// Generates operation SQL for a source table, baking in column names from col_meta.
// Runtime values are left as {{token}} substitution points.
//
// Columns flagged col_meta.in_grain define a display grain. When one is set the
// initial load (get_agg) and every operation return rows pre-aggregated to that
// grain and keyed on pf_gkey, instead of raw forecast rows keyed on pf_id.
//
// Tokens baked in at generation time:  column names, source schema.table
// Tokens substituted at request time:  {{fc_table}}, {{where_clause}}, {{exclude_clause}},
//                                      {{version_id}}, {{logid}}, {{pf_user}}, {{note}},
//                                      {{params}}, {{slice}}, {{date_from}}, {{date_to}},
//                                      {{value_incr}}, {{units_incr}}, {{set_clause}}, {{scale_factor}}

// wrap a column name in double quotes for safe use in SQL
function q(name) { return `"${name}"`; }

// The display grain: dimension/date columns flagged in_grain, plus pf_iter and
// pf_logid which are always part of it. Returns null when nothing is flagged —
// that is raw-row mode, where operations return whole rows and the client
// indexes on pf_id (the pre-grain behaviour).
//
// Keeping pf_logid in the grain is what makes the append model work: each
// operation's contribution stays a distinct row, so table.update() accumulates
// rather than replacing a bucket total, and undo can remove exactly that
// operation's rows.
function grainOf(colMeta) {
    const cols = colMeta
        .filter(c => c.in_grain && (c.role === 'dimension' || c.role === 'date'))
        .sort((a, b) => (a.opos || 0) - (b.opos || 0))
        .map(c => c.cname);
    if (cols.length === 0) return null;

    // pf_gkey must be unique per grain tuple. chr(31) (unit separator) joins the
    // parts and chr(30) stands in for NULL, so ('a', NULL) cannot collide with
    // (NULL, 'a') and a NULL stays distinct from an empty string — a collision
    // would silently merge two groups into one indexed row.
    const key = (pfx = '') => `concat_ws(chr(31), ${[
        ...cols.map(c => `COALESCE(${pfx}${q(c)}::text, chr(30))`),
        `${pfx}pf_iter`,
        `${pfx}pf_logid::text`
    ].join(', ')})`;

    const groupCols = (pfx = '') => [...cols.map(c => `${pfx}${q(c)}`), `${pfx}pf_iter`, `${pfx}pf_logid`];

    return { cols, key, groupCols };
}

function generateSQL(source, colMeta) {
    const dims = colMeta
        .filter(c => c.role === 'dimension')
        .sort((a, b) => (a.opos || 0) - (b.opos || 0))
        .map(c => c.cname);

    const valueCol = colMeta.find(c => c.role === 'value')?.cname;
    const unitsCol = colMeta.find(c => c.role === 'units')?.cname;
    const dateCol  = colMeta.find(c => c.role === 'date')?.cname;

    if (!valueCol) throw new Error('No value column defined in col_meta');
    if (!dateCol)  throw new Error('No date column defined in col_meta');
    if (dims.length === 0) throw new Error('No dimension columns defined in col_meta');

    const srcTable        = `"${source.schema}"."${source.tname}"`;
    const dataCols        = [...dims, dateCol, valueCol, unitsCol].filter(Boolean);
    const effectiveValue  = dataCols.includes(valueCol) ? valueCol : null;
    const effectiveUnits  = dataCols.includes(unitsCol) ? unitsCol : null;
    const insertCols      = [...dataCols.map(q), 'pf_iter', 'pf_logid', 'pf_user', 'pf_created_at'].join(', ');
    const selectData      = dataCols.map(q).join(', ');
    const dimsJoined      = dims.map(q).join(', ');

    // dim_period JOIN support: if the date column is the is_key of a dim_group,
    // dimension siblings with dim_period_col set are derived from pf.dim_period
    // instead of being copied raw from the source on baseline/reference load.
    const dateKeyGroup = colMeta.find(c => c.role === 'date' && c.is_key && c.dim_group)?.dim_group;
    const dimPeriodMap = new Map(
        dateKeyGroup
            ? colMeta
                .filter(c => c.role === 'dimension' && c.dim_group === dateKeyGroup && c.dim_period_col)
                .map(c => [c.cname, c.dim_period_col])
            : []
    );
    const hasDimPeriod = dimPeriodMap.size > 0;

    // display grain — when set, initial load and operations both return rows
    // pre-aggregated to it instead of raw forecast rows
    const grain = grainOf(colMeta);
    // A flag on anything other than a dimension/date column is ignored by grainOf,
    // which is what we want — the role change is the source of truth, not a stale flag.
    if (grain) {
        const missing = grain.cols.filter(c => !dataCols.includes(c));
        if (missing.length > 0) {
            throw new Error(
                `Grain columns are never populated in the forecast table: ${missing.join(', ')}`
            );
        }
        if (!effectiveValue && !effectiveUnits) {
            throw new Error('A grain requires at least one value or units column to aggregate');
        }
    }

    return {
        get_data:  buildGetData(),
        ...(grain ? { get_agg: buildGetAgg() } : {}),
        baseline:  buildBaseline(),
        reference: buildReference(),
        scale:     buildScale(),
        recode:    buildRecode(),
        clone:     buildClone(),
        undo:      buildUndo()
    };

    function buildGetData() {
        return `SELECT * FROM {{fc_table}}`;
    }

    // Aggregate the whole forecast table to the display grain. This is the initial
    // load for grain sources — the client loads the result into a native Perspective
    // table indexed on pf_gkey and its view sums across these rows, exactly as an
    // Excel pivot cache sums its data tab.
    function buildGetAgg() {
        return `
SELECT
    ${grainSelect()}
FROM {{fc_table}}
GROUP BY
    ${grain.groupCols().join('\n    ,')}`.trim();
    }

    // grain columns + pf_gkey + summed measures, in the leading-comma style the
    // rest of the generated SQL uses
    function grainSelect(pfx = '') {
        return [
            ...grain.groupCols(pfx),
            `${grain.key(pfx)} AS pf_gkey`,
            effectiveValue ? `SUM(${pfx}${q(effectiveValue)}) AS ${q(effectiveValue)}` : null,
            effectiveUnits ? `SUM(${pfx}${q(effectiveUnits)}) AS ${q(effectiveUnits)}` : null
        ].filter(Boolean).join('\n    ,');
    }

    // Tail of an operation statement: in grain mode the inserted rows come back
    // aggregated to grain (the client appends them and lets the view re-sum);
    // otherwise whole rows come back as before.
    function opTail(cte) {
        if (!grain) return `SELECT * FROM ${cte}`;
        return `
SELECT
    ${grainSelect()}
FROM ${cte}
GROUP BY
    ${grain.groupCols().join('\n    ,')}`.trim();
    }

    function buildLoadSelect(pfx) {
        // pfx: table alias prefix ('s.' when joining dim_period, '' otherwise)
        return dataCols.map(c => {
            if (c === dateCol)          return `(${pfx}${q(c)} + '{{date_offset}}'::interval)::date`;
            if (dimPeriodMap.has(c))    return `dp.${q(dimPeriodMap.get(c))} AS ${q(c)}`;
            return `${pfx}${q(c)}`;
        }).join(',\n        ');
    }

    function buildFromClause() {
        if (!hasDimPeriod) return srcTable;
        return `${srcTable} s\n    JOIN pf.dim_period dp`
            + ` ON dp.drange @> (s.${q(dateCol)} + '{{date_offset}}'::interval)::date`;
    }

    function buildBaseline() {
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'baseline', NULL, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT
        ${buildLoadSelect(hasDimPeriod ? 's.' : '')},
        'baseline', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM ${buildFromClause()}
    WHERE {{filter_clause}}
    RETURNING *
)
SELECT count(*) AS rows_affected FROM ins`.trim();
    }

    function buildReference() {
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'reference', NULL, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT
        ${buildLoadSelect(hasDimPeriod ? 's.' : '')},
        'reference', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM ${buildFromClause()}
    WHERE {{filter_clause}}
    RETURNING *
)
SELECT count(*) AS rows_affected FROM ins`.trim();
    }

    function buildScale() {
        const vSel = effectiveValue
            ? `round((${q(effectiveValue)} / NULLIF(total_value, 0)) * {{value_incr}}, 2)`
            : `0`;
        const uSel = effectiveUnits
            ? `round((${q(effectiveUnits)} / NULLIF(total_units, 0)) * {{units_incr}}, 5)`
            : `0`;
        const baseSelectParts = [
            ...dimsJoined ? [dimsJoined] : [],
            q(dateCol),
            effectiveValue  ? q(effectiveValue)  : null,
            effectiveUnits  ? q(effectiveUnits)  : null,
            effectiveValue  ? `sum(${q(effectiveValue)}) OVER () AS total_value`  : null,
            effectiveUnits  ? `sum(${q(effectiveUnits)}) OVER () AS total_units` : null
        ].filter(Boolean).join(',\n        ');
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'scale', '{{slice}}'::jsonb, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,base AS (
    SELECT
        ${baseSelectParts}
    FROM {{fc_table}}
    WHERE {{where_clause}}
    {{exclude_clause}}
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT
        ${[dimsJoined, q(dateCol), ...(effectiveValue ? [vSel] : []), ...(effectiveUnits ? [uSel] : [])].join(',\n        ')},
        'scale', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM base
    RETURNING *
)
${opTail('ins')}`.trim();
    }

    function buildRecode() {
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'recode', '{{slice}}'::jsonb, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,src AS (
    SELECT ${selectData}
    FROM {{fc_table}}
    WHERE {{where_clause}}
    {{exclude_clause}}
)
,neg AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT ${dimsJoined}, ${q(dateCol)}, ${effectiveValue ? `-${q(effectiveValue)}` : '0'}${effectiveUnits ? `, -${q(effectiveUnits)}` : ''},
           'recode', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM src
    RETURNING *
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT {{set_clause}}, ${q(dateCol)}, ${effectiveValue ? q(effectiveValue) : '0'}${effectiveUnits ? `, ${q(effectiveUnits)}` : ''},
           'recode', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM src
    RETURNING *
)
${grain ? `,allrows AS (
    SELECT * FROM neg
    UNION ALL
    SELECT * FROM ins
)
${opTail('allrows')}` : 'SELECT * FROM neg UNION ALL SELECT * FROM ins'}`.trim();
    }

    function buildClone() {
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'clone', '{{slice}}'::jsonb, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT
        {{set_clause}},
        ${q(dateCol)},
        ${effectiveValue ? `round(${q(effectiveValue)} * {{scale_factor}}, 2)` : '0'}${effectiveUnits ? `,\n        round(${q(effectiveUnits)} * {{scale_factor}}, 5)` : ''},
        'clone', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM {{fc_table}}
    WHERE {{where_clause}}
    {{exclude_clause}}
    RETURNING *
)
${opTail('ins')}`.trim();
    }

    function buildUndo() {
        // undo is executed as two separate queries in the route handler
        // (delete from fc_table first, then delete from pf.log) to avoid
        // FK constraint ordering issues within a single CTE statement.
        // This entry is a placeholder — the undo route uses it as a template reference.
        return `
-- step 1 (run first):
DELETE FROM {{fc_table}} WHERE pf_logid = {{logid}};
-- step 2 (run after step 1):
DELETE FROM pf.log WHERE id = {{logid}};`.trim();
    }
}

// substitute {{token}} placeholders in a SQL string
function applyTokens(sql, tokens) {
    let result = sql;
    for (const [key, value] of Object.entries(tokens)) {
        result = result.replace(new RegExp(`\\{\\{${key}\\}\\}`, 'g'), value ?? '');
    }
    return result;
}

// build a SQL WHERE clause string from a slice object
// only dimension columns are included; unrecognised keys are silently skipped
function buildWhere(slice, dimCols) {
    if (!slice || Object.keys(slice).length === 0) return 'TRUE';

    const allowed = new Set(dimCols);
    const parts = [];

    for (const [col, val] of Object.entries(slice)) {
        if (!allowed.has(col)) continue;
        if (Array.isArray(val)) {
            const escaped = val.map(v => esc(v));
            parts.push(`"${col}" IN ('${escaped.join("', '")}')`);
        } else {
            parts.push(`"${col}" = '${esc(val)}'`);
        }
    }

    return parts.length ? parts.join('\nAND ') : 'TRUE';
}

// build AND iter NOT IN (...) from a version's exclude_iters array
function buildExcludeClause(excludeIters) {
    if (!excludeIters || excludeIters.length === 0) return '';
    const list = excludeIters.map(i => `'${esc(i)}'`).join(', ');
    return `AND pf_iter NOT IN (${list})`;
}

// build the dimension columns portion of a SELECT for recode/clone
// replaces named dimensions with literal values, passes others through unchanged
function buildSetClause(dimCols, setObj) {
    return dimCols.map(col => {
        if (setObj && setObj[col] !== undefined) {
            return `'${esc(setObj[col])}' AS "${col}"`;
        }
        return `"${col}"`;
    }).join(', ');
}

// build a SQL WHERE clause from an array of filter objects { col, op, values }
// only allows columns with role 'date' or 'filter'
function buildFilterClause(filters, colMeta) {
    if (!filters || filters.length === 0) {
        const err = new Error('At least one filter is required');
        err.status = 400; throw err;
    }
    const allowed = new Set(
        colMeta.filter(c => c.role !== 'ignore').map(c => c.cname)
    );
    const parts = filters.map(({ col, op, values = [] }) => {
        if (!allowed.has(col)) {
            const err = new Error(`Column "${col}" is not available for baseline filtering`);
            err.status = 400; throw err;
        }
        const c = `"${col}"`;
        const v = values.map(x => `'${esc(String(x))}'`);
        switch (op) {
            case '=':           return `${c} = ${v[0]}`;
            case '!=':          return `${c} != ${v[0]}`;
            case 'IN':          return `${c} IN (${v.join(', ')})`;
            case 'NOT IN':      return `${c} NOT IN (${v.join(', ')})`;
            case 'BETWEEN':     return `${c} BETWEEN ${v[0]} AND ${v[1]}`;
            case 'IS NULL':     return `${c} IS NULL`;
            case 'IS NOT NULL': return `${c} IS NOT NULL`;
            default: {
                const err = new Error(`Unsupported operator "${op}"`);
                err.status = 400; throw err;
            }
        }
    });
    return parts.join('\nAND ');
}

// escape a value for safe SQL string substitution
function esc(val) {
    if (val === null || val === undefined) return '';
    return String(val).replace(/'/g, "''");
}

module.exports = { generateSQL, grainOf, applyTokens, buildWhere, buildExcludeClause, buildSetClause, buildFilterClause, esc };