package command

import (
	"fmt"
	"net/url"
	"sort"
	"strings"
)

type queryPair struct {
	key   string
	value string
}

// awsQueryEscape applies the AWS SigV4 percent-encoding rules.
// - Spaces must be encoded as %20 (not '+')
// - '~' must not be escaped
func awsQueryEscape(s string) string {
	esc := url.QueryEscape(s)
	esc = strings.ReplaceAll(esc, "+", "%20")
	esc = strings.ReplaceAll(esc, "%7E", "~")
	return esc
}

// canonicalizeQuery converts a raw query string into an AWS SigV4 canonical query string.
// It percent-encodes keys/values, sorts them, and joins as k=v pairs.
func canonicalizeQuery(raw string) (string, error) {
	if raw == "" {
		return "", nil
	}

	// Treat bare subresource values like "cors" as "cors=".
	if !strings.Contains(raw, "=") && !strings.HasSuffix(raw, "=") {
		raw += "="
	}

	// Parse manually instead of url.ParseQuery so we don't treat '+' as space.
	// S3 continuation tokens are opaque and may contain literal '+' characters.
	pairs := make([]queryPair, 0)
	for _, part := range strings.Split(raw, "&") {
		if part == "" {
			continue
		}
		kv := strings.SplitN(part, "=", 2)
		keyRaw := kv[0]
		valRaw := ""
		if len(kv) == 2 {
			valRaw = kv[1]
		}

		key, err := url.PathUnescape(keyRaw)
		if err != nil {
			return "", fmt.Errorf("error unescaping query key '%s': %w", keyRaw, err)
		}
		val, err := url.PathUnescape(valRaw)
		if err != nil {
			return "", fmt.Errorf("error unescaping query value for key '%s': %w", keyRaw, err)
		}
		pairs = append(pairs, queryPair{key: key, value: val})
	}

	sort.Slice(pairs, func(i, j int) bool {
		escapedKeyI, escapedKeyJ := awsQueryEscape(pairs[i].key), awsQueryEscape(pairs[j].key)
		if escapedKeyI != escapedKeyJ {
			return escapedKeyI < escapedKeyJ
		}
		escapedValueI, escapedValueJ := awsQueryEscape(pairs[i].value), awsQueryEscape(pairs[j].value)
		return escapedValueI < escapedValueJ
	})

	var b strings.Builder
	for i, p := range pairs {
		if i > 0 {
			b.WriteByte('&')
		}
		b.WriteString(awsQueryEscape(p.key))
		b.WriteByte('=')
		b.WriteString(awsQueryEscape(p.value))
	}
	return b.String(), nil
}