package agent

import (
	"context"
	"strings"
)

// fallbackBackend runs pi-native first. A failed turn is retried on the container pi-agent.
type fallbackBackend struct {
	primary  Backend
	fallback Backend
}

func (f *fallbackBackend) Name() string {
	if f.primary == nil {
		return "pi-native"
	}
	return f.primary.Name()
}

func (f *fallbackBackend) Execute(ctx context.Context, req Request) (*Result, error) {
	res, err := f.primary.Execute(ctx, req)
	if ctx.Err() != nil || succeeded(res, err) || f.fallback == nil {
		return res, err
	}
	fb, fbErr := f.fallback.Execute(ctx, req)
	if !succeeded(fb, fbErr) {
		return res, err
	}
	note := "pi-native failed; served by pi-agent"
	if res != nil && strings.TrimSpace(res.ErrorReason) != "" {
		note += ": " + strings.TrimSpace(res.ErrorReason)
	} else if err != nil {
		note += ": " + err.Error()
	}
	if strings.TrimSpace(fb.Logs) == "" {
		fb.Logs = note
	} else {
		fb.Logs = note + "\n" + fb.Logs
	}
	return fb, nil
}

func succeeded(res *Result, err error) bool {
	return err == nil && res != nil && res.Success
}