package rrdbinary

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

func Unmarshal(arch Architecture, data []byte, ptr interface{}) error {
	ptrValue := reflect.ValueOf(ptr)
	if ptrValue.Kind() != reflect.Ptr {
		return typeErrorf("ptr is a %v, not a pointer", ptrValue.Kind())
	}
	decoder := &unmarshaler{
		arch: arch,
		pos:  0,
		data: data,
	}
	return decoder.unmarshal(ptrValue, "")
}

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

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

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

func (d *unmarshaler) unmarshal(v reflect.Value, tag string) error {
	switch v.Type() {
	case reflect.TypeOf(String("")):
		return d.unmarshalString(v, tag)
	case reflect.TypeOf(Float(0)):
		return d.unmarshalFloat(v, tag)
	case reflect.TypeOf(Uint(0)):
		return d.unmarshalUint(v, tag)
	case reflect.TypeOf(Int(0)):
		return d.unmarshalInt(v, tag)
	case reflect.TypeOf(Unival(0)):
		return d.unmarshalUnival(v, tag)
	case reflect.TypeOf(Time(0)):
		return d.unmarshalTime(v, tag)
	default:
		switch v.Type().Kind() {
		case reflect.Struct:
			return d.unmarshalStruct(v, tag)
		case reflect.Array:
			return d.unmarshalArray(v, tag)
		default:
			return typeErrorf("invalid type for rrdbinary.Unmarshal: %v", v.Type())
		}
	}
}

func (d *unmarshaler) unmarshalStruct(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.unmarshal(v.Field(i), tag); err != nil {
			return fmt.Errorf("field %s: %w", fieldInfo.Name, err)
		}
	}
	return nil
}

func (d *unmarshaler) unmarshalArray(v reflect.Value, tag string) error {
	panicUnless(v.Kind() == reflect.Array)
	panicUnless(v.CanSet())

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

func (d *unmarshaler) unmarshalString(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(String("")))
	panicUnless(v.CanSet())

	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
	}

	v.SetString(string(data[:nul]))
	d.pos += size
	return nil
}

func (d *unmarshaler) unmarshalFloat(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(Float(0)))
	panicUnless(v.CanSet())

	if d.arch.FloatWidth != 8 {
		return archErrorf("rrdbinary does not support FloatWidth=%d; only supports 8", d.arch.FloatWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for float: %q", tag)
	}

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

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

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

	v.SetFloat(math.Float64frombits(d.arch.ByteOrder.Uint64(data)))
	d.pos += padding + d.arch.FloatWidth
	return nil
}

func (d *unmarshaler) unmarshalUint(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(Uint(0)))
	panicUnless(v.CanSet())

	if d.arch.IntWidth != 4 && d.arch.IntWidth != 8 {
		return archErrorf("rrdbinary does not support IntWidth=%d; only supports 4 or 8", d.arch.IntWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for uint: %q", tag)
	}

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

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

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

	switch d.arch.IntWidth {
	case 4:
		v.SetUint(uint64(d.arch.ByteOrder.Uint32(data)))
	case 8:
		v.SetUint(d.arch.ByteOrder.Uint64(data))
	}
	d.pos += padding + d.arch.IntWidth
	return nil
}

func (d *unmarshaler) unmarshalInt(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(Int(0)))
	panicUnless(v.CanSet())

	if d.arch.IntWidth != 4 && d.arch.IntWidth != 8 {
		return archErrorf("rrdbinary does not support IntWidth=%d; only supports 4 or 8", d.arch.IntWidth)
	}
	if tag != "" {
		return typeErrorf("invalid rrdbinary struct tag for int: %q", tag)
	}

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

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

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

	switch d.arch.IntWidth {
	case 4:
		v.SetInt(int64(int32(d.arch.ByteOrder.Uint32(data))))
	case 8:
		v.SetInt(int64(d.arch.ByteOrder.Uint64(data)))
	}
	d.pos += padding + d.arch.IntWidth
	return nil
}

func (d *unmarshaler) unmarshalUnival(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(Unival(0)))
	panicUnless(v.CanSet())

	if d.arch.UnivalWidth != 8 {
		return archErrorf("rrdbinary does not support UnivalWidth=%d; only supports 8", d.arch.UnivalWidth)
	}
	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)
	}

	v.SetUint(d.arch.ByteOrder.Uint64(data))
	d.pos += padding + d.arch.UnivalWidth
	return nil
}

func (d *unmarshaler) unmarshalTime(v reflect.Value, tag string) error {
	panicUnless(v.Type() == reflect.TypeOf(Time(0)))
	panicUnless(v.CanSet())

	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:
		v.SetInt(int64(int32(d.arch.ByteOrder.Uint32(data))))
	case 8:
		v.SetInt(int64(d.arch.ByteOrder.Uint64(data)))
	}
	d.pos += padding + d.arch.TimeWidth
	return nil
}