PostgresDialect.swift

import SQLKit

public struct PostgresDialect: SQLDialect {
    public init() {}
    
    public var name: String {
        "postgresql"
    }

    public var identifierQuote: any SQLExpression {
        SQLRaw(#"""#)
    }

    public var literalStringQuote: any SQLExpression {
        SQLRaw("'")
    }

    public var supportsAutoIncrement: Bool {
        true
    }

    public var autoIncrementClause: any SQLExpression {
        SQLRaw("GENERATED BY DEFAULT AS IDENTITY")
    }

    public var autoIncrementFunction: (any SQLExpression)? {
        nil
    }

    public func bindPlaceholder(at position: Int) -> any SQLExpression {
        SQLRaw("$\(position)")
    }

    public func literalBoolean(_ value: Bool) -> any SQLExpression {
        SQLRaw("\(value)")
    }

    public var literalDefault: any SQLExpression {
        SQLRaw("DEFAULT")
    }

    public var supportsIfExists: Bool {
        true
    }

    public var enumSyntax: SQLEnumSyntax {
        .typeName
    }

    public var supportsDropBehavior: Bool {
        true
    }

    public var supportsReturning: Bool {
        true
    }

    public var triggerSyntax: SQLTriggerSyntax {
        .init(
            create: [.supportsForEach, .postgreSQLChecks, .supportsCondition, .conditionRequiresParentheses, .supportsConstraints],
            drop: [.supportsCascade, .supportsTableName]
        )
    }

    public var alterTableSyntax: SQLAlterTableSyntax {
        .init(
            alterColumnDefinitionClause: SQLRaw("ALTER COLUMN"),
            alterColumnDefinitionTypeKeyword: SQLRaw("SET DATA TYPE")
        )
    }

    public func customDataType(for dataType: SQLDataType) -> (any SQLExpression)? {
        if case let .custom(expr) = dataType, (expr as? SQLRaw)?.sql == "TIMESTAMP" {
            return SQLRaw("TIMESTAMPTZ")
        } else if case .blob = dataType {
            return SQLRaw("BYTEA")
        } else {
            return nil
        }
    }

    public var upsertSyntax: SQLUpsertSyntax {
        .standard
    }

    public var unionFeatures: SQLUnionFeatures {
        [
            .union,     .unionAll,
            .intersect, .intersectAll,
            .except,    .exceptAll,
            .explicitDistinct,
            .parenthesizedSubqueries
        ]
    }

    public var sharedSelectLockExpression: (any SQLExpression)? {
        SQLRaw("FOR SHARE")
    }

    public var exclusiveSelectLockExpression: (any SQLExpression)? {
        SQLRaw("FOR UPDATE")
    }

    public func nestedSubpathExpression(in column: any SQLExpression, for path: [String]) -> (any SQLExpression)? {
        guard !path.isEmpty else { return nil }
        
        let descender = SQLList(
            [column] + path.dropLast().map(SQLLiteral.string(_:)),
            separator: SQLRaw("->")
        )
        let accessor = SQLList(
            [descender, SQLLiteral.string(path.last!)],
            separator: SQLRaw("->>")
        )
        
        return SQLGroupExpression(accessor)
    }
}