import {Request} from "./Request";
import {ErrorWithContext, HTTPStatus, BehaviorSubject} from "@extollo/util"
import {ServerResponse} from "http"

export class HeadersAlreadySentError extends ErrorWithContext {
    constructor(response: Response, headerName?: string) {
        super(`Cannot modify or re-send headers for this request as they have already been sent.`);
        this.context = { headerName }
    }
}

export class ResponseAlreadySentError extends ErrorWithContext {
    constructor(response: Response) {
        super(`Cannot modify or re-send response as it has already ended.`);
    }
}

export class Response {
    private headers: {[key: string]: string | string[]} = {}
    private _sentHeaders: boolean = false
    private _responseEnded: boolean = false
    private _status: HTTPStatus = HTTPStatus.OK
    public body: string = ''
    public readonly sending$: BehaviorSubject<Response> = new BehaviorSubject<Response>()
    public readonly sent$: BehaviorSubject<Response> = new BehaviorSubject<Response>()

    constructor(
        public readonly request: Request,
        protected readonly serverResponse: ServerResponse,
    ) { }

    public getStatus() {
        return this._status
    }

    public setStatus(status: HTTPStatus) {
        if ( this._sentHeaders ) throw new HeadersAlreadySentError(this, 'status')
        this._status = status
    }

    public get cookies() {
        return this.request.cookies
    }

    public getHeader(name: string): string | string[] | undefined {
        return this.headers[name]
    }

    public setHeader(name: string, value: string | string[]) {
        if ( this._sentHeaders ) throw new HeadersAlreadySentError(this, name)
        this.headers[name] = value
        return this
    }

    public setHeaders(data: {[name: string]: string | string[]}) {
        if ( this._sentHeaders ) throw new HeadersAlreadySentError(this)
        this.headers = {...this.headers, ...data}
        return this
    }

    public appendHeader(name: string, value: string | string[]) {
        if ( this._sentHeaders ) throw new HeadersAlreadySentError(this, name)
        if ( !Array.isArray(value) ) value = [value]
        let existing = this.headers[name] ?? []
        if ( !Array.isArray(existing) ) existing = [existing]

        existing = [...existing, ...value]
        if ( existing.length === 1 ) existing = existing[0]
        this.headers[name] = existing
    }

    public sendHeaders() {
        const headers = {} as any

        const setCookieHeaders = this.cookies.getSetCookieHeaders()
        if ( setCookieHeaders.length ) headers['Set-Cookie'] = setCookieHeaders

        for ( const key in this.headers ) {
            if ( !this.headers.hasOwnProperty(key) ) continue
            headers[key] = this.headers[key]
        }

        this.serverResponse.writeHead(this._status, headers)
        this._sentHeaders = true
    }

    public hasSentHeaders() {
        return this._sentHeaders
    }

    public async write(data: any) {
        return new Promise<void>((res, rej) => {
            if ( !this._sentHeaders ) this.sendHeaders()
            this.serverResponse.write(data, error => {
                if ( error ) rej(error)
                else res()
            })
        })
    }

    public async send() {
        await this.sending$.next(this)
        this.setHeader('Content-Length', String(this.body?.length ?? 0))
        await this.write(this.body ?? '')
        this.end()
        await this.sent$.next(this)
    }

    public end() {
        if ( this._responseEnded ) throw new ResponseAlreadySentError(this)
        this._sentHeaders = true
        this.serverResponse.end()
    }

    // location?
}