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// Copyright 2022 Connor Logan. All rights reserved. MIT License.
// TODO: Add support for arrays of handlers  // TODO: Don't throw errors when using advanced URLPattern syntax (just use the// unknown type on the client when they use it instead)  
import { http } from "./deps.ts";import { requestContext } from "./http.ts";
import type { RouterRequest, RouterShape, Handler } from "./client.ts";
/** * Handler that routes requests to Rpcs (endpoints) or other Stacks (routers). */export interface Stack<S extends RouterShape = RouterShape> {  (req: RouterRequest<S>, connInfo: http.ConnInfo): Promise<Response>;  /**   * The routes specified when this Stack was constructed.   */  readonly routes: S;}
const nextPathGroupName = "__nextPath";
/** * Constructs a new Stack handler using the provided routes object. Keys can be * a subset of the URLPattern syntax when group capturing is desired. See the * documentation for more information about how Stack routing works. TODO: the * documentation about how Stack routing works */export function stack<S extends RouterShape>(routes: S): Stack<S> {  // Stack routes can only use some of the features of URLPattern. If attempts  // are made to use features that aren't supported, throw an error  for (const [k, _] of Object.entries(routes)) {    const split = k.split("/").filter(v => !!v);
    // Trailing wildcard needs to be let through    if (split[split.length-1] === "*") {      split.pop();    }
    // Make sure the stack route is simple    for (const s of split) {      if (        !s.match(/^:[a-zA-Z_$][a-zA-Z_$0-9]$/) &&        !s.match(/^[^:*?(){}]*$/) // TODO: I don't think this is fully correct      ) {        throw new SyntaxError(          `"${k}" isn't a valid stack route. Stack routes only support basic path segments and named path segments (groups). Non-trailing wildcards, RegExp, optionals, and other advanced URLPattern syntax is not supported`,        );      }    }  }
  const handlers: Record<string, Handler | Handler[]> = {};  for (const k of Object.keys(routes)) {    const v = routes[k];    if (v && typeof v === "object" && !Array.isArray(v)) {      handlers[k] = stack(v);    } else if (v) {      handlers[k] = v;    }  }
  // Sort the handlers like this:  //   1. Solo wildcards are always last  //   2. By path depth. Paths with more path segments get tested sooner.  //      (Trailing wildcards don't affect path depth)  //   3. For two paths that have the same depth, index order is used (lower  //      index === higher priority)  const paths = Object.keys(handlers);  const sortedPaths: string[] = paths.sort((a, b) => {    if (a === b) {      return 0;    }        // #1    if (a === "*" || a === "/*") {      return 1;    }    if (b === "*" || b === "/*") {      return -1;    }
    // #2    if (a.endsWith("/*")) {      a = a.slice(0, a.length - 2);    }    if (b.endsWith("/*")) {      b = b.slice(0, b.length - 2);    }    const la = a.split("/").filter(v => !!v).length;    const lb = b.split("/").filter(v => !!v).length;    if (la !== lb) {      return lb - la;    }
    // #3    return paths.indexOf(a) - paths.indexOf(b);  });
  const patterns = new Map<URLPattern, Handler | Handler[]>();  for (const op of sortedPaths) {    let p = "/" + op.split("/").filter(v => !!v).join("/");
    // Sometimes the path might already end in a wildcard. If it does, remove it    // before adding the path capture wildcard    if (p.endsWith("/*")) {      p = p.slice(0, p.length - 2);    }    p = `${p}/:${nextPathGroupName}*/*?`;    patterns.set(new URLPattern(p, "http://_._"), handlers[op]);  }
  const handler = async (    req: Request,    conn: http.ConnInfo,  ): Promise<Response> => {    // Check for redirect    const reqCtx = requestContext(req);    if (reqCtx.redirect) {      return reqCtx.redirect;    }
    // When nothing matches, the last seen plaintext 404 error is returned,    // defaulting to this one    let last404 = new Response("404 not found", { status: 404 });
    for (const [pattern, handler] of patterns.entries()) {      const match = pattern.exec(reqCtx.path, "http://_._");      if (!match) {        continue;      }
      const groups = { ...reqCtx.groups, ...match.pathname.groups };      const path = `/${groups[nextPathGroupName] || ""}`;      delete groups[nextPathGroupName];
      const oPath = reqCtx.path;      const oGroups = reqCtx.groups;
      // The context object is only created once for every request, so      // modifications to the data object will be preserved across handling      // contexts      Object.assign(reqCtx, { path, groups });
      try {        if (Array.isArray(handler)) {          for (const h of handler) {            const response = await h(req, conn);            if (didMatch(response)) {              return response;            } else {              last404 = response;            }          }        } else {          const response = await handler(req, conn);          if (didMatch(response)) {            return response;          } else {            last404 = response;          }        }      } finally {        // Before moving on, put the path and groups back to their original        // state        Object.assign(req, { path: oPath, groups: oGroups });      }    }
    // When nothing matches, return the last 404    return last404;  };
  return Object.assign(handler, { routes });}
/** * Checks if a Response should be considered a "no match" response, indicating * to the stack if it should continue looking for matches or not. Currently, a * "no match" response is a 404 Reponse with a plaintext body. */function didMatch(response: Response): boolean {  if (response.status === 404) {    const mime = response.headers.get("content-type");    if (mime === "text/plain") {      return false;    }  }  return true;}