// Package agent wraps the ADK runner with the project's defaults.
//
// Keep this thin: construction, defaults, and the Run loop. Tool wiring,
// callbacks, and any business logic belong in sibling packages.
package agent

import (
	"context"
	"fmt"
	"iter"

	"google.golang.org/adk/agent"
	"google.golang.org/adk/agent/llmagent"
	"google.golang.org/adk/model"
	"google.golang.org/adk/runner"
	"google.golang.org/adk/session"
	"google.golang.org/genai"
)

// Config holds the minimum needed to spin up an agent + runner.
type Config struct {
	Name        string
	Description string
	Instruction string
	Model       model.LLM
}

// Agent is the runnable unit. Construct with New, drive with Run.
type Agent struct {
	name   string
	runner *runner.Runner
}

// New builds an llmagent and an in-memory-session runner around it.
func New(cfg Config) (*Agent, error) {
	if cfg.Name == "" {
		return nil, fmt.Errorf("agent: Name required")
	}
	if cfg.Model == nil {
		return nil, fmt.Errorf("agent: Model required")
	}

	ag, err := llmagent.New(llmagent.Config{
		Name:        cfg.Name,
		Description: cfg.Description,
		Model:       cfg.Model,
		Instruction: cfg.Instruction,
	})
	if err != nil {
		return nil, fmt.Errorf("agent: build llmagent: %w", err)
	}

	r, err := runner.New(runner.Config{
		AppName:           cfg.Name,
		Agent:             ag,
		SessionService:    session.InMemoryService(),
		AutoCreateSession: true,
	})
	if err != nil {
		return nil, fmt.Errorf("agent: build runner: %w", err)
	}

	return &Agent{name: cfg.Name, runner: r}, nil
}

// Run dispatches a single user turn and returns the event iterator.
// The caller is responsible for draining it and handling errors.
func (a *Agent) Run(ctx context.Context, userID, sessionID, text string) iter.Seq2[*session.Event, error] {
	msg := genai.NewContentFromText(text, "user")
	return a.runner.Run(ctx, userID, sessionID, msg, agent.RunConfig{})
}

// Name returns the registered agent name (also used as ADK AppName).
func (a *Agent) Name() string { return a.name }