PreviousProposalExtractor.swift

// This source file is part of the Swift.org open source project
//
// Copyright (c) 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors

import Markdown
import EvolutionMetadataModel

struct PreviousProposalExtractor: MarkupWalker, ValueExtractor {

    private var source: HeaderFieldSource
    init(source: HeaderFieldSource) { self.source = source }

    private var issues = IssueWrapper()
    private var previousProposalIDs: [String]? {
        _previousProposalIDs.isEmpty ? nil : _previousProposalIDs
    }
    private var _previousProposalIDs: [String] = []

    mutating func extractValue() -> ExtractionResult<[String]> {
        
        if let prevPropField = source["Previous Proposal", "Previous Proposals"] {
            visit(prevPropField.value)
            
            // validate that if the header field is here at least one proposal ID was found
            if _previousProposalIDs.isEmpty {
                issues.reportIssue(.previousProposalIDsExtractionFailure, source: source)
            }
        }
        
        return ExtractionResult(value: previousProposalIDs, warnings: issues.warnings, errors: issues.errors)
    }
    
    mutating func visitText(_ text: Text) -> () {
        // VALIDATION ENHANCEMENT: Potentially look for missing links or text that does not include a proposal ID
        for match in text.string.matches(of: /SE-\d{4}/) {
            _previousProposalIDs.append(String(match.0))
        }
    }
}