package host

import (
	"bytes"
	"context"
	"os"

	"github.com/carlosframework/platform/internal/rootstate"
)

// The caller holds the binding lock and has resolved the successor from the
// current root installation. A route edit never reaches this transition.
func (m claimUnitMaterializer) handover(ctx context.Context, old, next claimUnitBinding) error {
	if m.state == nil || m.read == nil || m.replace == nil || m.idle == nil || !old.valid() || !next.valid() || !old.Retired || next.Retiring || next.Retired || old.Shape != next.Shape || old.Owner == next.Owner {
		return os.ErrPermission
	}
	unlock, err := m.state.Lock(ctx, "materialize")
	if err != nil {
		return err
	}
	defer unlock()
	r, err := m.load(old.Owner.Host)
	if err != nil {
		return err
	}
	want, err := claimOwnedUnitDefinition(next)
	if err != nil {
		return err
	}
	previous := old
	previous.Retiring, previous.Retired = false, false
	if r.Binding == previous {
		if !r.Retired || r.Identity == (rootstate.FileIdentity{}) {
			return os.ErrPermission
		}
		raw, id, err := m.read(old.Shape.Unit)
		if err != nil {
			return err
		}
		if !id.Same(r.Identity) || !bytes.Equal(raw, claimRetiredUnitDefinition(old)) {
			return os.ErrPermission
		}
		r = claimUnitMaterialization{Binding: next, Digest: claimUnitDigest(want), Prior: old, PriorIdentity: r.Identity}
	}
	if r.Binding != next || r.Prior != old || r.Digest != claimUnitDigest(want) || r.Retiring || r.Retired {
		return os.ErrPermission
	}
	if err = m.save(r); err != nil {
		return err
	}
	raw, id, err := m.read(next.Shape.Unit)
	if err != nil {
		return err
	}
	if r.Identity == (rootstate.FileIdentity{}) && id.Same(r.PriorIdentity) && bytes.Equal(raw, claimRetiredUnitDefinition(old)) {
		if err = m.idle(next.Shape.Host); err != nil {
			return err
		}
		if err = m.replace(next.Shape.Unit, r.PriorIdentity, want); err != nil {
			return err
		}
		raw, id, err = m.read(next.Shape.Unit)
		if err != nil {
			return err
		}
	}
	if !bytes.Equal(raw, want) || id == (rootstate.FileIdentity{}) || (r.Identity != (rootstate.FileIdentity{}) && !r.Identity.Same(id)) {
		return os.ErrPermission
	}
	r.Identity = id
	return m.save(r)
}