import os
import re
from pathlib import Path

from fastapi import APIRouter
from pydantic import BaseModel

router = APIRouter()

SOURCES_DIR = Path(os.environ.get("SOURCES_DIR", "/data/sources"))
PAGES_DIR = Path(os.environ.get("PAGES_DIR", "/data/pages"))

# Matches markdown links: [text](slug) where slug has no protocol or path separators
_INTERNAL_LINK = re.compile(r"\[([^\]]+)\]\(([a-zA-Z0-9_-]+)\)")


class GraphNode(BaseModel):
    id: str
    published: bool
    title: str | None = None


class GraphEdge(BaseModel):
    source: str
    target: str


class GraphData(BaseModel):
    nodes: list[GraphNode]
    edges: list[GraphEdge]


def _all_page_names() -> set[str]:
    names: set[str] = set()
    if PAGES_DIR.is_dir():
        for f in PAGES_DIR.iterdir():
            if f.suffix == ".mu" and f.is_file():
                names.add(f.stem)
    if SOURCES_DIR.is_dir():
        for f in SOURCES_DIR.iterdir():
            if f.suffix == ".md" and f.is_file():
                names.add(f.stem)
    return names


def _extract_title(markdown: str) -> str | None:
    for line in markdown.splitlines():
        stripped = line.strip()
        if stripped.startswith("# "):
            return stripped[2:].strip()
    return None


@router.get("/graph", response_model=GraphData)
async def get_graph():
    all_names = _all_page_names()
    nodes: list[GraphNode] = []
    edges: list[GraphEdge] = []

    for name in sorted(all_names):
        md_path = SOURCES_DIR / f"{name}.md"
        mu_path = PAGES_DIR / f"{name}.mu"

        title = None
        if md_path.is_file():
            content = md_path.read_text(encoding="utf-8")
            title = _extract_title(content)

            # Parse internal links
            for match in _INTERNAL_LINK.finditer(content):
                target = match.group(2)
                if target in all_names:
                    edges.append(GraphEdge(source=name, target=target))

        nodes.append(GraphNode(
            id=name,
            published=mu_path.is_file(),
            title=title,
        ))

    return GraphData(nodes=nodes, edges=edges)