// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0

package store

import (
	"cmp"
	"errors"
	"fmt"
	"io/fs"
	"log/slog"
	"os"
	"path"
	"path/filepath"
	"slices"
	"strings"
	"time"

	"sourcedock.dev/petrbalvin/volumen/internal/post"
)

// CleanupStaleTombstones removes tombstones whose slug has a live post
// again, so a future undelete cannot clobber it. It writes inside the
// content directory, which is why it is a call of its own rather than a
// side effect of New: a read-only command must not mutate the tree it
// inspects.
func (s *Store) CleanupStaleTombstones() {
	root, err := s.openRoot()
	if err != nil {
		return
	}
	for _, slugDir := range s.revisionDirs() {
		live := s.restoreTargetPath(slugDir)
		if live == "" {
			continue
		}
		for _, entry := range readDirIn(root, slugDir) {
			name := entry.Name()
			if !strings.HasPrefix(name, ".deleted-") || !strings.HasSuffix(name, ".md") {
				continue
			}
			rel := path.Join(slugDir, name)
			if err := root.Remove(rel); err == nil {
				slog.Info("store: removed stale tombstone",
					"tombstone", filepath.Join(s.ContentDir, rel),
					"live", filepath.Join(s.ContentDir, live))
			}
		}
	}
}

// TombstonePath returns the newest .deleted-<stamp>.md for slug, or "".
// Tombstones are ordered by their delete stamp, falling back to the file
// modification time, so a delete that follows another within the same
// second still resolves to the later one.
func (s *Store) TombstonePath(slug string) string {
	root, err := s.openRoot()
	if err != nil {
		return ""
	}
	revDir := revisionsName(slug)
	type named struct {
		name  string
		mtime time.Time
	}
	var found []named
	for _, entry := range readDirIn(root, revDir) {
		name := entry.Name()
		if !strings.HasPrefix(name, ".deleted-") || !strings.HasSuffix(name, ".md") {
			continue
		}
		info, ok := statIn(root, revDir, name)
		if !ok {
			continue
		}
		found = append(found, named{name: name, mtime: info.ModTime()})
	}
	if len(found) == 0 {
		return ""
	}
	slices.SortFunc(found, func(a, b named) int {
		if c := b.mtime.Compare(a.mtime); c != 0 {
			return c
		}
		return strings.Compare(b.name, a.name)
	})
	return filepath.Join(s.ContentDir, revDir, found[0].name)
}

// Undelete restores a soft-deleted post from its newest tombstone.
func (s *Store) Undelete(slug string) *post.Post {
	tombstone := s.TombstonePath(slug)
	if tombstone == "" {
		return nil
	}
	root, err := s.openRoot()
	if err != nil {
		slog.Warn("store: cannot restore", "slug", slug, "error", err)
		return nil
	}
	rel, err := filepath.Rel(s.ContentDir, tombstone)
	if err != nil {
		return nil
	}
	content, err := root.ReadFile(rel)
	if err != nil {
		slog.Warn("store: failed to read tombstone", "path", tombstone, "error", err)
		return nil
	}
	p, err := post.Parse(string(content))
	if err != nil {
		slog.Warn("store: failed to parse tombstone", "path", tombstone, "error", err)
		return nil
	}
	if p.Slug() == "" {
		p.Metadata.Set("slug", slug)
	}
	name, err := s.defaultNameFor(p)
	if err != nil {
		slog.Warn("store: cannot restore", "slug", slug, "error", err)
		return nil
	}
	unlock := s.targetLock(filepath.Join(s.ContentDir, name))
	defer unlock()

	if _, err := root.Stat(name); err == nil {
		slog.Warn("store: cannot undelete, target exists", "slug", slug, "path", name)
		return nil
	}
	if err := root.MkdirAll(path.Dir(name), 0o755); err != nil {
		slog.Warn("store: failed to restore", "path", name, "error", err)
		return nil
	}
	if err := atomicWriteIn(root, name, content); err != nil {
		slog.Warn("store: failed to restore", "path", name, "error", err)
		return nil
	}
	p.Path = filepath.Join(s.ContentDir, name)
	if err := root.Remove(rel); err != nil {
		slog.Warn("store: restored post but could not remove the tombstone",
			"path", tombstone, "error", err)
	}
	s.pruneRevisions(slug)
	s.InvalidateCache()
	return p
}

// writeTombstone moves the post into the revision archive as a deleted
// marker. The copy carries an explicit lang so that undeleting a post
// that lived in a language subdirectory puts it back where it came from.
func (s *Store) writeTombstone(p *post.Post) error {
	if p.Path == "" {
		return fmt.Errorf("post has no path")
	}
	root, err := s.openRoot()
	if err != nil {
		return err
	}
	live, err := filepath.Rel(s.ContentDir, p.Path)
	if err != nil {
		return fmt.Errorf("locate %s: %w", p.Path, err)
	}
	// Two deletes of one slug can race between Find and the lock; the
	// second must not archive again, and the caller reports the post as
	// already gone rather than as a failure.
	if _, err := root.Stat(live); err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return fmt.Errorf("post %s: %w", p.Slug(), fs.ErrNotExist)
		}
		return fmt.Errorf("stat %s: %w", p.Path, err)
	}
	slug := p.Slug()
	if slug == "" {
		slug = strings.TrimSuffix(filepath.Base(p.Path), ".md")
	}
	if s.revisionLimit <= 0 {
		if err := root.Remove(live); err != nil {
			return fmt.Errorf("delete %s: %w", slug, err)
		}
		return nil
	}
	revDir := revisionsName(slug)
	if err := root.MkdirAll(revDir, 0o755); err != nil {
		return fmt.Errorf("create revision directory: %w", err)
	}
	stored := p.Clone()
	if lang := p.Lang(); lang != "" {
		if existing, present := stored.Metadata.Get("lang"); !present || existing == nil {
			stored.Metadata.Set("lang", lang)
		}
	}
	dumped, err := stored.ToFile()
	if err != nil {
		return fmt.Errorf("serialise %s: %w", slug, err)
	}
	// The archive directory is shared by every language variant of the
	// slug, so writes into it serialise on it rather than on the live
	// file, whose per-language locks would let two variants race for the
	// same stamp.
	unlock := s.targetLock(filepath.Join(s.ContentDir, revDir))
	defer unlock()
	stamp := time.Now().UTC().Format("20060102T150405Z")
	dest := path.Join(revDir, ".deleted-"+stamp+".md")
	for suffix := 1; ; suffix++ {
		if _, err := root.Stat(dest); err != nil {
			break
		}
		dest = path.Join(revDir, fmt.Sprintf(".deleted-%s-%d.md", stamp, suffix))
	}
	if err := atomicWriteIn(root, dest, []byte(dumped)); err != nil {
		return fmt.Errorf("tombstone %s: %w", slug, err)
	}
	s.pruneTombstones(revDir, dest)
	// The copy is durable, so the original can go. A crash between the
	// two leaves a live post and a tombstone, which CleanupStaleTombstones
	// resolves in favour of the live post.
	if err := root.Remove(live); err != nil {
		return fmt.Errorf("remove %s after tombstoning: %w", p.Path, err)
	}
	return nil
}

// pruneTombstones removes the tombstones an older delete left behind:
// only the newest is ever undeleted from, so keeping one bounds the
// archive against a create/delete cycle that would otherwise grow it
// forever (revision_limit deliberately does not count tombstones).
func (s *Store) pruneTombstones(revDir, keep string) {
	root, err := s.openRoot()
	if err != nil {
		return
	}
	for _, entry := range readDirIn(root, revDir) {
		name := entry.Name()
		if !strings.HasPrefix(name, ".deleted-") || !strings.HasSuffix(name, ".md") {
			continue
		}
		rel := path.Join(revDir, name)
		if rel == keep {
			continue
		}
		if err := root.Remove(rel); err != nil {
			slog.Warn("store: could not prune an old tombstone", "path", rel, "error", err)
		}
	}
}

// --- read path internals ---------------------------------------------------

// revisionsName returns the archive directory of a slug, relative to the
// content directory.
func revisionsName(slug string) string {
	safe := safeSlugRe.ReplaceAllString(slug, "-")
	// A slug of ".", "..", or similar must never become a directory path
	// component that walks out of the revisions tree.
	if safe == "" || strings.Trim(safe, ".") == "" {
		safe = "post"
	}
	return path.Join(revisionsDirname, safe)
}

// revisionDirs lists the archive directories, relative to the content
// directory.
func (s *Store) revisionDirs() []string {
	root, err := s.openRoot()
	if err != nil {
		return nil
	}
	var dirs []string
	for _, entry := range readDirIn(root, revisionsDirname) {
		if entry.IsDir() {
			dirs = append(dirs, path.Join(revisionsDirname, entry.Name()))
		}
	}
	return dirs
}

// restoreTargetPath finds a live post whose file name matches the encoded
// slug directory of a tombstone, as a path relative to the content
// directory.
func (s *Store) restoreTargetPath(slugDir string) string {
	root, err := s.openRoot()
	if err != nil {
		return ""
	}
	encoded := path.Base(slugDir)
	candidates := []string{encoded + ".md"}
	var names []string
	for _, entry := range readDirIn(root, ".") {
		if !entry.IsDir() {
			continue
		}
		name := entry.Name()
		if name == MediaDirName || name == revisionsDirname {
			continue
		}
		names = append(names, name)
	}
	slices.Sort(names)
	for _, name := range names {
		candidates = append(candidates, path.Join(name, encoded+".md"))
	}
	for _, candidate := range candidates {
		if _, err := root.Stat(candidate); err == nil {
			return candidate
		}
	}
	return ""
}

func (s *Store) archiveRevision(name, slug string) {
	if s.revisionLimit <= 0 {
		return
	}
	root, err := s.openRoot()
	if err != nil {
		slog.Warn("store: could not archive revision", "slug", slug, "error", err)
		return
	}
	existing, err := root.ReadFile(name)
	if err != nil {
		// A missing file is the ordinary first save; anything else
		// (permissions, I/O) would silently drop the previous version,
		// so it is logged rather than swallowed.
		if !errors.Is(err, fs.ErrNotExist) {
			slog.Warn("store: could not read the previous version to archive it",
				"slug", slug, "path", name, "error", err)
		}
		return
	}
	revDir := revisionsName(slug)
	if err := root.MkdirAll(revDir, 0o755); err != nil {
		slog.Warn("store: could not archive revision", "slug", slug, "error", err)
		return
	}
	// The archive directory is shared by every language variant of the
	// slug, so the write serialises on it; two variants saving in the
	// same second would otherwise pick the same stamp and write through
	// the same temp file.
	unlock := s.targetLock(filepath.Join(s.ContentDir, revDir))
	defer unlock()
	stamp := time.Now().UTC().Format("20060102T150405Z")
	dest := path.Join(revDir, stamp+".md")
	for suffix := 1; ; suffix++ {
		if _, err := root.Stat(dest); err != nil {
			break
		}
		dest = path.Join(revDir, fmt.Sprintf("%s-%d.md", stamp, suffix))
	}
	// The revision is a full copy of the previous file, so it goes
	// through the same atomic write as the post itself: a crash must not
	// leave a half-written revision in the history.
	if err := atomicWriteIn(root, dest, existing); err != nil {
		slog.Warn("store: could not archive revision", "slug", slug, "error", err)
		return
	}
	s.pruneRevisions(slug)
}

func (s *Store) pruneRevisions(slug string) {
	if s.revisionLimit <= 0 {
		return
	}
	entries := s.revisionEntries(slug)
	if len(entries) <= s.revisionLimit {
		return
	}
	root, err := s.openRoot()
	if err != nil {
		return
	}
	for _, e := range entries[:len(entries)-s.revisionLimit] {
		if err := root.Remove(path.Join(revisionsName(slug), e.name)); err != nil {
			slog.Warn("store: could not prune revision", "slug", slug, "name", e.name, "error", err)
		}
	}
}

type revisionEntry struct {
	name  string
	mtime int64
}

// revisionEntries lists revision files for slug (excluding delete
// tombstones), oldest first.
func (s *Store) revisionEntries(slug string) []revisionEntry {
	root, err := s.openRoot()
	if err != nil {
		return nil
	}
	revDir := revisionsName(slug)
	var out []revisionEntry
	for _, entry := range readDirIn(root, revDir) {
		name := entry.Name()
		if !strings.HasSuffix(name, ".md") || strings.HasPrefix(name, ".deleted-") {
			continue
		}
		info, ok := statIn(root, revDir, name)
		if !ok {
			continue
		}
		out = append(out, revisionEntry{name: name, mtime: info.ModTime().UnixNano()})
	}
	slices.SortFunc(out, func(a, b revisionEntry) int {
		if c := cmp.Compare(a.mtime, b.mtime); c != 0 {
			return c
		}
		return strings.Compare(a.name, b.name)
	})
	return out
}

// Revision is one archived revision as shown in the admin UI.
type Revision struct {
	Name string
	Size int64
	When string
}

// Revisions lists archived revisions for slug, newest first.
func (s *Store) Revisions(slug string) []Revision {
	entries := s.revisionEntries(slug)
	var out []Revision
	root, err := s.openRoot()
	if err != nil {
		return nil
	}
	revDir := revisionsName(slug)
	for _, rev := range slices.Backward(entries) {
		info, err := root.Stat(path.Join(revDir, rev.name))
		if err != nil {
			continue
		}
		out = append(out, Revision{
			Name: rev.name,
			Size: info.Size(),
			When: time.Unix(0, rev.mtime).UTC().Format("2006-01-02 15:04 UTC"),
		})
	}
	return out
}

func (s *Store) revisionPath(slug, name string) string {
	safeName := filepath.Base(name)
	if !strings.HasSuffix(safeName, ".md") {
		return ""
	}
	root, err := s.openRoot()
	if err != nil {
		return ""
	}
	rel := path.Join(revisionsName(slug), safeName)
	if _, err := root.Stat(rel); err != nil {
		return ""
	}
	return filepath.Join(s.ContentDir, rel)
}

// RevisionContent returns the raw Markdown of one archived revision.
func (s *Store) RevisionContent(slug, name string) string {
	path := s.revisionPath(slug, name)
	if path == "" {
		return ""
	}
	data, err := os.ReadFile(path)
	if err != nil {
		slog.Warn("store: cannot read revision", "slug", slug, "name", name, "error", err)
		return ""
	}
	return string(data)
}

// RestoreRevision replaces the post's content with an archived
// revision; the current state is archived first, so restoring is
// itself reversible.
func (s *Store) RestoreRevision(p *post.Post, name string) *post.Post {
	content := s.RevisionContent(p.Slug(), name)
	if content == "" {
		return nil
	}
	restored, err := post.Parse(content)
	if err != nil {
		slog.Warn("store: cannot restore revision", "slug", p.Slug(), "error", err)
		return nil
	}
	restored.Metadata.Set("slug", p.Slug())
	restored.Path = p.Path
	saved, err := s.Save(restored)
	if err != nil {
		slog.Warn("store: cannot restore revision", "slug", p.Slug(), "error", err)
		return nil
	}
	return saved
}