var fs = require('fs'),
    child_process = require('child_process'),
    temp = require('temp'),
    path = require('path'),
    logger = require('./logger').logger,
    Promise = require('promise') // jshint ignore:line
    ;

function cleanAndGetIndexes(text) {
    var addRules = {
        name: "add",
        openTag: "{+",
        replaceOpenTag: "",
        closeTag: "+}",
        replaceCloseTag: ""
    };
    var delRules = {
        name: "del",
        openTag: "[-",
        replaceOpenTag: "",
        closeTag: "-]",
        replaceCloseTag: ""
    };
    var rules = [addRules, delRules];

    var TagTypeEnum = {
        OPENING: 1,
        CLOSING: 2
    };

    function tagLookup(rules, text, pos) {
        var seen = false;
        var type = null;
        var rule = null;
        for (var i = 0; i < rules.length; i++) {
            var candidateTag = text.slice(pos, pos + rules[i].openTag.length);
            if (rules[i].openTag == candidateTag) {
                seen = true;
                type = TagTypeEnum.OPENING;
                rule = i;
                break;
            }
            candidateTag = text.slice(pos, pos + rules[i].closeTag.length);
            if (rules[i].closeTag == candidateTag) {
                seen = true;
                type = TagTypeEnum.CLOSING;
                rule = i;
                break;
            }
        }

        return {
            seen: seen,
            rule: rule,
            type: type
        };
    }

    var finalText = "";
    var posInFinalText = 0; // character that is going to be treated
    // The position in the original text: 
    var posInText = 0; // character that is going to be treated
    var StateEnum = {
        OUTSIDE_TAG: 1,
        INSIDE_TAG: 2
    };
    var state = StateEnum.OUTSIDE_TAG;
    var zones = [[], []];
    var currentTextBeginPos = 0;
    var currentTextEndPos = null;
    var currentTagBeginPos = null;
    var currentTagEndPos = null;
    var currentTag = null;

    function forward() {
        posInFinalText = posInFinalText + 1;
        posInText = posInText + 1;
    }

    function seenOpeningTag() {
        memorizeText();
        currentTagBeginPos = posInFinalText;
        finalText = finalText.concat(rules[currentTag].replaceOpenTag);
        posInFinalText = posInFinalText + rules[currentTag].replaceOpenTag.length;
        posInText = posInText + rules[currentTag].openTag.length;
        currentTextBeginPos = posInText;
    }

    function seenClosingTag() {
        memorizeText();
        finalText = finalText.concat(rules[currentTag].replaceCloseTag);
        posInFinalText = posInFinalText + rules[currentTag].replaceCloseTag.length;
        posInText = posInText + rules[currentTag].closeTag.length;
        currentTagEndPos = posInFinalText - 1;
        zones[currentTag].push({begin: currentTagBeginPos, end: currentTagEndPos});
        currentTextBeginPos = posInText;
    }

    function memorizeText() {
        currentTextEndPos = posInText - 1;
        if (currentTextEndPos >= currentTextBeginPos) {
            finalText = finalText.concat(text.slice(currentTextBeginPos, currentTextEndPos + 1));
        }
    }

    function end() {
        memorizeText();
    }

    while (posInText < text.length) {
        var tag = tagLookup(rules, text, posInText);
        if (tag.seen && tag.type == TagTypeEnum.OPENING) {
            if (state != StateEnum.OUTSIDE_TAG) {
                log.error("Opening tag while not outside tag (tags cannot be nested)");
                return null;
            }
            currentTag = tag.rule;
            seenOpeningTag();
            state = StateEnum.INSIDE_TAG;
        } else if (tag.seen && tag.type == TagTypeEnum.CLOSING) {
            if (state != StateEnum.INSIDE_TAG) {
                log.error("Closing tag while not inside tag.");
                return null;
            }
            if (currentTag != tag.rule) {
                log.error("Closing tag, but not of the same type as previously opened.");
                return null;
            }
            seenClosingTag();
            state = StateEnum.OUTSIDE_TAG;
        } else {
            forward();
        }
    }
    end();

    return {text: finalText, zones: zones};
}

function newTempDir() {
    return new Promise(function (resolve, reject) {
        temp.mkdir('gcc-explorer-diff', function (err, dirPath) {
            if (err)
                reject("Unable to open temp file: " + err);
            else
                resolve(dirPath);
        });
    });
}

var writeFile = Promise.denodeify(fs.writeFile);

function buildDiffHandler(config) {
    var maxFileSize = config.maxOutput;
    return function diffHandler(req, res) {
        var before = req.body.before;
        var after = req.body.after;
        var error;
        if (before === undefined) {
            error = 'Warning : Bad request : wrong "before"';
            logger.error(error);
            return next(new Error(error));
        }
        if (after === undefined) {
            error = 'Warning : Bad request : wrong "after"';
            logger.error(error);
            return next(new Error(error));
        }

        var tempBeforePath, tempAfterPath;
        newTempDir()
            .then(function (tmpDir) {
                tempBeforePath = path.join(tmpDir, "gcc-explorer-wdiff-before");
                tempAfterPath = path.join(tmpDir, "gcc-explorer-wdiff-after");
                return Promise.all(
                    writeFile(tempBeforePath, before),
                    writeFile(tempAfterPath, after)
                );
            })
            .then(function () {
                var truncated = false;
                var stdout = "";
                var child = child_process.spawn(config.wdiffExe, [tempBeforePath, tempAfterPath],
                    {maxBuffer: maxFileSize, detached: true});
                child.stdout.on('data', function (data) {
                    if (truncated) return;
                    if (stdout.length > maxFileSize) {
                        stdout += "\n[Truncated]";
                        truncated = true;
                        child.kill();
                        resolve(stdout);
                    }
                    stdout += data;
                });
                return new Promise(function (resolve, reject) {
                    child.on('error', function (e) {
                        reject(e);
                    });
                    child.on('exit', function () {
                        // See comment in compile.js - seems needed if the child has immediately exited
                        setTimeout(function () {
                            resolve(stdout);
                        }, 0);
                    });
                });
            })
            .then(function (output) {
                var cleaned = cleanAndGetIndexes(output);
                res.set('Content-Type', 'application/json');
                if (cleaned === null) {
                    res.end(JSON.stringify({
                        computedDiff: "Failed to clean the diff",
                        zones: null
                    }));
                } else {
                    res.end(JSON.stringify({
                        computedDiff: cleaned.text,
                        zones: cleaned.zones
                    }));
                }
            })
            .catch(function (err) {
                res.end(JSON.stringify({
                    computedDiff: "Failed to diff: " + err,
                    zones: null
                }));
            });
    };
}

module.exports = {
    buildDiffHandler: buildDiffHandler
};