import type { ImageAnswerMode, QuestionType } from "@/db/schema/form";
import {
  decodeCheckboxAnswer,
  encodeAnswerValue,
  formatStoredAnswer,
  type FormAnswerValue,
} from "@/lib/form/form-answer-values";
import { stripHtml } from "@/lib/utils";

export type SubmissionQuestion = {
  id: string;
  type: QuestionType;
  label: string;
  required: boolean;
  options?: string[] | null;
  allowOther: boolean;
  imageAnswerMode?: ImageAnswerMode;
};

export type SubmittedFormAnswer = {
  questionId: string;
  value: FormAnswerValue;
  imageCdnId?: string | null;
};

export type NormalizedSubmissionAnswer = {
  questionId: string;
  value: string;
  imageCdnId: string | null;
  displayValue: string;
};

export type StoredAnswerSnapshot = {
  value: string;
  imageCdnId: string | null;
};

export type OldAnswersByQuestionId = Record<
  string,
  string | StoredAnswerSnapshot | undefined
>;

function questionTitle(question: Pick<SubmissionQuestion, "label">) {
  return stripHtml(question.label);
}

function ensureSubmittedQuestionIdsBelongToForm(
  questions: SubmissionQuestion[],
  answersList: SubmittedFormAnswer[],
) {
  const questionsById = new Map(questions.map((question) => [question.id, question]));
  const submittedQuestionIds = new Set<string>();

  for (const answer of answersList) {
    if (!questionsById.has(answer.questionId) || submittedQuestionIds.has(answer.questionId)) {
      throw new Error("ข้อมูลคำตอบไม่ตรงกับแบบฟอร์ม");
    }
    submittedQuestionIds.add(answer.questionId);
  }

  return questionsById;
}

function normalizeCheckboxAnswer(
  question: SubmissionQuestion,
  rawValue: FormAnswerValue | undefined,
  imageCdnId: string | null,
): NormalizedSubmissionAnswer {
  if (
    rawValue !== undefined &&
    typeof rawValue !== "string" &&
    (!Array.isArray(rawValue) || rawValue.some((value) => typeof value !== "string"))
  ) {
    throw new Error(`รูปแบบคำตอบของ “${questionTitle(question)}” ไม่ถูกต้อง`);
  }

  const selectedValues = [...new Set(decodeCheckboxAnswer(rawValue))];
  if (selectedValues.some((value) => !value.trim() || value === "__OTHER__")) {
    throw new Error(`โปรดระบุคำตอบสำหรับ “${questionTitle(question)}”`);
  }
  if (question.required && selectedValues.length === 0) {
    throw new Error(`จำเป็นต้องตอบ “${questionTitle(question)}”`);
  }

  const standardOptions = question.options ?? [];
  const customValues = selectedValues.filter((value) => !standardOptions.includes(value));
  if ((!question.allowOther && customValues.length > 0) || customValues.length > 1) {
    throw new Error(`ตัวเลือกของ “${questionTitle(question)}” ไม่ถูกต้อง`);
  }

  return {
    questionId: question.id,
    value: encodeAnswerValue(selectedValues),
    imageCdnId,
    displayValue: selectedValues.join(", "),
  };
}

function normalizeScalarAnswer(
  question: SubmissionQuestion,
  rawValue: FormAnswerValue | undefined,
  imageCdnId: string | null,
): NormalizedSubmissionAnswer {
  if (rawValue !== undefined && typeof rawValue !== "string") {
    throw new Error(`รูปแบบคำตอบของ “${questionTitle(question)}” ไม่ถูกต้อง`);
  }

  const value = rawValue ?? "";
  if (value === "__OTHER__") {
    throw new Error(`โปรดระบุคำตอบสำหรับ “${questionTitle(question)}”`);
  }
  if (question.required && !value.trim()) {
    throw new Error(`จำเป็นต้องตอบ “${questionTitle(question)}”`);
  }
  if (
    question.type === "radio" &&
    value &&
    !(question.options ?? []).includes(value) &&
    !question.allowOther
  ) {
    throw new Error(`ตัวเลือกของ “${questionTitle(question)}” ไม่ถูกต้อง`);
  }

  return {
    questionId: question.id,
    value,
    imageCdnId,
    displayValue: value,
  };
}

function normalizeImageAnswer(
  question: SubmissionQuestion,
  rawImageCdnId: string | null | undefined,
) {
  const imageAnswerMode = question.imageAnswerMode ?? "none";
  const imageCdnId = typeof rawImageCdnId === "string" && rawImageCdnId.trim()
    ? rawImageCdnId.trim()
    : null;

  if (imageAnswerMode === "none") {
    return null;
  }
  if (imageAnswerMode === "required" && !imageCdnId) {
    throw new Error(`จำเป็นต้องอัปโหลดรูปสำหรับ “${questionTitle(question)}”`);
  }

  return imageCdnId;
}

export function normalizeSubmissionAnswers(
  questions: SubmissionQuestion[],
  answersList: SubmittedFormAnswer[],
) {
  ensureSubmittedQuestionIdsBelongToForm(questions, answersList);

  const submittedAnswers = new Map(
    answersList.map((answer) => [answer.questionId, answer]),
  );

  return questions.map((question) => {
    const submittedAnswer = submittedAnswers.get(question.id);
    const rawValue = submittedAnswer?.value;
    const imageCdnId = normalizeImageAnswer(question, submittedAnswer?.imageCdnId);
    return question.type === "checkbox"
      ? normalizeCheckboxAnswer(question, rawValue, imageCdnId)
      : normalizeScalarAnswer(question, rawValue, imageCdnId);
  });
}

export function displayAnswerValue(answer: Pick<NormalizedSubmissionAnswer, "displayValue" | "imageCdnId">) {
  return answer.displayValue || (answer.imageCdnId ? `/cdn/${answer.imageCdnId}` : "");
}

export function answersByTemplateIndex(
  questions: Pick<SubmissionQuestion, "id">[],
  normalizedAnswers: NormalizedSubmissionAnswer[],
) {
  const questionOrderMap = questions.reduce<Record<string, string>>((acc, question, index) => {
    acc[question.id] = String(index + 1);
    return acc;
  }, {});

  return normalizedAnswers.reduce<Record<string, string>>((acc, answer) => {
    const index = questionOrderMap[answer.questionId];
    if (index) acc[index] = displayAnswerValue(answer);
    return acc;
  }, {});
}

export function normalizeStoredAnswerSnapshot(
  snapshot: string | StoredAnswerSnapshot | undefined,
): StoredAnswerSnapshot {
  if (!snapshot) {
    return { value: "", imageCdnId: null };
  }
  if (typeof snapshot === "string") {
    return { value: snapshot, imageCdnId: null };
  }
  return {
    value: snapshot.value ?? "",
    imageCdnId: snapshot.imageCdnId ?? null,
  };
}

export function submissionUpdateText(
  questions: SubmissionQuestion[],
  normalizedAnswers: NormalizedSubmissionAnswer[],
  oldAnswersByQuestionId: OldAnswersByQuestionId,
) {
  const questionsById = new Map(questions.map((question) => [question.id, question]));
  const changed: string[] = [];

  for (const answer of normalizedAnswers) {
    const question = questionsById.get(answer.questionId);
    const oldSnapshot = normalizeStoredAnswerSnapshot(oldAnswersByQuestionId[answer.questionId]);
    const oldDisplayValue = question
      ? formatStoredAnswer(oldSnapshot.value, question.type)
      : oldSnapshot.value;
    const oldValue = oldDisplayValue || (oldSnapshot.imageCdnId ? `/cdn/${oldSnapshot.imageCdnId}` : "");
    const newValue = displayAnswerValue(answer);

    if (oldValue !== newValue) {
      const title = question ? questionTitle(question) : "Question";
      changed.push(
        `**${title}**: \`${oldValue || "Empty"}\` ➡️ \`${newValue || "Empty"}\``,
      );
    }
  }

  return changed.length > 0 ? changed.join("\n") : "No changes made.";
}