main.py

from fastapi import FastAPI, Path, HTTPException, Query
from fastapi.responses import JSONResponse
from pydantic import BaseModel, Field
from typing import Annotated, Optional
import json
app = FastAPI()

class Customer (BaseModel):
    id : Annotated[int, Field(...,description='ID of the customer', examples=[1,2,3])]
    name : Annotated[str,Field(...,description='Name of the customer', min_length=5)]
    amount : Annotated[int,Field(...,description='Total Loan Amount',gt=0)]
    status : Annotated[str,Field(...,description='Status of the loan')]
    city : Annotated[str,Field(...,description='City of the customer')]


class Customer_update(BaseModel):
    name : Annotated[Optional[str],Field(default=None,description='Name of the customer', min_length=5)]
    amount : Annotated[Optional[int],Field(default=None,description='Total Loan Amount',gt=0)]
    status : Annotated[Optional[str],Field(default=None,description='Status of the loan')]
    city : Annotated[Optional[str],Field(default=None,description='City of the customer')]


def getData():
    with open('test.json', 'r') as f:
        return json.load(f)

def saveData(data):
    with open('test.json','w') as f:
        json.dump(data,f)


@app.get('/')
def hello():
    return {'message' : 'This is a Loan Managment System API'}

@app.get('/about')
def aboutInfo():
    return {'message' : 'This is an API to manage your customers loans'}

@app.get('/customers')
def getUsers():
    data = getData()
    return data

@app.get('/customers/{customer_id}')
def viewCustomer(customer_id : int = Path(description='To access specific customer via an ID')):
    data = getData()

    target_idx = None

    for idx, customer in enumerate(data):
        if customer['id'] == customer_id :
            target_idx = idx
            break

    if target_idx != None :
        return data[target_idx]
    raise HTTPException(status_code= 404, detail='error : customer not found')


@app.get('/sort')
def sort_customers(sort_by: str = Query(...,description='Sort on amount or id'), order_by : str = Query('asc',description='asc or desc')) :

    if sort_by not in ['amount','id']:
        raise HTTPException(status_code= 400, detail='Invalid sort by field, select ONLY from amount or id')
    
    if order_by not in ['asc','desc']:
        raise HTTPException(status_code= 400, detail='Invalid order by field,select ONLY from asc or desc')
    
    data = getData()

    order = True if order_by=='desc' else False
    sorted_data = sorted(data, key= lambda x: x.get(sort_by,0), reverse= order)
    return sorted_data

@app.post('/create')
def create_customer(customer : Customer):
    data = getData()

    if any(item['id'] == customer.id for item in data ):
        raise HTTPException(400,detail='Customer already exists')
    
    data.append(customer.model_dump())
    
    saveData(data)

    return JSONResponse(status_code=201,content={'message':'Customer created Successfully'})

@app.put('/edit/{customer_id}')
def update_customer(customer_id : int, customer_update : Customer_update):
    data = getData()
    if not any (item['id'] == customer_id for item in data):
        raise HTTPException(status_code=404, detail='customer does not exist')
    
    target_idx = None
    for idx, customer in enumerate(data):
        if customer['id'] == customer_id :
            target_idx = idx
            break
    existing_customer_info = data[target_idx]

    updated_customer_info = customer_update.model_dump(exclude_unset=True)

    for key, value in updated_customer_info.items():
        existing_customer_info[key] = value

    existing_customer_info['id'] = customer_id
    customer_pydantic_obj = Customer(**existing_customer_info)

    existing_customer_info = customer_pydantic_obj.model_dump()

    data[target_idx] = existing_customer_info

    saveData(data)

    return JSONResponse(status_code=200,content={'message' : 'customer updated'})

@app.delete('/delete/{customer_id}')
def delete_customer(customer_id : int):
    data = getData()
    if not any(item['id'] == customer_id for item in data):
        raise HTTPException(status_code=404, detail='Customer does not exist')
    
    target_idx = None
    for idx,customer in enumerate(data):
        if customer['id'] == customer_id:
            target_idx = idx
            break

    del data[target_idx]
    saveData(data)
    return JSONResponse(status_code=200, content={'message' : 'Customer deleted successfully'})