use fix_common::StringId;
use fix_error::Error;
use gc_arena::{Gc, RefLock};
use smallvec::SmallVec;

use crate::value::NixType;
use crate::{
    AttrKeyData, AttrSet, BytecodeReader, List, OperandData, Step, StrictValue, Value,
    VmRuntimeCtx, VmRuntimeCtxExt,
};

impl<'gc> crate::Vm<'gc> {
    #[inline(always)]
    pub(crate) fn op_make_attrs(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let count = reader.read_u32() as usize;
        let mut entries: SmallVec<[AttrEntry; 4]> = SmallVec::with_capacity(count);
        for _ in 0..count {
            let key = reader.read_attr_key_data(ctx);
            let val = reader.read_operand_data(ctx);
            let _span_id = reader.read_u32();
            entries.push(AttrEntry { key, val });
        }
        let mut kv: SmallVec<[(crate::StringId, Value); 4]> = SmallVec::with_capacity(count);
        for entry in &entries {
            let key_sid = match &entry.key {
                AttrKeyData::Static(sid) => *sid,
                AttrKeyData::Dynamic(op) => {
                    let v = op.resolve(mc, self);
                    v.as_inline::<crate::StringId>()
                        .expect("dynamic attr key must be a string")
                }
            };
            let val = entry.val.resolve(mc, self);
            kv.push((key_sid, val));
        }
        kv.sort_by_key(|(k, _)| *k);
        let attrs = Gc::new(mc, AttrSet::from_sorted_unchecked(kv));
        self.push(Value::new_gc(attrs));
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_make_empty_attrs(&mut self) -> Step {
        self.push(self.empty_attrs);
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_select_static(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let _span_id = reader.read_u32();
        let key = reader.read_string_id();

        let attrset = self.try_force::<Gc<AttrSet>>(reader, mc)?;

        match attrset.lookup(key) {
            Some(v) => {
                self.push(v);
            }
            None => return self.select_skip(key, ctx, reader),
        }
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_select_dynamic(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let _span_id = reader.read_u32();

        let (attrset, key_val) = self.try_force::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;

        let key_sid = match ctx.get_string_id(key_val) {
            Ok(id) => id,
            Err(got) => return self.finish_type_err(NixType::String, got),
        };

        match attrset.lookup(key_sid) {
            Some(v) => {
                self.push(v);
            }
            None => return self.select_skip(key_sid, ctx, reader),
        }
        Step::Continue(())
    }

    /// Skip the rest of a **Select** attrpath after a missing attribute.
    /// Only recognises Select opcodes and jumps; encountering any other
    /// opcode means we've reached the end of the select sequence and
    /// should report the missing-attribute error.
    fn select_skip(
        &mut self,
        key: StringId,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
    ) -> Step {
        use fix_codegen::Op::*;
        loop {
            match reader.read_op() {
                SelectStatic => {
                    reader.set_pc(reader.pc() + 4 + 4);
                }
                SelectDynamic => {
                    reader.set_pc(reader.pc() + 4);
                }
                JumpIfSelectSucceeded => {
                    reader.set_pc(reader.pc() + 4);
                    break Step::Continue(());
                }
                JumpIfSelectFailed => {
                    let offset = reader.read_i32();
                    reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
                }
                _ => {
                    let name = ctx.resolve_string(key);
                    return self
                        .finish_err(Error::eval_error(format!("attribute '{name}' missing")));
                }
            }
        }
    }

    /// Skip the rest of a **HasAttr** attrpath after an intermediate
    /// lookup failed. Only recognises HasAttr opcodes and jumps.
    fn has_attr_skip(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
        use fix_codegen::Op::*;
        loop {
            match reader.read_op() {
                HasAttrPathStatic => {
                    reader.set_pc(reader.pc() + 4 + 4);
                }
                HasAttrPathDynamic => {
                    reader.set_pc(reader.pc() + 4);
                }
                HasAttrStatic => {
                    reader.set_pc(reader.pc() + 4);
                    break Step::Continue(());
                }
                JumpIfSelectFailed => {
                    let offset = reader.read_i32();
                    reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
                }
                HasAttrDynamic => {
                    break Step::Continue(());
                }
                HasAttrResolve => {
                    reader.set_pc(reader.pc() - 1);
                    break Step::Continue(());
                }
                other => {
                    unreachable!("unexpected opcode {:?} in has_attr_skip", other as u8)
                }
            }
        }
    }

    #[inline(always)]
    pub(crate) fn op_has_attr_path_static(
        &mut self,
        _ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let _span_id = reader.read_u32();
        let key = reader.read_string_id();

        let current = self.try_force::<StrictValue>(reader, mc)?;

        match current
            .as_gc::<AttrSet>()
            .and_then(|attrs| attrs.lookup(key))
        {
            Some(v) => {
                self.push(v);
            }
            None => return self.has_attr_skip(reader),
        }
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_has_attr_path_dynamic(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let _span_id = reader.read_u32();

        let (current, key_val) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;

        let key_sid = match ctx.get_string_id(key_val) {
            Ok(id) => id,
            Err(got) => return self.finish_type_err(NixType::String, got),
        };

        match current
            .as_gc::<AttrSet>()
            .and_then(|attrs| attrs.lookup(key_sid))
        {
            Some(v) => {
                self.push(v);
            }
            None => return self.has_attr_skip(reader),
        }
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_jump_if_select_failed(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
        // No-op
        let _offset = reader.read_i32();
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_jump_if_select_succeeded(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
        let offset = reader.read_i32();
        reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_has_attr_static(
        &mut self,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let key = reader.read_string_id();
        let current = self.try_force::<StrictValue>(reader, mc)?;

        self.push(Value::new_inline(
            current
                .as_gc::<AttrSet>()
                .and_then(|attrs| attrs.lookup(key))
                .is_some(),
        ));
        // Skip HasAttrResolve
        reader.set_pc(reader.pc() + 1);

        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_has_attr_dynamic(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let (current, dyn_key) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;

        let key_sid = match ctx.get_string_id(dyn_key) {
            Ok(id) => id,
            Err(got) => return self.finish_type_err(NixType::String, got),
        };

        self.push(Value::new_inline(
            current
                .as_gc::<AttrSet>()
                .and_then(|attrs| attrs.lookup(key_sid))
                .is_some(),
        ));
        // Skip HasAttrResolve
        reader.set_pc(reader.pc() + 1);

        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_has_attr_resolve(&mut self) -> Step {
        // If we reach here, has_attr check has failed, push false (AttrSet is already popped)
        self.push(Value::new_inline(false));
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_make_list(
        &mut self,
        ctx: &mut impl VmRuntimeCtx,
        reader: &mut BytecodeReader<'_>,
        mc: &gc_arena::Mutation<'gc>,
    ) -> Step {
        let count = reader.read_u32() as usize;
        let mut items: SmallVec<[Value; 4]> = SmallVec::with_capacity(count);
        for _ in 0..count {
            items.push(reader.read_operand_data(ctx).resolve(mc, self));
        }
        let list = Gc::new(
            mc,
            List {
                inner: RefLock::new(items),
            },
        );
        self.push(Value::new_gc(list));
        Step::Continue(())
    }

    #[inline(always)]
    pub(crate) fn op_make_empty_list(&mut self) -> Step {
        self.push(self.empty_list);
        Step::Continue(())
    }
}

pub(crate) struct AttrEntry {
    pub(crate) key: AttrKeyData,
    pub(crate) val: OperandData,
}