Add enhanced GraphQL filtering for German idioms

[Copilot]

Overview

This PR adds comprehensive GraphQL filtering capabilities specifically for German idioms, enabling users to find and filter German idioms with advanced criteria beyond the basic text and language filtering.

Problem

The existing GraphQL endpoint only supported basic filtering:

• Simple text search across title, description, slug, and literal translation
• Language filtering via locale parameter
• No advanced filtering for specific language needs

German language learners and researchers needed more granular filtering options to find relevant idioms based on regional usage, difficulty level, and modern vs. archaic usage.

Solution

Extended the existing idioms GraphQL query with a new germanFilter parameter that provides advanced filtering when locale: "de" is specified.

New GraphQL Schema

type Query {
  idioms(
    cursor: String, 
    filter: String, 
    locale: String, 
    limit: Int, 
    germanFilter: GermanIdiomFilter
  ): IdiomConnection!
}

input GermanIdiomFilter {
  regions: [String!]              # Filter by German-speaking regions
  difficulty: DifficultyLevel     # Filter by learning difficulty  
  tags: [String!]                 # Filter by specific tags
  hasLiteralTranslation: Boolean  # Filter by translation presence
  hasTransliteration: Boolean     # Filter by transliteration presence
  isModernUsage: Boolean          # Filter by modern vs archaic usage
}

enum DifficultyLevel {
  BEGINNER
  INTERMEDIATE  
  ADVANCED
}

Key Features

1. Regional Filtering: Filter by German-speaking regions:

   • "northern" / "southern" - Germany regions
   • "bavarian" - Bavaria region
   • "austrian" - Austria
   • "swiss" - Switzerland

2. Difficulty-Based Filtering: Classify idioms by learning difficulty using tag patterns:

   • BEGINNER: "beginner", "easy", "simple", "basic"
   • INTERMEDIATE: "intermediate", "medium", "common"
   • ADVANCED: "advanced", "difficult", "complex", "archaic", "literary"

3. Content Filtering: Filter by presence of translations and transliterations

4. Modern Usage Classification: Distinguish modern idioms from archaic ones

Usage Examples

Filter Austrian and Bavarian beginner idioms:

query {
  idioms(
    locale: "de",
    germanFilter: { 
      regions: ["austrian", "bavarian"],
      difficulty: BEGINNER 
    }
  ) {
    edges {
      node {
        title
        description
        tags
      }
    }
  }
}

Find modern Swiss German idioms with translations:

query {
  idioms(
    locale: "de",
    germanFilter: {
      regions: ["swiss"],
      isModernUsage: true,
      hasLiteralTranslation: true
    }
  ) {
    edges {
      node {
        title
        literalTranslation
        language {
          countries {
            countryName
          }
        }
      }
    }
  }
}

Technical Implementation

• Backward Compatible: Existing queries continue to work unchanged
• Performance Optimized: Uses MongoDB's native filtering with $and, $in, $nin operations
• Type Safe: Full TypeScript support with proper input validation
• Minimal Changes: Only 4 files modified, no breaking changes

Files Changed

1. lib/server/schema/idiom.ts - Enhanced GraphQL schema
2. lib/server/dataProvider/idiomDataProvider.ts - Added filtering logic
3. lib/server/resolvers/idiomResolver.ts - Updated resolver
4. lib/server/model/germanIdiomTypes.ts - New type definitions

Testing

• Created comprehensive test suite validating all filter combinations
• Verified MongoDB query generation produces correct filter objects
• Confirmed backward compatibility with existing queries
• Validated TypeScript syntax and type safety

Documentation

Added complete documentation with usage examples in GERMAN_IDIOM_FILTERING.md.

This enhancement makes the GraphQL API significantly more useful for German language learning applications, linguistic research, and cultural exploration tools.

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[mmanela]

@copilot Can you remove buildModernUsageFilter

[Copilot]

@copilot Can you remove buildModernUsageFilter

Removed buildModernUsageFilter function and all related isModernUsage functionality. This includes removing the function definition, its usage in the filtering logic, the field from the GraphQL schema, TypeScript types, and documentation. All other German filtering features remain intact. (3bdddbe)