// Phase 6A §3/§8 — course/module/activity completion and prerequisite locking, derived
// entirely from EXISTING sources of truth: progress (scenario completion, same table
// curriculum-rules.js already reads), achievements (assessment/capstone passes), and
// activity_completions (the ONLY new state this phase adds, and only for lesson-only
// activities that have nothing else to derive completion from). See
// docs/COURSE_CONTENT_MODEL.md §"completion rules" for the full rationale — this file must
// never become a second, independently-drifting copy of scenario/assessment completion.

const { loadProgress } = require('./progress');
const { loadContent } = require('./content');

function isActivityComplete(activity, ctx) {
  switch (activity.completion_behavior) {
    case 'auto_scenario':
      return ctx.progress[activity.scenario_id]?.status === 'completed';
    case 'auto_assessment':
      return ctx.passedAssessmentIds.has(activity.assessment_definition_id);
    case 'manual_marker':
    default:
      return ctx.completedActivityIds.has(activity.activity_id);
  }
}

// One query pass per student, reused across every activity in every course — same shape as
// curriculum-rules.js's caller-supplied progress map, just extended with the two new sources.
async function loadCompletionContext(pool, studentId) {
  const progress = await loadProgress(pool, studentId);
  const { rows: achievementRows } = await pool.query(
    `SELECT metadata->>'assessment_definition_id' AS assessment_definition_id FROM achievements
     WHERE student_id = $1 AND achievement_type IN ('assessment_completed', 'capstone_completed')
       AND metadata->>'assessment_definition_id' IS NOT NULL`,
    [studentId]
  );
  const passedAssessmentIds = new Set(achievementRows.map((r) => r.assessment_definition_id));
  const { rows: completionRows } = await pool.query(
    `SELECT activity_id FROM activity_completions WHERE student_id = $1`, [studentId]
  );
  const completedActivityIds = new Set(completionRows.map((r) => r.activity_id));
  return { progress, passedAssessmentIds, completedActivityIds };
}

// forInstructor: includes draft (unpublished) rows and each activity's instructor_notes.
// A student-facing caller must NEVER pass true — this is the one flag in this module that
// controls what an instructor sees vs. a student, and it comes from server-resolved identity
// (which route called this), never from a request parameter.
function shapeActivity(activity, ctx, forInstructor) {
  const content = loadContent(activity.content_path);
  return {
    activity_id: activity.activity_id,
    sequence: activity.sequence,
    activity_type: activity.activity_type,
    title: activity.title,
    status: activity.status,
    estimated_duration_minutes: activity.estimated_duration_minutes,
    scenario_id: activity.scenario_id,
    assessment_definition_id: activity.assessment_definition_id,
    completion_behavior: activity.completion_behavior,
    is_required: activity.is_required,
    complete: isActivityComplete(activity, ctx),
    body: content?.shared || null,
    ...(forInstructor ? { instructor_notes: content?.instructorNotes || null } : {}),
  };
}

// Phase 6B §18/§27 — an optional activity (independent-practice duplicates, advanced/CKS-exam-
// style extras) counts toward the displayed total/percent but NOT toward whether the module
// itself is "complete." Every Phase 6A activity has is_required=true (the column's default,
// unaffected by this), so this is purely additive — nothing that was complete before becomes
// incomplete now.
function totals(items) {
  const total = items.length;
  const completed = items.filter((i) => i.complete).length;
  const required = items.filter((i) => i.is_required !== false);
  const requiredComplete = required.filter((i) => i.complete).length;
  return {
    total, completed, pct: total ? Math.round((completed / total) * 100) : 0,
    complete: required.length > 0 && requiredComplete === required.length,
  };
}

// A prerequisite with zero content (a PLANNED module/course with nothing built yet) can never
// block anything — otherwise an honestly-empty PLANNED entry would permanently lock every real
// module/course that lists it as a prerequisite. See 022_course_content.sql's header comment
// and docs/COURSE_CONTENT_MODEL.md §"prerequisite/locking rule".
function prerequisitesSatisfied(prereqIds, byId) {
  return (prereqIds || []).every((id) => {
    const target = byId.get(id);
    if (!target) return true; // an unknown/removed prerequisite id never blocks
    return target._totals.total === 0 || target._totals.complete;
  });
}

// Builds the full course -> module -> activity tree for one student against one program,
// with real completion and prerequisite-based locking. Shared by the student self-paced route
// and the instructor curriculum view — forInstructor controls draft visibility and
// instructor_notes only, never the completion/locking logic itself (both surfaces must agree on
// what's actually true).
async function buildCourseTree(pool, { studentId, programId, forInstructor = false }) {
  const ctx = await loadCompletionContext(pool, studentId);
  const visClause = forInstructor ? '' : `AND visibility = 'published'`;

  const { rows: courseRows } = await pool.query(
    `SELECT * FROM courses WHERE program_id = $1 ${visClause} ORDER BY sequence`, [programId]
  );
  const { rows: moduleRows } = await pool.query(
    `SELECT * FROM course_modules WHERE course_id = ANY($1::text[]) ${visClause} ORDER BY sequence`,
    [courseRows.map((c) => c.course_id)]
  );
  const { rows: activityRows } = await pool.query(
    `SELECT * FROM module_activities WHERE module_id = ANY($1::text[]) ${visClause} ORDER BY sequence`,
    [moduleRows.map((m) => m.module_id)]
  );

  const activitiesByModule = new Map();
  for (const a of activityRows) {
    const shaped = shapeActivity(a, ctx, forInstructor);
    if (!activitiesByModule.has(a.module_id)) activitiesByModule.set(a.module_id, []);
    activitiesByModule.get(a.module_id).push(shaped);
  }

  const modulesByCourse = new Map();
  const moduleById = new Map();
  for (const m of moduleRows) {
    const activities = activitiesByModule.get(m.module_id) || [];
    const shaped = {
      module_id: m.module_id, sequence: m.sequence, title: m.title, description: m.description,
      objectives: m.objectives, estimated_duration_minutes: m.estimated_duration_minutes,
      status: m.status, prerequisites: m.prerequisites,
      activities, _totals: totals(activities),
    };
    moduleById.set(m.module_id, shaped);
    if (!modulesByCourse.has(m.course_id)) modulesByCourse.set(m.course_id, []);
    modulesByCourse.get(m.course_id).push(shaped);
  }
  // Locking depends on OTHER modules' _totals, so this has to be two separate passes over the
  // map, not one — computing and stripping _totals in the same iteration would make the result
  // depend on Map iteration order (a module whose _totals got stripped before a dependent
  // module's turn would look like it has zero content). Found by testing.
  for (const m of moduleById.values()) {
    m.locked = !prerequisitesSatisfied(m.prerequisites, moduleById);
  }
  for (const m of moduleById.values()) {
    m.complete = m._totals.complete;
    m.percent_complete = m._totals.pct;
    delete m._totals;
  }

  const courseById = new Map();
  const courses = courseRows.map((c) => {
    const modules = modulesByCourse.get(c.course_id) || [];
    const allActivities = modules.flatMap((m) => m.activities);
    const shaped = {
      course_id: c.course_id, sequence: c.sequence, title: c.title, description: c.description,
      objectives: c.objectives, estimated_duration_hours: c.estimated_duration_hours,
      status: c.status, prerequisites: c.prerequisites,
      modules, _totals: totals(allActivities),
    };
    courseById.set(c.course_id, shaped);
    return shaped;
  });
  for (const c of courses) {
    c.locked = !prerequisitesSatisfied(c.prerequisites, courseById);
  }
  for (const c of courses) {
    c.complete = c._totals.complete;
    c.percent_complete = c._totals.pct;
    delete c._totals;
  }

  return courses;
}

// Deterministic "resume learning" target: the first non-locked, incomplete activity in
// sequence order across the whole tree. Mirrors curriculum-rules.js's nextIncompleteScenario,
// just one level higher (activity, not scenario).
function findResumeTarget(courses) {
  for (const course of courses) {
    if (course.locked || course.complete) continue;
    for (const mod of course.modules) {
      if (mod.locked || mod.complete) continue;
      const next = mod.activities.find((a) => !a.complete);
      if (next) return { course_id: course.course_id, module_id: mod.module_id, activity_id: next.activity_id };
    }
  }
  return null;
}

module.exports = { buildCourseTree, findResumeTarget, loadCompletionContext, isActivityComplete };