package osbuild

import (

	"encoding/json"

	"errors"

)

// An Assembler turns a filesystem tree into a target image.

type Assembler struct {

	Name    string           `json:"name"`

	Options AssemblerOptions `json:"options"`

}

// AssemblerOptions specify the operations of a given assembler-type.

type AssemblerOptions interface {

	isAssemblerOptions()

}

type rawAssembler struct {

	Name    string          `json:"name"`

	Options json.RawMessage `json:"options"`

}

// UnmarshalJSON unmarshals JSON into an Assembler object. Each type of

// assembler has a custom unmarshaller for its options, selected based on the

// stage name.

func (assembler *Assembler) UnmarshalJSON(data []byte) error {

	var rawAssembler rawAssembler

	err := json.Unmarshal(data, &rawAssembler)

	if err != nil {

		return err

	}

	var options AssemblerOptions

	switch rawAssembler.Name {

	case "org.osbuild.ostree.commit":

		options = new(OSTreeCommitAssemblerOptions)

	case "org.osbuild.qemu":

		options = new(QEMUAssemblerOptions)

	case "org.osbuild.rawfs":

		options = new(RawFSAssemblerOptions)

	case "org.osbuild.tar":

		options = new(TarAssemblerOptions)

	default:

		return errors.New("unexpected assembler name")

	}

	err = json.Unmarshal(rawAssembler.Options, options)

	if err != nil {

		return err

	}

	assembler.Name = rawAssembler.Name

	assembler.Options = options

	return nil

}