package imgcache

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"sync"

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

// vipsOnce ensures vips is initialized exactly once.
var vipsOnce sync.Once

// initVips initializes libvips with quiet logging.
func initVips() {
	vipsOnce.Do(func() {
		vips.LoggingSettings(nil, vips.LogLevelError)
		vips.Startup(nil)
	})
}

// MaxInputDimension is the maximum allowed width or height for input images.
// Images larger than this are rejected to prevent DoS via decompression bombs.
const MaxInputDimension = 8192

// ErrInputTooLarge is returned when input image dimensions exceed MaxInputDimension.
var ErrInputTooLarge = errors.New("input image dimensions exceed maximum")

// ErrUnsupportedOutputFormat is returned when the requested output format is not supported.
var ErrUnsupportedOutputFormat = errors.New("unsupported output format")

// ImageProcessor implements the Processor interface using libvips via govips.
type ImageProcessor struct{}

// NewImageProcessor creates a new image processor.
func NewImageProcessor() *ImageProcessor {
	initVips()
	return &ImageProcessor{}
}

// Process transforms an image according to the request.
func (p *ImageProcessor) Process(
	_ context.Context,
	input io.Reader,
	req *ImageRequest,
) (*ProcessResult, error) {
	// Read input
	data, err := io.ReadAll(input)
	if err != nil {
		return nil, fmt.Errorf("failed to read input: %w", err)
	}

	// Decode image
	img, err := vips.NewImageFromBuffer(data)
	if err != nil {
		return nil, fmt.Errorf("failed to decode image: %w", err)
	}
	defer img.Close()

	// Get original dimensions
	origWidth := img.Width()
	origHeight := img.Height()

	// Detect input format
	inputFormat := p.detectFormat(img)

	// Validate input dimensions to prevent DoS via decompression bombs
	if origWidth > MaxInputDimension || origHeight > MaxInputDimension {
		return nil, ErrInputTooLarge
	}

	// Determine target dimensions
	targetWidth := req.Size.Width
	targetHeight := req.Size.Height

	// Handle dimension calculation
	if targetWidth == 0 && targetHeight == 0 {
		// Both are 0: keep original size
		targetWidth = origWidth
		targetHeight = origHeight
	} else if targetWidth == 0 {
		// Only height specified: calculate width proportionally
		targetWidth = origWidth * targetHeight / origHeight
	} else if targetHeight == 0 {
		// Only width specified: calculate height proportionally
		targetHeight = origHeight * targetWidth / origWidth
	}

	// Resize if needed
	if targetWidth != origWidth || targetHeight != origHeight {
		if err := p.resize(img, targetWidth, targetHeight, req.FitMode); err != nil {
			return nil, fmt.Errorf("failed to resize: %w", err)
		}
	}

	// Determine output format
	outputFormat := req.Format
	if outputFormat == FormatOriginal || outputFormat == "" {
		outputFormat = p.formatFromString(inputFormat)
	}

	// Encode to target format
	output, err := p.encode(img, outputFormat, req.Quality)
	if err != nil {
		return nil, fmt.Errorf("failed to encode: %w", err)
	}

	return &ProcessResult{
		Content:       io.NopCloser(bytes.NewReader(output)),
		ContentLength: int64(len(output)),
		ContentType:   ImageFormatToMIME(outputFormat),
		Width:         img.Width(),
		Height:        img.Height(),
		InputWidth:    origWidth,
		InputHeight:   origHeight,
		InputFormat:   inputFormat,
	}, nil
}

// SupportedInputFormats returns MIME types this processor can read.
func (p *ImageProcessor) SupportedInputFormats() []string {
	return []string{
		string(MIMETypeJPEG),
		string(MIMETypePNG),
		string(MIMETypeGIF),
		string(MIMETypeWebP),
		string(MIMETypeAVIF),
	}
}

// SupportedOutputFormats returns formats this processor can write.
func (p *ImageProcessor) SupportedOutputFormats() []ImageFormat {
	return []ImageFormat{
		FormatJPEG,
		FormatPNG,
		FormatGIF,
		FormatWebP,
		FormatAVIF,
	}
}

// detectFormat returns the format string from a vips image.
func (p *ImageProcessor) detectFormat(img *vips.ImageRef) string {
	format := img.Format()
	switch format {
	case vips.ImageTypeJPEG:
		return "jpeg"
	case vips.ImageTypePNG:
		return "png"
	case vips.ImageTypeGIF:
		return "gif"
	case vips.ImageTypeWEBP:
		return "webp"
	case vips.ImageTypeAVIF, vips.ImageTypeHEIF:
		return "avif"
	default:
		return "unknown"
	}
}

// resize resizes the image according to the fit mode.
func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMode) error {
	switch fit {
	case FitCover, "":
		// Resize and crop to fill exact dimensions (default)
		return img.Thumbnail(width, height, vips.InterestingCentre)

	case FitContain:
		// Resize to fit within dimensions, maintaining aspect ratio
		// Calculate target dimensions maintaining aspect ratio
		imgW, imgH := img.Width(), img.Height()
		scaleW := float64(width) / float64(imgW)
		scaleH := float64(height) / float64(imgH)
		scale := min(scaleW, scaleH)
		newW := int(float64(imgW) * scale)
		newH := int(float64(imgH) * scale)
		return img.Thumbnail(newW, newH, vips.InterestingNone)

	case FitFill:
		// Resize to exact dimensions (may distort) - use ThumbnailWithSize with Force
		return img.ThumbnailWithSize(width, height, vips.InterestingNone, vips.SizeForce)

	case FitInside:
		// Same as contain, but only shrink
		if img.Width() <= width && img.Height() <= height {
			return nil // Already fits
		}
		imgW, imgH := img.Width(), img.Height()
		scaleW := float64(width) / float64(imgW)
		scaleH := float64(height) / float64(imgH)
		scale := min(scaleW, scaleH)
		newW := int(float64(imgW) * scale)
		newH := int(float64(imgH) * scale)
		return img.Thumbnail(newW, newH, vips.InterestingNone)

	case FitOutside:
		// Resize so smallest dimension fits, may exceed target on other dimension
		imgW, imgH := img.Width(), img.Height()
		scaleW := float64(width) / float64(imgW)
		scaleH := float64(height) / float64(imgH)
		scale := max(scaleW, scaleH)
		newW := int(float64(imgW) * scale)
		newH := int(float64(imgH) * scale)
		return img.Thumbnail(newW, newH, vips.InterestingNone)

	default:
		return fmt.Errorf("%w: %s", ErrInvalidFitMode, fit)
	}
}

const defaultQuality = 85

// encode encodes an image to the specified format.
func (p *ImageProcessor) encode(img *vips.ImageRef, format ImageFormat, quality int) ([]byte, error) {
	if quality <= 0 {
		quality = defaultQuality
	}

	var params vips.ExportParams

	switch format {
	case FormatJPEG:
		params = vips.ExportParams{
			Format:  vips.ImageTypeJPEG,
			Quality: quality,
		}

	case FormatPNG:
		params = vips.ExportParams{
			Format: vips.ImageTypePNG,
		}

	case FormatGIF:
		params = vips.ExportParams{
			Format: vips.ImageTypeGIF,
		}

	case FormatWebP:
		params = vips.ExportParams{
			Format:  vips.ImageTypeWEBP,
			Quality: quality,
		}

	case FormatAVIF:
		params = vips.ExportParams{
			Format:  vips.ImageTypeAVIF,
			Quality: quality,
		}

	default:
		return nil, fmt.Errorf("unsupported output format: %s", format)
	}

	output, _, err := img.Export(&params)
	if err != nil {
		return nil, err
	}

	return output, nil
}

// formatFromString converts a format string to ImageFormat.
func (p *ImageProcessor) formatFromString(format string) ImageFormat {
	switch format {
	case "jpeg":
		return FormatJPEG
	case "png":
		return FormatPNG
	case "gif":
		return FormatGIF
	case "webp":
		return FormatWebP
	case "avif":
		return FormatAVIF
	default:
		return FormatJPEG
	}
}