import * as fs from "fs";
import path from "path";

interface LetterGroup {
  offset: number;
  length: number;
  packages: string[];
}

const INPUT = path.join(__dirname, "..", "src", "runtime", "cli", "add_completions.txt");
const OUTPUT = path.join(__dirname, "..", "src", "runtime", "cli", "add_completions.rs");

// Read and parse input file
const content = fs.readFileSync(INPUT, "utf8");
const packages = content
  .split("\n")
  .map(line => line.trim())
  .filter(line => line.length > 0)
  .sort();

// Group packages by first letter
const letterGroups = new Map<string, LetterGroup>();
let currentOffset = 0;
let maxListSize = 0;

for (const pkg of packages) {
  if (pkg.length === 0) continue;
  const firstLetter = pkg[0].toLowerCase();
  if (!letterGroups.has(firstLetter)) {
    letterGroups.set(firstLetter, {
      offset: currentOffset,
      length: 0,
      packages: [],
    });
  }
  const group = letterGroups.get(firstLetter)!;
  group.packages.push(pkg);
  group.length++;
  maxListSize = Math.max(maxListSize, group.length);
}

// Create a single buffer with all package data
const dataChunks: Buffer[] = [];
let totalUncompressed = 0;

// Store total package count first
const totalCountBuf = Buffer.alloc(4);
totalCountBuf.writeUInt32LE(packages.length, 0);
dataChunks.push(totalCountBuf);
totalUncompressed += 4;

// Then all packages with length prefixes
for (const pkg of packages) {
  const lenBuf = Buffer.alloc(2);
  lenBuf.writeUInt16LE(pkg.length, 0);
  dataChunks.push(lenBuf);
  dataChunks.push(Buffer.from(pkg, "utf8"));
  totalUncompressed += 2 + pkg.length;
}

const uncompressedData = Buffer.concat(dataChunks);

// Compress with zstd (level 1, matching the old `zstd -1` CLI invocation)
const compressedData = Bun.zstdCompressSync(uncompressedData, { level: 1 });

// Calculate compression ratio
const totalCompressed = compressedData.length;
const ratio = ((totalCompressed / totalUncompressed) * 100).toFixed(1);

console.log("\nCompression statistics:");
console.log(`Uncompressed size: ${totalUncompressed} bytes`);
console.log(`Compressed size: ${totalCompressed} bytes`);
console.log(`Compression ratio: ${ratio}%`);

// Generate index entries
const letters = "abcdefghijklmnopqrstuvwxyz";
const indexEntries: string[] = [];
let offset = 0;
for (const letter of letters) {
  const group = letterGroups.get(letter);
  const len = group?.length ?? 0;
  indexEntries.push(`    (${offset}, ${len}), // ${letter}`);
  offset += len;
}

// Split the compressed blob into 16-byte rows for readability
const blobLines: string[] = [];
for (let i = 0; i < compressedData.length; i += 16) {
  const row = [...compressedData.slice(i, i + 16)].join(", ");
  blobLines.push(`    ${row},`);
}

const out = `// Auto-generated by misctools/generate-add-completions.ts. Do not edit.
//
// Regenerate after editing src/runtime/cli/add_completions.txt:
//
//   bun misctools/generate-add-completions.ts
//
// Compressing the completions list saves about 100 KB of binary size.

use bun_core::Once;

#[repr(u8)]
#[derive(Copy, Clone, Eq, PartialEq)]
pub(crate) enum FirstLetter {
${[...letters].map(l => `    ${l.toUpperCase()} = b'${l}',`).join("\n")}
}

/// Largest per-letter package list length.
pub(crate) const BIGGEST_LIST: usize = ${maxListSize};

const UNCOMPRESSED_SIZE: usize = ${totalUncompressed};

/// (offset, length) into the decompressed package list for each letter a-z.
const INDEX: [(usize, usize); 26] = [
${indexEntries.join("\n")}
];

static COMPRESSED_DATA: &[u8] = &[
${blobLines.join("\n")}
];

struct Table {
    _decompressed: Vec<u8>,
    packages: Vec<&'static [u8]>,
}

static TABLE: Once<Table> = <Once<Table>>::new();

fn build_table() -> Table {
    let decompressed = bun_zstd::decompress_alloc(COMPRESSED_DATA)
        .expect("add_completions: zstd decompress failed");
    debug_assert_eq!(decompressed.len(), UNCOMPRESSED_SIZE);

    // SAFETY: the decompressed Vec is moved into TABLE (a process-lifetime
    // Once) and never dropped or reallocated, so its storage is valid for
    // 'static. The package slices below borrow this storage.
    let data: &'static [u8] =
        unsafe { core::slice::from_raw_parts(decompressed.as_ptr(), decompressed.len()) };

    let total = u32::from_le_bytes([data[0], data[1], data[2], data[3]]) as usize;
    let mut packages: Vec<&'static [u8]> = Vec::with_capacity(total);
    let mut pos: usize = 4;
    for _ in 0..total {
        let len = u16::from_le_bytes([data[pos], data[pos + 1]]) as usize;
        pos += 2;
        packages.push(&data[pos..pos + len]);
        pos += len;
    }

    Table { _decompressed: decompressed, packages }
}

/// Decompress the package-name table. Idempotent.
pub fn init() {
    TABLE.get_or_init(build_table);
}

/// Returns the slice of package names beginning with \`letter\`.
pub(crate) fn get_packages(letter: FirstLetter) -> &'static [&'static [u8]] {
    let table = TABLE.get_or_init(build_table);
    let (offset, length) = INDEX[(letter as u8 - b'a') as usize];
    if length == 0 {
        return &[];
    }
    &table.packages[offset..offset + length]
}
`;

fs.writeFileSync(OUTPUT, out);
try {
  const { execSync } = await import("child_process");
  execSync(`rustfmt "${OUTPUT}"`, { stdio: "inherit" });
} catch {
  // rustfmt not available; committed output is already formatted reasonably
}

console.log(`\nGenerated ${OUTPUT} for ${packages.length} packages`);