// The chroot package is able to create an Amazon AMI without requiring
// the launch of a new instance for every build. It does this by attaching
// and mounting the root volume of another AMI and chrooting into that
// directory. It then creates an AMI from that attached drive.
package chroot

import (
	"errors"
	"log"
	"runtime"

	"github.com/aws/aws-sdk-go/service/ec2"
	"github.com/mitchellh/multistep"
	awscommon "github.com/mitchellh/packer/builder/amazon/common"
	"github.com/mitchellh/packer/common"
	"github.com/mitchellh/packer/helper/config"
	"github.com/mitchellh/packer/packer"
	"github.com/mitchellh/packer/template/interpolate"
)

// The unique ID for this builder
const BuilderId = "mitchellh.amazon.chroot"

// Config is the configuration that is chained through the steps and
// settable from the template.
type Config struct {
	common.PackerConfig    `mapstructure:",squash"`
	awscommon.AccessConfig `mapstructure:",squash"`
	awscommon.AMIConfig    `mapstructure:",squash"`

	ChrootMounts   [][]string `mapstructure:"chroot_mounts"`
	CommandWrapper string     `mapstructure:"command_wrapper"`
	CopyFiles      []string   `mapstructure:"copy_files"`
	DevicePath     string     `mapstructure:"device_path"`
	MountPath      string     `mapstructure:"mount_path"`
	SourceAmi      string     `mapstructure:"source_ami"`

	ctx *interpolate.Context
}

type wrappedCommandTemplate struct {
	Command string
}

type Builder struct {
	config Config
	runner multistep.Runner
}

func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
	b.config.ctx = &interpolate.Context{Funcs: awscommon.TemplateFuncs}
	err := config.Decode(&b.config, &config.DecodeOpts{
		Interpolate:        true,
		InterpolateContext: b.config.ctx,
		InterpolateFilter: &interpolate.RenderFilter{
			Exclude: []string{
				"command_wrapper",
				"mount_path",
			},
		},
	}, raws...)
	if err != nil {
		return nil, err
	}

	// Defaults
	if b.config.ChrootMounts == nil {
		b.config.ChrootMounts = make([][]string, 0)
	}

	if b.config.CopyFiles == nil {
		b.config.CopyFiles = make([]string, 0)
	}

	if len(b.config.ChrootMounts) == 0 {
		b.config.ChrootMounts = [][]string{
			[]string{"proc", "proc", "/proc"},
			[]string{"sysfs", "sysfs", "/sys"},
			[]string{"bind", "/dev", "/dev"},
			[]string{"devpts", "devpts", "/dev/pts"},
			[]string{"binfmt_misc", "binfmt_misc", "/proc/sys/fs/binfmt_misc"},
		}
	}

	if len(b.config.CopyFiles) == 0 {
		b.config.CopyFiles = []string{"/etc/resolv.conf"}
	}

	if b.config.CommandWrapper == "" {
		b.config.CommandWrapper = "{{.Command}}"
	}

	if b.config.MountPath == "" {
		b.config.MountPath = "/mnt/packer-amazon-chroot-volumes/{{.Device}}"
	}

	// Accumulate any errors
	var errs *packer.MultiError
	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.ctx)...)
	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.ctx)...)

	for _, mounts := range b.config.ChrootMounts {
		if len(mounts) != 3 {
			errs = packer.MultiErrorAppend(
				errs, errors.New("Each chroot_mounts entry should be three elements."))
			break
		}
	}

	if b.config.SourceAmi == "" {
		errs = packer.MultiErrorAppend(errs, errors.New("source_ami is required."))
	}

	if errs != nil && len(errs.Errors) > 0 {
		return nil, errs
	}

	log.Println(common.ScrubConfig(b.config, b.config.AccessKey, b.config.SecretKey))
	return nil, nil
}

func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packer.Artifact, error) {
	if runtime.GOOS != "linux" {
		return nil, errors.New("The amazon-chroot builder only works on Linux environments.")
	}

	config, err := b.config.Config()
	if err != nil {
		return nil, err
	}

	ec2conn := ec2.New(config)

	wrappedCommand := func(command string) (string, error) {
		ctx := *b.config.ctx
		ctx.Data = &wrappedCommandTemplate{Command: command}
		return interpolate.Render(b.config.CommandWrapper, &ctx)
	}

	// Setup the state bag and initial state for the steps
	state := new(multistep.BasicStateBag)
	state.Put("config", &b.config)
	state.Put("ec2", ec2conn)
	state.Put("hook", hook)
	state.Put("ui", ui)
	state.Put("wrappedCommand", CommandWrapper(wrappedCommand))

	// Build the steps
	steps := []multistep.Step{
		&StepInstanceInfo{},
		&awscommon.StepSourceAMIInfo{
			SourceAmi:          b.config.SourceAmi,
			EnhancedNetworking: b.config.AMIEnhancedNetworking,
		},
		&StepCheckRootDevice{},
		&StepFlock{},
		&StepPrepareDevice{},
		&StepCreateVolume{},
		&StepAttachVolume{},
		&StepEarlyUnflock{},
		&StepMountDevice{},
		&StepMountExtra{},
		&StepCopyFiles{},
		&StepChrootProvision{},
		&StepEarlyCleanup{},
		&StepSnapshot{},
		&StepRegisterAMI{},
		&awscommon.StepAMIRegionCopy{
			Regions: b.config.AMIRegions,
		},
		&awscommon.StepModifyAMIAttributes{
			Description: b.config.AMIDescription,
			Users:       b.config.AMIUsers,
			Groups:      b.config.AMIGroups,
		},
		&awscommon.StepCreateTags{
			Tags: b.config.AMITags,
		},
	}

	// Run!
	if b.config.PackerDebug {
		b.runner = &multistep.DebugRunner{
			Steps:   steps,
			PauseFn: common.MultistepDebugFn(ui),
		}
	} else {
		b.runner = &multistep.BasicRunner{Steps: steps}
	}

	b.runner.Run(state)

	// If there was an error, return that
	if rawErr, ok := state.GetOk("error"); ok {
		return nil, rawErr.(error)
	}

	// If there are no AMIs, then just return
	if _, ok := state.GetOk("amis"); !ok {
		return nil, nil
	}

	// Build the artifact and return it
	artifact := &awscommon.Artifact{
		Amis:           state.Get("amis").(map[string]string),
		BuilderIdValue: BuilderId,
		Conn:           ec2conn,
	}

	return artifact, nil
}

func (b *Builder) Cancel() {
	if b.runner != nil {
		log.Println("Cancelling the step runner...")
		b.runner.Cancel()
	}
}