package ws

import (
	"bufio"
	"bytes"
	"fmt"
	"reflect"
	"unsafe"

	"github.com/gobwas/httphead"
)

// SelectFromSlice creates accept function that could be used as Protocol/Extension
// select during upgrade.
func SelectFromSlice(accept []string) func(string) bool {
	if len(accept) > 16 {
		mp := make(map[string]struct{}, len(accept))
		for _, p := range accept {
			mp[p] = struct{}{}
		}
		return func(p string) bool {
			_, ok := mp[p]
			return ok
		}
	}
	return func(p string) bool {
		for _, ok := range accept {
			if p == ok {
				return true
			}
		}
		return false
	}
}

// SelectEqual creates accept function that could be used as Protocol/Extension
// select during upgrade.
func SelectEqual(v string) func(string) bool {
	return func(p string) bool {
		return v == p
	}
}

func strToBytes(str string) (bts []byte) {
	s := (*reflect.StringHeader)(unsafe.Pointer(&str))
	b := (*reflect.SliceHeader)(unsafe.Pointer(&bts))
	b.Data = s.Data
	b.Len = s.Len
	b.Cap = s.Len
	return
}

func btsToString(bts []byte) (str string) {
	return *(*string)(unsafe.Pointer(&bts))
}

// asciiToInt converts bytes to int.
func asciiToInt(bts []byte) (ret int, err error) {
	// ASCII numbers all start with the high-order bits 0011.
	// If you see that, and the next bits are 0-9 (0000 - 1001) you can grab those
	// bits and interpret them directly as an integer.
	var n int
	if n = len(bts); n < 1 {
		return 0, fmt.Errorf("converting empty bytes to int")
	}
	for i := 0; i < n; i++ {
		if bts[i]&0xf0 != 0x30 {
			return 0, fmt.Errorf("%s is not a numeric character", string(bts[i]))
		}
		ret += int(bts[i]&0xf) * pow(10, n-i-1)
	}
	return ret, nil
}

// pow for integers implementation.
// See Donald Knuth, The Art of Computer Programming, Volume 2, Section 4.6.3
func pow(a, b int) int {
	p := 1
	for b > 0 {
		if b&1 != 0 {
			p *= a
		}
		b >>= 1
		a *= a
	}
	return p
}

func bsplit3(bts []byte, sep byte) (b1, b2, b3 []byte) {
	a := bytes.IndexByte(bts, sep)
	b := bytes.IndexByte(bts[a+1:], sep)
	if a == -1 || b == -1 {
		return bts, nil, nil
	}
	b += a + 1
	return bts[:a], bts[a+1 : b], bts[b+1:]
}

func btrim(bts []byte) []byte {
	var i, j int
	for i = 0; i < len(bts) && (bts[i] == ' ' || bts[i] == '\t'); {
		i++
	}
	for j = len(bts); j > i && (bts[j-1] == ' ' || bts[j-1] == '\t'); {
		j--
	}
	return bts[i:j]
}

func strHasToken(header, token string) (has bool) {
	return btsHasToken(strToBytes(header), strToBytes(token))
}

func btsHasToken(header, token []byte) (has bool) {
	httphead.ScanTokens(header, func(v []byte) bool {
		has = btsEqualFold(v, token)
		return !has
	})
	return
}

const (
	toLower  = 'a' - 'A'      // for use with OR.
	toUpper  = ^byte(toLower) // for use with AND.
	toLower8 = uint64(toLower) |
		uint64(toLower)<<8 |
		uint64(toLower)<<16 |
		uint64(toLower)<<24 |
		uint64(toLower)<<32 |
		uint64(toLower)<<40 |
		uint64(toLower)<<48 |
		uint64(toLower)<<56
)

// Algorithm below is like standard textproto/CanonicalMIMEHeaderKey, except
// that it operates with slice of bytes and modifies it inplace without copying.
func canonicalizeHeaderKey(k []byte) {
	upper := true
	for i, c := range k {
		if upper && 'a' <= c && c <= 'z' {
			k[i] &= toUpper
		} else if !upper && 'A' <= c && c <= 'Z' {
			k[i] |= toLower
		}
		upper = c == '-'
	}
}

// readLine reads line from br. It reads until '\n' and returns bytes without
// '\n' or '\r\n' at the end.
// It returns err if and only if line does not end in '\n'. Note that read
// bytes returned in any case of error.
//
// It is much like the textproto/Reader.ReadLine() except the thing that it
// returns raw bytes, instead of string. That is, it avoids copying bytes read
// from br.
//
// textproto/Reader.ReadLineBytes() is also makes copy of resulting bytes to be
// safe with future I/O operations on br.
//
// We could control I/O operations on br and do not need to make additional
// copy for safety.
//
// NOTE: it may return copied flag to notify that returned buffer is safe to
// use.
func readLine(br *bufio.Reader) ([]byte, error) {
	var line []byte
	for {
		bts, err := br.ReadSlice('\n')
		if err == bufio.ErrBufferFull {
			// Copy bytes because next read will discard them.
			line = append(line, bts...)
			continue
		}

		// Avoid copy of single read.
		if line == nil {
			line = bts
		} else {
			line = append(line, bts...)
		}

		if err != nil {
			return line, err
		}

		// Size of line is at least 1.
		// In other case bufio.ReadSlice() returns error.
		n := len(line)

		// Cut '\n' or '\r\n'.
		if n > 1 && line[n-2] == '\r' {
			line = line[:n-2]
		} else {
			line = line[:n-1]
		}

		return line, nil
	}
}

// strEqualFold checks s to be case insensitive equal to p.
// Note that p must be only ascii letters. That is, every byte in p belongs to
// range ['a','z'] or ['A','Z'].
func strEqualFold(s, p string) bool {
	return btsEqualFold(strToBytes(s), strToBytes(p))
}

// btsEqualFold checks s to be case insensitive equal to p.
// Note that p must be only ascii letters. That is, every byte in p belongs to
// range ['a','z'] or ['A','Z'].
func btsEqualFold(s, p []byte) bool {
	if len(s) != len(p) {
		return false
	}
	n := len(s)
	// Prepare manual conversion on bytes that not lay in uint64.
	m := n % 8
	for i := 0; i < m; i++ {
		if s[i]|toLower != p[i]|toLower {
			return false
		}
	}
	// Iterate over uint64 parts of s.
	n = (n - m) >> 3
	if n == 0 {
		// There are no more bytes to compare.
		return true
	}

	for i := 0; i < n; i++ {
		x := m + (i << 3)
		av := *(*uint64)(unsafe.Pointer(&s[x]))
		bv := *(*uint64)(unsafe.Pointer(&p[x]))
		if av|toLower8 != bv|toLower8 {
			return false
		}
	}

	return true
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func nonZero(a, b int) int {
	if a != 0 {
		return a
	}
	return b
}
