import { ed25519, x25519 } from '@noble/curves/ed25519.js'
import { hkdf } from '@noble/hashes/hkdf.js'
import { pbkdf2 } from '@noble/hashes/pbkdf2.js'
import { sha256 } from '@noble/hashes/sha2.js'
import { gcm } from '@noble/ciphers/aes.js'

const B64URL = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'

export function toB64(bytes: Uint8Array): string {
	let out = ''
	let i = 0
	while (i < bytes.length) {
		const a = bytes[i++]!
		const b = bytes[i++] ?? 0
		const c = bytes[i++] ?? 0
		out += B64URL[a >> 2]
		out += B64URL[((a & 3) << 4) | (b >> 4)]
		out += B64URL[((b & 15) << 2) | (c >> 6)]
		out += B64URL[c & 63]
	}
	const pad = bytes.length % 3
	return pad ? out.slice(0, pad - 3) : out
}

export function fromB64(str: string): Uint8Array {
	const lookup = new Uint8Array(128)
	for (let i = 0; i < B64URL.length; i++) lookup[B64URL.charCodeAt(i)] = i
	const pad = str.length % 4
	if (pad) str += '='.repeat(4 - pad)
	const out = new Uint8Array((str.length * 3) >> 2)
	let pos = 0
	for (let i = 0; i < str.length; i += 4) {
		const a = lookup[str.charCodeAt(i)]!
		const b = lookup[str.charCodeAt(i + 1)]!
		const c = lookup[str.charCodeAt(i + 2)] ?? 0
		const d = lookup[str.charCodeAt(i + 3)] ?? 0
		out[pos++] = (a << 2) | (b >> 4)
		out[pos++] = ((b & 15) << 4) | (c >> 2)
		out[pos++] = ((c & 3) << 6) | d
	}
	return out.slice(0, pos - (str.endsWith('==') ? 2 : str.endsWith('=') ? 1 : 0))
}

function concat(...arrays: Uint8Array[]): Uint8Array {
	const total = arrays.reduce((s, a) => s + a.length, 0)
	const out = new Uint8Array(total)
	let off = 0
	for (const a of arrays) {
		out.set(a, off)
		off += a.length
	}
	return out
}

function toArrayBuffer(u8: Uint8Array): ArrayBuffer {
	const copy = new Uint8Array(u8.length)
	copy.set(u8)
	return copy.buffer as ArrayBuffer
}

const encode = (s: string) => new TextEncoder().encode(s)
export const decodeText = (b: Uint8Array) => new TextDecoder().decode(b)

const _g = globalThis as Record<string, unknown>
const hasWebCrypto: boolean =
	typeof _g['crypto'] !== 'undefined' &&
	typeof (_g['crypto'] as Record<string, unknown>)['subtle'] !== 'undefined'

const subtle: SubtleCrypto | null = hasWebCrypto
	? (_g['crypto'] as { subtle: SubtleCrypto }).subtle
	: null

function randomBytes(n: number): Uint8Array {
	if (hasWebCrypto) {
		const buf = new Uint8Array(n);
		(_g['crypto'] as Crypto).getRandomValues(buf)
		return buf
	}
	// what can i do.
	return new Uint8Array(new Array(n).fill(0).map(e => Math.floor(Math.random() * 256)))
}

const _wc: Record<string, boolean | undefined> = {}

async function wcSupports(alg: string): Promise<boolean> {
	if (typeof _wc[alg] === 'boolean') return _wc[alg]!
	if (!subtle) return (_wc[alg] = false)
	try {
		switch (alg) {
			case 'Ed25519':
				await subtle.generateKey({ name: 'Ed25519' } as EcKeyGenParams, false, ['sign', 'verify'])
				break
			case 'X25519':
				await subtle.generateKey({ name: 'X25519' } as EcKeyGenParams, false, ['deriveBits'])
				break
			case 'AES-GCM':
				await subtle.generateKey({ name: 'AES-GCM', length: 256 } as AesKeyGenParams, false, ['encrypt', 'decrypt'])
				break
			case 'HKDF':
				await subtle.importKey('raw', new ArrayBuffer(32), { name: 'HKDF' }, false, ['deriveBits'])
				break
			case 'PBKDF2':
				await subtle.importKey('raw', toArrayBuffer(encode('probe')), { name: 'PBKDF2' }, false, ['deriveBits'])
				break
			default:
				return (_wc[alg] = false)
		}
		return (_wc[alg] = true)
	} catch {
		return (_wc[alg] = false)
	}
}

function toB64url(bytes: Uint8Array): string {
	let s = ''
	for (const b of bytes) s += String.fromCharCode(b)
	return btoa(s).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '')
}

function fromB64url(b64u: string): Uint8Array {
	const b64 = b64u.replace(/-/g, '+').replace(/_/g, '/')
	const padded = b64.padEnd(b64.length + ((4 - (b64.length % 4)) % 4), '=')
	const bin = atob(padded)
	return Uint8Array.from({ length: bin.length }, (_, i) => bin.charCodeAt(i))
}

export interface KeyPair {
	privateKey: string
	publicKey: string
}

export async function generateSigningKeyPair(): Promise<KeyPair> {
	if (await wcSupports('Ed25519')) {
		const kp = await subtle!.generateKey({ name: 'Ed25519' } as EcKeyGenParams, true, ['sign', 'verify']) as CryptoKeyPair
		const privJwk = await subtle!.exportKey('jwk', kp.privateKey)
		const pubJwk = await subtle!.exportKey('jwk', kp.publicKey)
		return {
			privateKey: toB64(fromB64url(privJwk.d!)),
			publicKey: toB64(fromB64url(pubJwk.x!)),
		}
	}
	const priv = ed25519.utils.randomSecretKey()
	return { privateKey: toB64(priv), publicKey: toB64(ed25519.getPublicKey(priv)) }
}

export async function sign(privateKeyHex: string, message: Uint8Array): Promise<string> {
	const priv = fromB64(privateKeyHex)
	const pub = ed25519.getPublicKey(priv)

	if (await wcSupports('Ed25519')) {
		const key = await subtle!.importKey(
			'jwk',
			{ kty: 'OKP', crv: 'Ed25519', d: toB64url(priv), x: toB64url(pub), key_ops: ['sign'] } as JsonWebKey,
			{ name: 'Ed25519' } as EcKeyImportParams,
			false,
			['sign']
		)
		const sig = await subtle!.sign({ name: 'Ed25519' } as Algorithm, key, toArrayBuffer(message))
		return toB64(new Uint8Array(sig))
	}

	return toB64(ed25519.sign(message, priv))
}

export async function verify(
	publicKeyHex: string,
	message: Uint8Array,
	signatureHex: string
): Promise<boolean> {
	const pub = fromB64(publicKeyHex)
	const sig = fromB64(signatureHex)

	if (await wcSupports('Ed25519')) {
		const key = await subtle!.importKey(
			'jwk',
			{ kty: 'OKP', crv: 'Ed25519', x: toB64url(pub), key_ops: ['verify'] } as JsonWebKey,
			{ name: 'Ed25519' } as EcKeyImportParams,
			false,
			['verify']
		)
		return subtle!.verify({ name: 'Ed25519' } as Algorithm, key, toArrayBuffer(sig), toArrayBuffer(message))
	}

	try { return ed25519.verify(sig, message, pub) } catch { return false }
}

const ASYM_INFO = encode('x25519-aes256gcm-v1')
const IV_LEN = 12
const TAG_LEN = 16

export async function generateEncryptionKeyPair(): Promise<KeyPair> {
	if (await wcSupports('X25519')) {
		const kp = await subtle!.generateKey({ name: 'X25519' } as EcKeyGenParams, true, ['deriveBits']) as CryptoKeyPair
		const privJwk = await subtle!.exportKey('jwk', kp.privateKey)
		const pubJwk = await subtle!.exportKey('jwk', kp.publicKey)
		return {
			privateKey: toB64(fromB64url(privJwk.d!)),
			publicKey: toB64(fromB64url(pubJwk.x!)),
		}
	}
	const priv = x25519.utils.randomSecretKey()
	return { privateKey: toB64(priv), publicKey: toB64(x25519.getPublicKey(priv)) }
}

async function dhSharedSecret(priv: Uint8Array, peerPub: Uint8Array): Promise<Uint8Array> {
	if (await wcSupports('X25519')) {
		const myPub = x25519.getPublicKey(priv)
		const privKey = await subtle!.importKey(
			'jwk',
			{ kty: 'OKP', crv: 'X25519', d: toB64url(priv), x: toB64url(myPub) } as JsonWebKey,
			{ name: 'X25519' } as EcKeyImportParams,
			false,
			['deriveBits']
		)
		const pubKey = await subtle!.importKey(
			'jwk',
			{ kty: 'OKP', crv: 'X25519', x: toB64url(peerPub) } as JsonWebKey,
			{ name: 'X25519' } as EcKeyImportParams,
			false,
			[]
		)
		return new Uint8Array(
			await subtle!.deriveBits({ name: 'X25519', public: pubKey } as EcdhKeyDeriveParams, privKey, 256)
		)
	}
	return x25519.getSharedSecret(priv, peerPub)
}

async function hkdfDerive(ikm: Uint8Array, salt: Uint8Array, info: Uint8Array, outLen = 32): Promise<Uint8Array> {
	if (await wcSupports('HKDF')) {
		const ikmKey = await subtle!.importKey('raw', toArrayBuffer(ikm), { name: 'HKDF' }, false, ['deriveBits'])
		return new Uint8Array(
			await subtle!.deriveBits(
				{ name: 'HKDF', hash: 'SHA-256', salt: toArrayBuffer(salt), info: toArrayBuffer(info) } as HkdfParams,
				ikmKey,
				outLen * 8
			)
		)
	}
	return hkdf(sha256, ikm, salt, info, outLen)
}

export async function encryptAsymmetric(recipientPublicKeyHex: string, plaintext: Uint8Array): Promise<string> {
	const recipientPub = fromB64(recipientPublicKeyHex)

	let ephPriv: Uint8Array, ephPub: Uint8Array
	if (await wcSupports('X25519')) {
		const kp = await subtle!.generateKey({ name: 'X25519' } as EcKeyGenParams, true, ['deriveBits']) as CryptoKeyPair
		const privJwk = await subtle!.exportKey('jwk', kp.privateKey)
		const pubJwk = await subtle!.exportKey('jwk', kp.publicKey)
		ephPriv = fromB64url(privJwk.d!)
		ephPub = fromB64url(pubJwk.x!)
	} else {
		ephPriv = x25519.utils.randomSecretKey()
		ephPub = x25519.getPublicKey(ephPriv)
	}

	const shared = await dhSharedSecret(ephPriv, recipientPub)
	const aesKey = await hkdfDerive(shared, ephPub, ASYM_INFO, 32)
	const iv = randomBytes(IV_LEN)
	const enc = await aesEncrypt(aesKey, iv, plaintext)

	return toB64(concat(ephPub, iv, enc))
}

export async function decryptAsymmetric(privateKeyHex: string, ciphertextHex: string): Promise<Uint8Array> {
	const priv = fromB64(privateKeyHex)
	const packed = fromB64(ciphertextHex)
	const minLen = 32 + IV_LEN + TAG_LEN
	if (packed.length < minLen)
		throw new Error(`Ciphertext too short: ${packed.length} < ${minLen} bytes`)

	let off = 0
	const ephPub = packed.slice(off, (off += 32))
	const iv = packed.slice(off, (off += IV_LEN))
	const enc = packed.slice(off)

	const shared = await dhSharedSecret(priv, ephPub)
	const aesKey = await hkdfDerive(shared, ephPub, ASYM_INFO, 32)
	return aesDecrypt(aesKey, iv, enc)
}

export async function generateSymmetricKey(): Promise<string> {
	if (await wcSupports('AES-GCM')) {
		const key = await subtle!.generateKey({ name: 'AES-GCM', length: 256 } as AesKeyGenParams, true, ['encrypt', 'decrypt']) as CryptoKey
		return toB64(new Uint8Array(await subtle!.exportKey('raw', key)))
	}
	return toB64(randomBytes(32))
}

export async function encryptSymmetric(keyHex: string, plaintext: Uint8Array): Promise<string> {
	const key = fromB64(keyHex)
	if (key.length !== 32) throw new Error('AES key must be 32 bytes (64 hex chars)')
	const iv = randomBytes(IV_LEN)
	return toB64(concat(iv, await aesEncrypt(key, iv, plaintext)))
}

export async function decryptSymmetric(keyHex: string, ciphertextHex: string): Promise<Uint8Array> {
	const key = fromB64(keyHex)
	if (key.length !== 32) throw new Error('AES key must be 32 bytes (64 hex chars)')
	const packed = fromB64(ciphertextHex)
	if (packed.length < IV_LEN + TAG_LEN)
		throw new Error(`Ciphertext too short: ${packed.length} < ${IV_LEN + TAG_LEN} bytes`)
	return aesDecrypt(key, packed.slice(0, IV_LEN), packed.slice(IV_LEN))
}

export interface DerivedKey {
	key: string
	salt: string
}

export async function deriveKeyFromPassword(
	password: string,
	saltHex?: string,
	iterations = 310_000
): Promise<DerivedKey> {
	const salt = saltHex ? fromB64(saltHex) : randomBytes(16)
	const pass = encode(password)
	let keyBytes: Uint8Array

	if (await wcSupports('PBKDF2')) {
		const baseKey = await subtle!.importKey('raw', toArrayBuffer(pass), { name: 'PBKDF2' }, false, ['deriveBits'])
		keyBytes = new Uint8Array(
			await subtle!.deriveBits(
				{ name: 'PBKDF2', hash: 'SHA-256', salt: toArrayBuffer(salt), iterations } as Pbkdf2Params,
				baseKey,
				256
			)
		)
	} else {
		keyBytes = pbkdf2(sha256, pass, salt, { c: iterations, dkLen: 32 })
	}
	return { key: toB64(keyBytes), salt: toB64(salt) }
}

export async function deriveKeyHKDF(ikmHex: string, info: string, saltHex?: string): Promise<string> {
	const ikm = fromB64(ikmHex)
	const salt = saltHex ? fromB64(saltHex) : new Uint8Array(32)
	return toB64(await hkdfDerive(ikm, salt, encode(info), 32))
}

async function aesEncrypt(key: Uint8Array, iv: Uint8Array, plaintext: Uint8Array): Promise<Uint8Array> {
	if (await wcSupports('AES-GCM')) {
		const ck = await subtle!.importKey('raw', toArrayBuffer(key), 'AES-GCM', false, ['encrypt'])
		return new Uint8Array(
			await subtle!.encrypt({ name: 'AES-GCM', iv: toArrayBuffer(iv) } as AesGcmParams, ck, toArrayBuffer(plaintext))
		)
	}
	return gcm(key, iv).encrypt(plaintext)
}

async function aesDecrypt(key: Uint8Array, iv: Uint8Array, ct: Uint8Array): Promise<Uint8Array> {
	if (await wcSupports('AES-GCM')) {
		const ck = await subtle!.importKey('raw', toArrayBuffer(key), 'AES-GCM', false, ['decrypt'])
		return new Uint8Array(
			await subtle!.decrypt({ name: 'AES-GCM', iv: toArrayBuffer(iv) } as AesGcmParams, ck, toArrayBuffer(ct))
		)
	}
	return gcm(key, iv).decrypt(ct)
}