// Package backend — stateless one-shot operations.
// These functions provide request/response LLM access without session state.
package backend

import (
	"context"
	"fmt"
	"strings"
)

// GenerateRequest is the input for a stateless one-shot generation.
type GenerateRequest struct {
	Prompt  string `json:"prompt"`
	System  string `json:"system"`
	Backend string `json:"backend"`
	Model   string `json:"model"`
}

// Generate performs a stateless one-shot LLM generation with no session context.
// Returns the full model response text.
func Generate(ctx context.Context, req GenerateRequest) (string, error) {
	if req.Prompt == "" {
		return "", fmt.Errorf("empty prompt")
	}
	be, err := NewWithName(req.Backend)
	if err != nil {
		return "", err
	}
	if req.Model != "" {
		be.SetModel(req.Model)
	}
	var msgs []Message
	if req.System != "" {
		msgs = append(msgs, Message{Role: "system", Content: req.System})
	}
	msgs = append(msgs, Message{Role: "user", Content: req.Prompt})
	ch, err := be.ChatStream(ctx, msgs, nil, GenerationParams{})
	if err != nil {
		return "", err
	}
	var sb strings.Builder
	for ev := range ch {
		sb.WriteString(ev.Content)
	}
	return sb.String(), nil
}