jobtrackingapp/JobTrackerApi/Controllers/GmailController.cs

using System.Security.Claims;
using JobTrackerApi.Data;
using JobTrackerApi.Models;
using JobTrackerApi.Services;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

namespace JobTrackerApi.Controllers;

[ApiController]
[Route("api/gmail")]
[Authorize]
public sealed class GmailController : ControllerBase
{
    private readonly IGmailOAuthService _gmail;
    private readonly JobTrackerContext _db;
    private readonly IConfiguration _cfg;

    public GmailController(IGmailOAuthService gmail, JobTrackerContext db, IConfiguration cfg)
    {
        _gmail = gmail;
        _db = db;
        _cfg = cfg;
    }

    public sealed record GmailImportResultDto(int Imported, int Skipped, string? ThreadId);
    public sealed record GmailImportMessageResultDto(int Imported, int Skipped, string MessageId, string? ThreadId, Correspondence? Message);
    public sealed record ImportGmailMessageRequest(int JobApplicationId, string MessageId);
    public sealed record ImportGmailThreadRequest(int JobApplicationId, string ThreadId, string[] MessageIds);
    public sealed record GmailJobMatchReasonDto(string Label, string Value, int Points);
    public sealed record GmailJobMatchedMessageDto(
        string Id,
        string ThreadId,
        string Subject,
        string From,
        string To,
        DateTimeOffset? Date,
        string Snippet,
        int Score,
        string Confidence,
        bool AlreadyImported,
        IReadOnlyList<string> MatchedQueries,
        IReadOnlyList<GmailJobMatchReasonDto> MatchReasons);
    public sealed record GmailJobMatchedThreadDto(
        string ThreadId,
        string Subject,
        int Score,
        string Confidence,
        bool HasImportedMessages,
        int ImportedMessageCount,
        int MessageCount,
        DateTimeOffset? LatestDate,
        IReadOnlyList<string> MatchedQueries,
        IReadOnlyList<GmailJobMatchReasonDto> MatchReasons,
        IReadOnlyList<GmailJobMatchedMessageDto> Messages);
    public sealed record GmailJobMatchesResponseDto(
        int JobApplicationId,
        string JobTitle,
        string CompanyName,
        string? RecruiterName,
        string? RecruiterEmail,
        IReadOnlyList<string> Queries,
        int CandidateMessageCount,
        int CandidateThreadCount,
        IReadOnlyList<GmailJobMatchedThreadDto> Threads);

    [HttpGet("status")]
    public async Task<IActionResult> Status(CancellationToken cancellationToken)
    {
        var ownerUserId = GetRequiredOwnerUserId();
        var connection = await _gmail.GetConnectionAsync(ownerUserId, cancellationToken);
        return Ok(new
        {
            connected = connection is not null,
            gmailAddress = connection?.GmailAddress,
            connectedAt = connection?.ConnectedAt,
            lastSyncedAt = connection?.LastSyncedAt,
        });
    }

    [HttpGet("connect-url")]
    public IActionResult ConnectUrl()
    {
        var ownerUserId = GetRequiredOwnerUserId();
        var url = _gmail.BuildAuthorizationUrl(ownerUserId, GetRedirectUri());
        return Ok(new { url });
    }

    [HttpGet("job-candidates")]
    public async Task<ActionResult<GmailJobMatchesResponseDto>> JobCandidates(
        [FromQuery] int jobApplicationId,
        [FromQuery] string? queryOverride,
        [FromQuery] int maxResultsPerQuery = 6,
        CancellationToken cancellationToken = default)
    {
        if (jobApplicationId <= 0) return BadRequest("Valid jobApplicationId is required.");

        var ownerUserId = GetRequiredOwnerUserId();
        var job = await _db.JobApplications
            .Where(x => x.OwnerUserId == ownerUserId)
            .Include(x => x.Company)
            .Include(x => x.Messages)
            .FirstOrDefaultAsync(x => x.Id == jobApplicationId, cancellationToken);
        if (job is null) return NotFound("Job application not found.");

        var queries = BuildJobQueries(job, queryOverride);
        var candidateMessages = await _gmail.ListJobCandidateMessagesAsync(ownerUserId, queries, maxResultsPerQuery, cancellationToken);
        var importedMessageIds = job.Messages
            .Where(message => !string.IsNullOrWhiteSpace(message.ExternalMessageId))
            .Select(message => message.ExternalMessageId!)
            .ToHashSet(StringComparer.Ordinal);
        var importedThreadIds = job.Messages
            .Where(message => !string.IsNullOrWhiteSpace(message.ExternalThreadId))
            .Select(message => message.ExternalThreadId!)
            .ToHashSet(StringComparer.Ordinal);

        var rankedMessages = candidateMessages
            .Select(message => ScoreMessage(job, message, importedMessageIds.Contains(message.Message.Id), importedThreadIds.Contains(message.Message.ThreadId)))
            .Where(result => result.Score > 0 || result.AlreadyImported)
            .OrderByDescending(result => result.Score)
            .ThenByDescending(result => result.Message.Date ?? DateTimeOffset.MinValue)
            .ToList();

        var threads = rankedMessages
            .GroupBy(result => string.IsNullOrWhiteSpace(result.Message.ThreadId) ? result.Message.Id : result.Message.ThreadId, StringComparer.Ordinal)
            .Select(group =>
            {
                var ordered = group
                    .OrderByDescending(item => item.Score)
                    .ThenByDescending(item => item.Message.Date ?? DateTimeOffset.MinValue)
                    .ToList();
                var latestDate = ordered
                    .Select(item => item.Message.Date)
                    .OrderByDescending(item => item ?? DateTimeOffset.MinValue)
                    .FirstOrDefault();
                var combinedReasons = ordered
                    .SelectMany(item => item.Reasons)
                    .GroupBy(reason => new { reason.Label, reason.Value, reason.Points })
                    .Select(reason => reason.First())
                    .OrderByDescending(reason => reason.Points)
                    .ThenBy(reason => reason.Label, StringComparer.Ordinal)
                    .ThenBy(reason => reason.Value, StringComparer.Ordinal)
                    .Take(8)
                    .ToList();
                var matchedQueries = ordered
                    .SelectMany(item => item.MatchedQueries)
                    .Distinct(StringComparer.OrdinalIgnoreCase)
                    .OrderBy(query => query, StringComparer.OrdinalIgnoreCase)
                    .ToList();
                var hasImportedMessages = ordered.Any(item => item.AlreadyImported);
                var importedMessageCount = ordered.Count(item => item.AlreadyImported);
                var threadScore = ordered.Max(item => item.Score) + Math.Min(ordered.Count - 1, 2);
                var representative = ordered[0].Message;

                return new GmailJobMatchedThreadDto(
                    group.Key,
                    string.IsNullOrWhiteSpace(representative.Subject) ? "(no subject)" : representative.Subject,
                    threadScore,
                    ToConfidence(threadScore),
                    hasImportedMessages,
                    importedMessageCount,
                    ordered.Count,
                    latestDate,
                    matchedQueries,
                    combinedReasons,
                    ordered.Select(item => new GmailJobMatchedMessageDto(
                        item.Message.Id,
                        item.Message.ThreadId,
                        item.Message.Subject,
                        item.Message.From,
                        item.Message.To,
                        item.Message.Date,
                        item.Message.Snippet,
                        item.Score,
                        ToConfidence(item.Score),
                        item.AlreadyImported,
                        item.MatchedQueries,
                        item.Reasons)).ToList());
            })
            .OrderByDescending(thread => thread.Score)
            .ThenByDescending(thread => thread.LatestDate ?? DateTimeOffset.MinValue)
            .ToList();

        return Ok(new GmailJobMatchesResponseDto(
            job.Id,
            job.JobTitle,
            job.Company?.Name ?? string.Empty,
            job.Company?.RecruiterName,
            job.Company?.RecruiterEmail,
            queries,
            rankedMessages.Count,
            threads.Count,
            threads));
    }

    [AllowAnonymous]
    [HttpGet("oauth/callback")]
    public async Task<IActionResult> Callback([FromQuery] string? code, [FromQuery] string? state, [FromQuery] string? error, CancellationToken cancellationToken)
    {
        if (!string.IsNullOrWhiteSpace(error))
        {
            return Content(BuildPopupHtml(false, $"Google returned an error: {error}"), "text/html");
        }

        if (string.IsNullOrWhiteSpace(code) || string.IsNullOrWhiteSpace(state))
        {
            return Content(BuildPopupHtml(false, "Missing Google OAuth code or state."), "text/html");
        }

        var ownerUserId = _gmail.ConsumeState(state);
        if (string.IsNullOrWhiteSpace(ownerUserId))
        {
            return Content(BuildPopupHtml(false, "This Gmail connection request is no longer valid. Start the connection again."), "text/html");
        }

        try
        {
            var result = await _gmail.ExchangeCodeAsync(ownerUserId, code, GetRedirectUri(), cancellationToken);
            return Content(BuildPopupHtml(true, $"Connected Gmail: {result.GmailAddress}"), "text/html");
        }
        catch (Exception ex)
        {
            return Content(BuildPopupHtml(false, ex.Message), "text/html");
        }
    }

    [HttpDelete("connection")]
    public async Task<IActionResult> Disconnect(CancellationToken cancellationToken)
    {
        var ownerUserId = GetRequiredOwnerUserId();
        await _gmail.DisconnectAsync(ownerUserId, cancellationToken);
        return NoContent();
    }

    [HttpGet("messages")]
    public async Task<IActionResult> Messages([FromQuery] string? query, [FromQuery] int maxResults = 12, CancellationToken cancellationToken = default)
    {
        var ownerUserId = GetRequiredOwnerUserId();
        var items = await _gmail.ListMessagesAsync(ownerUserId, query, maxResults, cancellationToken);
        return Ok(items);
    }

    [HttpPost("import")]
    public async Task<ActionResult<GmailImportMessageResultDto>> Import([FromBody] ImportGmailMessageRequest request, CancellationToken cancellationToken)
    {
        try
        {
            if (request.JobApplicationId <= 0) return BadRequest("Valid jobApplicationId is required.");
            if (string.IsNullOrWhiteSpace(request.MessageId)) return BadRequest("MessageId is required.");

            var ownerUserId = GetRequiredOwnerUserId();
            var job = await _db.JobApplications.Include(x => x.Company).FirstOrDefaultAsync(x => x.Id == request.JobApplicationId, cancellationToken);
            if (job is null) return NotFound("Job application not found.");

            var existing = await _db.Correspondences.FirstOrDefaultAsync(
                x => x.JobApplicationId == request.JobApplicationId && x.ExternalMessageId == request.MessageId,
                cancellationToken);
            if (existing is not null)
            {
                return Ok(new GmailImportMessageResultDto(0, 1, request.MessageId, existing.ExternalThreadId, existing));
            }

            var created = await ImportSingleMessageAsync(ownerUserId, job, request.MessageId, cancellationToken);
            await _db.SaveChangesAsync(cancellationToken);
            return Ok(new GmailImportMessageResultDto(1, 0, request.MessageId, created.ExternalThreadId, created));
        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }
    }

    [HttpPost("import-thread")]
    public async Task<ActionResult<GmailImportResultDto>> ImportThread([FromBody] ImportGmailThreadRequest request, CancellationToken cancellationToken)
    {
        if (request.JobApplicationId <= 0) return BadRequest("Valid jobApplicationId is required.");
        if (string.IsNullOrWhiteSpace(request.ThreadId)) return BadRequest("ThreadId is required.");
        if (request.MessageIds is null || request.MessageIds.Length == 0) return BadRequest("At least one messageId is required.");

        var ownerUserId = GetRequiredOwnerUserId();
        var job = await _db.JobApplications.Include(x => x.Company).FirstOrDefaultAsync(x => x.Id == request.JobApplicationId, cancellationToken);
        if (job is null) return NotFound("Job application not found.");

        var distinctIds = request.MessageIds.Where(x => !string.IsNullOrWhiteSpace(x)).Select(x => x.Trim()).Distinct(StringComparer.Ordinal).ToList();
        var existingIds = await _db.Correspondences
            .Where(x => x.JobApplicationId == request.JobApplicationId && x.ExternalMessageId != null && distinctIds.Contains(x.ExternalMessageId))
            .Select(x => x.ExternalMessageId!)
            .ToListAsync(cancellationToken);

        var skipped = existingIds.Count;
        var imported = 0;
        foreach (var messageId in distinctIds)
        {
            if (existingIds.Contains(messageId, StringComparer.Ordinal)) continue;
            await ImportSingleMessageAsync(ownerUserId, job, messageId, cancellationToken);
            imported++;
        }

        await _db.SaveChangesAsync(cancellationToken);
        return Ok(new GmailImportResultDto(imported, skipped, request.ThreadId));
    }

    private async Task<Correspondence> ImportSingleMessageAsync(string ownerUserId, JobApplication job, string messageId, CancellationToken cancellationToken)
    {
        var detail = await _gmail.GetMessageAsync(ownerUserId, messageId, cancellationToken);
        var me = await _gmail.GetConnectionAsync(ownerUserId, cancellationToken);
        var gmailAddress = me?.GmailAddress ?? string.Empty;
        var isMe = detail.From.Contains(gmailAddress, StringComparison.OrdinalIgnoreCase);
        var messageDate = detail.Date?.LocalDateTime ?? DateTime.Now;

        var message = new Correspondence
        {
            JobApplicationId = job.Id,
            From = isMe ? "Me" : "Company",
            Subject = string.IsNullOrWhiteSpace(detail.Subject) ? null : detail.Subject.Trim(),
            Channel = "Email",
            ExternalMessageId = detail.Id,
            ExternalThreadId = string.IsNullOrWhiteSpace(detail.ThreadId) ? null : detail.ThreadId.Trim(),
            ExternalFrom = string.IsNullOrWhiteSpace(detail.From) ? null : detail.From.Trim(),
            ExternalTo = string.IsNullOrWhiteSpace(detail.To) ? null : detail.To.Trim(),
            Content = string.IsNullOrWhiteSpace(detail.BodyText) ? detail.Snippet : detail.BodyText,
            Date = messageDate,
        };

        _db.Correspondences.Add(message);
        if (job.Company is not null)
        {
            job.Company.LastContactedAt = messageDate;
        }

        if (!isMe && (!job.ResponseReceived || job.ResponseDate is null || messageDate < job.ResponseDate.Value))
        {
            var oldResponse = $"{job.ResponseReceived}:{job.ResponseDate?.ToString("o")}";
            job.ResponseReceived = true;
            job.ResponseDate = messageDate;
            _db.JobEvents.Add(new JobEvent
            {
                JobApplicationId = job.Id,
                Type = "ReplyReceived",
                OldValue = oldResponse,
                NewValue = $"{job.ResponseReceived}:{job.ResponseDate?.ToString("o")}",
                Note = detail.Subject,
                At = messageDate
            });
        }

        return message;
    }

    private static IReadOnlyList<string> BuildJobQueries(JobApplication job, string? queryOverride)
    {
        var queries = new List<string>();
        void Add(string? query)
        {
            if (!string.IsNullOrWhiteSpace(query))
            {
                queries.Add(query.Trim());
            }
        }

        Add(queryOverride);

        if (!string.IsNullOrWhiteSpace(job.Company?.RecruiterEmail))
        {
            Add($"(from:{job.Company.RecruiterEmail.Trim()} OR to:{job.Company.RecruiterEmail.Trim()}) newer_than:365d");
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.RecruiterName))
        {
            Add($"\"{job.Company.RecruiterName.Trim()}\" newer_than:365d");
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.Name) && !string.IsNullOrWhiteSpace(job.JobTitle))
        {
            Add($"\"{job.Company.Name.Trim()}\" \"{job.JobTitle.Trim()}\" newer_than:365d");
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.Name))
        {
            Add($"\"{job.Company.Name.Trim()}\" (application OR interview OR recruiter OR role OR position) newer_than:365d");
        }

        if (!string.IsNullOrWhiteSpace(job.JobTitle))
        {
            Add($"subject:\"{job.JobTitle.Trim()}\" newer_than:365d");
        }

        foreach (var subject in job.Messages
                     .Select(message => message.Subject)
                     .Where(subject => !string.IsNullOrWhiteSpace(subject))
                     .Distinct(StringComparer.OrdinalIgnoreCase)
                     .Take(2))
        {
            Add($"subject:\"{subject!.Trim()}\" newer_than:365d");
        }

        if (queries.Count == 0)
        {
            Add("newer_than:365d (application OR interview OR recruiter OR role OR position)");
        }

        return queries.Distinct(StringComparer.OrdinalIgnoreCase).ToList();
    }

    private static GmailScoredMessage ScoreMessage(JobApplication job, GmailQueryMatchedMessage candidate, bool alreadyImported, bool threadAlreadyImported)
    {
        var reasons = new List<GmailJobMatchReasonDto>();
        var score = 0;
        var message = candidate.Message;
        var subject = message.Subject ?? string.Empty;
        var from = message.From ?? string.Empty;
        var to = message.To ?? string.Empty;
        var snippet = message.Snippet ?? string.Empty;
        var haystack = $"{subject} {from} {to} {snippet}";

        if (candidate.MatchedQueries.Count > 0)
        {
            var queryHitPoints = Math.Min(12, candidate.MatchedQueries.Count * 4);
            score += queryHitPoints;
            reasons.Add(new GmailJobMatchReasonDto("queryHits", candidate.MatchedQueries.Count.ToString(), queryHitPoints));
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.Name) && ContainsValue(haystack, job.Company.Name))
        {
            score += 18;
            reasons.Add(new GmailJobMatchReasonDto("company", job.Company.Name.Trim(), 18));
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.RecruiterEmail) && (ContainsValue(from, job.Company.RecruiterEmail) || ContainsValue(to, job.Company.RecruiterEmail)))
        {
            score += 20;
            reasons.Add(new GmailJobMatchReasonDto("recruiterEmail", job.Company.RecruiterEmail.Trim(), 20));
        }

        if (!string.IsNullOrWhiteSpace(job.Company?.RecruiterName) && ContainsValue(haystack, job.Company.RecruiterName))
        {
            score += 12;
            reasons.Add(new GmailJobMatchReasonDto("recruiter", job.Company.RecruiterName.Trim(), 12));
        }

        foreach (var token in SplitTerms(job.JobTitle).Take(4))
        {
            if (!ContainsValue(haystack, token)) continue;
            score += 5;
            reasons.Add(new GmailJobMatchReasonDto("jobTitle", token, 5));
        }

        foreach (var subjectLine in job.Messages
                     .Select(existing => existing.Subject)
                     .Where(existing => !string.IsNullOrWhiteSpace(existing))
                     .Distinct(StringComparer.OrdinalIgnoreCase)
                     .Take(2))
        {
            if (!ContainsValue(subject, subjectLine!)) continue;
            score += 8;
            reasons.Add(new GmailJobMatchReasonDto("existingSubject", subjectLine!.Trim(), 8));
        }

        if (message.Date is { } messageDate)
        {
            var ageDays = Math.Abs((DateTimeOffset.UtcNow - messageDate).TotalDays);
            if (ageDays <= 45)
            {
                score += 4;
                reasons.Add(new GmailJobMatchReasonDto("recency", "45d", 4));
            }
            else if (ageDays <= 180)
            {
                score += 2;
                reasons.Add(new GmailJobMatchReasonDto("recency", "180d", 2));
            }
        }

        if (threadAlreadyImported && !alreadyImported)
        {
            reasons.Add(new GmailJobMatchReasonDto("status", "thread-already-imported", 0));
        }

        if (alreadyImported)
        {
            reasons.Add(new GmailJobMatchReasonDto("status", "already-imported", 0));
        }

        reasons = reasons
            .GroupBy(reason => new { reason.Label, reason.Value, reason.Points })
            .Select(group => group.First())
            .OrderByDescending(reason => reason.Points)
            .ThenBy(reason => reason.Label, StringComparer.Ordinal)
            .ThenBy(reason => reason.Value, StringComparer.Ordinal)
            .ToList();

        return new GmailScoredMessage(message, alreadyImported, score, candidate.MatchedQueries, reasons);
    }

    private static bool ContainsValue(string haystack, string? value)
    {
        return !string.IsNullOrWhiteSpace(value)
            && haystack.Contains(value.Trim(), StringComparison.OrdinalIgnoreCase);
    }

    private static IEnumerable<string> SplitTerms(string? value)
    {
        if (string.IsNullOrWhiteSpace(value)) yield break;

        foreach (var token in value
                     .Split(new[] { ' ', '/', '-', ',', '.', '(', ')', ':' }, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
                     .Where(token => token.Length >= 3)
                     .Distinct(StringComparer.OrdinalIgnoreCase))
        {
            yield return token;
        }
    }

    private static string ToConfidence(int score)
    {
        return score switch
        {
            >= 30 => "high",
            >= 16 => "medium",
            _ => "low"
        };
    }

    private string GetRequiredOwnerUserId()
    {
        return User.FindFirstValue(ClaimTypes.NameIdentifier) ?? User.FindFirstValue("sub")
            ?? throw new InvalidOperationException("Authenticated user id is missing.");
    }

    private string GetRedirectUri()
    {
        var configured = (_cfg["Google:GmailRedirectUri"] ?? _cfg["Google:RedirectUri"] ?? "").Trim();
        if (!string.IsNullOrWhiteSpace(configured)) return configured;

        var publicBaseUrl = (_cfg["App:PublicBaseUrl"] ?? "").Trim().TrimEnd('/');
        if (!string.IsNullOrWhiteSpace(publicBaseUrl))
        {
            return $"{publicBaseUrl}/api/gmail/oauth/callback";
        }

        return $"{Request.Scheme}://{Request.Host}/api/gmail/oauth/callback";
    }

    private static string BuildPopupHtml(bool success, string message)
    {
        var escaped = System.Net.WebUtility.HtmlEncode(message);
        var status = success ? "connected" : "error";
        var title = success ? "Gmail connected" : "Gmail connection failed";
        var serializedMessage = System.Text.Json.JsonSerializer.Serialize(message);
        return $@"<!doctype html>
<html>
<head>
  <meta charset=""utf-8"" />
  <title>Gmail connection</title>
</head>
<body style=""font-family:Segoe UI,Arial,sans-serif;padding:24px;line-height:1.5;"">
  <h2>{title}</h2>
  <p>{escaped}</p>
  <p>You can close this window.</p>
  <script>
    if (window.opener) {{
      window.opener.postMessage({{ source: 'jobtracker-gmail-oauth', status: '{status}', message: {serializedMessage} }}, '*');
    }}
    window.close();
  </script>
</body>
</html>";
    }

    private sealed record GmailScoredMessage(
        GmailMessageSummary Message,
        bool AlreadyImported,
        int Score,
        IReadOnlyList<string> MatchedQueries,
        IReadOnlyList<GmailJobMatchReasonDto> Reasons);
}