from __future__ import annotations

import io

from reportlab.lib import colors
from reportlab.lib.pagesizes import A4, landscape
from reportlab.lib.styles import getSampleStyleSheet
from reportlab.lib.units import cm
from reportlab.platypus import (
    Paragraph,
    SimpleDocTemplate,
    Spacer,
    Table,
    TableStyle,
)

_PAGE_W, _ = landscape(A4)
_MARGIN = 1.5 * cm
_HEADER_BG = colors.HexColor("#1a56db")
_ROW_BG = colors.HexColor("#eef2ff")


def _pdf_table(rows: list[dict]) -> Table:
    if not rows:
        table_data: list[list] = [["No data available"]]
        n_cols = 1
    else:
        headers = list(rows[0].keys())
        n_cols = len(headers)
        table_data = [headers] + [
            [str(row.get(h, "")) for h in headers] for row in rows
        ]

    col_w = (_PAGE_W - 2 * _MARGIN) / n_cols
    t = Table(table_data, colWidths=[col_w] * n_cols, repeatRows=1)

    style: list = [
        ("BACKGROUND",    (0, 0), (-1, 0),  _HEADER_BG),
        ("TEXTCOLOR",     (0, 0), (-1, 0),  colors.white),
        ("FONTNAME",      (0, 0), (-1, 0),  "Helvetica-Bold"),
        ("FONTSIZE",      (0, 0), (-1, 0),  8),
        ("FONTNAME",      (0, 1), (-1, -1), "Helvetica"),
        ("FONTSIZE",      (0, 1), (-1, -1), 7),
        ("ALIGN",         (0, 0), (-1, -1), "LEFT"),
        ("VALIGN",        (0, 0), (-1, -1), "MIDDLE"),
        ("GRID",          (0, 0), (-1, -1), 0.25, colors.HexColor("#d1d5db")),
        ("TOPPADDING",    (0, 0), (-1, -1), 3),
        ("BOTTOMPADDING", (0, 0), (-1, -1), 3),
        ("LEFTPADDING",   (0, 0), (-1, -1), 5),
        ("RIGHTPADDING",  (0, 0), (-1, -1), 5),
    ]
    for i in range(1, len(table_data)):
        bg = _ROW_BG if i % 2 == 1 else colors.white
        style.append(("BACKGROUND", (0, i), (-1, i), bg))

    t.setStyle(TableStyle(style))
    return t


def to_pdf_bytes(rows: list[dict], title: str, subtitle: str = "") -> bytes:
    """Serialise *rows* to a single-sheet PDF and return the raw bytes."""
    buf = io.BytesIO()
    styles = getSampleStyleSheet()
    story = []

    story.append(Paragraph(title, styles["Title"]))
    if subtitle:
        story.append(Spacer(1, 0.2 * cm))
        story.append(Paragraph(subtitle, styles["Normal"]))
    story.append(Spacer(1, 0.5 * cm))
    story.append(_pdf_table(rows))

    doc = SimpleDocTemplate(
        buf,
        pagesize=landscape(A4),
        leftMargin=_MARGIN,
        rightMargin=_MARGIN,
        topMargin=_MARGIN,
        bottomMargin=_MARGIN,
    )
    doc.build(story)
    return buf.getvalue()