h0 = 0x67452301
h1 = 0xEFCDAB89
h2 = 0x98BADCFE
h3 = 0x10325476
h4 = 0xC3D2E1F0

for t in range(0, 80):
    temp = LEFT_ROTATE(a, 5) + f(t, b, c, d) + e + K(t) + W[t]
    e = d
    d = c
    c = LEFT_ROTATE(b, 30)
    b = a
    a = temp

h0 = (h0 + a) & 0xFFFFFFFF
h1 = (h1 + b) & 0xFFFFFFFF  
h2 = (h2 + c) & 0xFFFFFFFF
h3 = (h3 + d) & 0xFFFFFFFF
h4 = (h4 + e) & 0xFFFFFFFF

package main

import (
	"encoding/binary"
	"fmt"
)

// SHA1 结构体
type SHA1 struct {
	h [5]uint32
}

// 初始化SHA1常量
func NewSHA1() *SHA1 {
	return &SHA1{
		h: [5]uint32{
			0x67452301,
			0xEFCDAB89,
			0x98BADCFE,
			0x10325476,
			0xC3D2E1F0,
		},
	}
}

// 填充消息
func padMessage(message []byte) []byte {
	originalLength := len(message)
	originalBitLength := uint64(originalLength * 8)

	// 添加1比特（0x80字节）
	padded := append(message, 0x80)

	// 填充0直到长度满足 (长度 % 64 == 56)
	for len(padded)%64 != 56 {
		padded = append(padded, 0x00)
	}

	// 添加原始消息长度的64位表示（大端序）
	lengthBytes := make([]byte, 8)
	binary.BigEndian.PutUint64(lengthBytes, originalBitLength)
	padded = append(padded, lengthBytes...)

	return padded
}

// 循环左移
func leftRotate(n uint32, shift uint) uint32 {
	return (n << shift) | (n >> (32 - shift))
}

// 主要的SHA1处理函数
func (s *SHA1) Process(chunk []byte) {
	if len(chunk) != 64 {
		panic("chunk size must be 64 bytes")
	}

	// 将512位块分成16个32位字
	var w [80]uint32
	for i := 0; i < 16; i++ {
		w[i] = binary.BigEndian.Uint32(chunk[i*4 : (i+1)*4])
	}

	// 扩展16个字到80个字
	for i := 16; i < 80; i++ {
		w[i] = leftRotate(w[i-3]^w[i-8]^w[i-14]^w[i-16], 1)
	}

	// 初始化工作变量
	a, b, c, d, e := s.h[0], s.h[1], s.h[2], s.h[3], s.h[4]

	// 主循环
	for i := 0; i < 80; i++ {
		var f, k uint32

		switch {
		case i < 20:
			f = (b & c) | (^b & d)
			k = 0x5A827999
		case i < 40:
			f = b ^ c ^ d
			k = 0x6ED9EBA1
		case i < 60:
			f = (b & c) | (b & d) | (c & d)
			k = 0x8F1BBCDC
		default:
			f = b ^ c ^ d
			k = 0xCA62C1D6
		}

		temp := leftRotate(a, 5) + f + e + k + w[i]
		e = d
		d = c
		c = leftRotate(b, 30)
		b = a
		a = temp
	}

	// 添加到当前哈希值
	s.h[0] += a
	s.h[1] += b
	s.h[2] += c
	s.h[3] += d
	s.h[4] += e
}

// 计算SHA1哈希
func (s *SHA1) Sum(message []byte) [20]byte {
	// 重置初始哈希值
	s.h = [5]uint32{
		0x67452301,
		0xEFCDAB89,
		0x98BADCFE,
		0x10325476,
		0xC3D2E1F0,
	}

	// 填充消息
	padded := padMessage(message)

	// 处理每个512位块
	for i := 0; i < len(padded); i += 64 {
		s.Process(padded[i : i+64])
	}

	// 将哈希值转换为字节数组
	var result [20]byte
	for i, h := range s.h {
		binary.BigEndian.PutUint32(result[i*4:(i+1)*4], h)
	}

	return result
}

// 将字节数组转换为十六进制字符串
func bytesToHex(b [20]byte) string {
	const hexChars = "0123456789abcdef"
	var result [40]byte
	for i, v := range b {
		result[i*2] = hexChars[v>>4]
		result[i*2+1] = hexChars[v&0x0F]
	}
	return string(result[:])
}