use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

/// Represents a calendar event with all its properties
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub struct CalendarEvent {
    /// Unique identifier for the event (UID field in iCal)
    pub uid: String,
    
    /// Summary/title of the event
    pub summary: Option<String>,
    
    /// Detailed description of the event
    pub description: Option<String>,
    
    /// Start date and time of the event
    pub start: DateTime<Utc>,
    
    /// End date and time of the event
    pub end: Option<DateTime<Utc>>,
    
    /// Location where the event takes place
    pub location: Option<String>,
    
    /// Event status (TENTATIVE, CONFIRMED, CANCELLED)
    pub status: EventStatus,
    
    /// Event classification (PUBLIC, PRIVATE, CONFIDENTIAL)
    pub class: EventClass,
    
    /// Event priority (0-9, where 0 is undefined, 1 is highest, 9 is lowest)
    pub priority: Option<u8>,
    
    /// Organizer of the event
    pub organizer: Option<String>,
    
    /// List of attendees
    pub attendees: Vec<String>,
    
    /// Categories/tags for the event
    pub categories: Vec<String>,
    
    /// Date and time when the event was created
    pub created: Option<DateTime<Utc>>,
    
    /// Date and time when the event was last modified
    pub last_modified: Option<DateTime<Utc>>,
    
    /// Recurrence rule (RRULE)
    pub recurrence_rule: Option<String>,
    
    /// All-day event flag
    pub all_day: bool,
    
    /// ETag from CalDAV server for conflict detection
    pub etag: Option<String>,
    
    /// URL/href of this event on the CalDAV server
    pub href: Option<String>,
}

/// Event status enumeration
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub enum EventStatus {
    Tentative,
    Confirmed,
    Cancelled,
}

impl Default for EventStatus {
    fn default() -> Self {
        EventStatus::Confirmed
    }
}

/// Event classification enumeration
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub enum EventClass {
    Public,
    Private,
    Confidential,
}

impl Default for EventClass {
    fn default() -> Self {
        EventClass::Public
    }
}

/// CalDAV client for fetching and parsing calendar events
pub struct CalDAVClient {
    config: crate::config::CalDAVConfig,
    http_client: reqwest::Client,
}

impl CalDAVClient {
    /// Create a new CalDAV client with the given configuration
    pub fn new(config: crate::config::CalDAVConfig) -> Self {
        Self {
            config,
            http_client: reqwest::Client::new(),
        }
    }

    /// Fetch calendar events from the CalDAV server
    /// 
    /// This method performs a REPORT request to get calendar data and parses
    /// the returned iCalendar format into CalendarEvent structs.
    pub async fn fetch_events(&self, calendar_path: &str) -> Result<Vec<CalendarEvent>, CalDAVError> {
        // CalDAV REPORT request to get calendar events
        let report_body = r#"<?xml version="1.0" encoding="utf-8" ?>
<c:calendar-query xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:caldav">
    <d:prop>
        <d:getetag/>
        <c:calendar-data/>
    </d:prop>
    <c:filter>
        <c:comp-filter name="VCALENDAR">
            <c:comp-filter name="VEVENT"/>
        </c:comp-filter>
    </c:filter>
</c:calendar-query>"#;

        let url = if calendar_path.starts_with("http") {
            calendar_path.to_string()
        } else {
            format!("{}{}", self.config.server_url.trim_end_matches('/'), calendar_path)
        };

        let response = self.http_client
            .request(reqwest::Method::from_bytes(b"REPORT").unwrap(), &url)
            .header("Authorization", format!("Basic {}", self.config.get_basic_auth()))
            .header("Content-Type", "application/xml")
            .header("Depth", "1")
            .header("User-Agent", "calendar-app/0.1.0")
            .body(report_body)
            .send()
            .await
            .map_err(CalDAVError::RequestError)?;

        if !response.status().is_success() && response.status().as_u16() != 207 {
            return Err(CalDAVError::ServerError(response.status().as_u16()));
        }

        let body = response.text().await.map_err(CalDAVError::RequestError)?;
        self.parse_calendar_response(&body)
    }

    /// Parse CalDAV XML response containing calendar data
    fn parse_calendar_response(&self, xml_response: &str) -> Result<Vec<CalendarEvent>, CalDAVError> {
        let mut events = Vec::new();
        
        // Extract calendar data from XML response
        // This is a simplified parser - in production, you'd want a proper XML parser
        let calendar_data_sections = self.extract_calendar_data(xml_response);
        
        for calendar_data in calendar_data_sections {
            if let Ok(parsed_events) = self.parse_ical_data(&calendar_data.data) {
                for mut event in parsed_events {
                    event.etag = calendar_data.etag.clone();
                    event.href = calendar_data.href.clone();
                    events.push(event);
                }
            }
        }

        Ok(events)
    }

    /// Extract calendar data sections from CalDAV XML response
    fn extract_calendar_data(&self, xml_response: &str) -> Vec<CalendarDataSection> {
        let mut sections = Vec::new();
        
        // Simple regex-based extraction (in production, use a proper XML parser)
        // Look for <d:response> blocks containing calendar data
        for response_block in xml_response.split("<d:response>").skip(1) {
            if let Some(end_pos) = response_block.find("</d:response>") {
                let response_content = &response_block[..end_pos];
                
                let href = self.extract_xml_content(response_content, "href").unwrap_or_default();
                let etag = self.extract_xml_content(response_content, "getetag").unwrap_or_default();
                
                if let Some(calendar_data) = self.extract_xml_content(response_content, "calendar-data") {
                    sections.push(CalendarDataSection {
                        href: if href.is_empty() { None } else { Some(href) },
                        etag: if etag.is_empty() { None } else { Some(etag) },
                        data: calendar_data,
                    });
                }
            }
        }
        
        sections
    }

    /// Extract content from XML tags (simple implementation)
    fn extract_xml_content(&self, xml: &str, tag: &str) -> Option<String> {
        // Handle both with and without namespace prefixes
        let patterns = [
            format!("<{}>(.*?)</{}>", tag, tag),
            format!("<{}>(.*?)</.*:{}>", tag, tag),
            format!("<.*:{}>(.*?)</{}>", tag, tag),
            format!("<.*:{}>(.*?)</.*:{}>", tag, tag),
        ];
        
        for pattern in &patterns {
            if let Ok(re) = regex::Regex::new(pattern) {
                if let Some(captures) = re.captures(xml) {
                    if let Some(content) = captures.get(1) {
                        return Some(content.as_str().trim().to_string());
                    }
                }
            }
        }
        
        None
    }

    /// Parse iCalendar data into CalendarEvent structs
    fn parse_ical_data(&self, ical_data: &str) -> Result<Vec<CalendarEvent>, CalDAVError> {
        let mut events = Vec::new();
        
        // Parse the iCal data using the ical crate
        let reader = ical::IcalParser::new(ical_data.as_bytes());
        
        for calendar in reader {
            let calendar = calendar.map_err(|e| CalDAVError::ParseError(e.to_string()))?;
            
            for event in calendar.events {
                if let Ok(calendar_event) = self.parse_ical_event(event) {
                    events.push(calendar_event);
                }
            }
        }
        
        Ok(events)
    }

    /// Parse a single iCal event into a CalendarEvent struct
    fn parse_ical_event(&self, event: ical::parser::ical::component::IcalEvent) -> Result<CalendarEvent, CalDAVError> {
        let mut properties: HashMap<String, String> = HashMap::new();
        
        // Extract all properties from the event
        for property in event.properties {
            properties.insert(property.name.to_uppercase(), property.value.unwrap_or_default());
        }

        // Required UID field
        let uid = properties.get("UID")
            .ok_or_else(|| CalDAVError::ParseError("Missing UID field".to_string()))?
            .clone();

        // Parse start time (required)
        let start = properties.get("DTSTART")
            .ok_or_else(|| CalDAVError::ParseError("Missing DTSTART field".to_string()))?;
        let start = self.parse_datetime(start, properties.get("DTSTART"))?;

        // Parse end time (optional - use start time if not present)
        let end = if let Some(dtend) = properties.get("DTEND") {
            Some(self.parse_datetime(dtend, properties.get("DTEND"))?)
        } else if let Some(duration) = properties.get("DURATION") {
            // TODO: Parse duration and add to start time
            Some(start)
        } else {
            None
        };

        // Determine if it's an all-day event
        let all_day = properties.get("DTSTART")
            .map(|s| !s.contains("T"))
            .unwrap_or(false);

        // Parse status
        let status = properties.get("STATUS")
            .map(|s| match s.to_uppercase().as_str() {
                "TENTATIVE" => EventStatus::Tentative,
                "CANCELLED" => EventStatus::Cancelled,
                _ => EventStatus::Confirmed,
            })
            .unwrap_or_default();

        // Parse classification
        let class = properties.get("CLASS")
            .map(|s| match s.to_uppercase().as_str() {
                "PRIVATE" => EventClass::Private,
                "CONFIDENTIAL" => EventClass::Confidential,
                _ => EventClass::Public,
            })
            .unwrap_or_default();

        // Parse priority
        let priority = properties.get("PRIORITY")
            .and_then(|s| s.parse::<u8>().ok())
            .filter(|&p| p <= 9);

        // Parse categories
        let categories = properties.get("CATEGORIES")
            .map(|s| s.split(',').map(|c| c.trim().to_string()).collect())
            .unwrap_or_default();

        // Parse dates
        let created = properties.get("CREATED")
            .and_then(|s| self.parse_datetime(s, None).ok());
        
        let last_modified = properties.get("LAST-MODIFIED")
            .and_then(|s| self.parse_datetime(s, None).ok());

        Ok(CalendarEvent {
            uid,
            summary: properties.get("SUMMARY").cloned(),
            description: properties.get("DESCRIPTION").cloned(),
            start,
            end,
            location: properties.get("LOCATION").cloned(),
            status,
            class,
            priority,
            organizer: properties.get("ORGANIZER").cloned(),
            attendees: Vec::new(), // TODO: Parse attendees
            categories,
            created,
            last_modified,
            recurrence_rule: properties.get("RRULE").cloned(),
            all_day,
            etag: None, // Set by caller
            href: None, // Set by caller
        })
    }

    /// Discover available calendar collections on the server
    pub async fn discover_calendars(&self) -> Result<Vec<String>, CalDAVError> {
        // First, try to discover user calendars if we have a calendar path in config
        if let Some(calendar_path) = &self.config.calendar_path {
            println!("Using configured calendar path: {}", calendar_path);
            return Ok(vec![calendar_path.clone()]);
        }

        println!("No calendar path configured, discovering calendars...");

        // Try different common CalDAV discovery paths
        let user_calendar_path = format!("/calendars/{}/", self.config.username);
        let user_dav_calendar_path = format!("/dav.php/calendars/{}/", self.config.username);
        
        let discovery_paths = vec![
            "/calendars/",
            user_calendar_path.as_str(),
            user_dav_calendar_path.as_str(),
            "/dav.php/calendars/",
        ];

        let mut all_calendars = Vec::new();

        for path in discovery_paths {
            println!("Trying discovery path: {}", path);
            if let Ok(calendars) = self.discover_calendars_at_path(&path).await {
                println!("Found {} calendar(s) at {}", calendars.len(), path);
                all_calendars.extend(calendars);
            }
        }

        // Remove duplicates
        all_calendars.sort();
        all_calendars.dedup();

        Ok(all_calendars)
    }

    /// Discover calendars at a specific path
    async fn discover_calendars_at_path(&self, path: &str) -> Result<Vec<String>, CalDAVError> {
        let propfind_body = r#"<?xml version="1.0" encoding="utf-8" ?>
<d:propfind xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:caldav">
    <d:prop>
        <d:resourcetype />
        <d:displayname />
        <c:supported-calendar-component-set />
    </d:prop>
</d:propfind>"#;

        let url = format!("{}{}", self.config.server_url.trim_end_matches('/'), path);

        let response = self.http_client
            .request(reqwest::Method::from_bytes(b"PROPFIND").unwrap(), &url)
            .header("Authorization", format!("Basic {}", self.config.get_basic_auth()))
            .header("Content-Type", "application/xml")
            .header("Depth", "2") // Deeper search to find actual calendars
            .header("User-Agent", "calendar-app/0.1.0")
            .body(propfind_body)
            .send()
            .await
            .map_err(CalDAVError::RequestError)?;

        if response.status().as_u16() != 207 {
            return Err(CalDAVError::ServerError(response.status().as_u16()));
        }

        let body = response.text().await.map_err(CalDAVError::RequestError)?;
        println!("Discovery response for {}: {}", path, body);
        
        let mut calendar_paths = Vec::new();
        
        // Extract calendar collection URLs from the response
        for response_block in body.split("<d:response>").skip(1) {
            if let Some(end_pos) = response_block.find("</d:response>") {
                let response_content = &response_block[..end_pos];
                
                // Look for actual calendar collections (not just containers)
                if response_content.contains("<c:supported-calendar-component-set") || 
                   (response_content.contains("<d:collection/>") && 
                    response_content.contains("calendar")) {
                    if let Some(href) = self.extract_xml_content(response_content, "href") {
                        // Only include actual calendar paths, not container directories
                        if href.ends_with('/') && href.contains("calendar") && !href.ends_with("/calendars/") {
                            calendar_paths.push(href);
                        }
                    }
                }
            }
        }
        
        Ok(calendar_paths)
    }

    /// Parse iCal datetime format
    fn parse_datetime(&self, datetime_str: &str, _original_property: Option<&String>) -> Result<DateTime<Utc>, CalDAVError> {
        use chrono::TimeZone;
        
        // Handle different iCal datetime formats
        let cleaned = datetime_str.replace("TZID=", "").trim().to_string();
        
        // Try different parsing formats
        let formats = [
            "%Y%m%dT%H%M%SZ",        // UTC format: 20231225T120000Z
            "%Y%m%dT%H%M%S",         // Local format: 20231225T120000
            "%Y%m%d",                // Date only: 20231225
        ];
        
        for format in &formats {
            if let Ok(dt) = chrono::NaiveDateTime::parse_from_str(&cleaned, format) {
                return Ok(Utc.from_utc_datetime(&dt));
            }
            if let Ok(date) = chrono::NaiveDate::parse_from_str(&cleaned, format) {
                return Ok(Utc.from_utc_datetime(&date.and_hms_opt(0, 0, 0).unwrap()));
            }
        }
        
        Err(CalDAVError::ParseError(format!("Unable to parse datetime: {}", datetime_str)))
    }
}

/// Helper struct for extracting calendar data from XML responses
#[derive(Debug)]
struct CalendarDataSection {
    pub href: Option<String>,
    pub etag: Option<String>,
    pub data: String,
}

/// CalDAV-specific error types
#[derive(Debug, thiserror::Error)]
pub enum CalDAVError {
    #[error("HTTP request failed: {0}")]
    RequestError(#[from] reqwest::Error),
    
    #[error("CalDAV server returned error: {0}")]
    ServerError(u16),
    
    #[error("Failed to parse calendar data: {0}")]
    ParseError(String),
    
    #[error("Configuration error: {0}")]
    ConfigError(String),
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::CalDAVConfig;

    /// Integration test that fetches real calendar events from the Baikal server
    /// 
    /// This test requires a valid .env file and a calendar with some events
    #[tokio::test]
    async fn test_fetch_calendar_events() {
        let config = CalDAVConfig::from_env()
            .expect("Failed to load CalDAV config from environment");
        
        let client = CalDAVClient::new(config);
        
        // First discover available calendars using PROPFIND
        println!("Discovering calendars...");
        let discovery_result = client.discover_calendars().await;
        
        match discovery_result {
            Ok(calendar_paths) => {
                println!("Found {} calendar collection(s)", calendar_paths.len());
                
                if calendar_paths.is_empty() {
                    println!("No calendars found - this might be normal for a new server");
                    return;
                }
                
                // Try the first available calendar
                let calendar_path = &calendar_paths[0];
                println!("Trying to fetch events from: {}", calendar_path);
                
                match client.fetch_events(calendar_path).await {
                    Ok(events) => {
                        println!("Successfully fetched {} calendar events", events.len());
                        
                        for (i, event) in events.iter().take(3).enumerate() {
                            println!("\n--- Event {} ---", i + 1);
                            println!("UID: {}", event.uid);
                            println!("Summary: {:?}", event.summary);
                            println!("Start: {}", event.start);
                            println!("End: {:?}", event.end);
                            println!("All Day: {}", event.all_day);
                            println!("Status: {:?}", event.status);
                            println!("Location: {:?}", event.location);
                            println!("Description: {:?}", event.description);
                            println!("ETag: {:?}", event.etag);
                            println!("HREF: {:?}", event.href);
                        }
                        
                        // Validate that events have required fields
                        for event in &events {
                            assert!(!event.uid.is_empty(), "Event UID should not be empty");
                            // All events should have a start time
                            assert!(event.start > DateTime::from_timestamp(0, 0).unwrap(), "Event should have valid start time");
                        }
                        
                        println!("\n✓ Calendar event fetching test passed!");
                    }
                    Err(e) => {
                        println!("Error fetching events from {}: {:?}", calendar_path, e);
                        println!("This might be normal if the calendar is empty");
                    }
                }
            }
            Err(e) => {
                println!("Error discovering calendars: {:?}", e);
                println!("This might be normal if no calendars are set up yet");
            }
        }
    }

    /// Test parsing a sample iCal event
    #[test]
    fn test_parse_ical_event() {
        let sample_ical = r#"BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Test//Test//EN
BEGIN:VEVENT
UID:test-event-123@example.com
DTSTART:20231225T120000Z
DTEND:20231225T130000Z
SUMMARY:Test Event
DESCRIPTION:This is a test event
LOCATION:Test Location
STATUS:CONFIRMED
CLASS:PUBLIC
PRIORITY:5
CREATED:20231220T100000Z
LAST-MODIFIED:20231221T150000Z
CATEGORIES:work,important
END:VEVENT
END:VCALENDAR"#;

        let config = CalDAVConfig {
            server_url: "https://example.com".to_string(),
            username: "test".to_string(),
            password: "test".to_string(),
            calendar_path: None,
            tasks_path: None,
        };
        
        let client = CalDAVClient::new(config);
        let events = client.parse_ical_data(sample_ical)
            .expect("Should be able to parse sample iCal data");

        assert_eq!(events.len(), 1);
        
        let event = &events[0];
        assert_eq!(event.uid, "test-event-123@example.com");
        assert_eq!(event.summary, Some("Test Event".to_string()));
        assert_eq!(event.description, Some("This is a test event".to_string()));
        assert_eq!(event.location, Some("Test Location".to_string()));
        assert_eq!(event.status, EventStatus::Confirmed);
        assert_eq!(event.class, EventClass::Public);
        assert_eq!(event.priority, Some(5));
        assert_eq!(event.categories, vec!["work", "important"]);
        assert!(!event.all_day);
        
        println!("✓ iCal parsing test passed!");
    }

    /// Test datetime parsing
    #[test]
    fn test_datetime_parsing() {
        let config = CalDAVConfig {
            server_url: "https://example.com".to_string(),
            username: "test".to_string(),
            password: "test".to_string(),
            calendar_path: None,
            tasks_path: None,
        };
        
        let client = CalDAVClient::new(config);
        
        // Test UTC format
        let dt1 = client.parse_datetime("20231225T120000Z", None)
            .expect("Should parse UTC datetime");
        println!("Parsed UTC datetime: {}", dt1);
        
        // Test date-only format (should be treated as all-day)
        let dt2 = client.parse_datetime("20231225", None)
            .expect("Should parse date-only");
        println!("Parsed date-only: {}", dt2);
        
        // Test local format
        let dt3 = client.parse_datetime("20231225T120000", None)
            .expect("Should parse local datetime");
        println!("Parsed local datetime: {}", dt3);
        
        println!("✓ Datetime parsing test passed!");
    }

    /// Test event status parsing
    #[test]
    fn test_event_enums() {
        // Test status parsing
        assert_eq!(EventStatus::default(), EventStatus::Confirmed);
        
        // Test class parsing  
        assert_eq!(EventClass::default(), EventClass::Public);
        
        println!("✓ Event enum tests passed!");
    }
}