function find_boundary_tr(initial_tr, iterate_row) {
    var j;
    var skip_same_td_check = false;
    var tr = initial_tr;

    // If the selection boundary is somewhere that does not have a
    // parent tr, we should let the browser handle the copy-paste
    // entirely on its own
    if (tr.length === 0) {
        return;
    }

    // If the selection boundary is on a table row that does not have an
    // associated message id (because the user clicked between messages),
    // then scan downwards until we hit a table row with a message id.
    // To ensure we can't enter an infinite loop, bail out (and let the
    // browser handle the copy-paste on its own) if we don't hit what we
    // are looking for within 10 rows.
    for (j = 0; !tr.is('.message_row') && j < 10; j += 1) {
        tr = iterate_row(tr);
    }
    if (j === 10) {
        return;
    } else if (j !== 0) {
        // If we updated tr, then we are not dealing with a selection
        // that is entirely within one td, and we can skip the same td
        // check (In fact, we need to because it won't work correctly
        // in this case)
        skip_same_td_check = true;
    }
    return [rows.id(tr), skip_same_td_check];
}

function construct_recipient_header(message_row) {
    var message_header_content = rows.get_message_recipient_header(message_row)
        .text()
        .replace(/\s+/g, " ")
        .replace(/^\s/, "").replace(/\s$/, "");
    return $('<p>').append($('<strong>').text(message_header_content));
}

/*
The techniques we use in this code date back to
2013 and may be obsolete today (and may not have
been even the best workaround back then).

https://github.com/zulip/zulip/commit/fc0b7c00f16316a554349f0ad58c6517ebdd7ac4

The idea is that we build a temp div, let jQuery process the
selection, then restore the selection on a zero-second timer back
to the original selection.

Do not be afraid to change this code if you understand
how modern browsers deal with copy/paste.  Just test
your changes carefully.
*/
function construct_copy_div(div, start_id, end_id) {
    var start_row = current_msg_list.get_row(start_id);
    var start_recipient_row = rows.get_message_recipient_row(start_row);
    var start_recipient_row_id = rows.id_for_recipient_row(start_recipient_row);
    var should_include_start_recipient_header = false;

    var last_recipient_row_id = start_recipient_row_id;
    for (var row = start_row; rows.id(row) <= end_id; row = rows.next_visible(row)) {
        var recipient_row_id = rows.id_for_recipient_row(rows.get_message_recipient_row(row));
        // if we found a message from another recipient,
        // it means that we have messages from several recipients,
        // so we have to add new recipient's bar to final copied message
        // and wouldn't forget to add start_recipient's bar at the beginning of final message
        if (recipient_row_id !== last_recipient_row_id) {
            div.append(construct_recipient_header(row));
            last_recipient_row_id = recipient_row_id;
            should_include_start_recipient_header = true;
        }
        var message = current_msg_list.get(rows.id(row));
        var message_firstp = $(message.content).slice(0, 1);
        message_firstp.prepend(message.sender_full_name + ": ");
        div.append(message_firstp);
        div.append($(message.content).slice(1));
    }

    if (should_include_start_recipient_header) {
        div.prepend(construct_recipient_header(start_row));
    }
}

function select_div(div, selection) {
    div.css({
        position: 'absolute',
        left: '-99999px',
        // Color and background is made according to "day mode"
        // exclusively here because when copying the content
        // into, say, Gmail compose box, the styles come along.
        // This is done to avoid copying the content with dark
        // background when using the app in night mode.
        // We can avoid other custom styles since they are wrapped
        // inside another parent such as `.message_content`.
        color: '#333',
        background: '#FFF',
    })
        .attr('id', 'copytempdiv');
    $('body').append(div);
    selection.selectAllChildren(div[0]);
}

function remove_div(div, ranges, selection) {
    window.setTimeout(function () {
        selection = window.getSelection();
        selection.removeAllRanges();
        _.each(ranges, function (range) {
            selection.addRange(range);
        });
        $('#copytempdiv').remove();
    }, 0);
}

exports.copy_handler = function () {
    // This is the main handler for copying message content via
    // `ctrl+C` in Zulip (note that this is totally independent of the
    // "select region" copy behavior on Linux; that is handled
    // entirely by the browser, our HTML layout, and our use of the
    // no-select/auto-select CSS classes).  We put considerable effort
    // into producing a nice result that pastes well into other tools.
    // Our user-facing specification is the following:
    //
    // * If the selection is contained within a single message, we
    //   want to just copy the portion that was selected, which we
    //   implement by letting the browser handle the ctrl+C event.
    //
    // * Otherwise, we want to copy the bodies of all messages that
    //   were partially covered by the selection.

    var selection = window.getSelection();
    var analysis = exports.analyze_selection(selection);
    var ranges = analysis.ranges;
    var start_id = analysis.start_id;
    var end_id = analysis.end_id;
    var skip_same_td_check = analysis.skip_same_td_check;
    var div = $('<div>');

    if (start_id === undefined || end_id === undefined) {
        // In this case either the starting message or the ending
        // message is not defined, so this is definitely not a
        // multi-message selection and we can let the browser handle
        // the copy.
        document.execCommand('copy');
        return;
    }

    if (!skip_same_td_check && start_id === end_id) {
        // Check whether the selection both starts and ends in the
        // same message.  If so, Let the browser handle this.
        document.execCommand('copy');
        return;
    }

    // We've now decided to handle the copy event ourselves.
    //
    // We construct a temporary div for what we want the copy to pick up.
    // We construct the div only once, rather than for each range as we can
    // determine the starting and ending point with more confidence for the
    // whole selection. When constructing for each `Range`, there is a high
    // chance for overlaps between same message ids, avoiding which is much
    // more difficult since we can get a range (start_id and end_id) for
    // each selection `Range`.
    construct_copy_div(div, start_id, end_id);

    // Select div so that the browser will copy it
    // instead of copying the original selection
    select_div(div, selection);
    document.execCommand('copy');
    remove_div(div, ranges, selection);
};

exports.analyze_selection = function (selection) {
    // Here we analyze our selection to determine if part of a message
    // or multiple messages are selected.
    //
    // Firefox and Chrome handle selection of multiple messages
    // differently. Firefox typically creates multiple ranges for the
    // selection, whereas Chrome typically creates just one.
    //
    // Our goal in the below loop is to compute and be prepared to
    // analyze the combined range of the selections, and copy their
    // full content.

    var i;
    var range;
    var ranges = [];
    var startc;
    var endc;
    var initial_end_tr;
    var start_id;
    var end_id;
    var start_data;
    var end_data;
    // skip_same_td_check is true whenever we know for a fact that the
    // selection covers multiple messages (and thus we should no
    // longer consider letting the browser handle the copy event).
    var skip_same_td_check = false;

    for (i = 0; i < selection.rangeCount; i += 1) {
        range = selection.getRangeAt(i);
        ranges.push(range);

        startc = $(range.startContainer);
        start_data = find_boundary_tr($(startc.parents('.selectable_row, .message_header')[0]), function (row) {
            return row.next();
        });
        if (start_data === undefined) {
            // Skip any selection sections that don't intersect a message.
            continue;
        }
        if (start_id === undefined) {
            // start_id is the Zulip message ID of the first message
            // touched by the selection.
            start_id = start_data[0];
        }

        endc = $(range.endContainer);
        // If the selection ends in the bottom whitespace, we should
        // act as though the selection ends on the final message.
        // This handles the issue that Chrome seems to like selecting
        // the compose_close button when you go off the end of the
        // last message
        if (endc.attr('id') === "bottom_whitespace" || endc.attr('id') === "compose_close") {
            initial_end_tr = $(".message_row").last();
            // The selection goes off the end of the message feed, so
            // this is a multi-message selection.
            skip_same_td_check = true;
        } else {
            initial_end_tr = $(endc.parents('.selectable_row')[0]);
        }
        end_data = find_boundary_tr(initial_end_tr, function (row) {
            return row.prev();
        });

        if (end_data === undefined) {
            // Skip any selection sections that don't intersect a message.
            continue;
        }
        if (end_data[0] !== undefined) {
            end_id = end_data[0];
        }

        if (start_data[1] || end_data[1]) {
            // If the find_boundary_tr call for either the first or
            // the last message covered by the selection
            skip_same_td_check = true;
        }
    }

    return {
        ranges: ranges,
        start_id: start_id,
        end_id: end_id,
        skip_same_td_check: skip_same_td_check,
    };
};

exports.paste_handler_converter = function (paste_html) {
    var converters = {
        converters: [
            {
                filter: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'],
                replacement: function (content) {
                    return content;
                },
            },

            {
                filter: ['em', 'i'],
                replacement: function (content) {
                    return '*' + content + '*';
                },
            },
            {
                // Checks for raw links without custom text or title.
                filter: function (node) {
                    return node.nodeName === "A" &&
                      node.href === node.innerHTML &&
                      node.href === node.title;
                },
                replacement: function (content) {
                    return content;
                },
            },
            {
                // Checks for escaped ordered list syntax.
                filter: function (node) {
                    return /(\d+)\\\. /.test(node.innerHTML);
                },
                replacement: function (content) {
                    return content.replace(/(\d+)\\\. /g, '$1. ');
                },
            },
        ],
    };
    var markdown_html = toMarkdown(paste_html, converters);

    // Now that we've done the main conversion, we want to remove
    // any HTML tags that weren't converted to markdown-style
    // text, since Bugdown doesn't support those.
    var div = document.createElement("div");
    div.innerHTML = markdown_html;
    // Using textContent for modern browsers, innerText works for Internet Explorer
    var markdown_text = div.textContent || div.innerText || "";
    markdown_text = markdown_text.trim();
    // Removes newlines before the start of a list and between list elements.
    markdown_text = markdown_text.replace(/\n+([*+-])/g, '\n$1');
    return markdown_text;
};

exports.paste_handler = function (event) {
    var clipboardData = event.originalEvent.clipboardData;
    if (!clipboardData) {
        // On IE11, ClipboardData isn't defined.  One can instead
        // access it with `window.clipboardData`, but even that
        // doesn't support text/html, so this code path couldn't do
        // anything special anyway.  So we instead just let the
        // default paste handler run on IE11.
        return;
    }

    if (clipboardData.getData) {
        var paste_html = clipboardData.getData('text/html');
        if (paste_html && page_params.development_environment) {
            var text = exports.paste_handler_converter(paste_html);
            var mdImageRegex = /^!\[.*\]\(.*\)$/;
            if (text.match(mdImageRegex)) {
                // This block catches cases where we are pasting an
                // image into Zulip, which should be handled by the
                // jQuery filedrop library, not this code path.
                return;
            }
            event.preventDefault();
            event.stopPropagation();
            compose_ui.insert_syntax_and_focus(text);
        }
    }
};

exports.initialize = function () {
    $("#compose-textarea").bind('paste', exports.paste_handler);
    $('body').on('paste', '#message_edit_form', exports.paste_handler);
};

window.copy_and_paste = exports;