/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import * as e from '@angular/compiler/src/expression_parser/ast';  // e for expression AST
import * as t from '@angular/compiler/src/render3/r3_ast';         // t for template AST

import {isTemplateNode, isTemplateNodeWithKeyAndValue, isWithin} from './utils';

/**
 * Contextual information for a target position within the template.
 */
export interface TemplateTarget {
  /**
   * Target position within the template.
   */
  position: number;

  /**
   * The template node (or AST expression) closest to the search position.
   */
  node: t.Node|e.AST;

  /**
   * The `t.Template` which contains the found node or expression (or `null` if in the root
   * template).
   */
  context: t.Template|null;

  /**
   * The immediate parent node of the targeted node.
   */
  parent: t.Node|e.AST|null;
}

/**
 * Return the template AST node or expression AST node that most accurately
 * represents the node at the specified cursor `position`.
 *
 * @param template AST tree of the template
 * @param position target cursor position
 */
export function getTargetAtPosition(template: t.Node[], position: number): TemplateTarget|null {
  const path = TemplateTargetVisitor.visitTemplate(template, position);
  if (path.length === 0) {
    return null;
  }

  const candidate = path[path.length - 1];
  if (isTemplateNodeWithKeyAndValue(candidate)) {
    const {keySpan, valueSpan} = candidate;
    const isWithinKeyValue =
        isWithin(position, keySpan) || (valueSpan && isWithin(position, valueSpan));
    if (!isWithinKeyValue) {
      // If cursor is within source span but not within key span or value span,
      // do not return the node.
      return null;
    }
  }

  // Walk up the result nodes to find the nearest `t.Template` which contains the targeted node.
  let context: t.Template|null = null;
  for (let i = path.length - 2; i >= 0; i--) {
    const node = path[i];
    if (node instanceof t.Template) {
      context = node;
      break;
    }
  }

  let parent: t.Node|e.AST|null = null;
  if (path.length >= 2) {
    parent = path[path.length - 2];
  }

  return {position, node: candidate, context, parent};
}

/**
 * Visitor which, given a position and a template, identifies the node within the template at that
 * position, as well as records the path of increasingly nested nodes that were traversed to reach
 * that position.
 */
class TemplateTargetVisitor implements t.Visitor {
  // We need to keep a path instead of the last node because we might need more
  // context for the last node, for example what is the parent node?
  readonly path: Array<t.Node|e.AST> = [];

  static visitTemplate(template: t.Node[], position: number): Array<t.Node|e.AST> {
    const visitor = new TemplateTargetVisitor(position);
    visitor.visitAll(template);
    return visitor.path;
  }

  // Position must be absolute in the source file.
  private constructor(private readonly position: number) {}

  visit(node: t.Node) {
    const {start, end} = getSpanIncludingEndTag(node);
    if (isWithin(this.position, {start, end})) {
      const length = end - start;
      const last: t.Node|e.AST|undefined = this.path[this.path.length - 1];
      if (last) {
        const {start, end} = isTemplateNode(last) ? getSpanIncludingEndTag(last) : last.sourceSpan;
        const lastLength = end - start;
        if (length > lastLength) {
          // The current node has a span that is larger than the last node found
          // so we do not descend into it. This typically means we have found
          // a candidate in one of the root nodes so we do not need to visit
          // other root nodes.
          return;
        }
      }
      this.path.push(node);
      node.visit(this);
    }
  }

  visitElement(element: t.Element) {
    this.visitAll(element.attributes);
    this.visitAll(element.inputs);
    this.visitAll(element.outputs);
    this.visitAll(element.references);
    this.visitAll(element.children);
  }

  visitTemplate(template: t.Template) {
    this.visitAll(template.attributes);
    this.visitAll(template.inputs);
    this.visitAll(template.outputs);
    this.visitAll(template.templateAttrs);
    this.visitAll(template.references);
    this.visitAll(template.variables);
    this.visitAll(template.children);
  }

  visitContent(content: t.Content) {
    t.visitAll(this, content.attributes);
  }

  visitVariable(variable: t.Variable) {
    // Variable has no template nodes or expression nodes.
  }

  visitReference(reference: t.Reference) {
    // Reference has no template nodes or expression nodes.
  }

  visitTextAttribute(attribute: t.TextAttribute) {
    // Text attribute has no template nodes or expression nodes.
  }

  visitBoundAttribute(attribute: t.BoundAttribute) {
    const visitor = new ExpressionVisitor(this.position);
    visitor.visit(attribute.value, this.path);
  }

  visitBoundEvent(event: t.BoundEvent) {
    const isTwoWayBinding =
        this.path.some(n => n instanceof t.BoundAttribute && event.name === n.name + 'Change');
    if (isTwoWayBinding) {
      // For two-way binding aka banana-in-a-box, there are two matches:
      // BoundAttribute and BoundEvent. Both have the same spans. We choose to
      // return BoundAttribute because it matches the identifier name verbatim.
      // TODO: For operations like go to definition, ideally we want to return
      // both.
      this.path.pop();  // remove bound event from the AST path
      return;
    }
    const visitor = new ExpressionVisitor(this.position);
    visitor.visit(event.handler, this.path);
  }

  visitText(text: t.Text) {
    // Text has no template nodes or expression nodes.
  }

  visitBoundText(text: t.BoundText) {
    const visitor = new ExpressionVisitor(this.position);
    visitor.visit(text.value, this.path);
  }

  visitIcu(icu: t.Icu) {
    for (const boundText of Object.values(icu.vars)) {
      this.visit(boundText);
    }
    for (const boundTextOrText of Object.values(icu.placeholders)) {
      this.visit(boundTextOrText);
    }
  }

  visitAll(nodes: t.Node[]) {
    for (const node of nodes) {
      this.visit(node);
    }
  }
}

class ExpressionVisitor extends e.RecursiveAstVisitor {
  // Position must be absolute in the source file.
  constructor(private readonly position: number) {
    super();
  }

  visit(node: e.AST, path: Array<t.Node|e.AST>) {
    if (node instanceof e.ASTWithSource) {
      // In order to reduce noise, do not include `ASTWithSource` in the path.
      // For the purpose of source spans, there is no difference between
      // `ASTWithSource` and and underlying node that it wraps.
      node = node.ast;
    }
    // The third condition is to account for the implicit receiver, which should
    // not be visited.
    if (isWithin(this.position, node.sourceSpan) && !(node instanceof e.ImplicitReceiver)) {
      path.push(node);
      node.visit(this, path);
    }
  }
}

function getSpanIncludingEndTag(ast: t.Node) {
  const result = {
    start: ast.sourceSpan.start.offset,
    end: ast.sourceSpan.end.offset,
  };
  // For Element and Template node, sourceSpan.end is the end of the opening
  // tag. For the purpose of language service, we need to actually recognize
  // the end of the closing tag. Otherwise, for situation like
  // <my-component></my-comp¦onent> where the cursor is in the closing tag
  // we will not be able to return any information.
  if ((ast instanceof t.Element || ast instanceof t.Template) && ast.endSourceSpan) {
    result.end = ast.endSourceSpan.end.offset;
  }
  return result;
}