uniq: Improve POSIX compliance

Adds -d, -c, -i, -f and -s options.
It differs a little bit from other implementations,
but it does the trick and corresponds to POSIX's description

Userland/Utilities/uniq.cpp

@@ -4,76 +4,111 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/CharacterTypes.h>
 #include <AK/RefPtr.h>
+#include <AK/StringView.h>
 #include <LibCore/ArgsParser.h>
+#include <LibCore/Stream.h>
 #include <LibCore/System.h>
-#include <errno.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 
-struct linebuf {
-    char* buf = NULL;
-    size_t len = 0;
-};
-
-static FILE* get_stream(char const* filepath, char const* perms)
+static ErrorOr<void> write_line_content(StringView line, size_t count, bool duplicates_only, bool print_count, Core::Stream::File& outfile)
 {
-    FILE* ret;
+    if (duplicates_only && count <= 1)
+        return {};
 
-    if (filepath == nullptr) {
-        if (perms[0] == 'r')
-            return stdin;
-        return stdout;
+    if (print_count)
+        TRY(outfile.write(String::formatted("{} {}\n", count, line).bytes()));
+    else
+        TRY(outfile.write(String::formatted("{}\n", line).bytes()));
+    return {};
+}
+
+static StringView skip(StringView line, unsigned char_skip_count, unsigned field_skip_count)
+{
+    line = line.trim("\n"sv);
+    if (field_skip_count) {
+        bool in_field = false;
+        int field_index = 0;
+        unsigned current_field = 0;
+        for (size_t i = 0; i < line.length(); i++) {
+            char c = line[i];
+            if (is_ascii_space(c)) {
+                in_field = false;
+                field_index = i;
+                if (++current_field > field_skip_count)
+                    break;
+            } else if (!in_field) {
+                in_field = true;
+            }
+        }
+        line = line.substring_view(field_index);
     }
-
-    ret = fopen(filepath, perms);
-    if (ret == nullptr) {
-        perror("fopen");
-        exit(1);
-    }
-
-    return ret;
+    char_skip_count = min(char_skip_count, line.length());
+    return line.substring_view(char_skip_count);
 }
 
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     TRY(Core::System::pledge("stdio rpath wpath cpath"));
 
-    char const* inpath = nullptr;
-    char const* outpath = nullptr;
+    StringView inpath;
+    StringView outpath;
+    bool duplicates_only = false;
+    bool unique_only = false;
+    bool ignore_case = false;
+    bool print_count = false;
+    unsigned skip_chars = 0;
+    unsigned skip_fields = 0;
+
     Core::ArgsParser args_parser;
+    args_parser.add_option(duplicates_only, "Only print duplicated lines", "repeated", 'd');
+    args_parser.add_option(unique_only, "Only print unique lines (default)", "unique", 'u');
+    args_parser.add_option(ignore_case, "Ignore case when comparing lines", "ignore-case", 'i');
+    args_parser.add_option(print_count, "Prefix each line by its number of occurrences", "count", 'c');
+    args_parser.add_option(skip_chars, "Skip N chars", "skip-chars", 's', "N");
+    args_parser.add_option(skip_fields, "Skip N fields", "skip-fields", 'f', "N");
     args_parser.add_positional_argument(inpath, "Input file", "input", Core::ArgsParser::Required::No);
     args_parser.add_positional_argument(outpath, "Output file", "output", Core::ArgsParser::Required::No);
     args_parser.parse(arguments);
 
-    FILE* infile = get_stream(inpath, "r");
-    FILE* outfile = get_stream(outpath, "w");
-
-    struct linebuf buffers[2];
-    struct linebuf* previous = &(buffers[0]);
-    struct linebuf* current = &(buffers[1]);
-    bool first_run = true;
-    for (;;) {
-        errno = 0;
-        ssize_t rc = getline(&(current->buf), &(current->len), infile);
-        if (rc < 0 && errno != 0) {
-            perror("getline");
-            exit(1);
-        }
-        if (rc < 0)
-            break;
-        if (!first_run && strcmp(current->buf, previous->buf) == 0)
-            continue;
-
-        fputs(current->buf, outfile);
-        swap(current, previous);
-        first_run = false;
+    if (!unique_only && !duplicates_only) {
+        unique_only = true;
+    } else if (unique_only && duplicates_only) {
+        // Printing duplicated and unique lines shouldn't print anything
+        return 0;
     }
 
-    fclose(infile);
-    fclose(outfile);
+    auto infile = TRY(Core::Stream::BufferedFile::create(TRY(Core::Stream::File::open_file_or_standard_stream(inpath, Core::Stream::OpenMode::Read))));
+    auto outfile = TRY(Core::Stream::File::open_file_or_standard_stream(outpath, Core::Stream::OpenMode::Write));
+
+    size_t count = 0;
+    ByteBuffer previous_buf = TRY(ByteBuffer::create_uninitialized(1024));
+    ByteBuffer current_buf = TRY(ByteBuffer::create_uninitialized(1024));
+
+    StringView previous = TRY(infile->read_line(previous_buf));
+    StringView previous_to_compare = skip(previous, skip_chars, skip_fields);
+
+    while (TRY(infile->can_read_line())) {
+        // FIXME: The buffer does not automatically resize,
+        // and this will return EMSGSIZE if the read line
+        // is more than 1024 bytes.
+        StringView current = TRY(infile->read_line(current_buf));
+
+        StringView current_to_compare = skip(current, skip_chars, skip_fields);
+        bool lines_equal = ignore_case ? current_to_compare.equals_ignoring_case(previous_to_compare) : current_to_compare == previous_to_compare;
+        if (!lines_equal) {
+            TRY(write_line_content(previous, count, duplicates_only, print_count, *outfile));
+            count = 1;
+        } else {
+            count++;
+        }
+        swap(current_to_compare, previous_to_compare);
+        swap(current_buf, previous_buf);
+        swap(current, previous);
+    }
+
+    TRY(write_line_content(previous, count, duplicates_only, print_count, *outfile));
 
     return 0;
 }