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package liquibase.configuration;

import liquibase.command.CommandScope;
import liquibase.configuration.core.DefaultsFileValueProvider;

/**
 * Defines a way for {@link LiquibaseConfiguration} to find configured values.
 */
public interface ConfigurationValueProvider {

    /**
     * Returns the precedence of values returned by this provider. Higher a provider with higher precedence overrides values from lower precedence providers.
     * 


     * Standard provider precedence:
     * 
     *     400 {@link liquibase.configuration.core.ScopeValueProvider}
     *     350 {@link liquibase.configuration.core.DeprecatedConfigurationValueProvider}
     *     250 Integration specific providers
     *     300: TODO JNDI attributes
     *     250: TODO Servlet Context
     *     200 {@link liquibase.configuration.core.SystemPropertyValueProvider}
     *     150 EnvironmentValueProvider
     *     100: TODO profile/context specific properties files
     *     50: {@link DefaultsFileValueProvider}
     * 
     */
    int getPrecedence();

    /**
     * Lookup the given key(s) in this source.
     * It is up to the implementation to provide any "smoothing" or translation of key names.
     * For example, an EnvironmentValueProvider will look check environment variables containing _'s rather than .'s.
     *
     * @param keyAndAliases an array of keys to check, where the first element is the canonical key name, any aliases for that key as later elements.
     *
     * @return null if the key is not defined in this provider.
     */
    ProvidedValue getProvidedValue(String... keyAndAliases);

    /**
     * Perform any validation of keys/values stored in this provider for the given commandScope.
     * For example, check for keys that do not match anything expected.
     */
    void validate(CommandScope commandScope) throws IllegalArgumentException;
}