package loop

import (
	"context"
	"encoding/json"
	"fmt"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/model"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/persist"
)

// checkpointState is the durable snapshot persisted at every step. Carrying the
// message window and the step index lets a long-running task be resumed from the
// latest checkpoint without losing context (design §1 durable execution).
type checkpointState struct {
	Step       int             `json:"step"`
	Messages   []model.Message `json:"messages"`
	StopReason string          `json:"stop_reason,omitempty"`
}

// saveCheckpoint persists a snapshot at step. It never fails the run: a nil store
// is a no-op and a marshal/save error is logged.
func (l *Loop) saveCheckpoint(ctx context.Context, sessionID string, step int, messages []model.Message, stopReason string) {
	if l.checkpoint == nil {
		return
	}
	state := checkpointState{
		Step:       step,
		Messages:   messages,
		StopReason: stopReason,
	}
	buf, err := json.Marshal(state)
	if err != nil {
		l.log.Warn("checkpoint marshal", "step", step, "error", err)
		return
	}
	cp := &persist.Checkpoint{
		ID:      fmt.Sprintf("%s:%d", sessionID, step),
		AgentID: sessionID,
		Step:    step,
		State:   buf,
	}
	if err := l.checkpoint.Save(ctx, cp); err != nil {
		l.log.Warn("checkpoint save", "step", step, "error", err)
	}
}