// C headers, read through libclang, written in Finch.
//
// What `import "stdio.h"` teaches the compiler: the C functions, the constants (enum values and
// plain #define numbers), the extern variables (stdout) and the structs. The same job as
// src/cimport.cpp, done by calling libclang's C API through Finch's own C import -- which is
// what makes this the part that closes the bootstrap: to compile this file the self-hosted
// compiler has to read libclang's headers with this very code.
//
// C structs by value appear in types as the named type `module "C"`.
import ast
import "clang-c/Index.h"
link "clang"

struct CFunc {
    str name
    str header          // the import it came from
    ast.Type ret
    []ast.Type params
    bool variadic
    str unsupported     // non-empty: why Finch can't call it (yet)
}

struct CConst {         // enum values and simple #define numbers
    bool isFloat
    int i
    float f
    str text            // a float as written, so no digits are lost: 3.14159265358979323846
}

struct CField {
    str name
    ast.Type ty
    int offset          // bytes
    int size
    int align
    bool hidden         // unions, bit fields, unmappable types: kept for layout only
}

struct CStruct {
    str name
    []CField fields
    int size
    int align
    str unsupported     // why it can't be used by value (pointers to it still work)
    bool hasHidden
}

struct CImports {
    map[str]CFunc fns
    map[str]CConst consts
    map[str]ast.Type globals
    map[str]CStruct structs
    []str structOrder   // the order they were defined in
}

// A header to read: the path as written, and where it was written, for error messages.
struct Header {
    str path
    str where
}

// Where a C type is used decides how `char *` looks in Finch: in function signatures it is a
// `str`; inside structs, globals and behind pointers it stays a raw `ptr[char]`.
struct Mapped {
    ast.Type ty
    str why
    bool ok
}

struct Importer {
    CImports out
    ptr tu
    str header
    map[str]str recordNames     // record USR -> Finch name (a typedef name wins)
    map[str]bool defining       // USR -> true while its fields are being mapped
    int anon
}

fn text(CXString s) -> str {
    out := clang_getCString(s)
    clang_disposeString(s)
    return out
}

fn ok(ast.Type t) -> Mapped {
    return Mapped(ty: t, ok: true)
}

fn no(str why) -> Mapped {
    return Mapped(why: why, ok: false)
}

fn fixed(ast.Type elem, int count) -> ast.Type {
    t := ast.Type(kind: "fixed", count: count)
    t.elem.push(elem)
    return t
}

// ---------- the system's header folders ----------

// Ask the system C compiler where it looks for headers, so we find the same stdio.h it would.
fn systemIncludeArgs() -> []str {
    []str dirs
    tmp := "/tmp/finch_cc_dirs.txt"
    shell("cc -E -v -x c /dev/null 2> '" + tmp + "' > /dev/null")
    if !file_exists(tmp) {
        return dirs
    }
    inList := false
    for line in read_file(tmp).split("\n") {
        l := line.trim()
        if l.starts_with("#include <...> search starts here:") {
            inList = true
            continue
        }
        if l.starts_with("End of search list.") {
            break
        }
        if !inList || l.len == 0 {
            continue
        }
        // macOS: "/.../Frameworks (framework directory)"
        if l.ends_with(" (framework directory)") {
            dirs.push("-iframework" + l.sub(0, l.len - 22))
        } else {
            dirs.push("-isystem" + l)
        }
    }
    shell("rm -f '" + tmp + "'")
    return dirs
}

// ---------- records ----------

// The Finch name of a C record: its typedef name, its tag, or a made-up one.
fn recordName(ptr[Importer] imp, CXType t) -> str {
    decl := clang_getTypeDeclaration(t)
    usr := text(clang_getCursorUSR(decl))
    if imp.recordNames.has(usr) {
        return imp.recordNames[usr]
    }
    name := text(clang_getCursorSpelling(decl))
    if name.len == 0 || name.contains(" ") {
        imp.anon += 1
        name = "anon_struct_" + str(imp.anon)
    }
    imp.recordNames[usr] = name
    return name
}

// Fill out.structs[name] for a complete record; returns its name, or "" if it can't be one.
fn defineRecord(ptr[Importer] imp, CXType type) -> str {
    t := clang_getCanonicalType(type)
    decl := clang_getTypeDeclaration(t)
    usr := text(clang_getCursorUSR(decl))
    name := recordName(imp, t)
    if imp.out.structs.has(name) || imp.defining.has(usr) {
        return name
    }
    size := int(clang_Type_getSizeOf(t))
    if size < 0 {
        return ""           // incomplete (opaque) struct
    }
    imp.defining[usr] = true
    s := CStruct(name: name, size: size, align: int(clang_Type_getAlignOf(t)))
    if clang_getCursorKind(decl) == CXCursor_UnionDecl {
        s.unsupported = "is a C union"
    }
    // the fields are collected by a callback that gets the importer and the struct through one pointer
    ctx := FieldCtx(imp: imp, s: addr(s))
    clang_Type_visitFields(t, addr(visitField), addr(ctx))
    imp.defining.remove(usr)
    imp.out.structs[name] = s
    imp.out.structOrder.push(name)
    return name
}

struct FieldCtx {
    ptr[Importer] imp
    ptr[CStruct] s
}

fn visitField(CXCursor field, ptr data) -> i32 {
    ptr[FieldCtx] c = data
    f := CField(name: text(clang_getCursorSpelling(field)))
    ft := clang_getCanonicalType(clang_getCursorType(field))
    f.offset = int(clang_Cursor_getOffsetOfField(field)) / 8
    f.size = int(clang_Type_getSizeOf(ft))
    f.align = int(clang_Type_getAlignOf(ft))
    if clang_Cursor_isBitField(field) != 0 {
        c.s.unsupported = "has bit fields"
        f.hidden = true
    } else if ft.kind == CXType_Record && clang_getCursorKind(clang_getTypeDeclaration(ft)) == CXCursor_UnionDecl {
        f.hidden = true     // unions are kept as opaque bytes
    } else {
        m := mapType(c.imp, ft, false)
        if m.ok {
            f.ty = m.ty
        } else {
            f.hidden = true
        }
    }
    if f.hidden {
        c.s.hasHidden = true
    }
    if f.name.len == 0 {
        f.hidden = true
    }
    c.s.fields.push(f)
    return CXVisit_Continue
}

// ---------- types ----------

fn sized(int size, bool signed) -> Mapped {
    if size == 1 {
        if signed {
            return ok(ast.simple("i8"))
        }
        return ok(ast.simple("u8"))
    }
    if size == 2 {
        if signed {
            return ok(ast.simple("i16"))
        }
        return ok(ast.simple("u16"))
    }
    if size == 4 {
        if signed {
            return ok(ast.simple("i32"))
        }
        return ok(ast.simple("u32"))
    }
    if size == 8 {
        if signed {
            return ok(ast.simple("int"))
        }
        return ok(ast.simple("u64"))
    }
    return no("uses a " + str(size * 8) + "-bit number")
}

// C type -> Finch type. Not ok (with a reason) if Finch can't express it.
// `signature`: a char * is a str (a function's parameters and result); anywhere else it stays a ptr[char].
fn mapType(ptr[Importer] imp, CXType type, bool signature) -> Mapped {
    t := clang_getCanonicalType(type)
    size := int(clang_Type_getSizeOf(t))
    k := t.kind
    if k == CXType_Void {
        return ok(ast.simple("void"))
    }
    if k == CXType_Bool {
        return ok(ast.simple("bool"))
    }
    if k == CXType_Char_S || k == CXType_Char_U {
        return ok(ast.simple("char"))
    }
    if k == CXType_SChar || k == CXType_Short || k == CXType_Int || k == CXType_Long || k == CXType_LongLong {
        return sized(size, true)
    }
    if k == CXType_UChar || k == CXType_UShort || k == CXType_UInt || k == CXType_ULong || k == CXType_ULongLong {
        return sized(size, false)
    }
    if k == CXType_Enum {
        return sized(size, true)
    }
    if k == CXType_Float {
        return ok(ast.simple("f32"))
    }
    if k == CXType_Double {
        return ok(ast.simple("float"))
    }
    if k == CXType_Pointer {
        pointee := clang_getCanonicalType(clang_getPointeeType(t))
        if (pointee.kind == CXType_Char_S || pointee.kind == CXType_Char_U) && signature {
            return ok(ast.simple("str"))        // char* in a signature is a C string
        }
        if pointee.kind == CXType_Void || pointee.kind == CXType_FunctionProto || pointee.kind == CXType_FunctionNoProto {
            return ok(ast.simple("ptr"))        // an opaque `ptr` you can pass around
        }
        inner := mapType(imp, pointee, false)
        if !inner.ok || inner.ty.kind == "void" || inner.ty.kind == "fixed" {
            return ok(ast.simple("ptr"))
        }
        return ok(ast.ptrTo(inner.ty))
    }
    if k == CXType_Record {
        if clang_getCursorKind(clang_getTypeDeclaration(t)) == CXCursor_UnionDecl {
            return no("uses a C union by value")
        }
        name := defineRecord(imp, t)
        if name.len == 0 {
            return no("uses an incomplete C struct by value")
        }
        return ok(ast.Type(kind: "named", name: name, module: "C"))
    }
    if k == CXType_ConstantArray {
        inner := mapType(imp, clang_getArrayElementType(t), false)
        if !inner.ok {
            return inner
        }
        return ok(fixed(inner.ty, int(clang_getArraySize(t))))
    }
    if k == CXType_LongDouble {
        return no("uses long double")
    }
    return no("uses the C type '" + text(clang_getTypeSpelling(t)) + "'")
}

// ---------- #define numbers ----------

struct Number {
    CConst c
    bool ok
}

// "0x1F", "010", "10UL" -> the value, and whether the text was a whole number
fn parseInt(str lit) -> Number {
    s := lit
    base := 10
    if s.starts_with("0x") || s.starts_with("0X") {
        base = 16
        s = s.sub(2, s.len)
    } else if s.len > 1 && s[0] == '0' {
        base = 8
        s = s.sub(1, s.len)
    }
    n := 0
    seen := false
    i := 0
    while i < s.len {
        c := s[i]
        d := 99
        if c >= '0' && c <= '9' {
            d = int(c) - int('0')
        } else if c >= 'a' && c <= 'f' {
            d = int(c) - int('a') + 10
        } else if c >= 'A' && c <= 'F' {
            d = int(c) - int('A') + 10
        }
        if d >= base {
            break
        }
        n = n * base + d
        seen = true
        i += 1
    }
    // what is left may only be suffixes: 10UL
    while i < s.len {
        if !"uUlL".contains(str(s[i])) {
            return Number()
        }
        i += 1
    }
    if !seen && base != 8 {
        return Number()
    }
    return Number(c: CConst(i: n), ok: true)
}

// Simple #defines: a single number, maybe negative, maybe in parentheses.
fn macroValue(ptr[Importer] imp, CXCursor c) -> Number {
    ptr[CXToken] tokens = null
    u32 n = 0
    clang_tokenize(imp.tu, clang_getCursorExtent(c), addr(tokens), addr(n))
    []str parts
    for k in 1..int(n) {            // token 0 is the macro's name
        if clang_getTokenKind(tokens[k]) == CXToken_Comment {
            continue
        }
        parts.push(text(clang_getTokenSpelling(imp.tu, tokens[k])))
    }
    clang_disposeTokens(imp.tu, tokens, n)

    while parts.len >= 2 && parts[0] == "(" && parts[parts.len - 1] == ")" {
        parts.remove(0)
        parts.pop()
    }
    neg := false
    if parts.len == 2 && parts[0] == "-" {
        neg = true
        parts.remove(0)
    }
    if parts.len != 1 {
        return Number()
    }
    lit := parts[0]
    if lit.len == 0 || !((lit[0] >= '0' && lit[0] <= '9') || lit[0] == '.') {
        return Number()
    }
    isFloat := (lit.contains(".") || lit.contains("e") || lit.contains("E")) && !lit.starts_with("0x")
    if isFloat {
        body := lit
        while body.len > 0 && "fFlL".contains(str(body[body.len - 1])) {
            body = body.sub(0, body.len - 1)
        }
        v := float(body) or {
            return Number()
        }
        if neg {
            v = 0.0 - v
        }
        return Number(c: CConst(isFloat: true, f: v, text: body), ok: true)
    }
    r := parseInt(lit)
    if r.ok && neg {
        r.c.i = 0 - r.c.i
    }
    return r
}

// ---------- the top level ----------

fn visitTop(CXCursor c, CXCursor parent, ptr data) -> i32 {
    ptr[Importer] imp = data
    visit(imp, c)
    return CXChildVisit_Continue
}

fn visit(ptr[Importer] imp, CXCursor c) {
    name := text(clang_getCursorSpelling(c))
    kind := clang_getCursorKind(c)
    if kind == CXCursor_TypedefDecl {
        // typedef struct {...} Name;  ->  the struct is called Name in Finch
        u := clang_getCanonicalType(clang_getTypedefDeclUnderlyingType(c))
        if u.kind == CXType_Record {
            usr := text(clang_getCursorUSR(clang_getTypeDeclaration(u)))
            // prefer the typedef name, unless the struct is already known under its tag
            used := imp.recordNames.has(usr) && imp.out.structs.has(imp.recordNames[usr])
            if !used && !imp.out.structs.has(name) {
                imp.recordNames[usr] = name
            }
        }
    } else if kind == CXCursor_FunctionDecl {
        if imp.out.fns.has(name) {
            return
        }
        f := CFunc(name: name, header: imp.header)
        if clang_Cursor_getStorageClass(c) == CX_SC_Static {
            f.unsupported = "is a static inline C function (it has no code to link against)"
            imp.out.fns[name] = f
            return
        }
        ft := clang_getCanonicalType(clang_getCursorType(c))
        if ft.kind == CXType_FunctionNoProto {
            f.unsupported = "has no parameter list in its C declaration"
            imp.out.fns[name] = f
            return
        }
        r := mapType(imp, clang_getResultType(ft), true)
        if r.ok {
            f.ret = r.ty
        } else {
            f.unsupported = r.why
        }
        n := int(clang_getNumArgTypes(ft))
        for k in 0..n {
            if f.unsupported.len > 0 {
                break
            }
            p := mapType(imp, clang_getArgType(ft, u32(k)), true)
            if p.ok {
                f.params.push(p.ty)
            } else {
                f.unsupported = p.why
            }
        }
        f.variadic = clang_isFunctionTypeVariadic(ft) != 0
        imp.out.fns[name] = f
    } else if kind == CXCursor_VarDecl {
        if clang_Cursor_getStorageClass(c) != CX_SC_Extern || imp.out.globals.has(name) {
            return
        }
        g := mapType(imp, clang_getCursorType(c), false)
        if g.ok {
            imp.out.globals[name] = g.ty
        }
    } else if kind == CXCursor_StructDecl {
        if clang_isCursorDefinition(c) != 0 && name.len > 0 && !name.contains(" ") {
            usr := text(clang_getCursorUSR(c))
            if !imp.recordNames.has(usr) {
                imp.recordNames[usr] = name
            }
        }
    } else if kind == CXCursor_EnumDecl {
        clang_visitChildren(c, addr(visitTop), imp)
    } else if kind == CXCursor_EnumConstantDecl {
        if !imp.out.consts.has(name) {
            imp.out.consts[name] = CConst(i: int(clang_getEnumConstantDeclValue(c)))
        }
    } else if kind == CXCursor_MacroDefinition {
        if clang_Cursor_isMacroBuiltin(c) != 0 || clang_Cursor_isMacroFunctionLike(c) != 0 {
            return
        }
        v := macroValue(imp, c)
        if v.ok && !imp.out.consts.has(name) {
            imp.out.consts[name] = v.c
        }
    }
}

// Read every header in `headers`; `dirs` are searched first for "local.h" headers.
fn importHeaders([]Header headers, []str dirs) -> CImports! {
    imp := Importer()
    if headers.len == 0 {
        return imp.out
    }
    []str args = ["-x", "c", "-std=gnu11"]
    for d in dirs {
        args.push("-I" + d)
    }
    for d in systemIncludeArgs() {
        args.push(d)
    }
    []ptr[char] argv
    for i in 0..args.len {
        argv.push(args[i].ptr)
    }
    index := clang_createIndex(0, 0)
    for h in headers {
        src := "#include \"" + h.path + "\"\n"
        file := CXUnsavedFile(Filename: "finch_import.c".ptr, Contents: src.ptr, Length: u64(src.len))
        ptr tu = null
        flags := CXTranslationUnit_DetailedPreprocessingRecord | CXTranslationUnit_SkipFunctionBodies
        err := clang_parseTranslationUnit2(index, "finch_import.c", argv.ptr, i32(argv.len), addr(file), 1, u32(flags), addr(tu))
        if err != CXError_Success || tu == null {
            return error(h.where + ": error: couldn't read C header '" + h.path + "'")
        }
        nd := int(clang_getNumDiagnostics(tu))
        for k in 0..nd {
            d := clang_getDiagnostic(tu, u32(k))
            if clang_getDiagnosticSeverity(d) >= CXDiagnostic_Error {
                msg := text(clang_getDiagnosticSpelling(d))
                clang_disposeDiagnostic(d)
                if msg.contains("file not found") {
                    // "'GL/gl.h' file not found": it may be a header that this one includes
                    missing := msg.sub(1, msg.sub(1, msg.len).find("'") + 1)
                    if missing == h.path {
                        return error(h.where + ": error: can't find the C header '" + h.path + "'")
                    }
                    return error(h.where + ": error: can't find the C header '" + missing + "', which '" + h.path + "' includes (is its library's development package installed?)")
                }
                return error(h.where + ": error: C header '" + h.path + "' has an error: " + msg)
            }
            clang_disposeDiagnostic(d)
        }
        imp.tu = tu
        imp.header = h.path
        clang_visitChildren(clang_getTranslationUnitCursor(tu), addr(visitTop), addr(imp))
        clang_disposeTranslationUnit(tu)
    }
    clang_disposeIndex(index)
    return imp.out
}