// Generates operation SQL for a source table, baking in column names from col_meta.
// Runtime values are left as {{token}} substitution points.
//
// 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}"`; }

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 (!unitsCol) throw new Error('No units 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}`;
    // exclude 'id' — forecast table has its own bigserial id primary key
    const dataCols        = [...dims, dateCol, valueCol, unitsCol].filter(c => c !== 'id');
    const effectiveValue  = dataCols.includes(valueCol) ? valueCol : null;
    const effectiveUnits  = dataCols.includes(unitsCol) ? unitsCol : null;
    const insertCols      = [...dataCols.map(q), 'iter', 'logid', 'pf_user', 'created_at'].join(', ');
    const selectData      = dataCols.map(q).join(', ');
    const dimsJoined      = dims.map(q).join(', ');

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

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

    function buildBaseline() {
        const baselineSelect = dataCols.map(c =>
            c === dateCol ? `(${q(c)} + '{{date_offset}}'::interval)::date` : q(c)
        ).join(', ');
        return `
WITH
ilog AS (
    INSERT INTO pf.log (version_id, pf_user, operation, slice, params, note)
    VALUES ({{version_id}}, '{{pf_user}}', 'baseline', NULL, '{{params}}'::jsonb, '{{note}}')
    RETURNING id
)
,del AS (
    DELETE FROM {{fc_table}} WHERE iter = 'baseline'
)
,ins AS (
    INSERT INTO {{fc_table}} (${insertCols})
    SELECT ${baselineSelect}, 'baseline', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM ${srcTable}
    WHERE ${q(dateCol)} BETWEEN '{{date_from}}' AND '{{date_to}}'
    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 ${selectData}, 'reference', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM ${srcTable}
    WHERE ${q(dateCol)} BETWEEN '{{date_from}}' AND '{{date_to}}'
    RETURNING *
)
SELECT * 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 *
)
SELECT * FROM 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)}` : '0'},
           '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) : '0'},
           'recode', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM src
    RETURNING *
)
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'},
        ${effectiveUnits ? `round(${q(effectiveUnits)} * {{scale_factor}}, 5)` : '0'},
        'clone', (SELECT id FROM ilog), '{{pf_user}}', now()
    FROM {{fc_table}}
    WHERE {{where_clause}}
    {{exclude_clause}}
    RETURNING *
)
SELECT * FROM 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 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
// validates all keys against the allowed dimension column list
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)) {
            throw new Error(`"${col}" is not a dimension column`);
        }
        if (Array.isArray(val)) {
            const escaped = val.map(v => esc(v));
            parts.push(`"${col}" IN ('${escaped.join("', '")}')`);
        } else {
            parts.push(`"${col}" = '${esc(val)}'`);
        }
    }

    return parts.join('\nAND ');
}

// 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 => `'${esc(i)}'`).join(', ');
    return `AND iter NOT IN (${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(', ');
}

// 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, applyTokens, buildWhere, buildExcludeClause, buildSetClause, esc };