#!/usr/bin/env python

import urllib2
import h5py
import datetime as dt
import os.path
import sys

BASE_URL = "http://www.star.nesdis.noaa.gov/smcd/spb/fwu/homepage/" + \
           "AVHRR/Op_Cal_AVHRR/"

URLS = {
    "Metop-B":
    {"ch1": BASE_URL + "Metop1_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "Metop1_AVHRR_Libya_ch2.txt",
     "ch3a": BASE_URL + "Metop1_AVHRR_Libya_ch3a.txt"},
    "Metop-A":
    {"ch1": BASE_URL + "Metop2_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "Metop2_AVHRR_Libya_ch2.txt",
     "ch3a": BASE_URL + "Metop2_AVHRR_Libya_ch3a.txt"},
    "NOAA-16":
    {"ch1": BASE_URL + "N16_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "N16_AVHRR_Libya_ch2.txt"},
    "NOAA-17":
    {"ch1": BASE_URL + "N17_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "N17_AVHRR_Libya_ch2.txt",
     "ch3a": BASE_URL + "N17_AVHRR_Libya_ch3a.txt"},
    "NOAA-18":
    {"ch1": BASE_URL + "N18_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "N18_AVHRR_Libya_ch2.txt"},
    "NOAA-19":
    {"ch1": BASE_URL + "N19_AVHRR_Libya_ch1.txt",
     "ch2": BASE_URL + "N19_AVHRR_Libya_ch2.txt"}
}

def get_page(url):
    '''Retrieve the given page.'''
    return urllib2.urlopen(url).read()

def get_coeffs(page):
    '''Parse coefficients from the page.'''
    coeffs = {}
    coeffs['datetime'] = []
    coeffs['slope1'] = []
    coeffs['intercept1'] = []
    coeffs['slope2'] = []
    coeffs['intercept2'] = []

    slope1_idx, intercept1_idx, slope2_idx, intercept2_idx = \
        None, None, None, None

    date_idx = 0
    for row in page.lower().split('\n'):
        row = row.split()
        if len(row) == 0:
            continue
        if row[0] == 'update':
            # Get the column indices from the header line
            slope1_idx = row.index('slope_lo')
            intercept1_idx = row.index('int_lo')
            slope2_idx = row.index('slope_hi')
            intercept2_idx = row.index('int_hi')
            continue

        if slope1_idx is None:
            continue

        # In some cases the fields are connected, skip those rows
        if max([slope1_idx, intercept1_idx,
                slope2_idx, intercept2_idx]) >= len(row):
            continue

        try:
            dat = dt.datetime.strptime(row[date_idx], "%m/%d/%Y")
        except ValueError:
            continue

        coeffs['datetime'].append([dat.year, dat.month, dat.day])
        coeffs['slope1'].append(float(row[slope1_idx]))
        coeffs['intercept1'].append(float(row[intercept1_idx]))
        coeffs['slope2'].append(float(row[slope2_idx]))
        coeffs['intercept2'].append(float(row[intercept2_idx]))

    return coeffs

def get_all_coeffs():
    '''Get all available calibration coefficients for the satellites.'''
    coeffs = {}

    for platform in URLS.keys():
        if platform not in coeffs:
            coeffs[platform] = {}
        for chan in URLS[platform].keys():
            url = URLS[platform][chan]
            print url
            page = get_page(url)
            coeffs[platform][chan] = get_coeffs(page)

    return coeffs

def save_coeffs(coeffs, out_dir=''):
    '''Save calibration coefficients to HDF5 files.'''
    for platform in coeffs.keys():
        fname = os.path.join(out_dir, "%s_calibration_data.h5" % platform)
        fid = h5py.File(fname, 'w')
        
        for chan in coeffs[platform].keys():
            fid.create_group(chan)
            fid[chan]['datetime'] = coeffs[platform][chan]['datetime']
            fid[chan]['slope1'] = coeffs[platform][chan]['slope1']
            fid[chan]['intercept1'] = coeffs[platform][chan]['intercept1']
            fid[chan]['slope2'] = coeffs[platform][chan]['slope2']
            fid[chan]['intercept2'] = coeffs[platform][chan]['intercept2']

        fid.close()
        print "Calibration coefficients saved for %s" % platform

def main():
    '''Create calibration coefficient files for AVHRR'''
    out_dir = sys.argv[1]
    coeffs = get_all_coeffs()
    save_coeffs(coeffs, out_dir=out_dir)

if __name__ == "__main__":
    main()