// NOTE: This middleware is not needed for most applications.
// Browsers and typical HTTP clients do not compress request bodies,
// so decompressing requests is unnecessary unless you explicitly expect
// gzip-compressed payloads from known clients.

package middleware

import (
	"compress/gzip"
	"io"
	"net/http"
	"strings"
)

// DecompressOptions configures the decompression middleware
type DecompressOptions struct {
	// MaxSize is the maximum size of the decompressed body in bytes
	// Zero means no limit
	MaxSize int64
}

// DefaultDecompressOptions provides sensible default options
func DefaultDecompressOptions() *DecompressOptions {
	return &DecompressOptions{
		MaxSize: 10 << 20, // 10MB
	}
}

// Decompress creates a middleware that decompresses HTTP requests with gzip content encoding
func Decompress(opts *DecompressOptions) Middleware {
	// Use default options if none provided
	if opts == nil {
		opts = DefaultDecompressOptions()
	}

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Check if the request has Content-Encoding header
			contentEncoding := r.Header.Get("Content-Encoding")

			// If not compressed, pass through
			if contentEncoding == "" {
				next.ServeHTTP(w, r)
				return
			}

			// Check if gzip encoded
			if strings.Contains(contentEncoding, "gzip") {
				// Create a gzip reader
				gz, err := gzip.NewReader(r.Body)
				if err != nil {
					http.Error(w, "Invalid gzip body", http.StatusBadRequest)
					return
				}
				defer gz.Close()

				// Add limit reader if max size is specified
				var bodyReader io.Reader = gz
				if opts.MaxSize > 0 {
					bodyReader = io.LimitReader(gz, opts.MaxSize)
				}

				// Replace the body with a decompressed reader
				r.Body = io.NopCloser(bodyReader)

				// Remove the content-encoding header to signal that the body is now decompressed
				r.Header.Del("Content-Encoding")

				// Adjust content length because the body has been decompressed
				r.Header.Del("Content-Length")
			}

			// Call the next handler with the decompressed body
			next.ServeHTTP(w, r)
		})
	}
}

// DecompressDefault creates a middleware that decompresses HTTP requests with default options
func DecompressDefault() Middleware {
	return Decompress(nil)
}