from flask import Blueprint, jsonify, request

from crudkit.api._cursor import encode_cursor, decode_cursor
from crudkit.core.service import _is_truthy

def generate_crud_blueprint(model, service):
    bp = Blueprint(model.__name__.lower(), __name__)

    @bp.get('/')
    def list_items():
        args = request.args.to_dict(flat=True)

        # legacy detection
        legacy_offset = "offset" in args or "page" in args

        # sane limit default
        try:
            limit = int(args.get("limit", 50))
        except Exception:
            limit = 50
        args["limit"] = limit

        if legacy_offset:
            # Old behavior: honor limit/offset, same CRUDSpec goodies
            items = service.list(args)
            return jsonify([obj.as_dict() for obj in items])

        # New behavior: keyset seek with cursors
        key, backward = decode_cursor(args.get("cursor"))

        window = service.seek_window(
            args,
            key=key,
            backward=backward,
            include_total=_is_truthy(args.get("include_total", "1")),
        )

        desc_flags = list(window.order.desc)
        body = {
            "items": [obj.as_dict() for obj in window.items],
            "limit": window.limit,
            "next_cursor": encode_cursor(window.last_key, desc_flags, backward=False),
            "prev_cursor": encode_cursor(window.first_key, desc_flags, backward=True),
            "total": window.total,
        }

        resp = jsonify(body)
        # Optional Link header
        links = []
        if body["next_cursor"]:
            links.append(f'<{request.base_url}?cursor={body["next_cursor"]}&limit={window.limit}>; rel="next"')
        if body["prev_cursor"]:
            links.append(f'<{request.base_url}?cursor={body["prev_cursor"]}&limit={window.limit}>; rel="prev"')
        if links:
            resp.headers["Link"] = ", ".join(links)
        return resp

    @bp.get('/<int:id>')
    def get_item(id):
        item = service.get(id, request.args)
        try:
            return jsonify(item.as_dict())
        except Exception as e:
            return jsonify({"status": "error", "error": str(e)})

    @bp.post('/')
    def create_item():
        obj = service.create(request.json)
        try:
            return jsonify(obj.as_dict())
        except Exception as e:
            return jsonify({"status": "error", "error": str(e)})

    @bp.patch('/<int:id>')
    def update_item(id):
        obj = service.update(id, request.json)
        try:
            return jsonify(obj.as_dict())
        except Exception as e:
            return jsonify({"status": "error", "error": str(e)})

    @bp.delete('/<int:id>')
    def delete_item(id):
        service.delete(id)
        try:
            return jsonify({"status": "success"}), 204
        except Exception as e:
            return jsonify({"status": "error", "error": str(e)})

    return bp