from __future__ import annotations
import fitz  # PyMuPDF
from .models import Node, SourceMeta
from .ids import stable_id
from .normalize import normalize_text

def parse_pdf(manifest_path: str, source: SourceMeta) -> Node:
    # Very light heuristic: create sections when font size increases significantly
    import json
    with open(manifest_path) as f:
        m = json.load(f)
    doc = fitz.open(m["artifact_path"])
    pages = doc.page_count
    root = Node(node_id=stable_id(source.sha256 or source.url, "PDF"), path=[], label="ROOT", text="", children=[])
    current = Node(node_id=stable_id(source.sha256 or source.url, "PDF_BODY"), path=["Body"], label="Body", title="Body", text="", children=[], page_span=(1, pages))
    root.children.append(current)

    for i in range(pages):
        page = doc.load_page(i)
        blocks = page.get_text("dict")["blocks"]
        for b in blocks:
            if "lines" not in b: continue
            # compute an average font size in the block
            sizes = []
            texts = []
            for l in b["lines"]:
                for s in l["spans"]:
                    sizes.append(s.get("size", 0))
                    texts.append(s.get("text", ""))
            text = normalize_text(" ".join(texts))
            if not text: continue
            avg = sum(sizes)/len(sizes) if sizes else 0
            # Simple split: treat abnormally large text as a heading
            if avg >= 14 and len(text) <= 140:
                # start a new subsection
                sec_path = ["Body", text]
                node = Node(node_id=stable_id(source.sha256 or source.url, "/".join(sec_path)),
                            path=sec_path, label=text, title=text, text="", page_span=(i+1, i+1))
                current.children.append(node)
            else:
                if current.children:
                    current.children[-1].text += (("\n\n" if current.children[-1].text else "") + text)
                else:
                    current.text += (("\n\n" if current.text else "") + text)
    doc.close()
    return root