/* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */
/* exported getCompletions, getCommonPrefix, getDeclaredConstants */

// Returns a list of potential completions for text. Completions either
// follow a dot (e.g. foo.ba -> bar) or they are picked from globalCompletionList (e.g. fo -> foo)
// commandHeader is prefixed on any expression before it is eval'ed.  It will most likely
// consist of global constants that might not carry over from the calling environment.
//
// This function is likely the one you want to call from external modules
function getCompletions(text, commandHeader, globalCompletionList) {
    let methods = [];
    let expr_, base;
    let attrHead = '';
    if (globalCompletionList == null) {
        globalCompletionList = [];
    }

    let offset = getExpressionOffset(text, text.length - 1);
    if (offset >= 0) {
        text = text.slice(offset);

        // Look for expressions like "Main.panel.foo" and match Main.panel and foo
        let matches = text.match(/(.*)\.(.*)/);
        if (matches) {
            [expr_, base, attrHead] = matches;

            methods = getPropertyNamesFromExpression(base, commandHeader).filter(
                attr => attr.slice(0, attrHead.length) == attrHead
            );
        }

        // Look for the empty expression or partially entered words
        // not proceeded by a dot and match them against global constants
        matches = text.match(/^(\w*)$/);
        if (text == '' || matches) {
            [expr_, attrHead] = matches;
            methods = globalCompletionList.filter(
                attr => attr.slice(0, attrHead.length) == attrHead
            );
        }
    }

    return [methods, attrHead];
}


//
// A few functions for parsing strings of javascript code.
//

// Identify characters that delimit an expression.  That is,
// if we encounter anything that isn't a letter, '.', ')', or ']',
// we should stop parsing.
function isStopChar(c) {
    return !c.match(/[\w.)\]]/);
}

// Given the ending position of a quoted string, find where it starts
function findMatchingQuote(expr, offset) {
    let quoteChar = expr.charAt(offset);
    for (let i = offset - 1; i >= 0; --i) {
        if (expr.charAt(i) == quoteChar && expr.charAt(i - 1) != '\\') {
            return i;
        }
    }
    return -1;
}

// Given the ending position of a regex, find where it starts
function findMatchingSlash(expr, offset) {
    for (let i = offset - 1; i >= 0; --i) {
        if (expr.charAt(i) == '/' && expr.charAt(i - 1) != '\\') {
            return i;
        }
    }
    return -1;
}

// If expr.charAt(offset) is ')' or ']',
// return the position of the corresponding '(' or '[' bracket.
// This function does not check for syntactic correctness.  e.g.,
// findMatchingBrace("[(])", 3) returns 1.
function findMatchingBrace(expr, offset) {
    let closeBrace = expr.charAt(offset);
    let openBrace = ({ ')': '(', ']': '[' })[closeBrace];

    function findTheBrace(expr, offset) {
        if (offset < 0) {
            return -1;
        }

        if (expr.charAt(offset) == openBrace) {
            return offset;
        }
        if (expr.charAt(offset).match(/['"]/)) {
            return findTheBrace(expr, findMatchingQuote(expr, offset) - 1);
        }
        if (expr.charAt(offset) == '/') {
            return findTheBrace(expr, findMatchingSlash(expr, offset) - 1);
        }
        if (expr.charAt(offset) == closeBrace) {
            return findTheBrace(expr, findTheBrace(expr, offset - 1) - 1);
        }

        return findTheBrace(expr, offset - 1);

    }

    return findTheBrace(expr, offset - 1);
}

// Walk expr backwards from offset looking for the beginning of an
// expression suitable for passing to eval.
// There is no guarantee of correct javascript syntax between the return
// value and offset.  This function is meant to take a string like
// "foo(Obj.We.Are.Completing" and allow you to extract "Obj.We.Are.Completing"
function getExpressionOffset(expr, offset) {
    while (offset >= 0) {
        let currChar = expr.charAt(offset);

        if (isStopChar(currChar)) {
            return offset + 1;
        }

        if (currChar.match(/[)\]]/)) {
            offset = findMatchingBrace(expr, offset);
        }

        --offset;
    }

    return offset + 1;
}

// Things with non-word characters or that start with a number
// are not accessible via .foo notation and so aren't returned
function isValidPropertyName(w) {
    return !(w.match(/\W/) || w.match(/^\d/));
}

// To get all properties (enumerable and not), we need to walk
// the prototype chain ourselves
function getAllProps(obj) {
    if (obj === null || obj === undefined) {
        return [];
    }
    return Object.getOwnPropertyNames(obj).concat( getAllProps(Object.getPrototypeOf(obj)) );
}

// Given a string _expr_, returns all methods
// that can be accessed via '.' notation.
// e.g., expr="({ foo: null, bar: null, 4: null })" will
// return ["foo", "bar", ...] but the list will not include "4",
// since methods accessed with '.' notation must star with a letter or _.
function getPropertyNamesFromExpression(expr, commandHeader = '') {
    let obj = {};
    if (!isUnsafeExpression(expr)) {
        try {
            obj = eval(commandHeader + expr);
        } catch (e) {
            return [];
        }
    } else {
        return [];
    }

    let propsUnique = {};
    if (typeof obj === 'object') {
        let allProps = getAllProps(obj);
        // Get only things we are allowed to complete following a '.'
        allProps = allProps.filter( isValidPropertyName );

        // Make sure propsUnique contains one key for every
        // property so we end up with a unique list of properties
        allProps.map(p => propsUnique[p] = null);
    }
    return Object.keys(propsUnique).sort();
}

// Given a list of words, returns the longest prefix they all have in common
function getCommonPrefix(words) {
    let word = words[0];
    for (let i = 0; i < word.length; i++) {
        for (let w = 1; w < words.length; w++) {
            if (words[w].charAt(i) != word.charAt(i))
                return word.slice(0, i);
        }
    }
    return word;
}

// Returns true if there is reason to think that eval(str)
// will modify the global scope
function isUnsafeExpression(str) {
    // Remove any blocks that are quoted or are in a regex
    function removeLiterals(str) {
        if (str.length == 0) {
            return '';
        }

        let currChar = str.charAt(str.length - 1);
        if (currChar == '"' || currChar == '\'') {
            return removeLiterals(str.slice(0, findMatchingQuote(str, str.length - 1)));
        } else if (currChar == '/') {
            return removeLiterals(str.slice(0, findMatchingSlash(str, str.length - 1)));
        }

        return removeLiterals(str.slice(0, str.length - 1)) + currChar;
    }

    // Check for any sort of assignment
    // The strategy used is dumb: remove any quotes
    // or regexs and comparison operators and see if there is an '=' character.
    // If there is, it might be an unsafe assignment.

    let prunedStr = removeLiterals(str);
    prunedStr = prunedStr.replace(/[=!]==/g, '');    //replace === and !== with nothing
    prunedStr = prunedStr.replace(/[=<>!]=/g, '');    //replace ==, <=, >=, != with nothing

    if (prunedStr.match(/[=]/)) {
        return true;
    } else if (prunedStr.match(/;/)) {
        // If we contain a semicolon not inside of a quote/regex, assume we're unsafe as well
        return true;
    }

    return false;
}

// Returns a list of global keywords derived from str
function getDeclaredConstants(str) {
    let ret = [];
    str.split(';').forEach(s => {
        let base_, keyword;
        let match = s.match(/const\s+(\w+)\s*=/);
        if (match) {
            [base_, keyword] = match;
            ret.push(keyword);
        }
    });

    return ret;
}