// src/messages/__tests__/dedup.test.ts
import {
  SystemMessage,
  HumanMessage,
  AIMessage,
  ToolMessage,
} from '@langchain/core/messages';
import type { BaseMessage } from '@langchain/core/messages';
import { deduplicateSystemMessages } from '../dedup';

describe('deduplicateSystemMessages', () => {
  it('returns empty array unchanged', () => {
    const result = deduplicateSystemMessages([]);
    expect(result.messages).toEqual([]);
    expect(result.removedCount).toBe(0);
  });

  it('returns single message unchanged', () => {
    const msgs = [new SystemMessage('Hello')];
    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(1);
    expect(result.removedCount).toBe(0);
  });

  it('preserves conversation with no duplicates', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('You are helpful'),
      new HumanMessage('Hello'),
      new AIMessage('Hi there'),
      new SystemMessage('Summary of prior context'),
      new HumanMessage('What about X?'),
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(5);
    expect(result.removedCount).toBe(0);
  });

  it('removes duplicate system messages', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('You are helpful'),
      new SystemMessage('[Conversation Summary]\nUser discussed X'),
      new HumanMessage('Hello'),
      new AIMessage('Hi'),
      new SystemMessage('[Conversation Summary]\nUser discussed X'), // duplicate
      new HumanMessage('What?'),
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(5);
    expect(result.removedCount).toBe(1);
    // Verify the duplicate at index 4 was removed
    expect(result.messages.map((m) => m.getType())).toEqual([
      'system',
      'system',
      'human',
      'ai',
      'human',
    ]);
  });

  it('keeps the first occurrence of duplicate system messages', () => {
    const duplicateContent = 'Context was compressed. Summary follows.';
    const msgs: BaseMessage[] = [
      new SystemMessage('Main prompt'),
      new SystemMessage(duplicateContent), // first occurrence
      new HumanMessage('Q1'),
      new AIMessage('A1'),
      new SystemMessage(duplicateContent), // duplicate
      new HumanMessage('Q2'),
      new AIMessage('A2'),
      new SystemMessage(duplicateContent), // another duplicate
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(6);
    expect(result.removedCount).toBe(2);
  });

  it('never removes non-system messages', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('Prompt'),
      new HumanMessage('Same content'),
      new AIMessage('Same content'),
      new HumanMessage('Same content'), // duplicate content but not system
      new AIMessage('Same content'), // duplicate content but not system
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(5);
    expect(result.removedCount).toBe(0);
  });

  it('always preserves the first system message (main prompt)', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('Main system prompt'),
      new HumanMessage('Hello'),
      new SystemMessage('Main system prompt'), // duplicate of first
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.messages).toHaveLength(2);
    expect(result.removedCount).toBe(1);
    // First system message is preserved
    expect(result.messages[0].content as string).toBe('Main system prompt');
  });

  it('handles tool messages correctly (never deduped)', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('Prompt'),
      new HumanMessage('Q'),
      new AIMessage({
        content: 'Using tool',
        tool_calls: [{ id: 'tc1', name: 'test', args: {} }],
      }),
      new ToolMessage({ content: 'result', tool_call_id: 'tc1' }),
      new SystemMessage('Post-prune note'),
      new AIMessage({
        content: 'Using tool',
        tool_calls: [{ id: 'tc2', name: 'test', args: {} }],
      }),
      new ToolMessage({ content: 'result', tool_call_id: 'tc2' }),
      new SystemMessage('Post-prune note'), // duplicate system msg
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.removedCount).toBe(1);
    // Tool messages are all preserved
    const toolMsgs = result.messages.filter((m) => m.getType() === 'tool');
    expect(toolMsgs).toHaveLength(2);
  });

  it('does not mutate input array', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('Prompt'),
      new SystemMessage('Dup'),
      new SystemMessage('Dup'),
    ];
    const originalLength = msgs.length;

    deduplicateSystemMessages(msgs);
    expect(msgs.length).toBe(originalLength);
  });

  it('handles mixed duplicate patterns', () => {
    const msgs: BaseMessage[] = [
      new SystemMessage('A'),
      new SystemMessage('B'),
      new SystemMessage('A'), // dup of first
      new HumanMessage('Q'),
      new SystemMessage('B'), // dup
      new SystemMessage('C'),
      new SystemMessage('C'), // dup
    ];

    const result = deduplicateSystemMessages(msgs);
    expect(result.removedCount).toBe(3);
    expect(result.messages).toHaveLength(4);
    expect(
      result.messages.map((m) => {
        if (typeof m.content === 'string') return m.content;
        return '';
      })
    ).toEqual(['A', 'B', 'Q', 'C']);
  });
});