package main

import (
	"bufio"
	"fmt"
	"io"

	"github.com/golang/protobuf/proto"
	"github.com/golang/snappy"
	"github.com/jordanorelli/hyperstone/bit"
	"github.com/jordanorelli/hyperstone/dota"
)

type parser struct {
	// the source of replay bytes. Must NOT be compressed.
	source *bufio.Reader

	dumpDatagrams bool
	dumpPackets   bool
}

func newParser(r io.Reader) *parser {
	br := bufio.NewReaderSize(r, 1<<16)
	return &parser{source: br}
}

func (p *parser) start() error {
	ok, err := p.checkHeader()
	if err != nil {
		return wrap(err, "parser start error")
	}
	if !ok {
		return fmt.Errorf("parser start error: invalid header")
	}
	if _, err := p.source.Discard(8); err != nil {
		return wrap(err, "parser start error")
	}
	return nil
}

func (p *parser) run() error {
	for {
		gram, err := p.readDatagram()
		if err != nil {
			return wrap(err, "read datagram error in run loop")
		}
		p.handleDataGram(gram)
	}
}

func (p *parser) handleDataGram(d *dataGram) error {
	if p.dumpDatagrams {
		fmt.Println(d)
	}

	if len(d.body) == 0 {
		return nil
	}

	msg, err := d.Open(&messages)
	if err != nil {
		fmt.Printf("datagram open error: %v\n", err)
		return nil
	}

	switch v := msg.(type) {
	case *dota.CDemoPacket:
		p.handleDemoPacket(v)
	}
	return nil
}

func (p *parser) handleDemoPacket(packet *dota.CDemoPacket) error {
	br := bit.NewBytesReader(packet.GetData())
	for {
		t := entityType(br.ReadUBitVar())
		s := br.ReadVarInt()
		b := make([]byte, s)
		br.Read(b)
		switch err := br.Err(); err {
		case nil:
			break
		case io.EOF:
			return nil
		default:
			return err
		}
		if p.dumpPackets {
			fmt.Printf("\t%v\n", entity{t: t, size: uint32(s), body: b})
		}
		e := messages.BuildEntity(t)
		if e == nil {
			fmt.Printf("\tno known entity for type id %d size: %d\n", int(t), len(b))
			continue
		}
		err := proto.Unmarshal(b, e)
		if err != nil {
			fmt.Printf("entity unmarshal error: %v\n", err)
		}
	}
}

// DecodeVarint reads a varint-encoded integer from the source reader.
// It returns the value as a uin64 and any errors encountered. The reader will
// be advanced by the number of bytes needed to consume this value. On error,
// the reader will not be advanced.
//
// This is the format for the
// int32, int64, uint32, uint64, bool, and enum
func (p *parser) decodeVarint() (uint64, error) {
	// protobuf defines values that are up to 64 bits wide. The largest value
	// stored in a protobuf varint is 64 data bits, which in varint encoding,
	// would require 10 bytes.
	buf, err := p.source.Peek(10)
	if err != nil {
		return 0, wrap(err, "decode varint couldn't peek 10 bytes")
	}

	var x uint64
	var s uint
	for i, b := range buf {
		// when msb is 0, we're at the last byte of the value
		if b < 0x80 {
			if _, err := p.source.Discard(i + 1); err != nil {
				return 0, wrap(err, "decode varint couldn't discard %d bytes", i)
			}
			return x | uint64(b)<<s, nil
		}

		// otherwise, include the 7 least significant bits in our value
		x |= uint64(b&0x7f) << s
		s += 7
	}

	return 0, fmt.Errorf("decode varint never saw the end of varint")
}

// reads n bytes from the source into the scratch buffer. the returned slice is
// the beginning of the scratch buffer. it will be corrupted on the next call
// to readn or the next operation that utilizes the scratch buffer.
func (p *parser) readn(n int) ([]byte, error) {
	buf := make([]byte, n)
	if _, err := io.ReadFull(p.source, buf); err != nil {
		return nil, wrap(err, "error reading %d bytes", n)
	}
	return buf, nil
}

// checks whether we have an acceptable header at the current reader position.
func (p *parser) checkHeader() (bool, error) {
	buf, err := p.readn(8)
	if err != nil {
		return false, wrap(err, "unable to read header bytes")
	}
	return string(buf) == replayHeader, nil
}

// reads the next datagram type indicator off the wire. Also looks for a
// compression flag, returning true if the contents to follow are snappy
// compressed, false otherwise.
func (p *parser) readDatagramType() (datagramType, bool, error) {
	n, err := p.decodeVarint()
	if err != nil {
		return EDemoCommands_DEM_Error, false, wrap(err, "readDatagramType couldn't read varint")
	}

	compressed := false
	if n&0x40 > 0 {
		compressed = true
		n &^= 0x40
	}
	return datagramType(n), compressed, nil
}

func (p *parser) readDatagram() (*dataGram, error) {
	cmd, compressed, err := p.readDatagramType()
	if err != nil {
		return nil, wrap(err, "readDatagram couldn't get a command")
	}

	tick, err := p.decodeVarint()
	if err != nil {
		return nil, wrap(err, "readDatagram couldn't read the tick value")
	}

	size, err := p.decodeVarint()
	if err != nil {
		return nil, wrap(err, "readDatagram couldn't read the size value")
	}

	if size > 0 {
		buf := make([]byte, int(size))
		if _, err := io.ReadFull(p.source, buf); err != nil {
			return nil, wrap(err, "readDatagram couldn't read datagram body")
		}

		if compressed {
			var err error
			buf, err = snappy.Decode(nil, buf)
			if err != nil {
				return nil, wrap(err, "readDatagram couldn't snappy decode body")
			}
		}
		// TODO: pool these!
		return &dataGram{cmd, int64(tick), buf}, nil
	}

	// TODO: pool these!
	return &dataGram{cmd, int64(tick), nil}, nil
}