#!/usr/bin/env python3
"""Regenerate the auto-generated model list section of README.md.

Reads data/fal_registry.json and rewrites ONLY the section between
`<!-- BEGIN GENERATED MODEL LIST -->` and `<!-- END GENERATED MODEL LIST -->`
in README.md. Everything outside the markers is left untouched, and running
the script twice in a row produces no diff.

Usage:
    python scripts/build_readme.py
"""

from __future__ import annotations

import json
import sys
from pathlib import Path
from typing import Any

REPO_ROOT = Path(__file__).resolve().parents[1]
REGISTRY_PATH = REPO_ROOT / "data" / "fal_registry.json"
README_PATH = REPO_ROOT / "README.md"

BEGIN_MARKER = "<!-- BEGIN GENERATED MODEL LIST -->"
END_MARKER = "<!-- END GENERATED MODEL LIST -->"

MODEL_URL_TEMPLATE = "https://fal.ai/models/{endpoint_id}"


def load_registry(path: Path) -> dict[str, Any]:
    try:
        with open(path, encoding="utf-8") as handle:
            registry = json.load(handle)
    except (OSError, ValueError) as err:
        raise SystemExit(f"Failed to read registry at {path}: {err}") from err
    if not isinstance(registry.get("models"), list):
        raise SystemExit(f"Registry at {path} has no 'models' list")
    return registry


def escape_cell(text: str) -> str:
    """Make a value safe inside a markdown table cell."""
    return " ".join(str(text).split()).replace("|", "\\|")


def group_by_category(
    models: list[dict[str, Any]],
) -> list[tuple[str, list[dict[str, Any]]]]:
    """Group models by category, categories sorted by size desc then name."""
    grouped: dict[str, list[dict[str, Any]]] = {}
    for model in models:
        category = str(model.get("category") or "other")
        grouped = {**grouped, category: [*grouped.get(category, []), model]}
    return sorted(grouped.items(), key=lambda item: (-len(item[1]), item[0]))


def model_sort_key(model: dict[str, Any]) -> tuple[str, str]:
    title = str(model.get("title") or model.get("endpoint_id") or "")
    return (title.casefold(), str(model.get("endpoint_id") or ""))


def render_model_row(model: dict[str, Any]) -> str:
    endpoint_id = str(model.get("endpoint_id") or "")
    title = escape_cell(model.get("title") or endpoint_id)
    lab = escape_cell(model.get("lab") or "—") or "—"
    output = escape_cell(model.get("output_kind") or "json")
    url = MODEL_URL_TEMPLATE.format(endpoint_id=endpoint_id)
    endpoint_cell = f"[`{escape_cell(endpoint_id)}`]({url})"
    return f"| {title} | {endpoint_cell} | {lab} | {output} |"


def render_category(category: str, models: list[dict[str, Any]]) -> str:
    rows = [render_model_row(m) for m in sorted(models, key=model_sort_key)]
    count = len(models)
    noun = "model" if count == 1 else "models"
    return "\n".join(
        [
            "<details>",
            f"<summary><strong>{category}</strong> — {count} {noun}</summary>",
            "",
            "| Model | Endpoint | Lab | Output |",
            "| --- | --- | --- | --- |",
            *rows,
            "",
            "</details>",
        ]
    )


def render_generated_section(registry: dict[str, Any]) -> str:
    models = registry["models"]
    model_count = registry.get("model_count", len(models))
    published = [str(m.get("published_at", "")) for m in registry.get("models", [])]
    generated_date = max(published)[:10] if any(published) else "unknown"
    summary = (
        f"{model_count} models · newest model {generated_date} · "
        "refresh with `scripts/build_registry.py`"
    )
    blocks = [
        render_category(category, grouped)
        for category, grouped in group_by_category(models)
    ]
    return "\n\n".join([summary, *blocks])


def replace_between_markers(readme: str, generated: str) -> str:
    begin = readme.find(BEGIN_MARKER)
    end = readme.find(END_MARKER)
    if begin == -1 or end == -1 or end < begin:
        raise SystemExit(
            f"README.md must contain '{BEGIN_MARKER}' followed by '{END_MARKER}'"
        )
    head = readme[: begin + len(BEGIN_MARKER)]
    tail = readme[end:]
    return f"{head}\n\n{generated}\n\n{tail}"


def main() -> int:
    registry = load_registry(REGISTRY_PATH)
    try:
        readme = README_PATH.read_text(encoding="utf-8")
    except OSError as err:
        raise SystemExit(f"Failed to read {README_PATH}: {err}") from err

    updated = replace_between_markers(readme, render_generated_section(registry))
    if updated == readme:
        print(f"README.md already up to date ({registry.get('model_count')} models)")
        return 0

    README_PATH.write_text(updated, encoding="utf-8")
    print(
        f"README.md model list regenerated: {registry.get('model_count')} models, "
        f"{len(group_by_category(registry['models']))} categories"
    )
    return 0


if __name__ == "__main__":
    sys.exit(main())