package normalize

import (
	"context"
	"fmt"

	"gitea.maximumdirect.net/ejr/feedkit/event"
)

// Normalizer converts one event shape into another.
//
// A Normalizer is typically domain-owned code (weatherfeeder/newsfeeder/...)
// that knows how to interpret a specific upstream payload and produce a
// normalized payload.
//
// Normalizers are selected via Match(). The matching strategy is intentionally
// flexible: implementations may match on Schema, Kind, Source, or any other
// Event fields.
type Normalizer interface {
	// Match reports whether this normalizer applies to the given event.
	//
	// Common patterns:
	//   - match on e.Schema (recommended for versioning)
	//   - match on e.Source (useful if Schema is empty)
	//   - match on (e.Kind + e.Source), etc.
	Match(e event.Event) bool

	// Normalize transforms the incoming event into a new (or modified) event.
	//
	// Return values:
	//   - (out, nil) where out != nil: emit the normalized event
	//   - (nil, nil): drop the event (treat as policy drop)
	//   - (nil, err): fail the pipeline
	//
	// Note: If you simply want to pass the event through unchanged, return &in.
	Normalize(ctx context.Context, in event.Event) (*event.Event, error)
}

// Func is an ergonomic adapter that lets you define a Normalizer with functions.
//
// Example:
//
//	n := normalize.Func{
//	  MatchFn: func(e event.Event) bool { return e.Schema == "raw.openweather.current.v1" },
//	  NormalizeFn: func(ctx context.Context, in event.Event) (*event.Event, error) {
//	    // ... map in.Payload -> normalized payload ...
//	  },
//	}
type Func struct {
	MatchFn     func(e event.Event) bool
	NormalizeFn func(ctx context.Context, in event.Event) (*event.Event, error)

	// Optional: helps produce nicer panic/error messages if something goes wrong.
	Name string
}

func (f Func) Match(e event.Event) bool {
	if f.MatchFn == nil {
		return false
	}
	return f.MatchFn(e)
}

func (f Func) Normalize(ctx context.Context, in event.Event) (*event.Event, error) {
	if f.NormalizeFn == nil {
		return nil, fmt.Errorf("normalize.Func(%s): NormalizeFn is nil", f.safeName())
	}
	return f.NormalizeFn(ctx, in)
}

func (f Func) safeName() string {
	if f.Name == "" {
		return "<unnamed>"
	}
	return f.Name
}