// Copyright lowRISC contributors.
// Licensed under the Apache License, Version 2.0, see LICENSE for details.
// SPDX-License-Identifier: Apache-2.0

use crate::util::parse_int::ParseInt;
use anyhow::{ensure, Result};
use std::fs::File;
use std::io::Read;
use std::path::{Path, PathBuf};
use thiserror::Error;

#[derive(Debug, Error)]
pub enum ImageError {
    #[error("Incomplete read: expected to read {0} bytes but read {1} bytes")]
    IncompleteRead(usize, usize),
}

#[derive(Debug)]
pub enum ImageChunk {
    Concat(PathBuf),
    Offset(PathBuf, usize),
}

#[derive(Debug, Default)]
pub struct ImageAssembler {
    pub size: usize,
    pub mirrored: bool,
    pub chunks: Vec<ImageChunk>,
}

impl ImageAssembler {
    /// Creates an `ImageAssembler` with a given `size` and mirroring parameters.
    pub fn with_params(size: usize, mirrored: bool) -> Self {
        ImageAssembler {
            size,
            mirrored,
            ..Default::default()
        }
    }

    /// Creates an `ImageAssembler` with default parameters for OpenTitan: a 1MiB image which is mirrored.
    pub fn new() -> Self {
        Self::with_params(0x100000, true)
    }

    /// Parse a list of strings into chunks to be assembled.
    /// Each string may be a filename or a filename@offset describing where in the assembled image the contents of the file should appear.
    /// The offset is an integer expressed in any of the bases accepted by [`ParseInt`].
    pub fn parse(&mut self, chunks: &[impl AsRef<str>]) -> Result<()> {
        for chunk in chunks {
            if let Some((file, offset)) = chunk.as_ref().split_once('@') {
                self.chunks.push(ImageChunk::Offset(
                    PathBuf::from(file),
                    usize::from_str(offset)?,
                ));
            } else {
                self.chunks
                    .push(ImageChunk::Concat(PathBuf::from(chunk.as_ref())));
            }
        }
        Ok(())
    }

    // Read a file into a buffer.  Ensure the entire file is read.
    fn read(path: &Path, buf: &mut [u8]) -> Result<usize> {
        let mut file = File::open(path)?;
        let len = file.metadata()?.len() as usize;
        let n = file.read(buf)?;
        ensure!(len == n, ImageError::IncompleteRead(len, n));
        Ok(n)
    }

    /// Assemble the image according to the parameters and parsed chunk specifications.
    pub fn assemble(&self) -> Result<Vec<u8>> {
        let size = if self.mirrored {
            self.size / 2
        } else {
            self.size
        };
        let mut image = vec![0xff; size];
        let mut pos = 0;
        for chunk in &self.chunks {
            match chunk {
                ImageChunk::Concat(path) => {
                    let n = Self::read(path, &mut image[pos..])?;
                    pos += n;
                }
                ImageChunk::Offset(path, offset) => {
                    let n = Self::read(path, &mut image[*offset..])?;
                    pos = offset + n;
                }
            }
        }
        if self.mirrored {
            image.extend_from_within(..size);
        }
        Ok(image)
    }
}

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

    fn testdata(s: &str) -> String {
        let mut result = "sw/host/opentitanlib/src/util/testdata/".to_string();
        result.push_str(s);
        result
    }

    #[test]
    fn test_assemble_concat() -> Result<()> {
        // Test image assembly by concatenation.
        let mut image = ImageAssembler::with_params(16, false);
        image.parse(&[testdata("hello.txt"), testdata("world.txt")])?;
        let data = image.assemble()?;
        assert_eq!(data, b"HelloWorld\xff\xff\xff\xff\xff\xff");
        Ok(())
    }

    #[test]
    fn test_assemble_offset() -> Result<()> {
        // Test image assembly by explicit offsets.
        let mut image = ImageAssembler::with_params(16, false);
        image.parse(&[
            testdata("hello.txt@0"),
            testdata("world.txt@0x8"),
        ])?;
        let data = image.assemble()?;
        assert_eq!(data, b"Hello\xff\xff\xffWorld\xff\xff\xff");
        Ok(())
    }

    #[test]
    fn test_assemble_mirrored() -> Result<()> {
        // Test image assembly with mirroring.
        let mut image = ImageAssembler::with_params(20, true);
        image.parse(&[testdata("hello.txt"), testdata("world.txt")])?;
        let data = image.assemble()?;
        assert_eq!(data, b"HelloWorldHelloWorld");
        Ok(())
    }

    #[test]
    fn test_assemble_mirrored_offset_error() -> Result<()> {
        // Test image assembly where one of the source files isn't read completely.
        let mut image = ImageAssembler::with_params(16, true);
        image.parse(&[
            testdata("hello.txt@0"),
            testdata("world.txt@0x5"),
        ])?;
        let err = image.assemble().unwrap_err();
        assert_eq!(
            err.to_string(),
            "Incomplete read: expected to read 5 bytes but read 3 bytes"
        );
        Ok(())
    }
}