import { contentType } from "jsr:@std/media-types";
import { transpile } from "jsr:@deno/emit";
import config from "./deno.json" with { type: "json" };

const jsContentType = contentType(".js");

export enum MediaType {
    TypeScript,
    JSX,
    TSX,
};

// https://github.com/denoland/deno_ast/blob/ea1ccec37e1aa8e5e1e70f983a7ed1472d0e132a/src/media_type.rs#L117
const customContentType = {
    [MediaType.TypeScript]: "text/typescript; charset=utf-8",
    [MediaType.JSX]: "text/jsx; charset=utf-8",
    [MediaType.TSX]: "text/tsx; charset=utf-8",
};

async function rewriteTsResponse(response: Response, url: URL, mediaType: MediaType) {
    const tsCode = await response.text();
    const targetUrlStr = url.toString();
    try {
        const result = await transpile(url, {
            importMap: config,
            compilerOptions: config.compilerOptions,
            load(specifier) {
                if (specifier !== targetUrlStr) {
                    return Promise.resolve({
                        kind: "module",
                        specifier,
                        content: "",
                        headers: { "content-type": "application/javascript; charset=utf-8" },
                    });
                } else {
                    return Promise.resolve({
                        kind: "module",
                        specifier,
                        content: tsCode,
                        headers: {
                            "content-type": customContentType[mediaType],
                        },
                    });
                }
            },
        });
        const jsCode = result.get(targetUrlStr);
        const { headers } = response;
        headers.set("content-type", jsContentType);
        headers.delete("content-length");

        return new Response(jsCode, {
            status: response.status,
            statusText: response.statusText,
            headers,
        });
    } catch (e) {
        console.error(e);
        return new Response(`${e}`, {
            status: 500,
            statusText: `${e}`,
            headers: response.headers,
        });
    }
}

export default async function transpileResponse(response: Response, requestUrl: string, filepath?: string): Promise<Response> {
    const url = new URL(`ts-serve:///${ requestUrl }`);
    if (response.status !== 200) {
        return response;
    }
    const pathname = filepath !== undefined ? filepath : url.pathname;
    const extension = pathname.split('.').at(-1) ?? null;
    switch (extension) {
        case 'ts': return await rewriteTsResponse(response, url, MediaType.TypeScript);
        case 'tsx': return await rewriteTsResponse(response, url, MediaType.TSX);
        case 'jsx': return await rewriteTsResponse(response, url, MediaType.JSX);
        default: return response;
    }
}