5 files changed, 148 insertions, 46 deletions

diff --git a/filesystem/CMakeLists.txt b/filesystem/CMakeLists.txt
index 55430e6..04390f4 100644
--- a/filesystem/CMakeLists.txt
+++ b/filesystem/CMakeLists.txt
@@ -3,9 +3,13 @@ cmake_minimum_required(VERSION 3.0)
 project(filesystem)
 
 add_library(filesystem
-  src/filesystem.c)
+  src/filesystem.c
+  src/path.c)
 
 target_include_directories(filesystem PUBLIC
   include)
 
+target_link_libraries(filesystem PRIVATE
+  cassert)
+
 target_compile_options(filesystem PRIVATE -Wall -Wextra)
diff --git a/filesystem/include/filesystem.h b/filesystem/include/filesystem.h
index 3dce87f..1c354b7 100644
--- a/filesystem/include/filesystem.h
+++ b/filesystem/include/filesystem.h
@@ -3,7 +3,6 @@
  */
 #pragma once
 
-#include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 
@@ -12,8 +11,3 @@ size_t get_file_size(FILE* file);
 
 /// Read the entire contents of the file into memory.
 void* read_file(const char* filepath);
-
-/// Make a path relative to the parent directory of a file.
-bool make_relative_path(
-    const char* filepath, const char* path, char* relative,
-    size_t relative_length);
diff --git a/filesystem/include/path.h b/filesystem/include/path.h
new file mode 100644
index 0000000..8ad885d
--- /dev/null
+++ b/filesystem/include/path.h
@@ -0,0 +1,38 @@
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef struct path {
+  char*  data;
+  size_t size; // Does not include null terminator. 0 if data is null.
+} path;
+
+/// Create a new path.
+path path_new(const char*);
+
+/// Free the path's memory.
+void path_del(path*);
+
+/// Return a C string from the path.
+static inline const char* path_cstr(path p) { return p.data; }
+
+/// Return true if the path is empty, false otherwise.
+static inline bool path_empty(path p) {
+  assert((p.data != 0) || (p.size == 0)); // null data -> 0 size
+  return p.data != 0;
+}
+
+/// Returns the parent directory, or empty path if the given path has no parent.
+/// The returned path is a slice of the input path; this function does not
+/// allocate.
+path path_parent_dir(path);
+
+/// Concatenate two paths.
+path path_concat(path left, path right);
+
+/// Make a path relative to the parent directory of a file.
+bool path_make_relative(
+    const char* filepath, const char* path, char* relative,
+    size_t relative_length);
diff --git a/filesystem/src/filesystem.c b/filesystem/src/filesystem.c
index f6bb693..b228e85 100644
--- a/filesystem/src/filesystem.c
+++ b/filesystem/src/filesystem.c
@@ -1,6 +1,7 @@
 #include <filesystem.h>
 
 #include <assert.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -54,42 +55,3 @@ cleanup:
   }
   return 0;
 }
-
-bool make_relative_path(
-    const char* filepath, const char* path, char* relative,
-    size_t relative_length) {
-  assert(filepath);
-  assert(path);
-  assert(relative);
-
-  const size_t filepath_len = strlen(filepath);
-  const size_t path_len     = strlen(path);
-  assert(filepath_len < relative_length);
-  assert(path_len < relative_length);
-
-  // Handle empty filepath.
-  if (filepath_len == 0) {
-    memcpy(relative, path, path_len);
-    return true;
-  }
-
-  // Search for the last / in the file path to get its parent directory.
-  assert(filepath_len > 0);
-  size_t tm_dir_len = 0;
-  for (tm_dir_len = strlen(filepath) - 1; tm_dir_len > 0; --tm_dir_len) {
-    if (filepath[tm_dir_len] == '/') {
-      break;
-    }
-  }
-  tm_dir_len++; // Preserve the backslash.
-
-  // Copy the file path where the parent dir ends.
-  // Make sure there is enough space in the output.
-  if ((tm_dir_len + path_len + 1) >= relative_length) {
-    return false;
-  }
-  memcpy(relative, filepath, tm_dir_len);
-  memcpy(&relative[tm_dir_len], path, path_len);
-
-  return true;
-}
diff --git a/filesystem/src/path.c b/filesystem/src/path.c
new file mode 100644
index 0000000..2ce5a04
--- /dev/null
+++ b/filesystem/src/path.c
@@ -0,0 +1,104 @@
+#include <path.h>
+
+#include <cassert.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const path Empty = (path){0, 0};
+
+path path_new(const char* str) {
+  assert(str);
+  const size_t size = strlen(str);
+  if (size > 0) {
+    char* data = calloc(size + 1, sizeof(char)); // +1 for null
+    memcpy(data, str, size);
+    data[size] = 0;
+    return (path){data, size};
+  }
+  return Empty;
+}
+
+void path_del(path* path) {
+  if (path) {
+    free(path->data);
+    path->data = 0;
+    path->size = 0;
+  }
+}
+
+path path_parent_dir(path p) {
+  assert(p.data);
+
+  if (p.size == 0) {
+    return Empty;
+  }
+  size_t i = p.size - 1;
+  // If the path ends with '/', skip the characters.
+  while ((i > 0) && (p.data[i] == '/')) {
+    i--;
+  }
+  // Search backwards for the parent dir.
+  for (; i > 0; --i) {
+    if (p.data[i] == '/') {
+      return (path){p.data, i + 1};
+    }
+  }
+  return Empty; // No parent.
+}
+
+path path_concat(path left, path right) {
+  assert(left.data);
+  assert(right.data);
+
+  // +1 for separator.
+  const size_t out_size = left.size + right.size + 1;
+  // +1 for null.
+  char* out = calloc(out_size + 1, sizeof(char));
+  ASSERT(out);
+
+  memcpy(out, left.data, left.size);
+  out[left.size] = '/';
+  memcpy(out + left.size + 1, right.data, right.size);
+  out[out_size] = 0;
+
+  return (path){out, out_size};
+}
+
+bool path_make_relative(
+    const char* filepath, const char* path, char* relative,
+    size_t relative_length) {
+  assert(filepath);
+  assert(path);
+  assert(relative);
+
+  const size_t filepath_len = strlen(filepath);
+  const size_t path_len     = strlen(path);
+  assert(filepath_len < relative_length);
+  assert(path_len < relative_length);
+
+  // Handle empty filepath.
+  if (filepath_len == 0) {
+    memcpy(relative, path, path_len);
+    return true;
+  }
+
+  // Search for the last / in the file path to get its parent directory.
+  assert(filepath_len > 0);
+  size_t tm_dir_len = 0;
+  for (tm_dir_len = strlen(filepath) - 1; tm_dir_len > 0; --tm_dir_len) {
+    if (filepath[tm_dir_len] == '/') {
+      break;
+    }
+  }
+  tm_dir_len++; // Preserve the backslash.
+
+  // Copy the file path where the parent dir ends.
+  // Make sure there is enough space in the output.
+  if ((tm_dir_len + path_len + 1) >= relative_length) {
+    return false;
+  }
+  memcpy(relative, filepath, tm_dir_len);
+  memcpy(&relative[tm_dir_len], path, path_len);
+
+  return true;
+}