class Element:
    pass

class ElementSupply:
    pass

class TreeDisplay:
    pass

# TreeDisplay plan(s):
#
# [ ] 1. Render a basic tree thing from an ElementSupply
# [ ]   1.1. Take/own a curses window
# [ ]   1.2. Keep track of the text internally
# [ ]   1.3. Retrieve elements from an ElementSupply
# [ ]   1.4. Render elements to text depending on width of curses window
# [ ]   1.5. Do indentation
# [ ]   1.6. Use "..." where a thing can't be rendered
# [ ] 2. Scroll and anchor to messages
# [ ]   2.1. Listen to key presses
# [ ]   2.2. Scroll up/down single lines
# [ ]   2.3. Render starting from the anchor
# [ ]   2.4. Some sort of culling, but preserve CONSISTENCY!
# [ ] 3. Focus on single message
# [ ]   3.1. Keep track of focused message
# [ ]   3.2. Move focused message
# [ ]   3.3. Keep message visible on screen
# [ ]   3.4. Set anchor to focus when focus is visible
# [ ]   3.5. Find anchor solution for when focus is offscreen
# [ ] 4. Collapse element threads
# [ ]   4.1. Collapse thread at any element
# [ ]   4.2. Auto-collapse threads when they can't be displayed
# [ ]   4.3. Focus collapsed messages
# [ ]   4.4. Move focus when a hidden message would have focus
# [ ] 5. Interaction with elements
# [ ]   5.1. Forward key presses
# [ ]   5.2. Mouse clicks + message attributes
# [ ]   5.3. Element visibility
# [ ]   5.4. Request more elements when the top of the element supply is hit
# [ ]   5.5. ... and various other things

# STRUCTURE
#
# No async!
#
# The TreeView "owns" and completely fills one curses window.
#
# When rendering things, the TreeDisplay takes elements from the ElementSupply
# as needed. This should be a fast operation.
#
# When receiving key presses, the ones that are not interpreted by the TreeView
# are passed onto the currently focused element (if any).
#
# When receiving mouse clicks, the clicked-on element is focused and then the
# click and attributes of the clicked character are passed onto the focused
# element.
#
# (TODO: Notify focused elements? Make "viewed/new" state for elements
# possible?)
#
#
#
# DESIGN PRINCIPLES
#
# Layout: See below
#
# Color support: Definitely.
# No-color-mode: Not planned.
# => Colors required.

# The tree display can display a tree-like structure of elements.
#
# Each element consists of:
# 1. a way to display the element
# 2. a way to forward key presses to the element
# 3. element-specific attributes (Attributes), including:
#   3.1 "id", the element's hashable id
#   3.2 optionally "parent_id", the element's parent's hashable id
#
# (TODO: A way to notify the element that it is visible?)
#
# (TODO: Jump to unread messages, mark messages as read, up/down arrows like
# instant, message jump tags?)
#
# (TODO: Curses + threading/interaction etc.?)
#
#
#
# LAYOUT
#
# A tree display's basic structure is something like this:
#
# <element>
# | <element>
# | | <element>
# | | <element>
# | <element>
# | <element>
# | | <element>
# | | | <element>
# | <element>
# <element>
# | <element>
#
# It has an indentation string ("| " in the above example) that is prepended to
# each line according to its indentation. (TODO: Possibly add different types
# of indentation strings?)
#
# In general, "..." is inserted any time a message or other placeholder can't
# be displayed. (TODO: If "..." can't be displayed, it is shortened until it
# can be displayed?)
#
# Elements can be collapsed. Collapsed elements are displayed as "+ (<n>)"
# where <n> is the number of elements in the hidden subtree.
#
# If an element is so far right that it can't be displayed, the tree display
# first tries to collapse the tree. If the collapsed message can't be displayed
# either, it uses "..." as mentioned above.
#
# <element>
# | <element>
# | | <element>
# | | <element>
# | <element>
# | + (3)
# | <element>
# <element>
# | <element>
# | | <element>
# | | | <element>
# | | | | ...
#
#
#
# NAVIGATION
#
# For navigation, the following movements/keys are used (all other key presses
# are forwarded to the currently selected element, if there is one):
#
# LEFT (left arrow, h): move to the selected element's parent
#
# RIGHT (right arrow, l): move to the selected element's first child
#
# UP (up arrow, k): move to the element visually below the selected element
#
# DOWN (down arrow, j): move to the element visually above the selected element
#
# Mod + LEFT: move to the selected element's previous sibling, if one exists
#
# Mod + RIGHT: move to the selected element's next sibling, if one exists
#
# Mod + UP: scroll up by scroll step
#
# Mod + DOWN: scroll down by scroll step
#
#
# CURSES
#
# Main thread:
# - async
# - yaboli
# - curses: non-blocking input
# - curses: update visuals
# - run editor in async variant of subprocess or separate thread
#
#
#
# STRUCTURE
#
# ???