From 2be99d3a746734676fa736eb1d7afcdb9a4f5fd1 Mon Sep 17 00:00:00 2001
From: Devin Smith <devinsmith@deephaven.io>
Date: Mon, 6 Oct 2025 10:09:49 -0700
Subject: [PATCH] Add a custom DateTimeFormatter parser

---
 .../csv/parsers/DateTimeFormatterParser.java  | 123 ++++++++++++++++++
 1 file changed, 123 insertions(+)
 create mode 100644 src/main/java/io/deephaven/csv/parsers/DateTimeFormatterParser.java

diff --git a/src/main/java/io/deephaven/csv/parsers/DateTimeFormatterParser.java b/src/main/java/io/deephaven/csv/parsers/DateTimeFormatterParser.java
new file mode 100644
index 00000000..e2e87ba5
--- /dev/null
+++ b/src/main/java/io/deephaven/csv/parsers/DateTimeFormatterParser.java
@@ -0,0 +1,123 @@
+package io.deephaven.csv.parsers;
+
+import io.deephaven.csv.sinks.Sink;
+import io.deephaven.csv.util.CsvReaderException;
+import org.jetbrains.annotations.NotNull;
+
+import java.time.DateTimeException;
+import java.time.Instant;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.ChronoField;
+import java.time.temporal.TemporalAccessor;
+import java.util.Objects;
+
+import static java.time.temporal.ChronoField.INSTANT_SECONDS;
+import static java.time.temporal.ChronoField.NANO_OF_SECOND;
+
+/**
+ * A {@link DataType#CUSTOM} datetime parser.
+ */
+public final class DateTimeFormatterParser implements Parser<long[]> {
+
+    /**
+     * Creates a {@link DataType#CUSTOM} datetime parser according to the parsing logic of {@code formatter}. The
+     * formatter must {@link DateTimeFormatter#parse(CharSequence) parse} into a {@link TemporalAccessor} that supports
+     * fields {@link ChronoField#INSTANT_SECONDS} and {@link ChronoField#NANO_OF_SECOND}.
+     *
+     * @param formatter the formatter
+     * @return the parser
+     */
+    public static DateTimeFormatterParser of(final DateTimeFormatter formatter) {
+        if (!supportsInstant(formatter)) {
+            throw new IllegalArgumentException();
+        }
+        return new DateTimeFormatterParser(formatter.withResolverFields(INSTANT_SECONDS, NANO_OF_SECOND));
+    }
+
+    private static boolean supportsInstant(final DateTimeFormatter formatter) {
+        // TODO: we are really checking if the parsed result supports the fields
+        // INSTANT_SECONDS and NANO_OF_SECOND; not sure if this check is equivalent.
+        try {
+            formatter.format(Instant.EPOCH);
+            return true;
+        } catch (final DateTimeException e) {
+            return false;
+        }
+    }
+
+    private final DateTimeFormatter formatter;
+
+    private DateTimeFormatterParser(final DateTimeFormatter formatter) {
+        this.formatter = Objects.requireNonNull(formatter);
+    }
+
+    @NotNull
+    @Override
+    public ParserContext<long[]> makeParserContext(
+            final GlobalContext gctx,
+            final int chunkSize) {
+        final Sink<long[]> sink = gctx.sinkFactory().forDateTimeAsLong(gctx.colNum());
+        return new ParserContext<>(sink, null, DataType.CUSTOM, new long[chunkSize]);
+    }
+
+    @Override
+    public long tryParse(
+            final GlobalContext gctx,
+            final ParserContext<long[]> pctx,
+            final IteratorHolder ih,
+            final long begin,
+            final long end,
+            final boolean appending) throws CsvReaderException {
+        final boolean[] nulls = gctx.nullChunk();
+
+        final Sink<long[]> sink = pctx.sink();
+        final Long reservedValue = gctx.sinkFactory().reservedDateTimeAsLong();
+        final long[] values = pctx.valueChunk();
+
+        long current = begin;
+        int chunkIndex = 0;
+        do {
+            if (chunkIndex == values.length) {
+                sink.write(values, nulls, current, current + chunkIndex, appending);
+                current += chunkIndex;
+                chunkIndex = 0;
+            }
+            if (current + chunkIndex == end) {
+                break;
+            }
+            if (gctx.isNullCell(ih)) {
+                nulls[chunkIndex++] = true;
+                continue;
+            }
+            final TemporalAccessor temporalAccessor;
+            try {
+                temporalAccessor = formatter.parse(ih.bs());
+            } catch (final DateTimeParseException e) {
+                break;
+            }
+            final long instantSecs;
+            final int nanoOfSecond;
+            try {
+                instantSecs = temporalAccessor.getLong(INSTANT_SECONDS);
+                nanoOfSecond = temporalAccessor.get(NANO_OF_SECOND);
+            } catch (final DateTimeException | ArithmeticException e) {
+                break;
+            }
+            // TODO: strict math?
+            final long value = instantSecs * 1_000_000_000L + nanoOfSecond;
+            if (reservedValue != null && value == reservedValue) {
+                // If a reserved value is defined, it must not be present in the input.
+                break;
+            }
+            if (ih.bs().size() > 1) {
+                gctx.clearIsNullOrWidthOneSoFar();
+            }
+            values[chunkIndex] = value;
+            nulls[chunkIndex] = false;
+            ++chunkIndex;
+        } while (ih.tryMoveNext());
+        sink.write(values, nulls, current, current + chunkIndex, appending);
+        return current + chunkIndex;
+    }
+}