package workflowbridge

import (
	"errors"
	"regexp"
	"strings"
)

const DefaultTextModel = "deepseek-v4-1-flash-260910"
const DefaultBookModel = "doubao-seed-evolving"
const DefaultImageModel = "doubao-seedream-5-0-pro-260628"

var modelID = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9._-]{0,127}$`)
var errInvalidModel = errors.New("invalid model selection")

// Nodes carry only an Ark model/endpoint identifier. URL and credentials remain
// server configuration; choosing a model never silently falls back to another.
func selectedModel(step, model, custom string) (string, error) {
	var fallback string
	switch step {
	case "classify", "daily":
		fallback = DefaultTextModel
	case "write-book":
		fallback = DefaultBookModel
	case "illustrate":
		fallback = DefaultImageModel
	default:
		return "", nil
	}
	model = strings.TrimSpace(model)
	if model == "__custom__" {
		model = strings.TrimSpace(custom)
		if model == "" {
			return "", errInvalidModel
		}
	}
	if model == "" {
		if inCustom := strings.TrimSpace(custom); inCustom != "" {
			return "", errInvalidModel
		}
		model = fallback
	}
	if !modelID.MatchString(model) || model == "__custom__" {
		return "", errInvalidModel
	}
	if step == "illustrate" {
		if !strings.HasPrefix(model, "doubao-seedream-") && !strings.HasPrefix(model, "ep-") {
			return "", errInvalidModel
		}
	} else {
		for _, modality := range []string{"seedream", "seedance", "embedding", "seed3d"} {
			if strings.Contains(strings.ToLower(model), modality) {
				return "", errInvalidModel
			}
		}
	}
	return model, nil
}