add and parse timezone in date filter

eleventy.config.js

@@ -8,7 +8,37 @@ const toml = require("@iarna/toml");
 const fs = require("fs");
 const path = require("path");
 
+const TIME_ZONE = "America/Santiago";
+
 module.exports = function (eleventyConfig) {
+    eleventyConfig.addDateParsing(function (dateValue) {
+        // i know this is a deranged solution. sorry LOL
+        let localDate;
+        try {
+            if (dateValue instanceof Date && !isNaN(dateValue)) {
+                // handle filename dates (ie 2025-10-18-post.md)
+                localDate = DateTime.fromJSDate(dateValue, { zone: "utc" })
+                    .setZone(TIME_ZONE)
+                    .startOf("day"); // Set to midnight in America/Santiago
+            } else if (typeof dateValue === "string" && dateValue) {
+                // handle string dates (ie from front matter, if used)
+                localDate = DateTime.fromISO(dateValue, { zone: TIME_ZONE }).startOf("day");
+            } else {
+                // handle invalid input
+                console.warn(`Invalid date value: ${dateValue} for ${this.page.inputPath}`);
+                localDate = DateTime.now().setZone(TIME_ZONE).startOf("day");
+            }
+            if (!localDate || localDate.isValid === false) {
+                throw new Error(`Invalid date value (${dateValue}) for ${this.page.inputPath}: ${localDate?.invalidReason || "Unknown"}`);
+            }
+            return localDate.toJSDate();
+        } catch (error) {
+            console.error(`Date parsing error for ${this.page.inputPath}:`, error.message);
+            // fallback to current date in TIME_ZONE
+            return DateTime.now().setZone(TIME_ZONE).startOf("day").toJSDate();
+        }
+    });
+    
     eleventyConfig.setLayoutsDirectory("_layouts");
 
     eleventyConfig.addPassthroughCopy("img");
@@ -35,8 +65,26 @@ module.exports = function (eleventyConfig) {
         return filtered;
     });
 
-    eleventyConfig.addFilter("date", function (dateObj, format) {
-        return DateTime.fromJSDate(dateObj).toFormat(format);
+    eleventyConfig.addFilter("date", function (dateObj, format = "dd/MM/yyyy") {
+        let dt = dateObj;
+        // handle string dates
+        if (typeof dateObj === "string") {
+            dt = DateTime.fromISO(dateObj, { zone: TIME_ZONE }).toJSDate();
+        }
+        // handle DateTime objects (from addDateParsing)
+        if (dateObj instanceof DateTime) {
+            dt = dateObj.toJSDate();
+        }
+        // check dt as valid Date object
+        if (!(dt instanceof Date) || isNaN(dt)) {
+            console.log("Invalid date input:", dateObj);
+            return "";
+        }
+        // format in TIME_ZONE
+        const formatted = DateTime.fromJSDate(dt, { zone: TIME_ZONE })
+            .toFormat(format);
+        console.log("Date input:", dt, "Formatted:", formatted, "Timezone:", TIME_ZONE);
+        return formatted;
     });
 
     eleventyConfig.addPlugin(eleventySass);