// session_mutate.go — gemini session file path resolution. The actual
// JSONL rewrite is deferred (see plugin main.go MutateSession comment):
// gemini-cli uses its own tool-call id namespace that doesn't match
// Plexum's, so v1 ships as a logged no-op. This file owns the path
// resolver so the v2 rewriter has its entry point.
//
// Layout (observed):
//
//	~/.gemini/tmp/<workspace-basename>/chats/session-<ISO>-<sid>.jsonl
//
// where <sid> is the first 8 chars of the session_id captured into
// workspace/.plexum-gemini-session. We pick the file whose name
// contains that prefix; multiple matches → the most-recent by mtime.

package runner

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// FindGeminiSessionFile resolves the chat JSONL gemini-cli writes for
// the session id captured in workspace/.plexum-gemini-session.
// Returns ("", error) if no session id is recorded yet OR no chat
// file is on disk.
func FindGeminiSessionFile(workspace string) (string, error) {
	sid := loadSessionID(workspace)
	if sid == "" {
		return "", errors.New("no gemini session id captured yet")
	}
	prefix := sid
	if len(prefix) > 8 {
		prefix = prefix[:8]
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	root := filepath.Join(home, ".gemini", "tmp")
	wsName := filepath.Base(workspace)
	candidates := []string{
		filepath.Join(root, wsName, "chats"),
		// Fallback dirs (older / alternate gemini-cli versions). We
		// glob defensively so an operator's custom layout still
		// surfaces something for telemetry.
	}
	entries := []os.DirEntry{}
	chosenDir := ""
	for _, dir := range candidates {
		es, err := os.ReadDir(dir)
		if err == nil {
			entries = es
			chosenDir = dir
			break
		}
	}
	if chosenDir == "" {
		return "", fmt.Errorf("no gemini chats dir under %s", root)
	}
	// Pick the newest session-*.jsonl whose name contains the sid prefix.
	type cand struct {
		path  string
		mtime int64
	}
	var matches []cand
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".jsonl") {
			continue
		}
		if !strings.Contains(e.Name(), prefix) {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}
		matches = append(matches, cand{
			path:  filepath.Join(chosenDir, e.Name()),
			mtime: info.ModTime().UnixNano(),
		})
	}
	if len(matches) == 0 {
		return "", fmt.Errorf("no chat file matching session_id prefix %q in %s", prefix, chosenDir)
	}
	sort.Slice(matches, func(i, j int) bool { return matches[i].mtime > matches[j].mtime })
	return matches[0].path, nil
}