From 91c058105e88ac552f070a57bef47d9d753f5a52 Mon Sep 17 00:00:00 2001
From: vikingowl <christian@nachtigall.dev>
Date: Sat, 18 Apr 2026 12:24:49 +0200
Subject: [PATCH] feat(discovery/crawler): mittelalterkalender.info parser

---
 .../discovery/crawler/mittelalterkalender.go  | 127 ++++++++++++++++++
 .../crawler/mittelalterkalender_test.go       |  38 ++++++
 2 files changed, 165 insertions(+)
 create mode 100644 backend/internal/domain/discovery/crawler/mittelalterkalender.go
 create mode 100644 backend/internal/domain/discovery/crawler/mittelalterkalender_test.go

diff --git a/backend/internal/domain/discovery/crawler/mittelalterkalender.go b/backend/internal/domain/discovery/crawler/mittelalterkalender.go
new file mode 100644
index 0000000..9ce64e7
--- /dev/null
+++ b/backend/internal/domain/discovery/crawler/mittelalterkalender.go
@@ -0,0 +1,127 @@
+package crawler
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/PuerkitoBio/goquery"
+)
+
+// MittelalterkalenderSource scrapes www.mittelalterkalender.info. Page has
+// twelve monthly <table>s; each has columns: Beginn | Ende | Titel | PLZ | Ort |
+// [Details link].
+type MittelalterkalenderSource struct {
+	fetcher *Fetcher
+	urls    []string
+}
+
+func NewMittelalterkalender(f *Fetcher, urls []string) *MittelalterkalenderSource {
+	return &MittelalterkalenderSource{fetcher: f, urls: urls}
+}
+
+func (s *MittelalterkalenderSource) Name() string { return "mittelalterkalender" }
+
+func (s *MittelalterkalenderSource) Fetch(ctx context.Context) ([]RawEvent, error) {
+	var all []RawEvent
+	for i, url := range s.urls {
+		if i > 0 {
+			if err := sleepCtx(ctx, 2*time.Second); err != nil {
+				return all, err
+			}
+		}
+		body, err := s.fetcher.Get(ctx, url, "")
+		if err != nil {
+			return all, fmt.Errorf("mittelalterkalender %s: %w", url, err)
+		}
+		events, err := parseMittelalterkalender(body, url)
+		if err != nil {
+			return all, fmt.Errorf("mittelalterkalender parse %s: %w", url, err)
+		}
+		all = append(all, events...)
+	}
+	return all, nil
+}
+
+func parseMittelalterkalender(data []byte, sourceURL string) ([]RawEvent, error) {
+	doc, err := goquery.NewDocumentFromReader(bytes.NewReader(data))
+	if err != nil {
+		return nil, err
+	}
+	var events []RawEvent
+	doc.Find("table tr").Each(func(_ int, tr *goquery.Selection) {
+		cells := tr.Find("td")
+		if cells.Length() < 5 {
+			return
+		}
+		// First cell contains start date followed by " bis " span; extract just the date.
+		beginnText := strings.TrimSpace(cells.Eq(0).Text())
+		// Remove the "bis" suffix (cell text is "DD.MM.YYYY bis")
+		if idx := strings.Index(beginnText, " bis"); idx > 0 {
+			beginnText = beginnText[:idx]
+		}
+		beginn := strings.TrimSpace(beginnText)
+		ende := strings.TrimSpace(cells.Eq(1).Text())
+		titel := strings.TrimSpace(cells.Eq(2).Text())
+		plz := strings.TrimSpace(cells.Eq(3).Text())
+		ort := strings.TrimSpace(cells.Eq(4).Text())
+
+		if titel == "" || beginn == "" {
+			return
+		}
+		start := parseDEDate(beginn)
+		if start == nil {
+			return
+		}
+		end := parseDEDate(ende)
+
+		detailURL := ""
+		if cells.Length() >= 6 {
+			href, ok := cells.Eq(5).Find("a").First().Attr("href")
+			if ok {
+				detailURL = resolveURL(sourceURL, strings.TrimSpace(href))
+			}
+		}
+
+		events = append(events, RawEvent{
+			SourceName: "mittelalterkalender",
+			SourceURL:  sourceURL,
+			DetailURL:  detailURL,
+			Name:       titel,
+			City:       ort,
+			PLZ:        plz,
+			Land:       InferLand(plz),
+			StartDate:  start,
+			EndDate:    end,
+		})
+	})
+	return events, nil
+}
+
+// resolveURL joins a relative href against the source URL. Leaves absolute
+// URLs untouched; empty input returns empty.
+func resolveURL(source, href string) string {
+	if href == "" {
+		return ""
+	}
+	if strings.HasPrefix(href, "http://") || strings.HasPrefix(href, "https://") {
+		return href
+	}
+	if strings.HasPrefix(href, "/") {
+		// Strip path from source, keep scheme://host.
+		// Simple impl — source is always a full URL from our config.
+		end := strings.Index(source[len("https://"):], "/")
+		if end < 0 {
+			return source + href
+		}
+		return source[:len("https://")+end] + href
+	}
+	// Relative to current dir — drop filename from source.
+	lastSlash := strings.LastIndex(source, "/")
+	if lastSlash < 0 {
+		return source + "/" + href
+	}
+	return source[:lastSlash+1] + href
+}
diff --git a/backend/internal/domain/discovery/crawler/mittelalterkalender_test.go b/backend/internal/domain/discovery/crawler/mittelalterkalender_test.go
new file mode 100644
index 0000000..0b0b926
--- /dev/null
+++ b/backend/internal/domain/discovery/crawler/mittelalterkalender_test.go
@@ -0,0 +1,38 @@
+package crawler
+
+import (
+	"os"
+	"testing"
+)
+
+func TestMittelalterkalenderParse(t *testing.T) {
+	data, err := os.ReadFile("testdata/mittelalterkalender.html")
+	if err != nil {
+		t.Fatal(err)
+	}
+	events, err := parseMittelalterkalender(data, "https://www.mittelalterkalender.info/mittelaltermarkt/mittelalterfeste-2026-nach-datum.php")
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	t.Logf("Parsed %d events", len(events))
+	if len(events) < 10 {
+		t.Fatalf("got %d events; expected at least 10", len(events))
+	}
+	e := events[0]
+	if e.SourceName != "mittelalterkalender" {
+		t.Errorf("SourceName = %q", e.SourceName)
+	}
+	if e.Name == "" {
+		t.Error("Name empty")
+	}
+	if e.City == "" {
+		t.Error("City empty")
+	}
+	if e.StartDate == nil {
+		t.Error("StartDate nil")
+	}
+	// Land inferred from PLZ via InferLand.
+	if e.Land == "" && e.PLZ != "" {
+		t.Errorf("Land empty but PLZ=%q", e.PLZ)
+	}
+}