package amf

import (
	"errors"
	"encoding/binary"
	"math"
)

type AMFObj map[interface{}]interface{} // interface mostly so root obj can be included as an index of ints

// always a msg type of 20 for AMF0
func DecodeAMF(data *[]byte) (AMFObj, error) {
	var byte_idx uint32
	var root_obj_idx int // top level object can be referred to as int
	amf_root_obj := make(AMFObj)
	for {
		// read the next thing and store it under the given root index
		top_level_obj, err := read_next(data, &byte_idx)
		if err != nil {
			return amf_root_obj, err
		}
		amf_root_obj[root_obj_idx] = top_level_obj

		root_obj_idx += 1
		if byte_idx == uint32(len(*data)) { // check if full message read
			break
		}
	}
	return amf_root_obj, nil
}

// generic wrapper to read n bytes, what I tried to avoid with ReadChunk in rtmp
func read_bytes(data *[]byte, byte_idx *uint32, n uint32) ([]byte, error) {
	if int(*byte_idx + n) > len(*data) {
		return make([]byte, 0), errors.New("Read goes past end")
	}
	read_slice := (*data)[*byte_idx:*byte_idx + n]
	*byte_idx += n
	return read_slice, nil
}

// assuming the next thing is a number, read it
// format is 8 bytes encoded big-endian as float64
func read_number(data *[]byte, byte_idx *uint32) (float64, error) {
	float_bytes, err := read_bytes(data, byte_idx, 8)
	if err != nil {
		return 0.0, err
	}
	return math.Float64frombits(binary.BigEndian.Uint64(float_bytes)), nil
}

// assuming next is boolean, read
// format is 1 byte, 0 for false 1 for true
func read_bool(data *[]byte, byte_idx *uint32) (bool, error) {
	bool_byte, err := read_bytes(data, byte_idx, 1)
	if err != nil {
		return false, err
	}
	if bool_byte[0] > 1 {
		return false, errors.New("bool byte must be 0 or 1")
	}
	return bool_byte[0] != 0, nil
}

// assuming next is string, read
// format is 2 bytes for string len n, next n bytes are ascii chars
func read_string(data *[]byte, byte_idx *uint32) (string, error) {
	string_len, err := read_bytes(data, byte_idx, 2)
	if err != nil {
		return "", err
	}
	string_bytes, err := read_bytes(data, byte_idx, uint32(binary.BigEndian.Uint16(string_len)))
	if err != nil {
		return "", err
	}
	return string(string_bytes), err
}

// assuming next is an object, read
// format is always a string for a key, then a marker to determine next data type then data
// ends with an empty string for a key followed by a 9
func read_object(data *[]byte, byte_idx *uint32) (AMFObj, error) {
	root_obj := make(AMFObj)
	for {
		key, err := read_string(data, byte_idx)
		if err != nil {
			return root_obj, err
		}
		if key == "" {
			if end_byte, err := read_bytes(data, byte_idx, 1); err != nil {
				return root_obj, err
			} else if end_byte[0] != 9 {
				return root_obj, errors.New("Object should end but didnt")
			}
			return root_obj, nil
		}
		val, err := read_next(data, byte_idx)
		if err != nil {
			return root_obj, err
		}
		root_obj[key] = val
	}

}

// read the next thing
// read the next byte to determine the data type, then call one of the above to read
// defined as AMF0 spec
func read_next(data *[]byte, byte_idx *uint32) (interface{}, error) {
	data_type, err := read_bytes(data, byte_idx, 1)
	var next_obj interface{}
	if err != nil {
		return nil, err
	}
	switch data_type[0] {
	case 0:
		next_obj, err = read_number(data, byte_idx)
	case 1:
		next_obj, err = read_bool(data, byte_idx)
	case 2:
		next_obj, err = read_string(data, byte_idx)
	case 3:
		next_obj, err = read_object(data, byte_idx)
	case 5: // null marker, no extra empty bytes, just skip to next object
		return nil, nil
	default:
		return nil, errors.New("Unhandled data type")
	}
	if err != nil {
		return nil, err
	}
	return next_obj, nil
}