'use strict';

// timezones can be defined either by an numeric offset in seconds or by
// a valid (case-insensitive) tz/PG name;
// they include abbreviations defined by PG (which have precedence and
// are fixed offsets, not handling DST) or general names that can handle DST.
function timezone (tz) {
    if (isFinite(tz)) {
        return `INTERVAL '${tz} seconds'`;
    }
    return `'${tz}'`;
}

// We assume t is a TIMESTAMP WITH TIME ZONE.
// If this was to be used with a t which is a TIMESTAMP or TIME (no time zone)
// it should be converted with `timezone('utc',t)` to a type with time zone.
// Note that by default CARTO uses timestamp with time zone columns for dates
// and VectorMapConfigAdapter converts them to epoch numbers.
// So, for using this with aggregations, relying on dates & times
// converted to UTC UNIX epoch numbers, apply `to_timestamp` to the
// (converted) column.
function timeExpression (t, tz) {
    if (tz !== undefined) {
        return `timezone(${timezone(tz)}, ${t})`;
    }
    return t;
}

function epochWithDefaults (epoch) {
    /* jshint maxcomplexity:9 */ // goddammit linter, I like this as is!!
    const format = /^(\d\d\d\d)(?:\-?(\d\d)(?:\-?(\d\d)(?:[T\s]?(\d\d)(?:(\d\d)(?:\:(\d\d))?)?)?)?)?$/; // eslint-disable-line no-useless-escape
    const match = (epoch || '').match(format) || [];
    const year = match[1] || '0001';
    const month = match[2] || '01';
    const day = match[3] || '01';
    const hour = match[4] || '00';
    const minute = match[5] || '00';
    const second = match[6] || '00';
    return `${year}-${month}-${day}T${hour}:${minute}:${second}`;
}

// Epoch should be an ISO timestamp literal without time zone
// (it is interpreted as in the defined timzezone for the input time)
// It can be partial, e.g. 'YYYY', 'YYYY-MM', 'YYYY-MM-DDTHH', etc.
// Defaults are applied: YYYY=0001, MM=01, DD=01, HH=00, MM=00, S=00
// It returns a timestamp without time zone
function epochExpression (epoch) {
    return `TIMESTAMP '${epoch}'`;
}

const YEARSPAN = "(date_part('year', $t)-date_part('year', $epoch))";
// Note that SECONDSPAN is not a UTC epoch, but an epoch in the specified TZ,
// so we can use it to compute any multiple of seconds with it  without using date_part or date_trunc
const SECONDSPAN = "(date_part('epoch', $t) - date_part('epoch', $epoch))";

const serialParts = {
    second: {
        sql: `FLOOR(${SECONDSPAN})`,
        zeroBased: true
    },
    minute: {
        sql: `FLOOR(${SECONDSPAN}/60)`,
        zeroBased: true
    },
    hour: {
        sql: `FLOOR(${SECONDSPAN}/3600)`,
        zeroBased: true
    },
    day: {
        sql: `1 + FLOOR(${SECONDSPAN}/86400)`,
        zeroBased: false
    },
    week: {
        sql: `1 + FLOOR(${SECONDSPAN}/(7*86400))`,
        zeroBased: false
    },
    month: {
        sql: `1 + date_part('month', $t) - date_part('month', $epoch) + 12*${YEARSPAN}`,
        zeroBased: false
    },
    quarter: {
        sql: `1 + date_part('quarter', $t) - date_part('quarter', $epoch) + 4*${YEARSPAN}`,
        zeroBased: false
    },
    semester: {
        sql: `1 + FLOOR((date_part('month', $t) - date_part('month', $epoch))/6) + 2*${YEARSPAN}`,
        zeroBased: false
    },
    trimester: {
        sql: `1 + FLOOR((date_part('month', $t) - date_part('month', $epoch))/4) + 3*${YEARSPAN}`,
        zeroBased: false
    },
    year: {
        // for the default epoch this coincides with date_part('year', $t)
        sql: `1 + ${YEARSPAN}`,
        zeroBased: false
    },
    decade: {
        // for the default epoch this coincides with date_part('decade', $t)
        sql: `FLOOR((${YEARSPAN} + 1)/10)`,
        zeroBased: true
    },
    century: {
        // for the default epoch this coincides with date_part('century', $t)
        sql: `1 + FLOOR(${YEARSPAN}/100)`,
        zeroBased: false
    },
    millennium: {
        // for the default epoch this coincides with date_part('millennium', $t)
        sql: `1 + FLOOR(${YEARSPAN}/1000)`,
        zeroBased: false
    }
};

function serialSqlExpr (params) {
    const { sql, zeroBased } = serialParts[params.units];
    const column = timeExpression(params.time, params.timezone);
    const epoch = epochExpression(params.starting);
    const serial = sql.replace(/\$t/g, column).replace(/\$epoch/g, epoch);
    let expr = serial;
    if (params.count !== 1) {
        if (zeroBased) {
            expr = `FLOOR((${expr})/(${params.count}::double precision))::int`;
        } else {
            expr = `CEIL((${expr})/(${params.count}::double precision))::int`;
        }
    } else {
        expr = `(${expr})::int`;
    }
    return expr;
}

const isoParts = {
    second: 'to_char($t, \'YYYY-MM-DD"T"HH24:MI:SS\')',
    minute: 'to_char($t, \'YYYY-MM-DD"T"HH24:MI\')',
    hour: 'to_char($t, \'YYYY-MM-DD"T"HH24\')',
    day: 'to_char($t, \'YYYY-MM-DD\')',
    month: 'to_char($t, \'YYYY-MM\')',
    year: 'to_char($t, \'YYYY\')',
    week: 'to_char($t, \'IYYY-"W"IW\')',
    quarter: 'to_char($t, \'YYYY-"Q"Q\')',
    semester: 'to_char($t, \'YYYY"S"\') || to_char(CEIL(date_part(\'month\', $t)/6), \'9\')',
    trimester: 'to_char($t, \'YYYY"t"\') || to_char(CEIL(date_part(\'month\', $t)/4), \'9\')',
    decade: 'to_char(date_part(\'decade\', $t), \'"D"999\')',
    century: 'to_char($t, \'"C"CC\')',
    millennium: 'to_char(date_part(\'millennium\', $t), \'"M"999\')'
};

function isoSqlExpr (params) {
    const column = timeExpression(params.time, params.timezone);
    if (params.count > 1) {
        // TODO: it would be sensible to return the ISO of the first unit in the period
        throw new Error('Multiple time units not supported for ISO format');
    }
    return isoParts[params.units].replace(/\$t/g, column);
}

const cyclicParts = {
    dayOfWeek: 'date_part(\'isodow\', $t)', // 1 = monday to 7 = sunday;
    dayOfMonth: 'date_part(\'day\', $t)', // 1 to 31
    dayOfYear: 'date_part(\'doy\', $t)', // 1 to 366
    hourOfDay: 'date_part(\'hour\', $t)', // 0 to 23
    monthOfYear: 'date_part(\'month\', $t)', // 1 to 12
    quarterOfYear: 'date_part(\'quarter\', $t)', // 1 to 4
    semesterOfYear: 'FLOOR((date_part(\'month\', $t)-1)/6.0) + 1', // 1 to 2
    trimesterOfYear: 'FLOOR((date_part(\'month\', $t)-1)/4.0) + 1', // 1 to 3
    weekOfYear: 'date_part(\'week\', $t)', // 1 to 53
    minuteOfHour: 'date_part(\'minute\', $t)' // 0 to 59
};

function cyclicSqlExpr (params) {
    const column = timeExpression(params.time, params.timezone);
    return cyclicParts[params.units].replace(/\$t/g, column);
}

const ACCEPTED_PARAMETERS = ['time', 'units', 'timezone', 'count', 'starting', 'format'];
const REQUIRED_PARAMETERS = ['time', 'units'];

function validateParameters (params, checker) {
    const errors = [];
    const presentParams = Object.keys(params);
    const invalidParams = presentParams.filter(param => !ACCEPTED_PARAMETERS.includes(param));
    if (invalidParams.length) {
        errors.push(`Invalid parameters: ${invalidParams.join(', ')}`);
    }
    const missingParams = REQUIRED_PARAMETERS.filter(param => !presentParams.includes(param));
    if (missingParams.length) {
        errors.push(`Missing parameters: ${missingParams.join(', ')}`);
    }
    const paramsErrors = checker(params);
    errors.push(...paramsErrors.errors);
    if (errors.length) {
        throw new Error(`Invalid time dimension:\n${errors.join('\n')}`);
    }
    return paramsErrors.params;
}

const VALID_CYCLIC_UNITS = Object.keys(cyclicParts);
const VALID_SERIAL_UNITS = Object.keys(serialParts);
const VALID_ISO_UNITS = Object.keys(isoParts);

function cyclicCheckParams (params) {
    const errors = [];
    if (!VALID_CYCLIC_UNITS.includes(params.units)) {
        errors.push(`Invalid units "${params.units}"`);
    }
    if (params.count && params.count > 1) {
        errors.push(`Count ${params.count} not supported for cyclic ${params.units}`);
    }
    return { errors: errors, params: params };
}

function serialCheckParams (params) {
    const errors = [];
    if (!VALID_SERIAL_UNITS.includes(params.units)) {
        errors.push(`Invalid grouping units "${params.units}"`);
    }
    return { errors: errors, params: Object.assign({}, params, { starting: epochWithDefaults(params.starting) }) };
}

function isoCheckParams (params) {
    const errors = [];
    if (!VALID_ISO_UNITS.includes(params.units)) {
        errors.push(`Invalid units "${params.units}"`);
    }
    if (params.starting) {
        errors.push("Parameter 'starting' not supported for ISO format");
    }
    return { errors: errors, params: params };
}

const CLASSIFIERS = {
    cyclic: {
        sqlExpr: cyclicSqlExpr,
        checkParams: cyclicCheckParams
    },
    iso: {
        sqlExpr: isoSqlExpr,
        checkParams: isoCheckParams
    },
    serial: {
        sqlExpr: serialSqlExpr,
        checkParams: serialCheckParams
    }
};

function isCyclic (units) {
    return VALID_CYCLIC_UNITS.includes(units);
}

function classifierFor (params) {
    let classifier = 'serial';
    if (params.units && isCyclic(params.units)) {
        classifier = 'cyclic';
    } else if (params.format === 'iso') {
        classifier = 'iso';
    }
    return CLASSIFIERS[classifier];
}

function classificationSql (params) {
    const classifier = classifierFor(params);
    params = validateParameters(params, classifier.checkParams);
    return { sql: classifier.sqlExpr(params), effectiveParams: params };
}

module.exports = classificationSql;