import type { TuitionLessonSeed } from "./physicsLessonSeeds";

/**
 * A deterministic objective map for a curated lesson seed.
 *
 * The content author supplies the goal, explanation blocks, formulas, and
 * board-answer prompts. This function only gives those authored parts stable
 * identifiers so evidence can say exactly what it assessed. It does not ask an
 * AI to infer progress or invent a syllabus objective.
 */
export type LessonObjective = {
  id: string;
  statement: string;
  kind: "concept" | "formula" | "application" | "board_answer";
};

function stableObjectiveId(seed: TuitionLessonSeed, index: number): string {
  return `${seed.chapterId}:${seed.missionId}:OBJ${index + 1}`;
}

function explainableStatement(value: string): string {
  const trimmed = value.trim().replace(/[.]+$/, "");
  if (!trimmed) return "Explain the source-backed lesson idea.";
  if (/^(explain|define|describe|compare|calculate|derive|write|identify|use|solve)\b/i.test(trimmed)) {
    return `${trimmed}.`;
  }
  if (/^master\b/i.test(trimmed)) return `${trimmed.replace(/^master\b/i, "Explain")}.`;
  if (/^understand\b/i.test(trimmed)) return `${trimmed.replace(/^understand\b/i, "Explain")}.`;
  return `Explain ${trimmed}.`;
}

function missionIdea(seed: TuitionLessonSeed): string {
  return seed.missionTitle.replace(/^M\d+\s*:\s*/i, "").trim() || seed.chapterTitle;
}

function isGenericBlockHeading(value: string): boolean {
  return /^(understanding|exam focus|remember|quick recap|key points?|in brief)\b/i.test(value.trim());
}

export function objectivesForLessonSeed(seed: TuitionLessonSeed): LessonObjective[] {
  const statements: Array<Omit<LessonObjective, "id">> = [
    { kind: "concept", statement: explainableStatement(seed.goal) },
    { kind: "concept", statement: `Explain the key idea in ${missionIdea(seed)}.` },
  ];

  for (const block of seed.teach.explanationBlocks.slice(0, 3)) {
    if (block.heading.trim() && !isGenericBlockHeading(block.heading)) {
      statements.push({ kind: "concept", statement: explainableStatement(block.heading) });
    }
  }

  for (const formula of seed.formulas.slice(0, 2)) {
    if (formula.formula.trim()) {
      statements.push({
        kind: "formula",
        statement: `Use ${formula.formula.trim()} with the correct symbols and units.`,
      });
    }
  }

  if (seed.contentType === "numerical" || seed.quiz.some((question) => question.type === "numerical")) {
    statements.push({
      kind: "application",
      statement: "Solve a similar application question with the method and final unit shown.",
    });
  }

  const boardAnswer = seed.examAnswers[0];
  if (boardAnswer) {
    statements.push({
      kind: "board_answer",
      statement: `Write a concise ${boardAnswer.marks}-mark board answer using the required points.`,
    });
  }

  const unique = new Map<string, Omit<LessonObjective, "id">>();
  for (const objective of statements) {
    const key = objective.statement.toLocaleLowerCase("en-IN");
    if (!unique.has(key)) unique.set(key, objective);
  }

  return [...unique.values()].slice(0, 6).map((objective, index) => ({
    ...objective,
    id: stableObjectiveId(seed, index),
  }));
}