package domain

import (
	"fmt"

	contract "git.cin.su/m/Assistant/contracts/situation"
)

// FocusStack is a rebuildable, situation-owned projection. Push suspends the
// previous active frame; Pop resumes its parent and never deletes a frame.
type FocusStack struct{ frames []contract.FocusFrame }

func NewFocusStack(frames []contract.FocusFrame) (FocusStack, error) {
	stack := FocusStack{frames: append([]contract.FocusFrame(nil), frames...)}
	for _, frame := range stack.frames {
		if err := frame.Validate(); err != nil {
			return FocusStack{}, err
		}
	}
	return stack, nil
}

func (s FocusStack) Frames() []contract.FocusFrame {
	return append([]contract.FocusFrame(nil), s.frames...)
}

func (s FocusStack) Current() (contract.FocusFrame, error) {
	for i := len(s.frames) - 1; i >= 0; i-- {
		if s.frames[i].State == contract.FocusActive {
			return s.frames[i], nil
		}
	}
	return contract.FocusFrame{}, ErrNoActiveFocus
}

func (s FocusStack) Push(frame contract.FocusFrame) (FocusStack, error) {
	if err := frame.Validate(); err != nil {
		return FocusStack{}, err
	}
	if frame.State != contract.FocusActive {
		return FocusStack{}, fmt.Errorf("pushed frame must be active")
	}
	frames := s.Frames()
	if len(frames) > 0 {
		current, err := s.Current()
		if err == nil {
			for i := range frames {
				if frames[i].ID == current.ID {
					frames[i].State = contract.FocusSuspended
					break
				}
			}
			frame.ParentFrameRef = &current.ID
		}
	}
	frames = append(frames, frame)
	return FocusStack{frames: frames}, nil
}

func (s FocusStack) Pop() (FocusStack, contract.FocusFrame, error) {
	current, err := s.Current()
	if err != nil {
		return FocusStack{}, contract.FocusFrame{}, err
	}
	frames := s.Frames()
	for i := range frames {
		if frames[i].ID == current.ID {
			frames[i].State = contract.FocusSuspended
			break
		}
	}
	if current.ParentFrameRef != nil {
		for i := range frames {
			if frames[i].ID == *current.ParentFrameRef {
				frames[i].State = contract.FocusActive
				break
			}
		}
	}
	return FocusStack{frames: frames}, current, nil
}

// ProjectFocusProjection retains the V1 API as a read projection only.
func ProjectFocusProjection(frame contract.FocusFrame, project contract.ProjectDescriptor) contract.ActiveProjectFocus {
	return contract.ActiveProjectFocus{ActorID: frame.ActorID, PrincipalID: frame.PrincipalID, ProjectID: contract.ProjectID(project.ID), ProjectDisplayName: project.DisplayName, Provenance: contract.ProjectResolutionProvenance(frame.Provenance), ConfidenceMillis: frame.ConfidenceMillis, SourceUtteranceID: frame.SourceUtteranceRef, UpdatedAtUnixMillis: int64(frame.RecordedAt)}
}