package main

import (
	"errors"
	"fmt"
	"strings"

	"reasonix/internal/agent"
	"reasonix/internal/control"
	"reasonix/internal/sessioncatalog"
)

const (
	aiSessionTitleMaxTurns     = 3
	aiSessionTitleMaxTurnRunes = 500
)

// AIRenameSession generates a title from an open topic's own conversation and
// applies it as an explicit title on that physical session. Binding generation
// and persistence to the same controller/path prevents a tab switch from
// routing a delayed provider response into the newly active conversation.
func (a *App) AIRenameSession(topicID string) (string, error) {
	topicID = strings.TrimSpace(topicID)
	if topicID == "" {
		return "", fmt.Errorf("empty topic id")
	}
	ctrl := a.controllerForTopic(topicID)
	if ctrl == nil {
		return "", fmt.Errorf("session is not open; open it before using AI rename")
	}
	sessionDir := ctrl.SessionDir()
	sessionPath := strings.TrimSpace(ctrl.SessionPath())
	if sessionPath == "" {
		if scope, workspaceRoot, ok := a.findTopicLocation(topicID); ok {
			sessionPath = a.catalogSessionPathForTopic(scope, workspaceRoot, topicID)
		}
	}
	validated, _, err := validateSessionPath(sessionDir, sessionPath)
	if err != nil {
		return "", fmt.Errorf("AI rename session: %w", err)
	}
	expectedTitle := ""
	if meta, ok, loadErr := agent.LoadBranchMeta(validated); loadErr != nil {
		return "", fmt.Errorf("AI rename session: read current title: %w", loadErr)
	} else if ok {
		expectedTitle = meta.CustomTitle
	}
	users := topicTitleUserTurnsFromSession(validated)
	if len(users) == 0 {
		return "", fmt.Errorf("session has no user messages to analyze")
	}
	title, err := ctrl.GenerateSessionTitle(a.bootContext(), sessionTitleTranscript(users))
	if err != nil {
		return "", err
	}
	if !a.topicControllerOwnsSession(topicID, ctrl, validated) {
		return "", fmt.Errorf("session changed while AI rename was running; try again")
	}
	if err := a.renameSessionInDirIfTitleUnchanged(sessionDir, validated, expectedTitle, title); err != nil {
		if errors.Is(err, agent.ErrSessionTitleChanged) {
			return "", fmt.Errorf("session title changed while AI rename was running; try again")
		}
		return "", err
	}
	return title, nil
}

func (a *App) controllerForTopic(topicID string) *control.Controller {
	a.mu.RLock()
	defer a.mu.RUnlock()
	var found *control.Controller
	for _, tab := range a.runtimeTabsLocked() {
		if tab == nil || strings.TrimSpace(tab.TopicID) != topicID || tab.Ctrl == nil {
			continue
		}
		if ctrl, ok := tab.Ctrl.(*control.Controller); ok {
			if tab.ID == a.activeTabID {
				return ctrl
			}
			if found != nil && found != ctrl {
				return nil
			}
			found = ctrl
		}
	}
	return found
}

func (a *App) topicControllerOwnsSession(topicID string, ctrl *control.Controller, sessionPath string) bool {
	a.mu.RLock()
	defer a.mu.RUnlock()
	for _, tab := range a.runtimeTabsLocked() {
		if tab == nil || tab.TopicID != topicID || tab.Ctrl != ctrl {
			continue
		}
		return sessionRuntimeKey(tab.currentSessionPath()) == sessionRuntimeKey(sessionPath)
	}
	return false
}

func sessionTitleTranscript(users []string) string {
	parts := make([]string, 0, aiSessionTitleMaxTurns)
	for _, user := range users {
		if len(parts) >= aiSessionTitleMaxTurns {
			break
		}
		user = strings.TrimSpace(user)
		if runes := []rune(user); len(runes) > aiSessionTitleMaxTurnRunes {
			user = string(runes[:aiSessionTitleMaxTurnRunes])
		}
		if user != "" {
			parts = append(parts, user)
		}
	}
	return strings.Join(parts, "\n\n")
}

func sessionPreviewForPath(path string) string {
	path = strings.TrimSpace(path)
	if path == "" {
		return ""
	}
	if meta, ok, err := agent.LoadBranchMeta(path); err == nil && ok {
		if preview := strings.TrimSpace(meta.Preview); preview != "" {
			return preview
		}
	}
	preview, ok, err := agent.LoadSessionPreviewFromDisplayIndex(path)
	if err != nil || !ok {
		return ""
	}
	return preview
}

func topicSessionPreview(sessions []sessioncatalog.SessionRecord, path string) string {
	for _, session := range sessions {
		if sessionRuntimeKey(session.Path) == sessionRuntimeKey(path) {
			return strings.TrimSpace(session.Preview)
		}
	}
	return ""
}