/*
Copyright 2019 New Vector Ltd
Copyright 2019, 2020 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import { AllHtmlEntities } from 'html-entities';
import cheerio from 'cheerio';
import escapeHtml from "escape-html";

import Markdown from '../Markdown';
import { makeGenericPermalink } from "../utils/permalinks/Permalinks";
import EditorModel from "./model";
import SettingsStore from '../settings/SettingsStore';
import SdkConfig from '../SdkConfig';
import { Type } from './parts';

export function mdSerialize(model: EditorModel): string {
    return model.parts.reduce((html, part) => {
        switch (part.type) {
            case Type.Newline:
                return html + "\n";
            case Type.Plain:
            case Type.Emoji:
            case Type.Command:
            case Type.PillCandidate:
            case Type.AtRoomPill:
                return html + part.text;
            case Type.RoomPill:
                // Here we use the resourceId for compatibility with non-rich text clients
                // See https://github.com/vector-im/element-web/issues/16660
                return html +
                    `[${part.resourceId.replace(/[[\\\]]/g, c => "\\" + c)}](${makeGenericPermalink(part.resourceId)})`;
            case Type.UserPill:
                return html +
                    `[${part.text.replace(/[[\\\]]/g, c => "\\" + c)}](${makeGenericPermalink(part.resourceId)})`;
        }
    }, "");
}

interface ISerializeOpts {
    forceHTML?: boolean;
    useMarkdown?: boolean;
}

export function htmlSerializeIfNeeded(
    model: EditorModel,
    { forceHTML = false, useMarkdown = true }: ISerializeOpts = {},
): string {
    if (!useMarkdown) {
        return escapeHtml(textSerialize(model)).replace(/\n/g, '<br/>');
    }

    const md = mdSerialize(model);
    return htmlSerializeFromMdIfNeeded(md, { forceHTML });
}

export function htmlSerializeFromMdIfNeeded(md: string, { forceHTML = false } = {}): string {
    // copy of raw input to remove unwanted math later
    const orig = md;

    if (SettingsStore.getValue("feature_latex_maths")) {
        const patternNames = ['tex', 'latex'];
        const patternTypes = ['display', 'inline'];
        const patternDefaults = {
            "tex": {
                // detect math with tex delimiters, inline: $...$, display $$...$$
                // preferably use negative lookbehinds, not supported in all major browsers:
                // const displayPattern = "^(?<!\\\\)\\$\\$(?![ \\t])(([^$]|\\\\\\$)+?)\\$\\$$";
                // const inlinePattern = "(?:^|\\s)(?<!\\\\)\\$(?!\\s)(([^$]|\\\\\\$)+?)(?<!\\\\|\\s)\\$";

                // conditions for display math detection $$...$$:
                // - pattern starts and ends on a new line
                // - left delimiter ($$) is not escaped by backslash
                "display": "(^)\\$\\$(([^$]|\\\\\\$)+?)\\$\\$$",

                // conditions for inline math detection $...$:
                // - pattern starts at beginning of line, follows whitespace character or punctuation
                // - pattern is on a single line
                // - left and right delimiters ($) are not escaped by backslashes
                // - left delimiter is not followed by whitespace character
                // - right delimiter is not prefixed with whitespace character
                "inline":
                    "(^|\\s|[.,!?:;])(?!\\\\)\\$(?!\\s)(([^$\\n]|\\\\\\$)*([^\\\\\\s\\$]|\\\\\\$)(?:\\\\\\$)?)\\$",
            },
            "latex": {
                // detect math with latex delimiters, inline: \(...\), display \[...\]

                // conditions for display math detection \[...\]:
                // - pattern starts and ends on a new line
                // - pattern is not empty
                "display": "(^)\\\\\\[(?!\\\\\\])(.*?)\\\\\\]$",

                // conditions for inline math detection \(...\):
                // - pattern starts at beginning of line or is not prefixed with backslash
                // - pattern is not empty
                "inline": "(^|[^\\\\])\\\\\\((?!\\\\\\))(.*?)\\\\\\)",
            },
        };

        patternNames.forEach(function(patternName) {
            patternTypes.forEach(function(patternType) {
                // get the regex replace pattern from config or use the default
                const pattern = (((SdkConfig.get("latex_maths_delims") ||
                    {})[patternType] || {})["pattern"] || {})[patternName] ||
                    patternDefaults[patternName][patternType];

                md = md.replace(RegExp(pattern, "gms"), function(m, p1, p2) {
                    const p2e = AllHtmlEntities.encode(p2);
                    switch (patternType) {
                        case "display":
                            return `${p1}<div data-mx-maths="${p2e}">\n\n</div>\n\n`;
                        case "inline":
                            return `${p1}<span data-mx-maths="${p2e}"></span>`;
                    }
                });
            });
        });

        // make sure div tags always start on a new line, otherwise it will confuse
        // the markdown parser
        md = md.replace(/(.)<div/g, function(m, p1) { return `${p1}\n<div`; });
    }

    const parser = new Markdown(md);
    if (!parser.isPlainText() || forceHTML) {
        // feed Markdown output to HTML parser
        const phtml = cheerio.load(parser.toHTML(), {
            // @ts-ignore: The `_useHtmlParser2` internal option is the
            // simplest way to both parse and render using `htmlparser2`.
            _useHtmlParser2: true,
            decodeEntities: false,
        });

        if (SettingsStore.getValue("feature_latex_maths")) {
            // original Markdown without LaTeX replacements
            const parserOrig = new Markdown(orig);
            const phtmlOrig = cheerio.load(parserOrig.toHTML(), {
                // @ts-ignore: The `_useHtmlParser2` internal option is the
                // simplest way to both parse and render using `htmlparser2`.
                _useHtmlParser2: true,
                decodeEntities: false,
            });

            // since maths delimiters are handled before Markdown,
            // code blocks could contain mangled content.
            // replace code blocks with original content
            phtmlOrig('code').each(function(i) {
                phtml('code').eq(i).text(phtmlOrig('code').eq(i).text());
            });

            // add fallback output for latex math, which should not be interpreted as markdown
            phtml('div, span').each(function(i, e) {
                const tex = phtml(e).attr('data-mx-maths');
                if (tex) {
                    phtml(e).html(`<code>${tex}</code>`);
                }
            });
        }
        return phtml.html();
    }
    // ensure removal of escape backslashes in non-Markdown messages
    if (md.indexOf("\\") > -1) {
        return parser.toPlaintext();
    }
}

export function textSerialize(model: EditorModel): string {
    return model.parts.reduce((text, part) => {
        switch (part.type) {
            case Type.Newline:
                return text + "\n";
            case Type.Plain:
            case Type.Emoji:
            case Type.Command:
            case Type.PillCandidate:
            case Type.AtRoomPill:
                return text + part.text;
            case Type.RoomPill:
                // Here we use the resourceId for compatibility with non-rich text clients
                // See https://github.com/vector-im/element-web/issues/16660
                return text + `${part.resourceId}`;
            case Type.UserPill:
                return text + `${part.text}`;
        }
    }, "");
}

export function containsEmote(model: EditorModel): boolean {
    const hasCommand = startsWith(model, "/me ", false);
    const hasArgument = model.parts[0]?.text?.length > 4 || model.parts.length > 1;
    return hasCommand && hasArgument;
}

export function startsWith(model: EditorModel, prefix: string, caseSensitive = true): boolean {
    const firstPart = model.parts[0];
    // part type will be "plain" while editing,
    // and "command" while composing a message.
    let text = firstPart?.text || '';
    if (!caseSensitive) {
        prefix = prefix.toLowerCase();
        text = text.toLowerCase();
    }

    return firstPart && (firstPart.type === Type.Plain || firstPart.type === Type.Command) && text.startsWith(prefix);
}

export function stripEmoteCommand(model: EditorModel): EditorModel {
    // trim "/me "
    return stripPrefix(model, "/me ");
}

export function stripPrefix(model: EditorModel, prefix: string): EditorModel {
    model = model.clone();
    model.removeText({ index: 0, offset: 0 }, prefix.length);
    return model;
}

export function unescapeMessage(model: EditorModel): EditorModel {
    const { parts } = model;
    if (parts.length) {
        const firstPart = parts[0];
        // only unescape \/ to / at start of editor
        if (firstPart.type === Type.Plain && firstPart.text.startsWith("\\/")) {
            model = model.clone();
            model.removeText({ index: 0, offset: 0 }, 1);
        }
    }
    return model;
}