⏳ Fixed-Term ETH Deposit Simulator

A fixed-term deposit smart contract where users can lock ETH for a set duration and automatically earn simple fixed interest upon maturity.

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🧩 Overview

This smart contract simulates a traditional fixed(TradFi) deposit account using Ethereum.

Users deposit ETH for a fixed period. After the term expires, Chainlink Automation detects maturity and automatically triggers a payout of the principal + interest.

This project focuses on time-based automation, state transitions, and decentralized payout scheduling — no randomness, multi-user pooling, or external oracles beyond time and automation.

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🛠️ Features

• ✅ Fixed-term locking – Users deposit ETH that remains locked for a predefined duration.
• 💰 Earn fixed interest – Upon maturity, users receive their deposit plus a simple fixed interest (funded from contract preload for simplicity).
• ⚙️ Chainlink Automation – Automatically calls the payout function when the term ends.
• ⏲️ Time-based logic – Uses block.timestamp for duration tracking.
• 🔒 State control – Transitions from OPEN → LOCKED → PAYING_OUT.
• 🧪 Fully testable – Includes Foundry tests with time manipulation (vm.warp) and upkeep simulation.

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📄 Contract Flow

1. Deposit ETH

   • User calls depositEth() with the required minimum deposit.
   • Contract locks and starts the fixed-term timer.

2. Wait for Term Completion

   • Contract tracks elapsed time using block.timestamp.
   • During this period, ETH remains locked and cannot be withdrawn.

3. Chainlink Automation Check

   • Chainlink Automation regularly calls checkUpkeep() to see if the term has ended.
   • When maturity is reached, performUpkeep() automatically triggers.

4. Payout Execution

   • Contract transitions to the PAYING_OUT state.
   • Payout function releases principal + fixed interest back to the depositor.

5. Reset or End

   • Once payout completes, the contract resets and emits the completed fixed deposit.

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🔧 Constructor Parameters

Parameter	Type	Description
minimumDeposit	uint256	The minimum eth deposit needed to enter the contract.
termPeriod	uint256	Duration (in seconds) of the fixed deposit term.

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⚙️ Example Setup (Local / Anvil)

• Contract is preloaded with 0.1 ETH to fund interest payments.
• Chainlink AutomationRegistrar is mocked locally for testing.
• Foundry test suite uses:
  • vm.warp() to simulate time passing
  • vm.deal() to assign ETH balances
  • vm.recordLogs() to assert Automation-triggered state changes

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🧱 Project Goals

This project demonstrates:

• Automated smart contract execution (via Chainlink Automation)
• Deterministic time-based logic
• Secure payout mechanisms
• Strong test-driven smart contract development

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🧪 Example Test Scenarios

• ✅ User deposits ETH → contract locks funds
• ⏳ Time passes beyond term → upkeep becomes true
• ⚙️ Chainlink Automation triggers payout
• 💸 Payout transfers principal + interest
• 🔁 Contract resets to allow future deposits

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