use std::ops;

use crate::IndexSet;
use rustpython_compiler_core::{
    CodeFlags, CodeObject, CodeUnit, ConstantData, InstrDisplayContext, Instruction, Label,
    Location, OpArg,
};

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct BlockIdx(pub u32);
impl BlockIdx {
    pub const NULL: BlockIdx = BlockIdx(u32::MAX);
    const fn idx(self) -> usize {
        self.0 as usize
    }
}
impl ops::Index<BlockIdx> for [Block] {
    type Output = Block;
    fn index(&self, idx: BlockIdx) -> &Block {
        &self[idx.idx()]
    }
}
impl ops::IndexMut<BlockIdx> for [Block] {
    fn index_mut(&mut self, idx: BlockIdx) -> &mut Block {
        &mut self[idx.idx()]
    }
}
impl ops::Index<BlockIdx> for Vec<Block> {
    type Output = Block;
    fn index(&self, idx: BlockIdx) -> &Block {
        &self[idx.idx()]
    }
}
impl ops::IndexMut<BlockIdx> for Vec<Block> {
    fn index_mut(&mut self, idx: BlockIdx) -> &mut Block {
        &mut self[idx.idx()]
    }
}

#[derive(Debug, Copy, Clone)]
pub struct InstructionInfo {
    pub instr: Instruction,
    pub arg: OpArg,
    pub target: BlockIdx,
    pub location: Location,
}

// TODO: look into using petgraph for handling blocks and stuff? it's heavier than this, but it
// might enable more analysis/optimizations
#[derive(Debug)]
pub struct Block {
    pub instructions: Vec<InstructionInfo>,
    pub next: BlockIdx,
}
impl Default for Block {
    fn default() -> Self {
        Block {
            instructions: Vec::new(),
            next: BlockIdx::NULL,
        }
    }
}

pub struct CodeInfo {
    pub flags: CodeFlags,
    pub posonlyarg_count: usize, // Number of positional-only arguments
    pub arg_count: usize,
    pub kwonlyarg_count: usize,
    pub source_path: String,
    pub first_line_number: usize,
    pub obj_name: String, // Name of the object that created this code object

    pub blocks: Vec<Block>,
    pub current_block: BlockIdx,
    pub constants: IndexSet<ConstantData>,
    pub name_cache: IndexSet<String>,
    pub varname_cache: IndexSet<String>,
    pub cellvar_cache: IndexSet<String>,
    pub freevar_cache: IndexSet<String>,
}
impl CodeInfo {
    pub fn finalize_code(mut self, optimize: u8) -> CodeObject {
        if optimize > 0 {
            self.dce();
        }

        let max_stackdepth = self.max_stackdepth();
        let cell2arg = self.cell2arg();

        let CodeInfo {
            flags,
            posonlyarg_count,
            arg_count,
            kwonlyarg_count,
            source_path,
            first_line_number,
            obj_name,

            mut blocks,
            current_block: _,
            constants,
            name_cache,
            varname_cache,
            cellvar_cache,
            freevar_cache,
        } = self;

        let mut instructions = Vec::new();
        let mut locations = Vec::new();

        let mut block_to_offset = vec![Label(0); blocks.len()];
        loop {
            let mut num_instructions = 0;
            for (idx, block) in iter_blocks(&blocks) {
                block_to_offset[idx.idx()] = Label(num_instructions as u32);
                for instr in &block.instructions {
                    num_instructions += instr.arg.instr_size()
                }
            }

            instructions.reserve_exact(num_instructions);
            locations.reserve_exact(num_instructions);

            let mut recompile_extended_arg = false;
            let mut next_block = BlockIdx(0);
            while next_block != BlockIdx::NULL {
                let block = &mut blocks[next_block];
                for info in &mut block.instructions {
                    let (op, arg, target) = (info.instr, &mut info.arg, info.target);
                    if target != BlockIdx::NULL {
                        let new_arg = OpArg(block_to_offset[target.idx()].0);
                        recompile_extended_arg |= new_arg.instr_size() != arg.instr_size();
                        *arg = new_arg;
                    }
                    let (extras, lo_arg) = arg.split();
                    locations.extend(std::iter::repeat(info.location).take(arg.instr_size()));
                    instructions.extend(
                        extras
                            .map(|byte| CodeUnit::new(Instruction::ExtendedArg, byte))
                            .chain([CodeUnit { op, arg: lo_arg }]),
                    );
                }
                next_block = block.next;
            }

            if !recompile_extended_arg {
                break;
            }

            instructions.clear();
            locations.clear()
        }

        CodeObject {
            flags,
            posonlyarg_count,
            arg_count,
            kwonlyarg_count,
            source_path,
            first_line_number,
            obj_name,

            max_stackdepth,
            instructions: instructions.into_boxed_slice(),
            locations: locations.into_boxed_slice(),
            constants: constants.into_iter().collect(),
            names: name_cache.into_iter().collect(),
            varnames: varname_cache.into_iter().collect(),
            cellvars: cellvar_cache.into_iter().collect(),
            freevars: freevar_cache.into_iter().collect(),
            cell2arg,
        }
    }

    fn cell2arg(&self) -> Option<Box<[isize]>> {
        if self.cellvar_cache.is_empty() {
            return None;
        }

        let total_args = self.arg_count
            + self.kwonlyarg_count
            + self.flags.contains(CodeFlags::HAS_VARARGS) as usize
            + self.flags.contains(CodeFlags::HAS_VARKEYWORDS) as usize;

        let mut found_cellarg = false;
        let cell2arg = self
            .cellvar_cache
            .iter()
            .map(|var| {
                self.varname_cache
                    .get_index_of(var)
                    // check that it's actually an arg
                    .filter(|i| *i < total_args)
                    .map_or(-1, |i| {
                        found_cellarg = true;
                        i as isize
                    })
            })
            .collect::<Box<[_]>>();

        if found_cellarg {
            Some(cell2arg)
        } else {
            None
        }
    }

    fn dce(&mut self) {
        for block in &mut self.blocks {
            let mut last_instr = None;
            for (i, ins) in block.instructions.iter().enumerate() {
                if ins.instr.unconditional_branch() {
                    last_instr = Some(i);
                    break;
                }
            }
            if let Some(i) = last_instr {
                block.instructions.truncate(i + 1);
            }
        }
    }

    fn max_stackdepth(&self) -> u32 {
        let mut maxdepth = 0u32;
        let mut stack = Vec::with_capacity(self.blocks.len());
        let mut startdepths = vec![u32::MAX; self.blocks.len()];
        startdepths[0] = 0;
        stack.push(BlockIdx(0));
        const DEBUG: bool = false;
        'process_blocks: while let Some(block) = stack.pop() {
            let mut depth = startdepths[block.idx()];
            if DEBUG {
                eprintln!("===BLOCK {}===", block.0);
            }
            let block = &self.blocks[block];
            for i in &block.instructions {
                let instr = &i.instr;
                let effect = instr.stack_effect(i.arg, false);
                if DEBUG {
                    let display_arg = if i.target == BlockIdx::NULL {
                        i.arg
                    } else {
                        OpArg(i.target.0)
                    };
                    let instr_display = instr.display(display_arg, self);
                    eprint!("{instr_display}: {depth} {effect:+} => ");
                }
                let new_depth = depth.checked_add_signed(effect).unwrap();
                if DEBUG {
                    eprintln!("{new_depth}");
                }
                if new_depth > maxdepth {
                    maxdepth = new_depth
                }
                // we don't want to worry about Break/Continue, they use unwinding to jump to
                // their targets and as such the stack size is taken care of in frame.rs by setting
                // it back to the level it was at when SetupLoop was run
                if i.target != BlockIdx::NULL
                    && !matches!(
                        instr,
                        Instruction::Continue { .. } | Instruction::Break { .. }
                    )
                {
                    let effect = instr.stack_effect(i.arg, true);
                    let target_depth = depth.checked_add_signed(effect).unwrap();
                    if target_depth > maxdepth {
                        maxdepth = target_depth
                    }
                    stackdepth_push(&mut stack, &mut startdepths, i.target, target_depth);
                }
                depth = new_depth;
                if instr.unconditional_branch() {
                    continue 'process_blocks;
                }
            }
            stackdepth_push(&mut stack, &mut startdepths, block.next, depth);
        }
        if DEBUG {
            eprintln!("DONE: {maxdepth}");
        }
        maxdepth
    }
}

impl InstrDisplayContext for CodeInfo {
    type Constant = ConstantData;
    fn get_constant(&self, i: usize) -> &ConstantData {
        &self.constants[i]
    }
    fn get_name(&self, i: usize) -> &str {
        self.name_cache[i].as_ref()
    }
    fn get_varname(&self, i: usize) -> &str {
        self.varname_cache[i].as_ref()
    }
    fn get_cellname(&self, i: usize) -> &str {
        self.cellvar_cache
            .get_index(i)
            .unwrap_or_else(|| &self.freevar_cache[i - self.cellvar_cache.len()])
            .as_ref()
    }
}

fn stackdepth_push(
    stack: &mut Vec<BlockIdx>,
    startdepths: &mut [u32],
    target: BlockIdx,
    depth: u32,
) {
    let block_depth = &mut startdepths[target.idx()];
    if *block_depth == u32::MAX || depth > *block_depth {
        *block_depth = depth;
        stack.push(target);
    }
}

fn iter_blocks(blocks: &[Block]) -> impl Iterator<Item = (BlockIdx, &Block)> + '_ {
    let mut next = BlockIdx(0);
    std::iter::from_fn(move || {
        if next == BlockIdx::NULL {
            return None;
        }
        let (idx, b) = (next, &blocks[next]);
        next = b.next;
        Some((idx, b))
    })
}