package builtin

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
	"sync"

	"nub/internal/tool"
)

// TodoTool hält eine In-Memory-Todo-Liste im Session-State (5.3) — nicht im
// Baum persistiert. Zustand lebt im Tool selbst, deshalb Pointer-Registrierung
// (&TodoTool{}) statt eines Werttyps.
type TodoTool struct {
	mu    sync.Mutex
	items []TodoItem
}

type TodoItem struct {
	Content string `json:"content"`
	Status  string `json:"status"` // pending | in_progress | completed
}

func (*TodoTool) Name() string { return "todo" }
func (*TodoTool) Description() string {
	return "Ersetzt die aktuelle Todo-Liste. Für lange Tasks: Fortschritt sichtbar halten."
}

func (*TodoTool) Schema() json.RawMessage {
	return json.RawMessage(`{
		"type": "object",
		"properties": {
			"items": {
				"type": "array",
				"items": {
					"type": "object",
					"properties": {
						"content": {"type": "string"},
						"status":  {"type": "string", "enum": ["pending", "in_progress", "completed"]}
					},
					"required": ["content", "status"]
				}
			}
		},
		"required": ["items"]
	}`)
}

type todoInput struct {
	Items []TodoItem `json:"items"`
}

func (t *TodoTool) Run(ctx context.Context, input json.RawMessage, env tool.Env) (tool.Result, error) {
	var in todoInput
	if err := json.Unmarshal(input, &in); err != nil {
		return tool.Result{ForModel: "invalid input: " + err.Error(), IsError: true}, nil
	}
	for _, it := range in.Items {
		switch it.Status {
		case "pending", "in_progress", "completed":
		default:
			return tool.Result{ForModel: fmt.Sprintf("invalid status %q", it.Status), IsError: true}, nil
		}
	}

	t.mu.Lock()
	t.items = in.Items
	items := make([]TodoItem, len(t.items))
	copy(items, t.items)
	t.mu.Unlock()

	return tool.Result{ForModel: renderTodos(items), ForUI: TodoResult{Items: items}}, nil
}

type TodoResult struct {
	Items []TodoItem
}

func renderTodos(items []TodoItem) string {
	if len(items) == 0 {
		return "todo list is empty"
	}
	var b strings.Builder
	for _, it := range items {
		mark := " "
		switch it.Status {
		case "in_progress":
			mark = "~"
		case "completed":
			mark = "x"
		}
		fmt.Fprintf(&b, "[%s] %s\n", mark, it.Content)
	}
	return b.String()
}