if (typeof crypto === 'undefined' || !crypto.subtle)
    throw new Error('SubtleCrypto not supported!')

/**
 * @typedef JwtAlgorithm
 * @type {'ES256'|'ES384'|'ES512'|'HS256'|'HS384'|'HS512'|'RS256'|'RS384'|'RS512'}
 */
export type JwtAlgorithm = 'ES256'|'ES384'|'ES512'|'HS256'|'HS384'|'HS512'|'RS256'|'RS384'|'RS512'

/**
 * @typedef JwtAlgorithms
 */
export interface JwtAlgorithms {
    [key: string]: SubtleCryptoImportKeyAlgorithm
}

/**
 * @typedef JwtHeader
 * @prop {string} [typ] Type
 */
export interface JwtHeader {
    /**
     * Type (default: `"JWT"`)
     *
     * @default "JWT"
     */
    typ?: string

    [key: string]: any
}

/**
 * @typedef JwtPayload
 * @prop {string} [iss] Issuer
 * @prop {string} [sub] Subject
 * @prop {string | string[]} [aud] Audience
 * @prop {string} [exp] Expiration Time
 * @prop {string} [nbf] Not Before
 * @prop {string} [iat] Issued At
 * @prop {string} [jti] JWT ID
 */
export interface JwtPayload {
    /** Issuer */
    iss?: string

    /** Subject */
    sub?: string

    /** Audience */
    aud?: string | string[]

    /** Expiration Time */
    exp?: number

    /** Not Before */
    nbf?: number

    /** Issued At */
    iat?: number

    /** JWT ID */
    jti?: string

    [key: string]: any
}

/**
 * @typedef JwtOptions
 * @prop {JwtAlgorithm | string} algorithm
 */
export interface JwtOptions {
    algorithm?: JwtAlgorithm | string
}

/**
 * @typedef JwtSignOptions
 * @extends JwtOptions
 * @prop {JwtHeader} [header]
 */
export interface JwtSignOptions extends JwtOptions {
    header?: JwtHeader
}

/**
 * @typedef JwtVerifyOptions
 * @extends JwtOptions
 * @prop {boolean} [throwError=false] If `true` throw error if checks fail. (default: `false`)
 */
export interface JwtVerifyOptions extends JwtOptions {
    /**
     * If `true` all expiry checks will be skipped
    */
    skipValidation?: boolean

    /**
     * If `true` throw error if checks fail. (default: `false`)
     *
     * @default false
    */
    throwError?: boolean
}

/**
 * @typedef JwtData
 * @prop {JwtHeader} header
 * @prop {JwtPayload} payload
 */
export interface JwtData {
    header: JwtHeader
    payload: JwtPayload
}

const algorithms: JwtAlgorithms = {
    ES256: { name: 'ECDSA', namedCurve: 'P-256', hash: { name: 'SHA-256' } },
    ES384: { name: 'ECDSA', namedCurve: 'P-384', hash: { name: 'SHA-384' } },
    ES512: { name: 'ECDSA', namedCurve: 'P-521', hash: { name: 'SHA-512' } },
    HS256: { name: 'HMAC', hash: { name: 'SHA-256' } },
    HS384: { name: 'HMAC', hash: { name: 'SHA-384' } },
    HS512: { name: 'HMAC', hash: { name: 'SHA-512' } },
    RS256: { name: 'RSASSA-PKCS1-v1_5', hash: { name: 'SHA-256' } },
    RS384: { name: 'RSASSA-PKCS1-v1_5', hash: { name: 'SHA-384' } },
    RS512: { name: 'RSASSA-PKCS1-v1_5', hash: { name: 'SHA-512' } }
}

function bytesToByteString(bytes: Uint8Array): string {
    let byteStr = ''
    for (let i = 0; i < bytes.byteLength; i++) {
        byteStr += String.fromCharCode(bytes[i])
    }
    return byteStr
}

function byteStringToBytes(byteStr: string): Uint8Array {
    let bytes = new Uint8Array(byteStr.length)
    for (let i = 0; i < byteStr.length; i++) {
        bytes[i] = byteStr.charCodeAt(i)
    }
    return bytes
}

function arrayBufferToBase64String(arrayBuffer: ArrayBuffer): string {
    return btoa(bytesToByteString(new Uint8Array(arrayBuffer)))
}

function base64StringToArrayBuffer(b64str: string): ArrayBuffer {
    return byteStringToBytes(atob(b64str)).buffer
}

function textToArrayBuffer(str: string): ArrayBuffer {
    return byteStringToBytes(decodeURI(encodeURIComponent(str)))
}

// @ts-ignore
function arrayBufferToText(arrayBuffer: ArrayBuffer): string {
    return bytesToByteString(new Uint8Array(arrayBuffer))
}

function arrayBufferToBase64Url(arrayBuffer: ArrayBuffer): string {
    return arrayBufferToBase64String(arrayBuffer).replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_')
}

function base64UrlToArrayBuffer(b64url: string): ArrayBuffer {
    return base64StringToArrayBuffer(b64url.replace(/-/g, '+').replace(/_/g, '/').replace(/\s/g, ''))
}

function textToBase64Url(str: string): string {
    return btoa(str).replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_')
}

function pemToBinary(pem: string): ArrayBuffer {
    return base64StringToArrayBuffer(pem.replace(/-+(BEGIN|END).*/g, '').replace(/\s/g, ''))
}

async function importTextSecret(key: string, algorithm: SubtleCryptoImportKeyAlgorithm): Promise<CryptoKey> {
    return await crypto.subtle.importKey("raw", textToArrayBuffer(key), algorithm, true, ["verify", "sign"])
}

async function importJwk(key: JsonWebKey, algorithm: SubtleCryptoImportKeyAlgorithm): Promise<CryptoKey> {
    return await crypto.subtle.importKey("jwk", key, algorithm, true, ["verify", "sign"])
}

async function importPublicKey(key: string, algorithm: SubtleCryptoImportKeyAlgorithm): Promise<CryptoKey> {
    return await crypto.subtle.importKey("spki", pemToBinary(key), algorithm, true, ["verify"])
}

async function importPrivateKey(key: string, algorithm: SubtleCryptoImportKeyAlgorithm): Promise<CryptoKey> {
    return await crypto.subtle.importKey("pkcs8", pemToBinary(key), algorithm, true, ["sign"])
}

async function importKey(key: string | JsonWebKey, algorithm: SubtleCryptoImportKeyAlgorithm): Promise<CryptoKey> {
    if (typeof key === 'object')
        return importJwk(key, algorithm)

    if (typeof key !== 'string')
        throw new Error('Unsupported key type!')

    if (key.includes('PUBLIC'))
        return importPublicKey(key, algorithm)

    if (key.includes('PRIVATE'))
        return importPrivateKey(key, algorithm)

    return importTextSecret(key, algorithm)
}

function decodePayload(raw: string): JwtHeader | JwtPayload | null {
    try {
        raw += '='.repeat(4-(raw.length % 4))
        return JSON.parse(atob(raw))
    } catch {
        return null
    }
}

/**
 * Verifies the integrity of the token and returns a boolean value.
 *
 * @param {string} token The token string generated by `jwt.sign()`.
 * @param {string | JsonWebKey} secret The string which was used to sign the payload.
 * @param {JWTVerifyOptions | JWTAlgorithm} options The options object or the algorithm.
 * @throws {Error | string} Throws an error `string` if the token is invalid or an `Error-Object` if there's a validation issue.
 * @returns {Promise<boolean>} Returns `true` if signature, `nbf` (if set) and `exp` (if set) are valid, otherwise returns `false`.
 */
export async function verify(token: string, secret: string | JsonWebKey, options: JwtVerifyOptions | JwtAlgorithm = { algorithm: 'HS256', skipValidation: false, throwError: false }): Promise<boolean> {
    if (typeof options === 'string')
        options = { algorithm: options, throwError: false }

    options = { algorithm: 'HS256', skipValidation: false, throwError: false, ...options }

    if (typeof token !== 'string')
        throw new Error('token must be a string')

    if (typeof secret !== 'string' && typeof secret !== 'object')
        throw new Error('secret must be a string or a JWK object')

    if (typeof options.algorithm !== 'string')
        throw new Error('options.algorithm must be a string')

    const tokenParts = token.split('.')

    if (tokenParts.length !== 3)
        throw new Error('token must consist of 3 parts')

    const algorithm: SubtleCryptoImportKeyAlgorithm = algorithms[options.algorithm]

    if (!algorithm)
        throw new Error('algorithm not found')

    const { payload } = decode(token)

    if (!options.skipValidation && !payload) {
        if (options.throwError)
            throw 'PARSE_ERROR'

        return false
    }

    if (!options.skipValidation && payload.nbf && payload.nbf > Math.floor(Date.now() / 1000)) {
        if (options.throwError)
            throw 'NOT_YET_VALID'

        return false
    }

    if (!options.skipValidation && payload.exp && payload.exp <= Math.floor(Date.now() / 1000)) {
        if (options.throwError)
            throw 'EXPIRED'

        return false
    }

    const key = await importKey(secret, algorithm)

    return await crypto.subtle.verify(algorithm, key, base64UrlToArrayBuffer(tokenParts[2]), textToArrayBuffer(`${tokenParts[0]}.${tokenParts[1]}`))
}

/**
 * Signs a payload and returns the token
 *
 * @param {JwtPayload} payload The payload object. To use `nbf` (Not Before) and/or `exp` (Expiration Time) add `nbf` and/or `exp` to the payload.
 * @param {string | JsonWebKey} secret A string which is used to sign the payload.
 * @param {JwtSignOptions | JwtAlgorithm | string} [options={ algorithm: 'HS256', header: { typ: 'JWT' } }] The options object or the algorithm.
 * @throws {Error} If there's a validation issue.
 * @returns {Promise<string>} Returns token as a `string`.
 */
export async function sign(payload: JwtPayload, secret: string | JsonWebKey, options: JwtSignOptions | JwtAlgorithm = 'HS256'): Promise<string> {
    if (typeof options === 'string')
        options = { algorithm: options }
    options = { algorithm: 'HS256', header: { typ: 'JWT' }, ...options }

    if (!payload || typeof payload !== 'object')
        throw new Error('payload must be an object')

    if (!secret || (typeof secret !== 'string' && typeof secret !== 'object'))
        throw new Error('secret must be a string or a JWK object')

    if (typeof options.algorithm !== 'string')
        throw new Error('options.algorithm must be a string')

    const algorithm: SubtleCryptoImportKeyAlgorithm = algorithms[options.algorithm]

    if (!algorithm)
        throw new Error('algorithm not found')

    if (!payload.iat)
        payload.iat = Math.floor(Date.now() / 1000)

    const partialToken = `${textToBase64Url(JSON.stringify({ ...options.header, alg: options.algorithm }))}.${textToBase64Url(JSON.stringify(payload))}`

    const key = await importKey(secret, algorithm)
    const signature = await crypto.subtle.sign(algorithm, key, textToArrayBuffer(partialToken))

    return `${partialToken}.${arrayBufferToBase64Url(signature)}`
}

/**
 * Returns the payload **without** verifying the integrity of the token. Please use `jwt.verify()` first to keep your application secure!
 *
 * @param {string} token The token string generated by `jwt.sign()`.
 * @returns {JwtData} Returns an `object` containing `header` and `payload`.
 */
export function decode(token: string): JwtData {
    return {
        header: decodePayload(token.split('.')[0].replace(/-/g, '+').replace(/_/g, '/')) as JwtHeader,
        payload: decodePayload(token.split('.')[1].replace(/-/g, '+').replace(/_/g, '/')) as JwtPayload
    }
}

export default {
    sign,
    verify,
    decode
}