package hst

import (
	"encoding/gob"
	"slices"
	"strings"

	"hakurei.app/check"
	"hakurei.app/fhs"
)

func init() { gob.Register(new(FSOverlay)) }

// FilesystemOverlay is the type string of an overlay mount point.
const FilesystemOverlay = "overlay"

// FSOverlay represents an overlay mount point.
type FSOverlay struct {
	// Pathname in the container mount namespace.
	Target *check.Absolute `json:"dst"`

	// Any filesystem, does not need to be on a writable filesystem, must not be nil.
	Lower []*check.Absolute `json:"lower"`
	// The upperdir is normally on a writable filesystem, leave as nil to mount
	// Lower readonly.
	Upper *check.Absolute `json:"upper,omitempty"`
	// The workdir needs to be an empty directory on the same filesystem as
	// Upper, must not be nil if Upper is populated.
	Work *check.Absolute `json:"work,omitempty"`
}

func (o *FSOverlay) Valid() bool {
	if o == nil || o.Target == nil {
		return false
	}

	for _, a := range o.Lower {
		if a == nil {
			return false
		}
	}

	if o.Upper != nil { // rw
		return o.Work != nil || len(o.Lower) > 0
	} else { // ro
		return len(o.Lower) >= 2
	}
}

func (o *FSOverlay) Path() *check.Absolute {
	if !o.Valid() {
		return nil
	}
	return o.Target
}

func (o *FSOverlay) Host() []*check.Absolute {
	if !o.Valid() {
		return nil
	}
	p := make([]*check.Absolute, 0, 2+len(o.Lower))
	if o.Upper != nil {
		p = append(p, o.Upper)
		if o.Work != nil {
			p = append(p, o.Work)
		}
	}
	p = append(p, o.Lower...)
	return p
}

func (o *FSOverlay) Apply(z *ApplyState) {
	if !o.Valid() {
		return
	}

	if o.Upper != nil {
		if o.Target.Is(fhs.AbsRoot) {
			z.NoRemountRoot = true
		}
		if o.Work != nil {
			z.Overlay(o.Target, o.Upper, o.Work, o.Lower...)
		} else {
			z.OverlayEphemeral(o.Target, slices.Concat(
				[]*check.Absolute{o.Upper},
				o.Lower,
			)...)
		}
	} else {
		z.OverlayReadonly(o.Target, o.Lower...)
	}
}

func (o *FSOverlay) String() string {
	if !o.Valid() {
		return "<invalid>"
	}

	lower := make([]string, len(o.Lower))
	for i, a := range o.Lower {
		lower[i] = check.EscapeOverlayDataSegment(a.String())
	}

	if o.Upper != nil {
		if o.Work != nil {
			return "w*" + strings.Join(append([]string{
				check.EscapeOverlayDataSegment(o.Target.String()),
				check.EscapeOverlayDataSegment(o.Upper.String()),
				check.EscapeOverlayDataSegment(o.Work.String())},
				lower...), check.SpecialOverlayPath)
		}
		return "e*" + strings.Join(append([]string{
			check.EscapeOverlayDataSegment(o.Target.String()),
			check.EscapeOverlayDataSegment(o.Upper.String())},
			lower...), check.SpecialOverlayPath)

	} else {
		return "*" + strings.Join(append([]string{
			check.EscapeOverlayDataSegment(o.Target.String())},
			lower...), check.SpecialOverlayPath)
	}
}
