discourse-placeholder-theme-component/common/header.html

<script type="text/discourse-plugin" version="0.8.30">
  api.decorateCooked(($cooked, postWidget) => {
    const VALID_TAGS = "h1, h2, h3, h4, h5, h6, p, code, blockquote, .md-table, li";
    const DELIMITER = "=";

    // http://davidwalsh.name/javascript-debounce-function
    function debounce(func, wait, immediate) {
      let timeout;

      return function() {
        const context = this,
          args = arguments;

        const later = function() {
          timeout = null;
          if (!immediate) func.apply(context, args);
        };

        const callNow = immediate && !timeout;

        clearTimeout(timeout);
        timeout = setTimeout(later, wait);

        if (callNow) func.apply(context, args);
      };
    }

    function processChange($cooked, inputEvent, mappings) {
      const value = inputEvent.target.value;
      const key = inputEvent.target.dataset.key;

      if (postWidget) {
        const placeholderIdentifier = `d-placeholder-${postWidget.widget.attrs.topicId}-${postWidget.widget.attrs.id}-${key}`;
        if (value) {
          $.cookie(placeholderIdentifier, value);
        } else {
          $.removeCookie(placeholderIdentifier);
        }
      }

      let newValue;
      if (value && value.length && value !== "none") {
        newValue = value;
      } else {
        newValue = `${DELIMITER}${key}${DELIMITER}`;
      }

      $cooked.find(VALID_TAGS).each((index, elem) => {
        let replaced = false;
        const mapping = mappings[index];
        let newInnnerHTML = elem.innerHTML;
        let diff = 0;

        if (!mapping) {
          return;
        }

        mapping.forEach(m => {
          if (m.pattern !== `${DELIMITER}${key}${DELIMITER}`) {
            m.position = m.position + diff;
            return;
          }

          replaced = true;

          const previousLength = m.length;
          const prefix = newInnnerHTML.slice(0, m.position + diff);
          const suffix = newInnnerHTML.slice(
            m.position + diff + m.length,
            newInnnerHTML.length
          );
          newInnnerHTML = `${prefix}${newValue}${suffix}`;

          m.length = newValue.length;
          m.position = m.position + diff;
          diff = diff + newValue.length - previousLength;
        });

        if (replaced) {
          elem.innerHTML = newInnnerHTML;
        }
      });
    }

    function addSelectOption(select, options = {}) {
      const option = document.createElement("option");
      option.classList.add("discourse-placeholder-option");
      option.value = options.value;
      option.text = options.description || options.value;

      if (options.selected) {
        option.setAttribute("selected", true);
      }

      select.appendChild(option);
    }

    function processPlaceholders(placeholders, $cooked, mappings) {
      const keys = Object.keys(placeholders);
      const pattern = `(${DELIMITER}(?:${keys.join("|")})${DELIMITER})`;
      const regex = new RegExp(pattern, "g");

      $cooked.find(VALID_TAGS).each((index, elem) => {
        const innerHTML = elem.innerHTML;
        let match;

        mappings[index] = mappings[index] || [];

        while ((match = regex.exec(innerHTML)) != null) {
          mappings[index].push({
            pattern: match[1],
            position: match.index,
            length: match[1].length
          });
        }
      });
    }

    const mappings = [];
    const placeholders = {};

    $cooked.find(".d-wrap[data-wrap=placeholder]:not(.placeholdered)").each((index, elem) => {
      const dataKey = elem.dataset.key;
      if (!dataKey) {
        return;
      }

      let valueFromCookie;
      if (postWidget) {
        const placeholderIdentifier = `d-placeholder-${postWidget.widget.attrs.topicId}-${postWidget.widget.attrs.id}`;
        valueFromCookie = $.cookie(`${placeholderIdentifier}-${dataKey}`);
      }

      const defaultValue = valueFromCookie || elem.dataset.default;
      const defaultValues = (elem.dataset.defaults || "").split(",").filter(x => x);
      const description = elem.dataset.description;

      placeholders[dataKey] = {
        default: defaultValue,
        defaults: defaultValues,
        description
      }

      elem.classList.add("placeholdered")

      const span = document.createElement("span");
      span.classList.add("discourse-placeholder-name")
      span.innerText = dataKey;
      elem.appendChild(span)

      if (defaultValues && defaultValues.length) {
        const select = document.createElement("select");
        select.classList.add("discourse-placeholder-select")
        select.dataset.key = dataKey;

        if (description) {
          addSelectOption(select, { value: "none", description });
        }

        defaultValues.forEach(value =>
          addSelectOption(select, {
            value,
            selected: defaultValue === value
          })
        );

        elem.appendChild(select);
      } else {
        const input = document.createElement("input");
        input.classList.add("discourse-placeholder-value")
        input.dataset.key = dataKey;

        if (description) {
          input.setAttribute("placeholder", description);
        }

        if (valueFromCookie || defaultValue) {
          input.value = valueFromCookie || defaultValue;
        }

        elem.appendChild(input)
      }
    })

    if (Object.keys(placeholders).length > 0) {
      processPlaceholders(placeholders, $cooked, mappings);
    }

    $cooked
      .on(
        "input",
        ".discourse-placeholder-value",
        debounce(inputEvent => {
          processChange($cooked, inputEvent, mappings);
        }, 250)
      )
      .on(
        "change",
        ".discourse-placeholder-select",
        debounce(inputEvent => {
          processChange($cooked, inputEvent, mappings);
        }, 250)
      );
    
    Ember.run.later(() => {
      // trigger fake event to setup initial state
      Object.keys(placeholders).forEach(placeholderKey => {
        const placeholder = placeholders[placeholderKey];

        const value =
          placeholder.default ||
          (placeholder.defaults.length && !placeholder.description
            ? placeholder.defaults[0]
            : null);

        processChange(
          $cooked,
          { target: { value, dataset: { key: placeholderKey } } },
          mappings
        );
      });
    }, 500);
  });
</script>