"use strict";

var helpers = require("postcss-helpers");
var util = require("util");

/**
 * Checks validity of config object.
 * @private
 * @param   {Object} config Configuration object
 */
var validateConfig = function (config) {
    if (!config || !config.rules) {
        throw new Error("You must configure at least one replace rule.");
    }

    if (!Array.isArray(config.rules) && typeof config.rules !== "function") {
        throw new Error("Rules must be an Array or Function.");
    }

    if (Array.isArray(config.rules)) {
        config.rules.forEach(function (rule) {
            if (!rule.from && !rule.to) {
                throw new Error(
                    'Rules must be in { from: "from", to: "to" } format.'
                );
            } else if (
                typeof rule.from !== "string" &&
                !util.types.isRegExp(rule.from)
            ) {
                throw new Error("Rule.from must be a String or RegExp.");
            } else if (["string", "function"].indexOf(typeof rule.to) === -1) {
                throw new Error("Rule.to must be a String or Function.");
            }
        });
    }

    if (
        config.properties &&
        !Array.isArray(config.properties) &&
        !(typeof config.properties === "boolean")
    ) {
        throw new Error("Properties must be an Array of Strings or Boolean.");
    }

    if (Array.isArray(config.properties)) {
        config.properties.forEach(function (prop) {
            if (typeof prop !== "string") {
                throw new Error('Items in "properties" array must be Strings.');
            }
        });
    }
};

/**
 * Returns callback function for URI replacement based on config params.
 * @private
 * @param   {Array}    rules Array of objects with "from" and "to" keys to use
 *                            as arguments to String.replace.
 * @returns {Function} Callback function.
 */
var useRulesCallback = function (rules) {
    rules = rules;
    return function (uri) {
        var modified = false;
        var original = uri.href();

        rules.forEach(function (rule) {
            if (modified) {
                return;
            }

            var tmp = original.replace(rule.from, rule.to);

            if (tmp !== original) {
                modified = true;
                uri.href(tmp);
            }
        });
    };
};

/**
 * Plugin body.
 * @param   {Boolean}        config.imports    If set to true, will also replace @import values.
 * @param   {Array|Boolean}  config.properties List of css properties to update or false.
 * @param   {Array|Function} config.rules      Array of replace params or
 *                                              callback function.
 * @returns {Function} PostCSS plugin.
 */
var urlrewrite = function (config) {
    validateConfig(config);

    // Choosing which callback to use: One received from user or autogenerated
    // from params.
    var callback = Array.isArray(config.rules)
        ? useRulesCallback(config.rules)
        : config.rules;

    // Function to update @import URIs
    var updateImport = function (atRule) {
        if (atRule.name !== "import") {
            return;
        }

        var helper = helpers.createImportHelper(atRule.params);

        callback(helper.URI);
        atRule.params = helper.getModifiedRule();
    };

    // Function to update declarations URIs
    var updateDecl = function (decl) {
        if (config.properties === false) {
            return;
        }
        if (
            Array.isArray(config.properties) &&
            config.properties.indexOf(decl.prop) === -1
        ) {
            return;
        }
        if (!decl.value.match(helpers.regexp.URLS)) {
            return;
        }

        var helper = helpers.createUrlsHelper(decl.value);

        helper.URIS.forEach(callback);
        decl.value = helper.getModifiedRule();
    };

    return function (style) {
        if (config.imports) {
            style.walkAtRules(updateImport);
        }
        if (config.properties !== false) {
            style.walkDecls(updateDecl);
        }
    };
};

module.exports = urlrewrite;