// SPDX-License-Identifier: MIT

package checker

import (
	"context"
	"errors"

	sdk "git.happydns.org/checker-sdk-go/checker"
)

// ErrNoCollector is returned by Collect when the provider was constructed
// without a CollectFn (e.g. when registered host-side as an externalizable-only
// provider). Callers should route the observation to an external checker.
var ErrNoCollector = errors.New("dnsviz: provider has no local collector; use an external checker")

// CollectFn is the function signature for the DNSViz data collection step.
// The checker package is decoupled from the subprocess invocation so it can
// be imported without GPL obligations. Implementations live in the binary or
// plugin layer (see internal/collect).
type CollectFn func(ctx context.Context, opts sdk.CheckerOptions) (any, error)

// Provider returns a new DNSViz observation provider backed by the given
// collect function.
func Provider(collect CollectFn) sdk.ObservationProvider {
	return &dnsvizProvider{collect: collect}
}

type dnsvizProvider struct{ collect CollectFn }

func (p *dnsvizProvider) Key() sdk.ObservationKey {
	return ObservationKeyDNSViz
}

func (p *dnsvizProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (any, error) {
	if p.collect == nil {
		return nil, ErrNoCollector
	}
	return p.collect(ctx, opts)
}