/**
 * ChatSelectionHighlightController
 *
 * Manages persistent selection highlight for the Chat panel.
 * Uses an independent CM6 StateField (via `createPersistentHighlight`) to avoid
 * conflicts with SelectionHighlight used by QuickAsk and CustomCommandModal.
 */

import { EditorView } from "@codemirror/view";
import { MarkdownView, type WorkspaceLeaf } from "obsidian";

import type CopilotPlugin from "@/main";
import { CHAT_VIEWTYPE } from "@/constants";
import type { SelectedTextContext } from "@/types/message";
import { logError, logWarn } from "@/logger";
import {
  createPersistentHighlight,
  type PersistentHighlightRange,
} from "@/editor/persistentHighlight";

// ============================================================================
// Independent CM6 Highlight Instance (isolated from SelectionHighlight)
// ============================================================================

/**
 * Chat-owned persistent highlight primitives.
 * Completely independent from the QuickAsk/CustomCommandModal highlight.
 */
const chatHighlight = createPersistentHighlight("copilot-chat-selection-highlight");

/**
 * Hide chat selection highlight on a specific EditorView.
 * Used for global cleanup during plugin unload.
 * @param view - The EditorView to clear highlight from
 */
export function hideChatSelectionHighlight(view: EditorView): void {
  try {
    const effects = chatHighlight.buildEffects(view, null);
    if (effects.length > 0) {
      view.dispatch({ effects });
    }
  } catch {
    // Ignore errors during cleanup (view may be destroyed)
  }
}

// ============================================================================
// Controller
// ============================================================================

/**
 * Snapshot of the current highlight state.
 * Used for idempotency checks and safe cleanup.
 */
interface Snapshot {
  view: EditorView;
  from: number;
  to: number;
}

/**
 * Options for ChatSelectionHighlightController.
 */
export interface ChatSelectionHighlightControllerOptions {
  /** Close QuickAsk when entering Chat. Default: false */
  closeQuickAskOnChatFocus?: boolean;
}

/**
 * Controller that manages Chat-owned persistent selection highlight lifecycle.
 *
 * This controller uses an independent CM6 StateField to avoid conflicts with
 * SelectionHighlight used by QuickAsk and CustomCommandModal.
 *
 * Key features:
 * - Persists editor selection when focus moves to Chat panel
 * - Automatically clears highlight when leaving Chat
 * - Supports both mouse click and keyboard navigation to Chat
 * - Idempotent: avoids redundant dispatches
 */
export class ChatSelectionHighlightController {
  private readonly plugin: CopilotPlugin;
  private readonly closeQuickAskOnChatFocus: boolean;

  /** Last active Markdown leaf, used for fallback when active view is already Chat */
  private lastActiveMarkdownLeaf: WorkspaceLeaf | null = null;
  /** Whether the last active leaf was a MarkdownView */
  private lastActiveLeafWasMarkdown = false;
  /** Snapshot of current highlight for idempotency and cleanup */
  private snapshot: Snapshot | null = null;

  /**
   * Creates a new ChatSelectionHighlightController.
   * @param plugin - The CopilotPlugin instance
   * @param options - Optional configuration
   */
  constructor(plugin: CopilotPlugin, options?: ChatSelectionHighlightControllerOptions) {
    this.plugin = plugin;
    this.closeQuickAskOnChatFocus = options?.closeQuickAskOnChatFocus ?? false;
  }

  // --------------------------------------------------------------------------
  // Lifecycle
  // --------------------------------------------------------------------------

  /**
   * Initializes the controller state from the current active leaf.
   * Call once during plugin onload.
   */
  initialize(): void {
    const markdownView = this.plugin.app.workspace.getActiveViewOfType(MarkdownView);
    const leaf = markdownView?.leaf ?? null;
    this.lastActiveLeafWasMarkdown = !!markdownView;
    if (this.lastActiveLeafWasMarkdown && leaf) {
      this.lastActiveMarkdownLeaf = leaf;
    }
  }

  /**
   * Cleans up the controller state.
   * Call during plugin onunload.
   */
  cleanup(): void {
    this.clear();
    this.lastActiveMarkdownLeaf = null;
    this.lastActiveLeafWasMarkdown = false;
  }

  // --------------------------------------------------------------------------
  // Event Handlers
  // --------------------------------------------------------------------------

  /**
   * Handles active-leaf-change event.
   * Manages highlight lifecycle based on leaf transitions:
   * - Entering Chat from Markdown: persists selection highlight
   * - Leaving Chat: clears highlight
   * @param leaf - The newly active leaf, or null
   */
  handleActiveLeafChange(leaf: WorkspaceLeaf | null): void {
    const prevWasMarkdown = this.lastActiveLeafWasMarkdown;
    const nextType = leaf?.getViewState().type ?? null;
    const nextIsMarkdown = !!(leaf?.view instanceof MarkdownView);

    // Update tracking
    this.lastActiveLeafWasMarkdown = nextIsMarkdown;
    if (nextIsMarkdown && leaf) {
      this.lastActiveMarkdownLeaf = leaf;
    }

    // Leaving Chat: clear highlight
    if (this.snapshot && nextType !== CHAT_VIEWTYPE) {
      this.clear();
    }

    // Entering Chat from Markdown: persist with fallback allowed
    if (nextType === CHAT_VIEWTYPE && prevWasMarkdown) {
      if (this.closeQuickAskOnChatFocus) {
        this.plugin.quickAskController?.close(false);
      }

      // Use fallback because active leaf is already Chat at this point
      this.persist({ useFallback: true });
    }
  }

  /**
   * Persists highlight when user clicks into Chat panel.
   * Uses capture phase to run before focus changes.
   * Does not use fallback - only works if MarkdownView is currently active.
   */
  persistFromPointerDown(): void {
    // Early exit if no MarkdownView is active (e.g., user is already in Chat).
    if (!this.plugin.app.workspace.getActiveViewOfType(MarkdownView)) {
      return;
    }

    this.persist({ useFallback: false });
  }

  /**
   * Clears highlight if no note contexts remain after removal.
   * @param nextContexts - The remaining contexts after removal
   */
  clearIfNoNoteContexts(nextContexts: ReadonlyArray<SelectedTextContext>): void {
    if (!nextContexts.some((ctx) => ctx.sourceType === "note")) {
      this.clear();
    }
  }

  /**
   * Clears highlight when starting a new chat session.
   */
  clearForNewChat(): void {
    this.clear();
  }

  // --------------------------------------------------------------------------
  // Internal: CM6 Operations
  // --------------------------------------------------------------------------

  /**
   * Persists the current editor selection as a CM6 decoration highlight.
   * @param options - Configuration for this persist operation
   * @param options.useFallback - Whether to use lastActiveMarkdownLeaf if active view is not Markdown
   */
  private persist(options: { useFallback: boolean }): void {
    const cm = this.getEditorView(options.useFallback);
    if (!cm) return;

    const sel = cm.state.selection.main;
    if (sel.from === sel.to) return;

    const from = sel.from;
    const to = sel.to;

    // Idempotency: skip if same highlight already exists
    const current = this.getHighlightRange(cm);
    if (
      this.snapshot?.view === cm &&
      this.snapshot.from === from &&
      this.snapshot.to === to &&
      current?.from === from &&
      current?.to === to
    ) {
      return;
    }

    // Clear previous highlight on different view and reset snapshot
    // This ensures snapshot is always in sync: either null or pointing to current highlight
    if (this.snapshot && this.snapshot.view !== cm) {
      this.hideHighlight(this.snapshot.view);
      this.snapshot = null; // Clear immediately to avoid stale reference
    }

    // Only update snapshot if dispatch succeeds (avoids state desync on view destroyed)
    const success = this.showHighlight(cm, from, to);
    if (success) {
      this.snapshot = { view: cm, from, to };
    }
  }

  /**
   * Clears the current highlight unconditionally.
   * Always clears to avoid "stuck" highlights when document changes
   * cause mapPos to shift the range.
   */
  private clear(): void {
    if (!this.snapshot) return;

    this.hideHighlight(this.snapshot.view);
    this.snapshot = null;
  }

  /**
   * Gets the EditorView to use for highlight operations.
   * @param allowFallback - Whether to fall back to lastActiveMarkdownLeaf
   * @returns The EditorView, or null if not available
   */
  private getEditorView(allowFallback: boolean): EditorView | null {
    const active = this.plugin.app.workspace.getActiveViewOfType(MarkdownView);
    if (active?.editor?.cm) {
      return active.editor.cm;
    }

    if (allowFallback && this.lastActiveMarkdownLeaf?.view instanceof MarkdownView) {
      return this.lastActiveMarkdownLeaf.view.editor?.cm ?? null;
    }

    return null;
  }

  // --------------------------------------------------------------------------
  // Internal: CM6 Highlight Primitives (delegating to factory instance)
  // --------------------------------------------------------------------------

  /**
   * Shows a highlight on the given EditorView.
   * Automatically installs the extension if not already present.
   * @param view - The EditorView to highlight
   * @param from - Start offset
   * @param to - End offset
   * @returns true if effects were dispatched successfully, false otherwise
   */
  private showHighlight(view: EditorView, from: number, to: number): boolean {
    try {
      const effects = chatHighlight.buildEffects(view, { from, to });
      if (effects.length === 0) {
        // No effects to dispatch (e.g., invalid range) — not a success
        return false;
      }
      view.dispatch({ effects });
      return true;
    } catch (error) {
      logError("ChatSelectionHighlight show failed:", error);
      return false;
    }
  }

  /**
   * Hides the highlight on the given EditorView.
   * Uses logWarn instead of logError since failures during cleanup
   * are often due to view being destroyed (normal race condition).
   * @param view - The EditorView to clear highlight from
   */
  private hideHighlight(view: EditorView): void {
    try {
      const effects = chatHighlight.buildEffects(view, null);
      if (effects.length > 0) {
        view.dispatch({ effects });
      }
    } catch (error) {
      // Use warn instead of error - failures here are often due to
      // view being destroyed, which is a normal race condition
      logWarn("ChatSelectionHighlight hide failed (view may be destroyed):", error);
    }
  }

  /**
   * Gets the current highlight range from the EditorView.
   * @param view - The EditorView to query
   * @returns The current highlight range, or null if none
   */
  private getHighlightRange(view: EditorView): PersistentHighlightRange | null {
    return chatHighlight.getRange(view);
  }
}