package imagerequest

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"strings"
)

// VariantKey is a SHA256 hash identifying a specific image variant (hex-encoded).
type VariantKey string

// CacheKey generates a unique key for a request variant.
// Format: sha256(host:path:query:width:height:format:quality:fit_mode)
// The path and query go through escapePercentAndColon, so that a ":" in
// either cannot be taken for the one between them.
func CacheKey(req *Request) VariantKey {
	data := fmt.Sprintf("%s:%s:%s:%d:%d:%s:%d:%s",
		req.Source.Host,
		escapePercentAndColon(req.Source.Path),
		escapePercentAndColon(req.Source.Query),
		req.Transform.Size.Width,
		req.Transform.Size.Height,
		req.Transform.Format,
		req.Transform.Quality,
		req.Transform.FitMode,
	)
	h := sha256.Sum256([]byte(data))

	return VariantKey(hex.EncodeToString(h[:]))
}

// escapePercentAndColon returns s with each "%" written as "%25" and each
// ":" as "%3A", so that the result holds no ":".
func escapePercentAndColon(s string) string {
	s = strings.ReplaceAll(s, "%", "%25")

	return strings.ReplaceAll(s, ":", "%3A")
}