Add path API

3 files changed, 771 insertions, 0 deletions

diff --git a/src/index_range.h b/src/index_range.h
new file mode 100644
index 0000000..1e06e90
--- /dev/null
+++ b/src/index_range.h
@@ -0,0 +1,28 @@
+// Copyright 2022 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#ifndef ZIX_INDEX_RANGE_H
+#define ZIX_INDEX_RANGE_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef struct {
+  size_t begin; ///< Index to the first character
+  size_t end;   ///< Index one past the last character
+} ZixIndexRange;
+
+static inline ZixIndexRange
+zix_make_range(const size_t begin, const size_t end)
+{
+  const ZixIndexRange result = {begin, end};
+  return result;
+}
+
+static inline bool
+zix_is_empty_range(const ZixIndexRange range)
+{
+  return range.begin == range.end;
+}
+
+#endif // ZIX_INDEX_RANGE_H
diff --git a/src/path.c b/src/path.c
new file mode 100644
index 0000000..aa787b3
--- /dev/null
+++ b/src/path.c
@@ -0,0 +1,712 @@
+// Copyright 2007-2022 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#include "zix/path.h"
+
+#include "index_range.h"
+#include "path_iter.h"
+
+#include "zix/string_view.h"
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+
+static const ZixIndexRange two_range = {0U, 2U};
+static const ZixIndexRange one_range = {0U, 1U};
+
+#ifdef _WIN32
+
+#  define ZIX_DIR_SEP '\\' // Backslash is preferred on Windows
+
+static inline bool
+is_dir_sep(const char c)
+{
+  return c == '/' || c == '\\';
+}
+
+static inline bool
+is_any_sep(const char c)
+{
+  return c == '/' || c == ':' || c == '\\';
+}
+
+static bool
+is_root_name_char(const char c)
+{
+  return c && !is_dir_sep(c);
+}
+
+static ZixIndexRange
+zix_path_root_name_range(const char* const path)
+{
+  ZixIndexRange result = {0U, 0U};
+
+  if (path) {
+    if (((path[0] >= 'A' && path[0] <= 'Z') ||
+         (path[0] >= 'a' && path[0] <= 'z')) &&
+        path[1] == ':') {
+      // A root that starts with a letter then ':' has a name like "C:"
+      result.end = 2U;
+
+    } else if (is_dir_sep(path[0]) && is_dir_sep(path[1]) &&
+               is_root_name_char(path[2])) {
+      // A root that starts with two separators has a name like "\\host"
+      result.end = 2U;
+      while (is_root_name_char(path[result.end])) {
+        ++result.end;
+      }
+    }
+  }
+
+  return result;
+}
+
+#else
+
+#  define ZIX_DIR_SEP '/' // Slash is the only separator on other platforms
+
+static inline bool
+is_dir_sep(const char c)
+{
+  return c == '/';
+}
+
+static inline bool
+is_any_sep(const char c)
+{
+  return c == '/';
+}
+
+static inline ZixIndexRange
+zix_path_root_name_range(const char* const path)
+{
+  (void)path;
+  return zix_make_range(0U, 0U);
+}
+
+#endif
+
+typedef struct {
+  ZixIndexRange name;
+  ZixIndexRange dir;
+} ZixRootSlices;
+
+static ZixRootSlices
+zix_path_root_slices(const char* const path)
+{
+  // A root name not trailed by a separator has no root directory
+  const ZixIndexRange name    = zix_path_root_name_range(path);
+  const size_t        dir_len = (size_t)(path && is_dir_sep(path[name.end]));
+  if (!dir_len) {
+    const ZixRootSlices result = {name, {name.end, name.end}};
+    return result;
+  }
+
+  // Skip redundant root directory separators
+  ZixIndexRange dir = {name.end, name.end + dir_len};
+  while (is_dir_sep(path[dir.end])) {
+    dir.begin = dir.end++;
+  }
+
+  const ZixRootSlices result = {name, dir};
+  return result;
+}
+
+static bool
+zix_string_ranges_equal(const char* const   lhs,
+                        const ZixIndexRange lhs_range,
+                        const char* const   rhs,
+                        const ZixIndexRange rhs_range)
+{
+  const size_t lhs_len = lhs_range.end - lhs_range.begin;
+  const size_t rhs_len = rhs_range.end - rhs_range.begin;
+
+  return lhs_len == rhs_len &&
+         (lhs_len == 0 ||
+          !strncmp(lhs + lhs_range.begin, rhs + rhs_range.begin, lhs_len));
+}
+
+static ZixIndexRange
+zix_path_root_path_range(const char* const path)
+{
+  const ZixRootSlices root    = zix_path_root_slices(path);
+  const size_t        dir_len = (size_t)!zix_is_empty_range(root.dir);
+
+  return zix_is_empty_range(root.name)
+           ? root.dir
+           : zix_make_range(root.name.begin, root.name.end + dir_len);
+}
+
+static ZixIndexRange
+zix_path_parent_path_range(const ZixStringView path)
+{
+  if (!path.length) {
+    return zix_make_range(0U, 0U); // Empty paths have no parent
+  }
+
+  // Find the first relevant character (skip leading root path if any)
+  const ZixIndexRange root = zix_path_root_path_range(path.data);
+  const size_t        p    = root.begin;
+
+  // Scan backwards starting at the last character
+  size_t l = path.length - 1U;
+  if (is_dir_sep(path.data[l])) {
+    // Rewind to the last relevant separator (skip trailing redundant ones)
+    while (l > p && is_dir_sep(path.data[l - 1U])) {
+      --l;
+    }
+  } else {
+    // Rewind to the last relevant character (skip trailing name)
+    while (l > p && !is_dir_sep(path.data[l])) {
+      --l;
+    }
+  }
+
+  if (l <= root.end) {
+    return root;
+  }
+
+  // Drop trailing separators
+  while (l > p && is_dir_sep(path.data[l])) {
+    --l;
+  }
+
+  return zix_make_range(root.begin, root.begin + l + 1U - p);
+}
+
+static ZixIndexRange
+zix_path_filename_range(const ZixStringView path)
+{
+  // Find the first filename character (skip leading root path if any)
+  const size_t begin = zix_path_root_path_range(path.data).end;
+  if (begin == path.length || is_dir_sep(path.data[path.length - 1U])) {
+    return zix_make_range(0U, 0U);
+  }
+
+  // Scan backwards to find the first character after the last separator
+  size_t f = path.length - 1U;
+  while (f > begin && !is_dir_sep(path.data[f - 1])) {
+    --f;
+  }
+
+  return zix_make_range(f, path.length);
+}
+
+static ZixIndexRange
+zix_path_stem_range(const ZixStringView path)
+{
+  const ZixIndexRange name = zix_path_filename_range(path);
+
+  ZixIndexRange stem = name;
+  if (!zix_is_empty_range(stem) &&
+      !zix_string_ranges_equal(path.data, stem, ".", one_range) &&
+      !zix_string_ranges_equal(path.data, stem, "..", two_range)) {
+    // Scan backwards to the last "." after the last directory separator
+    --stem.end;
+    while (stem.end > stem.begin && path.data[stem.end] != '.') {
+      --stem.end;
+    }
+  }
+
+  return zix_is_empty_range(stem) ? name : stem;
+}
+
+static ZixIndexRange
+zix_path_extension_range(const ZixStringView path)
+{
+  const ZixIndexRange stem = zix_path_stem_range(path);
+
+  return zix_is_empty_range(stem)
+           ? stem
+           : zix_make_range(stem.end, stem.end + path.length - stem.end);
+}
+
+char*
+zix_path_join(ZixAllocator* const allocator,
+              const char* const   a,
+              const char* const   b)
+{
+  const ZixStringView b_view = zix_optional_string(b);
+  if (!a || !a[0]) {
+    return zix_string_view_copy(allocator, b_view);
+  }
+
+  const ZixStringView a_view = zix_optional_string(a);
+  const ZixRootSlices a_root = zix_path_root_slices(a);
+  const ZixRootSlices b_root = zix_path_root_slices(b);
+
+#ifdef _WIN32
+  // If the RHS has a different root name, just copy it
+  if (b_root.name.end &&
+      !zix_string_ranges_equal(a, a_root.name, b, b_root.name)) {
+    return zix_string_view_copy(allocator, b_view);
+  }
+#endif
+
+  // Determine how to join paths
+  const bool a_has_root_dir = !zix_is_empty_range(a_root.dir);
+  const bool a_has_filename = zix_path_has_filename(a_view.data);
+  size_t     prefix_len     = a_view.length;
+  bool       add_sep        = false;
+  if (!zix_is_empty_range(b_root.dir)) {
+    prefix_len = a_root.name.end; // Omit any path from a
+  } else if (a_has_filename || (!a_has_root_dir && zix_path_is_absolute(a))) {
+    add_sep = true; // Add a preferred separator after a
+  }
+
+  const size_t path_len = prefix_len + (size_t)add_sep + b_view.length;
+  char* const  path     = (char*)zix_calloc(allocator, path_len + 1U, 1U);
+
+  if (path) {
+    memcpy(path, a, prefix_len);
+
+    size_t p = prefix_len;
+    if (add_sep) {
+      path[p++] = ZIX_DIR_SEP;
+    }
+
+    if (b_view.length > b_root.name.end) {
+      memcpy(path + p, b + b_root.name.end, b_view.length - b_root.name.end);
+      path[p + b_view.length] = '\0';
+    }
+  }
+
+  return path;
+}
+
+char*
+zix_path_preferred(ZixAllocator* const allocator, const char* const path)
+{
+  const ZixStringView path_view = zix_string(path);
+  char* const result = (char*)zix_calloc(allocator, path_view.length + 1U, 1U);
+
+  if (result) {
+    for (size_t i = 0U; i < path_view.length; ++i) {
+      result[i] = (char)(is_dir_sep(path[i]) ? ZIX_DIR_SEP : path[i]);
+    }
+  }
+
+  return result;
+}
+
+char*
+zix_path_lexically_normal(ZixAllocator* const allocator, const char* const path)
+{
+  static const char sep = ZIX_DIR_SEP;
+
+  /* Loosely following the normalization algorithm from
+     <https://en.cppreference.com/w/cpp/filesystem/path>, but in such a way
+     that only a single buffer (the result) is needed.  This means that
+     dot-dot segments are relatively expensive, but it beats a stack in
+     everyday common cases. */
+
+  if (!path[0]) {
+    return (char*)zix_calloc(allocator, 1U, 1U); // The empty path is normal
+  }
+
+  // Allocate a result buffer, with space for one additional character
+  const ZixStringView path_view = zix_string(path);
+  const size_t        path_len  = path_view.length;
+  char* const         result = (char*)zix_calloc(allocator, path_len + 2U, 1);
+  size_t              r      = 0U;
+
+  // Copy root, normalizing separators as we go
+  const ZixIndexRange root     = zix_path_root_path_range(path);
+  const size_t        root_len = root.end - root.begin;
+  for (size_t i = 0; i < root_len; ++i) {
+    result[r++] = (char)(is_dir_sep(path[i]) ? sep : path[i]);
+  }
+
+  // Copy path, removing dot entries and collapsing separators as we go
+  for (size_t i = root.end; i < path_len; ++i) {
+    if (is_dir_sep(path[i])) {
+      if ((i >= root.end) && ((r == root.end + 1U && result[r - 1] == '.') ||
+                              (r >= root.end + 2U && result[r - 2] == sep &&
+                               result[r - 1] == '.'))) {
+        // Remove dot entry and any immediately following separators
+        result[--r] = '\0';
+
+      } else {
+        // Replace separators with a single preferred separator
+        result[r++] = sep;
+      }
+
+      // Collapse redundant separators
+      while (is_dir_sep(path[i + 1])) {
+        ++i;
+      }
+
+    } else {
+      result[r++] = path[i];
+    }
+  }
+
+  // Collapse any dot-dot entries following a directory name
+  size_t last = r;
+  size_t next = 0;
+  for (size_t i = root_len; i < r;) {
+    if (last < r && i > 2 && i + 1 <= r && result[i - 2] == sep &&
+        result[i - 1] == '.' && result[i] == '.' &&
+        (!result[i + 1] || is_dir_sep(result[i + 1]))) {
+      if (i < r && result[i + 1] == sep) {
+        ++i;
+      }
+
+      const size_t suffix_len = r - i - 1U;
+      memmove(result + last, result + i + 1, suffix_len);
+      r         = r - ((r - last) - suffix_len);
+      result[r] = '\0';
+      i         = 0;
+      last      = r;
+      next      = 0;
+    } else {
+      if (i >= 1 && result[i - 1] == sep) {
+        next = i;
+      }
+
+      if (result[i] != sep && result[i] != '.') {
+        last = next;
+      }
+      ++i;
+    }
+  }
+
+  // Remove any dot-dot entries following the root directory
+  if (root_len && is_dir_sep(result[root_len - 1U])) {
+    size_t start = root_len;
+    while (start < r && result[start] == '.' && result[start + 1] == '.' &&
+           (result[start + 2] == sep || result[start + 2] == '\0')) {
+      start += (result[start + 2] == sep) ? 3U : 2U;
+    }
+
+    if (start > root_len) {
+      if (start < r) {
+        memmove(result + root_len, result + start, r - start);
+        r = root_len + r - start;
+      } else {
+        r = root_len;
+      }
+
+      result[r] = '\0';
+      return result;
+    }
+  }
+
+  // Remove trailing dot entry
+  if (r >= 2U && is_any_sep(result[r - 2]) && result[r - 1] == '.') {
+    result[r - 1] = '\0';
+  }
+
+  // Remove trailing dot-dot entry
+  if (r >= 3U && result[r - 3] == '.' && result[r - 2] == '.' &&
+      is_any_sep(result[r - 1])) {
+    result[r - 1] = '\0';
+  }
+
+  // If the path is empty, add a dot
+  if (!result[0]) {
+    result[0] = '.';
+    result[1] = '\0';
+  }
+
+  return result;
+}
+
+static ZixPathIter
+make_iter(const ZixPathIterState state, const ZixIndexRange range)
+{
+  const ZixPathIter result = {range, state};
+  return result;
+}
+
+ZixPathIter
+zix_path_begin(const char* const path)
+{
+  const ZixPathIter iter = {zix_path_root_name_range(path), ZIX_PATH_ROOT_NAME};
+
+  return (iter.range.end > iter.range.begin) ? iter
+         : path                              ? zix_path_next(path, iter)
+                                             : zix_path_next("", iter);
+}
+
+ZixPathIter
+zix_path_next(const char* const path, ZixPathIter iter)
+{
+  if (iter.state == ZIX_PATH_ROOT_NAME) {
+    if (is_dir_sep(path[iter.range.end])) {
+      return make_iter(ZIX_PATH_ROOT_DIRECTORY,
+                       zix_make_range(iter.range.end, iter.range.end + 1U));
+    }
+  }
+
+  if (iter.state <= ZIX_PATH_ROOT_DIRECTORY) {
+    iter.range.begin = iter.range.end;
+    iter.state       = ZIX_PATH_FILE_NAME;
+  }
+
+  if (iter.state == ZIX_PATH_FILE_NAME) {
+    // If the last range end was the end of the path, we're done
+    iter.range.begin = iter.range.end;
+    if (!path[iter.range.begin]) {
+      return make_iter(ZIX_PATH_END, iter.range);
+    }
+
+    // Skip any leading separators
+    while (is_dir_sep(path[iter.range.begin])) {
+      iter.range.begin = ++iter.range.end;
+    }
+
+    // Advance end to the next separator or path end
+    while (path[iter.range.end] && !is_dir_sep(path[iter.range.end])) {
+      ++iter.range.end;
+    }
+  }
+
+  return iter;
+}
+
+static size_t
+zix_path_append(char* const       buf,
+                const size_t      offset,
+                const char* const string,
+                const size_t      length)
+{
+  size_t o = offset;
+  if (offset) {
+    buf[o++] = ZIX_DIR_SEP;
+  }
+
+  memcpy(buf + o, string, length);
+  return o + length;
+}
+
+char*
+zix_path_lexically_relative(ZixAllocator* const allocator,
+                            const char* const   path,
+                            const char* const   base)
+{
+  // Mismatched roots can't be expressed in relative form
+  const ZixRootSlices path_root         = zix_path_root_slices(path);
+  const ZixRootSlices base_root         = zix_path_root_slices(base);
+  const bool          path_has_root_dir = !zix_is_empty_range(path_root.dir);
+  const bool          base_has_root_dir = !zix_is_empty_range(base_root.dir);
+  if (!zix_string_ranges_equal(path, path_root.name, base, base_root.name) ||
+      (zix_path_is_absolute(path) != zix_path_is_absolute(base)) ||
+      (!path_has_root_dir && base_has_root_dir)) {
+    return NULL;
+  }
+
+  // Find the first mismatching element in the paths (or the end)
+  ZixPathIter a = zix_path_begin(path);
+  ZixPathIter b = zix_path_begin(base);
+  while (a.state != ZIX_PATH_END && b.state != ZIX_PATH_END &&
+         a.state == b.state &&
+         zix_string_ranges_equal(path, a.range, base, b.range)) {
+    a = zix_path_next(path, a);
+    b = zix_path_next(base, b);
+  }
+
+  // Matching paths reduce to "."
+  if ((a.state == ZIX_PATH_END && b.state == ZIX_PATH_END) ||
+      (zix_is_empty_range(a.range) && b.state == ZIX_PATH_END)) {
+    return zix_string_view_copy(allocator, zix_string("."));
+  }
+
+  // Count the trailing non-matching entries in base
+  size_t n_base_up   = 0U;
+  size_t n_non_empty = 0U;
+  for (; b.state < ZIX_PATH_END; b = zix_path_next(base, b)) {
+    if (!zix_is_empty_range(b.range)) {
+      if (zix_string_ranges_equal(base, b.range, "..", two_range)) {
+        ++n_base_up;
+      } else if (!zix_string_ranges_equal(base, b.range, ".", one_range)) {
+        ++n_non_empty;
+      }
+    }
+  }
+
+  // Base can't have too many up-references
+  if (n_base_up > n_non_empty) {
+    return NULL;
+  }
+
+  const size_t n_up =
+    (a.state == ZIX_PATH_ROOT_DIRECTORY) ? 0U : (n_non_empty - n_base_up);
+
+  // A result with no up-references or names reduces to "."
+  if (n_up == 0 && a.state == ZIX_PATH_END) {
+    return zix_string_view_copy(allocator, zix_string("."));
+  }
+
+  // Allocate buffer for relative path result
+  const size_t path_len = strlen(path);
+  const size_t rel_len  = (n_up * 3U) + path_len - a.range.begin;
+  char* const  rel      = (char*)zix_calloc(allocator, rel_len + 1U, 1U);
+
+  // Write leading up-references
+  size_t offset = 0U;
+  for (size_t i = 0U; i < n_up; ++i) {
+    offset = zix_path_append(rel, offset, "..", 2U);
+  }
+
+  const char path_last = path[path_len - 1U];
+  if (a.range.begin < path_len) {
+    // Copy suffix from path (from `a` to the end)
+    const size_t suffix_len = path_len - a.range.begin;
+    offset = zix_path_append(rel, offset, path + a.range.begin, suffix_len);
+  } else if (n_up && path_len > 1 && is_dir_sep(path_last)) {
+    // Copy trailing directory separator from path
+    rel[offset++] = path_last;
+  }
+
+  rel[offset++] = '\0';
+  return rel;
+}
+
+// Decomposition
+
+static ZixStringView
+range_string_view(const char* const path, const ZixIndexRange range)
+{
+  return zix_substring(path + range.begin, range.end - range.begin);
+}
+
+#ifdef _WIN32
+
+ZixStringView
+zix_path_root_name(const char* const path)
+{
+  return range_string_view(path, zix_path_root_name_range(path));
+}
+
+#else
+
+ZixStringView
+zix_path_root_name(const char* const path)
+{
+  (void)path;
+  return zix_empty_string();
+}
+
+#endif
+
+ZixStringView
+zix_path_root_directory(const char* const path)
+{
+  return range_string_view(path, zix_path_root_slices(path).dir);
+}
+
+ZixStringView
+zix_path_root_path(const char* const path)
+{
+  return range_string_view(path, zix_path_root_path_range(path));
+}
+
+ZixStringView
+zix_path_relative_path(const char* const path)
+{
+  const ZixStringView path_view = zix_string(path);
+  const size_t        path_len  = path_view.length;
+  const ZixIndexRange root      = zix_path_root_path_range(path);
+
+  return range_string_view(path, zix_make_range(root.end, path_len));
+}
+
+ZixStringView
+zix_path_parent_path(const char* const path)
+{
+  return range_string_view(path, zix_path_parent_path_range(zix_string(path)));
+}
+
+ZixStringView
+zix_path_filename(const char* const path)
+{
+  return range_string_view(path, zix_path_filename_range(zix_string(path)));
+}
+
+ZixStringView
+zix_path_stem(const char* const path)
+{
+  return range_string_view(path, zix_path_stem_range(zix_string(path)));
+}
+
+ZixStringView
+zix_path_extension(const char* const path)
+{
+  return range_string_view(path,
+                           zix_path_extension_range(zix_optional_string(path)));
+}
+
+// Queries
+
+bool
+zix_path_has_root_path(const char* const path)
+{
+  return !zix_is_empty_range(zix_path_root_path_range(path));
+}
+
+bool
+zix_path_has_root_name(const char* const path)
+{
+  return !zix_is_empty_range(zix_path_root_name_range(path));
+}
+
+bool
+zix_path_has_root_directory(const char* const path)
+{
+  return !zix_is_empty_range(zix_path_root_slices(path).dir);
+}
+
+bool
+zix_path_has_relative_path(const char* const path)
+{
+  return path && path[zix_path_root_path_range(path).end];
+}
+
+bool
+zix_path_has_parent_path(const char* const path)
+{
+  return !zix_is_empty_range(
+    zix_path_parent_path_range(zix_optional_string(path)));
+}
+
+bool
+zix_path_has_filename(const char* const path)
+{
+  return !zix_is_empty_range(
+    zix_path_filename_range(zix_optional_string(path)));
+}
+
+bool
+zix_path_has_stem(const char* const path)
+{
+  return !zix_is_empty_range(zix_path_stem_range(zix_optional_string(path)));
+}
+
+bool
+zix_path_has_extension(const char* const path)
+{
+  return !zix_is_empty_range(
+    zix_path_extension_range(zix_optional_string(path)));
+}
+
+bool
+zix_path_is_absolute(const char* const path)
+{
+#ifdef _WIN32
+  const ZixRootSlices root = zix_path_root_slices(path);
+  return (!zix_is_empty_range(root.name) &&
+          (!zix_is_empty_range(root.dir) ||
+           (is_dir_sep(path[0]) && is_dir_sep(path[1]))));
+
+#else
+  return path && is_dir_sep(path[0]);
+#endif
+}
+
+bool
+zix_path_is_relative(const char* const path)
+{
+  return !zix_path_is_absolute(path);
+}
diff --git a/src/path_iter.h b/src/path_iter.h
new file mode 100644
index 0000000..b3b23e8
--- /dev/null
+++ b/src/path_iter.h
@@ -0,0 +1,31 @@
+// Copyright 2022 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#ifndef ZIX_PATH_ITER_H
+#define ZIX_PATH_ITER_H
+
+#include "index_range.h"
+
+#include "zix/attributes.h"
+
+typedef enum {
+  ZIX_PATH_ROOT_NAME,
+  ZIX_PATH_ROOT_DIRECTORY,
+  ZIX_PATH_FILE_NAME,
+  ZIX_PATH_END,
+} ZixPathIterState;
+
+typedef struct {
+  ZixIndexRange    range;
+  ZixPathIterState state;
+} ZixPathIter;
+
+ZIX_PURE_FUNC
+ZixPathIter
+zix_path_begin(const char* ZIX_NULLABLE path);
+
+ZIX_PURE_FUNC
+ZixPathIter
+zix_path_next(const char* ZIX_NONNULL path, ZixPathIter iter);
+
+#endif // ZIX_PATH_ITER_H