"""
Natural language date/time parser for ClearSkies Analytics Agent
Converts user queries like "yesterday", "Sept 25", "between 10:00 and 12:00 on Sept 24" into datetime objects
NO EXTERNAL DEPENDENCIES - works with just standard library
"""
from datetime import datetime, timedelta
from typing import Tuple, Optional
import re

class DateTimeParser:
    """Parse natural language date/time expressions"""
    
    def __init__(self, reference_date: Optional[datetime] = None):
        """
        Initialize parser
        
        Args:
            reference_date: Reference date for relative expressions (default: now)
        """
        self.reference_date = reference_date or datetime.now()
        
        # Month name mapping
        self.month_map = {
            'jan': 1, 'january': 1,
            'feb': 2, 'february': 2,
            'mar': 3, 'march': 3,
            'apr': 4, 'april': 4,
            'may': 5,
            'jun': 6, 'june': 6,
            'jul': 7, 'july': 7,
            'aug': 8, 'august': 8,
            'sep': 9, 'sept': 9, 'september': 9,
            'oct': 10, 'october': 10,
            'nov': 11, 'november': 11,
            'dec': 12, 'december': 12
        }
    
    def parse(self, text: str) -> Tuple[Optional[datetime], Optional[datetime]]:
        """
        Parse natural language date/time into start and end datetime
        
        Args:
            text: User input text containing date/time references
        
        Returns:
            Tuple of (start_datetime, end_datetime)
        """
        text = text.lower().strip()
        
        # Priority 1: Time range on specific date (most specific)
        result = self._try_time_range_on_date(text)
        if result:
            return result
        
        # Priority 2: Specific date patterns
        result = self._try_specific_patterns(text)
        if result:
            return result
        
        # Default: return None if no date found
        return None, None
    
    def _try_time_range_on_date(self, text: str) -> Optional[Tuple[datetime, datetime]]:
        """
        Handle patterns like:
        - "between 10:00 and 12:00 on Sept 24"
        - "from 10:00 to 12:00 on Sept 24"
        - "10:00 to 12:00 on Sept 24"
        """
        # Pattern 1: "between HH:MM and HH:MM on DATE"
        pattern1 = r'between\s+(\d{1,2}):(\d{2})\s+and\s+(\d{1,2}):(\d{2})\s+on\s+(.+?)$'
        match = re.search(pattern1, text, re.IGNORECASE)
        
        if match:
            start_hour = int(match.group(1))
            start_min = int(match.group(2))
            end_hour = int(match.group(3))
            end_min = int(match.group(4))
            date_str = match.group(5).strip()
            
            # Parse the date part (just the date, ignore times in date string)
            base_date = self._parse_date_only(date_str)
            if base_date:
                start = datetime(base_date.year, base_date.month, base_date.day, start_hour, start_min, 0, 0)
                end = datetime(base_date.year, base_date.month, base_date.day, end_hour, end_min, 59, 999999)
                return start, end
        
        # Pattern 2: "from HH:MM to HH:MM on DATE"
        pattern2 = r'from\s+(\d{1,2}):(\d{2})\s+to\s+(\d{1,2}):(\d{2})\s+on\s+(.+?)$'
        match = re.search(pattern2, text, re.IGNORECASE)
        
        if match:
            start_hour = int(match.group(1))
            start_min = int(match.group(2))
            end_hour = int(match.group(3))
            end_min = int(match.group(4))
            date_str = match.group(5).strip()
            
            base_date = self._parse_date_only(date_str)
            if base_date:
                start = datetime(base_date.year, base_date.month, base_date.day, start_hour, start_min, 0, 0)
                end = datetime(base_date.year, base_date.month, base_date.day, end_hour, end_min, 59, 999999)
                return start, end
        
        # Pattern 3: "HH:MM to HH:MM on DATE" (without "from")
        pattern3 = r'(\d{1,2}):(\d{2})\s+to\s+(\d{1,2}):(\d{2})\s+on\s+(.+?)$'
        match = re.search(pattern3, text, re.IGNORECASE)
        
        if match:
            start_hour = int(match.group(1))
            start_min = int(match.group(2))
            end_hour = int(match.group(3))
            end_min = int(match.group(4))
            date_str = match.group(5).strip()
            
            base_date = self._parse_date_only(date_str)
            if base_date:
                start = datetime(base_date.year, base_date.month, base_date.day, start_hour, start_min, 0, 0)
                end = datetime(base_date.year, base_date.month, base_date.day, end_hour, end_min, 59, 999999)
                return start, end
        
        return None
    
    def _parse_date_only(self, date_str: str) -> Optional[datetime]:
        """Parse a date string like 'Sept 24' or '9/24' into a datetime (time will be 00:00:00)"""
        
        # Try month name + day
        month_day_pattern = r'(jan|january|feb|february|mar|march|apr|april|may|jun|june|jul|july|aug|august|sep|sept|september|oct|october|nov|november|dec|december)[a-z]*\s+(\d{1,2})'
        match = re.search(month_day_pattern, date_str, re.IGNORECASE)
        if match:
            month_str = match.group(1).lower()
            month = self.month_map.get(month_str)
            day = int(match.group(2))
            year = self.reference_date.year
            
            # If the date is in the future, assume it was last year
            try:
                test_date = datetime(year, month, day)
                if test_date > self.reference_date:
                    year -= 1
                return datetime(year, month, day, 0, 0, 0)
            except ValueError:
                return None
        
        # Try MM/DD or M/D
        md_pattern = r'\b(\d{1,2})[/-](\d{1,2})\b'
        match = re.search(md_pattern, date_str)
        if match:
            month = int(match.group(1))
            day = int(match.group(2))
            year = self.reference_date.year
            try:
                return datetime(year, month, day, 0, 0, 0)
            except ValueError:
                return None
        
        # Try YYYY-MM-DD
        ymd_pattern = r'(\d{4})[/-](\d{1,2})[/-](\d{1,2})'
        match = re.search(ymd_pattern, date_str)
        if match:
            year = int(match.group(1))
            month = int(match.group(2))
            day = int(match.group(3))
            try:
                return datetime(year, month, day, 0, 0, 0)
            except ValueError:
                return None
        
        return None
    
    def _try_specific_patterns(self, text: str) -> Optional[Tuple[datetime, datetime]]:
        """Try to match specific common patterns"""
        
        # Month name + day (Sept 25, September 25th)
        month_day_pattern = r'(jan|january|feb|february|mar|march|apr|april|may|jun|june|jul|july|aug|august|sep|sept|september|oct|october|nov|november|dec|december)[a-z]*\s+(\d{1,2})'
        match = re.search(month_day_pattern, text, re.IGNORECASE)
        if match:
            month_str = match.group(1).lower()
            month = self.month_map.get(month_str)
            day = int(match.group(2))
            year = self.reference_date.year
            
            # If the date is in the future, assume it was last year
            try:
                test_date = datetime(year, month, day)
                if test_date > self.reference_date:
                    year -= 1
                
                start = datetime(year, month, day, 0, 0, 0)
                end = datetime(year, month, day, 23, 59, 59)
                return start, end
            except ValueError:
                pass
        
        # YYYY-MM-DD or YYYY/MM/DD
        ymd_pattern = r'(\d{4})[/-](\d{1,2})[/-](\d{1,2})'
        match = re.search(ymd_pattern, text)
        if match:
            try:
                year = int(match.group(1))
                month = int(match.group(2))
                day = int(match.group(3))
                
                start = datetime(year, month, day, 0, 0, 0)
                end = datetime(year, month, day, 23, 59, 59)
                return start, end
            except ValueError:
                pass
        
        # MM/DD or M/D
        md_pattern = r'\b(\d{1,2})[/-](\d{1,2})\b'
        match = re.search(md_pattern, text)
        if match:
            try:
                month = int(match.group(1))
                day = int(match.group(2))
                year = self.reference_date.year
                
                start = datetime(year, month, day, 0, 0, 0)
                end = datetime(year, month, day, 23, 59, 59)
                return start, end
            except ValueError:
                pass
        
        # Today
        if 'today' in text:
            start = self.reference_date.replace(hour=0, minute=0, second=0, microsecond=0)
            end = self.reference_date.replace(hour=23, minute=59, second=59, microsecond=999999)
            return start, end
        
        # Yesterday
        if 'yesterday' in text:
            yesterday = self.reference_date - timedelta(days=1)
            start = yesterday.replace(hour=0, minute=0, second=0, microsecond=0)
            end = yesterday.replace(hour=23, minute=59, second=59, microsecond=999999)
            return start, end
        
        # Last N hours
        hours_match = re.search(r'last (\d+) hour', text)
        if hours_match:
            hours = int(hours_match.group(1))
            end = self.reference_date
            start = end - timedelta(hours=hours)
            return start, end
        
        # Last N days
        days_match = re.search(r'last (\d+) day', text)
        if days_match:
            days = int(days_match.group(1))
            end = self.reference_date
            start = end - timedelta(days=days)
            return start, end
        
        # This week
        if 'this week' in text:
            start = self.reference_date - timedelta(days=self.reference_date.weekday())
            start = start.replace(hour=0, minute=0, second=0, microsecond=0)
            end = self.reference_date
            return start, end
        
        # Last week
        if 'last week' in text:
            end = self.reference_date - timedelta(days=self.reference_date.weekday())
            start = end - timedelta(days=7)
            start = start.replace(hour=0, minute=0, second=0, microsecond=0)
            end = end.replace(hour=23, minute=59, second=59, microsecond=999999)
            return start, end
        
        # This month
        if 'this month' in text:
            start = self.reference_date.replace(day=1, hour=0, minute=0, second=0, microsecond=0)
            end = self.reference_date
            return start, end
        
        # Time range patterns: "from X to Y"
        range_pattern = r'from\s+(.+?)\s+to\s+(.+?)(?:\s|$)'
        match = re.search(range_pattern, text, re.IGNORECASE)
        if match:
            start_str = match.group(1).strip()
            end_str = match.group(2).strip()
            
            # Try to parse each part recursively
            start_result = self.parse(start_str)
            end_result = self.parse(end_str)
            
            if start_result[0] and end_result[1]:
                return start_result[0], end_result[1]
        
        return None
    
    def extract_time_window(self, text: str) -> Optional[Tuple[datetime, datetime]]:
        """
        Extract time window from query, with helpful error messages
        
        Args:
            text: User query
        
        Returns:
            (start_time, end_time) or None if no time found
        """
        start, end = self.parse(text)
        
        if start and end:
            return start, end
        
        return None


# Test function
if __name__ == "__main__":
    print("Testing DateTimeParser...")
    
    parser = DateTimeParser(reference_date=datetime(2025, 9, 26, 14, 30))
    
    test_queries = [
        "yesterday",
        "today",
        "last 3 hours",
        "last 5 days",
        "Sept 25",
        "September 25th",
        "between 10:00 and 12:00 on Sept 24",
        "from 10:00 to 12:00 on Sept 24",
        "10:00 to 12:00 on Sept 24",
        "from Sept 24 to Sept 25",
        "this week",
        "last week",
        "9/25",
        "2025-09-25",
    ]
    
    print("\nTest queries:")
    for query in test_queries:
        start, end = parser.parse(query)
        if start and end:
            print(f"✅ '{query}'")
            print(f"   Start: {start}")
            print(f"   End:   {end}")
        else:
            print(f"❌ '{query}' - Could not parse")
        print()