// Package fitparser provides functionality to decode FIT (Flexible and Interoperable Data Transfer) files.
// FIT is a binary file format used by Garmin and other fitness device manufacturers.
package fitparser

import "time"

// Protocol and Profile versions
const (
	ProtocolVersionMajorShift = 4
	ProtocolVersionMajorMask  = 0xF0
	ProtocolVersionMinorMask  = 0x0F
	ProtocolVersion10         = 0x10
	ProtocolVersion20         = 0x20
	ProfileVersionMajor       = 21
	ProfileVersionMinor       = 188
)

// Base type definitions
const (
	BaseTypeEnum   = 0x00
	BaseTypeSint8  = 0x01
	BaseTypeUint8  = 0x02
	BaseTypeSint16 = 0x83
	BaseTypeUint16 = 0x84
	BaseTypeSint32 = 0x85
	BaseTypeUint32 = 0x86
	BaseTypeString = 0x07
	BaseTypeFloat32 = 0x88
	BaseTypeFloat64 = 0x89
	BaseTypeUint8z = 0x0A
	BaseTypeUint16z = 0x8B
	BaseTypeUint32z = 0x8C
	BaseTypeByte   = 0x0D
	BaseTypeSint64 = 0x8E
	BaseTypeUint64 = 0x8F
	BaseTypeUint64z = 0x90
)

// Base type flags
const (
	BaseTypeEndianFlag = 0x80
	BaseTypeNumMask    = 0x1F
)

// Invalid values for each type
const (
	EnumInvalid    = 0xFF
	Sint8Invalid   = 0x7F
	Uint8Invalid   = 0xFF
	Sint16Invalid  = 0x7FFF
	Uint16Invalid  = 0xFFFF
	Sint32Invalid  = 0x7FFFFFFF
	Uint32Invalid  = 0xFFFFFFFF
	StringInvalid  = 0x00
	Float32Invalid = 0xFFFFFFFF
	Float64Invalid = 0xFFFFFFFFFFFFFFFF
	Uint8zInvalid  = 0x00
	Uint16zInvalid = 0x0000
	Uint32zInvalid = 0x00000000
	ByteInvalid    = 0xFF
	Sint64Invalid  = 0x7FFFFFFFFFFFFFFF
	Uint64Invalid  = 0xFFFFFFFFFFFFFFFF
	Uint64zInvalid = 0x0000000000000000
)

// Header sizes
const (
	HeaderWithCRCSize    = 14
	HeaderWithoutCRCSize = 12
	HeaderMinSize        = 12
	CRCSize              = 2
)

// Record header bits
const (
	RecordHeaderMask             = 0x80
	RecordHeaderNormal           = 0x00
	RecordHeaderCompressedMask   = 0x80
	RecordHeaderLocalMesgNumMask = 0x0F
	RecordHeaderTimeMask         = 0x1F
)

// Message definition bits
const (
	MesgDefinitionMask        = 0x40
	MesgHeaderMask            = 0xF0
	LocalMesgNum              = 0x0F
	MesgDefinitionReserved    = 0x00
	DevDataMask               = 0x20
)

// FIT file signature
var FITSignature = [4]byte{'.', 'F', 'I', 'T'}

// FIT Epoch - Number of seconds between Unix Epoch and FIT Epoch (Dec 31, 1989 00:00:00 UTC)
const FITEpochSeconds = 631065600

// ConvertFITTimestamp converts a FIT timestamp to a Go time.Time
func ConvertFITTimestamp(fitTime uint32) time.Time {
	if fitTime == Uint32Invalid {
		return time.Time{}
	}
	return time.Unix(int64(fitTime)+FITEpochSeconds, 0).UTC()
}

// BaseTypeSize returns the size in bytes of the given base type
func BaseTypeSize(baseType byte) int {
	switch baseType & BaseTypeNumMask {
	case BaseTypeEnum, BaseTypeSint8, BaseTypeUint8, BaseTypeByte, BaseTypeUint8z:
		return 1
	case BaseTypeSint16, BaseTypeUint16, BaseTypeUint16z:
		return 2
	case BaseTypeSint32, BaseTypeUint32, BaseTypeUint32z, BaseTypeFloat32:
		return 4
	case BaseTypeSint64, BaseTypeUint64, BaseTypeUint64z, BaseTypeFloat64:
		return 8
	case BaseTypeString:
		return 1 // Variable length, but each character is 1 byte
	default:
		return 0
	}
}

// IsEndianType returns true if the base type requires endian conversion
func IsEndianType(baseType byte) bool {
	return (baseType & BaseTypeEndianFlag) != 0
}

// IsInvalidValue checks if a value is invalid for its type
func IsInvalidValue(baseType byte, value interface{}) bool {
	switch baseType & BaseTypeNumMask {
	case BaseTypeEnum, BaseTypeUint8:
		if v, ok := value.(uint8); ok {
			return v == Uint8Invalid
		}
	case BaseTypeSint8:
		if v, ok := value.(int8); ok {
			return v == Sint8Invalid
		}
	case BaseTypeUint16:
		if v, ok := value.(uint16); ok {
			return v == Uint16Invalid
		}
	case BaseTypeSint16:
		if v, ok := value.(int16); ok {
			return v == Sint16Invalid
		}
	case BaseTypeUint32:
		if v, ok := value.(uint32); ok {
			return v == Uint32Invalid
		}
	case BaseTypeSint32:
		if v, ok := value.(int32); ok {
			return v == Sint32Invalid
		}
	case BaseTypeUint64:
		if v, ok := value.(uint64); ok {
			return v == Uint64Invalid
		}
	case BaseTypeSint64:
		if v, ok := value.(int64); ok {
			return v == Sint64Invalid
		}
	case BaseTypeUint8z:
		if v, ok := value.(uint8); ok {
			return v == Uint8zInvalid
		}
	case BaseTypeUint16z:
		if v, ok := value.(uint16); ok {
			return v == Uint16zInvalid
		}
	case BaseTypeUint32z:
		if v, ok := value.(uint32); ok {
			return v == Uint32zInvalid
		}
	case BaseTypeUint64z:
		if v, ok := value.(uint64); ok {
			return v == Uint64zInvalid
		}
	}
	return false
}