt.Errorf("decode png for thumbhash: %w", err)
	}

	hash := thumbhash.EncodeImage(goImg)
	return width, height, base64.StdEncoding.EncodeToString(hash), nil
}

// ConvertAndResize loads the image at src, optionally resizes it to width pixels
// wide (maintaining aspect ratio), and exports it in the requested format.
//
// width <= 0 means no resize. format must be "webp" or "jpeg".
func ConvertAndResize(src string, width int, format string) ([]byte, error) {
	img, err := vips.NewImageFromFile(src)
	if err != nil {
		return nil, fmt.Errorf("load image %s: %w", src, err)
	}
	defer img.Close()

	if width > 0 && width < img.Width() {
		scale := float64(width) / float64(img.Width())
		if err := img.Resize(scale, vips.KernelLanczos3); err != nil {
			return nil, fmt.Errorf("resize: %w", err)
		}
	}

	switch format {
	case "webp":
		buf, _, err := img.ExportWebp(vips.NewWebpExportParams())
		if err != nil {
			return nil, fmt.Errorf("export webp: %w", err)
		}
		return buf, nil
	case "jpeg":
		buf, _, err := img.ExportJpeg(vips.NewJpegExportParams())
		if err != nil {
			return nil, fmt.Errorf("export jpeg: %w", err)
		}
		return buf, nil
	default:
		return nil, fmt.Errorf("unsupported format %q: must be webp or jpeg", format)
	}
}