FormFieldMapper.cs

using TXTextControl;

namespace TxFormFieldMapper;

internal sealed class FormFieldMapper(IReadOnlyList<string> jsonFieldNames, double minimumScore)
{
    private const double AmbiguityMargin = 0.08;

    private readonly IReadOnlyList<FieldNameCandidate> _jsonCandidates = jsonFieldNames
        .Distinct(StringComparer.OrdinalIgnoreCase)
        .Select(FieldNameCandidate.Create)
        .ToList();

    public IReadOnlyList<MapResult> RenameFormFields(FormFieldCollection formFields)
    {
        var results = new List<MapResult>();
        var cachedMatches = new Dictionary<string, MatchDecision>(StringComparer.OrdinalIgnoreCase);

        for (var i = 1; i <= formFields.Count; i++)
        {
            var field = formFields[i];
            if (field is null)
            {
                continue;
            }

            var originalName = field.Name ?? string.Empty;
            if (!cachedMatches.TryGetValue(originalName, out var decision))
            {
                decision = FindBestMatch(originalName);
                cachedMatches[originalName] = decision;
            }

            if (decision.ShouldRename && !string.Equals(field.Name, decision.JsonName, StringComparison.Ordinal))
            {
                field.Name = decision.JsonName;
            }

            results.Add(new MapResult(originalName, decision.JsonName, decision.Score, decision.Status));
        }

        return results;
    }

    private MatchDecision FindBestMatch(string formFieldName)
    {
        if (string.IsNullOrWhiteSpace(formFieldName))
        {
            return MatchDecision.Skipped(formFieldName, "skipped: empty field name");
        }

        var source = FieldNameCandidate.Create(formFieldName);
        var scored = _jsonCandidates
            .Select(candidate => new
            {
                Candidate = candidate,
                Score = FieldNameScorer.Score(source, candidate)
            })
            .OrderByDescending(item => item.Score)
            .ToList();

        if (scored.Count == 0)
        {
            return MatchDecision.Skipped(formFieldName, "skipped: no unused JSON fields left");
        }

        var best = scored[0];
        var secondScore = scored.Count > 1 ? scored[1].Score : 0;

        if (best.Score < minimumScore)
        {
            return MatchDecision.Skipped(best.Candidate.Original, "skipped: below threshold");
        }

        if (best.Score < 1 && best.Score - secondScore < AmbiguityMargin)
        {
            return MatchDecision.Skipped(best.Candidate.Original, "skipped: ambiguous");
        }

        var status = string.Equals(formFieldName, best.Candidate.Original, StringComparison.Ordinal)
            ? "already mapped"
            : "renamed";

        return new MatchDecision(best.Candidate.Original, best.Score, status, ShouldRename: true);
    }
}