package dsl

import (
	"bytes"
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"html"
	"math"
	"math/rand"
	"net/url"
	"regexp"
	"strings"
	"time"

	"github.com/Knetic/govaluate"
	"github.com/projectdiscovery/nuclei/v2/internal/collaborator"
	"github.com/projectdiscovery/nuclei/v2/pkg/types"
	"github.com/spaolacci/murmur3"
)

const (
	numbers              = "1234567890"
	letters              = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
	withCutSetArgsSize   = 2
	withBaseRandArgsSize = 3
	withMaxRandArgsSize  = withCutSetArgsSize
)

// HelperFunctions contains the dsl helper functions
func HelperFunctions() map[string]govaluate.ExpressionFunction {
	functions := make(map[string]govaluate.ExpressionFunction)

	functions["len"] = func(args ...interface{}) (interface{}, error) {
		length := len(types.ToString(args[0]))
		return float64(length), nil
	}

	functions["toupper"] = func(args ...interface{}) (interface{}, error) {
		return strings.ToUpper(types.ToString(args[0])), nil
	}

	functions["tolower"] = func(args ...interface{}) (interface{}, error) {
		return strings.ToLower(types.ToString(args[0])), nil
	}

	functions["replace"] = func(args ...interface{}) (interface{}, error) {
		return strings.ReplaceAll(types.ToString(args[0]), types.ToString(args[1]), types.ToString(args[2])), nil
	}

	functions["replace_regex"] = func(args ...interface{}) (interface{}, error) {
		compiled, err := regexp.Compile(types.ToString(args[1]))
		if err != nil {
			return nil, err
		}
		return compiled.ReplaceAllString(types.ToString(args[0]), types.ToString(args[2])), nil
	}

	functions["trim"] = func(args ...interface{}) (interface{}, error) {
		return strings.Trim(types.ToString(args[0]), types.ToString(args[2])), nil
	}

	functions["trimleft"] = func(args ...interface{}) (interface{}, error) {
		return strings.TrimLeft(types.ToString(args[0]), types.ToString(args[1])), nil
	}

	functions["trimright"] = func(args ...interface{}) (interface{}, error) {
		return strings.TrimRight(types.ToString(args[0]), types.ToString(args[1])), nil
	}

	functions["trimspace"] = func(args ...interface{}) (interface{}, error) {
		return strings.TrimSpace(types.ToString(args[0])), nil
	}

	functions["trimprefix"] = func(args ...interface{}) (interface{}, error) {
		return strings.TrimPrefix(types.ToString(args[0]), types.ToString(args[1])), nil
	}

	functions["trimsuffix"] = func(args ...interface{}) (interface{}, error) {
		return strings.TrimSuffix(types.ToString(args[0]), types.ToString(args[1])), nil
	}

	functions["reverse"] = func(args ...interface{}) (interface{}, error) {
		return reverseString(types.ToString(args[0])), nil
	}

	// encoding
	functions["base64"] = func(args ...interface{}) (interface{}, error) {
		sEnc := base64.StdEncoding.EncodeToString([]byte(types.ToString(args[0])))

		return sEnc, nil
	}

	// python encodes to base64 with lines of 76 bytes terminated by new line "\n"
	functions["base64_py"] = func(args ...interface{}) (interface{}, error) {
		sEnc := base64.StdEncoding.EncodeToString([]byte(types.ToString(args[0])))
		return insertInto(sEnc, 76, '\n'), nil
	}

	functions["base64_decode"] = func(args ...interface{}) (interface{}, error) {
		return base64.StdEncoding.DecodeString(types.ToString(args[0]))
	}

	functions["url_encode"] = func(args ...interface{}) (interface{}, error) {
		return url.PathEscape(types.ToString(args[0])), nil
	}

	functions["url_decode"] = func(args ...interface{}) (interface{}, error) {
		return url.PathUnescape(types.ToString(args[0]))
	}

	functions["hex_encode"] = func(args ...interface{}) (interface{}, error) {
		return hex.EncodeToString([]byte(types.ToString(args[0]))), nil
	}

	functions["hex_decode"] = func(args ...interface{}) (interface{}, error) {
		hx, _ := hex.DecodeString(types.ToString(args[0]))
		return string(hx), nil
	}

	functions["html_escape"] = func(args ...interface{}) (interface{}, error) {
		return html.EscapeString(types.ToString(args[0])), nil
	}

	functions["html_unescape"] = func(args ...interface{}) (interface{}, error) {
		return html.UnescapeString(types.ToString(args[0])), nil
	}

	// hashing
	functions["md5"] = func(args ...interface{}) (interface{}, error) {
		hash := md5.Sum([]byte(types.ToString(args[0])))

		return hex.EncodeToString(hash[:]), nil
	}

	functions["sha256"] = func(args ...interface{}) (interface{}, error) {
		h := sha256.New()
		_, err := h.Write([]byte(types.ToString(args[0])))

		if err != nil {
			return nil, err
		}
		return hex.EncodeToString(h.Sum(nil)), nil
	}

	functions["sha1"] = func(args ...interface{}) (interface{}, error) {
		h := sha1.New()
		_, err := h.Write([]byte(types.ToString(args[0])))

		if err != nil {
			return nil, err
		}
		return hex.EncodeToString(h.Sum(nil)), nil
	}

	functions["mmh3"] = func(args ...interface{}) (interface{}, error) {
		return fmt.Sprintf("%d", int32(murmur3.Sum32WithSeed([]byte(types.ToString(args[0])), 0))), nil
	}

	// search
	functions["contains"] = func(args ...interface{}) (interface{}, error) {
		return strings.Contains(types.ToString(args[0]), types.ToString(args[1])), nil
	}

	functions["regex"] = func(args ...interface{}) (interface{}, error) {
		compiled, err := regexp.Compile(types.ToString(args[0]))
		if err != nil {
			return nil, err
		}
		return compiled.MatchString(types.ToString(args[1])), nil
	}

	// random generators
	functions["rand_char"] = func(args ...interface{}) (interface{}, error) {
		chars := letters + numbers
		bad := ""
		if len(args) >= 1 {
			chars = types.ToString(args[0])
		}
		if len(args) >= withCutSetArgsSize {
			bad = types.ToString(args[1])
		}
		chars = trimAll(chars, bad)
		return chars[rand.Intn(len(chars))], nil
	}

	functions["rand_base"] = func(args ...interface{}) (interface{}, error) {
		l := 0
		bad := ""
		base := letters + numbers

		if len(args) >= 1 {
			l = args[0].(int)
		}
		if len(args) >= withCutSetArgsSize {
			bad = types.ToString(args[1])
		}
		if len(args) >= withBaseRandArgsSize {
			base = types.ToString(args[2])
		}
		base = trimAll(base, bad)
		return randSeq(base, l), nil
	}

	functions["rand_text_alphanumeric"] = func(args ...interface{}) (interface{}, error) {
		l := 0
		bad := ""
		chars := letters + numbers

		if len(args) >= 1 {
			l = args[0].(int)
		}
		if len(args) >= withCutSetArgsSize {
			bad = types.ToString(args[1])
		}
		chars = trimAll(chars, bad)
		return randSeq(chars, l), nil
	}

	functions["rand_text_alpha"] = func(args ...interface{}) (interface{}, error) {
		l := 0
		bad := ""
		chars := letters

		if len(args) >= 1 {
			l = args[0].(int)
		}
		if len(args) >= withCutSetArgsSize {
			bad = types.ToString(args[1])
		}
		chars = trimAll(chars, bad)
		return randSeq(chars, l), nil
	}

	functions["rand_text_numeric"] = func(args ...interface{}) (interface{}, error) {
		l := 0
		bad := ""
		chars := numbers

		if len(args) >= 1 {
			l = args[0].(int)
		}
		if len(args) >= withCutSetArgsSize {
			bad = types.ToString(args[1])
		}
		chars = trimAll(chars, bad)
		return randSeq(chars, l), nil
	}

	functions["rand_int"] = func(args ...interface{}) (interface{}, error) {
		min := 0
		max := math.MaxInt32

		if len(args) >= 1 {
			min = args[0].(int)
		}
		if len(args) >= withMaxRandArgsSize {
			max = args[1].(int)
		}
		return rand.Intn(max-min) + min, nil
	}

	// Time Functions
	functions["waitfor"] = func(args ...interface{}) (interface{}, error) {
		seconds := args[0].(float64)
		time.Sleep(time.Duration(seconds) * time.Second)
		return true, nil
	}

	// Collaborator
	functions["collab"] = func(args ...interface{}) (interface{}, error) {
		// check if collaborator contains a specific pattern
		return collaborator.DefaultCollaborator.Has(types.ToString(args[0])), nil
	}
	return functions
}

func reverseString(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}

func trimAll(s, cutset string) string {
	for _, c := range cutset {
		s = strings.ReplaceAll(s, string(c), "")
	}
	return s
}

func randSeq(base string, n int) string {
	b := make([]rune, n)
	for i := range b {
		b[i] = rune(base[rand.Intn(len(base))])
	}
	return string(b)
}

func insertInto(s string, interval int, sep rune) string {
	var buffer bytes.Buffer
	before := interval - 1
	last := len(s) - 1
	for i, char := range s {
		buffer.WriteRune(char)
		if i%interval == before && i != last {
			buffer.WriteRune(sep)
		}
	}
	buffer.WriteRune(sep)
	return buffer.String()
}