feat: make system prompt for chain configurable (#57)

Author: OskarStark

README.md

@@ -45,6 +45,7 @@ llm_chain:
             model:
                 name: 'GPT'
                 version: 'gpt-4o-mini'
+            system_prompt: 'You are a helpful assistant that can answer questions.' # The default system prompt of the chain
             tools:
                 - 'PhpLlm\LlmChain\Chain\ToolBox\Tool\SimilaritySearch'
         research:

src/DependencyInjection/Configuration.php

@@ -64,6 +64,14 @@ public function getConfigTreeBuilder(): TreeBuilder
                                 ->end()
                             ->end()
                             ->booleanNode('structured_output')->defaultTrue()->end()
+                            ->scalarNode('system_prompt')
+                                ->validate()
+                                    ->ifTrue(fn ($v) => null !== $v && '' === trim($v))
+                                    ->thenInvalid('The default system prompt must not be an empty string')
+                                ->end()
+                                ->defaultNull()
+                                ->info('The default system prompt of the chain')
+                            ->end()
                             ->arrayNode('tools')
                                 ->addDefaultsIfNotSet()
                                 ->treatFalseLike(['enabled' => false])

src/DependencyInjection/LlmChainExtension.php

@@ -18,6 +18,7 @@
 use PhpLlm\LlmChain\Bridge\Voyage\Voyage;
 use PhpLlm\LlmChain\Chain;
 use PhpLlm\LlmChain\Chain\InputProcessor;
+use PhpLlm\LlmChain\Chain\InputProcessor\SystemPromptInputProcessor;
 use PhpLlm\LlmChain\Chain\OutputProcessor;
 use PhpLlm\LlmChain\Chain\StructuredOutput\ChainProcessor as StructureOutputProcessor;
 use PhpLlm\LlmChain\Chain\ToolBox\Attribute\AsTool;
@@ -259,6 +260,17 @@ private function processChainConfig(string $name, array $config, ContainerBuilde
             $inputProcessors[] = new Reference(StructureOutputProcessor::class);
             $outputProcessors[] = new Reference(StructureOutputProcessor::class);
         }
+
+        // SYSTEM PROMPT
+        if (is_string($config['system_prompt'])) {
+            $systemPromptInputProcessorDefinition = new Definition(SystemPromptInputProcessor::class);
+            $systemPromptInputProcessorDefinition
+                ->setAutowired(true)
+                ->setArgument('$systemPrompt', $config['system_prompt']);
+
+            $inputProcessor[] = $systemPromptInputProcessorDefinition;
+        }
+
         $chainDefinition
             ->setArgument('$inputProcessors', $inputProcessors)
             ->setArgument('$outputProcessors', $outputProcessors);