using System.Text.RegularExpressions;

namespace Core.Parsers.EventOccurrence;

/// <summary>
/// Parses time and location from combined strings.
/// Extracts time using regex, then uses everything after the time as the location.
/// </summary>
public static class TimeLocationParser
{
    // Shared time value pattern: matches either NOON or a time with AM/PM (e.g., "10:30 a.m.", "3 p.m.")
    private static string TimeValuePattern => TimePatterns.TimeValue;

    // Regex to match time ranges like "10:30 a.m. - 12:00 p.m." or "10:30 a.m. - NOON"
    // Matches: time1 (optional dash time2/NOON), then location
    // The time group captures the full time range (including " - NOON" if present)
    // Note: Input is normalized via SanitizeInput, so only regular hyphens need to be handled
    private static readonly Regex TimeLocationRegex = new(
        $@"(?<Time>{TimeValuePattern}(?:\s*-\s*{TimeValuePattern})?)(?:\s+(?<Location>.+))?",
        RegexOptions.Compiled | RegexOptions.IgnoreCase);

    // Pattern for cleaning time components from location text
    // Matches optional dash, whitespace, time pattern, optional whitespace at start
    // Handles: "- 12:15 p.m. ", "12:15 p.m. ", "- NOON ", "NOON ", etc.
    private static readonly Regex TimeInLocationPattern = new(
        $@"^(?:-\s*)?{TimeValuePattern}(?:\s+|$)",
        RegexOptions.Compiled | RegexOptions.IgnoreCase);

    /// <summary>
    /// Parses time and location from the timeAndLocation string.
    /// Extracts time using regex, then uses everything after the time as the location (after cleaning time fragments).
    /// </summary>
    /// <param name="timeAndLocation">The combined time and location string.</param>
    /// <param name="time">Output parameter: the parsed time string.</param>
    /// <param name="location">Output parameter: the parsed location string.</param>
    public static void Parse(
        string timeAndLocation,
        out string time,
        out string location)
    {
        // Extract time using regex
        var timeLocationMatch = TimeLocationRegex.Match(timeAndLocation);
        
        if (!timeLocationMatch.Success)
        {
            // If time regex doesn't match, use the whole string as time
            time = timeAndLocation.Trim();
            location = string.Empty;
            return;
        }

        time = timeLocationMatch.Groups["Time"].Captures[0].Value.Trim();
        var locationPart = timeLocationMatch.Groups["Location"].Success 
            ? timeLocationMatch.Groups["Location"].Captures[0].Value.Trim() 
            : string.Empty;

        // No location part found, which is valid (some events might not have locations)
        if (string.IsNullOrWhiteSpace(locationPart))
        {
            location = string.Empty;
            return;
        }

        // Clean location of any remaining time fragments
        // (e.g., "– 12:15 p.m. Exhibit Hall C" -> "Exhibit Hall C")
        location = CleanLocationText(locationPart);
    }

    /// <summary>
    /// Cleans location text by removing any remaining time components from the start.
    /// Handles cases like "- 12:15 p.m. Exhibit Hall C" -> "Exhibit Hall C"
    /// Note: Input is normalized, so only regular hyphens need to be handled.
    /// </summary>
    public static string CleanLocationText(string locationText)
    {
        if (string.IsNullOrWhiteSpace(locationText))
            return string.Empty;
        
        // Remove time pattern from start, repeat until no more matches
        string previous;
        do
        {
            previous = locationText;
            locationText = TimeInLocationPattern.Replace(locationText, "").Trim();
        } while (locationText != previous && !string.IsNullOrWhiteSpace(locationText));
        
        // If result is empty or only whitespace, return empty
        return string.IsNullOrWhiteSpace(locationText) ? string.Empty : locationText;
    }
}