LibCore: Add format option for DateTime::to_string() (#1358)

2 files changed, 148 insertions, 5 deletions

diff --git a/Libraries/LibCore/DateTime.cpp b/Libraries/LibCore/DateTime.cpp
index e0ace57089..1836c2d6a7 100644
--- a/Libraries/LibCore/DateTime.cpp
+++ b/Libraries/LibCore/DateTime.cpp
@@ -24,7 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <AK/String.h>
+#include <AK/StringBuilder.h>
 #include <LibCore/DateTime.h>
 #include <sys/time.h>
 #include <time.h>
@@ -51,9 +51,152 @@ DateTime DateTime::from_timestamp(time_t timestamp)
     return dt;
 }
 
-String DateTime::to_string() const
+String DateTime::to_string(const String& format) const
 {
-    return String::format("%04u-%02u-%02u %02u:%02u:%02u", m_year, m_month, m_day, m_hour, m_minute, m_second);
+
+    const char wday_short_names[7][4] = {
+        "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+    };
+    const char wday_long_names[7][10] = {
+        "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
+    };
+    const char mon_short_names[12][4] = {
+        "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+    };
+    const char mon_long_names[12][10] = {
+        "January", "February", "March", "April", "May", "June",
+        "July", "Auguest", "September", "October", "November", "December"
+    };
+
+    struct tm tm;
+    localtime_r(&m_timestamp, &tm);
+    StringBuilder builder;
+    const int format_len = format.length();
+
+    for (int i = 0; i < format_len; ++i) {
+        if (format[i] != '%') {
+            builder.append(format[i]);
+        } else {
+            if (++i == format_len)
+                return String();
+
+            switch (format[i]) {
+            case 'a':
+                builder.append(wday_short_names[tm.tm_wday]);
+                break;
+            case 'A':
+                builder.append(wday_long_names[tm.tm_wday]);
+                break;
+            case 'b':
+                builder.append(mon_short_names[tm.tm_mon]);
+                break;
+            case 'B':
+                builder.append(mon_long_names[tm.tm_mon]);
+                break;
+            case 'C':
+                builder.appendf("%02d", (tm.tm_year + 1900) / 100);
+                break;
+            case 'd':
+                builder.appendf("%02d", tm.tm_mday);
+                break;
+            case 'D':
+                builder.appendf("%02d/%02d/%02d", tm.tm_mon + 1, tm.tm_mday, (tm.tm_year + 1900) % 100);
+                break;
+            case 'e':
+                builder.appendf("%2d", tm.tm_mday);
+                break;
+            case 'h':
+                builder.append(mon_short_names[tm.tm_mon]);
+                break;
+            case 'H':
+                builder.appendf("%02d", tm.tm_hour);
+                break;
+            case 'I':
+                builder.appendf("%02d", tm.tm_hour % 12);
+                break;
+            case 'j':
+                builder.appendf("%03d", tm.tm_yday + 1);
+                break;
+            case 'm':
+                builder.appendf("%02d", tm.tm_mon + 1);
+                break;
+            case 'M':
+                builder.appendf("%02d", tm.tm_min);
+                break;
+            case 'n':
+                builder.append('\n');
+                break;
+            case 'p':
+                builder.append(tm.tm_hour < 12 ? "a.m." : "p.m.");
+                break;
+            case 'r':
+                builder.appendf("%02d:%02d:%02d %s", tm.tm_hour % 12, tm.tm_min, tm.tm_sec, tm.tm_hour < 12 ? "a.m." : "p.m.");
+                break;
+            case 'R':
+                builder.appendf("%02d:%02d", tm.tm_hour, tm.tm_min);
+                break;
+            case 'S':
+                builder.appendf("%02d", tm.tm_sec);
+                break;
+            case 't':
+                builder.append('\t');
+                break;
+            case 'T':
+                builder.appendf("%02d:%02d:%02d", tm.tm_hour, tm.tm_min, tm.tm_sec);
+                break;
+            case 'u':
+                builder.appendf("%d", tm.tm_wday ? tm.tm_wday : 7);
+                break;
+            case 'U': {
+                const int wday_of_year_beginning = (tm.tm_wday + 6 * tm.tm_yday) % 7;
+                const int week_number = (tm.tm_yday + wday_of_year_beginning) / 7;
+                builder.appendf("%02d", week_number);
+                break;
+            }
+            case 'V': {
+                const int wday_of_year_beginning = (tm.tm_wday + 6 + 6 * tm.tm_yday) % 7;
+                int week_number = (tm.tm_yday + wday_of_year_beginning) / 7 + 1;
+                if (wday_of_year_beginning > 3) {
+                    if (tm.tm_yday >= 7 - wday_of_year_beginning)
+                        --week_number;
+                    else {
+                        const bool last_year_is_leap = ((tm.tm_year + 1900 - 1) % 4 == 0 && (tm.tm_year + 1900 - 1) % 100 != 0) || (tm.tm_year + 1900 - 1) % 400 == 0;
+                        const int days_of_last_year = 365 + last_year_is_leap;
+                        const int wday_of_last_year_beginning = (wday_of_year_beginning + 6 * days_of_last_year) % 7;
+                        week_number = (days_of_last_year + wday_of_last_year_beginning) / 7 + 1;
+                        if (wday_of_last_year_beginning > 3)
+                            --week_number;
+                    }
+                }
+                builder.appendf("%02d", week_number);
+                break;
+            }
+            case 'w':
+                builder.appendf("%d", tm.tm_wday);
+                break;
+            case 'W': {
+                const int wday_of_year_beginning = (tm.tm_wday + 6 + 6 * tm.tm_yday) % 7;
+                const int week_number = (tm.tm_yday + wday_of_year_beginning) / 7;
+                builder.appendf("%02d", week_number);
+                break;
+            }
+            case 'y':
+                builder.appendf("%02d", (tm.tm_year + 1900) % 100);
+                break;
+            case 'Y':
+                builder.appendf("%d", tm.tm_year + 1900);
+                break;
+            case '%':
+                builder.append('%');
+                break;
+            default:
+                return String();
+            }
+        }
+    }
+
+    return builder.build();
 }
 
 const LogStream& operator<<(const LogStream& stream, const DateTime& value)
diff --git a/Libraries/LibCore/DateTime.h b/Libraries/LibCore/DateTime.h
index a27a04c2d9..56a9b17680 100644
--- a/Libraries/LibCore/DateTime.h
+++ b/Libraries/LibCore/DateTime.h
@@ -26,7 +26,7 @@
 
 #pragma once
 
-#include <AK/Forward.h>
+#include <AK/String.h>
 #include <time.h>
 
 namespace Core {
@@ -43,7 +43,7 @@ public:
     unsigned minute() const { return m_minute; }
     unsigned second() const { return m_second; }
 
-    String to_string() const;
+    String to_string(const String& format = "%Y-%m-%d %H:%M:%S") const;
 
     static DateTime now();
     static DateTime from_timestamp(time_t);