from __future__ import annotations

from quart import Blueprint, g, jsonify, request
from sqlalchemy import func, select

from .auth import login_required
from .colors import normalize_color
from .db import session_scope
from .models.label import Label, NoteLabel
from .responses import json_error, not_found, parse_uuid
from .serialize import serialize_label

bp = Blueprint("labels", __name__, url_prefix="/api/labels")


def _serialize_label(label: Label, count: int | None = None) -> dict:
    data = serialize_label(label)
    if count is not None:
        data["count"] = count
    return data


async def _label_note_count(db, label_id) -> int:
    """How many notes carry this label (distinct — note_labels PK is note+label)."""
    return int(
        await db.scalar(select(func.count()).select_from(NoteLabel).where(NoteLabel.label_id == label_id)) or 0
    )


async def _merge_into(db, source: Label, target: Label) -> None:
    """Move every note tagged with `source` onto `target`, then delete `source`.

    Shared by the explicit `/merge` route and by a rename that lands on a name
    another tag already holds — those are the same operation, and having one body
    is what stops them drifting into two answers for one question.

    Note-body `#tags` are NOT rewritten, so a note whose body still literally
    contains the source `#tag` will re-mint that tag on its next edit. Retiring a
    tag means editing it out of the text; a known, documented nuance.
    """
    # Notes already carrying the target: a note can't hold the same label twice
    # (composite PK), so the source attachment there is just dropped as a dup.
    target_notes = set(
        (await db.scalars(select(NoteLabel.note_id).where(NoteLabel.label_id == target.id))).all()
    )
    source_rows = (await db.scalars(select(NoteLabel).where(NoteLabel.label_id == source.id))).all()
    by_note = {r.note_id: r.via_tag for r in source_rows}
    # Delete the source attachments first, then re-insert under the target — moving
    # by delete+insert avoids mutating a composite primary-key column in place.
    for row in source_rows:
        await db.delete(row)
    await db.flush()
    for note_id, via_tag in by_note.items():
        if note_id not in target_notes:
            db.add(NoteLabel(note_id=note_id, label_id=target.id, via_tag=via_tag))
    await db.delete(source)
    await db.flush()


async def _get_owned_label(db, label_id: str) -> Label | None:
    lid = parse_uuid(label_id)
    if lid is None:
        return None
    return await db.scalar(select(Label).where(Label.id == lid, Label.owner_id == g.user_id))


@bp.get("")
@login_required
async def list_labels():
    async with session_scope() as db:
        labels = (await db.scalars(select(Label).where(Label.owner_id == g.user_id).order_by(Label.name))).all()
        # One grouped query for all usage counts (0 for labels attached to nothing).
        counts = dict(
            (
                await db.execute(
                    select(NoteLabel.label_id, func.count(NoteLabel.note_id))
                    .where(NoteLabel.label_id.in_([lb.id for lb in labels]))
                    .group_by(NoteLabel.label_id)
                )
            ).all()
        ) if labels else {}
        return jsonify({"labels": [_serialize_label(lb, int(counts.get(lb.id, 0))) for lb in labels]})


@bp.post("")
@login_required
async def create_label():
    data = await request.get_json(silent=True) or {}
    name = (data.get("name") or "").strip()
    if not name:
        return json_error("tag name is required", 400)
    async with session_scope() as db:
        # Idempotent: creating an existing tag just returns it. Case-INSENSITIVE,
        # like the clients' `find_or_create_label` — a case-sensitive match here was
        # the path that MINTED the "Groceries" beside "groceries" pair that no synced
        # client can hold, since their `labels` index is unique on `lower(name)`.
        existing = await db.scalar(
            select(Label).where(Label.owner_id == g.user_id, func.lower(Label.name) == name.lower())
        )
        if existing is not None:
            return jsonify(_serialize_label(existing)), 200
        label = Label(owner_id=g.user_id, name=name, color=normalize_color(data.get("color")))
        db.add(label)
        await db.commit()
        await db.refresh(label)
        return jsonify(_serialize_label(label, 0)), 201


@bp.patch("/<label_id>")
@login_required
async def update_label(label_id: str):
    data = await request.get_json(silent=True) or {}
    has_name = "name" in data
    has_color = "color" in data
    if not has_name and not has_color:
        return json_error("nothing to update", 400)
    name = (data.get("name") or "").strip() if has_name else None
    if has_name and not name:
        return json_error("tag name is required", 400)
    async with session_scope() as db:
        label = await _get_owned_label(db, label_id)
        if label is None:
            return not_found()
        if has_name:
            # Case-INSENSITIVE, matching the clients' `find_or_create_label` and the
            # local store's `lower(name)` unique index. The Postgres constraint here
            # is on the raw name, so the database would happily hold "Groceries"
            # beside "groceries" — but no synced client can store both, so letting
            # one be made is letting a pull fail later on a phone.
            clash = await db.scalar(
                select(Label).where(
                    Label.owner_id == g.user_id,
                    func.lower(Label.name) == name.lower(),
                    Label.id != label.id,
                )
            )
            if clash is not None:
                # Renaming onto an existing tag MERGES the two rather than failing:
                # typing an existing tag's name onto this one says they are the same
                # thing. The OLDER row survives and takes the new spelling — age is
                # the one property that does not depend on which of the two the
                # caller happened to be renaming, so A→B and B→A agree. Ties go to
                # the incumbent. Mirrors `store::rename_label` exactly.
                if clash.created_at <= label.created_at:
                    survivor, doomed = clash, label
                else:
                    survivor, doomed = label, clash
                await _merge_into(db, doomed, survivor)
                label = survivor
            label.name = name
        if has_color:
            label.color = normalize_color(data.get("color"))
        await db.commit()
        await db.refresh(label)
        return jsonify(_serialize_label(label))


@bp.delete("/<label_id>")
@login_required
async def delete_label(label_id: str):
    async with session_scope() as db:
        label = await _get_owned_label(db, label_id)
        if label is None:
            return not_found()
        await db.delete(label)  # note_labels rows cascade
        await db.commit()
        return jsonify({"ok": True})


@bp.post("/<label_id>/merge")
@login_required
async def merge_label(label_id: str):
    """Merge `label_id` (source) INTO the label given by body {"into": <id>}: move
    every note tagged with the source onto the target, then delete the source. Both
    must be owned by the caller. Note-body `#tags` are NOT rewritten, so a note whose
    body still literally contains the source #tag will re-mint that label on its next
    edit — retire a tag by editing it out of the text (a known, documented nuance)."""
    data = await request.get_json(silent=True) or {}
    into = data.get("into")
    async with session_scope() as db:
        source = await _get_owned_label(db, label_id)
        target = await _get_owned_label(db, str(into)) if into is not None else None
        if source is None or target is None:
            return not_found()
        if source.id == target.id:
            return json_error("cannot merge a tag into itself", 400)
        await _merge_into(db, source, target)
        count = await _label_note_count(db, target.id)
        await db.commit()
        return jsonify(_serialize_label(target, count))