#!/usr/bin/env node

/**
* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/*
* Script to update the CLI help documentation.
*
* ## Notes
*
* -   When invoking this script, be sure to set the `NODE_PATH` environment variable to include project package directory. Otherwise, if the `NODE_PATH` does not include the project package directory, imported modules may not be resolved.
*/
'use strict';

// MODULES //

var resolve = require( 'path' ).resolve;
var logger = require( 'debug' );
var groupBy = require( '@stdlib/utils/group-by' );
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
var objectKeys = require( '@stdlib/utils/keys' );
var rpad = require( '@stdlib/string/right-pad' );
var capitalize = require( '@stdlib/string/capitalize' );
var writeFile = require( '@stdlib/fs/write-file' ).sync;
var CLI_COMMANDS = require( './../../bin/cli_commands.json' ); // WARNING: fragile as this may no longer be valid if either this script or the required file moves


// VARIABLES //

// Logger for debugging:
var debug = logger( 'update-cli-help' );

// Minimal usage text template:
var USAGE_TEXT = [
	'',
	'Usage: stdlib [options] <command> [args] [-- <options>]',
	'',
	'Options:',
	'',
	'  -h,    --help                   Print this message.',
	'  -V,    --version                Print the version.',
	'',
	'Commands:',
	''
];

// Path to usage text:
var USAGE_TEXT_OUT = resolve( __dirname, '..', '..', 'bin', 'usage.txt' );

// Number of character allowed for a usage text row:
var USAGE_TEXT_WIDTH = 80; // chars

// Number of characters allowed for usage text commands:
var USAGE_TEXT_CMD_WIDTH = 34; // 2 + 30 + 2 = 34 chars; at char 35, begin command description

// Indentation for usage text commands:
var USAGE_TEXT_CMD_INDENT = '  '; // 2 chars

// Number of characters allowed for usage text command names:
var USAGE_TEXT_CMD_NAME_WIDTH = 30;

// Gutter used to separate usage text commands from usage text command descriptions:
var USAGE_TEXT_CMD_GUTTER = '  '; // 2 chars


// FUNCTIONS //

/**
* Creates a CLI usage text.
*
* @private
* @param {ObjectArray} cmds - commands
* @returns {(string|Error)} usage text or an error
*/
function createUsageText( cmds ) {
	var groups;
	var keys;
	var rows;
	var txt;
	var key;
	var i;
	var j;

	txt = USAGE_TEXT.slice();

	// Group the CLI commands:
	groups = groupBy( cmds, indicator );

	// Begin with the "general" group:
	if ( hasOwnProp( groups, 'general' ) ) {
		rows = cmds2rows( groups.general.sort( commandNameComparator ) );
		if ( rows instanceof Error ) {
			return rows;
		}
		for ( i = 0; i < rows.length; i++ ) {
			txt.push( rows[ i ] );
		}
		txt.push( '' );
	}

	// Extract a sorted list of group names:
	keys = objectKeys( groups ).sort();

	// For each group other than "general", add a command section:
	for ( j = 0; j < keys.length; j++ ) {
		key = keys[ j ];
		if ( key === 'general' ) {
			// We have already processed the "general" command section...
			continue;
		}
		txt.push( capitalize( key )+':' );
		txt.push( '' );

		rows = cmds2rows( groups[ key ].sort( commandNameComparator ) );
		if ( rows instanceof Error ) {
			return rows;
		}
		for ( i = 0; i < rows.length; i++ ) {
			txt.push( rows[ i ] );
		}
		txt.push( '' );
	}

	// Add an extra trailing line:
	txt.push( '' );

	// Return the usage text:
	return txt.join( '\n' );
}

/**
* Returns the value used to group CLI commands.
*
* @private
* @param {Object} obj - collection element
* @returns {string} indicator value
*/
function indicator( obj ) {
	return obj.group;
}

/**
* Comparator function for sorting command names.
*
* @private
* @param {Object} a - first value
* @param {Object} b - second value
* @returns {integer} value indicating sort order
*/
function commandNameComparator( a, b ) {
	// Note: we give special preference to `help [command]` to ensure it tops the list of command names...
	if ( a.command === 'help [command]' ) {
		return -1;
	}
	if ( b.command === 'help [command]' ) {
		return 1;
	}
	if ( a.command < b.command ) {
		return -1;
	}
	if ( a.command > b.command ) {
		return 1;
	}
	return 0;
}

/**
* Processes a CLI command "group", returning a list of usage text rows.
*
* @private
* @param {ObjectArray} cmds - list of commands
* @returns {(StringArray|Error)} usage text rows
*/
function cmds2rows( cmds ) {
	var out;
	var row;
	var i;

	out = [];
	for ( i = 0; i < cmds.length; i++ ) {
		row = USAGE_TEXT_CMD_INDENT;
		row += rpad( cmds[ i ].command, USAGE_TEXT_CMD_NAME_WIDTH );
		row += USAGE_TEXT_CMD_GUTTER;
		if ( row.length > USAGE_TEXT_CMD_WIDTH ) {
			debug( 'Command name is too long. Command: %s.', cmds[ i ].command );
			return new Error( 'unexpected error. Command name is too long. Command: '+cmds[ i ].command+'.' );
		}
		row += cmds[ i ].description;
		if ( row.length > USAGE_TEXT_WIDTH ) {
			debug( 'Command description is too long. Command: %s.', cmds[ i ].command );
			return new Error( 'unexpected error. Command description is too long. Command: '+cmds[ i ].command+'.' );
		}
		out.push( row );
	}
	return out;
}


// MAIN //

/**
* Updates CLI help documentation.
*
* @private
* @returns {void}
*/
function main() {
	var opts;
	var txt;
	var err;

	opts = {
		'encoding': 'utf8'
	};

	debug( 'Generating CLI usage text...' );
	txt = createUsageText( CLI_COMMANDS );
	if ( txt instanceof Error ) {
		process.exitCode = 1;
		return console.error( 'Error: %s', txt.message ); // eslint-disable-line no-console
	}
	debug( 'Writing to file...' );
	err = writeFile( USAGE_TEXT_OUT, txt, opts );
	if ( err ) {
		process.exitCode = 1;
		debug( 'Encountered an error when attempting to write usage text. Error: %s', err.message );
		return console.error( 'Error: %s', err.message ); // eslint-disable-line no-console
	}
	debug( 'Successfully wrote to file.' );

	debug( 'Finished.' );
}

main();