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    var theme = store.get('mdbook-theme');
    if (theme === null || theme === undefined) { theme = 'light'; }

    set_theme(theme);

    // Syntax highlighting Configuration
    hljs.configure({
        tabReplace: '    ', // 4 spaces
        languages: [],      // Languages used for auto-detection
    });

    if (window.ace) {
        // language-rust class needs to be removed for editable
        // blocks or highlightjs will capture events
        $('code.editable').removeClass('language-rust');

        $('code').not('.editable').each(function(i, block) {
            hljs.highlightBlock(block);
        });
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        $('code').each(function(i, block) {
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    // Adding the hljs class gives code blocks the color css
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    });

    // Interesting DOM Elements
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    // Help keyboard navigation by always focusing on page content
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    // Toggle sidebar
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    // in relation to the whole screen (phone in portrait)
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            var popup = $('<div class="theme-popup"></div>')
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                popup.remove();
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    });

    function set_theme(theme) {
        let ace_theme;

        if (theme == 'coal' || theme == 'navy') {
            $("[href='ayu-highlight.css']").prop('disabled', true);
            $("[href='tomorrow-night.css']").prop('disabled', false);
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            ace_theme = "ace/theme/tomorrow_night";
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    // Hide Rust code lines prepended with a specific character
    var hiding_character = "#";

    $("code.language-rust").each(function(i, block){

        var code_block = $(this);
        var pre_block = $(this).parent();
        // hide lines
        var lines = code_block.html().split("\n");
        var first_non_hidden_line = false;
        var lines_hidden = false;

        for(var n = 0; n < lines.length; n++){
            if($.trim(lines[n])[0] == hiding_character){
                if(first_non_hidden_line){
                    lines[n] = "<span class=\"hidden\">" + "\n" + lines[n].replace(/(\s*)# ?/, "$1") + "</span>";
                }
                else {
                    lines[n] = "<span class=\"hidden\">" + lines[n].replace(/(\s*)# ?/, "$1") + "\n"  +  "</span>";
                }
                lines_hidden = true;
            }
            else if(first_non_hidden_line) {
                lines[n] = "\n" + lines[n];
            }
            else {
                first_non_hidden_line = true;
            }
        }
        code_block.html(lines.join(""));

        // If no lines were hidden, return
        if(!lines_hidden) { return; }

        // add expand button
        pre_block.prepend("<div class=\"buttons\"><i class=\"fa fa-expand\"></i></div>");

        pre_block.find("i").click(function(e){
            if( $(this).hasClass("fa-expand") ) {
                $(this).removeClass("fa-expand").addClass("fa-compress");
                pre_block.find("span.hidden").removeClass("hidden").addClass("unhidden");
            }
            else {
                $(this).removeClass("fa-compress").addClass("fa-expand");
                pre_block.find("span.unhidden").removeClass("unhidden").addClass("hidden");
            }
        });
    });

    // Process playpen code blocks
    $(".playpen").each(function(block){
        var pre_block = $(this);
        // Add play button
        var buttons = pre_block.find(".buttons");
        if( buttons.length === 0 ) {
            pre_block.prepend("<div class=\"buttons\"></div>");
            buttons = pre_block.find(".buttons");
        }
        buttons.prepend("<i class=\"fa fa-play play-button hidden\"></i>");
        buttons.prepend("<i class=\"fa fa-copy clip-button\"><i class=\"tooltiptext\"></i></i>");

        let code_block = pre_block.find("code").first();
        if (window.ace && code_block.hasClass("editable")) {
            buttons.prepend("<i class=\"fa fa-history reset-button\"></i>");
        }

        buttons.find(".play-button").click(function(e){
            run_rust_code(pre_block);
        });
        buttons.find(".clip-button").mouseout(function(e){
            hideTooltip(e.currentTarget);
        });
        buttons.find(".reset-button").click(function() {
            if (!window.ace) { return; }
            let editor = window.ace.edit(code_block.get(0));
            editor.setValue(editor.originalCode);
            editor.clearSelection();
        });
    });

    var clipboardSnippets = new Clipboard('.clip-button', {
        text: function(trigger) {
            hideTooltip(trigger);
            let playpen = $(trigger).parents(".playpen");
            return playpen_text(playpen);
        }
    });
    clipboardSnippets.on('success', function(e) {
            e.clearSelection();
            showTooltip(e.trigger, "Copied!");
    });
    clipboardSnippets.on('error', function(e) {
            showTooltip(e.trigger, "Clipboard error!");
    });

    $.ajax({
        url: "https://play.rust-lang.org/meta/crates",
        method: "POST",
        crossDomain: true,
        dataType: "json",
        contentType: "application/json",
        success: function(response){
            // get list of crates available in the rust playground
            let playground_crates = response.crates.map(function(item) {return item["id"];} );
            $(".playpen").each(function(block) {
                handle_crate_list_update($(this), playground_crates);
            });
        },
    });

});

function playpen_text(playpen) {
    let code_block = playpen.find("code").first();

    if (window.ace && code_block.hasClass("editable")) {
        let editor = window.ace.edit(code_block.get(0));
        return editor.getValue();
    } else {
        return code_block.get(0).textContent;
    }
}

function handle_crate_list_update(playpen_block, playground_crates) {
    // update the play buttons after receiving the response
    update_play_button(playpen_block, playground_crates);

    // and install on change listener to dynamically update ACE editors
    if (window.ace) {
        let code_block = playpen_block.find("code").first();
        if (code_block.hasClass("editable")) {
            let editor = window.ace.edit(code_block.get(0));
            editor.on("change", function(e){
                update_play_button(playpen_block, playground_crates);
            });
        }
    }
}

// updates the visibility of play button based on `no_run` class and
// used crates vs ones available on http://play.rust-lang.org
function update_play_button(pre_block, playground_crates) {
    var play_button = pre_block.find(".play-button");

    var classes = pre_block.find("code").attr("class").split(" ");
    // skip if code is `no_run`
    if (classes.indexOf("no_run") > -1) {
        play_button.addClass("hidden");
        return;
    }

    // get list of `extern crate`'s from snippet
    var txt = playpen_text(pre_block);
    var re = /extern\s+crate\s+([a-zA-Z_0-9]+)\s*;/g;
    var snippet_crates = [];
    while (item = re.exec(txt)) {
        snippet_crates.push(item[1]);
    }

    // check if all used crates are available on play.rust-lang.org
    var all_available = snippet_crates.every(function(elem) {
        return playground_crates.indexOf(elem) > -1;
    });

    if (all_available) {
        play_button.removeClass("hidden");
    } else {
        play_button.addClass("hidden");
    }
}

function hideTooltip(elem) {
    elem.firstChild.innerText="";
    elem.setAttribute('class', 'fa fa-copy clip-button');
}

function showTooltip(elem, msg) {
    elem.firstChild.innerText=msg;
    elem.setAttribute('class', 'fa fa-copy tooltipped');
}

function sidebarToggle() {
    var html = $("html");
    if ( html.hasClass("sidebar-hidden") ) {
        html.removeClass("sidebar-hidden").addClass("sidebar-visible");
        store.set('sidebar', 'visible');
    } else if ( html.hasClass("sidebar-visible") ) {
        html.removeClass("sidebar-visible").addClass("sidebar-hidden");
        store.set('sidebar', 'hidden');
    } else {
        if($("#sidebar").position().left === 0){
            html.addClass("sidebar-hidden");
            store.set('sidebar', 'hidden');
        } else {
            html.addClass("sidebar-visible");
            store.set('sidebar', 'visible');
        }
    }
}

function run_rust_code(code_block) {
    var result_block = code_block.find(".result");
    if(result_block.length === 0) {
        code_block.append("<code class=\"result hljs language-bash\"></code>");
        result_block = code_block.find(".result");
    }

    let text = playpen_text(code_block);;

    var params = {
        version: "stable",
        optimize: "0",
        code: text,
    };

    if(text.indexOf("#![feature") !== -1) {
        params.version = "nightly";
    }

    result_block.text("Running...");

    $.ajax({
        url: "https://play.rust-lang.org/evaluate.json",
        method: "POST",
        crossDomain: true,
        dataType: "json",
        contentType: "application/json",
        data: JSON.stringify(params),
        timeout: 15000,
        success: function(response){
            result_block.text(response.result);
        },
        error: function(qXHR, textStatus, errorThrown){
            result_block.text("Playground communication " + textStatus);
        },
    });
}