package app

import (
	"context"
	"flag"
	"fmt"
	"io"

	"gitea.maximumdirect.net/eric/narratio/internal/config"
	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
)

// Resume continues execution from the first non-succeeded stage in the manifest.
func Resume(ctx context.Context, args []string, out io.Writer) error {
	fs := flag.NewFlagSet("resume", flag.ContinueOnError)
	fs.SetOutput(io.Discard)

	var pipelinePath string
	var sessionPath string
	var force bool
	fs.StringVar(&pipelinePath, "config", "", "path to pipeline.yml")
	fs.StringVar(&sessionPath, "session", "", "path to session.yml")
	fs.BoolVar(&force, "force", false, "force stage execution")

	if err := fs.Parse(args); err != nil {
		return fmt.Errorf("resume: invalid flags: %w", err)
	}
	if fs.NArg() != 0 {
		return fmt.Errorf("resume: unexpected positional arguments")
	}
	if pipelinePath == "" || sessionPath == "" {
		return fmt.Errorf("resume: --config and --session are required")
	}

	cfg, err := config.Load(pipelinePath, sessionPath)
	if err != nil {
		return fmt.Errorf("resume: %w", err)
	}
	if err := config.Validate(cfg); err != nil {
		return fmt.Errorf("resume: %w", err)
	}

	full := BuildFullPlan()
	selected := full
	if !force {
		m, err := loadManifestIfPresent(ctx, cfg)
		if err != nil {
			return fmt.Errorf("resume: %w", err)
		}
		if m != nil {
			start := firstNonSucceededIndex(full, m)
			if start >= len(full) {
				_, err := fmt.Fprintf(out, "narratio resume: session %s has no remaining stages\n", cfg.Session.SessionID)
				return err
			}
			selected = full[start:]
		}
	}

	summary, err := executeStages(ctx, cfg, selected, RunOptions{Force: force})
	if err != nil {
		return fmt.Errorf("resume: %w", err)
	}

	_, err = fmt.Fprintf(
		out,
		"narratio resume: session %s; executed=%d skipped=%d; manifest=%s\n",
		summary.SessionID,
		len(summary.Executed),
		len(summary.Skipped),
		summary.ManifestPath,
	)
	return err
}

func loadManifestIfPresent(ctx context.Context, cfg *config.Config) (*manifest.Manifest, error) {
	path := manifestPathFor(cfg)
	exists, err := fileExists(path)
	if err != nil {
		return nil, fmt.Errorf("check manifest %q: %w", path, err)
	}
	if !exists {
		return nil, nil
	}
	store := &manifest.LocalStore{}
	m, err := store.Load(ctx, path)
	if err != nil {
		return nil, fmt.Errorf("load manifest %q: %w", path, err)
	}
	return m, nil
}