package psi

const (
	ESSDHeadLen       = 5
	DescriptorHeadLen = 2
)

// Program specific information
type PSI struct {
	pf  byte   // Point field
	pfb []byte // Pointer filler bytes
	tid byte   // Table ID
	ssi bool   // Sectiopn syntax indicator (1 for PAT, PMT, CAT)
	pb  bool   // Private bit (0 for PAT, PMT, CAT)
	sl  uint16 // Section length
	tss *TSS   // Table syntax section (length defined by SL) if length 0 then nil
}

// Table syntax section
type TSS struct {
	tie uint16 // Table ID extension
	v   byte   // Version number
	cni bool   // Current/next indicator
	sn  byte   // Section number
	lsn byte   // Last section number
	sd  SD     // Specific data PAT/PMT
	crc []byte // crc32 of entire table excluding pointer field, pointer filler bytes and the trailing CRC32
}

// Specific Data, (could be PAT or PMT)
type SD interface {
	Bytes() []byte
}

// Program association table, implements SD
type PAT struct {
	pn    uint16 // Program Number
	pmpid uint16 // Program map PID
}

// Program mapping table, implements SD
type PMT struct {
	pcrpid uint16       // Program clock reference pid
	pil    uint16       // Program info length
	pd     []Descriptor // Program descriptors
	essd   []ESSD       // Elementary stream specific data
}

// Elementary stream specific data
type ESSD struct {
	st   byte         // Stream type
	epid byte         // Elementary pid
	esil uint16       // Elementary stream
	esd  []Descriptor // Elementary stream desriptors
}

// Descriptor
type Desc struct {
	dt byte   // Descriptor tag
	dl byte   // Descriptor length
	dd []byte // Descriptor data
}

func ReadPSI(data []byte) *PSI {
	return nil
}

func (p *PSI) Bytes() (out []byte) {
	return nil
}

func (t *TSS) Fill(space []byte) error {
	return nil
}

func (p *PAT) Fill(space []byte) error {
	return nil
}

func (p *PMT) Fill(space []byte) error {
	checkSpace(space)
	return nil
}

func (d *Descriptor) Fill(space []byte) error {
	checkSpace(space, DescriptorHeadLen+int(d.dl))
	space[0] = d.dt
	space[1] = d.dl
	copy(space[2:], d.dd)
	return out
}

func (e *ESSD) Fill(space []byte) error {
	checkSpace(space, ESSDHeadLen+e.esil)
	return nil
}

func checkSpace(s []byte, c uint) {
	if s == nil {
		panic("Slice provided is nil")
	} else if len(s) != 0 {
		panic("Slice provided already has something in it")
	} else if cap(s) != c {
		panic("Slice provided has wrong capacity")
	}
}