use crate::interop::{SharedI32Buffer, SharedStats, SharedU8Buffer};
use libloading::Library;
use std::env;
use std::ffi::{CStr, CString};
use std::fs;
use std::os::raw::{c_char, c_int, c_uint};
use std::path::{Path, PathBuf};

type HsComputeStats = unsafe extern "C" fn(c_int, c_int, *mut SharedStats) -> c_int;
type HsSumSlice = unsafe extern "C" fn(*const c_int, usize) -> c_int;
type HsChecksumBytes = unsafe extern "C" fn(*const u8, usize) -> c_uint;
type HsMakeMessage = unsafe extern "C" fn(*const c_char, c_int, c_int) -> *mut c_char;
type HsMakeSequence = unsafe extern "C" fn(c_int, usize, *mut SharedI32Buffer) -> c_int;
type HsMakeBytePattern = unsafe extern "C" fn(u8, usize, *mut SharedU8Buffer) -> c_int;
type HsFreeString = unsafe extern "C" fn(*mut c_char);
type HsFreeI32Buffer = unsafe extern "C" fn(*mut c_int, usize, usize);
type HsFreeU8Buffer = unsafe extern "C" fn(*mut u8, usize, usize);
type HsInit = unsafe extern "C" fn(*mut c_int, *mut *mut *mut c_char);
type HsExit = unsafe extern "C" fn();

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct DemoArgs {
    pub name: String,
    pub left: i32,
    pub right: i32,
    pub library_path: Option<String>,
}

pub fn run_haskell_demo(args: &DemoArgs) -> Result<String, String> {
    let library_path = resolve_library_path(args.library_path.as_deref())?;
    let library = unsafe { Library::new(&library_path) }
        .map_err(|error| format!("failed to load {}: {error}", library_path.display()))?;
    let runtime = HaskellRuntime::start()?;

    let output = load_and_run(&library_path, &library, args);

    drop(runtime);
    output
}

struct HaskellRuntime {
    _rts_library: Library,
    hs_exit: HsExit,
}

impl HaskellRuntime {
    fn start() -> Result<Self, String> {
        let rts_library_path = resolve_rts_library_path()?;
        let rts_library = unsafe { Library::new(&rts_library_path) }.map_err(|error| {
            format!(
                "failed to load GHC RTS library {}: {error}",
                rts_library_path.display()
            )
        })?;
        let hs_init: HsInit = unsafe {
            *rts_library
                .get(b"hs_init\0")
                .map_err(|error| format!("failed to load hs_init: {error}"))?
        };
        let hs_exit: HsExit = unsafe {
            *rts_library
                .get(b"hs_exit\0")
                .map_err(|error| format!("failed to load hs_exit: {error}"))?
        };
        let mut argc: c_int = 1;
        let program_name = CString::new("integrations-hs-runtime")
            .map_err(|_| "failed to create runtime program name".to_string())?;
        let mut argv = vec![program_name.as_ptr() as *mut c_char, std::ptr::null_mut()];
        let mut argv_ptr = argv.as_mut_ptr();

        unsafe {
            hs_init(&mut argc, &mut argv_ptr);
        }

        Ok(Self {
            _rts_library: rts_library,
            hs_exit,
        })
    }
}

impl Drop for HaskellRuntime {
    fn drop(&mut self) {
        unsafe {
            (self.hs_exit)();
        }
    }
}

fn load_and_run(library_path: &Path, library: &Library, args: &DemoArgs) -> Result<String, String> {
    let compute_stats: HsComputeStats = unsafe {
        *library
            .get(b"hs_compute_stats\0")
            .map_err(|error| format!("failed to load hs_compute_stats: {error}"))?
    };
    let sum_slice: HsSumSlice = unsafe {
        *library
            .get(b"hs_sum_slice\0")
            .map_err(|error| format!("failed to load hs_sum_slice: {error}"))?
    };
    let checksum_bytes: HsChecksumBytes = unsafe {
        *library
            .get(b"hs_checksum_bytes\0")
            .map_err(|error| format!("failed to load hs_checksum_bytes: {error}"))?
    };
    let make_message: HsMakeMessage = unsafe {
        *library
            .get(b"hs_make_message\0")
            .map_err(|error| format!("failed to load hs_make_message: {error}"))?
    };
    let make_sequence: HsMakeSequence = unsafe {
        *library
            .get(b"hs_make_sequence\0")
            .map_err(|error| format!("failed to load hs_make_sequence: {error}"))?
    };
    let make_byte_pattern: HsMakeBytePattern = unsafe {
        *library
            .get(b"hs_make_byte_pattern\0")
            .map_err(|error| format!("failed to load hs_make_byte_pattern: {error}"))?
    };
    let free_string: HsFreeString = unsafe {
        *library
            .get(b"hs_free_string\0")
            .map_err(|error| format!("failed to load hs_free_string: {error}"))?
    };
    let free_i32_buffer: HsFreeI32Buffer = unsafe {
        *library
            .get(b"hs_free_i32_buffer\0")
            .map_err(|error| format!("failed to load hs_free_i32_buffer: {error}"))?
    };
    let free_u8_buffer: HsFreeU8Buffer = unsafe {
        *library
            .get(b"hs_free_u8_buffer\0")
            .map_err(|error| format!("failed to load hs_free_u8_buffer: {error}"))?
    };

    let mut stats = SharedStats::default();
    let status = unsafe { compute_stats(args.left, args.right, &mut stats) };
    if status != 0 {
        return Err(format!("hs_compute_stats returned status {status}"));
    }

    let name = CString::new(args.name.replace('\0', "?"))
        .map_err(|_| "failed to prepare demo name".to_string())?;
    let message_ptr = unsafe { make_message(name.as_ptr(), args.left, args.right) };
    if message_ptr.is_null() {
        return Err("hs_make_message returned a null pointer".to_string());
    }

    let message = unsafe { CStr::from_ptr(message_ptr) }
        .to_string_lossy()
        .into_owned();
    unsafe {
        free_string(message_ptr);
    }

    let sample_values: [c_int; 4] = [2, 4, 6, 8];
    let slice_sum = unsafe { sum_slice(sample_values.as_ptr(), sample_values.len()) };
    let sample_bytes: [u8; 4] = [72, 0, 105, 255];
    let byte_checksum = unsafe { checksum_bytes(sample_bytes.as_ptr(), sample_bytes.len()) };

    let mut sequence_buffer = SharedI32Buffer::default();
    let sequence_status = unsafe { make_sequence(args.left, 5, &mut sequence_buffer) };
    if sequence_status != 0 {
        return Err(format!("hs_make_sequence returned status {sequence_status}"));
    }

    let sequence_values = read_i32_buffer(&sequence_buffer)?;
    unsafe {
        free_i32_buffer(
            sequence_buffer.ptr,
            sequence_buffer.len,
            sequence_buffer.cap,
        );
    }

    let byte_seed = normalize_byte_seed(args.left);
    let mut byte_buffer = SharedU8Buffer::default();
    let byte_status = unsafe { make_byte_pattern(byte_seed, 6, &mut byte_buffer) };
    if byte_status != 0 {
        return Err(format!("hs_make_byte_pattern returned status {byte_status}"));
    }

    let returned_bytes = read_u8_buffer(&byte_buffer)?;
    unsafe {
        free_u8_buffer(byte_buffer.ptr, byte_buffer.len, byte_buffer.cap);
    }

    Ok(format!(
        "Rust -> Haskell demo\nLibrary: {}\nInputs: name={}, left={}, right={}\nStats from Haskell: total={}, product={}, gap={}\nMessage from Haskell: {}\nSlice sent to Haskell: {:?}\nHaskell summed slice to: {}\nVector returned from Haskell: {:?}\nByte slice sent to Haskell: {:?}\nHaskell checksummed bytes to: {}\nByte buffer returned from Haskell: {:?}",
        library_path.display(),
        args.name,
        args.left,
        args.right,
        stats.total,
        stats.product,
        stats.gap,
        message,
        sample_values,
        slice_sum,
        sequence_values,
        sample_bytes,
        byte_checksum,
        returned_bytes,
    ))
}

fn read_i32_buffer(buffer: &SharedI32Buffer) -> Result<Vec<c_int>, String> {
    if buffer.ptr.is_null() {
        if buffer.len == 0 {
            return Ok(Vec::new());
        }
        return Err("received a null buffer pointer with a non-zero length".to_string());
    }

    let values = unsafe { std::slice::from_raw_parts(buffer.ptr, buffer.len) };
    Ok(values.to_vec())
}

fn read_u8_buffer(buffer: &SharedU8Buffer) -> Result<Vec<u8>, String> {
    if buffer.ptr.is_null() {
        if buffer.len == 0 {
            return Ok(Vec::new());
        }
        return Err("received a null byte buffer pointer with a non-zero length".to_string());
    }

    let values = unsafe { std::slice::from_raw_parts(buffer.ptr, buffer.len) };
    Ok(values.to_vec())
}

fn normalize_byte_seed(value: i32) -> u8 {
    value.rem_euclid(256) as u8
}

fn resolve_library_path(explicit_path: Option<&str>) -> Result<PathBuf, String> {
    if let Some(path) = explicit_path {
        return Ok(PathBuf::from(path));
    }

    if let Ok(path) = env::var("HASKELL_FOREIGN_LIB") {
        return Ok(PathBuf::from(path));
    }

    let dist_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
        .join("haskell")
        .join("dist-newstyle");
    let mut matches = Vec::new();
    collect_matching_libraries(&dist_dir, &mut matches)?;
    matches.sort();

    matches.into_iter().next().ok_or_else(|| {
        "could not find the Haskell foreign library under haskell/dist-newstyle; run `make haskell-build` first or pass an explicit path".to_string()
    })
}

fn resolve_rts_library_path() -> Result<PathBuf, String> {
    if let Ok(path) = env::var("GHC_RTS_LIB") {
        return Ok(PathBuf::from(path));
    }

    let libdir = if let Ok(path) = env::var("GHC_LIBDIR") {
        PathBuf::from(path)
    } else {
        let output = std::process::Command::new("ghc")
            .arg("--print-libdir")
            .output()
            .map_err(|error| format!("failed to run `ghc --print-libdir`: {error}"))?;
        if !output.status.success() {
            return Err("`ghc --print-libdir` did not exit successfully".to_string());
        }
        PathBuf::from(String::from_utf8_lossy(&output.stdout).trim())
    };

    let mut matches = Vec::new();
    collect_matching_rts_libraries(&libdir, &mut matches)?;
    matches.sort_by_key(|path| rts_priority(path));
    matches
        .into_iter()
        .next()
        .ok_or_else(|| format!("could not find a GHC RTS library under {}", libdir.display()))
}

fn collect_matching_libraries(root: &Path, matches: &mut Vec<PathBuf>) -> Result<(), String> {
    if !root.exists() {
        return Ok(());
    }

    let entries = fs::read_dir(root)
        .map_err(|error| format!("failed to read {}: {error}", root.display()))?;
    for entry in entries {
        let entry = entry.map_err(|error| format!("failed to inspect {}: {error}", root.display()))?;
        let path = entry.path();
        if path.is_dir() {
            collect_matching_libraries(&path, matches)?;
            continue;
        }

        if is_haskell_foreign_library(&path) {
            matches.push(path);
        }
    }

    Ok(())
}

fn collect_matching_rts_libraries(root: &Path, matches: &mut Vec<PathBuf>) -> Result<(), String> {
    if !root.exists() {
        return Ok(());
    }

    let entries = fs::read_dir(root)
        .map_err(|error| format!("failed to read {}: {error}", root.display()))?;
    for entry in entries {
        let entry = entry.map_err(|error| format!("failed to inspect {}: {error}", root.display()))?;
        let path = entry.path();
        if path.is_dir() {
            collect_matching_rts_libraries(&path, matches)?;
            continue;
        }

        if is_rts_library(&path) {
            matches.push(path);
        }
    }

    Ok(())
}

fn is_haskell_foreign_library(path: &Path) -> bool {
    let Some(file_name) = path.file_name().and_then(|value| value.to_str()) else {
        return false;
    };

    let is_library = file_name.ends_with(".so")
        || file_name.ends_with(".dylib")
        || file_name.ends_with(".dll");

    is_library && file_name.contains("interop_hs")
}

fn is_rts_library(path: &Path) -> bool {
    let Some(file_name) = path.file_name().and_then(|value| value.to_str()) else {
        return false;
    };

    path.extension().and_then(|ext| ext.to_str()) == Some("so")
        && file_name.starts_with("libHSrts-")
}

fn rts_priority(path: &Path) -> (u8, String) {
    let file_name = path
        .file_name()
        .and_then(|value| value.to_str())
        .unwrap_or_default()
        .to_string();

    let rank = if file_name.contains("_debug") {
        3
    } else if file_name.contains("_thr") {
        1
    } else {
        0
    };

    (rank, file_name)
}