// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

import {Node, NodeType} from 'commonmark';

import {escapeRegex} from '@utils/markdown';

import type {UserMentionKey} from '@typings/global/markdown';

/* eslint-disable no-underscore-dangle */

const cjkPattern = /[\u3000-\u303f\u3040-\u309f\u30a0-\u30ff\uff00-\uff9f\u4e00-\u9faf\u3400-\u4dbf\uac00-\ud7a3]/;

// Combines adjacent text nodes into a single text node to make further transformation easier
export function combineTextNodes(ast: any) {
    const walker = ast.walker();

    let e;
    while ((e = walker.next())) {
        if (!e.entering) {
            continue;
        }

        const node = e.node;

        if (node.type !== 'text') {
            continue;
        }

        while (node._next && node._next.type === 'text') {
            const next = node._next;

            node.literal += next.literal;

            node._next = next._next;
            if (node._next) {
                node._next._prev = node;
            }

            if (node._parent._lastChild === next) {
                node._parent._lastChild = node;
            }
        }

        // Resume parsing after the current node since otherwise the walker would continue to parse any old text nodes
        // that have been merged into this one
        walker.resumeAt(node, false);
    }

    return ast;
}

// Add indices to the items of every list
export function addListItemIndices(ast: any) {
    const walker = ast.walker();

    let e;
    while ((e = walker.next())) {
        if (e.entering) {
            const node = e.node;

            if (node.type === 'list') {
                let i = node.listStart == null ? 1 : node.listStart; // List indices match what would be displayed in the UI

                for (let child = node.firstChild; child; child = child.next) {
                    child.index = i;

                    i += 1;
                }
            }
        }
    }

    return ast;
}

// Take all images that aren't inside of tables and move them to be children of the root document node.
// When this happens, their parent nodes are split into two, if necessary, with the version that follows
// the image having its "continue" field set to true to indicate that things like bullet points don't
// need to be rendered.
export function pullOutImages(ast: any) {
    const walker = ast.walker();

    let e;
    while ((e = walker.next())) {
        if (!e.entering) {
            continue;
        }

        const node = e.node;

        // Skip tables because we'll render images inside of those as links
        if (node.type === 'table') {
            walker.resumeAt(node, false);
            continue;
        }

        if (node.type === 'image' && node.parent?.type !== 'document') {
            pullOutImage(node);
        }
    }

    return ast;
}

function pullOutImage(image: any) {
    const parent = image.parent;

    if (parent?.type === 'link') {
        image.linkDestination = parent.destination;
    }
}

export function highlightMentions(ast: Node, mentionKeys: UserMentionKey[]) {
    const walker = ast.walker();

    let e;
    while ((e = walker.next())) {
        if (!e.entering) {
            continue;
        }

        const node = e.node;

        if (node.type === 'text' && node.literal) {
            const {index, mention} = getFirstMention(node.literal, mentionKeys);

            if (index === -1 || !mention) {
                continue;
            }

            const mentionNode = highlightTextNode(node, index, index + mention.key.length, 'mention_highlight');

            // Resume processing on the next node after the mention node which may include any remaining text
            // that was part of this one
            walker.resumeAt(mentionNode, false);
        } else if (node.type === 'at_mention') {
            const matches = mentionKeys.some((mention) => {
                const mentionName = '@' + node.mentionName;
                const flags = mention.caseSensitive ? '' : 'i';
                const pattern = new RegExp(`@${escapeRegex(mention.key.replace('@', ''))}\\.?\\b`, flags);

                return pattern.test(mentionName);
            });

            if (!matches) {
                continue;
            }

            const wrapper = new Node('mention_highlight');
            wrapNode(wrapper, node);

            // Skip processing the wrapper to prevent checking this node again as its child
            walker.resumeAt(wrapper, false);
        }
    }

    return ast;
}

// Given a string and an array of mention keys, returns the first mention that appears and its index.
export function getFirstMention(str: string, mentionKeys: UserMentionKey[]) {
    let firstMention = null;
    let firstMentionIndex = -1;

    for (const mention of mentionKeys) {
        if (mention.key.trim() === '') {
            continue;
        }

        const flags = mention.caseSensitive ? '' : 'i';
        let pattern;
        if (cjkPattern.test(mention.key)) {
            pattern = new RegExp(`${escapeRegex(mention.key)}`, flags);
        } else {
            pattern = new RegExp(`\\b${escapeRegex(mention.key)}_*\\b`, flags);
        }

        const match = pattern.exec(str);
        if (!match || match[0] === '') {
            continue;
        }

        if (firstMentionIndex === -1 || match.index < firstMentionIndex) {
            firstMentionIndex = match.index;
            firstMention = mention;
        }
    }

    return {
        index: firstMentionIndex,
        mention: firstMention,
    };
}

// Given a text node, start/end indices, and a highlight node type, splits it into up to three nodes:
// the text before the highlight (if any exists), the highlighted text, and the text after the highlight
// the end of the highlight (if any exists). Returns a node containing the highlighted text.
export function highlightTextNode(node: Node, start: number, end: number, type: NodeType) {
    const literal = node.literal;
    node.literal = literal!.substring(start, end);

    // Start by wrapping the node and then re-insert any non-highlighted code around it
    const highlighted = new Node(type);
    wrapNode(highlighted, node);

    if (start !== 0) {
        const before = new Node('text');
        before.literal = literal!.substring(0, start);

        highlighted.insertBefore(before);
    }

    if (end !== literal!.length) {
        const after = new Node('text');
        after.literal = literal!.substring(end);

        highlighted.insertAfter(after);
    }

    return highlighted;
}

// Wraps a given node in another node of the given type. The wrapper will take the place of
// the node in the AST relative to its parents and siblings, and it will have the node as
// its only child.
function wrapNode(wrapper: any, node: any) {
    // Set parent and update parent's children if necessary
    wrapper._parent = node._parent;
    if (node._parent._firstChild === node) {
        node._parent._firstChild = wrapper;
    }
    if (node._parent._lastChild === node) {
        node._parent._lastChild = wrapper;
    }

    // Set siblings and update those if necessary
    wrapper._prev = node._prev;
    node._prev = null;
    if (wrapper._prev) {
        wrapper._prev._next = wrapper;
    }

    wrapper._next = node._next;
    node._next = null;
    if (wrapper._next) {
        wrapper._next._prev = wrapper;
    }

    // Make node a child of wrapper
    wrapper._firstChild = node;
    wrapper._lastChild = node;
    node._parent = wrapper;
}