//! Contains all logic to lower wasm MIR into its binary
//! or textual representation.

const Emit = @This();
const std = @import("std");
const Mir = @import("Mir.zig");
const link = @import("../../link.zig");
const Module = @import("../../Module.zig");
const codegen = @import("../../codegen.zig");
const leb128 = std.leb;

/// Contains our list of instructions
mir: Mir,
/// Reference to the file handler
bin_file: *link.File,
/// Possible error message. When set, the value is allocated and
/// must be freed manually.
error_msg: ?*Module.ErrorMsg = null,
/// The binary representation that will be emit by this module.
code: *std.ArrayList(u8),
/// List of allocated locals.
locals: []const u8,
/// The declaration that code is being generated for.
decl: *Module.Decl,

// Debug information
/// Holds the debug information for this emission
dbg_output: codegen.DebugInfoOutput,
/// Previous debug info line
prev_di_line: u32,
/// Previous debug info column
prev_di_column: u32,
/// Previous offset relative to code section
prev_di_offset: u32,

const InnerError = error{
    OutOfMemory,
    EmitFail,
};

pub fn emitMir(emit: *Emit) InnerError!void {
    const mir_tags = emit.mir.instructions.items(.tag);
    // write the locals in the prologue of the function body
    // before we emit the function body when lowering MIR
    try emit.emitLocals();

    for (mir_tags) |tag, index| {
        const inst = @intCast(u32, index);
        switch (tag) {
            // block instructions
            .block => try emit.emitBlock(tag, inst),
            .loop => try emit.emitBlock(tag, inst),

            .dbg_line => try emit.emitDbgLine(inst),
            .dbg_epilogue_begin => try emit.emitDbgEpilogueBegin(),
            .dbg_prologue_end => try emit.emitDbgPrologueEnd(),

            // branch instructions
            .br_if => try emit.emitLabel(tag, inst),
            .br_table => try emit.emitBrTable(inst),
            .br => try emit.emitLabel(tag, inst),

            // relocatables
            .call => try emit.emitCall(inst),
            .call_indirect => try emit.emitCallIndirect(inst),
            .global_get => try emit.emitGlobal(tag, inst),
            .global_set => try emit.emitGlobal(tag, inst),
            .function_index => try emit.emitFunctionIndex(inst),
            .memory_address => try emit.emitMemAddress(inst),

            // immediates
            .f32_const => try emit.emitFloat32(inst),
            .f64_const => try emit.emitFloat64(inst),
            .i32_const => try emit.emitImm32(inst),
            .i64_const => try emit.emitImm64(inst),

            // memory instructions
            .i32_load => try emit.emitMemArg(tag, inst),
            .i64_load => try emit.emitMemArg(tag, inst),
            .f32_load => try emit.emitMemArg(tag, inst),
            .f64_load => try emit.emitMemArg(tag, inst),
            .i32_load8_s => try emit.emitMemArg(tag, inst),
            .i32_load8_u => try emit.emitMemArg(tag, inst),
            .i32_load16_s => try emit.emitMemArg(tag, inst),
            .i32_load16_u => try emit.emitMemArg(tag, inst),
            .i64_load8_s => try emit.emitMemArg(tag, inst),
            .i64_load8_u => try emit.emitMemArg(tag, inst),
            .i64_load16_s => try emit.emitMemArg(tag, inst),
            .i64_load16_u => try emit.emitMemArg(tag, inst),
            .i64_load32_s => try emit.emitMemArg(tag, inst),
            .i64_load32_u => try emit.emitMemArg(tag, inst),
            .i32_store => try emit.emitMemArg(tag, inst),
            .i64_store => try emit.emitMemArg(tag, inst),
            .f32_store => try emit.emitMemArg(tag, inst),
            .f64_store => try emit.emitMemArg(tag, inst),
            .i32_store8 => try emit.emitMemArg(tag, inst),
            .i32_store16 => try emit.emitMemArg(tag, inst),
            .i64_store8 => try emit.emitMemArg(tag, inst),
            .i64_store16 => try emit.emitMemArg(tag, inst),
            .i64_store32 => try emit.emitMemArg(tag, inst),

            // Instructions with an index that do not require relocations
            .local_get => try emit.emitLabel(tag, inst),
            .local_set => try emit.emitLabel(tag, inst),
            .local_tee => try emit.emitLabel(tag, inst),
            .memory_grow => try emit.emitLabel(tag, inst),
            .memory_size => try emit.emitLabel(tag, inst),

            // no-ops
            .end => try emit.emitTag(tag),
            .@"return" => try emit.emitTag(tag),
            .@"unreachable" => try emit.emitTag(tag),

            .select => try emit.emitTag(tag),

            // arithmetic
            .i32_eqz => try emit.emitTag(tag),
            .i32_eq => try emit.emitTag(tag),
            .i32_ne => try emit.emitTag(tag),
            .i32_lt_s => try emit.emitTag(tag),
            .i32_lt_u => try emit.emitTag(tag),
            .i32_gt_s => try emit.emitTag(tag),
            .i32_gt_u => try emit.emitTag(tag),
            .i32_le_s => try emit.emitTag(tag),
            .i32_le_u => try emit.emitTag(tag),
            .i32_ge_s => try emit.emitTag(tag),
            .i32_ge_u => try emit.emitTag(tag),
            .i64_eqz => try emit.emitTag(tag),
            .i64_eq => try emit.emitTag(tag),
            .i64_ne => try emit.emitTag(tag),
            .i64_lt_s => try emit.emitTag(tag),
            .i64_lt_u => try emit.emitTag(tag),
            .i64_gt_s => try emit.emitTag(tag),
            .i64_gt_u => try emit.emitTag(tag),
            .i64_le_s => try emit.emitTag(tag),
            .i64_le_u => try emit.emitTag(tag),
            .i64_ge_s => try emit.emitTag(tag),
            .i64_ge_u => try emit.emitTag(tag),
            .f32_eq => try emit.emitTag(tag),
            .f32_ne => try emit.emitTag(tag),
            .f32_lt => try emit.emitTag(tag),
            .f32_gt => try emit.emitTag(tag),
            .f32_le => try emit.emitTag(tag),
            .f32_ge => try emit.emitTag(tag),
            .f64_eq => try emit.emitTag(tag),
            .f64_ne => try emit.emitTag(tag),
            .f64_lt => try emit.emitTag(tag),
            .f64_gt => try emit.emitTag(tag),
            .f64_le => try emit.emitTag(tag),
            .f64_ge => try emit.emitTag(tag),
            .i32_add => try emit.emitTag(tag),
            .i32_sub => try emit.emitTag(tag),
            .i32_mul => try emit.emitTag(tag),
            .i32_div_s => try emit.emitTag(tag),
            .i32_div_u => try emit.emitTag(tag),
            .i32_and => try emit.emitTag(tag),
            .i32_or => try emit.emitTag(tag),
            .i32_xor => try emit.emitTag(tag),
            .i32_shl => try emit.emitTag(tag),
            .i32_shr_s => try emit.emitTag(tag),
            .i32_shr_u => try emit.emitTag(tag),
            .i64_add => try emit.emitTag(tag),
            .i64_sub => try emit.emitTag(tag),
            .i64_mul => try emit.emitTag(tag),
            .i64_div_s => try emit.emitTag(tag),
            .i64_div_u => try emit.emitTag(tag),
            .i64_and => try emit.emitTag(tag),
            .i64_or => try emit.emitTag(tag),
            .i64_xor => try emit.emitTag(tag),
            .i64_shl => try emit.emitTag(tag),
            .i64_shr_s => try emit.emitTag(tag),
            .i64_shr_u => try emit.emitTag(tag),
            .f32_abs => try emit.emitTag(tag),
            .f32_neg => try emit.emitTag(tag),
            .f32_ceil => try emit.emitTag(tag),
            .f32_floor => try emit.emitTag(tag),
            .f32_trunc => try emit.emitTag(tag),
            .f32_nearest => try emit.emitTag(tag),
            .f32_sqrt => try emit.emitTag(tag),
            .f32_add => try emit.emitTag(tag),
            .f32_sub => try emit.emitTag(tag),
            .f32_mul => try emit.emitTag(tag),
            .f32_div => try emit.emitTag(tag),
            .f32_min => try emit.emitTag(tag),
            .f32_max => try emit.emitTag(tag),
            .f32_copysign => try emit.emitTag(tag),
            .f64_abs => try emit.emitTag(tag),
            .f64_neg => try emit.emitTag(tag),
            .f64_ceil => try emit.emitTag(tag),
            .f64_floor => try emit.emitTag(tag),
            .f64_trunc => try emit.emitTag(tag),
            .f64_nearest => try emit.emitTag(tag),
            .f64_sqrt => try emit.emitTag(tag),
            .f64_add => try emit.emitTag(tag),
            .f64_sub => try emit.emitTag(tag),
            .f64_mul => try emit.emitTag(tag),
            .f64_div => try emit.emitTag(tag),
            .f64_min => try emit.emitTag(tag),
            .f64_max => try emit.emitTag(tag),
            .f64_copysign => try emit.emitTag(tag),
            .i32_wrap_i64 => try emit.emitTag(tag),
            .i64_extend_i32_s => try emit.emitTag(tag),
            .i64_extend_i32_u => try emit.emitTag(tag),
            .i32_extend8_s => try emit.emitTag(tag),
            .i32_extend16_s => try emit.emitTag(tag),
            .i64_extend8_s => try emit.emitTag(tag),
            .i64_extend16_s => try emit.emitTag(tag),
            .i64_extend32_s => try emit.emitTag(tag),
            .f32_demote_f64 => try emit.emitTag(tag),
            .f64_promote_f32 => try emit.emitTag(tag),
            .i32_reinterpret_f32 => try emit.emitTag(tag),
            .i64_reinterpret_f64 => try emit.emitTag(tag),
            .f32_reinterpret_i32 => try emit.emitTag(tag),
            .f64_reinterpret_i64 => try emit.emitTag(tag),
            .i32_trunc_f32_s => try emit.emitTag(tag),
            .i32_trunc_f32_u => try emit.emitTag(tag),
            .i32_trunc_f64_s => try emit.emitTag(tag),
            .i32_trunc_f64_u => try emit.emitTag(tag),
            .i64_trunc_f32_s => try emit.emitTag(tag),
            .i64_trunc_f32_u => try emit.emitTag(tag),
            .i64_trunc_f64_s => try emit.emitTag(tag),
            .i64_trunc_f64_u => try emit.emitTag(tag),
            .f32_convert_i32_s => try emit.emitTag(tag),
            .f32_convert_i32_u => try emit.emitTag(tag),
            .f32_convert_i64_s => try emit.emitTag(tag),
            .f32_convert_i64_u => try emit.emitTag(tag),
            .f64_convert_i32_s => try emit.emitTag(tag),
            .f64_convert_i32_u => try emit.emitTag(tag),
            .f64_convert_i64_s => try emit.emitTag(tag),
            .f64_convert_i64_u => try emit.emitTag(tag),
            .i32_rem_s => try emit.emitTag(tag),
            .i32_rem_u => try emit.emitTag(tag),
            .i64_rem_s => try emit.emitTag(tag),
            .i64_rem_u => try emit.emitTag(tag),
            .i32_popcnt => try emit.emitTag(tag),
            .i64_popcnt => try emit.emitTag(tag),
            .i32_clz => try emit.emitTag(tag),
            .i32_ctz => try emit.emitTag(tag),
            .i64_clz => try emit.emitTag(tag),
            .i64_ctz => try emit.emitTag(tag),

            .extended => try emit.emitExtended(inst),
        }
    }
}

fn offset(self: Emit) u32 {
    return @intCast(u32, self.code.items.len);
}

fn fail(emit: *Emit, comptime format: []const u8, args: anytype) InnerError {
    @setCold(true);
    std.debug.assert(emit.error_msg == null);
    // TODO: Determine the source location.
    emit.error_msg = try Module.ErrorMsg.create(emit.bin_file.allocator, emit.decl.srcLoc(), format, args);
    return error.EmitFail;
}

fn emitLocals(emit: *Emit) !void {
    const writer = emit.code.writer();
    try leb128.writeULEB128(writer, @intCast(u32, emit.locals.len));
    // emit the actual locals amount
    for (emit.locals) |local| {
        try leb128.writeULEB128(writer, @as(u32, 1));
        try writer.writeByte(local);
    }
}

fn emitTag(emit: *Emit, tag: Mir.Inst.Tag) !void {
    try emit.code.append(@enumToInt(tag));
}

fn emitBlock(emit: *Emit, tag: Mir.Inst.Tag, inst: Mir.Inst.Index) !void {
    const block_type = emit.mir.instructions.items(.data)[inst].block_type;
    try emit.code.append(@enumToInt(tag));
    try emit.code.append(block_type);
}

fn emitBrTable(emit: *Emit, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const extra = emit.mir.extraData(Mir.JumpTable, extra_index);
    const labels = emit.mir.extra[extra.end..][0..extra.data.length];
    const writer = emit.code.writer();

    try emit.code.append(std.wasm.opcode(.br_table));
    try leb128.writeULEB128(writer, extra.data.length - 1); // Default label is not part of length/depth
    for (labels) |label| {
        try leb128.writeULEB128(writer, label);
    }
}

fn emitLabel(emit: *Emit, tag: Mir.Inst.Tag, inst: Mir.Inst.Index) !void {
    const label = emit.mir.instructions.items(.data)[inst].label;
    try emit.code.append(@enumToInt(tag));
    try leb128.writeULEB128(emit.code.writer(), label);
}

fn emitGlobal(emit: *Emit, tag: Mir.Inst.Tag, inst: Mir.Inst.Index) !void {
    const label = emit.mir.instructions.items(.data)[inst].label;
    try emit.code.append(@enumToInt(tag));
    var buf: [5]u8 = undefined;
    leb128.writeUnsignedFixed(5, &buf, label);
    const global_offset = emit.offset();
    try emit.code.appendSlice(&buf);

    // globals can have index 0 as it represents the stack pointer
    try emit.decl.link.wasm.relocs.append(emit.bin_file.allocator, .{
        .index = label,
        .offset = global_offset,
        .relocation_type = .R_WASM_GLOBAL_INDEX_LEB,
    });
}

fn emitImm32(emit: *Emit, inst: Mir.Inst.Index) !void {
    const value: i32 = emit.mir.instructions.items(.data)[inst].imm32;
    try emit.code.append(std.wasm.opcode(.i32_const));
    try leb128.writeILEB128(emit.code.writer(), value);
}

fn emitImm64(emit: *Emit, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const value = emit.mir.extraData(Mir.Imm64, extra_index);
    try emit.code.append(std.wasm.opcode(.i64_const));
    try leb128.writeILEB128(emit.code.writer(), @bitCast(i64, value.data.toU64()));
}

fn emitFloat32(emit: *Emit, inst: Mir.Inst.Index) !void {
    const value: f32 = emit.mir.instructions.items(.data)[inst].float32;
    try emit.code.append(std.wasm.opcode(.f32_const));
    try emit.code.writer().writeIntLittle(u32, @bitCast(u32, value));
}

fn emitFloat64(emit: *Emit, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const value = emit.mir.extraData(Mir.Float64, extra_index);
    try emit.code.append(std.wasm.opcode(.f64_const));
    try emit.code.writer().writeIntLittle(u64, value.data.toU64());
}

fn emitMemArg(emit: *Emit, tag: Mir.Inst.Tag, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const mem_arg = emit.mir.extraData(Mir.MemArg, extra_index).data;
    try emit.code.append(@enumToInt(tag));

    // wasm encodes alignment as power of 2, rather than natural alignment
    const encoded_alignment = @ctz(mem_arg.alignment);
    try leb128.writeULEB128(emit.code.writer(), encoded_alignment);
    try leb128.writeULEB128(emit.code.writer(), mem_arg.offset);
}

fn emitCall(emit: *Emit, inst: Mir.Inst.Index) !void {
    const label = emit.mir.instructions.items(.data)[inst].label;
    try emit.code.append(std.wasm.opcode(.call));
    const call_offset = emit.offset();
    var buf: [5]u8 = undefined;
    leb128.writeUnsignedFixed(5, &buf, label);
    try emit.code.appendSlice(&buf);

    if (label != 0) {
        try emit.decl.link.wasm.relocs.append(emit.bin_file.allocator, .{
            .offset = call_offset,
            .index = label,
            .relocation_type = .R_WASM_FUNCTION_INDEX_LEB,
        });
    }
}

fn emitCallIndirect(emit: *Emit, inst: Mir.Inst.Index) !void {
    const type_index = emit.mir.instructions.items(.data)[inst].label;
    try emit.code.append(std.wasm.opcode(.call_indirect));
    // NOTE: If we remove unused function types in the future for incremental
    // linking, we must also emit a relocation for this `type_index`
    try leb128.writeULEB128(emit.code.writer(), type_index);
    try leb128.writeULEB128(emit.code.writer(), @as(u32, 0)); // TODO: Emit relocation for table index
}

fn emitFunctionIndex(emit: *Emit, inst: Mir.Inst.Index) !void {
    const symbol_index = emit.mir.instructions.items(.data)[inst].label;
    try emit.code.append(std.wasm.opcode(.i32_const));
    const index_offset = emit.offset();
    var buf: [5]u8 = undefined;
    leb128.writeUnsignedFixed(5, &buf, symbol_index);
    try emit.code.appendSlice(&buf);

    if (symbol_index != 0) {
        try emit.decl.link.wasm.relocs.append(emit.bin_file.allocator, .{
            .offset = index_offset,
            .index = symbol_index,
            .relocation_type = .R_WASM_TABLE_INDEX_SLEB,
        });
    }
}

fn emitMemAddress(emit: *Emit, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const mem = emit.mir.extraData(Mir.Memory, extra_index).data;
    const mem_offset = emit.offset() + 1;
    const is_wasm32 = emit.bin_file.options.target.cpu.arch == .wasm32;
    if (is_wasm32) {
        try emit.code.append(std.wasm.opcode(.i32_const));
        var buf: [5]u8 = undefined;
        leb128.writeUnsignedFixed(5, &buf, mem.pointer);
        try emit.code.appendSlice(&buf);
    } else {
        try emit.code.append(std.wasm.opcode(.i64_const));
        var buf: [10]u8 = undefined;
        leb128.writeUnsignedFixed(10, &buf, mem.pointer);
        try emit.code.appendSlice(&buf);
    }

    if (mem.pointer != 0) {
        try emit.decl.link.wasm.relocs.append(emit.bin_file.allocator, .{
            .offset = mem_offset,
            .index = mem.pointer,
            .relocation_type = if (is_wasm32) .R_WASM_MEMORY_ADDR_LEB else .R_WASM_MEMORY_ADDR_LEB64,
            .addend = mem.offset,
        });
    }
}

fn emitExtended(emit: *Emit, inst: Mir.Inst.Index) !void {
    const opcode = emit.mir.instructions.items(.secondary)[inst];
    switch (@intToEnum(std.wasm.PrefixedOpcode, opcode)) {
        .memory_fill => try emit.emitMemFill(),
        else => |tag| return emit.fail("TODO: Implement extension instruction: {s}\n", .{@tagName(tag)}),
    }
}

fn emitMemFill(emit: *Emit) !void {
    try emit.code.append(0xFC);
    try emit.code.append(0x0B);
    // When multi-memory proposal reaches phase 4, we
    // can emit a different memory index here.
    // For now we will always emit index 0.
    try leb128.writeULEB128(emit.code.writer(), @as(u32, 0));
}

fn emitDbgLine(emit: *Emit, inst: Mir.Inst.Index) !void {
    const extra_index = emit.mir.instructions.items(.data)[inst].payload;
    const dbg_line = emit.mir.extraData(Mir.DbgLineColumn, extra_index).data;
    try emit.dbgAdvancePCAndLine(dbg_line.line, dbg_line.column);
}

fn dbgAdvancePCAndLine(emit: *Emit, line: u32, column: u32) !void {
    if (emit.dbg_output != .dwarf) return;

    const dbg_line = &emit.dbg_output.dwarf.dbg_line;
    try dbg_line.ensureUnusedCapacity(11);
    dbg_line.appendAssumeCapacity(std.dwarf.LNS.advance_pc);
    // TODO: This must emit a relocation to calculate the offset relative
    // to the code section start.
    leb128.writeULEB128(dbg_line.writer(), emit.offset() - emit.prev_di_offset) catch unreachable;
    const delta_line = @intCast(i32, line) - @intCast(i32, emit.prev_di_line);
    if (delta_line != 0) {
        dbg_line.appendAssumeCapacity(std.dwarf.LNS.advance_line);
        leb128.writeILEB128(dbg_line.writer(), delta_line) catch unreachable;
    }
    dbg_line.appendAssumeCapacity(std.dwarf.LNS.copy);
    emit.prev_di_line = line;
    emit.prev_di_column = column;
    emit.prev_di_offset = emit.offset();
}

fn emitDbgPrologueEnd(emit: *Emit) !void {
    if (emit.dbg_output != .dwarf) return;

    try emit.dbg_output.dwarf.dbg_line.append(std.dwarf.LNS.set_prologue_end);
    try emit.dbgAdvancePCAndLine(emit.prev_di_line, emit.prev_di_column);
}

fn emitDbgEpilogueBegin(emit: *Emit) !void {
    if (emit.dbg_output != .dwarf) return;

    try emit.dbg_output.dwarf.dbg_line.append(std.dwarf.LNS.set_epilogue_begin);
    try emit.dbgAdvancePCAndLine(emit.prev_di_line, emit.prev_di_column);
}