package session

import (
	"fmt"
	"sort"
	"strings"
)

// DetectExternalChanges compares the current workspace state against the
// EndManifest recorded in .ctask/last-session-summary.json.
//
// Returns (nil, nil) if no summary exists (pre-v0.4 workspace or first
// session ever) — callers should treat this as "silently skip the warning".
//
// Returns a non-nil diff with empty slices when nothing changed outside a
// ctask session.
func DetectExternalChanges(wsDir string) (*ManifestDiff, error) {
	summary, err := ReadSummary(SummaryPath(wsDir))
	if err != nil {
		return nil, err
	}
	if summary == nil {
		return nil, nil
	}

	previous := &Manifest{
		CapturedAt: summary.EndedAt,
		Files:      append([]FileEntry{}, summary.EndManifest...),
	}
	current, err := CaptureManifest(wsDir)
	if err != nil {
		return nil, err
	}
	return DiffManifests(previous, current), nil
}

// FormatStaleWarning renders the Layer-3 warning shown when the workspace
// was modified outside a ctask session since the last session ended.
func FormatStaleWarning(summary *SessionSummary, diff *ManifestDiff) string {
	var b strings.Builder
	b.WriteString("[ctask] Workspace modified since last session ended:\n\n")
	fmt.Fprintf(&b, "  Last session: %s (%s, %s)\n\n",
		summary.EndedAt.Local().Format("2006-01-02 15:04"),
		summary.Hostname, summary.Agent)
	b.WriteString("  Modified since then:\n")

	lines := append([]string{}, diff.Modified...)
	sort.Strings(lines)
	for _, f := range lines {
		fmt.Fprintf(&b, "    %s (modified)\n", f)
	}
	added := append([]string{}, diff.Added...)
	sort.Strings(added)
	for _, f := range added {
		fmt.Fprintf(&b, "    %s (new file)\n", f)
	}
	deleted := append([]string{}, diff.Deleted...)
	sort.Strings(deleted)
	for _, f := range deleted {
		fmt.Fprintf(&b, "    %s (deleted)\n", f)
	}
	b.WriteString("\n  These changes were not made during a ctask session.\n")
	b.WriteString("  Review before continuing? [Y/n] ")
	return b.String()
}

// HasChanges returns true if diff reports any added/modified/deleted entries.
func HasChanges(d *ManifestDiff) bool {
	if d == nil {
		return false
	}
	return len(d.Added) > 0 || len(d.Modified) > 0 || len(d.Deleted) > 0
}