feat: wrote smart contract for fund request for project milestone

[davedumto]

🎯 Implement Standalone FundRequest Smart Contract

closes #99

📚 Overview

This PR implements a comprehensive standalone FundRequest smart contract in Cairo for the BudgetChain project. The contract manages fund requests tied to project milestones with robust validation, access controls, and automatic budget updates.

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✅ Issue Requirements Satisfied

1. Data Structures & Storage

• FundRequest struct with all required fields:

  • project_id: u64
  • milestone_id: u64
  • amount: u128
  • requester: ContractAddress
  • status: FundRequestStatus (Pending, Approved, Rejected)

• Events defined:

  • FundsRequested(project_id, request_id, milestone_id)
  • FundsReleased(project_id, request_id, milestone_id, amount)
  • FundsReturned(project_id, amount, project_owner)

• Storage setup includes:

  • Fund request mappings
  • Counters
  • Existence tracking

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2. Function Implementation

• create_fund_request: Project owners can create requests only for completed milestones
• approve_fund_request: Authorized approvers can approve requests and release funds
• reject_fund_request: Authorized approvers can reject pending requests
• Automatic project budget updates upon approval

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3. Validation & Access Control

• Milestone completion verification
• Multi-role access control:
  • Project owners: Create fund requests
  • Authorized approvers: Approve/reject requests
  • Contract owner: Manage approver permissions
• Request status validation (only pending requests can be modified)
• Input validation: Amount checks, zero address protection

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4. Event Emission

• FundsRequested: Emitted when a request is created
• FundsReleased: Emitted when funds are released
• FundsReturned: Defined and ready for future use

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🏗️ Technical Implementation

Core Architecture

trait IFundRequest<TContractState> {
    fn create_fund_request(ref self: TContractState, project_id: u64, milestone_id: u64, amount: u128) -> u64;
    fn approve_fund_request(ref self: TContractState, request_id: u64);
    fn reject_fund_request(ref self: TContractState, request_id: u64);
    // ... additional admin and getter functions
}

trait IProjectContract<TContractState> {
    fn is_milestone_completed(self: @TContractState, project_id: u64, milestone_id: u64) -> bool;
    fn get_project_owner(self: @TContractState, project_id: u64) -> ContractAddress;
    fn update_project_budget(ref self: TContractState, project_id: u64, amount: u128);
}

Security Features

• 🔒 Multi-layer authorization with role-based control
• 🛡️ Storage safety via existence tracking
• ⚡ Comprehensive input validation
• 🔐 Status protection to prevent invalid transitions

Key Technical Decisions

• Storage optimization via request_exists mapping
• Modular access control system
• Event-driven architecture
• Interface segregation for clarity

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🧪 Testing Coverage

Core Functionality

• ✅ Contract deployment and initialization
• ✅ Fund request creation with validation
• ✅ Approval and rejection workflows
• ✅ Status transitions

Security Tests

• ✅ Zero address validation
• ✅ Unauthorized access checks
• ✅ Invalid amount handling
• ✅ Non-existent request handling

Access Control

• ✅ Authorized approver management
• ✅ Owner-only function enforcement
• ✅ Project owner verification
• ✅ Multi-role permissions

Edge Cases

• ✅ Request existence verification
• ✅ Status transition validation
• ✅ Uninitialized data protection

Test Results:

• Tests run: 14
• Passed: 14
• Failed: 0
• Skipped: 0

---

📁 Files Added/Modified

New Files:

• src/fund_request.cairo: Main contract
• src/lib.cairo: Interfaces & exports
• tests/test_fund_request.cairo: Full test suite
• scripts/deploy.sh: Deployment automation

Configuration:

• Scarb.toml: Cairo project setup
• snfoundry.toml: Test configuration

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🚀 Integration Points

External Dependencies

• Validates milestone completion using IProjectContract
• Ensures only project owners create requests
• Updates budgets upon approval

Event Integration

• Emits events for state changes
• Supports frontend, auditing, and notifications

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🛡️ Security Considerations

Access Control Matrix

Function	Project Owner	Authorized Approver	Contract Owner	Public
create_fund_request	✅	❌	❌	❌
approve_fund_request	❌	✅	✅	❌
reject_fund_request	❌	✅	✅	❌
add_authorized_approver	❌	❌	✅	❌
Getters	✅	✅	✅	✅

Validation Layers

• Input validation on all parameters
• Authorization checks on all sensitive actions
• Status & state validations
• Business logic enforcement (milestone & ownership checks)

---

📋 Deployment Instructions

Build the contract:

cd budgetchain-app/onchain/budget_contract
scarb build

Run tests:

snforge test

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🔄 Future Enhancements

• Fund return functionality (FundsReturned event prepared)
• Batch request processing
• Multi-signature approval flows
• Time-based request expiration handling

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✅ Checklist

• All issue requirements implemented
• Comprehensive test coverage (14 passing tests)
• Security considerations addressed
• Documentation and comments added
• Integration interfaces defined
• Deployment scripts included
• Error handling implemented
• Events emitted for all state changes
• Access control fully implemented
• Cairo best practices followed

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🎯 Impact

This implementation provides BudgetChain with:

• Secure fund management tied to project milestones
• Full audit trail via comprehensive events
• Flexible, role-based authorization system
• Production-ready smart contract with full test coverage
• Seamless integration with project management systems

##Screenshots

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Name	Status	Preview	Comments	Updated (UTC)
budget-chain	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 30, 2025 4:32pm