//go:build linux

/*
Copyright 2013 The Perkeep Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package fs

import (
	"errors"
	"fmt"
	"math"
	"strconv"
	"time"
)

var timeFormats = []string{
	time.RFC3339Nano,
	time.RFC3339,
	time.RFC1123Z,
	time.RFC1123,
	time.UnixDate,
	time.ANSIC,
	time.RubyDate,
	"2006-01-02T15:04",
	"2006-01-02T15",
	"2006-01-02",
	"2006-01",
	"2006",
}

var errUnparseableTimestamp = errors.New("unparsable timestamp")

var powTable = []int{
	10e8,
	10e7,
	10e6,
	10e5,
	10e4,
	10e3,
	10e2,
	10e1,
	10,
	1,
}

// Hand crafted this parser since it's a really common path.
func parseCanonicalTime(in string) (time.Time, error) {
	if len(in) < 20 || in[len(in)-1] != 'Z' {
		return time.Time{}, errUnparseableTimestamp
	}

	if !(in[4] == '-' && in[7] == '-' && in[10] == 'T' &&
		in[13] == ':' && in[16] == ':' && (in[19] == '.' || in[19] == 'Z')) {
		return time.Time{}, fmt.Errorf("positionally incorrect: %v", in)
	}

	// 2012-08-28T21:24:35.37465188Z
	//     4  7  10 13 16 19
	// -----------------------------
	// 0-4  5  8  11 14 17 20

	year, err := strconv.Atoi(in[0:4])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing year: %v", err)
	}

	month, err := strconv.Atoi(in[5:7])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing month: %v", err)
	}

	day, err := strconv.Atoi(in[8:10])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing day: %v", err)
	}

	hour, err := strconv.Atoi(in[11:13])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing hour: %v", err)
	}

	minute, err := strconv.Atoi(in[14:16])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing minute: %v", err)
	}

	second, err := strconv.Atoi(in[17:19])
	if err != nil {
		return time.Time{}, fmt.Errorf("error parsing second: %v", err)
	}

	var nsecstr string
	if in[19] != 'Z' {
		nsecstr = in[20 : len(in)-1]
	}
	var nsec int

	if nsecstr != "" {
		nsec, err = strconv.Atoi(nsecstr)
		if err != nil {
			return time.Time{}, fmt.Errorf("error parsing nanoseconds: %v", err)
		}
	}

	nsec *= powTable[len(nsecstr)]

	return time.Date(year, time.Month(month), day,
		hour, minute, second, nsec, time.UTC), nil
}

func parseTime(in string) (time.Time, error) {
	// First, try a few numerics
	n, err := strconv.ParseInt(in, 10, 64)
	if err == nil {
		switch {
		case n > int64(math.MaxInt32)*1000:
			// nanosecond timestamps
			return time.Unix(n/1e9, n%1e9), nil
		case n > int64(math.MaxInt32):
			// millisecond timestamps
			return time.Unix(n/1000, (n%1000)*1e6), nil
		case n > 10000:
			// second timestamps
			return time.Unix(n, 0), nil
		}
	}
	rv, err := parseCanonicalTime(in)
	if err == nil {
		return rv, nil
	}
	for _, f := range timeFormats {
		parsed, err := time.Parse(f, in)
		if err == nil {
			return parsed, nil
		}
	}
	return time.Time{}, errUnparseableTimestamp
}