pragma solidity >=0.8.0;

// SPDX-License-Identifier: AGPL-3.0-or-later

contract AddressDeclarator {

	mapping( address => address[] ) declarationIndex;
	mapping( bytes32 => uint256 ) declarationContentIndex; // the _latest_ content pointer for the declarator to subject mapping
	mapping( address => address[] ) declarator;
	mapping( address => address[] ) declaratorReverse;

	bytes32[][] contents;

	// Implements Declarator
	event DeclarationAdded(address indexed _declarator, address indexed _subject, bytes32 indexed _topic, bytes32 _proof);

	constructor(bytes32 _initial) {
		addDeclaration(address(this),  _initial);
	}

	// Create a digest reference for a declarator and subject pair
	function toReference(address _declarator, address _subject) private pure returns ( bytes32 ) {
		bytes32 k;
		bytes memory addrMaterial = new bytes(40);
		bytes memory addrBytes = abi.encodePacked(_declarator);
		for (uint256 i = 0; i < 20; i++) {
			addrMaterial[i] = addrBytes[i];
		}
		addrBytes = abi.encodePacked(_subject);
		for (uint256 i = 0; i < 20; i++) {
			addrMaterial[i+20] = addrBytes[i];
		}
		k = sha256(addrMaterial);
		return k;
	}

	// Create a digest reference for a declarator and subject pair on top of the given digest
	function toReference(address _declarator, address _subject, bytes32 _digest) private pure returns ( bytes32[2] memory ) {
		bytes32 k;
		bytes32[2] memory ks;
		bytes memory signMaterial = new bytes(64);

		k = toReference(_declarator, _subject);
		for (uint256 i = 0; i < 32; i++) {
			signMaterial[i] = k[i];
		}
		for (uint256 i = 0; i < 32; i++) {
			signMaterial[i+32] = _digest[i];
		}

		ks[0] = k;
		ks[1] = sha256(signMaterial);

		return ks;
	}

	// Implements Declarator
	function declaratorCount(address _subject) public view returns ( uint256 ) {
		return declarator[_subject].length;
	}

	// Implements Declarator
	function declaratorAddressAt(address _subject, uint256 _idx) public view returns ( address ) {
		return declarator[_subject][_idx];
	}

	// Implements Declarator
	function addDeclaration(address _subject, bytes32 _proof, bytes32 _topic) public returns ( bool ) {
		bytes32[2] memory ks;
		bytes32[] memory declarationContents;
		uint256 idx;
		ks = toReference(tx.origin, _subject, _topic);
		idx = declarationContentIndex[ks[1]];
		if (idx == 0) { // This also works for the constructor :)
			declarator[_subject].push(tx.origin);
			contents.push(declarationContents);
			declarationIndex[tx.origin].push(_subject);
			idx = contents.length-1;
		}

		declarationContentIndex[ks[1]] = idx;
		contents[idx].push(_proof);

		return true;
	}

	// Implements Declarator
	function addDeclaration(address _subject, bytes32 _proof) public returns ( bool ) {
		return addDeclaration(_subject, _proof, bytes32(0));
	}

	// Implements Declarator
	function declaration(address _declarator, address _subject) public view returns ( bytes32[] memory ) {
		return declaration(_declarator, _subject, bytes32(0));
	}

	// Implements Declarator
	function declaration(address _declarator, address _subject, bytes32 _topic) public view returns ( bytes32[] memory ) {
		bytes32[2] memory k;
		uint256 idx;
		k = toReference(_declarator, _subject, _topic);
		idx = declarationContentIndex[k[1]];
		return contents[idx];
	}

	// Implements Declarator
	function declarationCount(address _declarator) public view returns ( uint256 ) {
		return declarationIndex[_declarator].length;
	}

	// Implements Declarator
	function declarationAddressAt(address _declarator, uint256 _idx) public view returns ( address ) {
		return declarationIndex[_declarator][_idx];
	}

	// Implements EIP165
	function supportsInterface(bytes4 _sum) public pure returns (bool) {
		if (_sum == 0x21b7493b) { // Implements Declarator
			return true;
		}
		if (_sum == 0x01ffc9a7) { // EIP165
			return true;
		}
		return false;
	}
}