package hostexec

import (
	"bytes"
	"context"
	"errors"
	"os"

	"github.com/carlosframework/platform/internal/rootparticipation"
	"github.com/carlosframework/platform/internal/rootstate"
)

func ReadRoot(ctx context.Context, store rootstate.Store, clock Clock, q ExecutionRequest, serving bool) (ExecutionRecord, error) {
	var r ExecutionRecord
	if store == nil || clock == nil {
		return r, ErrState
	}
	if _, err := store.Read("update.json"); !errors.Is(err, os.ErrNotExist) {
		return r, ErrLost
	}
	ledger := rootparticipation.Ledger{State: store}
	census, err := ledger.Census()
	if err != nil || census.NeverEnrolled {
		return r, errors.Join(err, ErrState)
	}
	raw, err := store.Read(q.Host + ".json")
	if serving {
		if errors.Is(err, os.ErrNotExist) {
			return r, nil
		}
		if err != nil {
			return r, err
		}
		if rootparticipation.Decode(raw, &r) != nil || r.Schema != 1 || !r.Request.Valid() || r.Token == "" || r.Replay == nil || r.Request.Host != q.Host || r.Status != "settled" || r.Authority.Migration != census.Migration || r.Authority.Box != census.Box || r.Authority.Enrollment != census.Enrollment {
			return r, ErrLost
		}
		return r, nil
	}
	if err != nil {
		return r, err
	}
	if rootparticipation.Decode(raw, &r) != nil || r.Schema != 1 || !r.Request.Valid() || !sameExecution(q, r) || r.Status != "active" || r.Authority.ParticipationOnly || r.Authority.Installation == "" || r.Authority.Migration != census.Migration || r.Authority.Box != census.Box || r.Authority.Enrollment != census.Enrollment || r.Token == "" {
		return r, ErrLost
	}
	boot, err := BootID()
	if err != nil || r.Peer.KernelBootID != boot {
		return r, ErrLost
	}
	_, now, err := clock.Now()
	if err != nil || now >= r.SafeUntil {
		return r, ErrLost
	}
	if err = ControllerAlive(ctx, r.Peer); err != nil {
		return r, err
	}
	if err := ctx.Err(); err != nil {
		return r, err
	}
	alive, err := rootstate.LiveHeld(store, q.Host+".live")
	if err != nil || !alive {
		return r, errors.Join(ErrLost, err)
	}
	again, err := store.Read(q.Host + ".json")
	if err != nil || !bytes.Equal(raw, again) {
		return r, ErrLost
	}
	_, now, err = clock.Now()
	if err != nil || now >= r.SafeUntil {
		return r, ErrLost
	}
	return r, nil
}