package cc

import (
	"context"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
)

// EncodeCwdForProjectsDir converts an absolute path to claude's projects-dir
// encoding: both '/' and '.' are replaced with '-'.
func EncodeCwdForProjectsDir(absPath string) string {
	return strings.NewReplacer("/", "-", ".", "-").Replace(absPath)
}

// ClaudeProjectsDir returns the claude transcript directory for a given cwd:
// <homeDir>/.claude/projects/<encoded-cwd>.
func ClaudeProjectsDir(homeDir, cwd string) string {
	return filepath.Join(homeDir, ".claude", "projects", EncodeCwdForProjectsDir(cwd))
}

// SessionWatchOpts configures WatchForNewSession.
type SessionWatchOpts struct {
	ProjectsDir string
	Timeout     time.Duration
}

// WatchForNewSession watches ProjectsDir for the first new .jsonl file that
// appears after the call, returning its basename without the .jsonl suffix
// (the claude session id). Returns ("", nil) on timeout or context cancellation,
// mirroring the TypeScript null-on-timeout semantics. MkdirAll ensures the
// target dir exists so a missing claude projects dir is handled symmetrically
// with the codex watcher — the first session is captured even if the dir was
// absent at call time.
func WatchForNewSession(ctx context.Context, opts SessionWatchOpts) (string, error) {
	// Ensure the target dir exists before snapshotting and watching.
	if err := os.MkdirAll(opts.ProjectsDir, 0o755); err != nil {
		return "", nil
	}

	// Snapshot existing .jsonl files so we only react to truly new ones.
	snapshot, err := snapshotJSONL(opts.ProjectsDir)
	if err != nil {
		return "", nil
	}

	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return "", nil
	}
	defer watcher.Close()

	if err := watcher.Add(opts.ProjectsDir); err != nil {
		return "", nil
	}

	timer := time.NewTimer(opts.Timeout)
	defer timer.Stop()

	for {
		select {
		case <-ctx.Done():
			return "", nil
		case <-timer.C:
			return "", nil
		case event, ok := <-watcher.Events:
			if !ok {
				return "", nil
			}
			if event.Op&(fsnotify.Create|fsnotify.Rename) == 0 {
				continue
			}
			name := filepath.Base(event.Name)
			if !strings.HasSuffix(name, ".jsonl") {
				continue
			}
			if snapshot[name] {
				continue
			}
			// Confirm the file actually exists (rename fires for deletes too).
			if _, err := os.Stat(event.Name); err != nil {
				continue
			}
			return strings.TrimSuffix(name, ".jsonl"), nil
		case _, ok := <-watcher.Errors:
			if !ok {
				return "", nil
			}
			// Non-fatal watcher error; keep watching.
		}
	}
}

// snapshotJSONL returns the set of .jsonl filenames currently in dir.
func snapshotJSONL(dir string) (map[string]bool, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}
	snap := make(map[string]bool, len(entries))
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".jsonl") {
			snap[e.Name()] = true
		}
	}
	return snap, nil
}