//! `comments <number> [--limit N | --tail N]` — list comments on an
//! issue or PR. Replaces the curl fallback.
//!
//! - `--limit N` returns the first N comments (oldest-first) — an
//!   explicit opt-in: a plain `comments` call used to read as "I've read
//!   this thread" when it was really "the oldest N of it", so the
//!   default moved to `--tail`'s window instead (see below).
//! - `--tail N` returns the *last* N comments, chronological — and with
//!   neither flag given, THIS is the default (N = 10): most-recent
//!   activity. Reads the issue's `comments` count first to compute which
//!   page holds the tail, then fetches only `ceil(N/50) + 1` pages —
//!   bounded by `N`, not thread length.
//! - **The count of comments outside whatever window is shown is
//!   always reported** — never a silent truncation.
//! - `--since <RFC3339>` filters to comments at or after that
//!   timestamp instead of a head/tail window — a cursor: feed the
//!   last-seen row's own `created_at` back in next time. Mutually
//!   exclusive with `--tail`; `--limit` clamps like `timeline`'s own
//!   does (see `crate::verbs::MAX_LIMIT`).
//!
//! Review *bodies* on PRs are always merged in too (`pulls/<n>/reviews`
//! isn't the issues/comments thread), tagged `[review: STATE]`, with a
//! `(N line comment(s) — see 'pr reviews')` pointer when a review has
//! inline comments — this verb never inlines those, `pr reviews` does.
//!
//! `--json` output is an object (`{"comments": [...], "more_before": N,
//! "more_after": N, "since_more": bool}`), not a bare array, so a
//! script can read the truncation info too. `--show-reactions` adds a
//! per-comment reaction summary — see that flag's own doc for the cost.

use anyhow::Result;
use clap::Args as ClapArgs;
use forgejo_api::structs::IssueGetCommentsQuery;
use serde_json::{Value, json};
use time::OffsetDateTime;

use crate::client::{Client, index};
use crate::notify;
use crate::verbs::{
    MAX_LIMIT, PAGE_SIZE, clamp_limit, comment_reactions, parse_rfc3339, print_json,
    reaction_summary, rfc3339,
};

#[derive(ClapArgs)]
pub struct Args {
    /// Issue or PR number.
    pub(crate) number: u64,
    /// Number of comments from the start of the thread (oldest-first),
    /// or (with `--since`) the most this call returns — capped at
    /// [`crate::verbs::MAX_LIMIT`] in the latter case. An explicit
    /// opt-in: with neither this nor `--tail` given, the default is the
    /// newest 10 (see `--tail`). Mutually exclusive with `--tail`.
    #[arg(long, conflicts_with = "tail")]
    limit: Option<u64>,
    /// Return the last `N` comments (chronological) — the most recent
    /// activity. This is the default (`N` = 10) when neither `--limit`
    /// nor `--tail` is given. Mutually exclusive with `--limit`/`--since`.
    #[arg(long, conflicts_with = "since")]
    tail: Option<usize>,
    /// Only show comments at or after this RFC3339 timestamp (same
    /// format this verb's own output prints). Mutually exclusive with
    /// `--tail`.
    #[arg(long)]
    since: Option<String>,
    /// Fetch + display each shown comment's reaction summary. Costs one
    /// extra request per comment shown — opt-in, not the default.
    #[arg(long)]
    show_reactions: bool,
}

pub fn run(client: &Client, args: Args) -> Result<()> {
    let repo = client.repo()?;
    // Truncation info: what sits outside the window we're about to show.
    // A `--tail`/default window has nothing after it (it ends at the
    // thread's current end); a `--limit` window has nothing before it (it
    // starts at the thread's beginning); a `--since` window is a boolean
    // "there's more" (no total exists for a since-filtered query) rather
    // than an exact count. `more_before`/`more_after` are derived from
    // `thread.len()` rather than the requested `n`/`limit` so a
    // shrunk-under-us thread (comments deleted mid-fetch) still reports
    // accurately instead of the number we merely asked for.
    let (thread, more_before, more_after, since_more, since_clamped) =
        if let Some(since_str) = &args.since {
            let since = parse_rfc3339(since_str)?;
            let (limit, clamped) = clamp_limit(args.limit.unwrap_or(10));
            let (thread, more) = fetch_since(client, args.number, since, limit)?;
            (thread, 0, 0, more, clamped)
        } else if let Some(limit) = args.limit {
            let total = fetch_total(client, args.number)?;
            let thread = fetch_head(client, args.number, limit)?;
            let more_after = total.saturating_sub(thread.len());
            (thread, 0, more_after, false, false)
        } else {
            // Default (no `--limit`/`--tail`/`--since`): same window as
            // an explicit `--tail 10` — the newest activity, not the
            // oldest. `args.tail` still wins if the agent passed a
            // different count explicitly.
            let n = args.tail.unwrap_or(10);
            let total = fetch_total(client, args.number)?;
            let thread = fetch_tail(client, args.number, n, total)?;
            let more_before = total.saturating_sub(thread.len());
            (thread, more_before, 0, false, false)
        };
    // Merge in PR review bodies (empty for issues — degrades to a
    // no-op) so review feedback isn't silently dropped.
    let mut comments = merge_chronological(thread, fetch_review_bodies(client, args.number));
    // Reading the thread clears its unread notification so the
    // read-before-comment guard (in `comment`) lets a reply through.
    notify::mark_read_best_effort(client, repo, args.number);
    let (owner, name) = client.owner_repo()?;
    attach_reactions(client, owner, name, &mut comments, args.show_reactions);
    if client.json_mode() {
        let trimmed: Vec<Value> = comments
            .iter()
            .map(|c| {
                json!({
                    "id": c.get("id"),
                    "user": c.get("user").and_then(|u| u.get("login")),
                    "created_at": c.get("created_at"),
                    "updated_at": c.get("updated_at"),
                    "body": c.get("body"),
                    "url": c.get("html_url"),
                    "kind": c.get("kind").and_then(Value::as_str).unwrap_or("comment"),
                    "state": c.get("state"),
                    "comments_count": c.get("comments_count"),
                    "attachments": attachment_json_from_value(c),
                    "reactions": c.get("reactions").cloned().unwrap_or_else(|| json!([])),
                })
            })
            .collect();
        print_json(&json!({
            "comments": trimmed,
            "more_before": more_before,
            "more_after": more_after,
            "since_more": since_more,
            "since_limit_clamped": since_clamped,
        }))
    } else {
        for c in &comments {
            let user = c
                .get("user")
                .and_then(|u| u.get("login"))
                .and_then(Value::as_str)
                .unwrap_or("?");
            let ts = c.get("created_at").and_then(Value::as_str).unwrap_or("?");
            let body = c.get("body").and_then(Value::as_str).unwrap_or("");
            if c.get("kind").and_then(Value::as_str) == Some("review") {
                let state = c.get("state").and_then(Value::as_str).unwrap_or("?");
                let n = c.get("comments_count").and_then(Value::as_i64).unwrap_or(0);
                if n > 0 {
                    println!(
                        "**{user} @ {ts}** [review: {state}] ({n} line comment(s) — see `hive-forge pr reviews {}`): {body}",
                        args.number
                    );
                } else {
                    println!("**{user} @ {ts}** [review: {state}]: {body}");
                }
            } else {
                println!("**{user} @ {ts}**: {body}");
            }
            for line in attachment_lines_from_value(c) {
                println!("{line}");
            }
            if let Some(summary) = c
                .get("reactions")
                .and_then(Value::as_array)
                .and_then(|r| reaction_summary(r))
            {
                println!("[reactions: {summary}]");
            }
            println!();
        }
        if since_clamped {
            println!(
                "(--limit {} is above the {MAX_LIMIT} cap --since can reliably detect truncation at — clamped)",
                args.limit.unwrap_or(10)
            );
        }
        if since_more {
            println!(
                "(more comments since this timestamp not shown — raise --limit or bump --since; exact count not available)"
            );
        }
        if let Some(note) = truncation_note(more_before, more_after) {
            println!("{note}");
        }
        Ok(())
    }
}

/// A one-line truncation note when the shown window doesn't cover the
/// whole thread — never a silent gap. `None` when both are zero (the
/// whole thread rode the wire). Returns a `String` rather than printing
/// directly so the three cases are unit-testable.
fn truncation_note(more_before: usize, more_after: usize) -> Option<String> {
    match (more_before > 0, more_after > 0) {
        (false, false) => None,
        (true, false) => Some(format!(
            "({more_before} earlier comment(s) not shown — use --limit to see the start of the thread)"
        )),
        (false, true) => Some(format!(
            "({more_after} more comment(s) not shown — use --tail N to see the latest instead)"
        )),
        (true, true) => Some(format!(
            "({more_before} earlier + {more_after} later comment(s) not shown — use --tail N)"
        )),
    }
}

/// Fetch + attach each shown comment's reaction list under a
/// `"reactions"` key, mutating in place so both the `--json` and
/// pretty-print branches see the same fetch. No-op when `show_reactions`
/// is false (the default) — the whole point of gating this behind a
/// flag is that a plain `comments` call costs nothing extra. Review
/// entries are skipped (synthesized, never have real reactions); a
/// per-comment fetch failure is swallowed rather than failing the whole
/// listing over one comment.
fn attach_reactions(
    client: &Client,
    owner: &str,
    name: &str,
    comments: &mut [Value],
    show_reactions: bool,
) {
    if !show_reactions {
        return;
    }
    for c in comments.iter_mut() {
        if c.get("kind").and_then(Value::as_str) == Some("review") {
            continue;
        }
        let Some(id) = c.get("id").and_then(Value::as_u64) else {
            continue;
        };
        if let Ok(reactions) = comment_reactions(client, owner, name, id)
            && let Some(obj) = c.as_object_mut()
        {
            obj.insert("reactions".to_owned(), json!(reactions));
        }
    }
}

/// Attachment display lines for a single comment's already-serialized
/// `assets` field — the shape this module's merge/render pipeline works
/// on (comments arrive as `Value`s, not the typed `Comment` struct, once
/// merged with synthesized review entries). Review entries carry no
/// `assets` field at all, so they naturally yield nothing here. Mirrors
/// [`crate::verbs::attachment_line`]'s `[file: <name>] <url>` format.
fn attachment_lines_from_value(c: &Value) -> Vec<String> {
    c.get("assets")
        .and_then(Value::as_array)
        .into_iter()
        .flatten()
        .filter_map(|a| {
            let name = a.get("name").and_then(Value::as_str).unwrap_or("?");
            let url = a.get("browser_download_url").and_then(Value::as_str)?;
            Some(format!("[file: {name}] {url}"))
        })
        .collect()
}

/// JSON form of [`attachment_lines_from_value`]'s data, for `--json`
/// output — same `{"name", "url"}` shape [`crate::verbs::attachment_json`]
/// produces from the typed struct.
fn attachment_json_from_value(c: &Value) -> Vec<Value> {
    c.get("assets")
        .and_then(Value::as_array)
        .into_iter()
        .flatten()
        .map(|a| {
            json!({
                "name": a.get("name"),
                "url": a.get("browser_download_url"),
            })
        })
        .collect()
}

/// Total comment count on an issue/PR, straight off the issue object.
/// Used both to plan `--tail`'s pagination and to report how many
/// comments sit outside whatever window ends up shown.
fn fetch_total(client: &Client, number: u64) -> Result<usize> {
    let (owner, name) = client.owner_repo()?;
    let issue = client
        .api()
        .issue_get_issue(owner, name, index(number)?)
        .send()?;
    Ok(issue
        .comments
        .and_then(|c| usize::try_from(c).ok())
        .unwrap_or(0))
}

/// Serialize a typed comment page back to the JSON `Value` shape the
/// merge + render pipeline works on (the structs serialize to the API
/// wire shape, so downstream field access is unchanged).
fn to_values<T: serde::Serialize>(items: Vec<T>) -> Result<Vec<Value>> {
    items
        .into_iter()
        .map(|c| serde_json::to_value(&c).map_err(Into::into))
        .collect()
}

/// Fetch a PR's review *bodies* and normalise them to the comment
/// shape so they merge alongside issue-thread comments.
///
/// Review summaries live in the `pulls/<n>/reviews` object, not the
/// issues/comments thread, so the plain comment listing misses them
/// — the review-body gap this fixes. Best-effort: returns empty on any
/// error — notably when `number` is an issue (no reviews endpoint) —
/// so callers degrade gracefully. Skips PENDING reviews (not yet
/// visible to others) and reviews with neither a body nor line
/// comments (a bare approval adds nothing to the thread). Deliberately
/// does NOT inline the per-line comments themselves: merging them into
/// this glance-first thread would spam anyone who just wants status.
/// `comments_count` carries a pointer to `pr reviews <n>` instead,
/// which prints the full per-line detail — see that verb
/// (`pr_reviews.rs`) for the exhaustive form. `created_at`
/// is synthesised from the review's `submitted_at` so the chronological
/// merge sorts uniformly; `kind:"review"` + the review `state` tag the
/// entry for display.
fn fetch_review_bodies(client: &Client, number: u64) -> Vec<Value> {
    let Ok((owner, name)) = client.owner_repo() else {
        return Vec::new();
    };
    let Ok(idx) = index(number) else {
        return Vec::new();
    };
    let reviews = client
        .api()
        .repo_list_pull_reviews(owner, name, idx)
        .send()
        .map(|(_, reviews)| reviews)
        .unwrap_or_default();
    reviews
        .into_iter()
        .filter_map(|r| {
            let state = r.state.as_deref().unwrap_or("").to_owned();
            if state == "PENDING" {
                return None;
            }
            let comments_count = r.comments_count.unwrap_or(0);
            if r.body.as_deref().unwrap_or("").trim().is_empty() && comments_count == 0 {
                return None;
            }
            let submitted = rfc3339(r.submitted_at);
            Some(json!({
                "id": r.id,
                "user": r.user,
                "created_at": submitted,
                "updated_at": submitted,
                "body": r.body,
                "html_url": r.html_url,
                "kind": "review",
                "state": state,
                "comments_count": comments_count,
            }))
        })
        .collect()
}

/// Merge issue-thread comments with review bodies and sort the
/// combined list chronologically by `created_at`. ISO-8601 timestamps
/// sort lexicographically in time order, so a plain string compare is
/// correct; the sort is stable, so same-timestamp entries keep fetch
/// order.
fn merge_chronological(mut items: Vec<Value>, reviews: Vec<Value>) -> Vec<Value> {
    items.extend(reviews);
    items.sort_by(|a, b| {
        let ka = a.get("created_at").and_then(Value::as_str).unwrap_or("");
        let kb = b.get("created_at").and_then(Value::as_str).unwrap_or("");
        ka.cmp(kb)
    });
    items
}

/// Fetch the first page's worth of comments (existing behaviour).
fn fetch_head(client: &Client, number: u64, limit: u64) -> Result<Vec<Value>> {
    let (owner, name) = client.owner_repo()?;
    let (_, comments) = client
        .api()
        .issue_get_comments(
            owner,
            name,
            index(number)?,
            IssueGetCommentsQuery::default(),
        )
        .page_size(u32::try_from(limit).unwrap_or(u32::MAX))
        .send()?;
    to_values(comments)
}

/// Fetch the last `n` comments on an issue/PR in chronological order.
/// `total` (the thread's comment count, from [`fetch_total`]) drives the
/// pagination plan and is the caller's, not fetched again here.
///
/// Forgejo orders `/issues/<n>/comments` oldest-first and has no
/// `direction=desc` knob, so naive "page everything and slice" pages
/// from the WRONG end on long threads — the first 1000 comments
/// instead of the last `n`. Fix: use `total` to know how many exist,
/// then start paginating from the page that contains item
/// `total - n`. Work is bounded by `ceil(n/50) + 1` page fetches,
/// regardless of thread length.
fn fetch_tail(client: &Client, number: u64, n: usize, total: usize) -> Result<Vec<Value>> {
    if n == 0 || total == 0 {
        return Ok(Vec::new());
    }
    let (owner, name) = client.owner_repo()?;
    let idx = index(number)?;
    // Cap `n` at the actual total so the math below stays in range
    // when the caller asks for more comments than exist.
    let n = n.min(total);
    let page_size = usize::try_from(PAGE_SIZE).unwrap_or(usize::MAX);
    // 0-based index of the first comment we want; integer-divide to
    // get the 1-based page that contains it.
    let start_idx = total - n;
    let start_page = (start_idx / page_size) + 1;
    let last_page = (total - 1) / page_size + 1;
    let mut merged: Vec<Value> = Vec::with_capacity(n + page_size);
    for page in start_page..=last_page {
        let (_, arr) = client
            .api()
            .issue_get_comments(owner, name, idx, IssueGetCommentsQuery::default())
            .page(u32::try_from(page).unwrap_or(u32::MAX))
            .page_size(u32::try_from(PAGE_SIZE).unwrap_or(u32::MAX))
            .send()?;
        if arr.is_empty() {
            // Page came back empty — either we miscounted (comments
            // deleted between the issue GET and now) or upstream's
            // playing tricks. Stop rather than spin.
            break;
        }
        merged.extend(to_values(arr)?);
    }
    // The first fetched page contains items from `start_page` × 50
    // back; we overshoot by `start_idx % 50` items. Slice the tail
    // to exactly `n` (or fewer if the count shrank under us).
    let overshoot = merged.len().saturating_sub(n);
    Ok(merged.into_iter().skip(overshoot).collect())
}

/// Fetch comments at or after `since`, capped at `limit` (already
/// clamped to [`crate::verbs::MAX_LIMIT`] by the caller). No total exists
/// for a since-filtered query — Forgejo's API reports none — so this
/// uses the same over-fetch-by-one trick `timeline`'s `--limit` does:
/// ask for `limit + 1`, and a full extra row means there's more. Returns
/// `(comments, more)`, `more` a boolean rather than an exact count.
fn fetch_since(
    client: &Client,
    number: u64,
    since: OffsetDateTime,
    limit: u64,
) -> Result<(Vec<Value>, bool)> {
    let (owner, name) = client.owner_repo()?;
    let query = IssueGetCommentsQuery {
        since: Some(since),
        ..Default::default()
    };
    let fetch_limit = limit.saturating_add(1);
    let (_, comments) = client
        .api()
        .issue_get_comments(owner, name, index(number)?, query)
        .page_size(u32::try_from(fetch_limit).unwrap_or(u32::MAX))
        .send()?;
    let mut values = to_values(comments)?;
    let limit = usize::try_from(limit).unwrap_or(usize::MAX);
    let more = values.len() > limit;
    values.truncate(limit);
    Ok((values, more))
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Pure helper mirroring the page-arithmetic in `fetch_tail`:
    /// given a total comment count + requested tail size, return
    /// the (`start_page`, `last_page`) pair the network loop would
    /// walk. Lets us pin the pagination plan — the part that's
    /// easy to off-by-one — without touching the network.
    fn tail_plan(total: usize, n: usize) -> (usize, usize) {
        let n = n.min(total);
        let page_size = usize::try_from(PAGE_SIZE).unwrap_or(usize::MAX);
        let start_idx = total - n;
        let start_page = (start_idx / page_size) + 1;
        let last_page = (total - 1) / page_size + 1;
        (start_page, last_page)
    }

    #[test]
    fn tail_plan_small_thread() {
        // 5 total, tail 2 → page 1 covers everything; trim happens
        // via the merged.len() - n overshoot calculation, not pages.
        assert_eq!(tail_plan(5, 2), (1, 1));
    }

    #[test]
    fn tail_plan_exact_page_boundary() {
        // 50 total, tail 3 → all on page 1 (items 1..50).
        assert_eq!(tail_plan(50, 3), (1, 1));
    }

    #[test]
    fn tail_plan_crosses_page_boundary() {
        // 51 total, tail 3 → start_idx=48 lives on page 1, item 51
        // lives on page 2; fetch both.
        assert_eq!(tail_plan(51, 3), (1, 2));
    }

    #[test]
    fn tail_plan_large_thread_bounded_pages() {
        // 5000 total, tail 3 → start_idx=4997 lives on page 100,
        // last_page=100. ONE page fetch on a 5000-comment thread —
        // the whole point of swapping to count-then-page (vs the
        // old "page everything, then slice the wrong end").
        assert_eq!(tail_plan(5000, 3), (100, 100));
    }

    #[test]
    fn tail_plan_large_thread_spans_two_pages() {
        // 5000 total, tail 60 → start_idx=4940 on page 99, item 5000
        // on page 100. Two fetches even for n > PAGE_SIZE.
        assert_eq!(tail_plan(5000, 60), (99, 100));
    }

    #[test]
    fn tail_plan_n_exceeds_total() {
        // 5 total, tail 100 → cap n at total; same plan as the
        // small-thread case above.
        assert_eq!(tail_plan(5, 100), (1, 1));
    }

    #[test]
    fn merge_interleaves_reviews_by_timestamp() {
        // A review submitted between two comments must land between
        // them, not appended at the end — that's the whole fix.
        let comments = vec![
            json!({"created_at": "2026-06-29T01:00:00Z", "body": "c1"}),
            json!({"created_at": "2026-06-29T01:20:00Z", "body": "c2"}),
        ];
        let reviews =
            vec![json!({"created_at": "2026-06-29T01:10:00Z", "body": "r1", "kind": "review"})];
        let merged = merge_chronological(comments, reviews);
        let bodies: Vec<&str> = merged
            .iter()
            .map(|v| v.get("body").and_then(Value::as_str).unwrap())
            .collect();
        assert_eq!(bodies, vec!["c1", "r1", "c2"]);
    }

    #[test]
    fn truncation_note_silent_when_nothing_hidden() {
        assert_eq!(truncation_note(0, 0), None);
    }

    #[test]
    fn truncation_note_after_only_points_at_tail() {
        let note = truncation_note(0, 40).unwrap();
        assert!(note.contains("40"), "{note}");
        assert!(note.contains("--tail"), "{note}");
    }

    #[test]
    fn truncation_note_before_only_points_at_limit() {
        // Regression: this used to (wrongly) suggest `--tail` — the flag
        // that produced the very window you're already looking at when
        // more_before is nonzero. `--limit` is what actually reaches the
        // start of the thread.
        let note = truncation_note(12, 0).unwrap();
        assert!(note.contains("12"), "{note}");
        assert!(note.contains("earlier"), "{note}");
        assert!(note.contains("--limit"), "{note}");
    }

    #[test]
    fn truncation_note_both_sides_mentions_both_counts() {
        let note = truncation_note(3, 7).unwrap();
        assert!(note.contains('3') && note.contains('7'), "{note}");
    }

    #[test]
    fn merge_with_no_reviews_is_identity() {
        // Issues have no reviews → fetch_review_bodies returns empty →
        // the merge must leave the comment thread untouched.
        let comments = vec![
            json!({"created_at": "2026-06-29T01:00:00Z", "body": "c1"}),
            json!({"created_at": "2026-06-29T01:20:00Z", "body": "c2"}),
        ];
        let merged = merge_chronological(comments, vec![]);
        let bodies: Vec<&str> = merged
            .iter()
            .map(|v| v.get("body").and_then(Value::as_str).unwrap())
            .collect();
        assert_eq!(bodies, vec!["c1", "c2"]);
    }
}