using Core.Entities;
using Core.Models;
using FuzzySharp;

namespace Core.Parsers;

public class StudentEventRankingParser : CsvParserBase
{
    public const int EventMatchThreshold = 70;
    public const int EventAmbiguityGap = 8;

    /// <summary>
    /// Informal names that share too little text with the catalog for fuzzy matching.
    /// Keyed by official <see cref="EventDefinition.Name"/>.
    /// </summary>
    private static readonly Dictionary<string, string[]> EventAliases = new(StringComparer.OrdinalIgnoreCase)
    {
        ["Junior Solar Sprint"] = ["Solar Racer", "Solar Race"],
        ["Challenging Technology Issues"] = ["Challenging Tech", "Challenging Technology"],
        ["Digital Photography"] = ["Digital Photo"],
        ["Forensic Technology"] = ["Forensics", "Forensic"],
        ["Microcontroller Design"] = ["Micro Controller", "Micro Controller Design"],
        ["Medical Technology"] = ["Med Tech"],
        ["Inventions & Innovations"] = ["Innovations & Inventions", "Inventions and Innovations"],
        ["System Control Technology"] = ["Systems Control Tech", "Systems Control Technology"],
        ["Structural Engineering"] = ["Structural Eng"],
        ["Drone Challenge (UAV)"] = ["Drone Challenge", "Drone"],
        ["Drone Challenge"] = ["Drone Challenge (UAV)", "Drone"],
        ["TSA Robotics"] = ["Robotics"],
        ["Audio Podcasting"] = ["Audio Podcast", "Podcasting"]
    };

    public StudentEventRankingParser(FileSystemInfo csvFile, bool ignoreBlankLines = true) : base(csvFile, ignoreBlankLines)
    {
    }

    public StudentEventRankingParser(StreamReader reader, bool ignoreBlankLines = true) : base(reader, ignoreBlankLines)
    {
    }

    public StudentEventRankingParseResult Parse(ICollection<Student> students, ICollection<EventDefinition> events)
    {
        var result = new StudentEventRankingParseResult();

        CsvReader.Read();
        CsvReader.ReadHeader();

        if (CsvReader.HeaderRecord is null ||
            !CsvReader.HeaderRecord.Contains("Student Name", StringComparer.OrdinalIgnoreCase))
        {
            result.Errors.Add("CSV must include a 'Student Name' column.");
            return result;
        }

        while (CsvReader.Read())
        {
            var rowNumber = CsvReader.Context.Parser?.Row ?? 0;
            var name = CsvReader.GetField("Student Name")?.Trim();
            if (string.IsNullOrEmpty(name))
                continue;

            var studentMatch = FuzzyStudentMatcher.Find(students, name);
            if (studentMatch is null)
            {
                result.Issues.Add(new StudentEventRankingIssue
                {
                    RowNumber = rowNumber,
                    RawStudentName = name,
                    IssueType = StudentEventRankingIssueType.UnmatchedStudent,
                    Message = $"No student matched '{name}'."
                });
                continue;
            }

            var (student, studentScore) = studentMatch.Value;
            var acceptedEventsForStudent = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
            var acceptedRanksForStudent = new HashSet<int>();

            for (var rank = 1; rank <= StudentEventRanking.MaxRank; rank++)
            {
                var eventName = CsvReader.GetField(rank.ToString())?.Trim();
                if (string.IsNullOrEmpty(eventName))
                    continue;

                var eventResolution = ResolveEvent(events, eventName);
                if (eventResolution.Status == EventMatchStatus.Unmatched)
                {
                    result.Issues.Add(new StudentEventRankingIssue
                    {
                        RowNumber = rowNumber,
                        Rank = rank,
                        RawStudentName = name,
                        RawEventName = eventName,
                        IssueType = StudentEventRankingIssueType.UnmatchedEvent,
                        Message = $"No event matched '{eventName}' for {student.FirstNameLastName} (rank {rank}).",
                        SuggestedEventName = eventResolution.BestEvent?.Name,
                        Score = eventResolution.BestScore
                    });
                    continue;
                }

                if (eventResolution.Status == EventMatchStatus.Ambiguous)
                {
                    result.Issues.Add(new StudentEventRankingIssue
                    {
                        RowNumber = rowNumber,
                        Rank = rank,
                        RawStudentName = name,
                        RawEventName = eventName,
                        IssueType = StudentEventRankingIssueType.AmbiguousEvent,
                        Message = $"'{eventName}' is ambiguous between '{eventResolution.BestEvent?.Name}' and '{eventResolution.RunnerUpEvent?.Name}' for {student.FirstNameLastName} (rank {rank}).",
                        SuggestedEventName = eventResolution.BestEvent?.Name,
                        Score = eventResolution.BestScore
                    });
                    continue;
                }

                var matchedEvent = eventResolution.BestEvent!;
                if (!acceptedEventsForStudent.Add($"{matchedEvent.Id}:{matchedEvent.Name}"))
                {
                    result.Issues.Add(new StudentEventRankingIssue
                    {
                        RowNumber = rowNumber,
                        Rank = rank,
                        RawStudentName = name,
                        RawEventName = eventName,
                        IssueType = StudentEventRankingIssueType.DuplicateEvent,
                        Message = $"{student.FirstNameLastName} already has '{matchedEvent.Name}' in this file.",
                        SuggestedEventName = matchedEvent.Name,
                        Score = eventResolution.BestScore
                    });
                    continue;
                }

                if (!acceptedRanksForStudent.Add(rank))
                {
                    result.Issues.Add(new StudentEventRankingIssue
                    {
                        RowNumber = rowNumber,
                        Rank = rank,
                        RawStudentName = name,
                        RawEventName = eventName,
                        IssueType = StudentEventRankingIssueType.DuplicateRank,
                        Message = $"{student.FirstNameLastName} already has a rank {rank} assignment in this file.",
                        SuggestedEventName = matchedEvent.Name,
                        Score = eventResolution.BestScore
                    });
                    continue;
                }

                result.Matches.Add(new StudentEventRankingMatch
                {
                    Ranking = new StudentEventRanking
                    {
                        Student = student,
                        EventDefinition = matchedEvent,
                        Rank = rank
                    },
                    RawStudentName = name,
                    RawEventName = eventName,
                    StudentScore = studentScore,
                    EventScore = eventResolution.BestScore,
                    RowNumber = rowNumber
                });
            }
        }

        if (result.Matches.Count == 0 && result.Errors.Count == 0)
            result.Warnings.Add("No rankings were accepted from the CSV.");

        return result;
    }

    private static EventResolution ResolveEvent(ICollection<EventDefinition> events, string eventName)
    {
        var scored = events
            .Select(e => (Event: e, Score: ScoreEvent(e, eventName)))
            .OrderByDescending(x => x.Score)
            .ToList();

        if (scored.Count == 0)
            return new EventResolution(EventMatchStatus.Unmatched, null, 0, null, 0);

        var best = scored[0];
        var runnerUp = scored.Count > 1 ? scored[1] : default;

        if (best.Score < EventMatchThreshold)
            return new EventResolution(EventMatchStatus.Unmatched, best.Event, best.Score, runnerUp.Event, runnerUp.Score);

        if (runnerUp.Event is not null && best.Score - runnerUp.Score < EventAmbiguityGap)
            return new EventResolution(EventMatchStatus.Ambiguous, best.Event, best.Score, runnerUp.Event, runnerUp.Score);

        return new EventResolution(EventMatchStatus.Matched, best.Event, best.Score, runnerUp.Event, runnerUp.Score);
    }

    private static int ScoreEvent(EventDefinition evt, string eventName)
    {
        List<string> names = [evt.Name];
        if (!string.IsNullOrWhiteSpace(evt.ShortName))
            names.Add(evt.ShortName);
        if (EventAliases.TryGetValue(evt.Name, out var aliases))
            names.AddRange(aliases);

        return names
            .Select(n => new[] { Fuzz.Ratio(n, eventName), Fuzz.TokenSetRatio(n, eventName), Fuzz.PartialRatio(n, eventName) }.Max())
            .DefaultIfEmpty(0)
            .Max();
    }

    private enum EventMatchStatus
    {
        Matched,
        Ambiguous,
        Unmatched
    }

    private readonly record struct EventResolution(
        EventMatchStatus Status,
        EventDefinition? BestEvent,
        int BestScore,
        EventDefinition? RunnerUpEvent,
        int RunnerUpScore);
}