pyWebLayout/tests/concrete/test_alignment_spacing.py

"""
Regression tests for word spacing under each alignment (spec S13).

Only justified text stretches word gaps to fill the measure. Left, centre and
right aligned text use a natural, constant word space and leave a ragged edge;
previously they distributed the residual space across the gaps, which produced
text that looked justified but did not reach the margin, with a right edge that
wobbled by several pixels from line to line.

The final line of a justified paragraph is also not stretched.
"""

import pytest

from pyWebLayout.abstract.block import Paragraph
from pyWebLayout.abstract.inline import Word
from pyWebLayout.concrete.page import Page
from pyWebLayout.concrete.text import (
    CenterRightAlignmentHandler,
    JustifyAlignmentHandler,
    LeftAlignmentHandler,
    Line,
)
from pyWebLayout.layout.document_layouter import paragraph_layouter
from pyWebLayout.style import Alignment, Font
from pyWebLayout.style.page_style import PageStyle


PAGE = (500, 400)
PADDING = (20, 20, 20, 20)


@pytest.fixture
def font():
    return Font(font_size=14)


def lay_out(font, alignment, text, size=PAGE):
    page = Page(size=size, style=PageStyle(border_width=0, padding=PADDING))
    paragraph = Paragraph(font)
    for word in text.split():
        paragraph.add_word(Word(word, font))
    paragraph_layouter(paragraph, page, alignment_override=alignment)
    return page


def rendered_lines(page):
    lines = [c for c in page.children if isinstance(c, Line) and c._text_objects]
    for line in lines:
        line.render()
    return lines


def gaps_of(line):
    """Observed pixel gaps between consecutive words on a rendered line."""
    tos = line._text_objects
    return [int(tos[i + 1]._origin[0]) - (int(tos[i]._origin[0]) + int(tos[i].width))
            for i in range(len(tos) - 1)]


BODY = ("Paragraph text that is automatically laid out when this paragraph does "
        "not fit on the current page the layouter will create a new page for it "
        "which differs from using an explicit page break marker in the source ") * 2


class TestLeftAlignmentUsesConstantSpacing:

    def test_gaps_are_uniform_within_a_line(self, font):
        page = lay_out(font, Alignment.LEFT, BODY)
        for line in rendered_lines(page):
            gaps = gaps_of(line)
            if len(gaps) > 1:
                assert max(gaps) - min(gaps) <= 1, \
                    f"left-aligned gaps should be constant, got {gaps}"

    def test_gaps_are_uniform_across_lines(self, font):
        """The regression: each line got its own stretch factor."""
        page = lay_out(font, Alignment.LEFT, BODY)
        all_gaps = [g for line in rendered_lines(page) for g in gaps_of(line)]
        assert max(all_gaps) - min(all_gaps) <= 1, \
            f"spacing must not vary line to line, got {sorted(set(all_gaps))}"

    def test_lines_do_not_reach_the_right_margin(self, font):
        """Left-aligned text is ragged; a flush right edge means it was stretched."""
        page = lay_out(font, Alignment.LEFT, BODY)
        right = page.content_rect[0] + page.content_rect[2]
        ends = [max(int(t._origin[0]) + int(t.width) for t in line._text_objects)
                for line in rendered_lines(page)]
        assert not all(right - e <= 1 for e in ends), \
            "every line reached the margin exactly - text was justified, not left aligned"

    def test_handler_returns_natural_spacing(self, font):
        handler = LeftAlignmentHandler()
        from pyWebLayout.concrete.text import Text
        from PIL import Image, ImageDraw
        draw = ImageDraw.Draw(Image.new("RGB", (10, 10)))
        texts = [Text(w, font, draw) for w in ["Hello", "World"]]

        spacing, position, overflow = handler.calculate_spacing_and_position(
            texts, 400, 3, 7, natural_spacing=5)

        assert spacing == 5, "natural spacing should be used verbatim when it fits"
        assert position == 0
        assert not overflow

    def test_handler_clamps_natural_spacing_to_bounds(self, font):
        handler = LeftAlignmentHandler()
        from pyWebLayout.concrete.text import Text
        from PIL import Image, ImageDraw
        draw = ImageDraw.Draw(Image.new("RGB", (10, 10)))
        texts = [Text(w, font, draw) for w in ["Hello", "World"]]

        assert handler.calculate_spacing_and_position(
            texts, 400, 3, 7, natural_spacing=99)[0] == 7
        assert handler.calculate_spacing_and_position(
            texts, 400, 3, 7, natural_spacing=1)[0] == 3


class TestJustifyStillFills:

    def test_body_lines_reach_the_margin(self, font):
        page = lay_out(font, Alignment.JUSTIFY, BODY)
        lines = rendered_lines(page)
        right = page.content_rect[0] + page.content_rect[2]

        for line in lines:
            if line.is_paragraph_end:
                continue
            end = max(int(t._origin[0]) + int(t.width) for t in line._text_objects)
            assert right - end <= 2, f"justified line fell {right - end}px short"

    def test_last_line_is_not_stretched(self, font):
        page = lay_out(font, Alignment.JUSTIFY,
                       BODY + " and then a deliberately short tail.")
        lines = rendered_lines(page)
        last = [line for line in lines if line.is_paragraph_end]
        assert last, "the final line of a completed paragraph must be marked"

        gaps = gaps_of(last[-1])
        if gaps:
            assert max(gaps) <= 8, \
                f"final line was justified across the measure, gaps={gaps}"

    def test_continued_paragraph_keeps_justification(self, font):
        """A paragraph split across pages: its lines are not paragraph ends."""
        page = lay_out(font, Alignment.JUSTIFY, BODY * 6, size=(500, 200))
        lines = rendered_lines(page)
        assert lines, "the page should hold some lines"
        assert not any(line.is_paragraph_end for line in lines), \
            "an unfinished paragraph has no final line on this page"


class TestCentreAndRight:

    def test_centre_uses_constant_spacing_and_is_centred(self, font):
        page = lay_out(font, Alignment.CENTER, BODY)
        right = page.content_rect[0] + page.content_rect[2]
        left = page.content_rect[0]

        for line in rendered_lines(page):
            tos = line._text_objects
            # Float extents: integer truncation of each end would itself skew the
            # comparison by a pixel.
            start = float(tos[0]._origin[0])
            end = float(tos[-1]._origin[0]) + tos[-1].width
            # Equal margins either side, within rounding of the half-space.
            assert abs((start - left) - (right - end)) <= 2, \
                f"line not centred: left margin {start - left}, right {right - end}"

    def test_right_aligned_lines_end_at_the_margin(self, font):
        page = lay_out(font, Alignment.RIGHT, BODY)
        right = page.content_rect[0] + page.content_rect[2]

        for line in rendered_lines(page):
            end = max(int(t._origin[0]) + int(t.width) for t in line._text_objects)
            assert right - end <= 2, f"right-aligned line fell {right - end}px short"