use crate::module::{FunctionCode, optimize_function_code};
use crate::{ParseError, ParserOptions, Result, conversion};
use alloc::sync::Arc;
use alloc::vec::Vec;
use core::ops::Range;
use tinywasm_types::ValueCounts;
use wasmparser::{FuncValidatorAllocations, ValidatorResources};

pub(crate) enum FunctionBodyInput<'a> {
    Borrowed(wasmparser::FunctionBody<'a>),
    Owned(OwnedFunctionBody),
}

pub(crate) struct OwnedFunctionBody {
    // A deferred stream code section is copied once, then shared by all queued
    // function jobs from that section.
    pub section_bytes: Arc<[u8]>,
    pub body_range: Range<usize>,
    pub body_offset: usize,
}

pub(crate) struct PendingFunction<'a> {
    pub ordinal: usize,
    pub results: ValueCounts,
    pub ty_idx: u32,
    pub func_to_validate: Option<wasmparser::FuncToValidate<ValidatorResources>>,
    pub body: FunctionBodyInput<'a>,
}

pub(crate) const MIN_FUNCTIONS: usize = 8;
const MIN_CODE_SECTION_BYTES: usize = 32 * 1024;
const MIN_FUNCTION_BODY_BYTES: usize = 4;

pub(crate) fn should_parallelize_function(body_len: usize) -> bool {
    body_len >= MIN_FUNCTION_BODY_BYTES
}

pub(crate) fn should_use_parallel(options: &ParserOptions, num_functions: usize, code_section_bytes: usize) -> bool {
    if num_functions < MIN_FUNCTIONS || code_section_bytes < MIN_CODE_SECTION_BYTES {
        return false;
    }

    worker_count(options, num_functions) > 1
}

fn worker_count(options: &ParserOptions, num_functions: usize) -> usize {
    let requested = options
        .parser_threads()
        .unwrap_or_else(|| std::thread::available_parallelism().map(|n| n.get()).unwrap_or(1))
        .max(1);

    requested.min(num_functions).max(1)
}

fn body_len(body: &FunctionBodyInput<'_>) -> usize {
    match body {
        FunctionBodyInput::Borrowed(func) => func.as_bytes().len(),
        FunctionBodyInput::Owned(body) => body.body_range.len(),
    }
}

fn process_function_job(
    job: PendingFunction<'_>,
    metadata: &crate::visit::ModuleMetadata,
    options: &ParserOptions,
    imported_func_count: usize,
    imported_memory_count: u32,
) -> Result<(usize, FunctionCode)> {
    let validator = job.func_to_validate.map(|func| func.into_validator(FuncValidatorAllocations::default()));
    let (code, _, _) = match job.body {
        FunctionBodyInput::Borrowed(func) => {
            conversion::convert_module_code(func, validator, Default::default(), metadata, job.ty_idx)?
        }
        FunctionBodyInput::Owned(body) => {
            let reader = wasmparser::BinaryReader::new(&body.section_bytes[body.body_range], body.body_offset);
            let func = wasmparser::FunctionBody::new(reader);
            conversion::convert_module_code(func, validator, Default::default(), metadata, job.ty_idx)?
        }
    };

    let code = optimize_function_code(
        code,
        options,
        job.results,
        (imported_func_count + job.ordinal) as u32,
        imported_memory_count,
    )?;

    Ok((job.ordinal, code))
}

pub(crate) fn process_pending(
    pending: Vec<PendingFunction<'_>>,
    metadata: &crate::visit::ModuleMetadata,
    options: &ParserOptions,
    imported_func_count: usize,
    imported_memory_count: u32,
) -> Result<Vec<FunctionCode>> {
    let (small_jobs, large_jobs): (Vec<_>, Vec<_>) =
        pending.into_iter().partition(|job| !should_parallelize_function(body_len(&job.body)));

    let mut codes = small_jobs
        .into_iter()
        .map(|job| process_function_job(job, metadata, options, imported_func_count, imported_memory_count))
        .collect::<Result<Vec<_>>>()?;

    let num_workers = worker_count(options, large_jobs.len());
    if num_workers == 1 {
        codes.extend(
            large_jobs
                .into_iter()
                .map(|job| process_function_job(job, metadata, options, imported_func_count, imported_memory_count))
                .collect::<Result<Vec<_>>>()?,
        );
    } else {
        let chunk_size = large_jobs.len().div_ceil(num_workers);
        let chunks = {
            let mut chunks = Vec::with_capacity(num_workers);
            let mut iter = large_jobs.into_iter();
            while let Some(first) = iter.next() {
                let mut chunk = alloc::vec![first];
                for _ in 1..chunk_size {
                    match iter.next() {
                        Some(job) => chunk.push(job),
                        None => break,
                    }
                }
                chunks.push(chunk);
            }
            chunks
        };

        let results: Vec<Result<(usize, FunctionCode)>> = std::thread::scope(|s| {
            let handles: Vec<_> = chunks
                .into_iter()
                .map(|chunk| {
                    s.spawn(move || {
                        chunk
                            .into_iter()
                            .map(|job| {
                                process_function_job(job, metadata, options, imported_func_count, imported_memory_count)
                            })
                            .collect::<Vec<_>>()
                    })
                })
                .collect();

            handles
                .into_iter()
                .flat_map(|handle| match handle.join() {
                    Ok(results) => results,
                    Err(_) => alloc::vec![Err(ParseError::Other("worker thread panicked".into()))],
                })
                .collect()
        });

        for result in results {
            codes.push(result?);
        }
    }

    codes.sort_by_key(|(ordinal, _)| *ordinal);
    Ok(codes.into_iter().map(|(_, code)| code).collect())
}