#!/usr/bin/env python3
import argparse
import concurrent.futures
import os
import re
import shutil
import subprocess
import sys
from typing import List, Optional, Tuple


def _run(cmd: List[str], input_text: Optional[str] = None) -> Tuple[int, str, str]:
    proc = subprocess.run(
        cmd,
        input=input_text,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        text=True,
        check=False,
    )
    return proc.returncode, proc.stdout, proc.stderr


def require(cmd: str, hint: str):
    if shutil.which(cmd) is None:
        print(f"Error: required command '{cmd}' not found. {hint}", file=sys.stderr)
        sys.exit(1)


def detect_repo_root() -> Optional[str]:
    code, out, _ = _run(["git", "rev-parse", "--show-toplevel"])
    if code != 0:
        return None
    return out.strip()


def ensure_dir(path: str):
    os.makedirs(path, exist_ok=True)


def pr_file_paths(out_dir: str) -> List[str]:
    if not os.path.isdir(out_dir):
        return []
    paths = []
    for name in os.listdir(out_dir):
        if re.match(r"PR-\d+\.md$", name):
            paths.append(os.path.join(out_dir, name))
    # Sort by PR number ascending
    def prnum(p: str) -> int:
        m = re.search(r"(\d+)", os.path.basename(p))
        return int(m.group(1)) if m else 0
    return sorted(paths, key=prnum)


def extract_pr_number(path: str) -> int:
    m = re.search(r"(\d+)", os.path.basename(path))
    return int(m.group(1)) if m else 0


def build_prompt(contents: str, reviewer: str, out_path: str) -> str:
    # We rely on `codex exec --output-last-message {out_path}` to write the
    # final message to disk. Instruct the agent to ONLY produce the final
    # document as its last message (no meta commentary), to avoid clutter.
    return (
        f"{contents}\n---\n"
        f"Summarize the takeaways from this PR review by {reviewer} into a concise, generalizable, and practical guide with two checklists: DOs and DON'Ts. "
        f"Add short, accurate code examples in fenced code blocks to illustrate each key point. "
        f"Output ONLY the final document as your final message — no preamble, no status notes, no explanations about saving files. "
        f"The CLI will save your final message to {out_path}."
    )


def run_codex_exec(prompt: str, last_message_file: Optional[str] = None) -> Tuple[int, str, str]:
    # Prefer a globally installed `codex`; fall back to cargo if needed.
    if shutil.which("codex") is not None:
        cmd = ["codex", "-c", "model_reasoning_effort=high", "exec"]
        if last_message_file:
            cmd.extend(["--output-last-message", last_message_file])
        return _run(cmd, input_text=prompt)
    # Fallback: use cargo run (may build; slower but reliable in dev)
    cmd = [
        "cargo",
        "run",
        "--quiet",
        "--bin",
        "codex",
        "--",
        "-c",
        "model_reasoning_effort=high",
        "exec",
    ]
    if last_message_file:
        cmd.extend(["--output-last-message", last_message_file])
    return _run(cmd, input_text=prompt)


def study_one(pr_md_path: str, reviewer: str, out_dir: str) -> Tuple[str, str]:
    pr_num = extract_pr_number(pr_md_path)
    try:
        with open(pr_md_path, "r", encoding="utf-8") as f:
            contents = f.read()
        ensure_dir(out_dir)
        out_path = os.path.join(out_dir, f"PR-{pr_num}-study.md")
        prompt = build_prompt(contents, reviewer, out_path)
        code, out, err = run_codex_exec(prompt, last_message_file=out_path)
        if code != 0:
            return pr_md_path, f"error: codex exec failed (exit {code}): {err.strip()}"
        # If Codex did not write the file for some reason, fall back to captured stdout.
        # Note: we only fallback when the output file is missing/empty to avoid
        # overwriting a valid summary produced by Codex.
        if (not os.path.isfile(out_path)) or os.path.getsize(out_path) == 0:
            try:
                with open(out_path, "w", encoding="utf-8") as f:
                    f.write(out)
            except Exception as e:
                return pr_md_path, f"error: failed to write fallback output: {e}"
        return pr_md_path, "ok"
    except Exception as e:
        return pr_md_path, f"error: {e}"


def main():
    parser = argparse.ArgumentParser(
        prog="study",
        description=(
            "Generate PR markdowns via lastprs, then summarize each via `codex exec`.\n"
            "Writes summaries to prs/<reviewer>/study/PR-<num>-study.md."
        ),
    )
    parser.add_argument("days", type=int, help="Number of days to look back (N)")
    parser.add_argument("reviewer", help="GitHub login of the reviewer")
    parser.add_argument(
        "repo",
        nargs="?",
        help="Repository in 'owner/repo' form; inferred from git origin if omitted (passed through to lastprs)",
    )
    parser.add_argument(
        "--jobs",
        "-j",
        type=int,
        default=10,
        help="Parallel jobs for summaries (default: 10)",
    )
    parser.add_argument(
        "--skip-generate",
        action="store_true",
        help="Skip running lastprs and reuse existing prs/<reviewer>/ files",
    )

    args = parser.parse_args()

    if args.days <= 0:
        print("Error: days must be a positive integer.", file=sys.stderr)
        sys.exit(2)

    # Check dependencies
    require("gh", "Install GitHub CLI: https://cli.github.com")
    # lastprs is shipped with this repo; prefer local copy, then PATH
    script_dir = os.path.dirname(os.path.abspath(__file__))
    lastprs_path = os.path.join(script_dir, "lastprs")
    if not (os.path.isfile(lastprs_path) and os.access(lastprs_path, os.X_OK)):
        require("lastprs", "Ensure the lastprs helper script is on PATH or present in this folder.")
        lastprs_path = "lastprs"

    # Determine paths
    repo_root = detect_repo_root() or os.getcwd()
    prs_dir = os.path.join(repo_root, "prs", args.reviewer)
    summaries_dir = os.path.join(prs_dir, "study")

    # 1) Generate PR markdowns if not skipping
    if not args.skip_generate:
        cmd = [lastprs_path, str(args.days), args.reviewer]
        if args.repo:
            cmd.append(args.repo)
        print("Generating PR markdowns via lastprs…", file=sys.stderr)
        code, out, err = _run(cmd)
        if code != 0:
            print(f"Error: lastprs failed (exit {code}): {err.strip()}", file=sys.stderr)
            sys.exit(code)
        # Echo a short summary
        sys.stderr.write(out.strip() + "\n")

    # 2) Discover PR files
    files = pr_file_paths(prs_dir)
    if not files:
        print(f"No PR markdowns found in {prs_dir}.", file=sys.stderr)
        sys.exit(0)

    print(f"Summarizing {len(files)} PR(s) to {summaries_dir}")

    # 3) Summarize via codex exec
    results: List[Tuple[str, str]] = []
    with concurrent.futures.ThreadPoolExecutor(max_workers=max(1, args.jobs)) as ex:
        futs = [ex.submit(study_one, p, args.reviewer, summaries_dir) for p in files]
        for fut in concurrent.futures.as_completed(futs):
            results.append(fut.result())

    ok = sum(1 for _, s in results if s == "ok")
    failures = [(p, s) for p, s in results if s != "ok"]
    for p, s in failures:
        print(f"{os.path.basename(p)}: {s}", file=sys.stderr)
    print(f"Done. {ok}/{len(files)} summaries succeeded.")


if __name__ == "__main__":
    main()