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Ameh Mathias Ejeh
Ameh Mathias Ejeh

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String Analysis RESTful API

#javascript #express #node #api

A modular Node.js/Express API service that analyzes strings and stores their computed properties.

Features

  • String analysis with multiple computed properties
  • SHA-256 based unique identification
  • RESTful API endpoints
  • Query filtering with standard parameters
  • Natural language query parsing
  • In-memory storage (easily replaceable with database)
  • Comprehensive error handling

Project Structure 

src/
├── index.js                          # Server entry point
├── app.js                            # Express app configuration
├── controllers/
│   └── stringController.js           # Request handlers
├── services/
│   ├── stringAnalyzer.js             # String analysis logic
│   ├── stringService.js              # Business logic layer
│   └── naturalLanguageParser.js      # NL query parser
├── repositories/
│   └── stringRepository.js           # Data access layer
├── routes/
│   └── stringRoutes.js               # Route definitions
└── middleware/
    ├── validation.js                 # Request validation
    └── errorHandler.js               # Error handling
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Installation 

npm install express
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Running the Server

// Production mode
npm start

// Development mode with auto-reload
npm run dev
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Server runs on http://localhost:3000.

API Endpoints

Create/Analyze String

  • POST /strings

Request:

{
  "value": "ameh mathias"
}
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Response (201 Created):

Error Responses:

  • 400 Bad Request - Invalid request body or missing "value" field
  • 422 Unprocessable Entity - Invalid data type for "value" (must be string)
  • 409 Conflict - String already exists

Get Specific String

  • GET /strings/{string_value}

Example: GET /strings/ameh%20mathias

Response (200 OK):

Error Response:

  • 404 Not Found - String does not exist

Get All Strings with Filtering

  • GET /strings Query Parameters:
  • is_palindrome - boolean (true/false)
  • min_length - integer (minimum string length)
  • max_length - integer (maximum string length)
  • word_count - integer (exact word count)
  • contains_character - string (single character)

Example: GET /strings?is_palindrome=true&min_length=3&word_count=1

Response (200 OK):

Error Response:

  • 400 Bad Request - Invalid query parameter values or types

Natural Language Filtering

  • GET /strings/filter-by-natural-language?query={natural_language_query}

Supported Query Patterns:

  • "all single word palindromic strings"
  • "strings longer than 10 characters"
  • "palindromic strings that contain the first vowel"
  • "strings containing the letter z"
  • "two word strings"
  • "strings between 5 and 20 characters"

Example: GET /strings/filter-by-natural-language?query=all%20single%20word%20palindromic%20strings

Response (200 OK):

{
    "data": [
        {
            "id": "31db973d2a73423e4a95ad7d5e9eed9d0a8e06c77ce7cb0c6f3b0d35b7f90625",
            "value": "ameh mathias",
            "properties": {
                "length": 12,
                "is_palindrome": false,
                "unique_characters": 8,
                "word_count": 2,
                "sha256_hash": "31db973d2a73423e4a95ad7d5e9eed9d0a8e06c77ce7cb0c6f3b0d35b7f90625",
                "character_frequency_map": {
                    "a": 3,
                    "m": 2,
                    "e": 1,
                    "h": 2,
                    " ": 1,
                    "t": 1,
                    "i": 1,
                    "s": 1
                }
            },
            "created_at": "2025-10-20T13:21:56.057Z"
        }
    ],
    "count": 1,
    "interpreted_query": {
        "original": "{natural_language_query}",
        "parsed_filters": {}
    }
}
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Error Responses:

  • 400 Bad Request - Unable to parse natural language query
  • 422 Unprocessable Entity - Query parsed but resulted in conflicting filters

Delete String

  • DELETE /strings/{string_value}

Example: DELETE /strings/ameh%20mathias

Response:
204 No Content (empty body)

Error Response:

  • 404 Not Found - String does not exist

String Properties

Each analyzed string includes:

Property Type Description
length integer Number of characters in the string
is_palindrome boolean Whether string reads the same forwards/backwards (case-insensitive)
unique_characters integer Count of distinct characters
word_count integer Number of words separated by whitespace
sha256_hash string SHA-256 hash for unique identification
character_frequency_map object Character-to-count mapping

Testing Examples

Using Postman 

# Create a string
POST http://localhost:3000/strings \
  -H "Content-Type: application/json" \
  -d '{"value": "racecar"}'

# Get a string
http://localhost:3000/strings/ameh%20mathias

# Get palindromes
"http://localhost:3000/strings?is_palindrome=true"

# Natural language query
"http://localhost:3000/strings/filter-by-natural-language?query=single%20word%20palindromic%20strings"

# Delete a string
DELETE http://localhost:3000/strings/ameh%20mathias
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Common status codes:

  • 400 - Bad Request (invalid input)
  • 404 - Not Found (resource doesn't exist)
  • 409 - Conflict (duplicate resource)
  • 422 - Unprocessable Entity (invalid data type)
  • 500 - Internal Server Error

View the Github Link

App is live at String Analysis API

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