// Copyright 2021 MengYX. All rights reserved.
//
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in https://go.dev/LICENSE.

// TeaCipher is a typescript port to golang.org/x/crypto/tea

// Package tea implements the TEA algorithm, as defined in Needham and
// Wheeler's 1994 technical report, “TEA, a Tiny Encryption Algorithm”. See
// http://www.cix.co.uk/~klockstone/tea.pdf for details.
//
// TEA is a legacy cipher and its short block size makes it vulnerable to
// birthday bound attacks (see https://sweet32.info). It should only be used
// where compatibility with legacy systems, not security, is the goal.

export class TeaCipher {
    // BlockSize is the size of a TEA block, in bytes.
    static readonly BlockSize = 8;

    // KeySize is the size of a TEA key, in bytes.
    static readonly KeySize = 16;

    // delta is the TEA key schedule constant.
    static readonly delta = 0x9e3779b9;

    // numRounds 64 is the standard number of rounds in TEA.
    static readonly numRounds = 64;

    k0: number
    k1: number
    k2: number
    k3: number
    rounds: number

    constructor(key: Uint8Array, rounds: number = TeaCipher.numRounds) {
        if (key.length != 16) {
            throw Error("incorrect key size")
        }
        if ((rounds & 1) != 0) {
            throw Error("odd number of rounds specified")
        }

        const k = new DataView(key.buffer)
        this.k0 = k.getUint32(0, false)
        this.k1 = k.getUint32(4, false)
        this.k2 = k.getUint32(8, false)
        this.k3 = k.getUint32(12, false)
        this.rounds = rounds
    }


    encrypt(dst: DataView, src: DataView) {
        if (src.byteLength != 8) {
            throw Error("src.byteLength != 8")
        }

        let v0 = src.getUint32(0, false)
        let v1 = src.getUint32(4, false)

        let sum = 0
        for (let i = 0; i < this.rounds / 2; i++) {
            sum = sum + TeaCipher.delta
            v0 += ((v1 << 4) + this.k0) ^ (v1 + sum) ^ ((v1 >>> 5) + this.k1)
            v1 += ((v0 << 4) + this.k2) ^ (v0 + sum) ^ ((v0 >>> 5) + this.k3)
        }

        dst.setUint32(0, v0, false)
        dst.setUint32(4, v1, false)
    }

    decrypt(dst: DataView, src: DataView) {
        let v0 = src.getUint32(0, false)
        let v1 = src.getUint32(4, false)

        let sum = TeaCipher.delta * this.rounds / 2
        for (let i = 0; i < this.rounds / 2; i++) {
            v1 -= ((v0 << 4) + this.k2) ^ (v0 + sum) ^ ((v0 >>> 5) + this.k3)
            v0 -= ((v1 << 4) + this.k0) ^ (v1 + sum) ^ ((v1 >>> 5) + this.k1)
            sum -= TeaCipher.delta
        }
        dst.setUint32(0, v0, false)
        dst.setUint32(4, v1, false)
    }
}