//! `cargo run -p benilla-formats --example dbc_diff -- <DBC name>` — what the realm changed in one
//! table, by reading the copy the client wins *and* the copy it shadows and diffing them row by row.
//!
//! The chain mounts several `patch-*` archives, so a table the realm rewrote usually still has
//! 1.12's own file sitting underneath it ([`Chain::copies`] lists every copy, *ascending*
//! priority). A goldens figure that moved is then answerable without a reference install: which
//! ids arrived, which left, and which kept their id while changing a column.
//!
//! The baseline is the highest copy in a **stock** archive — `dbc.MPQ`, `patch.MPQ`, `patch-2` are
//! 1.12's own, and `patch-3` upwards are the realm's — so the diff reads "what OctoWoW changed
//! about 1.12", not "what the last patch changed about the one before it". `--base=<archive>` picks
//! another one; `--all` lists what every copy holds.
//!
//! The diff is schema-free. Both files' headers give `field_count`/`record_size`, field 0 is the id
//! by convention, and a row is compared as its raw 4-byte slots — so a column whose meaning we have
//! not decoded still shows up as "row N differs at slot K". Strings live in a separate block per
//! file, so a slot holding a string offset is reported as a difference only when the *text* differs.
use std::collections::{BTreeMap, BTreeSet};

use anyhow::{bail, Context, Result};

/// One file's rows, keyed by field 0, plus the strings each slot may point into.
struct Table {
    fields: usize,
    rows: BTreeMap<u32, Vec<u32>>,
    strings: Vec<u8>,
}

/// The archives 1.12 itself shipped; anything else in `Data` is the realm's.
const STOCK: [&str; 3] = ["dbc.MPQ", "patch.MPQ", "patch-2.MPQ"];

fn file_name(p: &std::path::Path) -> &str {
    p.file_name().and_then(|n| n.to_str()).unwrap_or("")
}

fn u32_at(b: &[u8], off: usize) -> u32 {
    u32::from_le_bytes([b[off], b[off + 1], b[off + 2], b[off + 3]])
}

fn read(bytes: &[u8]) -> Result<Table> {
    if bytes.len() < 20 || &bytes[..4] != b"WDBC" {
        bail!("not a WDBC file");
    }
    let (records, fields, recsize, strsize) = (
        u32_at(bytes, 4) as usize,
        u32_at(bytes, 8) as usize,
        u32_at(bytes, 12) as usize,
        u32_at(bytes, 16) as usize,
    );
    if recsize != fields * 4 {
        bail!("record size {recsize} is not {fields} 4-byte slots");
    }
    let body = 20 + records * recsize;
    let mut rows = BTreeMap::new();
    for i in 0..records {
        let at = 20 + i * recsize;
        let slots: Vec<u32> = (0..fields).map(|f| u32_at(bytes, at + f * 4)).collect();
        rows.insert(slots[0], slots);
    }
    let strings = bytes.get(body..body + strsize).unwrap_or_default().to_vec();
    Ok(Table {
        fields,
        rows,
        strings,
    })
}

impl Table {
    /// The string at `off`, for the slots that hold an offset into the string block.
    fn text(&self, off: u32) -> &str {
        let s = self.strings.get(off as usize..).unwrap_or_default();
        let end = s.iter().position(|&b| b == 0).unwrap_or(s.len());
        std::str::from_utf8(&s[..end]).unwrap_or("<utf8>")
    }

    /// Whether `off` plausibly names a non-empty string in this file's block. A numeric slot can
    /// hold a value that lands inside the block by coincidence, so require `off` to be a string
    /// *start* — preceded by the NUL that ended the one before it — which rejects almost all of
    /// them. A small id or a float's bit pattern can still slip through, so a reported string is a
    /// hint to check, never proof the slot is textual.
    fn is_text(&self, off: u32) -> bool {
        let i = off as usize;
        i != 0
            && i < self.strings.len()
            && self.strings.get(i - 1) == Some(&0)
            && !self.text(off).is_empty()
    }
}

fn main() -> Result<()> {
    let Some(data) = benilla_formats::wow_data() else {
        eprintln!("no install: set WOW_DATA");
        std::process::exit(1);
    };
    let mut args = std::env::args().skip(1);
    let name = args.next().unwrap_or_else(|| {
        eprintln!("usage: dbc_diff <DBC name> [slot…]   e.g. dbc_diff CreatureSoundData.dbc 27 28");
        std::process::exit(2);
    });
    let name = if name.contains('\\') {
        name
    } else {
        format!("DBFilesClient\\{name}")
    };
    // Report only these slots when given; otherwise every slot that differs.
    let rest: Vec<String> = args.collect();
    let base_arg = rest
        .iter()
        .find_map(|a| a.strip_prefix("--base=").map(str::to_string));
    let row_arg: Option<u32> = rest
        .iter()
        .find_map(|a| a.strip_prefix("--row=").and_then(|n| n.parse().ok()));
    let only: BTreeSet<usize> = rest.iter().filter_map(|a| a.parse().ok()).collect();

    let chain = benilla_formats::Chain::open(&data).context("chain opens")?;
    let copies = chain.copies(&name);
    if copies.is_empty() {
        bail!("{name} is in no archive");
    }
    println!("{name}");
    for (p, size) in &copies {
        println!("  {:>12} bytes  {}", size, p.display());
        let _ = size;
    }
    if copies.len() < 2 {
        println!("\nonly one copy — nothing underneath it to diff against");
        return Ok(());
    }

    let open = |p: &std::path::Path| -> Result<Table> {
        let a = benilla_mpq::Archive::open(p).with_context(|| format!("open {}", p.display()))?;
        read(&a.read_file(&name)?)
    };
    // `copies` is ascending priority, so the client reads the last one.
    let win = open(copies[copies.len() - 1].0)?;

    let base = match base_arg {
        Some(ref want) => copies
            .iter()
            .find(|(p, _)| file_name(p).eq_ignore_ascii_case(want))
            .with_context(|| format!("{want} holds no copy of {name}"))?,
        // The highest stock copy: 1.12's own last word on the table.
        None => copies
            .iter()
            .rev()
            .find(|(p, _)| STOCK.iter().any(|s| file_name(p).eq_ignore_ascii_case(s)))
            .unwrap_or(&copies[0]),
    };
    println!(
        "\ndiffing {} against {}",
        file_name(copies[copies.len() - 1].0),
        file_name(base.0)
    );
    let old = open(base.0)?;

    // `--row=N` prints that row of the winning copy and of the baseline, text slots as text: for
    // naming the thing behind an id a decoded catalog only gave a number for, and for reading a row
    // the realm *deleted*, which is only legible in the copy underneath.
    if let Some(want) = row_arg {
        let dump = |t: &Table, label: &str| match t.rows.get(&want) {
            Some(r) => {
                let cells: Vec<String> = r
                    .iter()
                    .enumerate()
                    .map(|(f, &v)| {
                        if t.is_text(v) {
                            format!("[{f}] {:?}", t.text(v))
                        } else {
                            format!("[{f}] {v}")
                        }
                    })
                    .collect();
                println!("{label} row {want}: {}", cells.join("  "));
            }
            None => println!("{label} has no row {want}"),
        };
        println!();
        dump(&win, "wins ");
        dump(&old, "under");
        return Ok(());
    }
    println!(
        "\nwins: {} rows x {} fields      under: {} rows x {} fields",
        win.rows.len(),
        win.fields,
        old.rows.len(),
        old.fields
    );
    if win.fields != old.fields {
        println!("!! the field count moved — every decoded column is suspect");
    }

    let added: Vec<u32> = win
        .rows
        .keys()
        .filter(|k| !old.rows.contains_key(k))
        .copied()
        .collect();
    let gone: Vec<u32> = old
        .rows
        .keys()
        .filter(|k| !win.rows.contains_key(k))
        .copied()
        .collect();
    println!("added {} ids, removed {} ids", added.len(), gone.len());
    let show = |label: &str, v: &[u32]| {
        if !v.is_empty() {
            println!(
                "  {label}: {:?}{}",
                &v[..v.len().min(20)],
                if v.len() > 20 { " …" } else { "" }
            );
        }
    };
    show("added", &added);
    show("removed", &gone);

    // Rows that kept their id and changed a column.
    let mut changed: Vec<(u32, Vec<usize>)> = Vec::new();
    let mut per_slot: BTreeMap<usize, usize> = BTreeMap::new();
    for (id, now) in &win.rows {
        let Some(was) = old.rows.get(id) else {
            continue;
        };
        let mut slots = Vec::new();
        for f in 0..now.len().min(was.len()) {
            if now[f] == was[f] {
                continue;
            }
            // A string slot differs only when the text does: the offsets are per file.
            if win.is_text(now[f]) && old.is_text(was[f]) && win.text(now[f]) == old.text(was[f]) {
                continue;
            }
            if only.is_empty() || only.contains(&f) {
                slots.push(f);
            }
        }
        if !slots.is_empty() {
            for &f in &slots {
                *per_slot.entry(f).or_default() += 1;
            }
            changed.push((*id, slots));
        }
    }
    println!("rows that kept their id and changed: {}", changed.len());
    if !per_slot.is_empty() {
        println!("  per slot: {per_slot:?}");
    }
    for (id, slots) in changed.iter().take(25) {
        let (now, was) = (&win.rows[id], &old.rows[id]);
        let detail: Vec<String> = slots
            .iter()
            .map(|&f| {
                if win.is_text(now[f]) || old.is_text(was[f]) {
                    format!("[{f}] {:?} -> {:?}", old.text(was[f]), win.text(now[f]))
                } else {
                    format!("[{f}] {} -> {}", was[f], now[f])
                }
            })
            .collect();
        println!("  id {id}: {}", detail.join(", "));
    }
    if changed.len() > 25 {
        println!("  … {} more", changed.len() - 25);
    }
    Ok(())
}