package configsrc

import (
	"context"
	"fmt"
	"os"
	"time"

	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/object"
	"golang.org/x/crypto/ssh"

	"tug/internal/platform/replica"
)

type CheckpointHead struct {
	Commit string
	Time   time.Time
	Signer ssh.PublicKey
}

func InspectCheckpoint(ctx context.Context, stateDir string, in Input) (CheckpointHead, error) {
	var result CheckpointHead
	checkpoint, err := commitID(in.Checkpoint, false)
	if err != nil || checkpoint.IsZero() {
		return result, fmt.Errorf("no checkpoint is set; a first start needs no reset")
	}
	dir, err := os.MkdirTemp(stateDir, "config-checkpoint-")
	if err != nil {
		return result, err
	}
	defer os.RemoveAll(dir)
	s := &Source{dir: dir}
	auth, err := s.auth(in)
	if err != nil {
		return result, err
	}
	repo, err := s.repo()
	if err != nil {
		return result, err
	}
	head, err := replica.Fetch(ctx, repo, in.Remote.URL, auth, plumbing.ReferenceName("refs/heads/"+in.Remote.Branch))
	if err != nil {
		return result, fmt.Errorf("unreachable: %w", err)
	}
	if head.IsZero() {
		return result, errEmpty
	}
	key, refused, err := verify(repo.Storer, head, in.Signers)
	if err != nil {
		return result, err
	}
	if refused != nil {
		return result, fmt.Errorf("%s: %w", refused.kind, refused.cause)
	}
	found, err := walk(repo.Storer, head, checkpoint)
	if err != nil {
		return result, err
	}
	if found {
		return result, fmt.Errorf("the branch still holds the checkpoint; an ordinary start repairs the clone")
	}
	commit, err := object.GetCommit(repo.Storer, head)
	if err != nil {
		return result, err
	}
	return CheckpointHead{Commit: head.String(), Time: commit.Committer.When, Signer: key}, nil
}