"""Turn the statistics (and Claude's reviews, if any) into a Markdown report."""

from __future__ import annotations

from itemstats import TestStats


def fmt(x: float | None, digits: int = 2) -> str:
    return "n/a" if x is None else f"{x:.{digits}f}"


def build_report(quiz: dict, stats: TestStats, reviews: list | None = None) -> str:
    items_by_id = {item["id"]: item for item in quiz["items"]}
    reviews_by_id = {r.item_id: r for r in (reviews or [])}
    flagged = [s for s in stats.items if s.flags]

    lines = [
        f"# Item analysis: {quiz['title']}",
        "",
        f"- Learners: {stats.n_learners}",
        f"- Items: {stats.n_items}",
        f"- Mean score: {stats.mean_score:.2f} of {stats.n_items} (SD {stats.sd_score:.2f})",
        f"- Reliability (KR-20): {fmt(stats.kr20)}",
        f"- Items flagged: {len(flagged)}",
        "",
        "## All items",
        "",
        "| Item | Key | Difficulty (p) | Discrimination (r) | D index | KR-20 if removed | Flags |",
        "|---|---|---|---|---|---|---|",
    ]
    for s in stats.items:
        lines.append(
            f"| {s.item_id} | {s.key} | {fmt(s.difficulty)} | {fmt(s.discrimination)} | "
            f"{fmt(s.d_index)} | {fmt(s.alpha_if_deleted)} | {len(s.flags) or ''} |"
        )

    lines += ["", "## Flagged items", ""]
    if not flagged:
        lines.append("Nothing was flagged.")
    for s in flagged:
        item = items_by_id[s.item_id]
        lines += [f"### {s.item_id}: {item['stem']}", ""]
        lines += ["| Option | Text | Picked | Top 27% | Bottom 27% | r with rest of test |", "|---|---|---|---|---|---|"]
        for o in s.options:
            label = f"**{o.option}** (key)" if o.option == s.key else o.option
            lines.append(
                f"| {label} | {item['options'][o.option]} | {o.count} ({o.share:.0%}) | "
                f"{o.upper_share:.0%} | {o.lower_share:.0%} | {fmt(o.point_biserial)} |"
            )
        lines += ["", "Flags:", ""]
        lines += [f"- {flag}" for flag in s.flags]

        review = reviews_by_id.get(s.item_id)
        if review:
            lines += [
                "",
                f"Claude's read: **{review.action}** (likely cause: {review.likely_cause.replace('_', ' ')})",
                "",
                review.diagnosis,
            ]
            if review.revised_item:
                r = review.revised_item
                lines += ["", "Suggested revision:", "", f"> {r.stem}", ">"]
                for o in sorted(r.options, key=lambda o: o.letter):
                    mark = " (key)" if o.letter == r.key else ""
                    lines.append(f"> {o.letter}. {o.text}{mark}  ")
                lines += ["", review.what_changed]
        lines.append("")

    return "\n".join(lines).rstrip() + "\n"