feat(web): add package data layer with tests

Add package_data module for reading package information from the html
directory. Includes functions for listing packages, versions, and
checking if docs exist for specific packages.

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

tests/unit/dune

···
 (executable
  (name test_run_data)
  (libraries day10_web_data unix yojson))
+
+(executable
+ (name test_package_data)
+ (libraries day10_web_data unix))

tests/unit/test_package_data.ml

···
+(** Unit tests for package data reading *)
+
+let test_dir = ref ""
+
+let setup () =
+  let dir = Filename.temp_dir "test-pkg-data-" "" in
+  test_dir := dir;
+  dir
+
+let teardown () =
+  if !test_dir <> "" then begin
+    ignore (Sys.command (Printf.sprintf "rm -rf %s" !test_dir));
+    test_dir := ""
+  end
+
+let mkdir_p path =
+  let rec create dir =
+    if not (Sys.file_exists dir) then begin
+      create (Filename.dirname dir);
+      try Unix.mkdir dir 0o755 with Unix.Unix_error (Unix.EEXIST, _, _) -> ()
+    end
+  in
+  create path
+
+(** Test: list_packages returns packages from html/p directory *)
+let test_list_packages () =
+  let base_dir = setup () in
+  let html_dir = Filename.concat base_dir "html" in
+  mkdir_p (Filename.concat html_dir "p/base/0.16.0");
+  mkdir_p (Filename.concat html_dir "p/base/0.15.0");
+  mkdir_p (Filename.concat html_dir "p/core/0.16.0");
+
+  let packages = Day10_web_data.Package_data.list_packages ~html_dir in
+  assert (List.length packages = 3);
+  assert (List.mem ("base", "0.16.0") packages);
+  assert (List.mem ("base", "0.15.0") packages);
+  assert (List.mem ("core", "0.16.0") packages);
+
+  teardown ();
+  Printf.printf "PASS: test_list_packages\n%!"
+
+(** Test: list_package_versions returns versions for a package *)
+let test_list_package_versions () =
+  let base_dir = setup () in
+  let html_dir = Filename.concat base_dir "html" in
+  mkdir_p (Filename.concat html_dir "p/base/0.16.0");
+  mkdir_p (Filename.concat html_dir "p/base/0.15.0");
+  mkdir_p (Filename.concat html_dir "p/base/0.14.0");
+
+  let versions = Day10_web_data.Package_data.list_package_versions ~html_dir ~name:"base" in
+  assert (List.length versions = 3);
+  (* Should be sorted descending *)
+  assert (List.hd versions = "0.16.0");
+
+  teardown ();
+  Printf.printf "PASS: test_list_package_versions\n%!"
+
+(** Test: package_has_docs checks if docs exist *)
+let test_package_has_docs () =
+  let base_dir = setup () in
+  let html_dir = Filename.concat base_dir "html" in
+  mkdir_p (Filename.concat html_dir "p/base/0.16.0");
+
+  assert (Day10_web_data.Package_data.package_has_docs ~html_dir ~name:"base" ~version:"0.16.0");
+  assert (not (Day10_web_data.Package_data.package_has_docs ~html_dir ~name:"base" ~version:"0.15.0"));
+
+  teardown ();
+  Printf.printf "PASS: test_package_has_docs\n%!"
+
+(** Test: list_package_names returns unique package names *)
+let test_list_package_names () =
+  let base_dir = setup () in
+  let html_dir = Filename.concat base_dir "html" in
+  mkdir_p (Filename.concat html_dir "p/base/0.16.0");
+  mkdir_p (Filename.concat html_dir "p/base/0.15.0");
+  mkdir_p (Filename.concat html_dir "p/core/0.16.0");
+  mkdir_p (Filename.concat html_dir "p/async/0.16.0");
+
+  let names = Day10_web_data.Package_data.list_package_names ~html_dir in
+  assert (List.length names = 3);
+  assert (List.mem "base" names);
+  assert (List.mem "core" names);
+  assert (List.mem "async" names);
+
+  teardown ();
+  Printf.printf "PASS: test_list_package_names\n%!"
+
+let () =
+  Printf.printf "Running Package_data tests...\n%!";
+  test_list_packages ();
+  test_list_package_versions ();
+  test_package_has_docs ();
+  test_list_package_names ();
+  Printf.printf "\nAll Package_data tests passed!\n%!"

web/data/dune

···
 (library
  (name day10_web_data)
- (libraries unix yojson day10_lib))
+ (libraries unix yojson day10_lib)
+ (modules run_data package_data))

web/data/package_data.ml

···
+(** Read package data from day10's html directory *)
+
+let list_package_names ~html_dir =
+  let p_dir = Filename.concat html_dir "p" in
+  if Sys.file_exists p_dir && Sys.is_directory p_dir then
+    Sys.readdir p_dir
+    |> Array.to_list
+    |> List.filter (fun name ->
+        let path = Filename.concat p_dir name in
+        Sys.is_directory path)
+    |> List.sort String.compare
+  else
+    []
+
+let compare_versions v1 v2 =
+  (* Simple version comparison - compare segments numerically where possible *)
+  let parse v =
+    String.split_on_char '.' v
+    |> List.map (fun s -> try `Int (int_of_string s) with _ -> `Str s)
+  in
+  let rec cmp l1 l2 = match l1, l2 with
+    | [], [] -> 0
+    | [], _ -> -1
+    | _, [] -> 1
+    | `Int a :: t1, `Int b :: t2 ->
+        let c = Int.compare a b in if c <> 0 then c else cmp t1 t2
+    | `Str a :: t1, `Str b :: t2 ->
+        let c = String.compare a b in if c <> 0 then c else cmp t1 t2
+    | `Int _ :: _, `Str _ :: _ -> -1
+    | `Str _ :: _, `Int _ :: _ -> 1
+  in
+  cmp (parse v2) (parse v1)  (* Descending order *)
+
+let list_package_versions ~html_dir ~name =
+  let pkg_dir = Filename.concat (Filename.concat html_dir "p") name in
+  if Sys.file_exists pkg_dir && Sys.is_directory pkg_dir then
+    Sys.readdir pkg_dir
+    |> Array.to_list
+    |> List.filter (fun version ->
+        let path = Filename.concat pkg_dir version in
+        Sys.is_directory path)
+    |> List.sort compare_versions
+  else
+    []
+
+let list_packages ~html_dir =
+  list_package_names ~html_dir
+  |> List.concat_map (fun name ->
+      list_package_versions ~html_dir ~name
+      |> List.map (fun version -> (name, version)))
+
+let package_has_docs ~html_dir ~name ~version =
+  let path = Filename.concat html_dir
+    (Filename.concat "p" (Filename.concat name version)) in
+  Sys.file_exists path && Sys.is_directory path
+
+let docs_path ~name ~version =
+  Printf.sprintf "/docs/p/%s/%s/" name version

web/data/package_data.mli

···
+(** Read package data from day10's html directory *)
+
+(** List all (name, version) pairs with docs *)
+val list_packages : html_dir:string -> (string * string) list
+
+(** List unique package names *)
+val list_package_names : html_dir:string -> string list
+
+(** List all versions for a package name, sorted descending *)
+val list_package_versions : html_dir:string -> name:string -> string list
+
+(** Check if docs exist for a package version *)
+val package_has_docs : html_dir:string -> name:string -> version:string -> bool
+
+(** Get the docs URL path for a package *)
+val docs_path : name:string -> version:string -> string