from fastapi import FastAPI, HTTPException, Body
from pydantic import BaseModel, Field
from datetime import datetime, timezone
from typing import Literal
import pytz
from dateutil import parser as dateutil_parser

app = FastAPI(
    title="Secure Time Utilities API",
    version="1.0.0",
    description="Provides secure UTC/local time retrieval, formatting, timezone conversion, and comparison.",
)

# -------------------------------
# Pydantic models
# -------------------------------


class FormatTimeInput(BaseModel):
    format: str = Field(
        "%Y-%m-%d %H:%M:%S", description="Python strftime format string"
    )
    timezone: str = Field(
        "UTC", description="IANA timezone name (e.g., UTC, America/New_York)"
    )


class ConvertTimeInput(BaseModel):
    timestamp: str = Field(
        ..., description="ISO 8601 formatted time string (e.g., 2024-01-01T12:00:00Z)"
    )
    from_tz: str = Field(
        ..., description="Original IANA time zone of input (e.g. UTC or Europe/Berlin)"
    )
    to_tz: str = Field(..., description="Target IANA time zone to convert to")


class ElapsedTimeInput(BaseModel):
    start: str = Field(..., description="Start timestamp in ISO 8601 format")
    end: str = Field(..., description="End timestamp in ISO 8601 format")
    units: Literal["seconds", "minutes", "hours", "days"] = Field(
        "seconds", description="Unit for elapsed time"
    )


class ParseTimestampInput(BaseModel):
    timestamp: str = Field(
        ..., description="Flexible input timestamp string (e.g., 2024-06-01 12:00 PM)"
    )
    timezone: str = Field(
        "UTC", description="Assumed timezone if none is specified in input"
    )


# -------------------------------
# Routes
# -------------------------------


@app.get("/get_current_utc_time", summary="Current UTC time")
def get_current_utc():
    """
    Returns the current time in UTC in ISO format.
    """
    return {"utc": datetime.utcnow().replace(tzinfo=timezone.utc).isoformat()}


@app.get("/get_current_local_time", summary="Current Local Time")
def get_current_local():
    """
    Returns the current time in local timezone in ISO format.
    """
    return {"local_time": datetime.now().isoformat()}


@app.post("/format_time", summary="Format current time")
def format_current_time(data: FormatTimeInput):
    """
    Return the current time formatted for a specific timezone and format.
    """
    try:
        tz = pytz.timezone(data.timezone)
    except Exception:
        raise HTTPException(
            status_code=400, detail=f"Invalid timezone: {data.timezone}"
        )
    now = datetime.now(tz)
    try:
        return {"formatted_time": now.strftime(data.format)}
    except Exception as e:
        raise HTTPException(status_code=400, detail=f"Invalid format string: {e}")


@app.post("/convert_time", summary="Convert between timezones")
def convert_time(data: ConvertTimeInput):
    """
    Convert a timestamp from one timezone to another.
    """
    try:
        from_zone = pytz.timezone(data.from_tz)
        to_zone = pytz.timezone(data.to_tz)
    except Exception as e:
        raise HTTPException(status_code=400, detail=f"Invalid timezone: {e}")

    try:
        dt = dateutil_parser.parse(data.timestamp)
        if dt.tzinfo is None:
            dt = from_zone.localize(dt)
        else:
            dt = dt.astimezone(from_zone)
        converted = dt.astimezone(to_zone)
        return {"converted_time": converted.isoformat()}
    except Exception as e:
        raise HTTPException(status_code=400, detail=f"Invalid timestamp: {e}")


@app.post("/elapsed_time", summary="Time elapsed between timestamps")
def elapsed_time(data: ElapsedTimeInput):
    """
    Calculate the difference between two timestamps in chosen units.
    """
    try:
        start_dt = dateutil_parser.parse(data.start)
        end_dt = dateutil_parser.parse(data.end)
        delta = end_dt - start_dt
    except Exception as e:
        raise HTTPException(status_code=400, detail=f"Invalid timestamps: {e}")

    seconds = delta.total_seconds()
    result = {
        "seconds": seconds,
        "minutes": seconds / 60,
        "hours": seconds / 3600,
        "days": seconds / 86400,
    }

    return {"elapsed": result[data.units], "unit": data.units}


@app.post("/parse_timestamp", summary="Parse and normalize timestamps")
def parse_timestamp(data: ParseTimestampInput):
    """
    Parse human-friendly input timestamp and return standardized UTC ISO time.
    """
    try:
        tz = pytz.timezone(data.timezone)
        dt = dateutil_parser.parse(data.timestamp)
        if dt.tzinfo is None:
            dt = tz.localize(dt)
        dt_utc = dt.astimezone(pytz.utc)
        return {"utc": dt_utc.isoformat()}
    except Exception as e:
        raise HTTPException(status_code=400, detail=f"Could not parse: {e}")


@app.get("/list_time_zones", summary="All valid time zones")
def list_time_zones():
    """
    Return a list of all valid IANA time zones.
    """
    return pytz.all_timezones