mopdepth

# mopdepth

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A fast BAM/CRAM depth calculation tool written in Crystal, inspired by [mosdepth](https://github.com/brentp/mosdepth).

**This is an experiment to see if well-known tools can be ported to Crystal using “vibe coding”.**

## Features

- Fast depth calculation for BAM/CRAM files
- Multiple processing modes (fast mode, fragment mode, CIGAR-based)
- Per-base and region-based depth analysis
- BED file support for custom regions
- Window-based analysis
- Comprehensive filtering options (MAPQ, fragment length, flags)

## Installation

### Prerequisites

- Crystal
- hts-lib (for BAM/CRAM support)

### Build from source

```bash
git clone https://github.com/kojix2/mopdepth
cd mopdepth
shards install
shards build --release
```

## Usage

```bash
./mopdepth [options] <prefix> <BAM-or-CRAM>
```

### Basic example

```bash
./mopdepth output sample.bam
```

### Options

- `-t, --threads THREADS`: BAM decompression threads
- `-c, --chrom CHROM`: Restrict to chromosome
- `-b, --by BY`: BED file or numeric window size
- `-n, --no-per-base`: Skip per-base output
- `-Q, --mapq MAPQ`: MAPQ threshold
- `-l, --min-frag-len MIN`: Minimum fragment length
- `-u, --max-frag-len MAX`: Maximum fragment length
- `-x, --fast-mode`: Fast mode (read start/end positions only)
- `-a, --fragment-mode`: Count full fragment (proper pairs only)
- `-m, --use-median`: Use median for region stats instead of mean
- `-q, --quantize QUANTIZE`: Write quantized output (for example, `0:1:4:`)
- `-T, --thresholds THRESHOLDS`: Comma-separated thresholds for region coverage
- `-F, --flag FLAG`: Exclude reads with FLAG bits set
- `-i, --include-flag FLAG`: Include only reads with FLAG bits set
- `-R, --read-groups GROUPS`: Comma-separated read group IDs
- `-M, --mos`: Use mosdepth-compatible filenames (mosdepth.*); default is mopdepth.*
- `-v, --version`: Show version
- `-h, --help`: Show help message

### Processing modes

- **Default mode**: CIGAR-based depth calculation (most accurate)
- **Fast mode** (`-x`): Uses read start/end positions (faster but less accurate)
- **Fragment mode** (`-a`): Counts full fragments for paired-end reads

**Note**: Fast mode and fragment mode cannot be used together.

### Output files

- Summary: `<prefix>.(mopdepth|mosdepth).summary.txt`
- Per-base: `<prefix>.per-base.bed.gz` (unless `-n`)
- Global dist: `<prefix>.(mopdepth|mosdepth).global.dist.txt`
- Regions: `<prefix>.regions.bed.gz` (when `--by`)
- Region dist: `<prefix>.(mopdepth|mosdepth).region.dist.txt` (when `--by`)
- Quantized: `<prefix>.quantized.bed.gz` (when `--quantize`)
- Thresholds: `<prefix>.thresholds.bed.gz` (when `--thresholds` and `--by`)

By default, files are named with the `mopdepth.*` label. Use `-M/--mos` to switch to `mosdepth.*`.

### Summary file format

The summary file contains the following columns:

- `chrom`: Chromosome name
- `length`: Chromosome length
- `bases`: Total depth (sum of all depths)
- `mean`: Mean depth
- `min`: Minimum depth
- `max`: Maximum depth

## Examples

### Basic depth calculation

```bash
./mopdepth output sample.bam
```

### With BED regions

```bash
./mopdepth -b regions.bed output sample.bam
```

### Window-based analysis (1kb windows)

```bash
./mopdepth -b 1000 output sample.bam
```

### Fast mode with MAPQ filtering

```bash
./mopdepth -x -Q 20 output sample.bam
```

### Fragment mode for paired-end data

```bash
./mopdepth -a -l 100 -u 1000 output sample.bam
```

## License

MIT License