Add the library

Author: ashishb

.gitignore

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+### https://raw.github.com/github/gitignore/18e28746b0862059dbee8694fd366a679cb812fb/Go.gitignore
+
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+bin/
+

Makefile

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+build:
+	GO111MODULE=on go build -v -o bin/dateparse src/*.go
+
+go_lint:
+	GO111MODULE=on go mod tidy
+	GO111MODULE=on go vet ./src
+	golint -set_exit_status ./src/...
+	go tool fix src/
+	golangci-lint run
+
+lint: format go_lint
+
+format:
+	go fmt ./src/...
+
+clean:
+	GO111MODULE=on go clean --modcache
+	rm -rf bin/*
+
+test:
+	GO111MODULE=on go test ./src/... -v

go.mod

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+module dateparse
+
+go 1.14

src/date_utils.go

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+package dateparse
+
+import (
+	"strings"
+	"time"
+)
+
+// Remember the last successful format and reuse it to same time
+var lastSuccessfulFormat = time.RFC822Z
+
+// GetParsedDate can handle date coming from email header as well as
+// Calendar's date and time.
+// Different email clients seems to be using different date formats.
+// TODO: store the last use date pattern and try it first the next time.
+func GetParsedDate(date string) (*time.Time, error) {
+	// The expected time format is "Fri, 20 Mar 2020 17:05:25 +0000" but some email clients
+	// add extraneous information at the end, for example,
+	// "Fri, 20 Mar 2020 17:05:25 +0000 (UTC)"
+	// Try again by removing that
+	index := strings.Index(date, "(")
+	if index > 0 {
+		date = strings.TrimSpace(date[:index])
+	}
+	// Occasionally, dates have UT instead of UTC :/
+	if strings.HasSuffix(date, "UT") {
+		// Change to UT to UTC
+		date += "C"
+	}
+
+	//Another common case is when an extraneous GMT with timezone is present
+	// Mon, 25 Nov 2019 18:18:47 +0100 GMT
+	if strings.HasSuffix(date, "GMT") &&
+		strings.Contains(date, "+") {
+		date = strings.TrimSuffix(date, "GMT")
+	}
+	date = strings.TrimSpace(date)
+
+	// Remove commas
+	date = strings.ReplaceAll(date, ", ", " ")
+	date = strings.ReplaceAll(date, ",", " ")
+
+	formats := []string{
+		lastSuccessfulFormat,
+		"02 Jan 06 15:04 MST", // time.RFC822
+		"2 Jan 06 15:04:05 -0700",
+		"2 Jan 06 15:04:05 MST",
+		"2 Jan 2006 15:04:05 -0700",
+		"2 Jan 2006 15:04:05 MST",
+		"02 Jan 06 15:04:05 -0700",
+		"02 Jan 06 15:04:05 MST",
+		"02 Jan 2006 15:04:05 -0700",
+		"02 Jan 2006 15:04:05 MST",
+		"02 Jan 06 15:04 -0700", // time.RFC822Z,
+		// time.RFC1123 with comma removed
+		"Mon 02 Jan 2006 15:04:05 MST",
+		// time.RFC1123Z with comma removed
+		"Mon 02 Jan 2006 15:04:05 -0700",
+		"Mon 2 Jan 2006 15:04:05 -0700",
+		"Mon 2 Jan 2006 15:04:05 MST",
+		// time.RFC3339 with comma removed
+		"2006-01-02T15:04:05Z07:00",
+		"Jan _2 2006",
+		"January _2 2006",
+		"Monday, 02-Jan-06 15:04:05 MST", //	time.RFC850
+		// time.RFC850 with comma removed
+		"Monday 02-Jan-06 15:04:05 MST",
+		"Monday 02-Jan-2006 15:04:05 MST",
+	}
+	var tmpDate time.Time
+	var err error
+	for _, format := range formats {
+		tmpDate, err = time.Parse(format, date)
+		if err == nil {
+			// For faster parsing in the future
+			lastSuccessfulFormat = format
+			return &tmpDate, nil
+		}
+	}
+	return nil, err
+}

src/date_utils_test.go

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+package dateparse
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+var testDataFilename = filepath.Join("testdata", "date_entries.txt")
+
+func TestGetParsedDate(t *testing.T) {
+	data, err := ioutil.ReadFile(testDataFilename)
+	if err != nil {
+		t.Errorf("Failed to read file %s: %v", testDataFilename, err)
+		t.Fail()
+	}
+	for _, dateEntry := range strings.Split(string(data), "\n") {
+		if len(dateEntry) == 0 {
+			continue
+		}
+		_, err := GetParsedDate(dateEntry)
+		if err != nil {
+			t.Errorf("Failed to parse date from \"%s\": %v", dateEntry, err)
+		}
+		// t.Logf(`Parsed date is "%v"`, parsedDate)
+	}
+}

src/testdata/date_entries.txt

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+Sun, 10 Apr 2016 19:57:43 +0000
+Sat, 18 Apr 2020 16:32:33 -0700
+Sat, 18 Apr 2020 15:19:17 -0700
+Sat, 18 Apr 2020 09:24:59 +0000 (UTC)
+Sat, 18 Apr 2020 02:31:32 -0700
+Sat, 18 Apr 2020 02:31:54 -0700
+Mon, 20 Apr 2020 16:44:50 -0700
+Sat, 18 Apr 2020 04:45:08 +0000
+Sat, 18 Apr 2020 00:42:45 -0700
+Sat, 18 Apr 2020 11:05:42 -0700
+Sun, 19 Apr 2020 17:25:31 +0000 (UTC)
+Sun, 19 Apr 2020 11:24:35 -0700
+Sun, 19 Apr 2020 17:11:29 -0700
+Mon, 20 Apr 2020 16:50:47 +0000
+Sun, 10 Apr 2016 05:32:59 +0000
+Sun, 10 Apr 2016 05:35:08 +0000
+Sun, 10 Apr 2016 05:40:33 +0000
+Sun, 10 Apr 2016 05:41:09 +0000
+Sun, 10 Apr 2016 05:44:07 +0000
+Sun, 10 Apr 2016 05:52:17 +0000
+Sun, 10 Apr 2016 06:00:29 +0000
+Sun, 10 Apr 2016 06:04:22 +0000
+Sun, 10 Apr 2016 06:20:01 +0000
+Sun, 10 Apr 2016 06:33:58 +0000
+Sun, 10 Apr 2016 06:43:14 +0000
+Sun, 10 Apr 2016 06:49:24 +0000
+Sun, 10 Apr 2016 07:16:55 +0000
+Sun, 10 Apr 2016 07:29:06 +0000
+Sun, 10 Apr 2016 11:58:17 +0000
+Sun, 10 Apr 2016 19:57:43 +0000
+Mon, 25 Nov 2019 18:18:47 +0100 GMT
+Thursday 04-Jun-2020 20:45:05 UTC