"""Admin chatbot service — AI-powered student filtering & report generation."""

import json
import re
from collections import defaultdict
from datetime import datetime, timezone, timedelta
from io import BytesIO

from bson import ObjectId
from openpyxl import Workbook
from openpyxl.styles import Alignment, Border, Font, PatternFill, Side
from openpyxl.utils import get_column_letter

from database import get_db
from models.collections import (
    GROUP_TESTS,
    GROUP_TEST_RESULTS,
    JOB_DESCRIPTIONS,
    SKILLS,
    TOPICS,
    USERS,
)
from services.group_test_service import _refresh_topic_statuses
from utils.gemini import call_gemini
from utils.helpers import str_objectids


# ─── Gemini query parser ─────────────────────────────────────────────────────

async def _parse_query(query: str, group_tests: list[dict], jd_content: str | None) -> dict:
    """Ask Gemini to extract structured filter parameters from a natural-language query."""
    gt_list = [{"id": gt["id"], "name": gt["name"]} for gt in group_tests]

    jd_context = ""
    if jd_content:
        jd_context = (
            f"\n\nJob Description:\n{jd_content}\n"
            "Use this JD to rank students by skill relevance when use_jd_ranking is true."
        )

    prompt = (
        f'Admin query: "{query}"\n\n'
        f"Available group tests: {json.dumps(gt_list)}"
        f"{jd_context}\n\n"
        "Extract filter parameters and return ONLY a JSON object (no markdown, no extra text):\n"
        "{\n"
        '  "group_test_id": "<id from the list, or null if none matches>",\n'
        '  "group_test_name": "<matched name or null>",\n'
        '  "top_k": <integer or null>,\n'
        '  "min_score": <number 0-100 or null>,\n'
        '  "use_jd_ranking": <true if JD was provided and should influence ranking>,\n'
        '  "response_message": "<short 1-2 sentence message describing the filter result>"\n'
        "}\n\n"
        "Rules:\n"
        "- Match group_test_id to the best-fitting group test. null = show all students across all tests.\n"
        "- top_k: number from phrases like 'top 5', 'top k', 'best 10'. null = all.\n"
        "- min_score: extract from 'score above 70', 'minimum 80%'. null = no filter.\n"
        "- response_message: friendly description of what was filtered.\n"
        "Return ONLY valid JSON, no other text."
    )

    raw = await call_gemini(prompt)
    cleaned = raw.strip()
    if cleaned.startswith("```"):
        cleaned = re.sub(r"```[a-z]*\n?", "", cleaned).strip().rstrip("`").strip()
    try:
        return json.loads(cleaned)
    except Exception:
        # Fallback: return empty params so the caller can show a helpful message
        return {
            "group_test_id": None,
            "group_test_name": None,
            "top_k": None,
            "min_score": None,
            "use_jd_ranking": False,
            "response_message": "I couldn't understand the query. Please try something like: 'top 5 students in SWE group'.",
        }


# ─── Data helpers ─────────────────────────────────────────────────────────────

async def _user_info(user_id: str, db) -> dict:
    try:
        user = await db[USERS].find_one({"_id": ObjectId(user_id)})
    except Exception:
        user = None
    if not user:
        return {"reg_no": "N/A", "name": "", "email": ""}
    return {
        "reg_no": user.get("reg_no") or "N/A",
        "name": user.get("name", ""),
        "email": user.get("email", ""),
    }


async def _jd_skills(jd_id: str, db) -> tuple[str | None, list[str]]:
    """Return (jd_content_str, required_skills_list)."""
    try:
        doc = await db[JOB_DESCRIPTIONS].find_one({"_id": ObjectId(jd_id)})
    except Exception:
        doc = None
    if not doc:
        return None, []
    content = f"Title: {doc.get('title', '')}\n{doc.get('description', '')}"
    return content, doc.get("required_skills") or []


def _skill_match_pct(student_skills: list[str], jd_skills: list[str]) -> float | None:
    if not jd_skills:
        return None
    s_lower = [s.lower() for s in student_skills]
    j_lower = [s.lower() for s in jd_skills]
    matched = sum(1 for j in j_lower if any(j in s or s in j for s in s_lower))
    return round(matched / len(j_lower) * 100, 1)


# ─── Main query processor ────────────────────────────────────────────────────

async def process_chatbot_query(query: str, jd_id: str | None) -> dict:
    """Parse admin query, aggregate student data, apply filters, return ranked rows."""
    db = get_db()

    # Fetch all group tests
    gt_cursor = db[GROUP_TESTS].find({}).sort("created_at", -1)
    gt_docs = await gt_cursor.to_list(length=300)
    all_group_tests = [
        {
            "id": str(d["_id"]),
            "name": d.get("name", ""),
            "topic_ids": d.get("topic_ids") or [],
        }
        for d in gt_docs
    ]

    # Fetch JD if provided
    jd_content, jd_req_skills = (None, [])
    if jd_id:
        jd_content, jd_req_skills = await _jd_skills(jd_id, db)

    # Let Gemini parse the query
    parsed = await _parse_query(query, all_group_tests, jd_content)

    group_test_id: str | None = parsed.get("group_test_id")
    top_k: int | None = parsed.get("top_k")
    min_score: float | None = parsed.get("min_score")
    use_jd_ranking: bool = bool(parsed.get("use_jd_ranking")) and bool(jd_req_skills)
    response_message: str = parsed.get("response_message") or "Here are the filtered results."

    # Build topic column list from the matched group test
    topic_columns: list[dict] = []
    group_test_name: str = ""

    if group_test_id:
        gt_doc = next((g for g in all_group_tests if g["id"] == group_test_id), None)
        if gt_doc:
            group_test_name = gt_doc["name"]
            for tid in gt_doc["topic_ids"]:
                try:
                    t = await db[TOPICS].find_one({"_id": ObjectId(tid)})
                except Exception:
                    t = None
                if t:
                    topic_columns.append({"id": tid, "name": t.get("name", tid)})

    # Fetch relevant results
    results_filter = {"group_test_id": group_test_id} if group_test_id else {}
    results_cursor = db[GROUP_TEST_RESULTS].find(results_filter)
    results_docs = await results_cursor.to_list(length=2000)

    # Group by user_id; pick best attempt per user per group_test
    # Key: (user_id, group_test_id) → list of attempts
    attempts_map: dict[tuple, list] = defaultdict(list)
    for r in results_docs:
        key = (r.get("user_id", ""), r.get("group_test_id", ""))
        attempts_map[key].append(r)

    rows: list[dict] = []
    seen_users: set[str] = set()

    for (uid, gt_id), attempts in attempts_map.items():
        if not uid:
            continue

        # Refresh topic statuses and choose best attempt
        best = None
        for attempt in attempts:
            attempt = await _refresh_topic_statuses(attempt, db)
            score = attempt.get("overall_score") or 0
            if best is None or score > (best.get("overall_score") or 0):
                best = attempt

        user = await _user_info(uid, db)

        # Per-topic scores from best attempt
        topic_scores: dict[str, dict] = {}
        for tr in best.get("topic_results") or []:
            tid = tr.get("topic_id", "")
            topic_scores[tid] = {
                "topic_name": tr.get("topic_name", ""),
                "score": tr.get("overall_score"),
                "status": tr.get("status", "pending"),
            }

        # JD skill match
        skill_match: float | None = None
        if use_jd_ranking:
            skills_doc = await db[SKILLS].find_one({"user_id": uid})
            student_skills = (skills_doc or {}).get("skills") or []
            skill_match = _skill_match_pct(student_skills, jd_req_skills)

        row = {
            "user_id": uid,
            "reg_no": user["reg_no"],
            "name": user["name"],
            "email": user["email"],
            "group_test_id": gt_id,
            "group_test_name": best.get("group_test_name") or group_test_name,
            "overall_score": round(best.get("overall_score") or 0, 1),
            "total_attempts": len(attempts),
            "status": best.get("status", "in_progress"),
            "topic_scores": topic_scores,
            "skill_match": skill_match,
            "rank": 0,  # assigned below
        }
        rows.append(row)

    # If multiple group tests queried (no filter), collect unique topic columns
    if not group_test_id:
        topic_set: dict[str, str] = {}
        for r in rows:
            for tid, ts in r["topic_scores"].items():
                if tid not in topic_set:
                    topic_set[tid] = ts["topic_name"]
        topic_columns = [{"id": tid, "name": name} for tid, name in topic_set.items()]

    # Sort
    if use_jd_ranking:
        rows.sort(
            key=lambda r: (r["skill_match"] or 0) * 0.4 + (r["overall_score"] or 0) * 0.6,
            reverse=True,
        )
    else:
        rows.sort(key=lambda r: r["overall_score"] or 0, reverse=True)

    # Min score filter
    if min_score is not None:
        rows = [r for r in rows if (r["overall_score"] or 0) >= min_score]

    # Assign ranks
    for i, row in enumerate(rows):
        row["rank"] = i + 1

    # Top-k slice
    if top_k and top_k > 0:
        rows = rows[:top_k]

    return {
        "message": response_message,
        "group_test_name": group_test_name or "All Group Tests",
        "group_test_id": group_test_id,
        "topic_columns": topic_columns,
        "rows": rows,
        "total": len(rows),
    }


# ─── Update student ───────────────────────────────────────────────────────────

async def update_student_info(user_id: str, reg_no: str | None, name: str | None) -> dict:
    """Allow admin to correct a student's reg_no or name."""
    db = get_db()
    update: dict = {}
    if reg_no is not None:
        reg_no = reg_no.strip()
        if reg_no:
            # Uniqueness check
            existing = await db[USERS].find_one(
                {"reg_no": reg_no, "_id": {"$ne": ObjectId(user_id)}}
            )
            if existing:
                raise ValueError("This register number is already used by another student.")
            update["reg_no"] = reg_no
    if name is not None:
        name = name.strip()
        if name:
            update["name"] = name
    if not update:
        raise ValueError("Nothing to update.")
    await db[USERS].update_one({"_id": ObjectId(user_id)}, {"$set": update})
    user = await db[USERS].find_one({"_id": ObjectId(user_id)})
    return {
        "user_id": user_id,
        "reg_no": (user or {}).get("reg_no") or "N/A",
        "name": (user or {}).get("name", ""),
        "email": (user or {}).get("email", ""),
    }


# ─── Excel export ─────────────────────────────────────────────────────────────

_HEADER_FILL = PatternFill(start_color="1F4E79", end_color="1F4E79", fill_type="solid")
_ALT_FILL = PatternFill(start_color="D6E4F0", end_color="D6E4F0", fill_type="solid")
_SCORE_FILL = PatternFill(start_color="E8F5E9", end_color="E8F5E9", fill_type="solid")
_HEADER_FONT = Font(name="Calibri", bold=True, color="FFFFFF", size=11)
_DATA_FONT = Font(name="Calibri", size=10)
_BOLD_DATA_FONT = Font(name="Calibri", bold=True, size=10)
_CENTER = Alignment(horizontal="center", vertical="center", wrap_text=True)
_LEFT = Alignment(horizontal="left", vertical="center")


def _thin_border() -> Border:
    s = Side(style="thin", color="B0BEC5")
    return Border(left=s, right=s, top=s, bottom=s)


def generate_excel(rows: list[dict], topic_columns: list[dict], group_test_name: str) -> BytesIO:
    wb = Workbook()
    ws = wb.active
    ws.title = "Students"

    border = _thin_border()

    # ── Header row ────────────────────────────────────────────────────────────
    headers = ["Rank", "Reg No", "Name", "Email"]
    for tc in topic_columns:
        headers.append(f"{tc['name']}\nScore")
    headers += ["Overall\nScore", "Attempts", "Status"]
    if any(r.get("skill_match") is not None for r in rows):
        headers.append("JD Match\n(%)")

    for col_idx, header in enumerate(headers, 1):
        cell = ws.cell(row=1, column=col_idx, value=header)
        cell.font = _HEADER_FONT
        cell.fill = _HEADER_FILL
        cell.alignment = _CENTER
        cell.border = border
    ws.row_dimensions[1].height = 36

    # ── Data rows ─────────────────────────────────────────────────────────────
    for row_num, row in enumerate(rows, 2):
        use_alt = row_num % 2 == 0
        row_fill = _ALT_FILL if use_alt else None

        data: list = [
            row.get("rank", row_num - 1),
            row.get("reg_no", ""),
            row.get("name", ""),
            row.get("email", ""),
        ]

        for tc in topic_columns:
            ts = row.get("topic_scores", {}).get(tc["id"], {})
            score = ts.get("score")
            data.append(f"{score:.1f}%" if score is not None else "—")

        overall = row.get("overall_score")
        data.append(f"{overall:.1f}%" if overall is not None else "—")
        data.append(row.get("total_attempts", 1))
        data.append((row.get("status") or "").replace("_", " ").title())

        if any(r.get("skill_match") is not None for r in rows):
            sm = row.get("skill_match")
            data.append(f"{sm:.1f}%" if sm is not None else "—")

        for col_idx, value in enumerate(data, 1):
            cell = ws.cell(row=row_num, column=col_idx, value=value)
            cell.border = border
            cell.font = _DATA_FONT
            if col_idx in (1,):  # rank → bold + centered
                cell.font = _BOLD_DATA_FONT
                cell.alignment = _CENTER
            elif col_idx in (2, 3, 4):
                cell.alignment = _LEFT
            else:
                cell.alignment = _CENTER
            if row_fill:
                cell.fill = row_fill

        ws.row_dimensions[row_num].height = 20

    # ── Column widths ──────────────────────────────────────────────────────────
    col_widths = [6, 16, 22, 28]
    for _ in topic_columns:
        col_widths.append(14)
    col_widths += [14, 10, 14]
    if any(r.get("skill_match") is not None for r in rows):
        col_widths.append(12)

    for i, width in enumerate(col_widths, 1):
        ws.column_dimensions[get_column_letter(i)].width = width

    # ── Title row above headers ────────────────────────────────────────────────
    ws.insert_rows(1)
    title_cell = ws.cell(row=1, column=1, value=f"Student Results — {group_test_name}")
    title_cell.font = Font(name="Calibri", bold=True, size=13, color="1F4E79")
    title_cell.alignment = _LEFT
    ws.merge_cells(start_row=1, start_column=1, end_row=1, end_column=max(len(headers), 5))
    ws.row_dimensions[1].height = 28

    # ── Freeze header row ──────────────────────────────────────────────────────
    ws.freeze_panes = "A3"

    bio = BytesIO()
    wb.save(bio)
    bio.seek(0)
    return bio


# ─── Structured Student Filter (no Gemini) ───────────────────────────────────

def _parse_date(date_str: str | None, end_of_day: bool = False):
    """Parse YYYY-MM-DD string to UTC-aware datetime, or None."""
    if not date_str:
        return None
    try:
        dt = datetime.strptime(date_str.strip(), "%Y-%m-%d").replace(tzinfo=timezone.utc)
        if end_of_day:
            dt = dt + timedelta(days=1)
        return dt
    except ValueError:
        return None


def _compute_duration(started_at, completed_at) -> float | None:
    """Duration in minutes, rounded to 1 dp. Returns None if either timestamp missing."""
    if started_at is None or completed_at is None:
        return None
    try:
        # Handle both datetime objects and ISO strings
        if isinstance(started_at, str):
            started_at = datetime.fromisoformat(started_at.replace("Z", "+00:00"))
        if isinstance(completed_at, str):
            completed_at = datetime.fromisoformat(completed_at.replace("Z", "+00:00"))
        delta = completed_at - started_at
        return round(max(delta.total_seconds(), 0) / 60, 1)
    except Exception:
        return None


async def filter_students_structured(
    group_test_ids: list[str] | None,
    jd_id: str | None,
    start_date: str | None,
    end_date: str | None,
    top_k: int | None,
    min_score: float | None,
    sort_fields: list[str] | None = None,
    sort_orders: list[str] | None = None,
) -> dict:
    """Structured student filter — no Gemini, explicit params, composable."""
    db = get_db()

    # ── Fetch all group tests for metadata ────────────────────────────────────
    gt_cursor = db[GROUP_TESTS].find({}).sort("created_at", -1)
    gt_docs = await gt_cursor.to_list(length=300)
    all_group_tests: dict[str, dict] = {
        str(d["_id"]): {
            "id": str(d["_id"]),
            "name": d.get("name", ""),
            "topic_ids": d.get("topic_ids") or [],
        }
        for d in gt_docs
    }

    # ── Fetch JD info if provided ─────────────────────────────────────────────
    jd_content, jd_req_skills = (None, [])
    if jd_id:
        jd_content, jd_req_skills = await _jd_skills(jd_id, db)
    use_jd_ranking = bool(jd_req_skills)

    # ── Build MongoDB query ───────────────────────────────────────────────────
    results_filter: dict = {}

    if group_test_ids:
        results_filter["group_test_id"] = {"$in": group_test_ids}

    start_dt = _parse_date(start_date, end_of_day=False)
    end_dt = _parse_date(end_date, end_of_day=True)
    if start_dt or end_dt:
        date_filter: dict = {}
        if start_dt:
            date_filter["$gte"] = start_dt
        if end_dt:
            date_filter["$lt"] = end_dt
        results_filter["started_at"] = date_filter

    results_cursor = db[GROUP_TEST_RESULTS].find(results_filter)
    results_docs = await results_cursor.to_list(length=3000)

    # ── Collect topic columns from selected group tests ───────────────────────
    selected_gt_ids: set[str] = (
        set(group_test_ids) if group_test_ids
        else {str(d["_id"]) for d in gt_docs}
    )

    topic_columns: list[dict] = []
    topic_seen: set[str] = set()
    group_test_name = "All Group Tests"

    if group_test_ids and len(group_test_ids) == 1:
        gt = all_group_tests.get(group_test_ids[0])
        if gt:
            group_test_name = gt["name"]
            for tid in gt["topic_ids"]:
                if tid not in topic_seen:
                    topic_seen.add(tid)
                    try:
                        t = await db[TOPICS].find_one({"_id": ObjectId(tid)})
                    except Exception:
                        t = None
                    if t:
                        topic_columns.append({"id": tid, "name": t.get("name", tid)})
    elif group_test_ids and len(group_test_ids) > 1:
        names = [all_group_tests[gid]["name"] for gid in group_test_ids if gid in all_group_tests]
        group_test_name = ", ".join(names) if names else "Multiple Tests"
        for gid in group_test_ids:
            gt = all_group_tests.get(gid)
            if not gt:
                continue
            for tid in gt["topic_ids"]:
                if tid not in topic_seen:
                    topic_seen.add(tid)
                    try:
                        t = await db[TOPICS].find_one({"_id": ObjectId(tid)})
                    except Exception:
                        t = None
                    if t:
                        topic_columns.append({"id": tid, "name": t.get("name", tid)})

    # ── Group by (user_id, group_test_id) → pick best attempt ────────────────
    attempts_map: dict[tuple, list] = defaultdict(list)
    for r in results_docs:
        uid = r.get("user_id", "")
        gtid = r.get("group_test_id", "")
        if uid:
            attempts_map[(uid, gtid)].append(r)

    rows: list[dict] = []

    for (uid, gt_id), attempts in attempts_map.items():
        best = None
        for attempt in attempts:
            attempt = await _refresh_topic_statuses(attempt, db)
            score = attempt.get("overall_score") or 0
            if best is None or score > (best.get("overall_score") or 0):
                best = attempt

        user = await _user_info(uid, db)

        # Per-topic scores
        topic_scores: dict[str, dict] = {}
        for tr in best.get("topic_results") or []:
            tid = tr.get("topic_id", "")
            topic_scores[tid] = {
                "topic_name": tr.get("topic_name", ""),
                "score": tr.get("overall_score"),
                "status": tr.get("status", "pending"),
            }

        # JD skill match
        skill_match: float | None = None
        if use_jd_ranking:
            skills_doc = await db[SKILLS].find_one({"user_id": uid})
            student_skills = (skills_doc or {}).get("skills") or []
            skill_match = _skill_match_pct(student_skills, jd_req_skills)

        # Attempt time & duration
        started_at = best.get("started_at")
        completed_at = best.get("completed_at")
        attempt_time: str | None = None
        if started_at is not None:
            try:
                attempt_time = started_at.isoformat() if isinstance(started_at, datetime) else str(started_at)
            except Exception:
                attempt_time = None

        # Collect topic columns dynamically when showing all tests
        if not group_test_ids:
            gt = all_group_tests.get(gt_id)
            if gt:
                for tid in gt["topic_ids"]:
                    if tid not in topic_seen:
                        topic_seen.add(tid)
                        try:
                            t = await db[TOPICS].find_one({"_id": ObjectId(tid)})
                        except Exception:
                            t = None
                        if t:
                            topic_columns.append({"id": tid, "name": t.get("name", tid)})

        gt_info = all_group_tests.get(gt_id, {})

        row = {
            "user_id": uid,
            "reg_no": user["reg_no"],
            "name": user["name"],
            "email": user["email"],
            "group_test_id": gt_id,
            "group_test_name": best.get("group_test_name") or gt_info.get("name", ""),
            "overall_score": round(best.get("overall_score") or 0, 1),
            "total_attempts": len(attempts),
            "status": best.get("status", "in_progress"),
            "topic_scores": topic_scores,
            "skill_match": skill_match,
            "rank": 0,
            "attempt_time": attempt_time,
            "duration_minutes": _compute_duration(started_at, completed_at),
        }
        rows.append(row)

    # ── Min score filter ──────────────────────────────────────────────────────
    if min_score is not None:
        rows = [r for r in rows if (r["overall_score"] or 0) >= min_score]

    # ── Multi-sort ────────────────────────────────────────────────────────────
    _fields = sort_fields if sort_fields else ["time"]
    _orders = sort_orders if sort_orders else ["desc"]
    _INF = float("inf")
    _NEG_INF = float("-inf")

    def _row_key(r: dict, field: str, order: str):
        """Return a comparable key, handling None with order-aware sentinel."""
        desc = order.lower() == "desc"
        if field == "score":
            v = r.get("overall_score") or 0
            return -v if desc else v
        elif field == "duration":
            v = r.get("duration_minutes")
            if v is None:
                return _INF  # always sort None to end
            return -v if desc else v
        else:  # "time"
            v = r.get("attempt_time") or ""
            # For strings, desc means we negate via reverse tuple trick below
            return v

    # Apply sorts in reverse priority order (stable sort)
    paired = list(zip(_fields, _orders))
    for field, order in reversed(paired):
        desc = order.lower() == "desc"
        if field == "time":
            rows.sort(key=lambda r: r.get("attempt_time") or "", reverse=desc)
        elif field == "score":
            rows.sort(key=lambda r: r.get("overall_score") or 0, reverse=desc)
        elif field == "duration":
            rows.sort(
                key=lambda r: r["duration_minutes"] if r["duration_minutes"] is not None
                else (_NEG_INF if desc else _INF),
                reverse=desc,
            )

    # ── Assign ranks ──────────────────────────────────────────────────────────
    for i, row in enumerate(rows):
        row["rank"] = i + 1

    # ── Top-K slice ───────────────────────────────────────────────────────────
    if top_k and top_k > 0:
        rows = rows[:top_k]

    return {
        "group_test_name": group_test_name,
        "group_test_id": group_test_ids[0] if group_test_ids and len(group_test_ids) == 1 else None,
        "topic_columns": topic_columns,
        "rows": rows,
        "total": len(rows),
    }