package basic

import (
	"context"
	"fmt"
	"time"
)

// datetime returns the current time, optionally formatted with a Go reference
// layout and rendered in a named IANA timezone.
type datetime struct{}

const (
	// defaultDTFormat is the layout used when the caller supplies none.
	defaultDTFormat = time.RFC3339
	// defaultDTZone is the timezone used when the caller supplies none.
	defaultDTZone = "UTC"
	// maxDTFormatLen bounds a layout string to guard against absurd input.
	maxDTFormatLen = 128
	// maxDTZoneLen bounds a timezone name to guard against absurd input.
	maxDTZoneLen = 64
)

// Name returns the tool identifier.
func (datetime) Name() string { return "datetime" }

// Description explains what the tool does for the model.
func (datetime) Description() string {
	return "Return the current time, formatted with a Go reference layout and rendered in a named IANA timezone."
}

// Parameters returns the tool input JSON Schema.
func (datetime) Parameters() (map[string]any, error) {
	return map[string]any{
		"type": "object",
		"properties": map[string]any{
			"format":   map[string]any{"type": "string", "description": "Go reference layout, e.g. 2006-01-02 15:04:05"},
			"timezone": map[string]any{"type": "string", "description": "IANA timezone name, e.g. Asia/Shanghai"},
		},
	}, nil
}

// Execute returns the current time in the requested format and timezone.
func (datetime) Execute(ctx context.Context, args any) (any, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	m, err := asMap(args)
	if err != nil {
		return nil, err
	}
	layout, err := optString(m, "format", defaultDTFormat)
	if err != nil {
		return nil, err
	}
	if len(layout) > maxDTFormatLen {
		return nil, fmt.Errorf("basic: layout too long: %w", ErrInvalidArgument)
	}
	zone, err := optString(m, "timezone", defaultDTZone)
	if err != nil {
		return nil, err
	}
	if len(zone) > maxDTZoneLen {
		return nil, fmt.Errorf("basic: timezone name too long: %w", ErrInvalidArgument)
	}
	loc, err := time.LoadLocation(zone)
	if err != nil {
		return nil, fmt.Errorf("basic: invalid timezone %q: %w", zone, err)
	}
	now := time.Now().In(loc)
	return map[string]any{
		"now":      now.Format(layout),
		"unix":     now.Unix(),
		"timezone": zone,
		"format":   layout,
	}, nil
}