telfax/src/document/pdf.rs

use crate::error::{FaxError, Result};
use crate::document::convert::{DocumentFormat, FaxDocument, Page};
use crate::config::FaxResolution;
use std::path::Path;
use std::process::Command;

/// Convert PDF to FaxDocument using Ghostscript.
pub fn pdf_to_fax_document(pdf_path: &Path, resolution: FaxResolution) -> Result<FaxDocument> {
    let dpi_arg = match resolution {
        FaxResolution::Standard => "204x98",
        FaxResolution::Fine => "204x196",
        FaxResolution::SuperFine => "204x392",
    };

    let tiff_path = pdf_path.with_extension("fax.tif");
    tracing::info!("Converting PDF {} to TIFF {}", pdf_path.display(), tiff_path.display());

    let output = Command::new("gs")
        .arg("-dBATCH")
        .arg("-dNOPAUSE")
        .arg("-q")
        .arg("-sDEVICE=tiffgray")
        .arg(format!("-r{}", dpi_arg))
        .arg(format!("-sOutputFile={}", tiff_path.display()))
        .arg(pdf_path)
        .output()
        .map_err(|e| FaxError::document(format!("Failed to run ghostscript: {}", e)))?;

    tracing::info!("Ghostscript exit status: {:?}", output.status);
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        let stdout = String::from_utf8_lossy(&output.stdout);
        tracing::error!("Ghostscript stderr: {}", stderr);
        tracing::error!("Ghostscript stdout: {}", stdout);
        return Err(FaxError::document(format!(
            "Ghostscript failed: exit code {:?}",
            output.status.code()
        )));
    }

    let tiff_data = std::fs::read(&tiff_path)?;
    let doc = tiff_to_fax_document(&tiff_data)?;

    std::fs::remove_file(&tiff_path).ok();

    Ok(doc)
}

/// Read TIFF-F and convert to FaxDocument with 1-bit pixel data.
pub fn tiff_to_fax_document(tiff_data: &[u8]) -> Result<FaxDocument> {
    use tiff::decoder::Decoder;
    use std::io::Cursor;

    let mut cursor = Cursor::new(tiff_data);
    let mut decoder = Decoder::new(&mut cursor)
        .map_err(|e| FaxError::document(format!("Failed to open TIFF: {}", e)))?;

    let mut pages = Vec::new();

    loop {
        let (width, height) = decoder.dimensions()
            .map_err(|e| FaxError::document(format!("Failed to get TIFF dimensions: {}", e)))?;

        let bytes_per_row = width.div_ceil(8) as usize;
        let mut pixels = vec![0u8; bytes_per_row * height as usize];

        let mut result = decoder.read_image()
            .map_err(|e| FaxError::document(format!("Failed to read TIFF image: {}", e)))?;

        // Convert to 1-bit packed format
        let buffer = result.as_buffer(0);
        let img_data = buffer.as_bytes();

        // Process each pixel - TIFF is grayscale (8-bit), convert to 1-bit
        for (i, &byte) in img_data.iter().enumerate() {
            let pixel_idx = i % width as usize;
            let row_idx = i / width as usize;
            let byte_idx = pixel_idx / 8;
            let bit_idx = 7 - (pixel_idx % 8);

            // WhiteIsZero: 0=white, 255=black
            // We want: 1=black, 0=white (MSB first)
            if byte < 128 {
                let idx = row_idx * bytes_per_row + byte_idx;
                if idx < pixels.len() {
                    pixels[idx] |= 1 << bit_idx;
                }
            }
        }

        // Clamp to A4 fax width (1728 pels). US Letter at 204 DPI = 1734.
        let fax_width = width.min(1728);

        // If wider than A4, re-encode pixels at the clamped width
        let (pixels, width_pels) = if width > 1728 {
            let bytes_per_row = fax_width.div_ceil(8) as usize;
            let mut out = vec![0u8; bytes_per_row * height as usize];
            for y in 0..height {
                for x in 0..fax_width {
                    // img_data is 8-bit grayscale, one byte per pixel
                    let src_pixel = img_data[(y * width + x) as usize];
                    if src_pixel < 128 {
                        let dst_byte = y as usize * bytes_per_row + (x as usize / 8);
                        let dst_bit = 7 - (x % 8);
                        out[dst_byte] |= 1 << dst_bit;
                    }
                }
            }
            (out, fax_width)
        } else {
            (pixels, width)
        };

        pages.push(Page {
            pixels,
            width_pels,
            rows: height,
        });

        // Try to advance to next page
        match decoder.next_image() {
            Ok(_) => continue,
            Err(_) => break,
        }
    }

    if pages.is_empty() {
        return Err(FaxError::document("TIFF contains no pages"));
    }

    Ok(FaxDocument {
        pages,
        format: DocumentFormat::Tiff,
    })
}