// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module parser

import v.ast
import v.token

struct SqlPrefix {
    pos              token.Pos
    db_expr          ast.Expr
    tmp_inside_match bool
    is_dynamic       bool
}

struct SqlQueryDataItemsBlock {
    items        []ast.SqlQueryDataItem
    end_comments []ast.Comment
}

fn sql_aggregate_kind_from_name(name string) ast.SqlAggregateKind {
    return match name {
        'count' { .count }
        'sum' { .sum }
        'avg' { .avg }
        'min' { .min }
        'max' { .max }
        else { .none }
    }
}

fn (mut p Parser) parse_sql_select_field_name() ast.SqlSelectField {
    pos := p.tok.pos()
    mut parts := []string{}
    parts << p.check_name()
    for p.tok.kind == .dot {
        p.next()
        parts << p.check_name()
    }
    return ast.SqlSelectField{
        name: parts.join('.')
        pos:  pos.extend(p.prev_tok.pos())
    }
}

fn (mut p Parser) parse_sql_select_fields() []ast.SqlSelectField {
    mut fields := []ast.SqlSelectField{}
    for {
        if p.tok.kind != .name {
            p.error('expected an ORM select field before `from`')
            return fields
        }
        fields << p.parse_sql_select_field_name()
        if p.tok.kind != .comma {
            break
        }
        p.next()
    }
    return fields
}

// select from User
// insert user into User returning id
fn (mut p Parser) sql_expr() ast.Expr {
    prefix := p.sql_prefix()
    return p.sql_expr_after_prefix(prefix)
}

fn (mut p Parser) sql_stmt_or_expr() ast.Stmt {
    prefix := p.sql_prefix()
    if p.sql_stmt_can_be_value()
        && (p.tok.kind == .key_select || (p.tok.kind == .name && p.tok.lit == 'insert')) {
        expr := p.sql_expr_after_prefix(prefix)
        return ast.ExprStmt{
            expr: expr
            pos:  expr.pos()
        }
    }
    return p.sql_stmt_after_prefix(prefix)
}

fn (p &Parser) sql_stmt_can_be_value() bool {
    return p.inside_if_expr || p.inside_match_body || p.inside_or_expr
}

fn (mut p Parser) sql_prefix() SqlPrefix {
    tmp_inside_match := p.inside_match
    p.inside_orm = true
    p.inside_match = true
    pos := p.tok.pos()
    p.check_name()
    db_expr := p.check_expr(0) or {
        p.unexpected(prepend_msg: 'invalid expression:', expecting: 'database')
    }
    p.check(.lcbr)
    mut is_dynamic := false
    if p.tok.kind == .name && p.tok.lit == 'dynamic' {
        is_dynamic = true
        p.next()
    }
    return SqlPrefix{
        pos:              pos
        db_expr:          db_expr
        tmp_inside_match: tmp_inside_match
        is_dynamic:       is_dynamic
    }
}

fn (mut p Parser) sql_expr_after_prefix(prefix SqlPrefix) ast.Expr {
    is_dynamic := prefix.is_dynamic
    is_select := p.tok.kind == .key_select
    is_insert := p.tok.lit == 'insert'
    if !is_select && !is_insert {
        p.error('expected "select" or "insert" in an ORM expression')
    }
    if is_dynamic && !is_select {
        p.error('expected "select" after `dynamic` in an ORM expression')
    }
    p.next()
    // kind := if is_select { ast.SqlExprKind.select_ } else { ast.SqlExprKind.insert }
    mut inserted_var := ''
    mut aggregate_kind := ast.SqlAggregateKind.none
    mut aggregate_field := ''
    mut has_distinct := false
    mut requested_fields := []ast.SqlSelectField{}
    if is_insert {
        inserted_var = p.check_name()
        p.scope.mark_var_as_used(inserted_var)
        into := p.check_name()
        if into != 'into' {
            p.error('expecting `into`')
        }
    } else if is_select {
        if p.tok.kind == .name && p.tok.lit == 'distinct' {
            has_distinct = true
            p.next()
        }
        if p.tok.kind == .name {
            aggregate_kind = sql_aggregate_kind_from_name(p.tok.lit)
        }
        if aggregate_kind == .count {
            p.next()
            n := p.check_name() // from
            if n != 'from' {
                p.error('expecting "from" in a "select count" ORM statement')
            }
        } else if aggregate_kind != .none {
            p.next()
            if p.tok.kind != .lpar {
                p.error('expecting `(` after aggregate function in ORM select')
            }
            p.next()
            if p.tok.kind != .name {
                p.error('ORM aggregate functions only support a single field name argument')
            }
            aggregate_field = p.check_name()
            if p.tok.kind != .rpar {
                p.error('ORM aggregate functions only support a single field name argument')
            }
            p.next()
            n := p.check_name() // from
            if n != 'from' {
                p.error('expecting `from` after ORM aggregate function')
            }
        } else if p.tok.kind == .name && p.tok.lit == 'from' {
            p.next()
        } else {
            requested_fields = p.parse_sql_select_fields()
            n := p.check_name() // from
            if n != 'from' {
                p.error('expecting `from` after ORM select fields')
            }
        }
    }
    mut typ := ast.void_type

    table_pos := p.tok.pos()
    table_type := p.parse_type() // `User`

    // Parse JOIN clauses (e.g., `join Department on User.dept_id == Department.id`)
    mut joins := []ast.JoinClause{}
    for p.tok.kind == .name && p.tok.lit in ['join', 'left', 'right', 'full', 'inner'] {
        join_clause := p.parse_sql_join_clause()
        if join_clause.table_expr.typ != ast.void_type {
            joins << join_clause
        }
    }

    mut where_expr := ast.empty_expr
    has_where := p.tok.kind == .name && p.tok.lit == 'where'

    if has_where {
        p.next()
        where_expr = p.expr(0)
        if !is_dynamic {
            where_check_result := p.check_sql_where_expr_has_no_undefined_variables(&where_expr, [])
            if where_check_result is ast.NodeError {
                return where_check_result
            }
        }
    }

    mut has_limit := false
    mut limit_expr := ast.empty_expr
    mut has_offset := false
    mut offset_expr := ast.empty_expr
    mut has_order := false
    mut order_expr := ast.empty_expr
    mut has_desc := false
    if p.tok.kind == .name && p.tok.lit == 'order' {
        p.check_name() // `order`
        order_pos := p.tok.pos()
        if p.tok.kind == .name && p.tok.lit == 'by' {
            p.check_name() // `by`
        } else {
            return p.error_with_pos('use `order by` in ORM queries', order_pos)
        }
        has_order = true
        order_expr = p.expr(0)
        if p.tok.kind == .name && p.tok.lit in ['asc', 'desc'] {
            has_desc = p.tok.lit == 'desc'
            p.check_name() // `asc` or `desc`
        }
    }

    if p.tok.kind == .name && p.tok.lit == 'limit' {
        p.check_name() // `limit`
        has_limit = true
        limit_expr = p.expr(0)
    }

    if p.tok.kind == .name && p.tok.lit == 'offset' {
        p.check_name() // `offset`
        has_offset = true
        offset_expr = p.expr(0)
    }

    if aggregate_kind == .count {
        typ = ast.int_type
    } else if aggregate_kind != .none {
        typ = ast.void_type
    } else if table_type.has_flag(.generic) {
        typ = ast.new_type(p.table.find_or_register_array(table_type)).set_flag(.generic)
    } else {
        typ = ast.new_type(p.table.find_or_register_array(table_type))
    }

    p.check(.rcbr)
    p.inside_match = false
    p.inside_orm = false
    or_expr := p.parse_sql_or_block()
    p.inside_match = prefix.tmp_inside_match

    return ast.SqlExpr{
        aggregate_kind:   aggregate_kind
        aggregate_field:  aggregate_field
        is_insert:        is_insert
        typ:              typ.set_flag(.result)
        scope:            p.scope
        or_expr:          or_expr
        db_expr:          prefix.db_expr
        where_expr:       where_expr
        has_where:        has_where
        has_limit:        has_limit
        limit_expr:       limit_expr
        has_offset:       has_offset
        offset_expr:      offset_expr
        has_order:        has_order
        order_expr:       order_expr
        has_desc:         has_desc
        has_distinct:     has_distinct
        is_array:         aggregate_kind == .none
        is_generated:     false
        is_dynamic:       is_dynamic
        inserted_var:     inserted_var
        requested_fields: requested_fields
        pos:              prefix.pos.extend(p.prev_tok.pos())
        table_expr:       ast.TypeNode{
            typ: table_type
            pos: table_pos
        }
        joins:            joins
    }
}

// parse_sql_join_clause parses a JOIN clause like:
// `join Department on User.dept_id == Department.id`
// `left join Department on User.dept_id == Department.id`
// `inner join Department on User.dept_id == Department.id`
fn (mut p Parser) parse_sql_join_clause() ast.JoinClause {
    mut kind := ast.JoinKind.inner
    join_pos := p.tok.pos()

    // Check for join type prefix (left, right, full, inner)
    if p.tok.lit == 'left' {
        kind = .left
        p.next()
    } else if p.tok.lit == 'right' {
        kind = .right
        p.next()
    } else if p.tok.lit == 'full' {
        kind = .full_outer
        p.next()
        // Handle optional 'outer' keyword
        if p.tok.kind == .name && p.tok.lit == 'outer' {
            p.next()
        }
    } else if p.tok.lit == 'inner' {
        // 'inner' is optional, just skip it
        p.next()
    }

    // Now expect 'join'
    if p.tok.kind != .name || p.tok.lit != 'join' {
        p.error('expected `join` keyword after join type')
        return ast.JoinClause{}
    }
    p.next() // consume 'join'

    // Parse the joined table type
    table_pos := p.tok.pos()
    table_type := p.parse_type()

    // Expect 'on' keyword
    if p.tok.kind != .name || p.tok.lit != 'on' {
        p.error('expected `on` keyword after table name in JOIN clause')
        return ast.JoinClause{}
    }
    p.next() // consume 'on'

    // Parse the ON condition expression
    on_expr := p.expr(0)

    return ast.JoinClause{
        kind:       kind
        pos:        join_pos
        table_expr: ast.TypeNode{
            typ: table_type
            pos: table_pos
        }
        on_expr:    on_expr
    }
}

// insert user into User
// update User set nr_oders=nr_orders+1 where id == user_id
// delete
fn (mut p Parser) sql_stmt() ast.SqlStmt {
    prefix := p.sql_prefix()
    return p.sql_stmt_after_prefix(prefix)
}

fn (mut p Parser) sql_stmt_after_prefix(prefix SqlPrefix) ast.SqlStmt {
    mut pos := prefix.pos

    mut lines := []ast.SqlStmtLine{}

    for p.tok.kind != .rcbr {
        if p.tok.kind == .eof {
            p.unexpected_with_pos(pos, got: 'eof, while parsing an SQL statement')
            return ast.SqlStmt{}
        }
        lines << p.parse_sql_stmt_line(prefix.is_dynamic)
    }

    p.next()

    p.inside_orm = false
    p.inside_match = false
    mut or_expr := p.parse_sql_or_block()
    p.inside_match = prefix.tmp_inside_match

    pos.last_line = p.prev_tok.line_nr
    return ast.SqlStmt{
        pos:     pos.extend(p.prev_tok.pos())
        db_expr: prefix.db_expr
        lines:   lines
        or_expr: or_expr
    }
}

fn (mut p Parser) parse_sql_or_block() ast.OrExpr {
    mut stmts := []ast.Stmt{}
    mut kind := ast.OrKind.absent
    mut pos := p.tok.pos()
    mut or_scope := ast.empty_scope

    if p.tok.kind == .key_orelse {
        kind = .block
        stmts, pos, or_scope = p.or_block(.with_err_var)
    } else if p.tok.kind == .not {
        kind = .propagate_result
        or_scope = p.scope
        p.next()
    }

    return ast.OrExpr{
        stmts: stmts
        kind:  kind
        pos:   pos
        scope: or_scope
    }
}

fn (mut p Parser) parse_sql_stmt_line(is_dynamic bool) ast.SqlStmtLine {
    pre_comments := p.eat_comments()
    mut n := p.check_name() // insert
    pos := p.tok.pos()
    mut kind := ast.SqlStmtKind.insert
    if n == 'delete' {
        kind = .delete
    } else if n == 'upsert' {
        kind = .upsert
    } else if n == 'update' {
        kind = .update
    } else if n == 'create' {
        kind = .create
        table := p.check_name()
        if table != 'table' {
            p.error('expected `table` got `${table}`')
            return ast.SqlStmtLine{}
        }
        typ := p.parse_type()
        typ_pos := p.tok.pos()
        end_comments := p.eat_comments()
        return ast.SqlStmtLine{
            kind:         kind
            pos:          pos.extend(p.prev_tok.pos())
            table_expr:   ast.TypeNode{
                typ: typ
                pos: typ_pos
            }
            scope:        p.scope
            is_generated: false
            is_dynamic:   is_dynamic
            pre_comments: pre_comments
            end_comments: end_comments
        }
    } else if n == 'drop' {
        kind = .drop
        table := p.check_name()
        if table != 'table' {
            p.error('expected `table` got `${table}`')
            return ast.SqlStmtLine{}
        }
        typ := p.parse_type()
        typ_pos := p.tok.pos()
        end_comments := p.eat_comments()
        return ast.SqlStmtLine{
            kind:         kind
            pos:          pos.extend(p.prev_tok.pos())
            table_expr:   ast.TypeNode{
                typ: typ
                pos: typ_pos
            }
            is_generated: false
            is_dynamic:   is_dynamic
            scope:        p.scope
            pre_comments: pre_comments
            end_comments: end_comments
        }
    }
    if is_dynamic && kind != .update {
        p.error('`dynamic` is only supported for ORM `select` and `update` queries')
        return ast.SqlStmtLine{}
    }
    mut inserted_var := ''
    mut table_type := ast.no_type
    if kind != .delete {
        if kind == .update {
            table_type = p.parse_type()
        } else if kind in [.insert, .upsert] {
            expr := p.expr(0)
            if expr is ast.Ident {
                inserted_var = expr.name
            } else {
                p.error('can only insert variables')
                return ast.SqlStmtLine{}
            }
        }
    }
    n = p.check_name() // into
    mut updated_columns := []string{}
    mut update_exprs := []ast.Expr{cap: 5}
    mut update_data_expr := ast.empty_expr
    if kind in [.insert, .upsert] && n != 'into' {
        p.error('expecting `into`')
        return ast.SqlStmtLine{}
    } else if kind == .update {
        if n != 'set' {
            p.error('expecting `set`')
            return ast.SqlStmtLine{}
        }
        if is_dynamic {
            update_data_expr = p.expr(0)
        } else {
            for {
                column := p.check_name()
                updated_columns << column
                p.check(.assign)
                update_exprs << p.expr(0)
                if p.tok.kind == .comma {
                    p.check(.comma)
                } else {
                    break
                }
            }
        }
    } else if kind == .delete && n != 'from' {
        p.error('expecting `from`')
        return ast.SqlStmtLine{}
    }

    mut table_pos := p.tok.pos()
    mut where_expr := ast.empty_expr
    if kind in [.insert, .upsert] {
        table_pos = p.tok.pos()
        table_type = p.parse_type()
    } else if kind == .update {
        p.check_sql_keyword('where') or { return ast.SqlStmtLine{} }
        where_expr = p.expr(0)

        where_expr_result := p.check_sql_where_expr_has_no_undefined_variables(&where_expr, [])
        if where_expr_result is ast.NodeError {
            return ast.SqlStmtLine{}
        }
    } else if kind == .delete {
        table_pos = p.tok.pos()
        table_type = p.parse_type()
        p.check_sql_keyword('where') or { return ast.SqlStmtLine{} }
        where_expr = p.expr(0)

        where_expr_result := p.check_sql_where_expr_has_no_undefined_variables(&where_expr, [])
        if where_expr_result is ast.NodeError {
            return ast.SqlStmtLine{}
        }
    }
    end_comments := p.eat_comments()
    return ast.SqlStmtLine{
        table_expr:       ast.TypeNode{
            typ: table_type
            pos: table_pos
        }
        object_var:       inserted_var
        pos:              pos
        updated_columns:  updated_columns
        update_exprs:     update_exprs
        update_data_expr: update_data_expr
        kind:             kind
        where_expr:       where_expr
        is_generated:     false
        is_dynamic:       is_dynamic
        scope:            p.scope
        pre_comments:     pre_comments
        end_comments:     end_comments
    }
}

fn (p &Parser) is_sql_query_data_expr() bool {
    if p.tok.kind != .lcbr {
        return false
    }
    mut idx := 1
    for p.peek_token(idx).kind == .comment {
        idx++
    }
    mut first := p.peek_token(idx)
    if first.kind == .key_if {
        return true
    }
    has_leading_paren := first.kind == .lpar
    if has_leading_paren && p.sql_query_data_item_has_top_level_colon(idx) {
        return false
    }
    mut leading_parens := 0
    for first.kind == .lpar {
        leading_parens++
        idx++
        for p.peek_token(idx).kind == .comment {
            idx++
        }
        first = p.peek_token(idx)
    }
    if first.kind != .name {
        return false
    }
    idx++
    for p.peek_token(idx).kind == .dot && p.peek_token(idx + 1).kind == .name {
        idx += 2
    }
    for leading_parens > 0 && p.peek_token(idx).kind == .rpar {
        leading_parens--
        idx++
        for p.peek_token(idx).kind == .comment {
            idx++
        }
    }
    return is_sql_query_data_operator(p.peek_token(idx).kind)
}

fn (p &Parser) sql_query_data_item_has_top_level_colon(start_idx int) bool {
    mut idx := start_idx
    mut par_depth := 0
    mut bracket_depth := 0
    mut brace_depth := 0
    for {
        kind := p.peek_token(idx).kind
        match kind {
            .eof {
                return false
            }
            .comment {}
            .lpar {
                par_depth++
            }
            .rpar {
                if par_depth > 0 {
                    par_depth--
                }
            }
            .lsbr {
                bracket_depth++
            }
            .rsbr {
                if bracket_depth > 0 {
                    bracket_depth--
                }
            }
            .lcbr {
                brace_depth++
            }
            .rcbr {
                if brace_depth == 0 {
                    return false
                }
                brace_depth--
            }
            .comma {
                if par_depth == 0 && bracket_depth == 0 && brace_depth == 0 {
                    return false
                }
            }
            .colon {
                if par_depth == 0 && bracket_depth == 0 && brace_depth == 0 {
                    return true
                }
            }
            else {}
        }

        idx++
    }
    return false
}

fn is_sql_query_data_operator(kind token.Kind) bool {
    return kind in [.eq, .ne, .gt, .lt, .ge, .le, .key_like, .key_ilike, .key_in, .not_in, .key_is,
        .not_is]
}

fn (mut p Parser) sql_query_data_expr() ast.Expr {
    start_pos := p.tok.pos()
    block := p.parse_sql_query_data_items_block()
    return ast.SqlQueryDataExpr{
        pos:          start_pos.extend(p.prev_tok.pos())
        items:        block.items
        end_comments: block.end_comments
    }
}

fn (mut p Parser) parse_sql_query_data_items_block() SqlQueryDataItemsBlock {
    p.check(.lcbr)
    mut items := []ast.SqlQueryDataItem{}
    mut pending_comments := p.eat_comments()
    for {
        if p.tok.kind == .rcbr {
            break
        }
        if p.tok.kind == .eof {
            p.unexpected(got: 'eof, while parsing a dynamic ORM expression')
            break
        }
        mut item := p.parse_sql_query_data_item()
        item = sql_query_data_item_with_pre_comments(item, pending_comments)
        pending_comments = []
        item = sql_query_data_item_with_end_comments(item, p.eat_comments(same_line: true))
        if p.tok.kind == .comma {
            p.next()
            item = sql_query_data_item_with_end_comments(item, p.eat_comments(same_line: true))
            items << item
            pending_comments = p.eat_comments()
            continue
        }
        items << item
        pending_comments = p.eat_comments()
        if p.tok.kind != .rcbr {
            p.error('expected `,` or `}` in a dynamic ORM expression')
            break
        }
    }
    p.check(.rcbr)
    return SqlQueryDataItemsBlock{
        items:        items
        end_comments: pending_comments
    }
}

fn (mut p Parser) parse_sql_query_data_item() ast.SqlQueryDataItem {
    if p.tok.kind == .key_if {
        return p.parse_sql_query_data_if_item()
    }
    expr := p.expr(0)
    return ast.SqlQueryDataLeaf{
        pos:  expr.pos()
        expr: expr
    }
}

fn sql_query_data_item_with_pre_comments(item ast.SqlQueryDataItem, comments []ast.Comment) ast.SqlQueryDataItem {
    if comments.len == 0 {
        return item
    }
    return match item {
        ast.SqlQueryDataLeaf {
            mut leaf := item
            leaf.pre_comments << comments
            leaf
        }
        ast.SqlQueryDataIf {
            mut if_item := item
            if_item.pre_comments << comments
            if_item
        }
    }
}

fn sql_query_data_item_with_end_comments(item ast.SqlQueryDataItem, comments []ast.Comment) ast.SqlQueryDataItem {
    if comments.len == 0 {
        return item
    }
    return match item {
        ast.SqlQueryDataLeaf {
            mut leaf := item
            leaf.end_comments << comments
            leaf
        }
        ast.SqlQueryDataIf {
            mut if_item := item
            if_item.end_comments << comments
            if_item
        }
    }
}

fn (mut p Parser) parse_sql_query_data_if_guard_expr() ast.IfGuardExpr {
    p.open_scope()
    mut vars := []ast.IfGuardVar{}
    mut var_names := []string{}
    for {
        mut var := ast.IfGuardVar{}
        mut is_mut := false
        if p.tok.kind == .key_mut {
            is_mut = true
            p.next()
        }
        var.is_mut = p.scope_var_is_mut(is_mut)
        var.pos = p.tok.pos()
        var.name = p.check_name()
        var_names << var.name

        if p.scope.known_var(var.name) {
            p.error_with_pos('redefinition of `${var.name}`', var.pos)
        }
        vars << var
        if p.tok.kind != .comma {
            break
        }
        p.next()
    }
    p.check(.decl_assign)
    old_assign_rhs := p.inside_assign_rhs
    p.inside_assign_rhs = true
    expr := p.expr(0)
    p.inside_assign_rhs = old_assign_rhs
    if expr !in [ast.CallExpr, ast.IndexExpr, ast.PrefixExpr, ast.SelectorExpr, ast.Ident] {
        p.error_with_pos('if guard condition expression is illegal, it should return an Option',
            expr.pos())
    }
    p.check_undefined_variables(var_names, expr) or { p.error_with_pos(err.msg(), expr.pos()) }
    cond := ast.IfGuardExpr{
        vars: vars
        expr: expr
    }
    for var in vars {
        p.scope.register(ast.Var{
            name:   var.name
            is_mut: var.is_mut
            expr:   cond
            pos:    var.pos
        })
    }
    return cond
}

fn (mut p Parser) parse_sql_query_data_if_item() ast.SqlQueryDataItem {
    start_pos := p.tok.pos()
    mut branches := []ast.SqlQueryDataBranch{}
    mut has_else := false
    mut prev_guard := false
    for {
        branch_pos := p.tok.pos()
        p.check(.key_if)
        mut cond := ast.empty_expr
        mut has_guard_scope := false
        if p.peek_token_after_var_list().kind == .decl_assign {
            cond = p.parse_sql_query_data_if_guard_expr()
            has_guard_scope = true
            prev_guard = true
        } else {
            cond = p.expr(0)
            prev_guard = false
        }
        p.open_scope()
        block := p.parse_sql_query_data_items_block()
        p.close_scope()
        if has_guard_scope {
            p.close_scope()
        }
        branches << ast.SqlQueryDataBranch{
            pos:          branch_pos.extend(p.prev_tok.pos())
            cond:         cond
            items:        block.items
            end_comments: block.end_comments
        }
        comments_before_else := p.eat_comments()
        if p.tok.kind != .key_else {
            return ast.SqlQueryDataIf{
                pos:          start_pos.extend(p.prev_tok.pos())
                branches:     branches
                has_else:     has_else
                end_comments: comments_before_else
            }
        }
        if comments_before_else.len > 0 {
            last_idx := branches.len - 1
            branches[last_idx].end_comments << comments_before_else
        }
        has_else = true
        else_pos := p.tok.pos()
        p.next()
        if p.tok.kind == .key_if {
            continue
        }
        p.open_scope()
        if prev_guard {
            p.scope.register(ast.Var{
                name:         'err'
                typ:          ast.error_type
                pos:          p.tok.pos()
                is_used:      false
                is_stack_obj: true
                is_special:   true
            })
        }
        else_block := p.parse_sql_query_data_items_block()
        p.close_scope()
        branches << ast.SqlQueryDataBranch{
            pos:          else_pos.extend(p.prev_tok.pos())
            cond:         ast.empty_expr
            items:        else_block.items
            end_comments: else_block.end_comments
        }
        break
    }
    return ast.SqlQueryDataIf{
        pos:      start_pos.extend(p.prev_tok.pos())
        branches: branches
        has_else: has_else
    }
}

fn (mut p Parser) check_sql_keyword(name string) ?bool {
    if p.check_name() != name {
        p.error('ORM: expecting `${name}`')
        return none
    }
    return true
}

// check_sql_where_expr_has_no_undefined_variables recursively tries to find undefined variables in the right part of infix expressions.
fn (mut p Parser) check_sql_where_expr_has_no_undefined_variables(expr &ast.Expr, unacceptable_variable_names []string) ast.Expr {
    if expr is ast.Ident {
        if !p.scope.known_var(expr.name) {
            p.check_undefined_variables(unacceptable_variable_names, expr) or {
                return p.error_with_pos(err.msg(), expr.pos)
            }
        }
    } else if expr is ast.InfixExpr {
        if expr.left is ast.Ident {
            if expr.right is ast.Ident {
                return p.check_sql_where_expr_has_no_undefined_variables(expr.right, [
                    expr.left.name,
                ])
            }
        }

        left_check_result := p.check_sql_where_expr_has_no_undefined_variables(expr.left, [])

        if left_check_result is ast.NodeError {
            return left_check_result
        }

        variable_names := if expr.left is ast.Ident { [expr.left.name] } else { []string{} }
        right_check_result := p.check_sql_where_expr_has_no_undefined_variables(expr.right,
            variable_names)

        if right_check_result is ast.NodeError {
            return right_check_result
        }
    } else if expr is ast.ParExpr {
        return p.check_sql_where_expr_has_no_undefined_variables(expr.expr, [])
    }

    return ast.empty_expr
}