var path = require('path'),
    fs = require('fs'),
    External = require('./external'),
    Step = require('step'),
    _ = require('underscore')._,
    sys = require('sys'),
    mess = require('mess'),
    tree = require('mess/tree');

require.paths.unshift(path.join(__dirname, '..', 'lib'));

/**
 * Rendering circuitry for JSON map manifests.
 *
 * This is node-only for the time being.
 */

/**
 * Convert a two-element-per-item Array
 * into an object, for the purpose of checking membership
 * and replacing stuff.
 * @param {Array} list a list.
 */
var to = function(list) {
    return list && list[0] && _.reduce(list, function(m, r) {
        if (r && r.length > 1) {
          m[r[0]] = r[1];
        }
        return m;
    }, {});
};

mess.Renderer = function Renderer(env) {
    var env = {
        data_dir: env.data_dir || '/tmp/',
        local_data_dir: env.local_data_dir || '',
        validation_data: env.validation_data || false
    };
    return {
        /**
         * Keep a copy of passed-in environment variables
         */
        env: env,
        /**
         * Wrapper for downloading externals: likely removable
         *
         * @param {String} uri the URI of the resource.
         * @param {Function} callback
         */
        grab: function(uri, callback) {
            new External(this.env).process(uri, callback);
        },

        /**
         * Download any file-based remote datsources.
         *
         * Usable as an entry point: does not expect any modification to
         * the map object beyond JSON parsing.
         *
         * @param {Object} m map object.
         * @param {Function} callback
         */
        localizeExternals: function(m, callback) {
            var that = this;
            Step(
                function() {
                    var group = this.group();
                    m.Layer.forEach(function(l) {
                        if (l.Datasource.file) {
                            that.grab(l.Datasource.file, group());
                        }
                    });
                    if (m.Layer.length == 0) group()();
                },
                function(err, results) {
                    var result_map = to(results);
                    m.Layer = _.map(_.filter(m.Layer,
                        function(l) {
                            return l.Datasource.file &&
                                result_map[l.Datasource.file];
                        }),
                        function(l) {
                            l.Datasource.file = result_map[l.Datasource.file];
                            return l;
                        }
                    );
                    callback(err, m);
                }
            );
        },

        /**
         * Download any remote stylesheets
         *
         * @param {Object} m map object.
         * @param {Function} callback
         */
        localizeStyle: function(m, callback) {
            var that = this;
            Step(
                function() {
                    var group = this.group();
                    m.Stylesheet.forEach(function(s) {
                        if (!s.id) {
                            that.grab(s, group());
                        }
                    });
                    group()();
                },
                function(err, results) {
                    var result_map = to(results);
                    for (s in m.Stylesheet) {
                        if (!m.Stylesheet[s].id) {
                            m.Stylesheet[s] = result_map[m.Stylesheet[s]];
                        }
                    }
                    callback(err, m);
                }
            );
        },

        /**
         * Compile (already downloaded) styles with mess.js,
         * calling callback with an array of [map object, [stylesheet objects]]
         *
         * Called with the results of localizeStyle or localizeExternals:
         * expects not to handle downloading.
         *
         * @param {Object} m map object.
         * @param {Function} callback
         */
        style: function(m, callback) {
            var that = this;
            Step(
                function() {
                    var group = this.group();
                    m.Stylesheet.forEach(function(s) {
                        if (s.id) {
                            group()(null, [s.id, s.data]);
                        } else {
                            fs.readFile(s, 'utf-8', function(err, data) {
                                group()(err, [s, data]);
                            });
                        }
                    });
                },
                function(e, results) {
                    var options = {},
                        group = this.group();
                    for (var i = 0, l = results.length; i < l; i++) {
                        new mess.Parser(_.extend(_.extend({
                            filename: s
                        }, that.env), this.env)).parse(results[i][1],
                            function(err, tree) {
                            if (err) {
                                mess.writeError(err, options);
                                throw err;
                            } else {
                                try {
                                    group()(err, [
                                        results[i][0],
                                        tree]);
                                    return;
                                } catch (e) {
                                    throw e;
                                    return;
                                }
                            }
                        });
                    }
                },
                function(err, res) {
                    callback(err, m, res);
                }
            );
        },

        /**
         * Split definitions into sub-lists of definitions
         * containing rules pertaining to only one
         * symbolizer each
         */
        splitSymbolizers: function(definitions) {
            var bySymbolizer = {};
            for (var i = 0; i < definitions.length; i++) {
                definitions[i].symbolizers().forEach(function(sym) {
                    var index = sym + '/' + definitions[i].selector.attachment;
                    if(!bySymbolizer[index]) {
                        bySymbolizer[index] = [];
                    }
                    bySymbolizer[index].push(
                        definitions[i].filterSymbolizer(sym));
                });
            }
            return bySymbolizer;
        },

        /**
         * Pick the 'winners' - all elements that select
         * properly. Apply inherited styles from their
         * ancestors to them.
         */
        processChain: function(definitions) {
            // definitions are ordered in specificity,
            // high to low
            //
            // basically if 'this level' has
            // a filter, then keep going, otherwise
            // this is the final selector.
            var winners = [];
            var ancestors = [];
            var belowThreshold = false;

            while (def = definitions.shift()) {
                if (belowThreshold) {
                    ancestors.push(def)
                } else if (def.selector.specificity()[2] > 0) {
                    winners.push(def);
                } else {
                    winners.push(def);
                    // nothing below this level will win
                    belowThreshold = true;
                }
            }

            // iterate in reverse - low to high specificity
            for (var i = ancestors.length - 1; i >= 0; i--) {
                for (var j = 0; j < winners.length; j++) {
                    winners[j].inheritFrom(ancestors[i]);
                }
            }

            return this.resolveConditions(winners);
        },

        resolveConditions: function(definitions) {
            var rules = [];
            var negatedFilters = [];
            var negatedZoom = tree.ZoomFilter.newFromRange([0, Infinity]);

            for (var i = 0; i < definitions.length; i++) {
                var definition = definitions[i];
                var zooms = definition.selector.filters.filter(function(f) {
                    return f instanceof tree.ZoomFilter;
                });

                // Merge all zoom filters without overwriting existing zoom
                // filters; they might be referenced in other selectors.
                var zoom = tree.ZoomFilter.newFromRange([0, Infinity]);
                zooms.forEach(function(f) { zoom.intersection(f); });

                // Only add the negated current zoom when there actually are zoom filters.
                var negation = zooms.length ? zoom.negate() : false;

                zoom.intersection(negatedZoom);
                var zoomRanges = zoom.getRanges();
                if (!zoomRanges.length) {
                    continue;
                } else if (negation) {
                    // This zoom range has ranged. Add it so that future rules
                    // will exclude the current zoom.
                    negatedZoom.intersection(negation);
                }

                // Resolve regular filters.
                var filters = definition.selector.filters.filter(function(f) {
                    return f instanceof tree.Filter;
                });
                var negation = filters.map(function(f) { return f.negate(); });

                // add in existing negations
                // TODO: run uniq on this.
                filters.push.apply(filters, negatedFilters);

                // add this definition's filter's negations to the list
                negatedFilters.push.apply(negatedFilters, negation);

                definition.selector.filters = filters;
                definition.selector.zoom = zoom;

                // Add a separate rule for each zoom range.
                for (var j = 0; j < zoomRanges.length; j++) {
                    var rule = definition.clone();
                    rule.selector.zoom = tree.ZoomFilter.newFromRange(zoomRanges[j]);
                    rules.push(rule);
                }
            }
            return rules;
        },

        getMapProperties: function(rulesets, env) {
            var properties = [];
            rulesets.filter(function(r) {
                return r.selector.toCSS() === 'Map';
            }).forEach(function(r) {
                for (var i = 0; i < r.rules.length; i++) {
                    if (r.rules[i].eval) r.rules[i] = r.rules[i].eval(env);
                    properties.push(r.rules[i].toCSS());
                }
            });
            return properties.join('');
        },

        /**
         * Prepare full XML map output. Called with the results
         * of this.style
         *
         * @param {Array} res array of [map object, stylesheets].
         * @param {Function} callback
         */
        template: function(err, m, stylesheets, callback) {
            if (err) {
                callback(err);
                return;
            }

            var that = this,
                env = { frames: [] };

            /**
             * Add styles to a layer object
             *
             * @param {Object} layer the layer object.
             * @param {Array} stylesheets the results of ruleHash().
             * @return Formalized layer definition with .styles = [].
             */

            var rulesets = _.flatten(stylesheets.map(function(rulesets) {
                return rulesets[1].toList();
            }));

            var output = [];

            m.Layer.forEach(function(l) {
                l.styles = [];
                var classes = (l['class'] || '').split(/\s+/g);

                var matching = rulesets.filter(function(ruleset) {
                    return ruleset.selector.matches(l.id, classes);
                });

                // matching is an array of matching selectors,
                // in order from high specificity to low.
                var bySymbolizer = that.splitSymbolizers(matching);

                for (sym in bySymbolizer) {
                    // Create styles out of chains of one-symbolizer rules,
                    // and assign those styles to layers
                    var new_style = new mess.tree.Style(
                        l.id,
                        sym,
                        that.processChain(bySymbolizer[sym]));
                    l.styles.push(new_style.name());
                    output.push(new_style.toXML(env));
                }

                var nl = new mess.tree.Layer(l);
                output.push(nl.toXML());
            });

            // TODO: must change when background colors are available
            output.unshift(
                '<?xml version="1.0" '
                + 'encoding="utf-8"?>\n'
                + '<!DOCTYPE Map[]>\n'
                + '<Map '
                + this.getMapProperties(rulesets, env)
                + ' srs="+proj=merc +a=6378137 +b=6378137 '
                + '+lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m '
                + '+nadgrids=@null +no_defs">\n');

            output.push('</Map>');

            callback(null, output.join('\n'));
        },

        /**
         * Prepare a JML document (given as a string) into a
         * fully-localized XML file ready for Mapnik2 consumption
         *
         * @param {String} str the JSON file as a string.
         * @param {Function} callback to be called with err, XML representation.
         */
        render: function(str, callback) {
            var m = JSON.parse(str),
                that = this;
            this.localizeExternals(m, function(err, res) {
                that.localizeStyle(res, function(err, res) {
                    that.style(res, function(err, m, res) {
                        that.template(err, m, res, function(err, res) {
                            callback(err, res);
                        });
                    });
                });
            });
        }
    };
};

module.exports = mess;