package main

import (
	"crypto/sha1"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"strings"
)

var rom = []byte{
	0xA9, 0x16, 0x20, 0xC9, 0xFC, 0x85, 0x2E, 0x20,
	0xFA, 0xFC, 0xA0, 0x24, 0x20, 0xFD, 0xFC, 0xB0,
	0xF9, 0x20, 0xFD, 0xFC, 0xA0, 0x3B, 0x20, 0xEC,
	0xFC, 0x81, 0x3C, 0x45, 0x2E, 0x85, 0x2E, 0x20,
	0xBA, 0xFC, 0xA0, 0x35, 0x90, 0xF0, 0x20, 0xEC,
	0xFC, 0xC5, 0x2E, 0xF0, 0x0D, 0xA9, 0xC5, 0x20,
	0xED, 0xFD, 0xA9, 0xD2, 0x20, 0xED, 0xFD, 0x20,
	0xED, 0xFD, 0xA9, 0x87, 0x4C, 0xED, 0xFD, 0xA5,
	0x48, 0x48, 0xA5, 0x45, 0xA6, 0x46, 0xA4, 0x47,
	0x28, 0x60, 0x85, 0x45, 0x86, 0x46, 0x84, 0x47,
	0x08, 0x68, 0x85, 0x48, 0xBA, 0x86, 0x49, 0xD8,
	0x60, 0x20, 0x84, 0xFE, 0x20, 0x2F, 0xFB, 0x20,
	0x93, 0xFE, 0x20, 0x89, 0xFE, 0xD8, 0x20, 0x3A,
	0xFF, 0xA9, 0xAA, 0x85, 0x33, 0x20, 0x67, 0xFD,
	0x20, 0xC7, 0xFF, 0x20, 0xA7, 0xFF, 0x84, 0x34,
	0xA0, 0x17, 0x88, 0x30, 0xE8, 0xD9, 0xCC, 0xFF,
	0xD0, 0xF8, 0x20, 0xBE, 0xFF, 0xA4, 0x34, 0x4C,
	0x73, 0xFF, 0xA2, 0x03, 0x0A, 0x0A, 0x0A, 0x0A,
	0x0A, 0x26, 0x3E, 0x26, 0x3F, 0xCA, 0x10, 0xF8,
	0xA5, 0x31, 0xD0, 0x06, 0xB5, 0x3F, 0x95, 0x3D,
	0x95, 0x41, 0xE8, 0xF0, 0xF3, 0xD0, 0x06, 0xA2,
	0x00, 0x86, 0x3E, 0x86, 0x3F, 0xB9, 0x00, 0x02,
	0xC8, 0x49, 0xB0, 0xC9, 0x0A, 0x90, 0xD3, 0x69,
	0x88, 0xC9, 0xFA, 0xB0, 0xCD, 0x60, 0xA9, 0xFE,
	0x48, 0xB9, 0xE3, 0xFF, 0x48, 0xA5, 0x31, 0xA0,
	0x00, 0x84, 0x31, 0x60, 0xBC, 0xB2, 0xBE, 0xB2,
	0xEF, 0xC4, 0xB2, 0xA9, 0xBB, 0xA6, 0xA4, 0x06,
	0x95, 0x07, 0x02, 0x05, 0xF0, 0x00, 0xEB, 0x93,
	0xA7, 0xC6, 0x99, 0xB2, 0xC9, 0xBE, 0xC1, 0x35,
	0x8C, 0xC4, 0x96, 0xAF, 0x17, 0x17, 0x2B, 0x1F,
	0x83, 0x7F, 0x5D, 0xCC, 0xB5, 0xFC, 0x17, 0x17,
	0xF5, 0x03, 0xFB, 0x03, 0x62, 0xFA, 0x59, 0xFF,
}

func main() {
	// print40s(tobytes(expand(pad(rom[:0x37]))))
	fmt.Printf("%X\n", sha1.Sum(rom[:0]))
	// fmt.Printf("%X\n", shasum(rom[:0]))
	// fmt.Printf("%X\n", sha1.Sum(rom[:0x37]))
	fmt.Printf("%X\n", shasum(rom[:0x37]))
	fmt.Printf("%X\n", sha1.Sum(rom[:0x100]))
	// fmt.Printf("%X\n", shasum(rom[:0x100]))
}

func print40s(in []byte) {
	for i := 0; i < len(in); i += 20 {
		end := i + 20
		if end > len(in) {
			end = len(in)
		}
		fmt.Println(strings.ToUpper(hex.EncodeToString(in[i:end])))
	}
	fmt.Printf("length: %d 0x%x\n", len(in), len(in))
}

func pad(in []byte) []byte {
	out := make([]byte, len(in))
	copy(out, in)
	out = append(out, 0x80)
	for len(out)%64 != 56 {
		out = append(out, 0)
	}
	l := uint64(len(in)) << 3
	for i := uint(0); i < 8; i++ {
		out = append(out, byte(l>>(56-8*i)))
	}
	return out
}

func tobytes(in []uint32) []byte {
	out := make([]byte, len(in)*4)
	for i, w := range in {
		binary.BigEndian.PutUint32(out[i*4:], w)
	}
	return out
}

func expand(in []byte) []uint32 {
	if len(in) != 64 {
		panic(fmt.Sprintf("expand() expects 64-byte slices as input; got %d", len(in)))
	}
	var w [80]uint32
	for i := 0; i < 16; i++ {
		w[i] = binary.BigEndian.Uint32(in[i*4:])
	}

	for i := 16; i < 80; i++ {
		w[i] = w[i-3] ^ w[i-8] ^ w[i-14] ^ w[i-16]
		w[i] = w[i]<<1 + w[i]>>31
	}

	return w[:]
}

func shasum(in []byte) [20]byte {
	h0 := uint32(0x67452301)
	h1 := uint32(0xEFCDAB89)
	h2 := uint32(0x98BADCFE)
	h3 := uint32(0x10325476)
	h4 := uint32(0xC3D2E1F0)
	in2 := pad(in)
	_ = in2

	_ = h0
	_ = h1
	_ = h2
	_ = h3
	_ = h4

	for j := 0; j < len(in2); j += 64 {
		w := expand(in2[j : j+64])
		if len(w) != 80 {
			panic(fmt.Sprintf("expand should return 80 words; got %d", len(w)))
		}

		a := h0
		b := h1
		c := h2
		d := h3
		e := h4

		var f, k uint32

		for i, wi := range w {
			switch {
			case i <= 19:
				f = d ^ (b & (c ^ d))
				k = 0x5A827999
			case i <= 39:
				f = b ^ c ^ d
				k = 0x6ED9EBA1
			case i <= 59:
				f = (b & c) | (d & (b | c))
				k = 0x8F1BBCDC
			default:
				f = b ^ c ^ d
				k = 0xCA62C1D6
			}

			temp := ((a << 5) | (a >> 27)) + f + e + k + wi
			e = d
			d = c
			c = (b << 30) | (b >> 2)
			b = a
			a = temp
		}

		h0 += a
		h1 += b
		h2 += c
		h3 += d
		h4 += e
	}

	var result [20]byte
	binary.BigEndian.PutUint32(result[0:], h0)
	binary.BigEndian.PutUint32(result[4:], h1)
	binary.BigEndian.PutUint32(result[8:], h2)
	binary.BigEndian.PutUint32(result[12:], h3)
	binary.BigEndian.PutUint32(result[16:], h4)
	return result
}