const logA = [
  {
    logId: 1,
    author: "ABC",
    seqNo: 1,
    entryHash: "123A",
    referenceHash: null,
    message: {
      action: "create",
      fields: { text: "Pandas like to eat bamboo." },
    },
  },
  {
    logId: 1,
    author: "ABC",
    seqNo: 2,
    entryHash: "123B",
    referenceHash: "123A",
    message: {
      id: "123A",
      action: "update",
      fields: { text: "Pandas LOVE to eat bamboo." },
    },
  },
  {
    logId: 1,
    author: "ABC",
    seqNo: 3,
    entryHash: "123C",
    referenceHash: "123B",
    message: {
      id: "123A",
      action: "update",
      fields: { text: "Pandas LOVE to eat bamboo!" },
    },
  },
  {
    logId: 1,
    author: "ABC",
    seqNo: 4,
    entryHash: "123D",
    referenceHash: "234A",
    message: {
      id: "123A",
      action: "update",
      fields: { text: "Pandas LOVE to eat bamboo! But they HATE anchovies..." },
    },
  },
];

const logB = [
  {
    logId: 1,
    author: "DEF",
    seqNo: 1,
    entryHash: "234A",
    referenceHash: "123C",
    message: {
      id: "123A",
      action: "update",
      fields: { text: "Pandas LOVE to eat bamboo! But they hate anchovies..." },
    },
  },
  {
    logId: 1,
    author: "DEF",
    seqNo: 2,
    entryHash: "234B",
    referenceHash: "345A",
    message: {
      id: "123A",
      action: "update",
      fields: {
        text: "Pandas **LOVE** to eat bamboo! But they **HATE** anchovies and black coffee...",
      },
    },
  },
  {
    logId: 1,
    author: "DEF",
    seqNo: 3,
    entryHash: "234C",
    referenceHash: null,
    message: {
      action: "create",
      fields: { text: "Pandas have big eyes." },
    },
  },
];

const logC = [
  {
    logId: 1,
    author: "GHI",
    seqNo: 1,
    entryHash: "345A",
    referenceHash: "123D",
    message: {
      id: "123A",
      action: "update",
      fields: {
        text: "Pandas LOVE to eat bamboo! But they HATE anchovies and black coffee...",
      },
    },
  },
  {
    logId: 1,
    author: "GHI",
    seqNo: 2,
    entryHash: "345B",
    referenceHash: "234C",
    message: {
      id: "234C",
      action: "update",
      fields: {
        text: "Pandas have markings on their face which makes their eyes look big.",
      },
    },
  },
];

// Iterator which yields all root "create" entries
function* iterateRootEntries(allEntries) {
  for (entry of allEntries) {
    if (entry.message.action === "create") {
      yield entry;
    }
  }
}

// Iterator which plots update path for a root "create" entry
function* iterateUpdatePath(currentEntry, allEntries) {
  while (true) {
    let nextEntry = allEntries.find(
      (entry) => entry.referenceHash === currentEntry.entryHash
    );
    if (!nextEntry) break;
    currentEntry = nextEntry;
    yield formatLogItem(nextEntry);
  }
}

const createDataTree = (allEntries) => {
  const dataTree = [];
  const rootEntries = iterateRootEntries(allEntries);
  let createMessage = rootEntries.next();

  while (!createMessage.done) {
    dataTree.push([
      formatLogItem(createMessage.value),
      ...iterateUpdatePath(createMessage.value, allEntries),
    ]);
    createMessage = rootEntries.next();
  }
  return dataTree;
};

const createMaterializedView = (dataTree) => {
  let materializedView = {};
  for (path of dataTree) {
    materializedView[path[path.length - 1].id] = path[path.length - 1].value;
  }
  return materializedView;
};

const formatLogItem = (entry) => {
  return {
    id: entry.message.id ? entry.message.id : entry.entryHash,
    author: entry.author,
    value: entry.message.fields.text,
  };
};

const allEntries = [...logA, ...logB, ...logC];

const dataTree = createDataTree(allEntries);
console.log(dataTree); // => change log for each create message

let materializedView = createMaterializedView(dataTree);
console.log(materializedView); // => final updated message state
/* 
{
  '123A': 'Pandas **LOVE** to eat bamboo! But they **HATE** anchovies and black coffee...',
  '234C': 'Pandas have markings on their face which makes their eyes look big.'
}
*/