package rrdbinary

import (
	"bytes"
	"fmt"
	"math"
	"reflect"
	"strconv"
	"strings"
)

type Decoder struct {
	arch Architecture
	pos  int
	data []byte
}

func NewDecoder(arch Architecture, data []byte) *Decoder {
	return &Decoder{
		arch: arch,
		pos:  0,
		data: data,
	}
}

type unmarshaler interface {
	unmarshalRRD(d *Decoder, tag string) error
}

func Unmarshal(arch Architecture, data []byte, ptr interface{}) error {
	decoder := NewDecoder(arch, data)
	if err := decoder.Decode(ptr, ""); err != nil {
		return err
	}
	if err := decoder.Decode(&EOF{}, ""); err != nil {
		return err
	}
	return nil
}

func (d *Decoder) binError(ctxLen int, msg string) error {
	return NewBinError(msg, d.data, d.pos, ctxLen)
}

func (d *Decoder) binErrorf(ctxLen int, format string, a ...interface{}) error {
	return d.binError(ctxLen, fmt.Sprintf(format, a...))
}

func (d *Decoder) Decode(ptr interface{}, tag string) error {
	ptrValue := reflect.ValueOf(ptr)
	if ptrValue.Kind() != reflect.Ptr {
		return typeErrorf("ptr is a %v, not a pointer", ptrValue.Kind())
	}
	return d.decode(ptrValue.Elem(), tag)
}

func (d *Decoder) decode(v reflect.Value, tag string) error {
	if v.Kind() != reflect.Ptr && v.CanAddr() {
		vptr := v.Addr()
		if vptr.CanInterface() {
			if u, ok := vptr.Interface().(unmarshaler); ok {
				return u.unmarshalRRD(d, tag)
			}
		}
	}
	switch v.Type().Kind() {
	case reflect.Struct:
		return d.decodeStruct(v, tag)
	case reflect.Array, reflect.Slice:
		return d.decodeList(v, tag)
	default:
		return typeErrorf("invalid type for rrdbinary.Decoder: %v", v.Type())
	}
}

func (d *Decoder) decodeStruct(v reflect.Value, tag string) error {
	panicUnless(v.Kind() == reflect.Struct)
	panicUnless(v.CanSet())

	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for struct: %q", tag)
	}

	for i := 0; i < v.NumField(); i++ {
		fieldInfo := v.Type().Field(i)
		tag := fieldInfo.Tag.Get("rrdbinary")
		if tag == "-" {
			continue
		}
		if err := d.decode(v.Field(i), tag); err != nil {
			return fmt.Errorf("field %s: %w", fieldInfo.Name, err)
		}
	}
	return nil
}

func (d *Decoder) decodeList(v reflect.Value, tag string) error {
	panicUnless(v.Kind() == reflect.Array || v.Kind() == reflect.Slice)
	panicUnless(v.CanSet())

	for i := 0; i < v.Len(); i++ {
		if err := d.decode(v.Index(i), tag); err != nil {
			return fmt.Errorf("index %d: %w", i, err)
		}
	}
	return nil
}

func (obj *String) unmarshalRRD(d *Decoder, tag string) error {
	size := 0
	switch {
	case tag == "":
		// do nothing
	case strings.HasPrefix(tag, "size="):
		var err error
		size, err = strconv.Atoi(strings.TrimPrefix(tag, "size="))
		if err != nil {
			return typeErrorf("invalid rrdbinary struct tag for string: %q", tag)
		}
	default:
		return typeErrorf("invalid rrdbinary struct tag for string: %q", tag)
	}

	data := d.data[d.pos:]
	if size > 0 {
		if len(data) < size {
			return d.binErrorf(size, "unexpected end-of-file in %d-byte string", size)
		}
		data = data[:size]
	}

	nul := bytes.IndexByte(data, 0)
	if nul < 0 {
		if size > 0 {
			return d.binErrorf(size, "missing null-terminator on %d-byte string", size)
		} else {
			return d.binErrorf(16, "unexpected end-of-file looking for null-terminator on string")
		}
	}

	if size > 0 {
		for _, byte := range data[nul:] {
			if byte != 0 {
				return d.binErrorf(size, "garbage data after null-terminator on fixed %d-byte string", size)
			}
		}
	} else {
		size = nul + 1
	}

	*obj = String(data[:nul])
	d.pos += size
	return nil
}

func (obj *Double) unmarshalRRD(d *Decoder, tag string) error {
	if d.arch.DoubleWidth != 8 {
		return archErrorf("rrdbinary does not support DoubleWidth=%d; only supports 8", d.arch.DoubleWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for float: %q", tag)
	}

	data := d.data[d.pos:]

	padding := 0
	if d.pos%d.arch.DoubleAlign != 0 {
		padding = d.arch.DoubleAlign - (d.pos % d.arch.DoubleAlign)
	}
	if len(data) < padding {
		return d.binErrorf(padding+d.arch.DoubleWidth, "unexpected end-of-file in %d-byte padding-before-float", padding)
	}
	data = data[padding:]

	if len(data) < d.arch.DoubleWidth {
		return d.binErrorf(d.arch.DoubleWidth, "unexpected end-of-file in %d-byte float", d.arch.DoubleWidth)
	}

	*obj = Double(math.Float64frombits(d.arch.ByteOrder.Uint64(data)))
	d.pos += padding + d.arch.DoubleWidth
	return nil
}

func (obj *ULong) unmarshalRRD(d *Decoder, tag string) error {
	if d.arch.LongWidth != 4 && d.arch.LongWidth != 8 {
		return archErrorf("rrdbinary does not support LongWidth=%d; only supports 4 or 8", d.arch.LongWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for uint: %q", tag)
	}

	data := d.data[d.pos:]

	padding := 0
	if d.pos%d.arch.LongAlign != 0 {
		padding = d.arch.LongAlign - (d.pos % d.arch.LongAlign)
	}
	if len(data) < padding {
		return d.binErrorf(padding+d.arch.LongWidth, "unexpected end-of-file in %d-byte padding-before-uint", padding)
	}
	data = data[padding:]

	if len(data) < d.arch.LongWidth {
		return d.binErrorf(d.arch.LongWidth, "unexpected end-of-file in %d-byte uint", d.arch.LongWidth)
	}

	switch d.arch.LongWidth {
	case 4:
		*obj = ULong(d.arch.ByteOrder.Uint32(data))
	case 8:
		*obj = ULong(d.arch.ByteOrder.Uint64(data))
	}
	d.pos += padding + d.arch.LongWidth
	return nil
}

func (obj *Long) unmarshalRRD(d *Decoder, tag string) error {
	if d.arch.LongWidth != 4 && d.arch.LongWidth != 8 {
		return archErrorf("rrdbinary does not support LongWidth=%d; only supports 4 or 8", d.arch.LongWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for int: %q", tag)
	}

	data := d.data[d.pos:]

	padding := 0
	if d.pos%d.arch.LongAlign != 0 {
		padding = d.arch.LongAlign - (d.pos % d.arch.LongAlign)
	}
	if len(data) < padding {
		return d.binErrorf(padding+d.arch.LongWidth, "unexpected end-of-file in %d-byte padding-before-int", padding)
	}
	data = data[padding:]

	if len(data) < d.arch.LongWidth {
		return d.binErrorf(d.arch.LongWidth, "unexpected end-of-file in %d-byte int", d.arch.LongWidth)
	}

	switch d.arch.LongWidth {
	case 4:
		*obj = Long(int32(d.arch.ByteOrder.Uint32(data)))
	case 8:
		*obj = Long(d.arch.ByteOrder.Uint64(data))
	}
	d.pos += padding + d.arch.LongWidth
	return nil
}

func (obj *Unival) unmarshalRRD(d *Decoder, tag string) error {
	if d.arch.UnivalWidth != 8 {
		return archErrorf("rrdbinary does not support UnivalWidth=%d; only supports 8", d.arch.UnivalWidth)
	}
	if d.arch.ShortWidth != 2 && d.arch.ShortWidth != 4 {
		return archErrorf("rrdbinary does not support ShortWidth=%d; only supports 2 or 4", d.arch.ShortWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for unival: %q", tag)
	}

	data := d.data[d.pos:]

	padding := 0
	if d.pos%d.arch.UnivalAlign != 0 {
		padding = d.arch.UnivalAlign - (d.pos % d.arch.UnivalAlign)
	}
	if len(data) < padding {
		return d.binErrorf(padding+d.arch.UnivalWidth, "unexpected end-of-file in %d-byte padding-before-unival", padding)
	}
	data = data[padding:]

	if len(data) < d.arch.UnivalWidth {
		return d.binErrorf(d.arch.UnivalWidth, "unexpected end-of-file in %d-byte unival", d.arch.UnivalWidth)
	}

	*obj = Unival{
		arch: d.arch,
		data: data[:d.arch.UnivalWidth],
	}
	d.pos += padding + d.arch.UnivalWidth
	return nil
}

func (obj *Time) unmarshalRRD(d *Decoder, tag string) error {
	if d.arch.TimeWidth != 4 && d.arch.TimeWidth != 8 {
		return archErrorf("rrdbinary does not support TimeWidth=%d; only supports 4 or 8", d.arch.TimeWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for time: %q", tag)
	}

	data := d.data[d.pos:]

	padding := 0
	if d.pos%d.arch.TimeAlign != 0 {
		padding = d.arch.TimeAlign - (d.pos % d.arch.TimeAlign)
	}
	if len(data) < padding {
		return d.binErrorf(padding+d.arch.TimeWidth, "unexpected end-of-file in %d-byte padding-before-time", padding)
	}
	data = data[padding:]

	if len(data) < d.arch.TimeWidth {
		return d.binErrorf(d.arch.TimeWidth, "unexpected end-of-file in %d-byte time", d.arch.TimeWidth)
	}

	switch d.arch.TimeWidth {
	case 4:
		*obj = Time(int32(d.arch.ByteOrder.Uint32(data)))
	case 8:
		*obj = Time(d.arch.ByteOrder.Uint64(data))
	}
	d.pos += padding + d.arch.TimeWidth
	return nil
}

func (_ *EOF) unmarshalRRD(d *Decoder, tag string) error {
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for eof: %q", tag)
	}

	data := d.data[d.pos:]
	if len(data) > 0 {
		return d.binErrorf(16, "extra %d bytes of data after expected end-of-file", len(data))
	}

	return nil
}