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+;; SPDX-License-Identifier: CC0-1.0
+;;
+;; Copyright (C) 2023 Wojtek Kosior <koszko@koszko.org>
+
+(define-module (cantius)
+  #:use-module ((srfi srfi-26) #:select (cut))
+  #:use-module ((srfi srfi-34) #:select (guard raise))
+  #:use-module ((srfi srfi-35) #:select (condition &error &message))
+  #:use-module ((srfi srfi-128) #:select (make-default-comparator))
+  #:use-module ((srfi srfi-146) #:prefix s146:)
+  #:use-module ((ice-9 format) #:select (format))
+  #:use-module ((ice-9 control) #:select (let/ec))
+  #:use-module ((ice-9 exceptions) #:select
+                (exception-with-message? exception-message))
+  #:use-module ((system repl debug) #:select (terminal-width))
+  #:use-module ((web request) #:select (request-uri))
+  #:use-module ((web uri) #:prefix uri:)
+  #:use-module ((web response) #:select (build-response))
+  #:use-module ((fibers web server) #:select (run-server))
+  #:use-module ((de-paul-records) #:select
+                (define-immutable-record-type* match match-let match-let*)))
+
+
+
+(define-public current-path
+  (make-parameter #f))
+
+(define-public current-path-string
+  (make-parameter #f))
+
+(define-public %resource-root-path
+  (make-parameter '()))
+
+(export find-resource-file)
+(define* (find-resource-file file #:optional (root-path (%resource-root-path)))
+  (let loop ((paths root-path))
+    (match paths
+      (()
+       #f)
+      (((= (cut format #f "~a/~a" <> file) file-path)
+        . paths-rest)
+       (or (and (stat file-path #f) file-path)
+           (loop paths-rest))))))
+
+
+
+(define-immutable-record-type* endpoint
+  (handler #:default (lambda _ (raise (condition (&error)))))
+  (redirect/normalize-path? #:default 'true-by-default)
+  (redirect/remove-query? #:default 'true-by-default)
+  #:export? yes,of-course)
+
+(define-immutable-record-type* endpoint-tree-node
+  (direct-match #:default #f)
+  (any-match #:default #f)
+  (children #:default (s146:mapping (make-default-comparator))))
+
+(define-immutable-record-type* endset
+  (endpoints #:default (endpoint-tree-node))
+  ;;(resource-root-path #:default '())
+  ;;(fallback-handler #:default #f)
+  ;;(static-resource-headers #:default #f)
+  (redirect/normalize-path? #:default 'true-by-default)
+  (redirect/remove-query? #:default 'true-by-default)
+  #:export? sure,why-not)
+
+(define (endpoint-tree-+ tree path what)
+  (let recurse ((segments path)
+                (tree-node tree))
+    (define (processed-segments)
+      (list-head path (- (length path) (length segments))))
+
+    (match-let ((($* endpoint-tree-node direct-match any-match children)
+                 tree-node))
+      (when (endset? direct-match)
+        (raise (condition
+                (&error)
+                (&message (message (format #f "Endset already registered for ~s"
+                                           (processed-segments)))))))
+
+      (match segments
+        (()
+         (cond (direct-match
+                (raise (condition
+                        (&error)
+                        (&message (message (format #f "Endpoint already registered for ~s"
+                                                   path))))))
+               ((and (endset? what) (not (s146:mapping-empty? children)))
+                (raise (condition
+                        (&error)
+                        (&message (message (format #f "Endpoints already registered under ~s"
+                                                   path))))))
+               (#t
+                (endpoint-tree-node
+                 #:<- tree-node
+                 (direct-match what)))))
+
+        ('any
+         (cond (any-match
+                (raise (condition
+                        (&error)
+                        (&message (message (format #f "\"any\" endpoint already registered for ~s"
+                                                   path))))))
+               ((endset? what)
+                (raise (condition
+                        (&error)
+                        (&message (message (format #f "endset should be registered at normal path, not ~s"
+                                                   path))))))
+               (#t
+                (endpoint-tree-node
+                 #:<- tree-node
+                 (any-match what)))))
+
+        (((? string? current-segment) . segments-rest)
+         (endpoint-tree-node
+          #:<- tree-node
+          (children (s146:mapping-update/default
+                     children current-segment (cut recurse segments-rest <>)
+                     %null-endpoint-tree-node))))))))
+
+(define-public (endset-+ endset-obj path what)
+  (endset
+   #:<- endset-obj
+   (endpoints (endpoint-tree-+ (endset-endpoints endset-obj) path what))))
+
+(eval-when (compile load eval)
+  (define-immutable-record-type* path-spec
+    (path-syntax)
+    (extra-handler-args-syntax))
+
+  (define (syntax->path-spec x)
+    (let loop ((path-segments '())
+               (path-syntax x))
+      (syntax-case path-syntax (unquote unquote-splicing)
+        (()
+         (path-spec (path-syntax #``(#,@(reverse path-segments)))
+                    (extra-handler-args-syntax #'())))
+        (rest-arg
+         (identifier? #'rest-arg)
+         (path-spec (path-syntax #``(#,@(reverse path-segments) . any))
+                    (extra-handler-args-syntax #'(rest-arg))))
+        ((unquote list-expression)
+         (path-spec (path-syntax #``(#,@(reverse path-segments)
+                                     . ,list-expression))
+                    (extra-handler-args-syntax #'())))
+        ((segment-arg . rest)
+         (identifier? #'segment-arg)
+         (raise (condition
+                 (&error)
+                 (&message (message "Binding identifiers to path segments not yet supported")))))
+        (((unquote segment-expression) . rest)
+         (loop (cons #',segment-expression path-segments) #'rest))
+        (((unquote-splicing segments-expression) . rest)
+         (loop (cons #',@segments-expression path-segments) #'rest))
+        ((segment . rest)
+         (string? (syntax->datum #'segment))
+         (loop (cons #'segment path-segments) #'rest))))))
+
+(export define-endpoint)
+(define-syntax define-endpoint
+  (lambda (x)
+    (syntax-case x ()
+      ((_ endset-identifier handler-identifier path
+          ((init-form ...) ...)
+          handler-body handler-body-rest ...)
+       (and (identifier? #'webservice-identifier)
+            (identifier? #'handler-identifier))
+       (match (syntax->path-spec #'path)
+         (($* path-spec path-syntax extra-handler-args-syntax)
+          #`(begin
+              (define (handler-identifier
+                       #,(datum->syntax #'handler-identifier 'request)
+                       #,(datum->syntax #'handler-identifier 'body)
+                       . #,extra-handler-args-syntax)
+                handler-body handler-body-rest ...)
+
+              (define endset-identifier
+                (endset-+ endset-identifier #,path-syntax
+                          (endpoint (init-form ...) ...
+                                    (handler handler-identifier)))))))))))
+
+(define-immutable-record-type* endpoint-ref-result
+  (path-tail)
+  (endpoint))
+
+(define (endpoint-tree-ref tree path)
+  (let loop ((segments path)
+             (tree-node tree)
+             (best-any-match-endpoint #f)
+             (best-any-match-path #f))
+    (match segments
+      (()
+       (match tree-node
+         (($* endpoint-tree-node (direct-match (? identity endpoint)))
+          (endpoint-ref-result (path-tail #f)
+                               (endpoint endpoint)))
+         ((? (const best-any-match-endpoint))
+          (endpoint-ref-result (path-tail best-any-match-path)
+                               (endpoint best-any-match-endpoint)))
+         (_
+          #f)))
+
+      ((current-segment . segments-rest)
+       (match-let* (((best-any-match-endpoint best-any-match-path)
+                     (or (and=> (endpoint-tree-node-any-match tree-node)
+                                (cut list <> segments))
+                         (list best-any-match-endpoint best-any-match-path)))
+                    (children (endpoint-tree-node-children tree-node))
+                    (subnode (s146:mapping-ref/default children current-segment
+                                                       #f)))
+         (cond (subnode
+                (loop segments-rest subnode
+                      best-any-match-endpoint best-any-match-path))
+               (best-any-match-endpoint
+                (endpoint-ref-result (path-tail best-any-match-path)
+                                     (endpoint best-any-match-endpoint)))
+               (#t
+                #f)))))))
+
+(define* (query-endset endset path #:optional (default #f))
+  (define (do-it? . args)
+    (match args
+      ((less-specific 'true-by-default)
+       less-specific)
+      ((less-specific more-specific)
+       more-specific)))
+
+  (let loop ((endset endset)
+             (path path)
+             (*redirect/normalize-path? 'true-by-default)
+             (*redirect/remove-query? 'true-by-default))
+    (match-let ((($* endset
+                     endpoints
+                     (redirect/normalize-path?
+                      (= (cut do-it? *redirect/normalize-path? <>)
+                         redirect/normalize-path?))
+                     (redirect/remove-query?
+                      (= (cut do-it? *redirect/remove-query? <>)
+                         redirect/remove-query?)))
+                 endset))
+      (define (update-endpoint base-endpoint)
+        (endpoint
+         #:<- base-endpoint
+         (redirect/normalize-path? #:=> (cut do-it? redirect/normalize-path?
+                                             <>))
+         (redirect/remove-query? #:=> (cut do-it? redirect/remove-query? <>))))
+
+      (match (endpoint-tree-ref endpoints path)
+        (#f
+         default)
+        (($* endpoint-ref-result path-tail (endpoint (? endset? endset)))
+         (loop endset path-tail redirect/normalize-path?
+               redirect/remove-query?))
+        (ref-result
+         (endpoint-ref-result #:<- ref-result
+                              (endpoint #:=> update-endpoint)))))))
+
+
+
+(define %default-headers
+  '((content-type . (text/plain (charset . "utf-8")))))
+
+(export build-response*)
+(define* (build-response* #:key (redirect-to #f) (headers %default-headers)
+                          (code #f) #:rest args)
+  (define code*
+    (or code (if redirect-to 301 200)))
+
+  (define redirect-to*
+    (if (string? redirect-to)
+        (uri:string->uri redirect-to)
+        redirect-to))
+
+  (define headers*
+    (if redirect-to*
+        `((location . ,redirect-to*) . ,headers)
+        headers))
+
+  (let loop ((to-filter args)
+             (filtered '()))
+    (match to-filter
+      (()
+       (apply build-response #:code code* #:headers headers*
+              (reverse filtered)))
+      (((? (cut memq <> '(#:code #:headers #:redirect-to))) _ . rest)
+       (loop rest filtered))
+      ((keyword keyword-arg . rest)
+       (loop rest (cons* keyword-arg keyword filtered))))))
+
+(define %catchall-endpoint
+  (endpoint (handler (lambda (request body . _)
+                       (values (build-response* #:code 404)
+                               "There's no page with this address :(")))
+            (redirect/normalize-path? #f)
+            (redirect/remove-query? #f)))
+
+(define %catchall-ref-result
+  (endpoint-ref-result (path-tail #f)
+                       (endpoint %catchall-endpoint)))
+
+(define %ugly-uri-path-regex
+  (make-regexp ".+/(/|$)"))
+
+(define (exception->msg ex)
+  (format #f "~a~%~a~%"
+          (if (exception-with-message? ex)
+              (format #f "Error: ~a." (exception-message ex))
+              "Error occured.")
+          ex))
+
+(define (handler request body root-endset)
+  (match-let* ((uri (request-uri request))
+               (path-string (uri:uri-path uri))
+               (path (uri:split-and-decode-uri-path path-string))
+               (($* endpoint-ref-result path-tail endpoint)
+                (query-endset root-endset path %catchall-ref-result))
+               (($* endpoint redirect/normalize-path? redirect/remove-query?)
+                endpoint))
+    (define (normalized-path-string)
+      (format #f "/~a" (uri:encode-and-join-uri-path path)))
+
+    (define (redirect-path)
+      (if redirect/normalize-path?
+          (normalized-path-string)
+          (uri:uri-path (request-uri request))))
+
+    (define (redirect-query)
+      (if redirect/remove-query?
+          #f
+          (uri:uri-query uri)))
+
+    (if (or (and redirect/normalize-path?
+                 (regexp-exec %ugly-uri-path-regex path-string))
+            (and redirect/remove-query?
+                 (uri:uri-query uri)))
+        (values (build-response* #:redirect-to (uri:build-relative-ref
+                                                #:path (redirect-path)
+                                                #:query (redirect-query)))
+                "Redirect...")
+        (let/ec escape
+          (with-exception-handler
+              (lambda (ex)
+                (define msg
+                  (exception->msg ex))
+
+                (display msg (current-error-port))
+
+                (escape (build-response* #:code 500)
+                        (string-append
+                         msg
+                         "\nBacktrace:\n\n"
+                         (call-with-output-string
+                           (lambda (port)
+                             (terminal-width 80)
+                             (display-backtrace (make-stack #t 5 0) port))))))
+            (lambda ()
+              (parameterize ((current-path path)
+                             (current-path-string path-string))
+                (start-stack 'cantius-request
+                  (apply (endpoint-handler endpoint) request body
+                         (or (and=> path-tail list) '()))))))))))
+
+(define-public (run-cantius endset . server-args)
+  (apply run-server (cut handler <> <> endset) server-args))