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#ifndef Pegasus_WQLOperation_h
#define Pegasus_WQLOperation_h

#include <Pegasus/Common/Config.h>
#include <Pegasus/WQL/Linkage.h>

PEGASUS_NAMESPACE_BEGIN

/** Represents SQL where clause operators.

    These operators include the following:

    <ul>
        <li>OR</li>
        <li>AND</li>
        <li>NOT</li>
        <li>=</li>
        <li>&lt;&gt;</li>
        <li>&lt;</li>
        <li>&le;</li>
        <li>&gt;</li>
        <li>&ge;</li>
        <li>IS NULL</li>
        <li>IS NOT NULL</li>
        <li>IS TRUE</li>
        <li>IS NOT TRUE</li>
        <li>IS FALSE</li>
        <li>IS NOT FALSE</li>
    </ul>

    Here's an example of a SQL query that uses some of these operations.

    <pre>
        SELECT *
        FROM MyClass
        WHERE (x &gt; 10 OR y &le; 1.5) OR z = 19 AND name IS NOT NULL
    </pre>

    As the parser recognizes these operations, it adds the corresponding
    WQLOperation enumeration tag to the WQLSelectStatement by calling
    WQLSelectStatement::appendOperation().

    Operators may be converted to string by calling WQLOperationToString().

    Note that in expressions like this one:

    <pre>
        count IS TRUE
    </pre>

    The IS operator is NOT treated as a binary operator (which would take
    count and TRUE as its operands). Instead, the IS operator and TRUE operand
    are combined to form a single unary operation called "IS_TRUE". In this
    way, evaluation may be implemented by more efficiently (the TRUE operand
    is eliminated and therefore need not be handled). Conceptually, the above
    expression is equivalent to the following psuedo expression:

    <pre>
        IS_TRUE(count)
    </pre>

    Note that this technique is applied the following operations (also
    combined to be unary operations).

    <ul>
        <li>WQL_IS_NULL</li>
        <li>WQL_IS_NOT_NULL</li>
        <li>WQL_IS_TRUE</li>
        <li>WQL_IS_NOT_TRUE</li>
        <li>WQL_IS_FALSE</li>
        <li>WQL_IS_NOT_FALSE</li>
    </ul>
*/
enum WQLOperation
{
    WQL_OR,
    WQL_AND,
    WQL_NOT,
    WQL_EQ,
    WQL_NE,
    WQL_LT,
    WQL_LE,
    WQL_GT,
    WQL_GE,
    WQL_IS_NULL,
    WQL_IS_NOT_NULL,
    WQL_IS_TRUE,
    WQL_IS_NOT_TRUE,
    WQL_IS_FALSE,
    WQL_IS_NOT_FALSE
};

PEGASUS_WQL_LINKAGE const char* WQLOperationToString(WQLOperation x);

PEGASUS_NAMESPACE_END

#endif /* Pegasus_WQLOperation_h */