// Package repos discovers Git repositories under the configured roots and keeps
// a read-optimized in-memory index of their state. The repositories are the
// system of record; this index is a derived cache that can be rebuilt at any
// time. The scanner is strictly READ-ONLY (AGENT.md §1.3, §5).
package repos

import (
	"context"
	"log/slog"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"gitmanager/internal/git"
)

// State is the cached snapshot of one repository.
type State struct {
	Path      string    `json:"path"`
	Name      string    `json:"name"`
	Branch    string    `json:"branch"`
	Dirty     bool      `json:"dirty"`
	Ahead     int       `json:"ahead"`
	Behind    int       `json:"behind"`
	Remotes   []string  `json:"remotes"`
	UpdatedAt time.Time `json:"updatedAt"`
	Error     string    `json:"error,omitempty"` // set if refreshing this repo failed
}

// Index is a concurrency-safe map of repo path -> State.
type Index struct {
	mu    sync.RWMutex
	byKey map[string]State
}

func newIndex() *Index { return &Index{byKey: make(map[string]State)} }

func (i *Index) set(s State) {
	i.mu.Lock()
	defer i.mu.Unlock()
	i.byKey[s.Path] = s
}

// List returns a snapshot of all known repos, sorted by name then path.
func (i *Index) List() []State {
	i.mu.RLock()
	defer i.mu.RUnlock()
	out := make([]State, 0, len(i.byKey))
	for _, s := range i.byKey {
		out = append(out, s)
	}
	sort.Slice(out, func(a, b int) bool {
		if out[a].Name != out[b].Name {
			return out[a].Name < out[b].Name
		}
		return out[a].Path < out[b].Path
	})
	return out
}

// Scanner discovers repositories and refreshes the index on an interval.
type Scanner struct {
	git          *git.CLI
	log          *slog.Logger
	roots        []string
	maxDepth     int
	ignore       map[string]struct{}
	interval     time.Duration
	fetchEnabled bool

	Index *Index
}

// NewScanner builds a scanner. ignore is a set of directory names to skip.
func NewScanner(g *git.CLI, log *slog.Logger, roots []string, maxDepth int, ignore []string, interval time.Duration, fetchEnabled bool) *Scanner {
	ig := make(map[string]struct{}, len(ignore))
	for _, name := range ignore {
		ig[name] = struct{}{}
	}
	return &Scanner{
		git:          g,
		log:          log,
		roots:        roots,
		maxDepth:     maxDepth,
		ignore:       ig,
		interval:     interval,
		fetchEnabled: fetchEnabled,
		Index:        newIndex(),
	}
}

// Run does an immediate refresh, then refreshes every interval until ctx is done.
func (s *Scanner) Run(ctx context.Context) {
	s.Refresh(ctx)
	ticker := time.NewTicker(s.interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			s.Refresh(ctx)
		}
	}
}

// Refresh discovers repos and updates the index. Each repo is refreshed under
// its own timeout so a single slow/unreachable repo cannot stall the rest.
func (s *Scanner) Refresh(ctx context.Context) {
	paths := s.discover()
	s.log.Debug("scan discovered repositories", "count", len(paths))
	for _, p := range paths {
		select {
		case <-ctx.Done():
			return
		default:
		}
		s.Index.set(s.refreshOne(ctx, p))
	}
}

// RefreshRepo re-scans a single repository and updates the index. Used after a
// mutating action so the UI reflects the new state without waiting for the next
// full scan.
func (s *Scanner) RefreshRepo(ctx context.Context, path string) {
	s.Index.set(s.refreshOne(ctx, path))
}

func (s *Scanner) refreshOne(ctx context.Context, path string) State {
	rctx, cancel := context.WithTimeout(ctx, 20*time.Second)
	defer cancel()

	st := State{Path: path, Name: filepath.Base(path), UpdatedAt: time.Now()}

	if s.fetchEnabled {
		if err := s.git.Fetch(rctx, path); err != nil {
			s.log.Warn("scan fetch failed", "repo", path, "err", err)
		}
	}

	branch, err := s.git.CurrentBranch(rctx, path)
	if err != nil {
		st.Error = err.Error()
		return st
	}
	st.Branch = branch

	if dirty, err := s.git.IsDirty(rctx, path); err == nil {
		st.Dirty = dirty
	} else {
		st.Error = err.Error()
	}

	st.Ahead, st.Behind, _ = s.git.AheadBehind(rctx, path)

	if remotes, err := s.git.Remotes(rctx, path); err == nil {
		st.Remotes = remotes
	}

	return st
}

// discover walks each root looking for directories that contain a .git entry,
// recording the parent as a repo and not descending into it. Depth is measured
// relative to each root; ignored directory names are skipped.
func (s *Scanner) discover() []string {
	seen := make(map[string]struct{})
	var out []string

	for _, root := range s.roots {
		root = filepath.Clean(root)
		_ = filepath.WalkDir(root, func(path string, d os.DirEntry, err error) error {
			if err != nil {
				return nil // unreadable entry: skip, don't abort the walk
			}
			if !d.IsDir() {
				return nil
			}

			name := d.Name()
			if path != root {
				if _, skip := s.ignore[name]; skip {
					return filepath.SkipDir
				}
			}

			if depth(root, path) > s.maxDepth {
				return filepath.SkipDir
			}

			if hasGit(path) {
				if _, ok := seen[path]; !ok {
					seen[path] = struct{}{}
					out = append(out, path)
				}
				return filepath.SkipDir // don't descend into a repo
			}
			return nil
		})
	}
	return out
}

// hasGit reports whether dir is a git repository (a .git directory, or a .git
// file for worktrees/submodules).
func hasGit(dir string) bool {
	_, err := os.Stat(filepath.Join(dir, ".git"))
	return err == nil
}

// depth returns how many path segments below root path is (root itself is 0).
func depth(root, path string) int {
	rel, err := filepath.Rel(root, path)
	if err != nil || rel == "." {
		return 0
	}
	return strings.Count(rel, string(filepath.Separator)) + 1
}