package koboldsim

import (
	"errors"

	"git.chromaticdragon.app/kistaro/CardSimEngine/cardsim"
)

var (
	ErrOptionNotEnabled = errors.New("option not enabled")
	ErrPolicyNotEnacted = errors.New("cannot unenact policy that is not enacted")
)

type Policy interface {
	cardsim.CardOption[*KoboldMine]
	// Unenact reverses the previous enactment of this policy.
	Unenact(p *Player) error

	// LastEnacted informs this Policy which choice was last enacted and
	// which index it is under; this allows it to prepare to describe
	// itself differently depending on the last selected policy. If no
	// option has ever been chosen for this card, the index is -1.
	//
	// The Card that would present this Policy as an option must use this,
	// and provide the active policy that this is a candidate to replace,
	LastEnacted(int, Policy)

	// Is returns whether this policy is this other policy. This is a strict
	// identity equality check, don't do anything clever here.
	Is(Policy) bool
}

// A SwitchingCard is an issue card that remembers which option was selected
// previously, and undoes it before doing a different one. It is always valid
// to draw.
type SwitchingCard struct {
	Name       cardsim.Message
	Desc       cardsim.Message
	IsUrgent   bool
	After      func(*SwitchingCard, *Player, CardOption) error
	Policies   []Policy
	lastPolicy Policy
}

// Title implements Card.
func (s *SwitchingCard) Title(*Player) cardsim.Message {
	return s.Name
}

// Urgent implements Card.
func (s *SwitchingCard) Urgent(*Player) bool {
	return s.IsUrgent
}

// Drawn implements Card.
func (s *SwitchingCard) Drawn(*Player) bool {
	return true
}

// EventText implements Card.
func (s *SwitchingCard) EventText(*Player) (cardsim.Message, error) {
	return s.Desc, nil
}

// Options implements Card.
func (s *SwitchingCard) Options(*Player) ([]CardOption, error) {
	lastIdx := -1
	for i, p := range s.Policies {
		if p.Is(s.lastPolicy) {
			lastIdx = i
			break
		}
	}
	ret := make([]CardOption, len(s.Policies))
	for i, p := range s.Policies {
		p.LastEnacted(lastIdx, s.lastPolicy)
		ret[i] = p
	}
	return ret, nil
}

// Then implements Card.
func (s *SwitchingCard) Then(p *Player, o CardOption) error {
	newPolicy := o.(Policy)
	var errs cardsim.ErrorCollector
	if !newPolicy.Is(s.lastPolicy) {
		err := s.lastPolicy.Unenact(p)
		if cardsim.IsSeriousError(err) {
			return err
		}
		errs.Add(err)
	}
	s.lastPolicy = o.(Policy)
	if s.After != nil {
		errs.Add(s.After(s, p, o))
	}
	return errs.Emit()
}

// BasicPolicy is a straightfoward implementation of Policy. If the currently
// enacted option is re-enacted, it refunds the player's action point.
type BasicPolicy struct {
	UnenactedDesc  cardsim.Message
	EnactedDesc    cardsim.Message
	NothingChanged cardsim.Message
	Do             func(*Player) (cardsim.Message, error)
	Undo           func(*Player) error
	CanDo          func(*Player) bool

	currentlyEnacted bool
}

// YesWeCan returns true. It's the default value for BasicPolicy.CanDo / BasicPolicy.CanUndo.
func YesWeCan(*Player) bool {
	return true
}

// lastEnacted notifies b about the last-enacted policy in its group. It updates
// b.currentlyEnacted accordingly and returns itself.
//
// It also installs placeholders if CanDo or CanUndo is unspecified.
func (b *BasicPolicy) LastEnacted(_ int, p Policy) {
	b.currentlyEnacted = false
	if o, ok := p.(*BasicPolicy); ok && o == b {
		b.currentlyEnacted = true
	}
	if b.CanDo == nil {
		b.CanDo = YesWeCan
	}
}

// OptionText implements CardOption.
func (b *BasicPolicy) OptionText(*Player) (cardsim.Message, error) {
	if b.currentlyEnacted {
		return b.EnactedDesc, nil
	}
	return b.UnenactedDesc, nil
}

// Enact implements CardOption.
func (b *BasicPolicy) Enact(p *Player) (cardsim.Message, error) {
	if b.currentlyEnacted {
		p.ActionsRemaining++
		if b.NothingChanged == nil {
			b.NothingChanged = cardsim.MsgStr("You continue your current approach.")
		}
		return b.NothingChanged, nil
	}
	if !b.CanDo(p) {
		return nil, ErrOptionNotEnabled
	}
	return b.Do(p)
}

// Unenact implements Policy.
func (b *BasicPolicy) Unenact(p *Player) error {
	if !b.currentlyEnacted {
		return ErrPolicyNotEnacted
	}
	return b.Undo(p)
}

// Enabled implements CardOption.
func (b *BasicPolicy) Enabled(p *Player) bool {
	if b.currentlyEnacted {
		return true
	}
	if b.CanDo == nil {
		b.CanDo = YesWeCan
	}
	return b.CanDo(p)
}

func (b *BasicPolicy) Is(p Policy) bool {
	if o, ok := p.(*BasicPolicy); ok {
		return o == b
	}
	return false
}

// A DescResuilt is descriptive text for an option and the text result of
// enacting that option when it was described this way.
type DescResult struct {
	Desc   cardsim.Message
	Result cardsim.Message
}

// A VerbosePolicy is an extension to a BasicPolicy. It emits the BasicPolicy's
// `UnenactedDesc` and the message returned from Do only when no policy has ever
// been enacted for this card; otherwise, it looks up the description and result
// from a slice using the index of the last policy selected.
type VerbosePolicy struct {
	*BasicPolicy
	lastIdx int
	Content []DescResult
}

func (v *VerbosePolicy) LastEnacted(i int, p Policy) {
	v.lastIdx = i
	v.BasicPolicy.LastEnacted(i, p)
}

func (v *VerbosePolicy) OptionText(*Player) (cardsim.Message, error) {
	if v.lastIdx < 0 {
		return v.BasicPolicy.UnenactedDesc, nil
	}
	return v.Content[v.lastIdx].Desc, nil
}

func (v *VerbosePolicy) Enact(p *Player) (cardsim.Message, error) {
	msg, err := v.BasicPolicy.Enact(p)
	if v.lastIdx >= 0 {
		msg = v.Content[v.lastIdx].Result
	}
	return msg, err
}

func (v *VerbosePolicy) Is(p Policy) bool {
	if o, ok := p.(*VerbosePolicy); ok {
		return o == p
	}
	return false
}