SaraView/Client/LiveMarkdown.py

"""Live Markdown editing, like Obsidian's live preview: the file is shown
rendered, block by block, and clicking a block swaps it for its Markdown
(a heading shows its #s, a list its -s) to edit in place. Esc, or clicking
another block, puts it back rendered.

A block is what Markdown itself separates: a heading line, a fenced code
block, a horizontal rule, or a run of lines up to a blank line (a paragraph,
list, table or quote). The text between blocks (blank lines) is kept
byte for byte, so editing one block never reformats the rest of the file."""

import re
from dataclasses import dataclass
from typing import Callable, Optional

import flet as ft

import Core
from Core import CodeStyleSheet, MarkdownCodeTheme, MarkdownSheet, Palette

FenceStart = re.compile(r"^ {0,3}(`{3,}|~{3,})")
HeadingLine = re.compile(r"^ {0,3}(#{1,6})(\s|$)")
RuleLine = re.compile(r"^ {0,3}([-*_])( *\1){2,} *$")
IndentedLine = re.compile(r"^( {2,}|\t)\S")


@dataclass
class Block:
    Start: int  # offsets into the document; Text = Document[Start:End]
    End: int
    Kind: str  # "Heading", "Code", "Rule" or "Text"
    StartLine: int
    Level: int = 0  # heading level


def SplitBlocks(Document: str) -> list[Block]:
    Lines = Document.split("\n")
    Offsets: list[int] = []
    Position = 0
    for Line in Lines:
        Offsets.append(Position)
        Position += len(Line) + 1

    def LineEnd(Index: int) -> int:
        return Offsets[Index] + len(Lines[Index])

    Blocks: list[Block] = []
    Current: Optional[int] = None  # first line of the open Text block
    LastLine = -1  # last non-blank line of the open Text block
    Fence: Optional[tuple[str, int]] = None  # (character, length) of an open code fence
    FenceFrom = 0

    def CloseCurrent() -> None:
        nonlocal Current
        if Current is not None:
            Blocks.append(Block(Offsets[Current], LineEnd(LastLine), "Text", Current))
            Current = None

    for Index, Line in enumerate(Lines):
        if Fence is not None:
            Match = FenceStart.match(Line)
            if Match and Match.group(1)[0] == Fence[0] and len(Match.group(1)) >= Fence[1] and not Line.strip()[len(Match.group(1)):].strip():
                Blocks.append(Block(Offsets[FenceFrom], LineEnd(Index), "Code", FenceFrom))
                Fence = None
            continue
        if not Line.strip():
            CloseCurrent()
            continue
        Match = FenceStart.match(Line)
        if Match:
            CloseCurrent()
            Fence = (Match.group(1)[0], len(Match.group(1)))
            FenceFrom = Index
            continue
        Match = HeadingLine.match(Line)
        if Match:
            CloseCurrent()
            Blocks.append(Block(Offsets[Index], LineEnd(Index), "Heading", Index, len(Match.group(1))))
            continue
        Match = RuleLine.match(Line)
        # "---" right under text is a setext heading's underline, not a rule.
        if Match and (Current is None or Match.group(1) != "-"):
            CloseCurrent()
            Blocks.append(Block(Offsets[Index], LineEnd(Index), "Rule", Index))
            continue
        if Current is None:
            Previous = Blocks[-1] if Blocks else None
            # An indented line after blank lines continues a loose list
            # (or a list item's second paragraph) rather than starting a code block.
            if Previous is not None and Previous.Kind == "Text" and IndentedLine.match(Line):
                Blocks.pop()
                Current = Previous.StartLine
            else:
                Current = Index
        LastLine = Index
    CloseCurrent()
    if Fence is not None:  # never closed: runs to the last non-blank line
        Last = max((I for I in range(FenceFrom, len(Lines)) if Lines[I].strip()), default=FenceFrom)
        Blocks.append(Block(Offsets[FenceFrom], LineEnd(Last), "Code", FenceFrom))
    return Blocks


class LiveMarkdown(ft.Column):
    def __init__(self, Document: str, FontSize: int, OnChange: Callable[[], None],
                 OnFocusChange: Callable[[bool], None], OnTapLink: Callable):
        super().__init__(scroll=ft.ScrollMode.AUTO, expand=True, spacing=0,
                         horizontal_alignment=ft.CrossAxisAlignment.STRETCH)
        self.Document = Document
        self.FontSize = FontSize
        self.OnChange = OnChange
        self.OnFocusChange = OnFocusChange
        self.OnTapLink = OnTapLink
        self.Blocks: list[Block] = []
        self.BlockControls: list[ft.Control] = []
        # Rendered blocks by their text, reused when the layout is rebuilt so
        # only the edited part is rendered again.
        self.RenderCache: dict[str, list[ft.Control]] = {}
        self.EditingIndex: Optional[int] = None  # len(Blocks) is the new block at the end
        self.Field: Optional[ft.TextField] = None
        self._Layout(Update=False)

    # --- Text ------------------------------------------------------------

    @property
    def Text(self) -> str:
        """The whole document, including what's being typed in the open block."""
        if self.EditingIndex is None or self.Field is None:
            return self.Document
        return self._Spliced(self.Field.value or "")

    def SetText(self, Document: str, Update: bool = True) -> None:
        self.EditingIndex = None
        self.Field = None
        self.Document = Document
        self._Layout(Update)

    def _Spliced(self, NewText: str) -> str:
        """The document with the open block replaced by NewText."""
        Index = self.EditingIndex
        Document = self.Document
        if Index is None:
            return Document
        if Index == len(self.Blocks):  # a new block after the last one
            if not NewText.strip():
                return Document
            Base = Document
            if Base and not Base.endswith("\n"):
                Base += "\n"
            if Base and not Base.endswith("\n\n"):
                Base += "\n"
            return Base + NewText.rstrip("\n") + "\n"
        Current = self.Blocks[Index]
        if NewText.strip():
            return Document[:Current.Start] + NewText + Document[Current.End:]
        # Emptied: take its blank lines with it, so no gap is left behind.
        if Index + 1 < len(self.Blocks):
            return Document[:Current.Start] + Document[self.Blocks[Index + 1].Start:]
        if Index > 0:
            return Document[:self.Blocks[Index - 1].End] + Document[Current.End:]
        return Document[:Current.Start] + Document[Current.End:]

    # --- Editing ---------------------------------------------------------

    @property
    def IsEditing(self) -> bool:
        return self.EditingIndex is not None

    def Commit(self) -> None:
        """Puts the open block back rendered (re-splitting the document, since
        the edit may have made one block into several or merged it with the next)."""
        if self.EditingIndex is None:
            return
        self.Document = self.Text
        self.EditingIndex = None
        self.Field = None
        self.OnFocusChange(False)
        self._Layout()

    def _StartEditing(self, Index: int) -> None:
        self.EditingIndex = Index
        Item = self.Blocks[Index] if Index < len(self.Blocks) else None
        Value = self.Document[Item.Start:Item.End] if Item else ""
        Style = ft.TextStyle(size=self.FontSize, font_family=Core.ActiveFontFamily, color=Palette.Text)
        if Item is not None and Item.Kind == "Heading":
            # The heading stays its size and colour while its #s are showing.
            Style = getattr(MarkdownSheet(self.FontSize), f"h{Item.Level}_text_style")
        self.Field = ft.TextField(
            value=Value,
            multiline=True,
            min_lines=1,
            autofocus=True,
            border=ft.InputBorder.NONE,
            filled=True,
            fill_color=Palette.Mantle,
            content_padding=ft.Padding.symmetric(horizontal=8, vertical=6),
            text_style=Style,
            cursor_color=Palette.Mauve,
            on_change=lambda e: self.OnChange(),
            on_focus=lambda e: self.OnFocusChange(True),
        )
        self.OnFocusChange(True)
        self._Layout()

    def _OnBlockClicked(self, Control: ft.Control) -> None:
        if self.EditingIndex is not None:
            self.Commit()  # Flutter doesn't unfocus a field when something else is clicked
        # Find the block again in the (possibly rebuilt) layout.
        for Index, Controls in enumerate(self.BlockControls):
            if Controls is Control:
                self._StartEditing(Index)
                return

    def _OnEndClicked(self) -> None:
        if self.EditingIndex is not None:
            self.Commit()
        self._StartEditing(len(self.Blocks))

    # --- Rendering -------------------------------------------------------

    def _Render(self, Text: str) -> ft.Control:
        Rendered = ft.Container(
            content=ft.Markdown(
                value=Text,
                extension_set=ft.MarkdownExtensionSet.GITHUB_FLAVORED,
                md_style_sheet=MarkdownSheet(self.FontSize),
                code_theme=MarkdownCodeTheme(),
                code_style_sheet=CodeStyleSheet(),
                on_tap_link=self.OnTapLink,
            ),
            padding=ft.Padding.symmetric(horizontal=8, vertical=6),
            border_radius=4,
        )
        Rendered.on_click = lambda e, C=Rendered: self._OnBlockClicked(C)
        Rendered.on_hover = lambda e, C=Rendered: self._OnHover(C, e)
        return Rendered

    @staticmethod
    def _OnHover(Control: ft.Container, Event) -> None:
        Control.bgcolor = Palette.Mantle if str(Event.data).lower() == "true" else None
        Control.update()

    def _Layout(self, Update: bool = True) -> None:
        self.Blocks = SplitBlocks(self.Document)
        Cache = self.RenderCache
        self.RenderCache = {}
        self.BlockControls = []
        for Index, Item in enumerate(self.Blocks):
            if Index == self.EditingIndex:
                self.BlockControls.append(self.Field)
                continue
            Text = self.Document[Item.Start:Item.End]
            Reused = Cache.get(Text)
            Control = Reused.pop() if Reused else self._Render(Text)
            Control.bgcolor = None
            self.BlockControls.append(Control)
            self.RenderCache.setdefault(Text, []).append(Control)
        Controls = list(self.BlockControls)
        if self.EditingIndex == len(self.Blocks):
            Controls.append(self.Field)
        else:
            Hint = "Click to start writing." if not self.Blocks else "Click here to add more."
            Controls.append(ft.Container(
                content=ft.Text(Hint, color=Palette.Overlay0, italic=True, size=self.FontSize - 2),
                padding=ft.Padding.symmetric(horizontal=8, vertical=12),
                on_click=lambda e: self._OnEndClicked(),
            ))
        self.controls = Controls
        if Update:
            self.update()