// SPDX-License-Identifier: MIT

#include "asm/section.hpp"

#include <algorithm>
#include <deque>
#include <errno.h>
#include <inttypes.h>
#include <iterator>
#include <optional>
#include <stack>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

#include "helpers.hpp"
#include "itertools.hpp" // InsertionOrderedMap
#include "linkdefs.hpp"
#include "platform.hpp" // fseek
#include "util.hpp"     // xfclose, seekSize

#include "asm/fstack.hpp"
#include "asm/lexer.hpp"
#include "asm/main.hpp"
#include "asm/output.hpp"
#include "asm/rpn.hpp"
#include "asm/symbol.hpp"
#include "asm/warning.hpp"

using namespace std::literals;

struct UnionStackEntry {
	uint32_t start;
	uint32_t size;
};

struct SectionStackEntry {
	Section *section;
	Section *loadSection;
	std::pair<Symbol const *, Symbol const *> labelScopes;
	uint32_t offset;
	int32_t loadOffset;
	std::stack<UnionStackEntry> unionStack;
};

static Section *currentSection = nullptr;
static InsertionOrderedMap<std::string, Section> sections;

static uint32_t curOffset; // Offset into the current section (see `sect_GetSymbolOffset`)

static std::deque<SectionStackEntry> sectionStack;

static Section *currentLoadSection = nullptr;
static std::pair<Symbol const *, Symbol const *> currentLoadLabelScopes = {nullptr, nullptr};
static int32_t loadOffset; // Offset into the LOAD section's parent (see sect_GetOutputOffset)

static std::stack<UnionStackEntry> currentUnionStack;

[[nodiscard]]
static bool requireSection() {
	if (currentSection) {
		return true;
	}

	error("Cannot output data outside of a `SECTION`");
	return false;
}

[[nodiscard]]
static bool requireCodeSection() {
	if (!requireSection()) {
		return false;
	}

	if (sectTypeHasData(currentSection->type)) {
		return true;
	}

	error(
	    "Section \"%s\" cannot contain code or data (not `ROM0` or `ROMX`)",
	    currentSection->name.c_str()
	);
	return false;
}

size_t sect_CountSections() {
	return sections.size();
}

void sect_ForEach(void (*callback)(Section &)) {
	for (Section &sect : sections) {
		callback(sect);
	}
}

void sect_CheckSizes() {
	for (Section const &sect : sections) {
		if (uint32_t maxSize = sectionTypeInfo[sect.type].size; sect.size > maxSize) {
			error(
			    "Section \"%s\" grew too big (max size = 0x%" PRIX32 " bytes, reached 0x%" PRIX32
			    ")",
			    sect.name.c_str(),
			    maxSize,
			    sect.size
			);
		}
	}
}

Section *sect_FindSectionByName(std::string const &name) {
	auto index = sections.findIndex(name);
	return index ? &sections[*index] : nullptr;
}

static std::vector<std::string> sectErrors;

// Ideally we'd use a variadic template function and `std::forward` the variadic arguments to
// `snprintf`; but passing `fmt` to `snprintf` triggers a `-Wformat-security` warning which we
// can't prevent because GCC only supports the `[[gnu::format(printf, 1, 2)]]` attribute on
// C-style variadic functions, not on variadic templates; so we have to use `vsnprintf`.
[[gnu::format(printf, 1, 2)]]
static void sectError(char const *fmt, ...) {
	std::string result;
	va_list args1, args2;
	va_start(args1, fmt);
	va_copy(args2, args1);
	int len = vsnprintf(nullptr, 0, fmt, args1);
	va_end(args1);
	if (len < 0) {
		// LCOV_EXCL_START
		va_end(args2);
		fatal("Error describing the error that occurred when merging a section");
		// LCOV_EXCL_STOP
	} else if (len > 0) {
		result.resize(len);
		vsnprintf(result.data(), len + 1, fmt, args2);
	}
	va_end(args2);
	sectErrors.push_back(result);
}

static void mergeSectUnion(Section &sect, uint32_t org, uint8_t alignment, uint16_t alignOffset) {
	assume(alignment < 16); // Should be ensured by the caller
	uint32_t alignSize = 1u << alignment;
	uint32_t alignMask = alignSize - 1;

	assume(sect.align <= 16); // Left-shifting by 32 or more would be UB
	uint32_t sectAlignSize = 1u << sect.align;
	uint32_t sectAlignMask = sectAlignSize - 1;

	if (org != UINT32_MAX) {
		// If both are fixed, they must be the same
		if (sect.org != UINT32_MAX && sect.org != org) {
			sectError(
			    "Section \"%s\" already declared as fixed at different address $%04" PRIx32,
			    sect.name.c_str(),
			    sect.org
			);
		} else if (sect.align != 0 && ((org - sect.alignOfs) & sectAlignMask)) {
			sectError(
			    "Section \"%s\" already declared as aligned to %" PRIu32 " bytes (offset %" PRIu16
			    ")",
			    sect.name.c_str(),
			    sectAlignSize,
			    sect.alignOfs
			);
		} else {
			// Otherwise, just override
			sect.org = org;
		}

	} else if (alignment != 0) {
		// Make sure any fixed address given is compatible
		if (sect.org != UINT32_MAX) {
			if ((sect.org - alignOffset) & alignMask) {
				sectError(
				    "Section \"%s\" already declared as fixed at incompatible address $%04" PRIx32,
				    sect.name.c_str(),
				    sect.org
				);
			}
			// Check if alignment offsets are compatible
		} else if ((alignOffset & sectAlignMask) != (sect.alignOfs & alignMask)) {
			sectError(
			    "Section \"%s\" already declared with incompatible %" PRIu32
			    "-byte alignment (offset %" PRIu16 ")",
			    sect.name.c_str(),
			    sectAlignSize,
			    sect.alignOfs
			);
		} else if (alignment > sect.align) {
			// If the section is not fixed, its alignment is the largest of both
			sect.align = alignment;
			sect.alignOfs = alignOffset;
		}
	}
}

static void mergeFragments(Section &sect, uint32_t org, uint8_t alignment, uint16_t alignOffset) {
	assume(alignment < 16); // Should be ensured by the caller
	uint32_t alignSize = 1u << alignment;
	uint32_t alignMask = alignSize - 1;

	assume(sect.align <= 16); // Left-shifting by 32 or more would be UB
	uint32_t sectAlignSize = 1u << sect.align;
	uint32_t sectAlignMask = sectAlignSize - 1;

	// Fragments only need "compatible" constraints, and they end up with the strictest
	// combination of both.
	// The merging is however performed at the *end* of the original section!
	if (org != UINT32_MAX) {
		uint16_t curOrg = org - sect.size;

		// If both are fixed, they must be the same
		if (sect.org != UINT32_MAX && sect.org != curOrg) {
			sectError(
			    "Section \"%s\" already declared as fixed at incompatible address $%04" PRIx32,
			    sect.name.c_str(),
			    sect.org
			);
		} else if (sect.align != 0 && ((curOrg - sect.alignOfs) & sectAlignMask)) {
			sectError(
			    "Section \"%s\" already declared as aligned to %" PRIu32 " bytes (offset %" PRIu16
			    ")",
			    sect.name.c_str(),
			    sectAlignSize,
			    sect.alignOfs
			);
		} else {
			// Otherwise, just override
			sect.org = curOrg;
		}

	} else if (alignment != 0) {
		// Make sure any fixed address given is compatible
		if (uint32_t curOfs = (alignOffset - sect.size) & alignMask; sect.org != UINT32_MAX) {
			if ((sect.org - curOfs) & alignMask) {
				sectError(
				    "Section \"%s\" already declared as fixed at incompatible address $%04" PRIx32,
				    sect.name.c_str(),
				    sect.org
				);
			}
			// Check if alignment offsets are compatible
		} else if ((curOfs & sectAlignMask) != (sect.alignOfs & alignMask)) {
			sectError(
			    "Section \"%s\" already declared with incompatible %" PRIu32
			    "-byte alignment (offset %" PRIu16 ")",
			    sect.name.c_str(),
			    sectAlignSize,
			    sect.alignOfs
			);
		} else if (alignment > sect.align) {
			// If the section is not fixed, its alignment is the largest of both
			sect.align = alignment;
			sect.alignOfs = curOfs;
		}
	}
}

static void mergeSections(
    Section &sect,
    SectionType type,
    uint32_t org,
    uint32_t bank,
    uint8_t alignment,
    uint16_t alignOffset,
    SectionModifier mod
) {
	sectErrors.clear();

	if (type != sect.type) {
		sectError(
		    "Section \"%s\" already exists but with type `%s`",
		    sect.name.c_str(),
		    sectionTypeInfo[sect.type].name.c_str()
		);
	}

	if (sect.modifier != mod) {
		sectError(
		    "Section \"%s\" already declared as `SECTION %s`",
		    sect.name.c_str(),
		    sectionModNames[sect.modifier]
		);
	} else {
		switch (mod) {
		case SECTION_UNION:
		case SECTION_FRAGMENT: {
			void (*merge)(Section &, uint32_t, uint8_t, uint16_t) =
			    mod == SECTION_UNION ? mergeSectUnion : mergeFragments;
			merge(sect, org, alignment, alignOffset);

			// If the section's bank is unspecified, override it
			if (sect.bank == UINT32_MAX) {
				sect.bank = bank;
			}
			// If both specify a bank, it must be the same one
			else if (bank != UINT32_MAX && sect.bank != bank) {
				sectError(
				    "Section \"%s\" already declared with different bank %" PRIu32,
				    sect.name.c_str(),
				    sect.bank
				);
			}
			break;
		}

		case SECTION_NORMAL:
			// Only union/fragment sections can end up with multiple errors queued in `sectErrors`,
			// and they cannot encounter this error, so it's okay for this one to skip the queue.
			// Queueing it in `sectErrors` would require a sentinel value anyway (e.g. an empty
			// string) to handle the "no trace" callback.
			assume(sectErrors.empty());
			fatalNoTrace([&sect]() {
				fprintf(stderr, "Section \"%s\" already defined\n", sect.name.c_str());
				fstk_TraceCurrent();
				fputs("    and also:\n", stderr);
				sect.src->printBacktrace(sect.fileLine);
			});
			break;
		}
	}

	if (size_t nbSectErrors = sectErrors.size(); nbSectErrors == 1) {
		// If there was only one error, print it as a fatal error
		fatal("%s", sectErrors.front().c_str());
	} else if (nbSectErrors > 1) {
		// If there were multiple errors, print each of them, followed by a fatal summary error
		for (std::string const &message : sectErrors) {
			error("%s", message.c_str());
		}
		fatal(
		    "Cannot create section \"%s\" (%zu error%s)",
		    sect.name.c_str(),
		    nbSectErrors,
		    nbSectErrors == 1 ? "" : "s"
		);
	}
}

static Section *createSection(
    std::string const &name,
    SectionType type,
    uint32_t org,
    uint32_t bank,
    uint8_t alignment,
    uint16_t alignOffset,
    SectionModifier mod
) {
	// Add the new section to the list
	Section &sect = sections.add(name);

	sect.name = name;
	sect.type = type;
	sect.modifier = mod;
	sect.src = fstk_GetFileStack();
	sect.fileLine = lexer_GetLineNo();
	sect.size = 0;
	sect.org = org;
	sect.bank = bank;
	sect.align = alignment;
	sect.alignOfs = alignOffset;

	out_RegisterNode(sect.src);

	// It is only needed to allocate memory for ROM sections.
	if (sectTypeHasData(type)) {
		sect.data.resize(sectionTypeInfo[type].size);
	}

	return &sect;
}

static Section *createSectionFragmentLiteral(Section const &parent) {
	assume(sections.contains(parent.name));
	Section &sect = sections.addAnonymous();

	sect.name = parent.name;
	sect.type = parent.type;
	sect.modifier = SECTION_FRAGMENT;
	sect.src = fstk_GetFileStack();
	sect.fileLine = lexer_GetLineNo();
	sect.size = 0;
	sect.org = UINT32_MAX;
	sect.bank = parent.bank == 0 ? UINT32_MAX : parent.bank;
	sect.align = 0;
	sect.alignOfs = 0;

	out_RegisterNode(sect.src);

	// Section fragment literals must be ROM sections.
	assume(sectTypeHasData(sect.type));
	sect.data.resize(sectionTypeInfo[sect.type].size);

	return &sect;
}

static Section *getSection(
    std::string const &name,
    SectionType type,
    uint32_t org,
    SectionSpec const &attrs,
    SectionModifier mod
) {
	uint32_t bank = attrs.bank;
	uint8_t alignment = attrs.alignment;
	uint16_t alignOffset = attrs.alignOfs;

	assume(alignment <= 16); // Should be ensured by the caller
	uint32_t alignSize = 1u << alignment;
	uint32_t alignMask = alignSize - 1;

	// First, validate parameters, and normalize them if applicable

	if (bank != UINT32_MAX) {
		if (type != SECTTYPE_ROMX && type != SECTTYPE_VRAM && type != SECTTYPE_SRAM
		    && type != SECTTYPE_WRAMX) {
			error("`BANK` only allowed for `ROMX`, `WRAMX`, `SRAM`, or `VRAM` sections");
		} else if (bank < sectionTypeInfo[type].firstBank
		           || bank > sectionTypeInfo[type].lastBank) {
			error(
			    "%s bank value $%04" PRIx32 " out of range ($%04" PRIx32 " to $%04" PRIx32 ")",
			    sectionTypeInfo[type].name.c_str(),
			    bank,
			    sectionTypeInfo[type].firstBank,
			    sectionTypeInfo[type].lastBank
			);
		}
	} else if (sectTypeBanks(type) == 1) {
		// If the section type only has a single bank, implicitly force it
		bank = sectionTypeInfo[type].firstBank;
	}

	// This should be redundant, as the parser guarantees that `AlignmentSpec` will be valid.
	if (alignOffset >= alignSize) {
		// LCOV_EXCL_START
		error(
		    "Alignment offset (%" PRIu16 ") must be smaller than alignment size (%" PRIu32 ")",
		    alignOffset,
		    alignSize
		);
		alignOffset = 0;
		// LCOV_EXCL_STOP
	}

	if (org != UINT32_MAX) {
		if (org < sectionTypeInfo[type].startAddr || org > sectTypeEndAddr(type)) {
			error(
			    "Section \"%s\"'s fixed address $%04" PRIx32 " is outside of range [$%04" PRIx16
			    "; $%04" PRIx16 "]",
			    name.c_str(),
			    org,
			    sectionTypeInfo[type].startAddr,
			    sectTypeEndAddr(type)
			);
		}
	}

	if (alignment != 0) {
		// It doesn't make sense to have both alignment and org set
		if (org != UINT32_MAX) {
			if ((org - alignOffset) & alignMask) {
				error("Section \"%s\"'s fixed address does not match its alignment", name.c_str());
			}
			alignment = 0; // Ignore it if it's satisfied
		} else if (sectionTypeInfo[type].startAddr & alignMask) {
			error(
			    "Section \"%s\"'s alignment cannot be attained in %s",
			    name.c_str(),
			    sectionTypeInfo[type].name.c_str()
			);
			alignment = 0; // Ignore it if it's unattainable
			org = 0;
		} else if (alignment == 16) {
			// Treat an alignment of 16 as fixing the address.
			alignment = 0;
			org = alignOffset;
			// The address is known to be valid, since the alignment itself is.
		}
	}

	// Check if another section exists with the same name; merge if yes, otherwise create one

	Section *sect = sect_FindSectionByName(name);

	if (sect) {
		mergeSections(*sect, type, org, bank, alignment, alignOffset, mod);
	} else {
		sect = createSection(name, type, org, bank, alignment, alignOffset, mod);
	}

	return sect;
}

static void changeSection() {
	if (!currentUnionStack.empty()) {
		fatal("Cannot change the section within a `UNION`");
	}

	sym_ResetCurrentLabelScopes();
}

uint32_t Section::getID() const {
	// Section fragments share the same name but have different IDs, so search by identity
	if (auto search =
	        std::find_if(RANGE(sections), [this](Section const &s) { return &s == this; });
	    search != sections.end()) {
		return static_cast<uint32_t>(std::distance(sections.begin(), search));
	}
	return UINT32_MAX; // LCOV_EXCL_LINE
}

bool Section::isSizeKnown() const {
	// SECTION UNION and SECTION FRAGMENT can still grow
	if (modifier != SECTION_NORMAL) {
		return false;
	}

	// The current section (or current load section if within one) is still growing
	if (this == currentSection || this == currentLoadSection) {
		return false;
	}

	// Any section on the stack is still growing
	for (SectionStackEntry &entry : sectionStack) {
		if (entry.section && entry.section->name == name) {
			return false;
		}
	}

	return true;
}

void sect_NewSection(
    std::string const &name,
    SectionType type,
    uint32_t org,
    SectionSpec const &attrs,
    SectionModifier mod
) {
	if (name.find('\0') != std::string::npos) {
		fatal("Section names cannot contain '\\0' characters");
	}

	for (SectionStackEntry &entry : sectionStack) {
		if (entry.section && entry.section->name == name) {
			fatal("Section \"%s\" is already on the stack", name.c_str());
		}
	}

	if (mod == SECTION_UNION && sectTypeHasData(type)) {
		error("Cannot declare ROM sections as `UNION`");
		return;
	}

	if (currentLoadSection) {
		sect_EndLoadSection("SECTION");
	}

	Section *sect = getSection(name, type, org, attrs, mod);

	changeSection();
	curOffset = mod == SECTION_UNION ? 0 : sect->size;
	loadOffset = 0; // This is still used when checking for section size overflow!
	currentSection = sect;
}

void sect_SetLoadSection(
    std::string const &name,
    SectionType type,
    uint32_t org,
    SectionSpec const &attrs,
    SectionModifier mod
) {
	// Important info: currently, UNION and LOAD cannot interact, since UNION is prohibited in
	// "code" sections, whereas LOAD is restricted to them.
	// Therefore, any interactions are NOT TESTED, so lift either of those restrictions at
	// your own peril! ^^

	if (!requireCodeSection()) {
		return;
	}

	if (sectTypeHasData(type)) {
		error("`LOAD` blocks cannot create a ROM section");
		return;
	}

	if (currentLoadSection) {
		sect_EndLoadSection("LOAD");
	}

	Section *sect = getSection(name, type, org, attrs, mod);

	currentLoadLabelScopes = sym_GetCurrentLabelScopes();
	changeSection();
	loadOffset = curOffset - (mod == SECTION_UNION ? 0 : sect->size);
	curOffset -= loadOffset;
	currentLoadSection = sect;
}

void sect_EndLoadSection(char const *cause) {
	if (cause) {
		warning(WARNING_UNTERMINATED_LOAD, "`LOAD` block without `ENDL` terminated by `%s`", cause);
	}

	if (!currentLoadSection) {
		error("Found `ENDL` outside of a `LOAD` block");
		return;
	}

	changeSection();
	curOffset += loadOffset;
	loadOffset = 0;
	currentLoadSection = nullptr;
	sym_SetCurrentLabelScopes(currentLoadLabelScopes);
}

void sect_CheckLoadClosed() {
	if (currentLoadSection) {
		warning(WARNING_UNTERMINATED_LOAD, "`LOAD` block without `ENDL` terminated by EOF");
	}
}

Section *sect_GetSymbolSection() {
	return currentLoadSection ? currentLoadSection : currentSection;
}

uint32_t sect_GetSymbolOffset() {
	return curOffset;
}

uint32_t sect_GetOutputOffset() {
	return curOffset + loadOffset;
}

std::optional<uint32_t> sect_GetOutputBank() {
	return currentSection ? std::optional<uint32_t>(currentSection->bank) : std::nullopt;
}

Patch *sect_AddOutputPatch() {
	return currentSection ? &currentSection->patches.emplace_front() : nullptr;
}

// Returns how many bytes need outputting for the specified alignment and offset to succeed
uint32_t sect_GetAlignBytes(uint8_t alignment, uint16_t offset) {
	Section *sect = sect_GetSymbolSection();
	if (!sect) {
		return 0;
	}

	bool isFixed = sect->org != UINT32_MAX;

	// If the section is not aligned, no bytes are needed
	// (fixed sections count as being maximally aligned for this purpose)
	uint8_t curAlignment = isFixed ? 16 : sect->align;
	if (curAlignment == 0) {
		return 0;
	}

	// We need `(pcValue + curOffset + return value) & minAlignMask == offset`
	uint16_t pcValue = isFixed ? sect->org : sect->alignOfs;
	uint32_t minAlignMask = (1u << std::min(alignment, curAlignment)) - 1;
	return static_cast<uint16_t>(offset - curOffset - pcValue) & minAlignMask;
}

void sect_AlignPC(uint8_t alignment, uint16_t offset) {
	if (!requireSection()) {
		return;
	}

	assume(alignment <= 16); // Should be ensured by the caller
	uint32_t alignSize = 1u << alignment;
	uint32_t alignMask = alignSize - 1;

	Section *sect = sect_GetSymbolSection();
	assume(sect->align <= 16); // Left-shifting by 32 or more would be UB
	uint32_t sectAlignSize = 1u << sect->align;
	uint32_t sectAlignMask = sectAlignSize - 1;

	if (sect->org != UINT32_MAX) {
		if (uint32_t actualOffset = (sect->org + curOffset) & alignMask; actualOffset != offset) {
			error(
			    "Section is misaligned (at PC = $%04" PRIx32 ", expected ALIGN[%" PRIu32
			    ", %" PRIu32 "], got ALIGN[%" PRIu32 ", %" PRIu32 "])",
			    sect->org + curOffset,
			    alignment,
			    offset,
			    alignment,
			    actualOffset
			);
		}
	} else if (uint32_t actualOffset = (sect->alignOfs + curOffset) & alignMask;
	           sect->align != 0 && (actualOffset & sectAlignMask) != (offset & sectAlignMask)) {
		error(
		    "Section is misaligned ($%04" PRIx32 " bytes into the section, expected ALIGN[%" PRIu32
		    ", %" PRIu32 "], got ALIGN[%" PRIu32 ", %" PRIu32 "])",
		    curOffset,
		    alignment,
		    offset,
		    alignment,
		    actualOffset
		);
	} else if (alignment == 16) {
		// Treat an alignment large enough as fixing the address.
		// Note that this also ensures that a section's alignment never becomes 16 or greater.
		sect->align = 0; // Reset the alignment, since we're fixing the address.
		sect->org = offset - curOffset;
	} else if (alignment > sect->align) {
		sect->align = alignment;
		// We need `(sect->alignOfs + curOffset) & alignMask == offset`
		sect->alignOfs = (offset - curOffset) & alignMask;
	}
}

static void growSection(uint32_t growth) {
	if (growth > 0 && curOffset > UINT32_MAX - growth) {
		fatal("Section size would overflow internal counter");
	}
	curOffset += growth;
	if (uint32_t outOffset = sect_GetOutputOffset(); outOffset > currentSection->size) {
		currentSection->size = outOffset;
	}
	if (currentLoadSection && curOffset > currentLoadSection->size) {
		currentLoadSection->size = curOffset;
	}
}

static void writeByte(uint8_t byte) {
	if (uint32_t index = sect_GetOutputOffset(); index < currentSection->data.size()) {
		currentSection->data[index] = byte;
	}
	growSection(1);
}

static void writeWord(uint16_t value) {
	writeByte(value & 0xFF);
	writeByte(value >> 8);
}

static void writeLong(uint32_t value) {
	writeByte(value & 0xFF);
	writeByte(value >> 8);
	writeByte(value >> 16);
	writeByte(value >> 24);
}

static void createPatch(PatchType type, Expression const &expr, uint32_t pcShift) {
	out_CreatePatch(type, expr, sect_GetOutputOffset(), pcShift);
}

void sect_StartUnion() {
	// Important info: currently, UNION and LOAD cannot interact, since UNION is prohibited in
	// "code" sections, whereas LOAD is restricted to them.
	// Therefore, any interactions are NOT TESTED, so lift either of those restrictions at
	// your own peril! ^^

	if (!currentSection) {
		error("`UNION`s must be inside a `SECTION`");
		return;
	}
	if (sectTypeHasData(currentSection->type)) {
		error("Cannot use `UNION` inside of `ROM0` or `ROMX` sections");
		return;
	}

	currentUnionStack.push({.start = curOffset, .size = 0});
}

static void endUnionMember() {
	UnionStackEntry &member = currentUnionStack.top();
	uint32_t memberSize = curOffset - member.start;

	if (memberSize > member.size) {
		member.size = memberSize;
	}
	curOffset = member.start;
}

void sect_NextUnionMember() {
	if (currentUnionStack.empty()) {
		error("Found `NEXTU` outside of a `UNION` construct");
		return;
	}
	endUnionMember();
}

void sect_EndUnion() {
	if (currentUnionStack.empty()) {
		error("Found `ENDU` outside of a `UNION` construct");
		return;
	}
	endUnionMember();
	curOffset += currentUnionStack.top().size;
	currentUnionStack.pop();
}

void sect_CheckUnionClosed() {
	if (!currentUnionStack.empty()) {
		error("Unterminated `UNION` construct");
	}
}

void sect_ConstByte(uint8_t byte) {
	if (!requireCodeSection()) {
		return;
	}

	writeByte(byte);
}

void sect_ByteString(std::vector<int32_t> const &str) {
	if (!requireCodeSection()) {
		return;
	}

	for (int32_t unit : str) {
		if (!checkNBit(unit, 8, "All character units")) {
			break;
		}
	}

	for (int32_t unit : str) {
		writeByte(static_cast<uint8_t>(unit));
	}
}

void sect_WordString(std::vector<int32_t> const &str) {
	if (!requireCodeSection()) {
		return;
	}

	for (int32_t unit : str) {
		if (!checkNBit(unit, 16, "All character units")) {
			break;
		}
	}

	for (int32_t unit : str) {
		writeWord(static_cast<uint16_t>(unit));
	}
}

void sect_LongString(std::vector<int32_t> const &str) {
	if (!requireCodeSection()) {
		return;
	}

	for (int32_t unit : str) {
		writeLong(static_cast<uint32_t>(unit));
	}
}

void sect_Skip(uint32_t skip, bool ds) {
	if (!requireSection()) {
		return;
	}

	if (!sectTypeHasData(currentSection->type)) {
		growSection(skip);
	} else {
		if (!ds) {
			warning(
			    WARNING_EMPTY_DATA_DIRECTIVE,
			    "`%s` directive without data in ROM",
			    (skip == 4)   ? "DL"
			    : (skip == 2) ? "DW"
			                  : "DB"
			);
		}
		// We know we're in a code SECTION
		while (skip--) {
			writeByte(options.padByte);
		}
	}
}

void sect_RelByte(Expression const &expr, uint32_t pcShift) {
	if (!requireCodeSection()) {
		return;
	}

	if (!expr.isKnown()) {
		createPatch(PATCHTYPE_BYTE, expr, pcShift);
		writeByte(0);
	} else {
		writeByte(expr.value());
	}
}

void sect_RelBytes(uint32_t n, std::vector<Expression> const &exprs) {
	if (!requireCodeSection()) {
		return;
	}

	for (uint32_t i = 0; i < n; ++i) {
		if (Expression const &expr = exprs[i % exprs.size()]; !expr.isKnown()) {
			createPatch(PATCHTYPE_BYTE, expr, i);
			writeByte(0);
		} else {
			writeByte(expr.value());
		}
	}
}

void sect_RelWord(Expression const &expr, uint32_t pcShift) {
	if (!requireCodeSection()) {
		return;
	}

	if (!expr.isKnown()) {
		createPatch(PATCHTYPE_WORD, expr, pcShift);
		writeWord(0);
	} else {
		writeWord(expr.value());
	}
}

void sect_RelLong(Expression const &expr, uint32_t pcShift) {
	if (!requireCodeSection()) {
		return;
	}

	if (!expr.isKnown()) {
		createPatch(PATCHTYPE_LONG, expr, pcShift);
		writeLong(0);
	} else {
		writeLong(expr.value());
	}
}

void sect_PCRelByte(Expression const &expr, uint32_t pcShift) {
	if (!requireCodeSection()) {
		return;
	}

	if (Symbol const *pc = sym_GetPC(); !expr.isDiffConstant(pc)) {
		createPatch(PATCHTYPE_JR, expr, pcShift);
		writeByte(0);
	} else {
		Symbol const *sym = expr.symbolOf();
		// The offset wraps (jump from ROM to HRAM, for example)
		int16_t offset;

		// Offset is relative to the byte *after* the operand
		if (sym == pc) {
			offset = -2; // PC as operand to `jr` is lower than reference PC by 2
		} else {
			offset = sym->getValue() - (pc->getValue() + 1);
		}

		if (offset < -128 || offset > 127) {
			error(
			    "`JR` target must be between -128 and 127 bytes away, not %" PRId16
			    "; use `JP` instead",
			    offset
			);
			writeByte(0);
		} else {
			writeByte(offset);
		}
	}
}

bool sect_BinaryFile(std::string const &name, uint32_t startPos) {
	if (!requireCodeSection()) {
		return false;
	}

	FILE *file = nullptr;
	if (std::optional<std::string> fullPath = fstk_FindFile(name); fullPath) {
		file = fopen(fullPath->c_str(), "rb");
	}
	if (!file) {
		return fstk_FileError(name, "`INCBIN`");
	}
	Defer closeFile{[&] { xfclose(file); }};

	if (std::optional<uint64_t> fileSize = seekSize(file); fileSize.has_value()) {
		if (startPos > *fileSize) {
			error(
			    "Specified start position (%" PRIu32 ") is greater than length of \"%s\" (%" PRIu64
			    ")",
			    startPos,
			    name.c_str(),
			    *fileSize
			);
			return false;
		}
		// The file is seekable; skip to the specified start position
		fseek(file, startPos, SEEK_SET);
	} else {
		// LCOV_EXCL_START
		if (errno != ESPIPE) {
			error(
			    "Error determining size of `INCBIN` file \"%s\": %s", name.c_str(), strerror(errno)
			);
		}
		// The file isn't seekable, so we'll just skip bytes one at a time
		while (startPos--) {
			if (fgetc(file) == EOF) {
				error(
				    "Specified start position is greater than length of file \"%s\"", name.c_str()
				);
				return false;
			}
		}
		// LCOV_EXCL_STOP
	}

	for (int byte; (byte = fgetc(file)) != EOF;) {
		writeByte(byte);
	}

	if (ferror(file)) {
		// LCOV_EXCL_START
		error("Error reading `INCBIN` file \"%s\": %s", name.c_str(), strerror(errno));
		// LCOV_EXCL_STOP
	}
	return false;
}

bool sect_BinaryFileSlice(std::string const &name, uint32_t startPos, uint32_t length) {
	if (!requireCodeSection()) {
		return false;
	}
	if (length == 0) { // Don't even bother with 0-byte slices
		return false;
	}

	FILE *file = nullptr;
	if (std::optional<std::string> fullPath = fstk_FindFile(name); fullPath) {
		file = fopen(fullPath->c_str(), "rb");
	}
	if (!file) {
		return fstk_FileError(name, "`INCBIN`");
	}
	Defer closeFile{[&] { xfclose(file); }};

	if (std::optional<uint64_t> fileSize = seekSize(file); fileSize.has_value()) {
		if (startPos > *fileSize) {
			error(
			    "Specified start position (%" PRIu32 ") is greater than length of \"%s\" (%" PRIu64
			    ")",
			    startPos,
			    name.c_str(),
			    *fileSize
			);
			return false;
		} else if (length > *fileSize - startPos) {
			error(
			    "Specified range in `INCBIN` file \"%s\" is out of bounds (%" PRIu32 " + %" PRIu32
			    " > %" PRIu64 ")",
			    name.c_str(),
			    startPos,
			    length,
			    *fileSize
			);
			return false;
		}
		// The file is seekable; skip to the specified start position
		fseek(file, startPos, SEEK_SET);
	} else {
		// LCOV_EXCL_START
		if (errno != ESPIPE) {
			error(
			    "Error determining size of `INCBIN` file \"%s\": %s", name.c_str(), strerror(errno)
			);
		}
		// The file isn't seekable, so we'll just skip bytes one at a time
		while (startPos--) {
			if (fgetc(file) == EOF) {
				error(
				    "Specified start position is greater than length of file \"%s\"", name.c_str()
				);
				return false;
			}
		}
		// LCOV_EXCL_STOP
	}

	while (length--) {
		if (int byte = fgetc(file); byte != EOF) {
			writeByte(byte);
			// LCOV_EXCL_START
		} else if (ferror(file)) {
			error("Error reading `INCBIN` file \"%s\": %s", name.c_str(), strerror(errno));
		} else {
			error(
			    "Premature end of `INCBIN` file \"%s\" (%" PRId32 " bytes left to read)",
			    name.c_str(),
			    length + 1
			);
			// LCOV_EXCL_STOP
		}
	}
	return false;
}

void sect_PushSection() {
	sectionStack.push_front({
	    .section = currentSection,
	    .loadSection = currentLoadSection,
	    .labelScopes = sym_GetCurrentLabelScopes(),
	    .offset = curOffset,
	    .loadOffset = loadOffset,
	    .unionStack = {},
	});

	// Reset the section scope
	currentSection = nullptr;
	currentLoadSection = nullptr;
	sym_ResetCurrentLabelScopes();
	std::swap(currentUnionStack, sectionStack.front().unionStack);
}

void sect_PopSection() {
	if (sectionStack.empty()) {
		fatal("No entries in the section stack");
	}

	if (currentLoadSection) {
		sect_EndLoadSection("POPS");
	}

	SectionStackEntry entry = sectionStack.front();
	sectionStack.pop_front();

	changeSection();
	currentSection = entry.section;
	currentLoadSection = entry.loadSection;
	sym_SetCurrentLabelScopes(entry.labelScopes);
	curOffset = entry.offset;
	loadOffset = entry.loadOffset;
	std::swap(currentUnionStack, entry.unionStack);
}

void sect_CheckStack() {
	if (!sectionStack.empty()) {
		warning(WARNING_UNMATCHED_DIRECTIVE, "`PUSHS` without corresponding `POPS`");
	}
}

void sect_EndSection() {
	if (!currentSection) {
		fatal("Cannot end the section outside of a `SECTION`");
	}

	if (!currentUnionStack.empty()) {
		fatal("Cannot end the section within a `UNION`");
	}

	if (currentLoadSection) {
		sect_EndLoadSection("ENDSECTION");
	}

	// Reset the section scope
	currentSection = nullptr;
	sym_ResetCurrentLabelScopes();
}

InternedStr sect_PushSectionFragmentLiteral() {
	static uint64_t nextFragmentLiteralID = 0;

	// Like `requireCodeSection` but fatal
	if (!currentSection) {
		fatal("Cannot output fragment literals outside of a `SECTION`");
	}
	if (!sectTypeHasData(currentSection->type)) {
		fatal(
		    "Section \"%s\" cannot contain fragment literals (not `ROM0` or `ROMX`)",
		    currentSection->name.c_str()
		);
	}

	// This section has data (ROM0 or ROMX), so it cannot be a UNION
	assume(currentSection->modifier != SECTION_UNION);

	if (currentLoadSection) {
		fatal("`LOAD` blocks cannot contain fragment literals");
	}

	// A section containing a fragment literal has to become a fragment too
	currentSection->modifier = SECTION_FRAGMENT;

	Section *parent = currentSection;
	sect_PushSection(); // Resets `currentSection`

	Section *sect = createSectionFragmentLiteral(*parent);

	changeSection();
	curOffset = sect->size;
	currentSection = sect;

	// Return a symbol ID to use for the address of this section fragment
	return intern("$"s + std::to_string(nextFragmentLiteralID++));
}
