import logging
from io import BytesIO
from pathlib import Path
from typing import Final, Optional, Union, cast

from bs4 import BeautifulSoup, NavigableString, PageElement, Tag
from bs4.element import PreformattedString
from docling_core.types.doc import (
    DocItem,
    DocItemLabel,
    DoclingDocument,
    DocumentOrigin,
    GroupItem,
    GroupLabel,
    TableCell,
    TableData,
)
from docling_core.types.doc.document import ContentLayer
from typing_extensions import override

from docling.backend.abstract_backend import DeclarativeDocumentBackend
from docling.datamodel.base_models import InputFormat
from docling.datamodel.document import InputDocument

_log = logging.getLogger(__name__)

# tags that generate NodeItem elements
TAGS_FOR_NODE_ITEMS: Final = [
    "h1",
    "h2",
    "h3",
    "h4",
    "h5",
    "h6",
    "p",
    "pre",
    "ul",
    "ol",
    "li",
    "table",
    "figure",
    "img",
]


class HTMLDocumentBackend(DeclarativeDocumentBackend):
    @override
    def __init__(self, in_doc: "InputDocument", path_or_stream: Union[BytesIO, Path]):
        super().__init__(in_doc, path_or_stream)
        self.soup: Optional[Tag] = None
        # HTML file:
        self.path_or_stream = path_or_stream
        # Initialise the parents for the hierarchy
        self.max_levels = 10
        self.level = 0
        self.parents: dict[int, Optional[Union[DocItem, GroupItem]]] = {}
        for i in range(0, self.max_levels):
            self.parents[i] = None

        try:
            if isinstance(self.path_or_stream, BytesIO):
                text_stream = self.path_or_stream.getvalue()
                self.soup = BeautifulSoup(text_stream, "html.parser")
            if isinstance(self.path_or_stream, Path):
                with open(self.path_or_stream, "rb") as f:
                    html_content = f.read()
                    self.soup = BeautifulSoup(html_content, "html.parser")
        except Exception as e:
            raise RuntimeError(
                "Could not initialize HTML backend for file with "
                f"hash {self.document_hash}."
            ) from e

    @override
    def is_valid(self) -> bool:
        return self.soup is not None

    @classmethod
    @override
    def supports_pagination(cls) -> bool:
        return False

    @override
    def unload(self):
        if isinstance(self.path_or_stream, BytesIO):
            self.path_or_stream.close()

        self.path_or_stream = None

    @classmethod
    @override
    def supported_formats(cls) -> set[InputFormat]:
        return {InputFormat.HTML}

    @override
    def convert(self) -> DoclingDocument:
        # access self.path_or_stream to load stuff
        origin = DocumentOrigin(
            filename=self.file.name or "file",
            mimetype="text/html",
            binary_hash=self.document_hash,
        )

        doc = DoclingDocument(name=self.file.stem or "file", origin=origin)
        _log.debug("Trying to convert HTML...")

        if self.is_valid():
            assert self.soup is not None
            content = self.soup.body or self.soup
            # Replace <br> tags with newline characters
            # TODO: remove style to avoid losing text from tags like i, b, span, ...
            for br in content("br"):
                br.replace_with(NavigableString("\n"))

            headers = content.find(["h1", "h2", "h3", "h4", "h5", "h6"])
            self.content_layer = (
                ContentLayer.BODY if headers is None else ContentLayer.FURNITURE
            )
            self.walk(content, doc)
        else:
            raise RuntimeError(
                f"Cannot convert doc with {self.document_hash} because the backend "
                "failed to init."
            )
        return doc

    def walk(self, tag: Tag, doc: DoclingDocument) -> None:

        # Iterate over elements in the body of the document
        text: str = ""
        for element in tag.children:
            if isinstance(element, Tag):
                try:
                    self.analyze_tag(cast(Tag, element), doc)
                except Exception as exc_child:
                    _log.error(
                        f"Error processing child from tag {tag.name}: {repr(exc_child)}"
                    )
                    raise exc_child
            elif isinstance(element, NavigableString) and not isinstance(
                element, PreformattedString
            ):
                # Floating text outside paragraphs or analyzed tags
                text += element
                siblings: list[Tag] = [
                    item for item in element.next_siblings if isinstance(item, Tag)
                ]
                if element.next_sibling is None or any(
                    [item.name in TAGS_FOR_NODE_ITEMS for item in siblings]
                ):
                    text = text.strip()
                    if text and tag.name in ["div"]:
                        doc.add_text(
                            parent=self.parents[self.level],
                            label=DocItemLabel.TEXT,
                            text=text,
                            content_layer=self.content_layer,
                        )
                    text = ""

        return

    def analyze_tag(self, tag: Tag, doc: DoclingDocument) -> None:
        if tag.name in ["h1", "h2", "h3", "h4", "h5", "h6"]:
            self.handle_header(tag, doc)
        elif tag.name in ["p"]:
            self.handle_paragraph(tag, doc)
        elif tag.name in ["pre"]:
            self.handle_code(tag, doc)
        elif tag.name in ["ul", "ol"]:
            self.handle_list(tag, doc)
        elif tag.name in ["li"]:
            self.handle_list_item(tag, doc)
        elif tag.name == "table":
            self.handle_table(tag, doc)
        elif tag.name == "figure":
            self.handle_figure(tag, doc)
        elif tag.name == "img":
            self.handle_image(tag, doc)
        else:
            self.walk(tag, doc)

    def get_text(self, item: PageElement) -> str:
        """Get the text content of a tag."""
        parts: list[str] = self.extract_text_recursively(item)

        return "".join(parts) + " "

    # Function to recursively extract text from all child nodes
    def extract_text_recursively(self, item: PageElement) -> list[str]:
        result: list[str] = []

        if isinstance(item, NavigableString):
            return [item]

        tag = cast(Tag, item)
        if tag.name not in ["ul", "ol"]:
            for child in tag:
                # Recursively get the child's text content
                result.extend(self.extract_text_recursively(child))

        return ["".join(result) + " "]

    def handle_header(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles header tags (h1, h2, etc.)."""
        hlevel = int(element.name.replace("h", ""))
        text = element.text.strip()

        if hlevel == 1:
            self.content_layer = ContentLayer.BODY

            for key in self.parents.keys():
                self.parents[key] = None

            self.level = 1
            self.parents[self.level] = doc.add_text(
                parent=self.parents[0],
                label=DocItemLabel.TITLE,
                text=text,
                content_layer=self.content_layer,
            )
        else:
            if hlevel > self.level:

                # add invisible group
                for i in range(self.level + 1, hlevel):
                    self.parents[i] = doc.add_group(
                        name=f"header-{i}",
                        label=GroupLabel.SECTION,
                        parent=self.parents[i - 1],
                        content_layer=self.content_layer,
                    )
                self.level = hlevel

            elif hlevel < self.level:

                # remove the tail
                for key in self.parents.keys():
                    if key > hlevel:
                        self.parents[key] = None
                self.level = hlevel

            self.parents[hlevel] = doc.add_heading(
                parent=self.parents[hlevel - 1],
                text=text,
                level=hlevel - 1,
                content_layer=self.content_layer,
            )

    def handle_code(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles monospace code snippets (pre)."""
        if element.text is None:
            return
        text = element.text.strip()
        if text:
            doc.add_code(
                parent=self.parents[self.level],
                text=text,
                content_layer=self.content_layer,
            )

    def handle_paragraph(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles paragraph tags (p)."""
        if element.text is None:
            return
        text = element.text.strip()
        if text:
            doc.add_text(
                parent=self.parents[self.level],
                label=DocItemLabel.TEXT,
                text=text,
                content_layer=self.content_layer,
            )

    def handle_list(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles list tags (ul, ol) and their list items."""

        if element.name == "ul":
            # create a list group
            self.parents[self.level + 1] = doc.add_group(
                parent=self.parents[self.level],
                name="list",
                label=GroupLabel.LIST,
                content_layer=self.content_layer,
            )
        elif element.name == "ol":
            start_attr = element.get("start")
            start: int = (
                int(start_attr)
                if isinstance(start_attr, str) and start_attr.isnumeric()
                else 1
            )
            # create a list group
            self.parents[self.level + 1] = doc.add_group(
                parent=self.parents[self.level],
                name="ordered list" + (f" start {start}" if start != 1 else ""),
                label=GroupLabel.ORDERED_LIST,
                content_layer=self.content_layer,
            )
        self.level += 1

        self.walk(element, doc)

        self.parents[self.level + 1] = None
        self.level -= 1

    def handle_list_item(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles list item tags (li)."""
        nested_list = element.find(["ul", "ol"])

        parent = self.parents[self.level]
        if parent is None:
            _log.debug(f"list-item has no parent in DoclingDocument: {element}")
            return
        parent_label: str = parent.label
        index_in_list = len(parent.children) + 1
        if (
            parent_label == GroupLabel.ORDERED_LIST
            and isinstance(parent, GroupItem)
            and parent.name
        ):
            start_in_list: str = parent.name.split(" ")[-1]
            start: int = int(start_in_list) if start_in_list.isnumeric() else 1
            index_in_list += start - 1

        if nested_list:
            # Text in list item can be hidden within hierarchy, hence
            # we need to extract it recursively
            text: str = self.get_text(element)
            # Flatten text, remove break lines:
            text = text.replace("\n", "").replace("\r", "")
            text = " ".join(text.split()).strip()

            marker = ""
            enumerated = False
            if parent_label == GroupLabel.ORDERED_LIST:
                marker = str(index_in_list)
                enumerated = True

            if len(text) > 0:
                # create a list-item
                self.parents[self.level + 1] = doc.add_list_item(
                    text=text,
                    enumerated=enumerated,
                    marker=marker,
                    parent=parent,
                    content_layer=self.content_layer,
                )
                self.level += 1
                self.walk(element, doc)
                self.parents[self.level + 1] = None
                self.level -= 1
            else:
                self.walk(element, doc)

        elif element.text.strip():
            text = element.text.strip()

            marker = ""
            enumerated = False
            if parent_label == GroupLabel.ORDERED_LIST:
                marker = f"{str(index_in_list)}."
                enumerated = True
            doc.add_list_item(
                text=text,
                enumerated=enumerated,
                marker=marker,
                parent=parent,
                content_layer=self.content_layer,
            )
        else:
            _log.debug(f"list-item has no text: {element}")

    @staticmethod
    def parse_table_data(element: Tag) -> Optional[TableData]:
        nested_tables = element.find("table")
        if nested_tables is not None:
            _log.debug("Skipping nested table.")
            return None

        # Count the number of rows (number of <tr> elements)
        num_rows = len(element("tr"))

        # Find the number of columns (taking into account colspan)
        num_cols = 0
        for row in element("tr"):
            col_count = 0
            if not isinstance(row, Tag):
                continue
            for cell in row(["td", "th"]):
                if not isinstance(row, Tag):
                    continue
                val = cast(Tag, cell).get("colspan", "1")
                colspan = int(val) if (isinstance(val, str) and val.isnumeric()) else 1
                col_count += colspan
            num_cols = max(num_cols, col_count)

        grid: list = [[None for _ in range(num_cols)] for _ in range(num_rows)]

        data = TableData(num_rows=num_rows, num_cols=num_cols, table_cells=[])

        # Iterate over the rows in the table
        for row_idx, row in enumerate(element("tr")):
            if not isinstance(row, Tag):
                continue

            # For each row, find all the column cells (both <td> and <th>)
            cells = row(["td", "th"])

            # Check if each cell in the row is a header -> means it is a column header
            col_header = True
            for html_cell in cells:
                if isinstance(html_cell, Tag) and html_cell.name == "td":
                    col_header = False

            # Extract the text content of each cell
            col_idx = 0
            for html_cell in cells:
                if not isinstance(html_cell, Tag):
                    continue

                # extract inline formulas
                for formula in html_cell("inline-formula"):
                    math_parts = formula.text.split("$$")
                    if len(math_parts) == 3:
                        math_formula = f"$${math_parts[1]}$$"
                        formula.replace_with(NavigableString(math_formula))

                # TODO: extract content correctly from table-cells with lists
                text = html_cell.text

                # label = html_cell.name
                col_val = html_cell.get("colspan", "1")
                col_span = (
                    int(col_val)
                    if isinstance(col_val, str) and col_val.isnumeric()
                    else 1
                )
                row_val = html_cell.get("rowspan", "1")
                row_span = (
                    int(row_val)
                    if isinstance(row_val, str) and row_val.isnumeric()
                    else 1
                )

                while grid[row_idx][col_idx] is not None:
                    col_idx += 1
                for r in range(row_span):
                    for c in range(col_span):
                        grid[row_idx + r][col_idx + c] = text

                table_cell = TableCell(
                    text=text,
                    row_span=row_span,
                    col_span=col_span,
                    start_row_offset_idx=row_idx,
                    end_row_offset_idx=row_idx + row_span,
                    start_col_offset_idx=col_idx,
                    end_col_offset_idx=col_idx + col_span,
                    column_header=col_header,
                    row_header=((not col_header) and html_cell.name == "th"),
                )
                data.table_cells.append(table_cell)

        return data

    def handle_table(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles table tags."""

        table_data = HTMLDocumentBackend.parse_table_data(element)

        if table_data is not None:
            doc.add_table(
                data=table_data,
                parent=self.parents[self.level],
                content_layer=self.content_layer,
            )

    def get_list_text(self, list_element: Tag, level: int = 0) -> list[str]:
        """Recursively extract text from <ul> or <ol> with proper indentation."""
        result = []
        bullet_char = "*"  # Default bullet character for unordered lists

        if list_element.name == "ol":  # For ordered lists, use numbers
            for i, li in enumerate(list_element("li", recursive=False), 1):
                if not isinstance(li, Tag):
                    continue
                # Add numbering for ordered lists
                result.append(f"{'    ' * level}{i}. {li.get_text(strip=True)}")
                # Handle nested lists
                nested_list = li.find(["ul", "ol"])
                if isinstance(nested_list, Tag):
                    result.extend(self.get_list_text(nested_list, level + 1))
        elif list_element.name == "ul":  # For unordered lists, use bullet points
            for li in list_element("li", recursive=False):
                if not isinstance(li, Tag):
                    continue
                # Add bullet points for unordered lists
                result.append(
                    f"{'    ' * level}{bullet_char} {li.get_text(strip=True)}"
                )
                # Handle nested lists
                nested_list = li.find(["ul", "ol"])
                if isinstance(nested_list, Tag):
                    result.extend(self.get_list_text(nested_list, level + 1))

        return result

    def handle_figure(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles image tags (img)."""

        # Extract the image URI from the <img> tag
        # image_uri = root.xpath('//figure//img/@src')[0]

        contains_captions = element.find(["figcaption"])
        if not isinstance(contains_captions, Tag):
            doc.add_picture(
                parent=self.parents[self.level],
                caption=None,
                content_layer=self.content_layer,
            )
        else:
            texts = []
            for item in contains_captions:
                texts.append(item.text)

            fig_caption = doc.add_text(
                label=DocItemLabel.CAPTION,
                text=("".join(texts)).strip(),
                content_layer=self.content_layer,
            )
            doc.add_picture(
                parent=self.parents[self.level],
                caption=fig_caption,
                content_layer=self.content_layer,
            )

    def handle_image(self, element: Tag, doc: DoclingDocument) -> None:
        """Handles image tags (img)."""
        _log.debug(f"ignoring <img> tags at the moment: {element}")

        doc.add_picture(
            parent=self.parents[self.level],
            caption=None,
            content_layer=self.content_layer,
        )