/*
 * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
 * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#pragma once

#include <QColor>
#include <QList>
#include <QPalette>

#include "mimeparser.h"

/// One message's place in a rendered thread.
struct ThreadRenderItem
{
    ParsedMessage message;

    /// Matched messages render in full; unmatched collapse to a one-line stub.
    bool expanded = true;

    /// Disambiguates cid: references. Two newsletters in one thread commonly
    /// use the same Content-ID (cid:logo@example.org), which would collide in
    /// a single document, so every reference is rewritten to
    /// cid:<prefix>!<id>.
    ///
    /// Requirement on whatever generates this value: it must never contain
    /// '!'. The separator that makes cid:<prefix>!<id> unambiguous is the
    /// FIRST '!' in the namespaced string; that only holds if the prefix
    /// half is guaranteed free of the character, since the id half is
    /// attacker-controlled and may legitimately contain '!' itself. The
    /// documented "m<index>" form (e.g. "m0", "m1") satisfies this. Enforced
    /// with Q_ASSERT at both places that perform this concatenation
    /// (HtmlBuilder::namespaceCids and CidSchemeHandler::namespacedKey).
    QString cidPrefix;
};

/// Turns parsed messages into the HTML string handed to the web view.
///
/// Plain text goes through the same path as HTML so the view has one render
/// path rather than two. A whole thread renders as ONE document rather than one
/// view per message: a thread of newsletters can hold dozens of messages, and a
/// QWebEngineView each would spawn a Chromium render process each.
class HtmlBuilder
{
public:
    enum Mode {
        PreferHtml,  ///< Use the HTML part when the message has one.
        ForcePlain,  ///< Always render the plain part, escaped.
    };

    /// The colours the document's own stylesheet uses.
    ///
    /// Passed in rather than read from qApp inside the builder, so the CSS can
    /// be tested against a known palette without a running application, and so
    /// nothing here depends on widget state.
    ///
    /// **Scope.** These style the chrome around messages and the plain-text
    /// render. A message that brings its own HTML brings its own colours, and
    /// those are deliberately left alone: rewriting a sender's styling would
    /// break layouts that depend on it, and a newsletter that sets a white
    /// background is entitled to stay white.
    struct Palette {
        QColor background;  ///< The pane itself.
        QColor text;        ///< Body text.
        QColor dim;         ///< Headers and stubs: present but secondary.
        QColor border;      ///< Rules between messages.
        QColor quote;       ///< Quoted lines in plain text.
    };

    /// Derives the document palette from a widget palette.
    ///
    /// The dim and border colours are blends rather than fixed greys, which is
    /// what makes this work on a dark theme: a hardcoded #555 that reads as
    /// "subtle" on white is nearly invisible on near-black.
    static Palette paletteFrom(const QPalette &palette);

    /// The palette used when a caller supplies none: the running application's.
    /// Falls back to a light default with no QApplication, which only happens
    /// in a test that did not ask for a palette.
    static Palette defaultPalette();

    /// Single message, used for the error card and for tests.
    static QString build(const ParsedMessage &message, Mode mode);
    static QString build(const ParsedMessage &message, Mode mode,
                         const Palette &palette);

    /// The whole thread, oldest first.
    static QString buildThread(const QList<ThreadRenderItem> &items, Mode mode);
    static QString buildThread(const QList<ThreadRenderItem> &items, Mode mode,
                               const Palette &palette);

    /// Rewrites cid: URLs in an HTML body to their namespaced form.
    static QString namespaceCids(const QString &html, const QString &prefix);

private:
    static QString renderPlain(const QString &text);
    static QString renderBody(const ThreadRenderItem &item, Mode mode);
    static QString renderStub(const ParsedMessage &message);
    static QString document(const QString &bodyHtml, const Palette &palette);
    static QString styleSheet(const Palette &palette);
};