using System.Collections;
using System.Globalization;
using System.Text.RegularExpressions;
using MeetingAssistant.MeetingNotes;
using NCalc;

namespace MeetingAssistant.Workflow;

public interface IMeetingWorkflowEngine
{
    Task RunAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken);

    Task<string> TransformTranscriptLineAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken);

    Task<string> TransformAttendeeAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        return Task.FromResult(workflowEvent.AttendeeName ?? "");
    }
}

public sealed class NoopMeetingWorkflowEngine : IMeetingWorkflowEngine
{
    public static NoopMeetingWorkflowEngine Instance { get; } = new();

    public Task RunAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        return Task.CompletedTask;
    }

    public Task<string> TransformTranscriptLineAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        return Task.FromResult(workflowEvent.TranscriptLineText ?? "");
    }

    public Task<string> TransformAttendeeAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        return Task.FromResult(workflowEvent.AttendeeName ?? "");
    }
}

public sealed class MeetingWorkflowEngine : IMeetingWorkflowEngine
{
    private static readonly string[] ParameterNames =
    [
        "meeting.attendees.count",
        "meeting.attendees",
        "meeting.projects",
        "meeting.title",
        "meeting.state",
        "event.type",
        "state.from",
        "state.to",
        "speaker.name",
        MeetingWorkflowRuleSchema.PropertyTranscriptLine,
        MeetingWorkflowRuleSchema.ParameterTranscriptSpeaker,
        MeetingWorkflowRuleSchema.PropertyAttendeeName
    ];

    private readonly IMeetingWorkflowRulesProvider rulesProvider;
    private readonly IMeetingNoteStore meetingNoteStore;
    private readonly IMeetingArtifactStore meetingArtifactStore;
    private readonly ILogger<MeetingWorkflowEngine> logger;
    private readonly MeetingWorkflowTemplateRenderer templateRenderer = new();

    public MeetingWorkflowEngine(
        IMeetingWorkflowRulesProvider rulesProvider,
        IMeetingNoteStore meetingNoteStore,
        IMeetingArtifactStore meetingArtifactStore,
        ILogger<MeetingWorkflowEngine> logger)
    {
        this.rulesProvider = rulesProvider;
        this.meetingNoteStore = meetingNoteStore;
        this.meetingArtifactStore = meetingArtifactStore;
        this.logger = logger;
    }

    public async Task RunAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        _ = await RunCoreAsync(workflowEvent, options, cancellationToken);
    }

    public async Task<string> TransformTranscriptLineAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        if (workflowEvent.Type != MeetingWorkflowEventType.TranscriptLine)
        {
            throw new ArgumentException("Workflow event must be a transcript line event.", nameof(workflowEvent));
        }

        return await RunCoreAsync(workflowEvent, options, cancellationToken)
            ?? workflowEvent.TranscriptLineText
            ?? "";
    }

    public async Task<string> TransformAttendeeAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        if (workflowEvent.Type != MeetingWorkflowEventType.AttendeeAdded)
        {
            throw new ArgumentException("Workflow event must be an attendee added event.", nameof(workflowEvent));
        }

        return await RunCoreAsync(workflowEvent, options, cancellationToken)
            ?? workflowEvent.AttendeeName
            ?? "";
    }

    private async Task<string?> RunCoreAsync(
        MeetingWorkflowEvent workflowEvent,
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        var rules = await rulesProvider.GetRulesAsync(options, cancellationToken);
        var context = new MeetingWorkflowExecutionContext(workflowEvent);
        if (rules.Count == 0)
        {
            return context.ResultValue;
        }

        var meeting = await meetingNoteStore.ReadAsync(
            workflowEvent.Artifacts.MeetingNotePath,
            cancellationToken);
        var noteChanged = false;

        foreach (var rule in rules)
        {
            try
            {
                if (!MatchesTrigger(rule, workflowEvent) ||
                    !EvaluateConditions(rule.If, meeting, context))
                {
                    continue;
                }

                logger.LogInformation(
                    "Triggered meeting workflow rule {RuleName} for event {EventType}",
                    rule.Name,
                    workflowEvent.Type);
                var ruleNoteChanged = false;
                var originalTranscriptLine = context.TranscriptLine;
                var model = CreateTemplateModel(meeting, context);
                foreach (var step in rule.Steps)
                {
                    if (workflowEvent.Type == MeetingWorkflowEventType.AttendeeAdded &&
                        !IsAttendeeTransformStep(step))
                    {
                        throw new InvalidOperationException(
                            "attendee_added workflow rules can only transform attendee.name with set_property.");
                    }

                    var stepChanged = await ApplyStepAsync(
                        step,
                        meeting,
                        context,
                        options,
                        model,
                        cancellationToken);
                    ruleNoteChanged |= stepChanged;
                    noteChanged |= stepChanged;
                    model = CreateTemplateModel(meeting, context);
                }

                logger.LogInformation(
                    "Completed meeting workflow rule {RuleName} for event {EventType}; noteChanged={NoteChanged}, transcriptLineChanged={TranscriptLineChanged}",
                    rule.Name,
                    workflowEvent.Type,
                    ruleNoteChanged,
                    !string.Equals(originalTranscriptLine, context.TranscriptLine, StringComparison.Ordinal));
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
                throw;
            }
            catch (Exception exception)
            {
                logger.LogError(
                    exception,
                    "Meeting workflow rule {RuleName} failed for event {EventType}",
                    rule.Name,
                    workflowEvent.Type);
                throw;
            }
        }

        if (noteChanged)
        {
            var saved = await meetingNoteStore.SaveAsync(meeting, options, cancellationToken);
            await meetingArtifactStore.UpdateAssistantContextMeetingAsync(
                workflowEvent.Artifacts,
                saved,
                cancellationToken);
        }

        return context.ResultValue;
    }

    private static bool MatchesTrigger(
        MeetingWorkflowRule rule,
        MeetingWorkflowEvent workflowEvent)
    {
        if (rule.On.Count == 0)
        {
            return false;
        }

        return rule.On.Any(trigger => MatchesTrigger(trigger, workflowEvent));
    }

    private static bool MatchesTrigger(
        MeetingWorkflowTrigger trigger,
        MeetingWorkflowEvent workflowEvent)
    {
        if (trigger.Created is not null)
        {
            return workflowEvent.Type == MeetingWorkflowEventType.Created;
        }

        if (trigger.StateTransition is not null)
        {
            return workflowEvent.Type == MeetingWorkflowEventType.StateTransition &&
                workflowEvent.FromState is { } from &&
                workflowEvent.ToState is { } to &&
                MeetingWorkflowStateNames.EqualsRuleName(from, trigger.StateTransition.From) &&
                MeetingWorkflowStateNames.EqualsRuleName(to, trigger.StateTransition.To);
        }

        if (trigger.SpeakerIdentified is not null)
        {
            return workflowEvent.Type == MeetingWorkflowEventType.SpeakerIdentified &&
                (string.IsNullOrWhiteSpace(trigger.SpeakerIdentified.Name) ||
                    string.Equals(
                        trigger.SpeakerIdentified.Name.Trim(),
                        workflowEvent.SpeakerName,
                        StringComparison.OrdinalIgnoreCase));
        }

        if (trigger.TranscriptLine is not null)
        {
            return workflowEvent.Type == MeetingWorkflowEventType.TranscriptLine &&
                (string.IsNullOrWhiteSpace(trigger.TranscriptLine.Speaker) ||
                    string.Equals(
                        trigger.TranscriptLine.Speaker.Trim(),
                        workflowEvent.SpeakerName,
                        StringComparison.OrdinalIgnoreCase));
        }

        if (trigger.AttendeeAdded is not null)
        {
            return workflowEvent.Type == MeetingWorkflowEventType.AttendeeAdded &&
                MatchesAttendeeAddedTrigger(trigger.AttendeeAdded, workflowEvent.AttendeeName);
        }

        return false;
    }

    private static bool MatchesAttendeeAddedTrigger(
        MeetingWorkflowAttendeeAddedTrigger trigger,
        string? attendeeName)
    {
        var attendee = attendeeName ?? "";
        if (!string.IsNullOrWhiteSpace(trigger.EqualsValue) &&
            !string.Equals(attendee, trigger.EqualsValue.Trim(), StringComparison.OrdinalIgnoreCase))
        {
            return false;
        }

        if (!string.IsNullOrWhiteSpace(trigger.Contains) &&
            !attendee.Contains(trigger.Contains.Trim(), StringComparison.OrdinalIgnoreCase))
        {
            return false;
        }

        if (!string.IsNullOrWhiteSpace(trigger.Regex) &&
            !Regex.IsMatch(attendee, trigger.Regex, RegexOptions.IgnoreCase))
        {
            return false;
        }

        return true;
    }

    private bool EvaluateConditions(
        IReadOnlyList<MeetingWorkflowCondition> conditions,
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context)
    {
        return conditions.Count == 0 ||
            conditions.All(condition => EvaluateCondition(condition, meeting, context));
    }

    private bool EvaluateCondition(
        MeetingWorkflowCondition condition,
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context)
    {
        if (!string.IsNullOrWhiteSpace(condition.Condition))
        {
            return EvaluateExpression(condition.Condition, meeting, context);
        }

        if (condition.And is { Count: > 0 })
        {
            return condition.And.All(child => EvaluateCondition(child, meeting, context));
        }

        if (condition.Or is { Count: > 0 })
        {
            return condition.Or.Any(child => EvaluateCondition(child, meeting, context));
        }

        if (condition.Not is not null)
        {
            return !EvaluateCondition(condition.Not, meeting, context);
        }

        return true;
    }

    private bool EvaluateExpression(
        string expressionText,
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context)
    {
        var expression = new Expression(PrepareExpression(expressionText));
        foreach (var (name, value) in BuildParameters(meeting, context))
        {
            expression.Parameters[name] = value;
        }

        expression.Functions["contains"] = args =>
            Contains(args.Evaluate(0), Convert.ToString(args.Evaluate(1), CultureInfo.InvariantCulture));
        expression.Functions["starts_with"] = args =>
            Convert.ToString(args.Evaluate(0), CultureInfo.InvariantCulture)?.StartsWith(
                Convert.ToString(args.Evaluate(1), CultureInfo.InvariantCulture) ?? "",
                StringComparison.OrdinalIgnoreCase) == true;
        expression.Functions["ends_with"] = args =>
            Convert.ToString(args.Evaluate(0), CultureInfo.InvariantCulture)?.EndsWith(
                Convert.ToString(args.Evaluate(1), CultureInfo.InvariantCulture) ?? "",
                StringComparison.OrdinalIgnoreCase) == true;

        return Convert.ToBoolean(expression.Evaluate(), CultureInfo.InvariantCulture);
    }

    private async Task<bool> ApplyStepAsync(
        MeetingWorkflowStep step,
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context,
        MeetingAssistantOptions options,
        MeetingWorkflowTemplateModel model,
        CancellationToken cancellationToken)
    {
        var value = await RenderValueAsync(step.Value ?? "", model);
        switch (step.Uses.Trim().ToLowerInvariant())
        {
            case MeetingWorkflowRuleSchema.StepAddAttendee:
                var attendee = await TransformAttendeeAsync(
                    MeetingWorkflowEvent.AttendeeAdded(context.Event.Artifacts, value),
                    options,
                    cancellationToken);
                return AddUnique(meeting.Frontmatter.Attendees, attendee, MeetingAttendeeNames.NormalizeDisplayName);
            case MeetingWorkflowRuleSchema.StepRemoveAttendee:
                return RemoveValue(meeting.Frontmatter.Attendees, value);
            case MeetingWorkflowRuleSchema.StepAddProject:
                return AddUnique(meeting.Frontmatter.Projects, value, static project => project.Trim());
            case MeetingWorkflowRuleSchema.StepAddContext:
                await meetingArtifactStore.AppendAssistantContextAsync(
                    context.Event.Artifacts,
                    value,
                    cancellationToken);
                return false;
            case MeetingWorkflowRuleSchema.StepSetProperty when IsTranscriptLineProperty(step.Property ?? step.Name):
                SetTranscriptLine(context, value);
                return false;
            case MeetingWorkflowRuleSchema.StepSetProperty when IsAttendeeNameProperty(step.Property ?? step.Name):
                SetAttendeeName(context, value);
                return false;
            case MeetingWorkflowRuleSchema.StepSetProperty:
                return SetProperty(meeting, step.Property ?? step.Name, value);
            default:
                throw new InvalidOperationException($"Unknown meeting workflow step '{step.Uses}'.");
        }
    }

    private async Task<string> RenderValueAsync(
        string template,
        MeetingWorkflowTemplateModel model)
    {
        return await templateRenderer.RenderAsync(template, model);
    }

    private static bool SetProperty(
        MeetingNote meeting,
        string? property,
        string value)
    {
        var normalized = property?.Trim().ToLowerInvariant();
        if (normalized is MeetingWorkflowRuleSchema.PropertyTitle or MeetingWorkflowRuleSchema.PropertyMeetingTitle)
        {
            if (string.Equals(meeting.Frontmatter.Title, value, StringComparison.Ordinal))
            {
                return false;
            }

            meeting.Frontmatter.Title = value;
            return true;
        }

        throw new InvalidOperationException($"Unsupported meeting workflow property '{property}'.");
    }

    private static void SetTranscriptLine(
        MeetingWorkflowExecutionContext context,
        string value)
    {
        if (context.Event.Type != MeetingWorkflowEventType.TranscriptLine)
        {
            throw new InvalidOperationException("The transcript.line property can only be set during transcript_line events.");
        }

        if (string.Equals(context.TranscriptLine, value, StringComparison.Ordinal))
        {
            return;
        }

        context.TranscriptLine = value;
    }

    private static void SetAttendeeName(
        MeetingWorkflowExecutionContext context,
        string value)
    {
        if (context.Event.Type != MeetingWorkflowEventType.AttendeeAdded)
        {
            throw new InvalidOperationException("The attendee.name property can only be set during attendee_added events.");
        }

        if (string.Equals(context.AttendeeName, value, StringComparison.Ordinal))
        {
            return;
        }

        context.AttendeeName = value;
    }

    private static bool IsTranscriptLineProperty(string? property)
    {
        return MeetingWorkflowRuleSchema.IsProperty(property, MeetingWorkflowRuleSchema.PropertyTranscriptLine);
    }

    private static bool IsAttendeeNameProperty(string? property)
    {
        return MeetingWorkflowRuleSchema.IsProperty(property, MeetingWorkflowRuleSchema.PropertyAttendeeName);
    }

    private static bool IsAttendeeTransformStep(MeetingWorkflowStep step)
    {
        return MeetingWorkflowRuleSchema.IsStep(step.Uses, MeetingWorkflowRuleSchema.StepSetProperty) &&
            IsAttendeeNameProperty(step.Property ?? step.Name);
    }

    private static bool AddUnique(
        List<string> values,
        string value,
        Func<string, string> normalize)
    {
        var normalized = normalize(value);
        if (string.IsNullOrWhiteSpace(normalized) ||
            values.Any(existing => string.Equals(
                normalize(existing),
                normalized,
                StringComparison.OrdinalIgnoreCase)))
        {
            return false;
        }

        values.Add(normalized);
        return true;
    }

    private static bool RemoveValue(List<string> values, string value)
    {
        var normalized = MeetingAttendeeNames.NormalizeDisplayName(value);
        return values.RemoveAll(existing =>
            string.Equals(
                MeetingAttendeeNames.NormalizeDisplayName(existing),
                normalized,
                StringComparison.OrdinalIgnoreCase)) > 0;
    }

    private static bool Contains(object? haystack, string? needle)
    {
        if (string.IsNullOrEmpty(needle))
        {
            return true;
        }

        if (haystack is IEnumerable enumerable and not string)
        {
            return enumerable
                .Cast<object?>()
                .Select(item => Convert.ToString(item, CultureInfo.InvariantCulture))
                .Any(item => string.Equals(item, needle, StringComparison.OrdinalIgnoreCase));
        }

        return Convert.ToString(haystack, CultureInfo.InvariantCulture)?.Contains(
            needle,
            StringComparison.OrdinalIgnoreCase) == true;
    }

    private static string PrepareExpression(string expression)
    {
        var prepared = expression;
        foreach (var parameter in ParameterNames.OrderByDescending(name => name.Length))
        {
            prepared = Regex.Replace(
                prepared,
                $@"(?<![\[\w.]){Regex.Escape(parameter)}(?![\]\w.])",
                $"[{parameter}]",
                RegexOptions.IgnoreCase);
        }

        return prepared;
    }

    private static IReadOnlyDictionary<string, object?> BuildParameters(
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context)
    {
        var workflowEvent = context.Event;
        return new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase)
        {
            ["meeting.attendees.count"] = meeting.Frontmatter.Attendees.Count,
            ["meeting.attendees"] = meeting.Frontmatter.Attendees,
            ["meeting.projects"] = meeting.Frontmatter.Projects,
            ["meeting.title"] = meeting.Frontmatter.Title,
            ["meeting.state"] = workflowEvent.ToState is { } state ? MeetingWorkflowStateNames.ToRuleName(state) : "",
            ["event.type"] = workflowEvent.Type.ToString(),
            ["state.from"] = workflowEvent.FromState is { } from ? MeetingWorkflowStateNames.ToRuleName(from) : "",
            ["state.to"] = workflowEvent.ToState is { } to ? MeetingWorkflowStateNames.ToRuleName(to) : "",
            ["speaker.name"] = workflowEvent.SpeakerName,
            [MeetingWorkflowRuleSchema.PropertyTranscriptLine] = context.TranscriptLine ?? "",
            [MeetingWorkflowRuleSchema.ParameterTranscriptSpeaker] = workflowEvent.SpeakerName ?? "",
            [MeetingWorkflowRuleSchema.PropertyAttendeeName] = context.AttendeeName ?? ""
        };
    }

    private static MeetingWorkflowTemplateModel CreateTemplateModel(
        MeetingNote meeting,
        MeetingWorkflowExecutionContext context)
    {
        var workflowEvent = context.Event;
        return new MeetingWorkflowTemplateModel(
            new MeetingWorkflowMeetingModel(
                meeting.Frontmatter.Title,
                meeting.Frontmatter.Attendees,
                meeting.Frontmatter.Projects,
                workflowEvent.ToState is { } state ? MeetingWorkflowStateNames.ToRuleName(state) : ""),
            new MeetingWorkflowEventModel(
                workflowEvent.Type.ToString(),
                workflowEvent.FromState is { } from ? MeetingWorkflowStateNames.ToRuleName(from) : null,
                workflowEvent.ToState is { } to ? MeetingWorkflowStateNames.ToRuleName(to) : null),
            string.IsNullOrWhiteSpace(workflowEvent.SpeakerName)
                ? null
                : new MeetingWorkflowSpeakerModel(workflowEvent.SpeakerName),
            new MeetingWorkflowTranscriptModel(
                context.TranscriptLine ?? "",
                workflowEvent.SpeakerName ?? ""),
            string.IsNullOrWhiteSpace(context.AttendeeName)
                ? null
                : new MeetingWorkflowAttendeeModel(context.AttendeeName));
    }

    private sealed class MeetingWorkflowExecutionContext
    {
        public MeetingWorkflowExecutionContext(MeetingWorkflowEvent workflowEvent)
        {
            Event = workflowEvent;
            TranscriptLine = workflowEvent.TranscriptLineText;
            AttendeeName = workflowEvent.AttendeeName;
        }

        public MeetingWorkflowEvent Event { get; }

        public string? TranscriptLine { get; set; }

        public string? AttendeeName { get; set; }

        public string? ResultValue
        {
            get
            {
                return Event.Type == MeetingWorkflowEventType.AttendeeAdded
                    ? AttendeeName
                    : TranscriptLine;
            }
        }
    }
}