/**
 * db - a module that handles talking to the database (in this case, postgres).
 *
 * This module attempts to treat the database as an implementation detail. Methods are made available to
 * create tables, drop tables, insert rows, select rows, etc., without the caller needing to deal with SQL.
 */

"use strict";

var util = require("util");
var _ = require("underscore");
var tool = require("./tool");
var when = require("when");
var pg = require("pg");
var schema = require("./schema");
var log = tool.log();

var connectionString = process.argv[3];  // for example: "postgres://postgres:12345@localhost:5432/air"
var labels = ["year", "month", "day", "hour", "minute", "second"];

/**
 * Surrounds s with double quotes.
 */
function quoteName(s) {
    return '"' + s + '"';
}

/**
 * Surrounds s with single quotes.
 */
function quoteValue(s) {
    return "'" + s + "'";
}

/**
 * Returns a sql statement that drops the specified table.
 *
 * @param {Object} tableSpec an object that describes the table structure. This function requires the name: key to
 *                 hold the table's name.
 * @returns {{sql: string, args: Array}} an object {sql: x, args: y} representing a drop table statement.
 */
exports.dropTable = function dropTable(tableSpec) {
    return {sql: tool.format("DROP TABLE IF EXISTS {0};", quoteName(tableSpec.name)), args: []};
}

/**
 * Returns a sql statement that creates the specified table if it doesn't already exist.
 *
 * @param {Object} tableSpec an object that describes the table structure. This function requires the following keys:
 *            name: the name of the table;
 *            columns: an array of column objects:
 *                name: the name of the column;
 *                type: the type of the column;
 *                modifier: optional definition flags for the column, such as "NOT NULL";
 *            primary: an optional object to describe the table's primary key:
 *                name: the primary key's name;
 *                columns: an array of one or more column names that contribute to the primary key;
 * @returns {{sql: string, args: Array}} an object {sql: x, args: y} representing a create table statement.
 */
exports.createTable = function createTable(tableSpec) {
    var stmt = tool.format("CREATE TABLE IF NOT EXISTS {0} (\n    ", quoteName(tableSpec.name));
    stmt += tableSpec.columns.map(function(column) {
        return tool.format("{0} {1} {2}", quoteName(column.name), column.type, tool.coalesce(column.modifier, ""));
    }).join(",\n    ");
    if (tableSpec.primary) {
        stmt += tool.format(",\n    CONSTRAINT {0} PRIMARY KEY ({1})",
            quoteName(tableSpec.primary.name),
            tableSpec.primary.columns.map(function(columnName) { return quoteName(columnName); }).join(", "));
    }
    stmt += "\n) WITH (OIDS = FALSE);";
    if (tableSpec.owner) {
        stmt += tool.format("\nALTER TABLE {0} OWNER TO {1};", quoteName(tableSpec.name), tableSpec.owner);
    }
    return {sql: stmt, args: []};
}

/**
 * Returns a sql statement that either inserts or updates the provided row into the specified table.
 *
 * @param {Object} tableSpec an object that describes the table structure. This function requires the following keys:
 *            name: the name of the table;
 *            columns: an array of column objects:
 *                name: the name of the column;
 *                type: the type of the column;
 *            primary: an object to describe the table's primary key:
 *                name: the primary key's name;
 *                columns: an array of one or more column names that contribute to the primary key;
 * @param {Object} row an object of keys and values where keys correspond to column names.
 * @returns {{sql: string, args: Array}} an object {sql: x, args: y} representing an upsert statement.
 */
exports.upsert = function upsert(tableSpec, row) {
    /*  WITH new_values (id, field1, field2) AS (
            VALUES (CAST($1 AS foo), CAST($2 AS foo), CAST($3 AS foo))),
        upsert AS (
            UPDATE someTable m
                SET field1 = nv.field1,
                    field2 = nv.field2
            FROM new_values nv
            WHERE m.id = nv.id
            RETURNING m.*
        )
        INSERT INTO someTable (id, field1, field2)
        SELECT id, field1, field2
        FROM new_values
        WHERE NOT EXISTS (SELECT 1 FROM upsert up WHERE up.id = new_values.id) */

    var table = quoteName(tableSpec.name);
    var columns = tableSpec.columns;
    var quotedNames = columns.map(function(column) { return quoteName(column.name); });
    var allQuotedNames = quotedNames.join(", ");
    function idEqualityExpression(l, r) {
        return tableSpec.primary.columns.map(function(n) {
            return tool.format("{0}.{2} = {1}.{2}", l, r, quoteName(n));
        }).join(" AND ");
    }

    var values = [];
    var stmt = tool.format("WITH new_values ({0}) AS (\n    VALUES (\n        {1})),\n",
        allQuotedNames,
        columns.map(function(column, i) {
            var value = row[column.name];
            if (value === undefined) {
                value = null;
            }
            values.push(value);
            return tool.format("CAST(${0} AS {1})", i + 1, column.type);
        }).join(",\n        "));

    stmt += tool.format("upsert AS (\n    UPDATE {0} m SET\n        ", table);
    var provided = [];
    columns.forEach(function(column, i) {
        // Skip assignment of columns that have no value defined for them. This will retain the column value
        // of the row if it exists.
        if (row[column.name] !== undefined) {
            provided.push(quotedNames[i]);
        }
    });
    stmt += tool.format("{0}\n    FROM new_values nv\n    WHERE {1}\n    RETURNING m.*)\n",
        provided.map(function(col) {return tool.format("{0} = nv.{0}", col); }).join(",\n        "),
        idEqualityExpression("m", "nv"));

    stmt += tool.format(
        "INSERT INTO {0}({1})\nSELECT {1}\nFROM new_values\nWHERE NOT EXISTS (SELECT 1 FROM upsert up WHERE {2});\n",
        table,
        allQuotedNames,
        idEqualityExpression("up", "new_values"));

    return {sql: stmt, args: values};
}

/**
 * Builds a sql constraint clause for the provided date parts.
 */
function dateConstraint(date) {
    var parts = date.parts;
    var column = quoteName("date");
    var table = quoteName(schema.samples.name);

    if (date.current) {
        var condition = tool.format("(SELECT MAX({0}) FROM {1})", column, table);
        if (parts.length > 0) {
            // "date" = ((select max(date) from samples) + INTERVAL '-1 day -3 hour') order by date
            condition = tool.format("({0} + INTERVAL '{1}')",
                condition,
                parts.map(function(item, i) {
                    return item + " " + labels[i];
                }).join(" "));
        }
        return column + " = " + condition;
    }
    var str = tool.toISOString({year: parts[0], month: parts[1], day: parts[2], hour: parts[3], zone: date.zone});
    return tool.format(
        "{0} <= {1} AND {1} < CAST({0} AS TIMESTAMP WITH TIME ZONE) + INTERVAL '1 {2}'",
        quoteValue(str),
        column,
        labels[parts.length - 1]);
}

/**
 * Builds a sql constraint clause for station id, if necessary.
 */
function stationIdConstraint(constraints) {
    return constraints.stationId ? tool.format("{0} = {1}", quoteName("stationId"), constraints.stationId) : null;
}

/**
 * Builds a sql constraint clause for sample type, if necessary.
 */
function sampleTypeConstraint(constraints) {
    return /*constraints.sampleType ? quoteName(constraints.sampleType) + " IS NOT NULL" :*/ null;
}

/**
 * Returns a sql statement that selects samples matching the specified constraints.
 *
 * @param {Object} tableSpec
 * @param {Object} stationTableSpec
 * @param {Object} constraints an object the describes the constraints for the select, having the form:
 *                  date: {current: Boolean, parts: [year, month, day, hour], zone: string},
 *                  sampleType: string column name for sample, or null or "all" if all requested.
 *                  stationId: Number id of desired station, or null for all.
 * @returns {{sql: string, args: Array}} an object {sql: x, args: y} representing a sample select statement.
 */
exports.selectSamples = function(tableSpec, stationTableSpec, constraints) {
    log.info(constraints);
    var dateColumn = quoteName("date");
    var idColumn = quoteName("id");
    var stationIdColumn = quoteName("stationId");
    var longitudeColumn = quoteName("longitude");
    var latitudeColumn = quoteName("latitude");
    var table = quoteName(tableSpec.name);
    var stmt = tool.format("SELECT b.{0}, b.{1}, ", longitudeColumn, latitudeColumn);

    // First, decide which columns to select.
    if (constraints.sampleType && constraints.sampleType != "all") {
        // Select only one kind of sample, including the primary key columns. Treat date as text to preserve zone.
        stmt += tool.format("CAST({0} AS TEXT), {1}, {2} ",
            dateColumn,
            stationIdColumn,
            quoteName(constraints.sampleType));
    }
    else {
        // Select all sample kinds, including primary key columns. Treat date as text to preserve zone.
        var allColumns = tableSpec.columns.map(function(col) {
            return col.name != "date" ? quoteName(col.name) : tool.format("CAST({0} AS TEXT)", dateColumn);
        }).join(", ");
        stmt += allColumns;
    }

    // Next, constrain the results by date, station id, and sample type, where necessary.
    stmt += tool.format("\nFROM {0} a INNER JOIN {1} b ON a.{2} = b.{3}", table, quoteName(stationTableSpec.name), stationIdColumn, idColumn);
    stmt += tool.format("\nWHERE {0}", dateConstraint(constraints.date));
    var stationConstraint = stationIdConstraint(constraints);
    if (stationConstraint) {
        stmt += " AND " + stationConstraint;
    }
    var typeConstraint = sampleTypeConstraint(constraints);
    if (typeConstraint) {
        stmt += " AND " + typeConstraint;
    }

    // Finally, order by date descending, then station id.
    return {sql: stmt + tool.format("\nORDER BY {0} DESC, {1};", dateColumn, stationIdColumn), args: []};
}

/**
 * Returns a sql statement that selects all rows from the provided table.
 *
 * @param {Object} tableSpec
 * @returns {{sql: string, args: Array}} an object {sql: x, args: y} representing a select * statement.
 */
exports.selectAll = function(tableSpec) {
    var stmt = tool.format("SELECT * FROM {0}", quoteName(tableSpec.name));
    if (tableSpec.primary) {
        stmt += tool.format("\nORDER BY {0}", tableSpec.primary.columns.map(quoteName).join(", "));
    }
    return {sql: stmt, args: []};
}

function quoteColumn(name) {
    return name === "date" ?
        tool.format("CAST({0} AS TEXT)", quoteName(name)) :
        quoteName(name);
}

exports.selectSamplesCompact = function(constraints, columns) {
    var samples = schema.samples;
    var stations = schema.stations;

    var stmt = "";
    stmt += tool.format("SELECT {0}\n", columns.map(quoteColumn).join(", "));
    stmt += tool.format("FROM {0} s INNER JOIN {1} t ", quoteName(samples.name), quoteName(stations.name));
    stmt += tool.format("ON s.{0} = t.{1}\n", quoteName("stationId"), quoteName("id"));
    stmt += tool.format("WHERE {0}", dateConstraint(constraints.date));

    return {sql: stmt, args: []};
}

/**
 * Executes the specified statement, eventually.
 *
 * @param {Object} statement an object {sql: text, args: [x, y, z]}, were args are optional.
 * @returns {promise} a promise for the eventual processing of the statement
 */
exports.execute = function(statement) {
    var d = when.defer();

    pg.connect(connectionString, function(error, client, done) {
        if (error) {
            return d.reject(error);
        }

        var sql = typeof statement === "string" ? statement : statement.sql;
        var args = typeof statement === "string" ? [] : (statement.args || []);

        log.info(sql + (args.length > 0 ? "; " + args : ""));

        client.query(sql, args, function(error, result) {
            done();
            if (error) {
                return d.reject(error);
            }
            d.resolve(result);
        }).on("row", function(row) {
            d.notify(row);
        });
    });

    return d.promise;
}

/**
 * Executes the specified statements, eventually.
 *
 * @param {Array} statements an array of statement objects {sql: text, args: [x, y, z]}, were args are optional.
 * @returns {promise} a promise for the eventual processing of the statements
 */
exports.executeAll = function(statements) {
    var last = statements.length - 1;
    if (last < 0) {
        return when.resolve([]);
    }
    var d = when.defer();

    pg.connect(connectionString, function(error, client, done) {
        if (error) {
            return d.reject(error);
        }

        var statementPromises = statements.map(function(statement, index) {
            var sd = when.defer();
            var sql = typeof statement === "string" ? statement : statement.sql;
            var args = typeof statement === "string" ? [] : (statement.args || []);

//            log.info(/*sql + */(args.length > 0 ? "; " + args : ""));

            client.query(sql, args, function(error, result) {
                if (index == last || error) {
                    done();
                }
                if (error) {
                    return sd.reject(error);
                }
                sd.resolve(result);
            }).on("row", function(row) {
                sd.notify(row);
            });

            return sd.promise;
        });

        when.all(statementPromises).then(function(a) {
            d.resolve(a);
        });
    });
    return d.promise;
}

/**
 * Closes the database component, for shutdown.
 */
exports.done = function() {
    pg.end();
}