r"""Rebuild plan/ from the archived poc-modules snapshot.

The active working surface is plan/. This script is retained so the smaller
markdown slices can be regenerated from the archived legacy monolith when
needed.

Run with:
    .venv\Scripts\python.exe scripts\split_plan.py
"""

from __future__ import annotations

import re
import shutil
from dataclasses import dataclass, field
from pathlib import Path
from typing import Final

ROOT = Path(__file__).resolve().parents[1]
SOURCE = ROOT / "archive" / "poc-modules.md"
OUTPUT = ROOT / "plan"
SENTINEL = OUTPUT / ".generated-by-split-plan"
HEADING_RE = re.compile(r"^(#{1,6})\s+(.*)$")
MODULE_ID_RE = re.compile(r"\b(M\d{2}[a-z]?)\b", re.IGNORECASE)
QUESTION_ID_RE = re.compile(r"\b(Q\d+)\b", re.IGNORECASE)

BACKEND_SECTIONS: Final[list[str]] = [
    "Overview",
    "Spirit guardrails",
    "Architecture: three layers that must not collapse",
    "Trust model (critical — never flatten into one field)",
    "Dependency Graph (corrected)",
    "Critical Path",
    "Parallel Workstreams",
]
BACKEND_BLOCKERS: Final[list[str]] = ["Q1", "Q2", "Q4", "Q5", "Q6", "Q7"]
BACKEND_MODULES: Final[list[str]] = [
    "M01",
    "M03",
    "M08",
    "M11",
    "M13",
    "M14",
    "M15",
    "M17",
    "M20",
    "M21",
    "M22",
    "M23",
]

FRONTEND_SECTIONS: Final[list[str]] = [
    "Overview",
    "Spirit guardrails",
    "Architecture: three layers that must not collapse",
    "Parallel Workstreams",
    "First actions before writing any code (Wave 0 justification)",
]
FRONTEND_BLOCKERS: Final[list[str]] = ["Q1", "Q3", "Q4"]
FRONTEND_MODULES: Final[list[str]] = ["M17", "M18", "M19", "M22"]

LLM_SECTIONS: Final[list[str]] = [
    "Overview",
    "Spirit guardrails",
    "Trust model (critical — never flatten into one field)",
    "Critical Path",
    "Risk Register",
]
LLM_BLOCKERS: Final[list[str]] = ["Q1", "Q2", "Q5", "Q6"]
LLM_MODULES: Final[list[str]] = [
    "M02",
    "M04b",
    "M08",
    "M09",
    "M10",
    "M13",
    "M14",
    "M22",
]


@dataclass(slots=True)
class Section:
    level: int
    heading: str
    body_lines: list[str] = field(default_factory=list)
    children: list[Section] = field(default_factory=list)

    def title(self) -> str:
        return self.heading.strip()

    def content(self, *, heading_level: int = 1) -> str:
        lines = self.render(heading_level=heading_level)
        return "\n".join(lines).rstrip() + "\n"

    def render(self, *, heading_level: int) -> list[str]:
        lines = [f"{'#' * heading_level} {self.title()}", ""]
        lines.extend(self.body_lines)
        if self.body_lines and self.children:
            lines.append("")
        for index, child in enumerate(self.children):
            lines.extend(child.render(heading_level=heading_level + 1))
            if index < len(self.children) - 1:
                lines.append("")
        return lines


def slugify(value: str) -> str:
    value = value.strip().lower()
    value = value.replace("→", " to ")
    value = value.replace("/", " ")
    value = re.sub(r"[`*_(){}\[\]:.,!?'\"]", "", value)
    value = re.sub(r"[^a-z0-9]+", "-", value)
    return value.strip("-") or "section"


def parse_sections(text: str) -> tuple[list[str], list[Section]]:
    preamble: list[str] = []
    roots: list[Section] = []
    stack: list[Section] = []
    in_code_block = False

    for raw_line in text.splitlines():
        line = raw_line.rstrip()
        stripped = line.strip()
        if stripped.startswith("```"):
            in_code_block = not in_code_block

        match = None if in_code_block else HEADING_RE.match(line)
        if match:
            level = len(match.group(1))
            heading = match.group(2).strip()
            section = Section(level=level, heading=heading)
            while stack and stack[-1].level >= level:
                stack.pop()
            if stack:
                stack[-1].children.append(section)
            else:
                roots.append(section)
            stack.append(section)
            continue

        if stack:
            stack[-1].body_lines.append(line)
        else:
            preamble.append(line)

    return preamble, roots


def write_file(path: Path, content: str) -> None:
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(content, encoding="utf-8")


def clean_output_dir(output_dir: Path) -> None:
    if not output_dir.exists():
        return
    if not SENTINEL.exists():
        raise RuntimeError(
            f"Refusing to replace {output_dir} because it was not created by this script."
        )
    shutil.rmtree(output_dir)


def heading_link(path: Path) -> str:
    return path.relative_to(OUTPUT).as_posix()


def module_filename(section: Section) -> str:
    match = MODULE_ID_RE.search(section.title())
    module_id = match.group(1).lower() if match else "module"
    tail = slugify(MODULE_ID_RE.sub("", section.title(), count=1))
    return f"{module_id}-{tail}.md" if tail else f"{module_id}.md"


def require_path(path_map: dict[str, str], key: str) -> str:
    try:
        return path_map[key]
    except KeyError as exc:
        raise RuntimeError(f"Missing generated path for {key!r}") from exc


def normalize_module_id(module_id: str) -> str:
    return module_id.upper()


def question_filename(section: Section) -> str:
    match = QUESTION_ID_RE.search(section.title())
    question_id = match.group(1).lower() if match else "question"
    tail = slugify(QUESTION_ID_RE.sub("", section.title(), count=1))
    return f"{question_id}-{tail}.md" if tail else f"{question_id}.md"


def write_blocker_breakout(
    section: Section, *, section_paths: dict[str, str], blocker_paths: dict[str, str]
) -> None:
    blockers_dir = OUTPUT / "blockers"
    blockers_dir.mkdir(parents=True, exist_ok=True)

    readme_lines = [
        "# Blockers By Question",
        "",
        "Split from the pre-coding blockers section so agents can load one decision at a time.",
        "",
    ]

    for child in section.children:
        match = QUESTION_ID_RE.search(child.title())
        if match is None:
            continue
        question_id = match.group(1).upper()
        filename = question_filename(child)
        question_path = blockers_dir / filename
        write_file(question_path, child.content())
        rel_path = heading_link(question_path)
        blocker_paths[question_id] = rel_path
        readme_lines.append(f"- [{child.title()}]({filename})")

    write_file(blockers_dir / "README.md", "\n".join(readme_lines).rstrip() + "\n")
    section_paths["Blockers By Question"] = heading_link(blockers_dir / "README.md")


def write_agent_guide(
    *,
    filename: str,
    title: str,
    summary: str,
    section_keys: list[str],
    blocker_ids: list[str],
    module_ids: list[str],
    section_paths: dict[str, str],
    blocker_paths: dict[str, str],
    module_paths: dict[str, str],
) -> None:
    lines = [
        f"# {title}",
        "",
        summary,
        "",
        "Read the source file only when you need full surrounding prose; otherwise start from these slices.",
        "",
        "## Foundation",
        "",
    ]

    for key in section_keys:
        lines.append(f"- [{key}]({require_path(section_paths, key)})")

    lines.extend(["", "## Blockers", ""])
    for blocker_id in blocker_ids:
        lines.append(f"- [{blocker_id}]({require_path(blocker_paths, blocker_id)})")

    lines.extend(["", "## Modules", ""])
    for module_id in module_ids:
        lines.append(
            f"- [{module_id}]({require_path(module_paths, normalize_module_id(module_id))})"
        )

    write_file(OUTPUT / filename, "\n".join(lines).rstrip() + "\n")


def write_agent_guides(
    *,
    section_paths: dict[str, str],
    blocker_paths: dict[str, str],
    module_paths: dict[str, str],
) -> None:
    write_agent_guide(
        filename="for-backend.md",
        title="For Backend Agents",
        summary="Backend-heavy reading order for contracts, orchestration, validation, session management, and export work.",
        section_keys=BACKEND_SECTIONS,
        blocker_ids=BACKEND_BLOCKERS,
        module_ids=BACKEND_MODULES,
        section_paths=section_paths,
        blocker_paths=blocker_paths,
        module_paths=module_paths,
    )
    write_agent_guide(
        filename="for-frontend.md",
        title="For Frontend Agents",
        summary="Frontend-heavy reading order for the Gradio host, renderer boundary, and Cytoscape component work.",
        section_keys=FRONTEND_SECTIONS,
        blocker_ids=FRONTEND_BLOCKERS,
        module_ids=FRONTEND_MODULES,
        section_paths=section_paths,
        blocker_paths=blocker_paths,
        module_paths=module_paths,
    )
    write_agent_guide(
        filename="for-llm.md",
        title="For LLM Agents",
        summary="LLM-heavy reading order for structured output, prompting, validation boundaries, and model-facing risks.",
        section_keys=LLM_SECTIONS,
        blocker_ids=LLM_BLOCKERS,
        module_ids=LLM_MODULES,
        section_paths=section_paths,
        blocker_paths=blocker_paths,
        module_paths=module_paths,
    )


def build_plan(preamble: list[str], roots: list[Section]) -> None:
    clean_output_dir(OUTPUT)
    OUTPUT.mkdir(parents=True, exist_ok=True)
    SENTINEL.write_text("generated by scripts/split_plan.py\n", encoding="utf-8")

    title_section = next((section for section in roots if section.level == 1), None)
    if title_section is None:
        raise RuntimeError("Expected an H1 title in archive/poc-modules.md")

    h2_sections = [section for section in title_section.children if section.level == 2]
    if not h2_sections:
        raise RuntimeError("Expected H2 sections under the document title")

    index_lines = [
        "# Plan Index",
        "",
        "Originally generated from the archived `archive/poc-modules.md` snapshot by `scripts/split_plan.py`.",
        "`plan/` is now the active working surface; `archive/` keeps the legacy monolith and research notes.",
        "",
        "## Archive Snapshot",
        "",
        f"- `../archive/poc-modules.md` ({SOURCE.as_posix()})",
        "",
        "## Agent Reading Lists",
        "",
        "- [For backend agents](for-backend.md)",
        "- [For frontend agents](for-frontend.md)",
        "- [For LLM agents](for-llm.md)",
        "",
        "## Sections",
        "",
    ]
    section_paths: dict[str, str] = {}
    module_paths: dict[str, str] = {}
    blocker_paths: dict[str, str] = {}

    overview_lines = [f"# {title_section.title()}", ""]
    if preamble:
        overview_lines.extend(preamble)
        overview_lines.append("")
    overview_lines.extend(title_section.body_lines)
    write_file(OUTPUT / "00-overview.md", "\n".join(overview_lines).rstrip() + "\n")
    index_lines.append("- [Overview](00-overview.md)")
    section_paths["Overview"] = "00-overview.md"

    non_module_counter = 1
    for h2 in h2_sections:
        if h2.title() == "Module List":
            module_dir = OUTPUT / "modules"
            module_dir.mkdir(parents=True, exist_ok=True)
            module_index = [
                "# Modules",
                "",
                "Split from the `Module List` section.",
                "",
            ]
            for layer_index, layer in enumerate(h2.children, start=1):
                layer_slug = f"{layer_index:02d}-{slugify(layer.title())}"
                layer_dir = module_dir / layer_slug
                layer_dir.mkdir(parents=True, exist_ok=True)

                layer_readme_lines = [f"# {layer.title()}", ""]
                if layer.body_lines:
                    layer_readme_lines.extend(layer.body_lines)
                    layer_readme_lines.append("")
                layer_readme_lines.append("## Modules")
                layer_readme_lines.append("")

                for module in layer.children:
                    filename = module_filename(module)
                    module_path = layer_dir / filename
                    write_file(module_path, module.content())
                    layer_readme_lines.append(f"- [{module.title()}]({filename})")
                    match = MODULE_ID_RE.search(module.title())
                    if match is not None:
                        module_paths[match.group(1).upper()] = heading_link(module_path)

                write_file(
                    layer_dir / "README.md",
                    "\n".join(layer_readme_lines).rstrip() + "\n",
                )
                rel_layer = heading_link(layer_dir / "README.md")
                module_index.append(f"- [{layer.title()}]({rel_layer})")

            write_file(
                module_dir / "README.md", "\n".join(module_index).rstrip() + "\n"
            )
            index_lines.append("- [Modules](modules/README.md)")
            section_paths["Module List"] = "modules/README.md"
            continue

        filename = f"{non_module_counter:02d}-{slugify(h2.title())}.md"
        non_module_counter += 1
        write_file(OUTPUT / filename, h2.content())
        index_lines.append(f"- [{h2.title()}]({filename})")
        section_paths[h2.title()] = filename

        if (
            h2.title()
            == "Pre-coding blockers (resolve in order before assigning any module)"
        ):
            write_blocker_breakout(
                h2, section_paths=section_paths, blocker_paths=blocker_paths
            )
            index_lines.append("- [Blockers by question](blockers/README.md)")

    write_agent_guides(
        section_paths=section_paths,
        blocker_paths=blocker_paths,
        module_paths=module_paths,
    )
    write_file(OUTPUT / "README.md", "\n".join(index_lines).rstrip() + "\n")


def main() -> None:
    text = SOURCE.read_text(encoding="utf-8")
    preamble, roots = parse_sections(text)
    build_plan(preamble, roots)
    print(f"Wrote split plan to {OUTPUT}")


if __name__ == "__main__":
    main()