From fe93f65f6a5af8b147deb3d7d9da70ddeb68faaf Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Tue, 10 Dec 2024 11:31:02 +0000
Subject: [PATCH] Moved Grid to Aoc module.

---
 lib/aoc.ml  | 36 +++++++++++++++++++++++++++++++++++-
 lib/aoc.mli | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/lib/aoc.ml b/lib/aoc.ml
index 5082485..a216c19 100644
--- a/lib/aoc.ml
+++ b/lib/aoc.ml
@@ -21,7 +21,10 @@ let main prep parts =
         Printf.printf "Usage: %s <fname>\n" Sys.executable_name;
         exit 2
   with e ->
-    Printf.printf "An error occured: %s\n" (Printexc.to_string e);
+    Printf.fprintf stderr "An error occured: %s\n" (Printexc.to_string e);
+    if Printexc.backtrace_status () then (
+      Printf.fprintf stderr "Backtrace:\n";
+      Printexc.print_backtrace stderr);
     exit 1
 
 module IntPair = struct
@@ -32,3 +35,34 @@ module IntPair = struct
 end
 
 module IntPairSet = Set.Make (IntPair)
+
+module Grid = struct
+  type t = { grid : string; width : int; height : int }
+
+  let of_file fname =
+    let strs = strings_of_file fname in
+    let width = String.length (List.hd strs) in
+    let grid = List.fold_left ( ^ ) "" strs in
+    let height = String.length grid / width in
+    { grid; width; height }
+
+  let length grid = String.length grid.grid
+  let pos_of_idx grid idx = (idx mod grid.width, idx / grid.width)
+  let idx_of_pos grid (x, y) = x + (y * grid.width)
+  let get_by_idx grid idx = grid.grid.[idx]
+  let get_by_pos grid pos = get_by_idx grid (idx_of_pos grid pos)
+
+  let pos_is_valid grid (x, y) =
+    x >= 0 && x < grid.width && y >= 0 && y < grid.height
+
+  let idx_from_opt grid = String.index_from_opt grid.grid
+
+  let update_pos grid pos c =
+    let idx = idx_of_pos grid pos in
+    let builder = Buffer.create (length grid) in
+    Buffer.add_string builder (String.sub grid.grid 0 idx);
+    Buffer.add_char builder c;
+    Buffer.add_string builder
+      (String.sub grid.grid (idx + 1) (length grid - idx - 1));
+    { grid with grid = Buffer.contents builder }
+end
diff --git a/lib/aoc.mli b/lib/aoc.mli
index 409184e..8f50668 100644
--- a/lib/aoc.mli
+++ b/lib/aoc.mli
@@ -74,3 +74,50 @@ module IntPairSet : sig
   val add_seq : elt Seq.t -> t -> t
   val of_seq : elt Seq.t -> t
 end
+
+(** The [Grid] module is used to represent and manipulate a grid of characters.
+    Its main goals are to be non-mutable and have constant access times to
+    locations in the grid.
+
+    Grid locations can be accessed by index or (col, row) position. Indicies do
+    not guarantee an ordering on accesses - but iterating by index from 0 to
+    [Grid.length grid - 1] inclusive will cover the whole grid. *)
+module Grid : sig
+  type t
+  (** The type used to represent a grid *)
+
+  val of_file : string -> t
+  (** [Grid.of_file fname] returns a grid loaded from the file [fname] *)
+
+  val length : t -> int
+  (** [Grid.length grid] returns the length of the grid. *)
+
+  val get_by_idx : t -> int -> char
+  (** [Grid.get_by_idx grid idx] returns the character at index [idx] in [grid].
+  *)
+
+  val get_by_pos : t -> int * int -> char
+  (** [Grid.get_by_pos grid pos] returns the character at position [pos] in
+      [grid]. *)
+
+  val pos_of_idx : t -> int -> int * int
+  (** [Grid.pos_of_idx grid idx] returns the [(x, y)] position mapped by [idx]
+      in [grid]. *)
+
+  val idx_of_pos : t -> int * int -> int
+  (** [Grid.pos_of_idx grid pos] returns the index corresponding to [pos] in
+      [grid]. *)
+
+  val pos_is_valid : t -> int * int -> bool
+  (** [Grid.pos_is_valid grid pos] returns [true] if and only if [pos] is a
+      valid position in [grid]. *)
+
+  val idx_from_opt : t -> int -> char -> int option
+  (** [Grid.idx_from_opt grid start c] returns [Some idx] where [idx] is the
+      first location in [grid] at or after the [start] index which is [c]. It
+      returns [None] if [c] does not appear. *)
+
+  val update_pos : t -> int * int -> char -> t
+  (** [Grid.update_pos grid pos c] returns a grid with the character at position
+      [pos] changed to [c]. *)
+end