package pq

import (
	"bytes"
	"database/sql"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"fmt"
	"math"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/lib/pq/oid"
)

var time2400Regex = regexp.MustCompile(`^(24:00(?::00(?:\.0+)?)?)(?:[Z+-].*)?$`)

func binaryEncode(x any) ([]byte, error) {
	switch v := x.(type) {
	case []byte:
		return v, nil
	default:
		return encode(x, oid.T_unknown)
	}
}

func encode(x any, pgtypOid oid.Oid) ([]byte, error) {
	switch v := x.(type) {
	case int64:
		return strconv.AppendInt(nil, v, 10), nil
	case float64:
		return strconv.AppendFloat(nil, v, 'f', -1, 64), nil
	case []byte:
		if v == nil {
			return nil, nil
		}
		if pgtypOid == oid.T_bytea {
			return encodeBytea(v), nil
		}
		return v, nil
	case string:
		if pgtypOid == oid.T_bytea {
			return encodeBytea([]byte(v)), nil
		}
		return []byte(v), nil
	case bool:
		return strconv.AppendBool(nil, v), nil
	case time.Time:
		return formatTS(v), nil
	default:
		return nil, fmt.Errorf("pq: encode: unknown type for %T", v)
	}
}

func decode(ps *parameterStatus, s []byte, typ oid.Oid, f format) (any, error) {
	switch f {
	case formatBinary:
		return binaryDecode(s, typ)
	case formatText:
		return textDecode(ps, s, typ)
	default:
		panic("unreachable")
	}
}

func binaryDecode(s []byte, typ oid.Oid) (any, error) {
	switch typ {
	case oid.T_bytea:
		return s, nil
	case oid.T_int8:
		return int64(binary.BigEndian.Uint64(s)), nil
	case oid.T_int4:
		return int64(int32(binary.BigEndian.Uint32(s))), nil
	case oid.T_int2:
		return int64(int16(binary.BigEndian.Uint16(s))), nil
	case oid.T_uuid:
		b, err := decodeUUIDBinary(s)
		if err != nil {
			err = errors.New("pq: " + err.Error())
		}
		return b, err
	default:
		return nil, fmt.Errorf("pq: don't know how to decode binary parameter of type %d", uint32(typ))
	}

}

// decodeUUIDBinary interprets the binary format of a uuid, returning it in text format.
func decodeUUIDBinary(src []byte) ([]byte, error) {
	if len(src) != 16 {
		return nil, fmt.Errorf("pq: unable to decode uuid; bad length: %d", len(src))
	}

	dst := make([]byte, 36)
	dst[8], dst[13], dst[18], dst[23] = '-', '-', '-', '-'
	hex.Encode(dst[0:], src[0:4])
	hex.Encode(dst[9:], src[4:6])
	hex.Encode(dst[14:], src[6:8])
	hex.Encode(dst[19:], src[8:10])
	hex.Encode(dst[24:], src[10:16])

	return dst, nil
}

func textDecode(ps *parameterStatus, s []byte, typ oid.Oid) (any, error) {
	switch typ {
	case oid.T_char, oid.T_bpchar, oid.T_varchar, oid.T_text:
		return string(s), nil
	case oid.T_bytea:
		b, err := parseBytea(s)
		if err != nil {
			err = errors.New("pq: " + err.Error())
		}
		return b, err
	case oid.T_timestamptz:
		return parseTS(ps.currentLocation, string(s))
	case oid.T_timestamp, oid.T_date:
		return parseTS(nil, string(s))
	case oid.T_time:
		return parseTime("15:04:05", typ, s)
	case oid.T_timetz:
		return parseTime("15:04:05-07", typ, s)
	case oid.T_bool:
		return s[0] == 't', nil
	case oid.T_int8, oid.T_int4, oid.T_int2:
		i, err := strconv.ParseInt(string(s), 10, 64)
		if err != nil {
			err = errors.New("pq: " + err.Error())
		}
		return i, err
	case oid.T_float4, oid.T_float8:
		// We always use 64 bit parsing, regardless of whether the input text is for
		// a float4 or float8, because clients expect float64s for all float datatypes
		// and returning a 32-bit parsed float64 produces lossy results.
		f, err := strconv.ParseFloat(string(s), 64)
		if err != nil {
			err = errors.New("pq: " + err.Error())
		}
		return f, err
	}
	return s, nil
}

// appendEncodedText encodes item in text format as required by COPY
// and appends to buf
func appendEncodedText(buf []byte, x any) ([]byte, error) {
	switch v := x.(type) {
	case int64:
		return strconv.AppendInt(buf, v, 10), nil
	case float64:
		return strconv.AppendFloat(buf, v, 'f', -1, 64), nil
	case []byte:
		encodedBytea := encodeBytea(v)
		return appendEscapedText(buf, string(encodedBytea)), nil
	case string:
		return appendEscapedText(buf, v), nil
	case bool:
		return strconv.AppendBool(buf, v), nil
	case time.Time:
		return append(buf, formatTS(v)...), nil
	case nil:
		return append(buf, "\\N"...), nil
	default:
		return nil, fmt.Errorf("pq: encode: unknown type for %T", v)
	}
}

func appendEscapedText(buf []byte, text string) []byte {
	escapeNeeded := false
	startPos := 0
	var c byte

	// check if we need to escape
	for i := 0; i < len(text); i++ {
		c = text[i]
		if c == '\\' || c == '\n' || c == '\r' || c == '\t' {
			escapeNeeded = true
			startPos = i
			break
		}
	}
	if !escapeNeeded {
		return append(buf, text...)
	}

	// copy till first char to escape, iterate the rest
	result := append(buf, text[:startPos]...)
	for i := startPos; i < len(text); i++ {
		c = text[i]
		switch c {
		case '\\':
			result = append(result, '\\', '\\')
		case '\n':
			result = append(result, '\\', 'n')
		case '\r':
			result = append(result, '\\', 'r')
		case '\t':
			result = append(result, '\\', 't')
		default:
			result = append(result, c)
		}
	}
	return result
}

func parseTime(f string, typ oid.Oid, s []byte) (time.Time, error) {
	str := string(s)

	// Check for a minute and second offset in the timezone.
	if typ == oid.T_timestamptz || typ == oid.T_timetz {
		for i := 3; i <= 6; i += 3 {
			if str[len(str)-i] == ':' {
				f += ":00"
				continue
			}
			break
		}
	}

	// Special case for 24:00 time.
	// Unfortunately, golang does not parse 24:00 as a proper time.
	// In this case, we want to try "round to the next day", to differentiate.
	// As such, we find if the 24:00 time matches at the beginning; if so,
	// we default it back to 00:00 but add a day later.
	var is2400Time bool
	switch typ {
	case oid.T_timetz, oid.T_time:
		if matches := time2400Regex.FindStringSubmatch(str); matches != nil {
			// Concatenate timezone information at the back.
			str = "00:00:00" + str[len(matches[1]):]
			is2400Time = true
		}
	}
	t, err := time.Parse(f, str)
	if err != nil {
		return time.Time{}, errors.New("pq: " + err.Error())
	}
	if is2400Time {
		t = t.Add(24 * time.Hour)
	}
	return t, nil
}

var errInvalidTimestamp = errors.New("invalid timestamp")

type timestampParser struct {
	err error
}

func (p *timestampParser) expect(str string, char byte, pos int) {
	if p.err != nil {
		return
	}
	if pos+1 > len(str) {
		p.err = errInvalidTimestamp
		return
	}
	if c := str[pos]; c != char && p.err == nil {
		p.err = fmt.Errorf("expected '%v' at position %v; got '%v'", char, pos, c)
	}
}

func (p *timestampParser) mustAtoi(str string, begin int, end int) int {
	if p.err != nil {
		return 0
	}
	if begin < 0 || end < 0 || begin > end || end > len(str) {
		p.err = errInvalidTimestamp
		return 0
	}
	result, err := strconv.Atoi(str[begin:end])
	if err != nil {
		if p.err == nil {
			p.err = fmt.Errorf("expected number; got '%v'", str)
		}
		return 0
	}
	return result
}

// The location cache caches the time zones typically used by the client.
type locationCache struct {
	cache map[int]*time.Location
	lock  sync.Mutex
}

// All connections share the same list of timezones. Benchmarking shows that
// about 5% speed could be gained by putting the cache in the connection and
// losing the mutex, at the cost of a small amount of memory and a somewhat
// significant increase in code complexity.
var globalLocationCache = newLocationCache()

func newLocationCache() *locationCache {
	return &locationCache{cache: make(map[int]*time.Location)}
}

// Returns the cached timezone for the specified offset, creating and caching
// it if necessary.
func (c *locationCache) getLocation(offset int) *time.Location {
	c.lock.Lock()
	defer c.lock.Unlock()

	location, ok := c.cache[offset]
	if !ok {
		location = time.FixedZone("", offset)
		c.cache[offset] = location
	}

	return location
}

var (
	infinityTSEnabled  = false
	infinityTSNegative time.Time
	infinityTSPositive time.Time
)

const (
	infinityTSEnabledAlready        = "pq: infinity timestamp enabled already"
	infinityTSNegativeMustBeSmaller = "pq: infinity timestamp: negative value must be smaller (before) than positive"
)

// EnableInfinityTs controls the handling of Postgres' "-infinity" and
// "infinity" "timestamp"s.
//
// If EnableInfinityTs is not called, "-infinity" and "infinity" will return
// []byte("-infinity") and []byte("infinity") respectively, and potentially
// cause error "sql: Scan error on column index 0: unsupported driver -> Scan
// pair: []uint8 -> *time.Time", when scanning into a time.Time value.
//
// Once EnableInfinityTs has been called, all connections created using this
// driver will decode Postgres' "-infinity" and "infinity" for "timestamp",
// "timestamp with time zone" and "date" types to the predefined minimum and
// maximum times, respectively.  When encoding time.Time values, any time which
// equals or precedes the predefined minimum time will be encoded to
// "-infinity".  Any values at or past the maximum time will similarly be
// encoded to "infinity".
//
// If EnableInfinityTs is called with negative >= positive, it will panic.
// Calling EnableInfinityTs after a connection has been established results in
// undefined behavior.  If EnableInfinityTs is called more than once, it will
// panic.
func EnableInfinityTs(negative time.Time, positive time.Time) {
	if infinityTSEnabled {
		panic(infinityTSEnabledAlready)
	}
	if !negative.Before(positive) {
		panic(infinityTSNegativeMustBeSmaller)
	}
	infinityTSEnabled = true
	infinityTSNegative = negative
	infinityTSPositive = positive
}

// Testing might want to toggle infinityTSEnabled
func disableInfinityTS() {
	infinityTSEnabled = false
}

// This is a time function specific to the Postgres default DateStyle
// setting ("ISO, MDY"), the only one we currently support. This
// accounts for the discrepancies between the parsing available with
// time.Parse and the Postgres date formatting quirks.
func parseTS(currentLocation *time.Location, str string) (any, error) {
	switch str {
	case "-infinity":
		if infinityTSEnabled {
			return infinityTSNegative, nil
		}
		return []byte(str), nil
	case "infinity":
		if infinityTSEnabled {
			return infinityTSPositive, nil
		}
		return []byte(str), nil
	}
	t, err := ParseTimestamp(currentLocation, str)
	if err != nil {
		err = errors.New("pq: " + err.Error())
	}
	return t, err
}

// ParseTimestamp parses Postgres' text format. It returns a time.Time in
// currentLocation iff that time's offset agrees with the offset sent from the
// Postgres server. Otherwise, ParseTimestamp returns a time.Time with the
// fixed offset offset provided by the Postgres server.
func ParseTimestamp(currentLocation *time.Location, str string) (time.Time, error) {
	p := timestampParser{}

	monSep := strings.IndexRune(str, '-')
	// this is Gregorian year, not ISO Year
	// In Gregorian system, the year 1 BC is followed by AD 1
	year := p.mustAtoi(str, 0, monSep)
	daySep := monSep + 3
	month := p.mustAtoi(str, monSep+1, daySep)
	p.expect(str, '-', daySep)
	timeSep := daySep + 3
	day := p.mustAtoi(str, daySep+1, timeSep)

	minLen := monSep + len("01-01") + 1

	isBC := strings.HasSuffix(str, " BC")
	if isBC {
		minLen += 3
	}

	var hour, minute, second int
	if len(str) > minLen {
		p.expect(str, ' ', timeSep)
		minSep := timeSep + 3
		p.expect(str, ':', minSep)
		hour = p.mustAtoi(str, timeSep+1, minSep)
		secSep := minSep + 3
		p.expect(str, ':', secSep)
		minute = p.mustAtoi(str, minSep+1, secSep)
		secEnd := secSep + 3
		second = p.mustAtoi(str, secSep+1, secEnd)
	}
	remainderIdx := monSep + len("01-01 00:00:00") + 1
	// Three optional (but ordered) sections follow: the
	// fractional seconds, the time zone offset, and the BC
	// designation. We set them up here and adjust the other
	// offsets if the preceding sections exist.

	nanoSec := 0
	tzOff := 0

	if remainderIdx < len(str) && str[remainderIdx] == '.' {
		fracStart := remainderIdx + 1
		fracOff := strings.IndexAny(str[fracStart:], "-+Z ")
		if fracOff < 0 {
			fracOff = len(str) - fracStart
		}
		fracSec := p.mustAtoi(str, fracStart, fracStart+fracOff)
		nanoSec = fracSec * (1000000000 / int(math.Pow(10, float64(fracOff))))

		remainderIdx += fracOff + 1
	}
	if tzStart := remainderIdx; tzStart < len(str) && (str[tzStart] == '-' || str[tzStart] == '+') {
		// time zone separator is always '-' or '+' or 'Z' (UTC is +00)
		var tzSign int
		switch c := str[tzStart]; c {
		case '-':
			tzSign = -1
		case '+':
			tzSign = +1
		default:
			return time.Time{}, fmt.Errorf("expected '-' or '+' at position %v; got %v", tzStart, c)
		}
		tzHours := p.mustAtoi(str, tzStart+1, tzStart+3)
		remainderIdx += 3
		var tzMin, tzSec int
		if remainderIdx < len(str) && str[remainderIdx] == ':' {
			tzMin = p.mustAtoi(str, remainderIdx+1, remainderIdx+3)
			remainderIdx += 3
		}
		if remainderIdx < len(str) && str[remainderIdx] == ':' {
			tzSec = p.mustAtoi(str, remainderIdx+1, remainderIdx+3)
			remainderIdx += 3
		}
		tzOff = tzSign * ((tzHours * 60 * 60) + (tzMin * 60) + tzSec)
	} else if tzStart < len(str) && str[tzStart] == 'Z' {
		// time zone Z separator indicates UTC is +00
		remainderIdx += 1
	}

	var isoYear int

	if isBC {
		isoYear = 1 - year
		remainderIdx += 3
	} else {
		isoYear = year
	}
	if remainderIdx < len(str) {
		return time.Time{}, fmt.Errorf("expected end of input, got %v", str[remainderIdx:])
	}
	t := time.Date(isoYear, time.Month(month), day,
		hour, minute, second, nanoSec,
		globalLocationCache.getLocation(tzOff))

	if currentLocation != nil {
		// Set the location of the returned Time based on the session's
		// TimeZone value, but only if the local time zone database agrees with
		// the remote database on the offset.
		lt := t.In(currentLocation)
		_, newOff := lt.Zone()
		if newOff == tzOff {
			t = lt
		}
	}

	return t, p.err
}

// formatTS formats t into a format postgres understands.
func formatTS(t time.Time) []byte {
	if infinityTSEnabled {
		// t <= -infinity : ! (t > -infinity)
		if !t.After(infinityTSNegative) {
			return []byte("-infinity")
		}
		// t >= infinity : ! (!t < infinity)
		if !t.Before(infinityTSPositive) {
			return []byte("infinity")
		}
	}
	return FormatTimestamp(t)
}

// FormatTimestamp formats t into Postgres' text format for timestamps.
func FormatTimestamp(t time.Time) []byte {
	// Need to send dates before 0001 A.D. with " BC" suffix, instead of the
	// minus sign preferred by Go.
	// Beware, "0000" in ISO is "1 BC", "-0001" is "2 BC" and so on
	bc := false
	if t.Year() <= 0 {
		// flip year sign, and add 1, e.g: "0" will be "1", and "-10" will be "11"
		t = t.AddDate((-t.Year())*2+1, 0, 0)
		bc = true
	}
	b := []byte(t.Format("2006-01-02 15:04:05.999999999Z07:00"))

	_, offset := t.Zone()
	offset %= 60
	if offset != 0 {
		// RFC3339Nano already printed the minus sign
		if offset < 0 {
			offset = -offset
		}

		b = append(b, ':')
		if offset < 10 {
			b = append(b, '0')
		}
		b = strconv.AppendInt(b, int64(offset), 10)
	}

	if bc {
		b = append(b, " BC"...)
	}
	return b
}

// Parse a bytea value received from the server.  Both "hex" and the legacy
// "escape" format are supported.
func parseBytea(s []byte) (result []byte, err error) {
	if len(s) >= 2 && bytes.Equal(s[:2], []byte("\\x")) {
		// bytea_output = hex
		s = s[2:] // trim off leading "\\x"
		result = make([]byte, hex.DecodedLen(len(s)))
		_, err := hex.Decode(result, s)
		if err != nil {
			return nil, err
		}
	} else {
		// bytea_output = escape
		for len(s) > 0 {
			if s[0] == '\\' {
				// escaped '\\'
				if len(s) >= 2 && s[1] == '\\' {
					result = append(result, '\\')
					s = s[2:]
					continue
				}

				// '\\' followed by an octal number
				if len(s) < 4 {
					return nil, fmt.Errorf("invalid bytea sequence %v", s)
				}
				r, err := strconv.ParseUint(string(s[1:4]), 8, 8)
				if err != nil {
					return nil, fmt.Errorf("could not parse bytea value: %w", err)
				}
				result = append(result, byte(r))
				s = s[4:]
			} else {
				// We hit an unescaped, raw byte.  Try to read in as many as
				// possible in one go.
				i := bytes.IndexByte(s, '\\')
				if i == -1 {
					result = append(result, s...)
					break
				}
				result = append(result, s[:i]...)
				s = s[i:]
			}
		}
	}

	return result, nil
}

func encodeBytea(v []byte) (result []byte) {
	result = make([]byte, 2+hex.EncodedLen(len(v)))
	result[0] = '\\'
	result[1] = 'x'
	hex.Encode(result[2:], v)
	return result
}

// NullTime represents a [time.Time] that may be null.
// NullTime implements the [sql.Scanner] interface so
// it can be used as a scan destination, similar to [sql.NullString].
//
// Deprecated: this is an alias for [sql.NullTime].
type NullTime = sql.NullTime