package usecase

import (
	"context"

	"go.maximumdirect.net/promptkit/internal/domain"
)

// ConversationTurn is one delivery to a coordinator callback.
type ConversationTurn[R any] struct {
	Exchange       *domain.Exchange
	Result         *R
	RemainingTurns int
}

// CoordinationOutcome describes a normal coordinator termination.
type CoordinationOutcome string

const (
	CoordinationStopped   CoordinationOutcome = "stopped"
	CoordinationExhausted CoordinationOutcome = "exhausted"
)

// CoordinationResult holds a normal outcome or a completed undelivered result.
type CoordinationResult[R any] struct {
	Outcome     CoordinationOutcome
	Undelivered *R
}

// Coordinate advances one branch using the supplied callback and ordinary run.
func Coordinate[Q, R any](ctx context.Context, start *domain.Exchange, turns int,
	next func(context.Context, ConversationTurn[R]) (*Q, error),
	run func(context.Context, *domain.Exchange, *Q) (*R, *domain.Exchange, error),
) (CoordinationResult[R], error) {
	current := start
	var pending *R
	for {
		if err := ctx.Err(); err != nil {
			return CoordinationResult[R]{Undelivered: pending}, err
		}
		request, err := next(ctx, ConversationTurn[R]{Exchange: current, Result: pending, RemainingTurns: turns})
		pending = nil
		if contextErr := ctx.Err(); contextErr != nil {
			return CoordinationResult[R]{}, contextErr
		}
		if err != nil {
			return CoordinationResult[R]{}, err
		}
		if request == nil {
			return CoordinationResult[R]{Outcome: CoordinationStopped}, nil
		}
		if turns == 0 {
			return CoordinationResult[R]{Outcome: CoordinationExhausted}, nil
		}
		if err := ctx.Err(); err != nil {
			return CoordinationResult[R]{}, err
		}
		turns--
		var nextExchange *domain.Exchange
		pending, nextExchange, err = run(ctx, current, request)
		if err != nil {
			return CoordinationResult[R]{}, err
		}
		current = nextExchange
	}
}